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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..6833f05 --- /dev/null +++ b/.gitattributes @@ -0,0 +1,3 @@ +* text=auto +*.txt text +*.md text diff --git a/38072-8.txt b/38072-8.txt new file mode 100644 index 0000000..81a3ece --- /dev/null +++ b/38072-8.txt @@ -0,0 +1,1244 @@ +The Project Gutenberg EBook of Wind and Weather, by Alexander McAdie + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Wind and Weather + +Author: Alexander McAdie + +Release Date: November 21, 2011 [EBook #38072] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK WIND AND WEATHER *** + + + + +Produced by Chris Curnow, Martin Pettit and the Online +Distributed Proofreading Team at http://www.pgdp.net (This +file was produced from images generously made available +by The Internet Archive) + + + + + + +WIND AND WEATHER + + +[Illustration: Logo] + +THE MACMILLAN COMPANY +NEW YORK · BOSTON · CHICAGO · DALLAS +ATLANTA · SAN FRANCISCO + +MACMILLAN & CO., LIMITED +LONDON · BOMBAY · CALCUTTA +MELBOURNE + +THE MACMILLAN CO. OF CANADA, LTD. +TORONTO + + +[Illustration: HOW THE WIND RUFFLES THE TOP OF A FOG BANK + +_Frontispiece_] + + + + +WIND AND WEATHER + +BY ALEXANDER McADIE + +A. Lawrence Rotch Professor of Meteorology, Harvard +University and Director of the Blue Hill Observatory + +New York +THE MACMILLAN COMPANY +1922 + +_All rights reserved_ + + +Copyright, 1922, +By ALEXANDER McADIE. + +Set up and electrotyped. Published November, 1922. + + + + +LIST OF ILLUSTRATIONS + + + HOW THE WIND RUFFLES THE TOP + OF A FOG BANK _Frontispiece_ + + PAGE +FIG. 1. THE TOWER OF THE WINDS 13 + + " 2. BOREAS--THE NORTH WIND 19 + + " 3. KAIKIAS--THE NORTHEAST WIND 23 + + " 4. APHELIOTES--THE EAST WIND 29 + + " 5. EUROS--THE SOUTHEAST WIND 33 + + " 6. NOTOS--THE SOUTH WIND 37 + + " 7. LIPS--THE SOUTHWEST WIND 41 + + " 8. ALL STORMS LEAD TO NEW ENGLAND 45 + + " 9. ZEPHYROS--THE WEST WIND 49 + + " 10. PATHS OF HIGH AND LOW, JANUARY, 1922 55 + + " 11. SKIRON--THE NORTHWEST WIND 59 + + " 12. THE IDEALIZED STORM 63 + + " 13. TURNING OF WIND WITH ALTITUDE 67 + + " 14. VELOCITY OF SUMMER AND WINTER WINDS 73 + + " 15. BLUE HILL OBSERVATORY IN AN ICE STORM 79 + + + + +WIND AND WEATHER + + + + +THE TOWER OF THE WINDS + + +In Athens on the north side and near the base of the hill on which the +upper city--the Acropolis--is built, there is a small temple still +standing, altho its walls were completed twenty-two centuries ago. It is +known as the Tower of the Winds; but as a matter of fact, the citizens +of Athens used it to tell the hour of the day and the seasonal position +of the sun. It was a public timepiece. It served as a huge sun dial. +Water from a spring on the hillside filled the basins of a water clock +in the basement of the Tower. And so, whether the day was clear or +cloudy the measure of the outflow of water indicated the time elapsed. +Also there were markings or dials on each of the eight walls of the +temple, and the position of the shadow of a marker indicated the +seasonal advance or retreat of the sun as it moved north from the time +of the winter solstice and then south after the summer solstice. + +The sun is not an accurate time keeper and no one to-day runs his +business or keeps engagements on sun time. But the old Athenians were +quite content to do so; and their Tower served excellently for their +needs. And they did what we moderns fail to do, namely, give distinctive +names to the winds. They represented figuratively the characteristics of +the weather as the wind blew from each of the eight cardinal directions. + +[Illustration: FIG. 1. THE TOWER OF THE WINDS + +Erected in Athens, on the north side of the Acropolis, B. C. 150] + +The allegorical figures of the winds used in this little book are +reproductions of the eight bas-reliefs in the library of the Blue Hill +Observatory, placed there by the late Professor A. Lawrence Rotch. They +are copied from the frieze of the Tower of the Winds at Athens. + + + + +THE NAMES OF THE WINDS + + +Boreas, the north wind, is perhaps the most important of all winds. At +Athens this a cold, boisterous wind from the mountains of Thrace. The +noise of the gusts is so loud that the Greek sculptor symbolized the +tumult by placing a conch shell in the mouth of Boreas. His modern +namesake, the Bora of the Adriatic, is the same noisy, blustering, cold +wind-rush from the north. + +The northeast wind Kaikias is a trifle more pleasant looking than +Boreas, but still not much to brag about. Master of the squall and +thunderstorm, he carries in his shield an ample supply of hailstones, +ready to spill them on defenseless humanity. He might well serve as the +patron saint of air raiders dropping their bombs on helpless humans +below. + +Apheliotes, the east wind, is a graceful youth, with arms full of +flowers, fruit and wheat. Naturally this was a favorite wind, blowing in +from the sea, with frequent light showers. Some of us who dwell on the +Atlantic Coast, in more northern latitudes than Athens, do not always +regard with favor the east wind, associating it with chilly, damp and +sombre weather. Yet it is the harbinger of good--tempering the cold of +winter and the heat of summer. It is an angel of mercy in mid-summer +when the temperature is above the nineties and there is no air stirring. +Then it is, that we all welcome the refreshing wind from the sea. + +Euros, the southeast wind, and neighbor to Apheliotes, is a cross old +fellow, intent on the business of cloud making. He alone of all the +winds carries nothing in his hands. In the New Testament he becomes +Euroclydon, wind of the waves. He is no friend of the sailor; and the +seasick traveler prays to be rid of his company. + +The figure on the south face of the tower, Notos, is the master of the +warm rain. He carries with him a water jar which has just been emptied. +Compare his light flowing robes and half-clad neck and arms with the +close fitting jacket of old Boreas. At his shrine, hydraulic engineers +well might worship. + +Next, the Mariner's wind, Lips, the southwest favoring breeze bringing +the ships speedily into harbor; yes, into that Piraeus, famed in classic +history. Incidentally it is the southwest wind which differentiates the +climate of Great Britain from that of Labrador. This wind makes +Northwest Europe habitable; while on the other side of the Atlantic, in +similar latitudes, but under the influence of prevailing northwest +winds, we find Labrador--a section certainly misnamed, for it is not the +abode of farmers, as the name implies--but barren and bleak. What a +difference it would make thruout this region if the Gulf Stream +continued north, close to the shore, and the prevailing winds were _from +the east_. Our North Atlantic Coast would then be _the land of zephyrs_, +using the word in the sense of pleasant, gentle winds. + +[Illustration: FIG. 2. BOREAS--THE NORTH WIND] + +Zephyros, the west wind, is represented as a graceful youth, scantily +clad, with his arms filled with flowers. In Greece this wind traversed +the Ionian Sea and the Gulf of Corinth before reaching Athens. It is +quite unlike our west wind which blows across a continent, and is +continuously robbed of its water vapor on the long passage. The Ionian +wind is pleasantly moist and refreshing. + +Last of all, but by no means least important, is Skiron, lord of gusty +northwest gales. Freezing in winter, parching in summer, he carries with +him a brazen fire basket and spills a generous stream of hot air on all +below. His husky Highness might not inappropriately adorn legislative +halls and editorial sanctums. He would displace the blindfolded lady +holding scales very much out of balance. Think of the deep significance +of his presence. + +In our country the northwest is of all winds, except the west, most +persistent. For 1600 hours in a year, this wind is with us. Joining +forces with the west wind, these directions prevail one third of the +time. These northwest-west winds also have the greatest speed and +gustiness. The climate of the United States is essentially determined by +the prevalence of the north, northwest and west winds. + + + + +FORECASTING THE WEATHER + + +In old days, the _haruspices_ (for this is what the Romans called +weather men in the days of Caesar) proclaimed the will of the gods by +consulting the entrails of some freshly killed animal. Evidently these +haruspices did not always make correct forecasts; for there were some +Romans who openly questioned their worth. Cato, the Censor, is on record +as saying "that he wondered how one haruspex could look another in the +face without laughing!" + +[Illustration: FIG. 3. KAIKIAS--THE NORTHEAST WIND] + +The modern professional forecaster would scorn to consult the entrails. +There are however many amateur forecasters who foretell weather by their +aches and rheumatic pains. Probably there is a high correlation factor +between body sensations and dampness; and some individuals are quite +sensitive to changes in both relative and absolute humidity. This, +however, does not always mean that a storm is approaching. Humidity or +dampness is only one factor and may be quite local, whereas most storms +are wide-spread. + + + + +THE WEATHER MAP + + +The official forecaster consults a daily weather map and certain +auxiliary maps which show changes in pressure and temperature for twelve +hours or more. He examines closely the contours of pressure as shown on +the map. The synoptic map, as it is called, because it is a glance at +weather conditions over a large area at one and the same moment, is a +map on which are plotted pressure, temperature, wind direction, velocity +and rainfall. The lines of equal pressure or isobars generally curve and +inclose what is known as a cyclonic centre, or depression or LOW. The +arrows point in, but not exactly toward the centre of the depression. + +On the map there will probably appear also an area of high pressure +where the surface air flows leisurely outward and away from the place of +highest pressure. Such an area is called an anticyclone, a word first +used by Sir Francis Galton in 1863 to designate not only high pressure, +but general flow of the air in a reversed or opposite direction to that +of the low area or cyclone. The word cyclone was first used by +Piddington in 1843 in describing the flow of the air in the typhoons of +the East Indian Seas. It is from the Greek and literally means the coils +of a serpent. The word cyclone must possess some special merit in the +minds of journalists for it is quite commonly misused for tornado in +descriptions of the smaller and more destructive storm. + + + + +THE LOW + + +Cyclone is simply the generic name for a large rotating air mass. It is +a barometric depression or LOW and is characterized by a flow of air +inward and around a moving centre. The air circulation is +counter-clockwise in the northern hemisphere and clockwise in the south. + +Perhaps if the earth stopped rotating and there was no planetary +circulation, with the great west-moving trades and east-moving +"westerlies," the arrows on the weather map would all point directly +toward the centre of the LOW; but, as things are, there are some very +good reasons why air can not move directly into a LOW, that is at right +angles to the isobars. + +Moreover, the weather map does not indicate the true flow of the air, +for observations of the wind made at the ground tell only a part of the +story of the balance which the flowing air must maintain under the +action of various forces, such as gravitation, rotational deflection, +centrifugal tendency, and the various expansion and compression forces. + +The winds near the ground are modified both in velocity and direction by +friction. The free flow is often interfered with by topography. + + + + +THE TRUE AIR FLOW + + +One must rise above the ground some distance to get the true air flow, +or what is known as the gradient wind, the flow which balances the +gradient, i.e. a flow along the isobars. The gradient velocity is found +about 300 metres above the ground, and the gradient direction a little +higher. The lower clouds as a rule indicate true wind values very well; +and so, it is desirable in studying winds to use cloud directions and +velocities rather than surface values. In cloud work a nephoscope is +essential. The unaided eye, unless properly shielded, suffers from the +glare of a sunlit sky; and moreover, there are no fixed points or +references. A black mirror, with suitable sighting rods and measuring +devices, enables an observer to follow the cloud, estimate its height +and determine with accuracy the direction from which it is moving. There +is an average difference of 30 degrees between the cloud direction and +the surface wind; the upper direction being more to the right. At times +the directions may be opposite. + +[Illustration: FIG. 4. APHELIOTES--THE EAST WIND] + +It may seem surprising but few of us, except at sunrise and sunset, +really see what is going on in cloud land. + +Some meteorologists hold that the circulation of air 3000 to 5000 +metres above the ground controls the path and perhaps the intensity of +storms. It is therefore important to know something of the flow at high +levels if we would improve the forecasts. + + + + +LIMITATIONS OF MAP + + +The weather map fails to indicate what shifts of direction and changes +in velocity are likely to occur. The forecaster tries to anticipate +these, but he bases his conclusions chiefly upon an expected movement of +the low area; using the accumulated records of the paths of past storms. +But each storm is in reality a law unto itself; and while we know +something of the relations between pressure and flow of the air; as yet +we know very little about the relations of wind and weather. The problem +is complicated by the behavior of the load of water vapor. + +[Illustration: FIG. 5. EUROS--THE SOUTHEAST WIND] + +The Chief Forecaster of one of the great national weather services +recently wrote: + + + "Despite the fact that maps have now been drawn day by day for over + half a century, we may safely say that no two maps have been + identical." + + +It is perhaps unfortunate that so much attention has been given to the +cyclone or depression or LOW, and comparatively little to the HIGH or +anticyclone. For we are now beginning to understand that while there may +seem at first to be nothing specially noteworthy about a mass of air +where the pressure varies from 1020 to 1040 kilobars, that is, 2 to 4 +per cent _above_ a standard atmosphere, with isobars irregularly curved +and feeble surface winds, yet the anticyclone is more important than the +cyclone in determining weather sequence; for the progressive motion of +the cyclone depends largely upon the strength of the anticyclone. + + + + +OCEAN STORMS + + +Sir Napier Shaw, who has written much on the weather of the British +Isles, may be quoted here. + + + "Anyone who is interested in the weather is always on the lookout + for 'lows' and is very keen to know whether he is going to be on + the south of the centre or the north of it. He is, of course, + interested in the anticyclone too, because as long as an + anticyclone is there, there cannot be a depression; but it is the + depression which has the life and movement about it, giving it a + claim to the attention of everybody who wants to know what the + weather and its changes are going to be. + + "This has been recognized from the very earliest days of weather + maps with isobars. The depressions which pass over our shores + (Great Britain) mostly come from the west. Some of them come all + the way from America; one or two have been traced from the west + coast of Africa and so have crossed the Atlantic twice, first to + the westward and then to the eastward. Some have come all the way + from a sort of parent 'low' in the North Pacific Ocean. So general + is the tendency for 'lows' to go eastward that it was thought at + one time, particularly by the 'New York Herald,' that their + departure from the American Coast and subsequent arrival on our own + shores could be notified by cable, and we (the British) might thus + be forewarned of their approach, some three or four days in + advance. The attempt was made by the 'New York Herald' acting in + co-operation with the Meteorological Offices of the United Kingdom + and France. But a depression keeps to no beaten track; it has as + many paths for its centre as there are lines in a bundle of hay. + Though groups can be picked out there are many strays, and, + moreover, the depression changes its shape and intensity while it + travels, so that if you lose sight of it for a day you cannot be at + all sure of its identity." + + +[Illustration: FIG. 6. NOTOS--THE SOUTH WIND] + + + + +TRANSCONTINENTAL STORMS + + +If there is so much uncertainty in forecasting the path of a disturbance +at sea, how much more uncertain must it be on land? Elaborate statistics +of the average daily movement of various types of storms have been +officially published. The average speed of storms (not wind speeds) +across the United States is 11 metres per second or 25 miles an hour. +Storms travel more rapidly in winter than in summer, about half again as +fast; that is, summer storms travel 20 miles, and winter storms 30 +miles, an hour. + +[Illustration: FIG. 7. LIPS--THE SOUTHWEST WIND] + +The paths vary widely; from the Gulf storms moving northeast and West +Indian hurricanes recurving on the southern coast, to the storms from +Alberta and the west which move south and east. Ten types of storms, +classified according to the place of origin, are recognized by the +official forecasters of the United States. These are North Pacific, +Alberta, Northern Rocky Mountain, Colorado, Central, South Pacific, +Texas, East Gulf, South Atlantic and West Indian Hurricanes. A better +nomenclature would be (1) Alberta, (2) Washington, (3) Kootenay, (4) +Utah, (5) Kansas, (6) California, (7) Texas, (8) Louisiana, (9) +Florida, and (10) Hurricanes. + + + + +HURRICANES + + +Type 10 is the general class of tropical storms occurring chiefly in the +summer and fall which, drifting west, slowly work northward. Similar +storms are the typhoons and baguios of the East Indian and China Seas. + +The path and point of recurvature will be determined by the position of +the Bermuda Hyperbar, that is, the seasonal anticyclone of the Atlantic. +This accounts for the swinging east and north of these tracks as the +season progresses; for the hyperbar is slowly displaced east, the +maximum displacement occurring in September. + +[Illustration: BASE MAP BY GOODE + +FIG. 8. ALL STORMS LEAD TO NEW ENGLAND] + +Individual anticyclones also influence individual hurricanes. Thus a +hurricane passing west over Havana, will go farther west if a vigorous +"high" is spreading southeast over the Gulf States. And when this "high" +passes seaward, the hurricane will work around the southwest quadrant of +the "high," recurving and moving northeast. + + + + +STORM RENDEZVOUS + + +Altho storms originate or are first detected in nine different sections, +it is a fact worth mentioning that they all leave the United States in +the vicinity of New England or Nova Scotia. Some of the southern +depressions starting near the coast, pass to sea south of New York, but +in general an observer standing on Plymouth Rock can virtually encompass +within a radius of 500 kilometres, 300 miles, the paths of ninety per +cent of the storms that traverse the country. + +Thus a storm that originates in Texas (7) will probably pass close to +Cape Cod. Likewise, types (3) and (5); while the other types may pass a +little to the north or south. See Chart, Paths of Storms. + + + + +STORM PATHS + + +Forecasting then would seem to be very easy; for one would only have to +know the place of origin of the storm and the rate of travel, to +foretell exactly the time of arrival. Unfortunately these are only the +average paths; and as with most mean values, represent a value not often +experienced in fact. These paths then are not paths which any given +storm will follow. One must recall the story of the operating surgeon +who gave the average age of his patients in the operating room as 35. +There were but two patients, one 69 years old and the other 1 year old. + +[Illustration: FIG. 9. ZEPHYROS--THE WEST WIND] + +As a matter of fact the path of any individual depression depends upon +several factors, some of which are:--the prevailing eastward drift of +the air; the extent and motion of some anticyclone advancing before the +"LOW"; the duration and speed of relatively dry cold tongues of air from +the north; and the supply of water vapor brought from southern waters by +south winds. A depression can make little headway if to the north or +east the normal path is blocked by what is known as a stagnant "HIGH." +So therefore, if the anticyclone is a slow mover, a Texas storm, which +would normally pass not far from southern New England, may be deflected +farther north than when the HIGH moved rapidly east. So too, with the +storms which originate in the western part of the country. A slow moving +HIGH will prevent the LOW following it, from moving east at a normal +rate along the usual path. + +Anticyclones then, are the real weather controls. There are various +types, but all drift from the north or west. Occasionally they enter the +country from the Pacific, but the great majority come from Alberta and +move leisurely southeast, often reaching the South Atlantic States; but +more frequently recurving and passing to the north. + + + + +STAGNANT HIGHS + + +HIGHS are sometimes reinforced and this results in what is called a +stagnant HIGH. A good illustration of such a slow moving HIGH and its +consequences occurred during the last week of January, 1922. + +A surge of cold air from Alberta or farther north reached the +international boundary January 21st and spread slowly eastward, reaching +the Great Lakes on the 24th and the St. Lawrence Valley two days later. +Then seemingly it halted or moved slowly westward, retrograding. In +three days, that is, on the 29th, the centre of the HIGH was apparently +500 miles _west_ of where it had been on the 27th. After the 29th it +followed a normal track, moving slowly southeast, reaching the Atlantic +near Long Island. + +Meanwhile a depression on the south coast of Texas on the 25th, moved +across the Gulf of Mexico, passing over Southern Florida on the 27th and +advanced steadily northeast, reaching Cape Hatteras in 24 hours. Owing +to the presence of the anticyclone referred to above, the depression +recurved off Hatteras. The result was a memorable snow storm in Northern +Virginia and Maryland. At 8 p.m. January 27th, there had been a fall of +5 cms. (2 inches). Within the following twenty hours the average depth +in the city of Washington was 66 cms. (26 inches). The weight of the +snow caused the collapse of the roof of the Knickerbocker Theatre and +the death of 97 persons. + +The total snowfall in various coast cities was: + + + Raleigh 24 cms.* + Richmond 48 " + Washington 71 " + Baltimore 67 " + Wilmington 46 " + Philadelphia 31 " + Trenton 27 " + New York 18 " + New Haven 8 " + Boston 1 " + + *Note: To convert to inches multiply by 0.4. + + +The table shows clearly how the snow was formed. On the east side of the +LOW a stream of air, relatively warm, carried a load of water vapor, +approximately 13 grams in each cubic metre. + +[Illustration: BASE MAP BY GOODE + +FIG. 10. PATHS OF HIGH AND LOW, GREAT SNOW STORM OF JANUARY 27-28, 1922] + +This current was steered around the north side of the LOW and met the +north-northeast wind. Under the new conditions the air saturated could +hold only 2 or 3 grams; and so condensation and heavy precipitation +resulted. The region of maximum snowfall was near Washington, and it +will be seen that there is a proportional decrease north and south. The +snowfall at Washington was the heaviest ever known at that city. + +Unlike most storms, there was no strong cold northwest wind blowing into +the depression. The temperature rose slowly. It was less a contrast of +winds than a steady slow outward push of the anticyclone, and the +consequent turning of the path of the cyclone eastward. + + + + +LAWS OF FORECASTING + + +Buys Ballot's Law. + +"If you stand with your back to the wind the pressure decreases toward +your left, and increases toward your right." + +For navigators, this law is more generally expressed in the words of the +Hydrographic Office on "Cyclonic Storms." + +"Since the wind circulates counter-clockwise in the northern hemisphere, +the rule in that hemisphere is to face the wind, and the storm centre +will be at the right hand. If the wind traveled in exact circles, the +centre would be eight points (90 degrees) to the right when looking +directly in the wind's eye. But the wind follows a more or less spiral +path inward which brings the centre from eight to twelve points (90 to +135 degrees), to the right of the wind. The centre will bear more nearly +eight points from the direction of the lower clouds than from the +surface wind." + +[Illustration: FIG. 11. SKIRON--THE NORTHWEST WIND] + +The law given on the preceding page is named after C. H. D. Buys +Ballott, a Dutch meteorologist. It was announced in a paper published in +the _Comptes rendus_ in 1857. Two American writers on the Winds, J. H. +Coffin and William Ferrell, had however earlier found the law to hold. + + * * * * * + +While most of us study storms from a window at home and are not called +upon to handle a ship in a storm, yet it may not be out of place to +include here the diagram of the winds in an ideal storm and give the +rules for maneuvering. See Figure 12. The Winds in an Idealized Storm. +The rules apply only to storms in the northern hemisphere. + +"_Right or dangerous semicircle_,--Steamers: Bring the wind on the +starboard bow, make as much way as possible, and if obliged to heave-to, +do so head to sea. Sailing vessels: Keep close-hauled on the starboard +tack, make as much way as possible, and if obliged to heave-to, do so on +the starboard tack. + +_Left or navigable semicircle_,--Steam and sailing vessels: Bring the +wind on the starboard quarter, note the course and hold it. If obliged +to heave-to, steamers may do so stern to sea; sailing vessels on the +port tack. + +_On the storm track in front of center_,--Steam and sailing vessels: +Bring the wind two points on the starboard quarter, note the course and +hold it, and run for the left semicircle, and when in that semicircle +manoeuvre as above. + +On the storm track, in rear of center,--Avoid the center by the best +practicable route, having due regard to the tendency of cyclones to +recurve to the southward and eastward." + +[Illustration: FROM HYDROGRAPHIC OFFICE + +FIG. 12. THE WINDS IN AN IDEALIZED STORM] + + + + +WIND AND ALTITUDE + + +The law of the turning of the wind with altitude. + +A casual observation of the lower clouds where no means of measuring +small angles is available will not usually show any difference between +the motion of the clouds and the surface wind; but with the upper clouds +the case is different, and one readily detects a difference. + +Several thousand observations with various agencies, such as kites and +pilot balloons and more especially measurements made with theodolites +and nephoscopes, show that there is a definite twist to the right with +elevation. The amount of the deflection is shown in Figure 13. Turning +of the Wind with Altitude. Here the average yearly values are given for +directions and velocities. Thus if the mean wind direction at Blue Hill +is from a point a little to the north of west, 306 grads or 275 degrees, +and the mean velocity 7 metres per second; the clouds at 1000 metres +elevation will move from 312 or 280 degrees and at a speed of +approximately 11 metres per second (24 miles an hour). + +These however, are average values. In individual cases the difference +between surface winds and stratus clouds may be considerably greater. It +may be as much as 180 degrees; that is, the cloud may move directly +opposite to the wind. In general there will be a difference of 10 to 20 +degrees. + + + + +WIND AND RAIN + + +The law of wind direction, approximate cooling and rain. + +When the lower clouds are moving from the north or northwest, without +sharply defined edges, the LOW is east or northeast of the observer; and +rain or snow is not likely unless there is a rapidly falling +temperature. + +[Illustration: TURNING OF WIND WITH ALTITUDE, BLUE HILL + +FIG. 13. TURNING OF WIND WITH ALTITUDE] + +When a stream of warm air with a high absolute humidity flows north on +the east side of a LOW, and a cold northwest wind follows quickly after +the LOW, rain or snow may be expected. + +Any rapid chilling of warm, moist air produces cloudiness and rain or +snow; but a cold stream blowing into a warm area will not produce as +much rain as a warm stream blowing into a cold area. + + + + +DURATION OF WIND + + +The average duration of wind from various directions is as follows: + +From the north about 16 hours each week; from the northeast, the same; +from the east, 11 hours; from the southeast, 10 hours; from the south, +24 hours; from the southwest, 27 hours; from the west, 33 hours; and +from the northwest 31 hours. + +During an individual disturbance lasting about 36 hours, we may have 8 +hours of southwest wind; 4 hours of west wind, backing during the next 4 +hours to south; 2 hours of south wind; 2 hours of southeast wind; 2 +hours of east wind; 8 hours northeast wind and 4 hours north wind, 2 +hours northwest, when it may be considered that a new pressure +distribution prevails. + +The above values hold only for a storm moving with normal velocity. LOWS +are often blocked by slow moving HIGHS in advance. In such cases the +duration of east winds is greater. + + + + +THE WINDS OF A YEAR + + +The following table shows the marked increase in the prevalence of +northwest and west winds during winter months, the decrease in north +winds during July, the increase in northeast winds in May, also in east +winds; the increase of south and southwest winds in July; and the +falling off of southeast winds in December. See Table, page 72. + +In cities near the Atlantic Coast, a continuance of northeast wind, +especially in the fall and winter months, results in frequent altho not +necessarily heavy rains. On the other hand a period of continued +northwest and west wind is a dry period. + +In summer, southeast and east winds bring fog and cooler weather; while +southwest winds are favorable for the development of thunderstorms. + + +WINDS OF A YEAR + +TABLE I.--Number of Hours the Wind Blows from Different Directions. + + -------------------------------------------------------------------- + Jan. Mar. May July Sept. Nov. Year + Feb. Apr. June Aug. Oct. Dec. + + Boreas (N) 98 74 71 70 60 40 59 59 67 80 82 96 850 + Kaikias (NE) 41 46 65 94 101 55 79 79 77 91 48 30 819 + Apheliotes (E) 34 37 52 58 63 48 51 51 52 58 34 31 576 + Euros (SE) 37 37 45 41 54 45 62 62 52 45 39 34 534 + Notus (S) 82 66 95 99 143 155 128 128 118 93 81 65 1245 + Lips (SW) 112 77 81 79 118 170 135 135 133 108 119 131 1402 + Zephyros (W) 180 177 155 125 107 137 125 125 108 131 169 194 1732 + Skiron (NW) 160 162 183 154 98 94 105 105 113 138 148 163 1607 + -------------------------------------------------------------------- + + +[Illustration: FIG. 14. VELOCITY OF SUMMER AND WINTER WINDS IN METRES +PER SECOND] + + + + +THE SEA BREEZE + + +When the weather has been clear and moderately warm for two or more +days, and the winds are light and variable, there may occur on the third +day a moderate wind from the east, known as the sea-breeze. This occurs +during anticyclonic conditions. Preceding the sea-breeze, the winds are +very light, there are no clouds, and the temperature rises rapidly +during the forenoon. This heating is due to a slow dynamic compression +as the air slowly descends and the surface air does not flow away. There +is no cooling because there is no evaporation due to air movement. The +absolute humidity is low, often less than ten grams per cubic metre. +Cumulus clouds do not form because there is no uplift of the lower air +and consequently no chance for condensation of whatever water vapor may +be present. No thunder-heads form notwithstanding the heat. The heat, +while dry, is nevertheless extremely trying to men and animals. Relief +comes in the early hours of the afternoon by the arrival of the +sea-breeze. + +The usual explanation of the origin of the sea-breeze is that the land +being excessively warm, the air over a relatively cool ocean moves in to +take the place of the warm and therefore lighter air, which it is +assumed has risen. Unfortunately for this explanation, the air over the +land has _not_ risen; but on the contrary is falling slowly. Again the +sea-breeze does not begin at the place where the temperature contrast is +greatest, namely, just inside the shore line; but comes in from the sea. +Nor does the flow extend far inland, which would be the case if there +were up-rising currents. The sea-breeze is very shallow, generally not +extending upward more than 200 metres, and often not above 100 metres. +It does not penetrate far inland, as a rule not more than 15 +kilometres, 9 miles. + +The sea-breeze is probably caused by a slow descent of dry, warm air, on +an incline sloping from northeast to southwest. As it reaches the +surface it is twisted more to the right; that is, becomes an east wind. +It carries inland with it some of the air over the ocean which is much +cooler and heavily saturated. + + + + +MUGGY DAYS + + +There are certain days, more noticeable in summer than at other times, +when the air is heavily laden with water vapor; and there is little or +no cooling of the body due to evaporation. We perspire freely but as the +sweat does not evaporate, there is a constantly increasing amount of +water on the skin. + +[Illustration: FIG. 15. BLUE HILL OBSERVATORY DURING ICE STORM, NOVEMBER +29-30, 1922] + +It is not altogether a question of temperature, for another day may have +as high or even higher temperature. It is essentially a matter of +ventilation. On muggy days we are somewhat in the condition of the +unfortunate prisoners in the Black Hole at Calcutta. They did not die by +poisoning, as has generally been accepted, that is, lack of sufficient +oxygen and an excess of carbon dioxide; but because they were unable to +keep the skin sufficiently cool. There was no ventilation; no movement +of the air and the body became over-heated and exhaustion followed. No +matter how much water there may be on the skin if the surrounding space +is saturated, one feels oppressed. A vigorous fanning of the air helps +evaporation and cools us. That is why a brisk northwest wind routs a +muggy condition. + + + + +CASTILIAN DAYS + + +John Hay wrote of such days spent in Spain. We who live in a land where +the winds are more boisterous, occasionally experience what we call a +perfect day. Such days have easterly winds of two metres per second or +less than five miles an hour. The temperature is midway between freezing +and normal body temperature or about 70° F. The relative humidity is +approximately 75% and the absolute humidity 12 grams per cubic metre. +The table on page 72 explains the paucity of perfect days. The gusty, +boisterous winds, Skiron and Zephyros, blow too frequently. + +Perhaps certain of our national characteristics may be traceable to +this flow of the air and our climatic environment. + + + + + +End of the Project Gutenberg EBook of Wind and Weather, by Alexander McAdie + +*** END OF THIS PROJECT GUTENBERG EBOOK WIND AND WEATHER *** + +***** This file should be named 38072-8.txt or 38072-8.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/3/8/0/7/38072/ + +Produced by Chris Curnow, Martin Pettit and the Online +Distributed Proofreading Team at http://www.pgdp.net (This +file was produced from images generously made available +by The Internet Archive) + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Wind and Weather + +Author: Alexander McAdie + +Release Date: November 21, 2011 [EBook #38072] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK WIND AND WEATHER *** + + + + +Produced by Chris Curnow, Martin Pettit and the Online +Distributed Proofreading Team at http://www.pgdp.net (This +file was produced from images generously made available +by The Internet Archive) + + + + + + +</pre> + + +<p><span class='pagenum'><a name="Page_1" id="Page_1">[Pg 1]</a></span></p> + +<p class="bold2">WIND AND WEATHER</p> + +<hr /> + +<div class="center"><img src="images/coverpage.jpg" width='466' height='700' alt="coverpage" /></div> + +<hr /> + +<p><span class='pagenum'><a name="Page_2" id="Page_2">[Pg 2]</a></span></p> + +<div class="center"><img src="images/logo.jpg" width='200' height='63' alt="logo" /></div> + +<p class="center">THE MACMILLAN COMPANY<br /> +NEW YORK · BOSTON · CHICAGO · DALLAS<br /> +ATLANTA · SAN FRANCISCO<br /><br /> +<span class="smcap">MACMILLAN & CO., Limited</span><br /> +LONDON · BOMBAY · CALCUTTA<br />MELBOURNE<br /><br /> +<span class="smcap">THE MACMILLAN CO. OF CANADA, Ltd.</span><br />TORONTO</p> + +<hr /> + +<p><span class='pagenum'><a name="Page_4" id="Page_4">[Pg 4]</a></span></p> + +<div class="center"><a name="frontispiece.jpg" id="frontispiece.jpg"></a><img src="images/frontispiece.jpg" width='700' height='377' alt="How the Wind Ruffles the Top of a Fog Bank" /></div> + +<p class="bold"><span class="smcap">How the Wind Ruffles the Top of a Fog Bank</span></p> + + +<div class="block"><p class="right"><i>Frontispiece</i></p></div> + +<hr /> + +<p><span class='pagenum'><a name="Page_5" id="Page_5">[Pg 5]</a></span></p> + + +<h1><span>WIND<br />AND<br />WEATHER</span><br /><span id="id1">BY</span> <span>ALEXANDER McADIE</span></h1> + +<p class="center">A. Lawrence Rotch Professor of Meteorology, Harvard<br /> +University and Director of the Blue Hill<br />Observatory</p> + +<p class="tbrk"> </p> + +<div class="center"><img src="images/tp.jpg" width='16' height='30' alt="decoration" /></div> + +<p class="tbrk"> </p> + +<p class="center">New York<br />THE MACMILLAN COMPANY<br /> +1922<br /><br /><i>All rights reserved</i></p> + +<hr /> + +<p><span class='pagenum'><a name="Page_6" id="Page_6">[Pg 6]</a></span></p> + + +<p class="center">Copyright, 1922,<br />By ALEXANDER McADIE.</p> + +<hr class="smler" /> + +<p class="center">Set up and electrotyped. Published November, 1922.</p> + +<hr /> + +<p><span class='pagenum'><a name="Page_7" id="Page_7">[Pg 7]</a></span></p> + +<h2><span>LIST OF ILLUSTRATIONS</span></h2> + +<table summary="CONTENTS"> + <tr> + <td></td> + <td class="left">HOW THE WIND RUFFLES THE TOP<br /> + OF A FOG BANK</td> + <td><a href="#frontispiece.jpg"> <i>Frontispiece</i></a></td> + </tr> + <tr> + <td colspan="2"></td> + <td><span class="smaller">PAGE</span></td> + </tr> + <tr> + <td>FIG. 1.</td> + <td class="left"> THE TOWER OF THE WINDS</td> + <td><a href="#fig01.jpg">13</a></td> + </tr> + <tr> + <td>2.</td> + <td class="left"> BOREAS—THE NORTH WIND</td> + <td><a href="#fig02.jpg">19</a></td> + </tr> + <tr> + <td>3.</td> + <td class="left"> KAIKIAS—THE NORTHEAST WIND</td> + <td><a href="#fig03.jpg">23</a></td> + </tr> + <tr> + <td>4.</td> + <td class="left"> APHELIOTES—THE EAST WIND</td> + <td><a href="#fig04.jpg">29</a></td> + </tr> + <tr> + <td>5.</td> + <td class="left"> EUROS—THE SOUTHEAST WIND</td> + <td><a href="#fig05.jpg">33</a></td> + </tr> + <tr> + <td>6.</td> + <td class="left"> NOTOS—THE SOUTH WIND</td> + <td><a href="#fig06.jpg">37</a></td> + </tr> + <tr> + <td>7.</td> + <td class="left"> LIPS—THE SOUTHWEST WIND</td> + <td><a href="#fig07.jpg">41</a></td> + </tr> + <tr> + <td>8.</td> + <td class="left"> ALL STORMS LEAD TO NEW ENGLAND</td> + <td><a href="#fig08.jpg">45</a></td> + </tr> + <tr> + <td>9.</td> + <td class="left"> ZEPHYROS—THE WEST WIND</td> + <td><a href="#fig09.jpg">49</a></td> + </tr> + <tr> + <td>10.</td> + <td class="left"> PATHS OF HIGH AND LOW, JANUARY, 1922</td> + <td><a href="#fig10.jpg">55</a></td> + </tr> + <tr> + <td>11.</td> + <td class="left"> SKIRON—THE NORTHWEST WIND</td> + <td><a href="#fig11.jpg">59</a></td> + </tr> + <tr> + <td>12.</td> + <td class="left"> THE IDEALIZED STORM</td> + <td><a href="#fig12.jpg">63</a></td> + </tr> + <tr> + <td>13.</td> + <td class="left"> TURNING OF WIND WITH ALTITUDE</td> + <td><a href="#fig13.jpg">67</a></td> + </tr> + <tr> + <td>14.</td> + <td class="left"> VELOCITY OF SUMMER AND WINTER WINDS</td> + <td><a href="#fig14.jpg">73</a></td> + </tr> + <tr> + <td>15.</td> + <td class="left"> BLUE HILL OBSERVATORY IN AN ICE STORM</td> + <td><a href="#fig15.jpg">79</a></td> + </tr> +</table> + +<hr /> + +<p><span class='pagenum'><a name="Page_9" id="Page_9">[Pg 9]</a></span></p> + +<p class="bold2">WIND AND WEATHER</p> + +<hr /> + +<p><span class='pagenum'><a name="Page_11" id="Page_11">[Pg 11]</a></span></p> + +<p class="bold2">WIND AND WEATHER</p> + +<hr class="smler" /> + +<h2><span>THE TOWER OF THE WINDS</span></h2> + +<p>In Athens on the north side and near the base of the hill on which the +upper city—the Acropolis—is built, there is a small temple still +standing, altho its walls were completed twenty-two centuries ago. It is +known as the Tower of the Winds; but as a matter of fact, the citizens +of Athens used it to tell the hour of the day and the seasonal position +of the sun. It was a public timepiece. It served as a huge sun dial. +Water from a spring on the hillside filled the basins of a water clock +in the basement of the Tower. And so, whether the day was clear or +cloudy the measure of the outflow of water indicated the time elapsed. +Also there were markings or dials on each of the eight<span class='pagenum'><a name="Page_12" id="Page_12">[Pg 12]</a></span> walls of the +temple, and the position of the shadow of a marker indicated the +seasonal advance or retreat of the sun as it moved north from the time +of the winter solstice and then south after the summer solstice.</p> + +<p>The sun is not an accurate time keeper and no one to-day runs his +business or keeps engagements on sun time. But the old Athenians were +quite content to do so; and their Tower served excellently for their +needs. And they did what we moderns fail to do, namely, give distinctive +names to the winds. They represented figuratively the characteristics of +the weather as the wind blew from each of the eight cardinal directions.</p> + +<div class="center"><a name="fig01.jpg" id="fig01.jpg"></a><img src="images/fig01.jpg" width='475' height='700' alt="Fig. 1. The Tower of the Winds" /></div> + +<p class="bold"><span class="smcap">Fig. 1. The Tower of the Winds</span><br /> +Erected in Athens, on the north side of the Acropolis,<br />B. C. 150</p> + +<p>The allegorical figures of the winds used in this little book are +reproductions of the eight bas-reliefs in the library of the Blue Hill +Observatory, placed there by the late Professor A.<span class='pagenum'><a name="Page_15" id="Page_15">[Pg 15]</a></span> Lawrence Rotch. They +are copied from the frieze of the Tower of the Winds at Athens.</p> + +<hr /> + +<h2><span>THE NAMES OF THE WINDS</span></h2> + +<p>Boreas, the north wind, is perhaps the most important of all winds. At +Athens this a cold, boisterous wind from the mountains of Thrace. The +noise of the gusts is so loud that the Greek sculptor symbolized the +tumult by placing a conch shell in the mouth of Boreas. His modern +namesake, the Bora of the Adriatic, is the same noisy, blustering, cold +wind-rush from the north.</p> + +<p>The northeast wind Kaikias is a trifle more pleasant looking than +Boreas, but still not much to brag about. Master of the squall and +thunderstorm, he carries in his shield an ample supply of hailstones, +ready to spill them on defenseless humanity. He might well serve as<span class='pagenum'><a name="Page_16" id="Page_16">[Pg 16]</a></span> the +patron saint of air raiders dropping their bombs on helpless humans below.</p> + +<p>Apheliotes, the east wind, is a graceful youth, with arms full of +flowers, fruit and wheat. Naturally this was a favorite wind, blowing in +from the sea, with frequent light showers. Some of us who dwell on the +Atlantic Coast, in more northern latitudes than Athens, do not always +regard with favor the east wind, associating it with chilly, damp and +sombre weather. Yet it is the harbinger of good—tempering the cold of +winter and the heat of summer. It is an angel of mercy in mid-summer +when the temperature is above the nineties and there is no air stirring. +Then it is, that we all welcome the refreshing wind from the sea.</p> + +<p>Euros, the southeast wind, and neighbor to Apheliotes, is a cross old +fellow, intent on the business of cloud making. He alone of all the +winds carries nothing<span class='pagenum'><a name="Page_17" id="Page_17">[Pg 17]</a></span> in his hands. In the New Testament he becomes +Euroclydon, wind of the waves. He is no friend of the sailor; and the +seasick traveler prays to be rid of his company.</p> + +<p>The figure on the south face of the tower, Notos, is the master of the +warm rain. He carries with him a water jar which has just been emptied. +Compare his light flowing robes and half-clad neck and arms with the +close fitting jacket of old Boreas. At his shrine, hydraulic engineers +well might worship.</p> + +<p>Next, the Mariner's wind, Lips, the southwest favoring breeze bringing +the ships speedily into harbor; yes, into that Piraeus, famed in classic +history. Incidentally it is the southwest wind which differentiates the +climate of Great Britain from that of Labrador. This wind makes +Northwest Europe habitable; while on the other side of the Atlantic,<span class='pagenum'><a name="Page_18" id="Page_18">[Pg 18]</a></span> in +similar latitudes, but under the influence of prevailing northwest +winds, we find Labrador—a section certainly misnamed, for it is not the +abode of farmers, as the name implies—but barren and bleak. What a +difference it would make thruout this region if the Gulf Stream +continued north, close to the shore, and the prevailing winds were <i>from +the east</i>. Our North Atlantic Coast would then be <i>the land of zephyrs</i>, +using the word in the sense of pleasant, gentle winds.</p> + +<div class="center"><a name="fig02.jpg" id="fig02.jpg"></a><img src="images/fig02.jpg" width='700' height='508' alt="Fig. 2. Boreas The North Wind" /></div> + +<p class="bold"><span class="smcap">Fig. 2. Boreas—The North Wind</span></p> + +<p>Zephyros, the west wind, is represented as a graceful youth, scantily +clad, with his arms filled with flowers. In Greece this wind traversed +the Ionian Sea and the Gulf of Corinth before reaching Athens. It is +quite unlike our west wind which blows across a continent, and is +continuously robbed of its water vapor on the long passage. The Ionian +wind is pleasantly moist and refreshing.</p> + +<p><span class='pagenum'><a name="Page_21" id="Page_21">[Pg 21]</a></span></p><p>Last of all, but by no means least important, is Skiron, lord of gusty +northwest gales. Freezing in winter, parching in summer, he carries with +him a brazen fire basket and spills a generous stream of hot air on all +below. His husky Highness might not inappropriately adorn legislative +halls and editorial sanctums. He would displace the blindfolded lady +holding scales very much out of balance. Think of the deep significance +of his presence.</p> + +<p>In our country the northwest is of all winds, except the west, most +persistent. For 1600 hours in a year, this wind is with us. Joining +forces with the west wind, these directions prevail one third of the +time. These northwest-west winds also have the greatest speed and +gustiness. The climate of the United States is essentially determined by +the prevalence of the north, northwest and west winds.</p> + +<hr /> + +<p><span class='pagenum'><a name="Page_22" id="Page_22">[Pg 22]</a></span></p> + +<h2><span>FORECASTING THE WEATHER</span></h2> + +<p>In old days, the <i>haruspices</i> (for this is what the Romans called +weather men in the days of Caesar) proclaimed the will of the gods by +consulting the entrails of some freshly killed animal. Evidently these +haruspices did not always make correct forecasts; for there were some +Romans who openly questioned their worth. Cato, the Censor, is on record +as saying "that he wondered how one haruspex could look another in the +face without laughing!"</p> + +<div class="center"><a name="fig03.jpg" id="fig03.jpg"></a><img src="images/fig03.jpg" width='700' height='480' alt="Fig. 3. Kaikias The Northeast Wind" /></div> + +<p class="bold"><span class="smcap">Fig. 3. Kaikias—The Northeast Wind</span></p> + +<p>The modern professional forecaster would scorn to consult the entrails. +There are however many amateur forecasters who foretell weather by their +aches and rheumatic pains. Probably there is a high correlation factor +between body sensations and dampness; and some individuals are quite +sensitive to changes in both relative and absolute humidity.<span class='pagenum'><a name="Page_25" id="Page_25">[Pg 25]</a></span> This, +however, does not always mean that a storm is approaching. Humidity or +dampness is only one factor and may be quite local, whereas most storms +are wide-spread.</p> + +<hr /> + +<h2><span>THE WEATHER MAP</span></h2> + +<p>The official forecaster consults a daily weather map and certain +auxiliary maps which show changes in pressure and temperature for twelve +hours or more. He examines closely the contours of pressure as shown on +the map. The synoptic map, as it is called, because it is a glance at +weather conditions over a large area at one and the same moment, is a +map on which are plotted pressure, temperature, wind direction, velocity +and rainfall. The lines of equal pressure or isobars generally curve and +inclose what is known as a cyclonic centre, or depression or LOW. The +arrows point<span class='pagenum'><a name="Page_26" id="Page_26">[Pg 26]</a></span> in, but not exactly toward the centre of the depression.</p> + +<p>On the map there will probably appear also an area of high pressure +where the surface air flows leisurely outward and away from the place of +highest pressure. Such an area is called an anticyclone, a word first +used by Sir Francis Galton in 1863 to designate not only high pressure, +but general flow of the air in a reversed or opposite direction to that +of the low area or cyclone. The word cyclone was first used by +Piddington in 1843 in describing the flow of the air in the typhoons of +the East Indian Seas. It is from the Greek and literally means the coils +of a serpent. The word cyclone must possess some special merit in the +minds of journalists for it is quite commonly misused for tornado in +descriptions of the smaller and more destructive storm.</p> + +<hr /> + +<p><span class='pagenum'><a name="Page_27" id="Page_27">[Pg 27]</a></span></p> + +<h2><span>THE LOW</span></h2> + +<p>Cyclone is simply the generic name for a large rotating air mass. It is +a barometric depression or LOW and is characterized by a flow of air +inward and around a moving centre. The air circulation is +counter-clockwise in the northern hemisphere and clockwise in the south.</p> + +<p>Perhaps if the earth stopped rotating and there was no planetary +circulation, with the great west-moving trades and east-moving +"westerlies," the arrows on the weather map would all point directly +toward the centre of the LOW; but, as things are, there are some very +good reasons why air can not move directly into a LOW, that is at right +angles to the isobars.</p> + +<p>Moreover, the weather map does not indicate the true flow of the air, +for observations of the wind made at the<span class='pagenum'><a name="Page_28" id="Page_28">[Pg 28]</a></span> ground tell only a part of the +story of the balance which the flowing air must maintain under the +action of various forces, such as gravitation, rotational deflection, +centrifugal tendency, and the various expansion and compression forces.</p> + +<p>The winds near the ground are modified both in velocity and direction by +friction. The free flow is often interfered with by topography.</p> + +<hr /> + +<h2><span>THE TRUE AIR FLOW</span></h2> + +<p>One must rise above the ground some distance to get the true air flow, +or what is known as the gradient wind, the flow which balances the +gradient, i.e. a flow along the isobars. The gradient velocity is found +about 300 metres above the ground, and the gradient direction a little +higher. The lower clouds as a rule<span class='pagenum'><a name="Page_31" id="Page_31">[Pg 31]</a></span> indicate true wind values very well; +and so, it is desirable in studying winds to use cloud directions and +velocities rather than surface values. In cloud work a nephoscope is +essential. The unaided eye, unless properly shielded, suffers from the +glare of a sunlit sky; and moreover, there are no fixed points or +references. A black mirror, with suitable sighting rods and measuring +devices, enables an observer to follow the cloud, estimate its height +and determine with accuracy the direction from which it is moving. There +is an average difference of 30 degrees between the cloud direction and +the surface wind; the upper direction being more to the right. At times +the directions may be opposite.</p> + +<div class="center"><a name="fig04.jpg" id="fig04.jpg"></a><img src="images/fig04.jpg" width='700' height='458' alt="Fig. 4. Apheliotes The East Wind" /></div> + +<p class="bold"><span class="smcap">Fig. 4. Apheliotes—The East Wind</span></p> + +<p>It may seem surprising but few of us, except at sunrise and sunset, +really see what is going on in cloud land.</p> + +<p>Some meteorologists hold that the<span class='pagenum'><a name="Page_32" id="Page_32">[Pg 32]</a></span> circulation of air 3000 to 5000 +metres above the ground controls the path and perhaps the intensity of +storms. It is therefore important to know something of the flow at high +levels if we would improve the forecasts.</p> + +<hr /> + +<h2><span>LIMITATIONS OF MAP</span></h2> + +<p>The weather map fails to indicate what shifts of direction and changes +in velocity are likely to occur. The forecaster tries to anticipate +these, but he bases his conclusions chiefly upon an expected movement of +the low area; using the accumulated records of the paths of past storms. +But each storm is in reality a law unto itself; and while we know +something of the relations between pressure and flow of the air; as yet +we know very little about the relations of wind and weather. The problem +is <span class='pagenum'><a name="Page_35" id="Page_35">[Pg 35]</a></span>complicated by the behavior of the load of water vapor.</p> + +<div class="center"><a name="fig05.jpg" id="fig05.jpg"></a><img src="images/fig05.jpg" width='700' height='434' alt="Fig. 5. Euros The Southeast Wind" /></div> + +<p class="bold"><span class="smcap">Fig. 5. Euros—The Southeast Wind</span></p> + +<p>The Chief Forecaster of one of the great national weather services +recently wrote:</p> + +<blockquote><p>"Despite the fact that maps have now been drawn day by day for over +half a century, we may safely say that no two maps have been +identical."</p></blockquote> + +<p>It is perhaps unfortunate that so much attention has been given to the +cyclone or depression or LOW, and comparatively little to the HIGH or +anticyclone. For we are now beginning to understand that while there may +seem at first to be nothing specially noteworthy about a mass of air +where the pressure varies from 1020 to 1040 kilobars, that is, 2 to 4 +per cent <i>above</i> a standard atmosphere, with isobars irregularly curved +and feeble surface winds, yet the anticyclone is more important than the +cyclone in determining<span class='pagenum'><a name="Page_36" id="Page_36">[Pg 36]</a></span> weather sequence; for the progressive motion of +the cyclone depends largely upon the strength of the anticyclone.</p> + +<hr /> + +<h2><span>OCEAN STORMS</span></h2> + +<p>Sir Napier Shaw, who has written much on the weather of the British +Isles, may be quoted here.</p> + +<blockquote><p>"Anyone who is interested in the weather is always on the lookout +for 'lows' and is very keen to know whether he is going to be on +the south of the centre or the north of it. He is, of course, +interested in the anticyclone too, because as long as an +anticyclone is there, there cannot be a depression; but it is the +depression which has the life and movement about it, giving it a +claim to the attention of everybody who wants to know what the +weather and its changes are going to be.</p> + +<p><span class='pagenum'><a name="Page_39" id="Page_39">[Pg 39]</a></span></p><p>"This has been recognized from the very earliest days of weather +maps with isobars. The depressions which pass over our shores +(Great Britain) mostly come from the west. Some of them come all +the way from America; one or two have been traced from the west +coast of Africa and so have crossed the Atlantic twice, first to +the westward and then to the eastward. Some have come all the way +from a sort of parent 'low' in the North Pacific Ocean. So general +is the tendency for 'lows' to go eastward that it was thought at +one time, particularly by the 'New York Herald,' that their +departure from the American Coast and subsequent arrival on our own +shores could be notified by cable, and we (the British) might thus +be forewarned of their approach, some three or four days in +advance. The attempt was made by the 'New York<span class='pagenum'><a name="Page_40" id="Page_40">[Pg 40]</a></span> Herald' acting in +co-operation with the Meteorological Offices of the United Kingdom +and France. But a depression keeps to no beaten track; it has as +many paths for its centre as there are lines in a bundle of hay. +Though groups can be picked out there are many strays, and, +moreover, the depression changes its shape and intensity while it +travels, so that if you lose sight of it for a day you cannot be at +all sure of its identity."</p></blockquote> + +<div class="center"><a name="fig06.jpg" id="fig06.jpg"></a><img src="images/fig06.jpg" width='700' height='490' alt="Fig. 6. Notos—The South Wind" /></div> + +<p class="bold"><span class="smcap">Fig. 6. Notos—The South Wind</span></p> + +<hr /> + +<h2><span>TRANSCONTINENTAL STORMS</span></h2> + +<p>If there is so much uncertainty in forecasting the path of a disturbance +at sea, how much more uncertain must it be on land? Elaborate statistics +of the average daily movement of various types of storms have been +officially published. The average speed of storms<span class='pagenum'><a name="Page_43" id="Page_43">[Pg 43]</a></span> (not wind speeds) +across the United States is 11 metres per second or 25 miles an hour. +Storms travel more rapidly in winter than in summer, about half again as +fast; that is, summer storms travel 20 miles, and winter storms 30 miles, an hour.</p> + +<div class="center"><a name="fig07.jpg" id="fig07.jpg"></a><img src="images/fig07.jpg" width='700' height='498' alt="Fig. 7. Lips The Southwest Wind" /></div> + +<p class="bold"><span class="smcap">Fig. 7. Lips—The Southwest Wind</span></p> + +<p>The paths vary widely; from the Gulf storms moving northeast and West +Indian hurricanes recurving on the southern coast, to the storms from +Alberta and the west which move south and east. Ten types of storms, +classified according to the place of origin, are recognized by the +official forecasters of the United States. These are North Pacific, +Alberta, Northern Rocky Mountain, Colorado, Central, South Pacific, +Texas, East Gulf, South Atlantic and West Indian Hurricanes. A better +nomenclature would be (1) Alberta, (2) Washington, (3) Kootenay, (4) +Utah, (5) Kansas, (6) California, (7) Texas,<span class='pagenum'><a name="Page_44" id="Page_44">[Pg 44]</a></span> (8) Louisiana, (9) +Florida, and (10) Hurricanes.</p> + +<hr /> + +<h2><span>HURRICANES</span></h2> + +<p>Type 10 is the general class of tropical storms occurring chiefly in the +summer and fall which, drifting west, slowly work northward. Similar +storms are the typhoons and baguios of the East Indian and China Seas.</p> + +<p>The path and point of recurvature will be determined by the position of +the Bermuda Hyperbar, that is, the seasonal anticyclone of the Atlantic. +This accounts for the swinging east and north of these tracks as the +season progresses; for the hyperbar is slowly displaced east, the +maximum displacement occurring in September.</p> + +<div class="center"><a name="fig08.jpg" id="fig08.jpg"></a><img src="images/fig08.jpg" width='625' height='700' alt="Fig. 8. All Storms Lead to New England" /></div> + +<div class="block"><p>BASE MAP BY GOODE</p></div> + +<p class="bold"><span class="smcap">Fig. 8. All Storms Lead to New England</span></p> + +<p>Individual anticyclones also influence individual hurricanes. Thus a +hurricane passing west over Havana, will go<span class='pagenum'><a name="Page_47" id="Page_47">[Pg 47]</a></span> farther west if a vigorous +"high" is spreading southeast over the Gulf States. And when this "high" +passes seaward, the hurricane will work around the southwest quadrant of +the "high," recurving and moving northeast.</p> + +<hr /> + +<h2><span>STORM RENDEZVOUS</span></h2> + +<p>Altho storms originate or are first detected in nine different sections, +it is a fact worth mentioning that they all leave the United States in +the vicinity of New England or Nova Scotia. Some of the southern +depressions starting near the coast, pass to sea south of New York, but +in general an observer standing on Plymouth Rock can virtually encompass +within a radius of 500 kilometres, 300 miles, the paths of ninety per +cent of the storms that traverse the country.</p> + +<p>Thus a storm that originates in Texas (7) will probably pass close to +Cape Cod.<span class='pagenum'><a name="Page_48" id="Page_48">[Pg 48]</a></span> Likewise, types (3) and (5); while the other types may pass a +little to the north or south. See Chart, Paths of Storms.</p> + +<hr /> + +<h2><span>STORM PATHS</span></h2> + +<p>Forecasting then would seem to be very easy; for one would only have to +know the place of origin of the storm and the rate of travel, to +foretell exactly the time of arrival. Unfortunately these are only the +average paths; and as with most mean values, represent a value not often +experienced in fact. These paths then are not paths which any given +storm will follow. One must recall the story of the operating surgeon +who gave the average age of his patients in the operating room as 35. +There were but two patients, one 69 years old and the other 1 year old.</p> + +<div class="center"><a name="fig09.jpg" id="fig09.jpg"></a><img src="images/fig09.jpg" width='700' height='490' alt="Fig. 9. Zephyros The West Wind" /></div> + +<p class="bold"><span class="smcap">Fig. 9. Zephyros—The West Wind</span></p> + +<p>As a matter of fact the path of any individual depression depends upon +<span class='pagenum'><a name="Page_51" id="Page_51">[Pg 51]</a></span>several factors, some of which are:—the prevailing eastward drift of +the air; the extent and motion of some anticyclone advancing before the +"LOW"; the duration and speed of relatively dry cold tongues of air from +the north; and the supply of water vapor brought from southern waters by +south winds. A depression can make little headway if to the north or +east the normal path is blocked by what is known as a stagnant "HIGH." +So therefore, if the anticyclone is a slow mover, a Texas storm, which +would normally pass not far from southern New England, may be deflected +farther north than when the HIGH moved rapidly east. So too, with the +storms which originate in the western part of the country. A slow moving +HIGH will prevent the LOW following it, from moving east at a normal +rate along the usual path.</p> + +<p>Anticyclones then, are the real weather<span class='pagenum'><a name="Page_52" id="Page_52">[Pg 52]</a></span> controls. There are various +types, but all drift from the north or west. Occasionally they enter the +country from the Pacific, but the great majority come from Alberta and +move leisurely southeast, often reaching the South Atlantic States; but +more frequently recurving and passing to the north.</p> + +<hr /> + +<h2><span>STAGNANT HIGHS</span></h2> + +<p>HIGHS are sometimes reinforced and this results in what is called a +stagnant HIGH. A good illustration of such a slow moving HIGH and its +consequences occurred during the last week of January, 1922.</p> + +<p>A surge of cold air from Alberta or farther north reached the +international boundary January 21st and spread slowly eastward, reaching +the Great Lakes on the 24th and the St. Lawrence Valley two days later. +Then seemingly<span class='pagenum'><a name="Page_53" id="Page_53">[Pg 53]</a></span> it halted or moved slowly westward, retrograding. In +three days, that is, on the 29th, the centre of the HIGH was apparently +500 miles <i>west</i> of where it had been on the 27th. After the 29th it +followed a normal track, moving slowly southeast, reaching the Atlantic +near Long Island.</p> + +<p>Meanwhile a depression on the south coast of Texas on the 25th, moved +across the Gulf of Mexico, passing over Southern Florida on the 27th and +advanced steadily northeast, reaching Cape Hatteras in 24 hours. Owing +to the presence of the anticyclone referred to above, the depression +recurved off Hatteras. The result was a memorable snow storm in Northern +Virginia and Maryland. At 8 p.m. January 27th, there had been a fall of +5 cms. (2 inches). Within the following twenty hours the average depth +in the city of Washington was 66 cms. (26 inches).<span class='pagenum'><a name="Page_54" id="Page_54">[Pg 54]</a></span> The weight of the +snow caused the collapse of the roof of the Knickerbocker Theatre and +the death of 97 persons.</p> + +<p>The total snowfall in various coast cities was:</p> + +<table summary="total snowfall in various coast cities"> + <tr> + <td class="left">Raleigh</td> + <td class="left">24 cms.*</td> + </tr> + <tr> + <td class="left">Richmond</td> + <td class="left">48</td> + </tr> + <tr> + <td class="left">Washington</td> + <td class="left">71</td> + </tr> + <tr> + <td class="left">Baltimore</td> + <td class="left">67</td> + </tr> + <tr> + <td class="left">Wilmington</td> + <td class="left">46</td> + </tr> + <tr> + <td class="left">Philadelphia </td> + <td class="left">31</td> + </tr> + <tr> + <td class="left">Trenton</td> + <td class="left">27</td> + </tr> + <tr> + <td class="left">New York</td> + <td class="left">18</td> + </tr> + <tr> + <td class="left">New Haven</td> + <td class="left"> 8</td> + </tr> + <tr> + <td class="left">Boston</td> + <td class="left"> 1</td> + </tr> +</table> + +<div class="block"><p>*Note: To convert to inches multiply by 0.4.</p></div> + +<p>The table shows clearly how the snow was formed. On the east side of the +LOW a stream of air, relatively warm, carried a load of water vapor, +approximately 13 grams in each cubic metre.</p> + +<div class="center"><a name="fig10.jpg" id="fig10.jpg"></a><img src="images/fig10.jpg" width='625' height='700' alt="Fig. 10. Paths of High and Low, Great Snow Storm of January 27-28, 1922" /></div> + +<div class="block"><p>BASE MAP BY GOODE</p></div> + +<p class="bold"><span class="smcap">Fig. 10. Paths of High and Low, Great Snow Storm of January 27-28, 1922</span>]</p> + +<p><span class='pagenum'><a name="Page_57" id="Page_57">[Pg 57]</a></span></p><p>This current was steered around the north side of the LOW and met the +north-northeast wind. Under the new conditions the air saturated could +hold only 2 or 3 grams; and so condensation and heavy precipitation +resulted. The region of maximum snowfall was near Washington, and it +will be seen that there is a proportional decrease north and south. The +snowfall at Washington was the heaviest ever known at that city.</p> + +<p>Unlike most storms, there was no strong cold northwest wind blowing into +the depression. The temperature rose slowly. It was less a contrast of +winds than a steady slow outward push of the anticyclone, and the +consequent turning of the path of the cyclone eastward.</p> + +<hr /> + +<p><span class='pagenum'><a name="Page_58" id="Page_58">[Pg 58]</a></span></p> + +<h2><span>LAWS OF FORECASTING</span></h2> + +<p>Buys Ballot's Law.</p> + +<p>"If you stand with your back to the wind the pressure decreases toward +your left, and increases toward your right."</p> + +<p>For navigators, this law is more generally expressed in the words of the +Hydrographic Office on "Cyclonic Storms."</p> + +<p>"Since the wind circulates counter-clockwise in the northern hemisphere, +the rule in that hemisphere is to face the wind, and the storm centre +will be at the right hand. If the wind traveled in exact circles, the +centre would be eight points (90 degrees) to the right when looking +directly in the wind's eye. But the wind follows a more or less spiral +path inward which brings the centre from eight to twelve points (90 to +135 degrees), to the right of the wind. The centre will bear more nearly +eight points from the direction of the lower clouds than from the +surface wind."</p> + +<div class="center"><a name="fig11.jpg" id="fig11.jpg"></a><img src="images/fig11.jpg" width='700' height='425' alt="Fig. 11. Skiron The Northwest Wind" /></div> + +<p class="bold"><span class="smcap">Fig. 11. Skiron—The Northwest Wind</span></p> + +<p><span class='pagenum'><a name="Page_61" id="Page_61">[Pg 61]</a></span></p><p>The law given on the preceding page is named after C. H. D. Buys +Ballott, a Dutch meteorologist. It was announced in a paper published in +the <i>Comptes rendus</i> in 1857. Two American writers on the Winds, J. H. +Coffin and William Ferrell, had however earlier found the law to hold.</p> + +<p class="center">* * * * * *</p> + +<p>While most of us study storms from a window at home and are not called +upon to handle a ship in a storm, yet it may not be out of place to +include here the diagram of the winds in an ideal storm and give the +rules for maneuvering. See Figure 12. The Winds in an Idealized Storm. +The rules apply only to storms in the northern hemisphere.</p> + +<p>"<i>Right or dangerous semicircle</i>,—Steamers: Bring the wind on the +starboard bow, make as much way as possible, and if obliged to heave-to, +do so head to sea.<span class='pagenum'><a name="Page_62" id="Page_62">[Pg 62]</a></span> Sailing vessels: Keep close-hauled on the starboard +tack, make as much way as possible, and if obliged to heave-to, do so on +the starboard tack.</p> + +<p><i>Left or navigable semicircle</i>,—Steam and sailing vessels: Bring the +wind on the starboard quarter, note the course and hold it. If obliged +to heave-to, steamers may do so stern to sea; sailing vessels on the +port tack.</p> + +<p><i>On the storm track in front of center</i>,—Steam and sailing vessels: +Bring the wind two points on the starboard quarter, note the course and +hold it, and run for the left semicircle, and when in that semicircle +manoeuvre as above.</p> + +<p>On the storm track, in rear of center,—Avoid the center by the best +practicable route, having due regard to the tendency of cyclones to +recurve to the southward and eastward."</p> + +<div class="center"><a name="fig12.jpg" id="fig12.jpg"></a><img src="images/fig12.jpg" width='627' height='700' alt="Fig. 12. The Winds in an Idealized Storm" /></div> + +<div class="block"><p>FROM HYDROGRAPHIC OFFICE</p></div> + +<p class="bold"><span class="smcap">Fig. 12. The Winds in an Idealized Storm</span></p> + +<hr /> + +<p><span class='pagenum'><a name="Page_65" id="Page_65">[Pg 65]</a></span></p> + +<h2><span>WIND AND ALTITUDE</span></h2> + +<p>The law of the turning of the wind with altitude.</p> + +<p>A casual observation of the lower clouds where no means of measuring +small angles is available will not usually show any difference between +the motion of the clouds and the surface wind; but with the upper clouds +the case is different, and one readily detects a difference.</p> + +<p>Several thousand observations with various agencies, such as kites and +pilot balloons and more especially measurements made with theodolites +and nephoscopes, show that there is a definite twist to the right with +elevation. The amount of the deflection is shown in Figure 13. Turning +of the Wind with Altitude. Here the average yearly values are given for +directions and velocities. Thus if the mean wind direction at Blue Hill +is from a point a little to the north of west, 306 grads or 275 degrees, +and the mean velocity 7 metres per<span class='pagenum'><a name="Page_66" id="Page_66">[Pg 66]</a></span> second; the clouds at 1000 metres +elevation will move from 312 or 280 degrees and at a speed of +approximately 11 metres per second (24 miles an hour).</p> + +<p>These however, are average values. In individual cases the difference +between surface winds and stratus clouds may be considerably greater. It +may be as much as 180 degrees; that is, the cloud may move directly +opposite to the wind. In general there will be a difference of 10 to 20 degrees.</p> + +<hr /> + +<h2><span>WIND AND RAIN</span></h2> + +<p>The law of wind direction, approximate cooling and rain.</p> + +<p>When the lower clouds are moving from the north or northwest, without +sharply defined edges, the LOW is east or northeast of the observer; and +rain or snow is not likely unless there is a rapidly falling temperature.</p> + +<div class="center"><a name="fig13.jpg" id="fig13.jpg"></a><img src="images/fig13.jpg" width='699' height='700' alt="Fig. 13. Turning of Wind with Altitude" /></div> + +<p class="bold"><span class="smcap">Fig. 13. Turning of Wind with Altitude</span></p> + +<p><span class='pagenum'><a name="Page_69" id="Page_69">[Pg 69]</a></span></p><p>When a stream of warm air with a high absolute humidity flows north on +the east side of a LOW, and a cold northwest wind follows quickly after +the LOW, rain or snow may be expected.</p> + +<p>Any rapid chilling of warm, moist air produces cloudiness and rain or +snow; but a cold stream blowing into a warm area will not produce as +much rain as a warm stream blowing into a cold area.</p> + +<hr /> + +<p><span class='pagenum'><a name="Page_70" id="Page_70">[Pg 70]</a></span></p> + +<h2><span>DURATION OF WIND</span></h2> + +<p>The average duration of wind from various directions is as follows:</p> + +<p>From the north about 16 hours each week; from the northeast, the same; +from the east, 11 hours; from the southeast, 10 hours; from the south, +24 hours; from the southwest, 27 hours; from the west, 33 hours; and +from the northwest 31 hours.</p> + +<p>During an individual disturbance lasting about 36 hours, we may have 8 +hours of southwest wind; 4 hours of west wind, backing during the next 4 +hours to south; 2 hours of south wind; 2 hours of southeast wind; 2 +hours of east wind; 8 hours northeast wind and 4 hours north wind, 2 +hours northwest, when it may be considered that a new pressure +distribution prevails.</p> + +<p>The above values hold only for a storm moving with normal velocity. LOWS +are often blocked by slow moving HIGHS in advance. In such cases the +duration of east winds is greater.</p> + +<hr /> + +<p><span class='pagenum'><a name="Page_71" id="Page_71">[Pg 71]</a></span></p> + +<h2><span>THE WINDS OF A YEAR</span></h2> + +<p>The following table shows the marked increase in the prevalence of +northwest and west winds during winter months, the decrease in north +winds during July, the increase in northeast winds in May, also in east +winds; the increase of south and southwest winds in July; and the +falling off of southeast winds in December. See Table, page 72.</p> + +<p>In cities near the Atlantic Coast, a continuance of northeast wind, +especially in the fall and winter months, results in frequent altho not +necessarily heavy rains. On the other hand a period of continued +northwest and west wind is a dry period.</p> + +<p>In summer, southeast and east winds bring fog and cooler weather; while +southwest winds are favorable for the development of thunderstorms.</p> + +<p><span class='pagenum'><a name="Page_72" id="Page_72">[Pg 72]</a></span></p> + +<p class="bold">WINDS OF A YEAR</p> + +<p class="bold">TABLE I.—Number of Hours the Wind Blows from Different Directions.</p> + +<table class="bb bt" summary="Number of Hours the Wind Blows from Different Directions"> + <tr> + <td></td> + <td></td> + <td> Jan.</td> + <td> Feb.</td> + <td> Mar.</td> + <td> Apr.</td> + <td> May</td> + <td> June</td> + <td> July</td> + <td> Aug.</td> + <td> Sept.</td> + <td> Oct.</td> + <td> Nov.</td> + <td> Dec.</td> + <td> Year</td> + </tr> + <tr> + <td class="left">Boreas</td> + <td>(N)</td> + <td>98</td> + <td>74</td> + <td>71</td> + <td>70</td> + <td>60</td> + <td>40</td> + <td>59</td> + <td>59</td> + <td>67</td> + <td>80</td> + <td>82</td> + <td>96</td> + <td>850</td> + </tr> + <tr> + <td class="left">Kaikias</td> + <td>(NE)</td> + <td>41</td> + <td>46</td> + <td>65</td> + <td>94</td> + <td>101</td> + <td>55</td> + <td>79</td> + <td>79</td> + <td>77</td> + <td>91</td> + <td>48</td> + <td>30</td> + <td>819</td> + </tr> + <tr> + <td class="left">Apheliotes</td> + <td>(E)</td> + <td>34</td> + <td>37</td> + <td>52</td> + <td>58</td> + <td>63</td> + <td>48</td> + <td>51</td> + <td>51</td> + <td>52</td> + <td>58</td> + <td>34</td> + <td>31</td> + <td>576</td> + </tr> + <tr> + <td class="left">Euros</td> + <td>(SE)</td> + <td>37</td> + <td>37</td> + <td>45</td> + <td>41</td> + <td>54</td> + <td>45</td> + <td>62</td> + <td>62</td> + <td>52</td> + <td>45</td> + <td>39</td> + <td>34</td> + <td>534</td> + </tr> + <tr> + <td class="left">Notus</td> + <td>(S)</td> + <td>82</td> + <td>66</td> + <td>95</td> + <td>99</td> + <td>143</td> + <td>155</td> + <td>128</td> + <td>128</td> + <td>118</td> + <td>93</td> + <td>81</td> + <td>65</td> + <td>1245</td> + </tr> + <tr> + <td class="left">Lips</td> + <td>(SW)</td> + <td>112</td> + <td>77</td> + <td>81</td> + <td>79</td> + <td>118</td> + <td>170</td> + <td>135</td> + <td>135</td> + <td>133</td> + <td>108</td> + <td>119</td> + <td>131</td> + <td>1402</td> + </tr> + <tr> + <td class="left">Zephyros</td> + <td>(W)</td> + <td>180</td> + <td>177</td> + <td>155</td> + <td>125</td> + <td>107</td> + <td>137</td> + <td>125</td> + <td>125</td> + <td>108</td> + <td>131</td> + <td>169</td> + <td>194</td> + <td>1732</td> + </tr> + <tr> + <td class="left">Skiron</td> + <td>(NW)</td> + <td>160</td> + <td>162</td> + <td>183</td> + <td>154</td> + <td>98</td> + <td>94</td> + <td>105</td> + <td>105</td> + <td>113</td> + <td>138</td> + <td>148</td> + <td>163</td> + <td>1607</td> + </tr> +</table> + +<p class="tbrk"> </p> + +<div class="center"><a name="fig14.jpg" id="fig14.jpg"></a><img src="images/fig14.jpg" width='700' height='625' alt="Fig. 14. Velocity of Summer and Winter Winds in Metres per Second" /></div> + +<p class="bold"><span class="smcap">Fig. 14. Velocity of Summer and Winter Winds in Metres per Second</span></p> + +<hr /> + +<p><span class='pagenum'><a name="Page_75" id="Page_75">[Pg 75]</a></span></p> + +<h2><span>THE SEA BREEZE</span></h2> + +<p>When the weather has been clear and moderately warm for two or more +days, and the winds are light and variable, there may occur on the third +day a moderate wind from the east, known as the sea-breeze. This occurs +during anticyclonic conditions. Preceding the sea-breeze, the winds are +very light, there are no clouds, and the temperature rises rapidly +during the forenoon. This heating is due to a slow dynamic compression +as the air slowly descends and the surface air does not flow away. There +is no cooling because there is no evaporation due to air movement. The +absolute humidity is low, often less than ten grams per cubic metre. +Cumulus clouds do not form because there is no uplift of the lower air +and consequently no chance for condensation of whatever water vapor may +be present. No thunder-heads form notwithstanding the<span class='pagenum'><a name="Page_76" id="Page_76">[Pg 76]</a></span> heat. The heat, +while dry, is nevertheless extremely trying to men and animals. Relief +comes in the early hours of the afternoon by the arrival of the sea-breeze.</p> + +<p>The usual explanation of the origin of the sea-breeze is that the land +being excessively warm, the air over a relatively cool ocean moves in to +take the place of the warm and therefore lighter air, which it is +assumed has risen. Unfortunately for this explanation, the air over the +land has <i>not</i> risen; but on the contrary is falling slowly. Again the +sea-breeze does not begin at the place where the temperature contrast is +greatest, namely, just inside the shore line; but comes in from the sea. +Nor does the flow extend far inland, which would be the case if there +were up-rising currents. The sea-breeze is very shallow, generally not +extending upward more than 200 metres, and often not above 100 metres. +It<span class='pagenum'><a name="Page_77" id="Page_77">[Pg 77]</a></span> does not penetrate far inland, as a rule not more than 15 +kilometres, 9 miles.</p> + +<p>The sea-breeze is probably caused by a slow descent of dry, warm air, on +an incline sloping from northeast to southwest. As it reaches the +surface it is twisted more to the right; that is, becomes an east wind. +It carries inland with it some of the air over the ocean which is much +cooler and heavily saturated.</p> + +<hr /> + +<p><span class='pagenum'><a name="Page_78" id="Page_78">[Pg 78]</a></span></p> + +<h2><span>MUGGY DAYS</span></h2> + +<p>There are certain days, more noticeable in summer than at other times, +when the air is heavily laden with water vapor; and there is little or +no cooling of the body due to evaporation. We perspire freely but as the +sweat does not evaporate, there is a constantly increasing amount of +water on the skin.</p> + +<div class="center"><a name="fig15.jpg" id="fig15.jpg"></a><img src="images/fig15.jpg" width='700' height='551' alt="Fig. 15. Blue Hill Observatory During Ice Storm, November +29-30, 1922" /></div> + +<p class="bold"><span class="smcap">Fig. 15. Blue Hill Observatory During Ice Storm, November +29-30, 1922</span></p> + +<p>It is not altogether a question of temperature, for another day may have +as high or even higher temperature. It is essentially a matter of +ventilation. On muggy days we are somewhat in the condition of the +unfortunate prisoners in the Black Hole at Calcutta. They did not die by +poisoning, as has generally been accepted, that is, lack of sufficient +oxygen and an excess of carbon dioxide; but because they were unable to +keep the skin sufficiently cool. There was no ventilation; no movement +of the air and the body became over-heated and exhaustion followed. No +matter how<span class='pagenum'><a name="Page_81" id="Page_81">[Pg 81]</a></span> much water there may be on the skin if the surrounding space +is saturated, one feels oppressed. A vigorous fanning of the air helps +evaporation and cools us. That is why a brisk northwest wind routs a muggy condition.</p> + +<hr /> + +<h2><span>CASTILIAN DAYS</span></h2> + +<p>John Hay wrote of such days spent in Spain. We who live in a land where +the winds are more boisterous, occasionally experience what we call a +perfect day. Such days have easterly winds of two metres per second or +less than five miles an hour. The temperature is midway between freezing +and normal body temperature or about 70° F. The relative humidity is +approximately 75% and the absolute humidity 12 grams per cubic metre. +The table on page 72 explains the paucity of perfect days. The gusty, +boisterous winds, Skiron and Zephyros, blow too frequently.</p> + +<p><span class='pagenum'><a name="Page_82" id="Page_82">[Pg 82]</a></span></p><p>Perhaps certain of our national characteristics may be traceable to +this flow of the air and our climatic environment.</p> + + + + + + + + +<pre> + + + + + +End of the Project Gutenberg EBook of Wind and Weather, by Alexander McAdie + +*** END OF THIS PROJECT GUTENBERG EBOOK WIND AND WEATHER *** + +***** This file should be named 38072-h.htm or 38072-h.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/3/8/0/7/38072/ + +Produced by Chris Curnow, Martin Pettit and the Online +Distributed Proofreading Team at http://www.pgdp.net (This +file was produced from images generously made available +by The Internet Archive) + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Wind and Weather + +Author: Alexander McAdie + +Release Date: November 21, 2011 [EBook #38072] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK WIND AND WEATHER *** + + + + +Produced by Chris Curnow, Martin Pettit and the Online +Distributed Proofreading Team at http://www.pgdp.net (This +file was produced from images generously made available +by The Internet Archive) + + + + + + +WIND AND WEATHER + + +[Illustration: Logo] + +THE MACMILLAN COMPANY +NEW YORK . BOSTON . CHICAGO . DALLAS +ATLANTA . SAN FRANCISCO + +MACMILLAN & CO., LIMITED +LONDON . BOMBAY . CALCUTTA +MELBOURNE + +THE MACMILLAN CO. OF CANADA, LTD. +TORONTO + + +[Illustration: HOW THE WIND RUFFLES THE TOP OF A FOG BANK + +_Frontispiece_] + + + + +WIND AND WEATHER + +BY ALEXANDER McADIE + +A. Lawrence Rotch Professor of Meteorology, Harvard +University and Director of the Blue Hill Observatory + +New York +THE MACMILLAN COMPANY +1922 + +_All rights reserved_ + + +Copyright, 1922, +By ALEXANDER McADIE. + +Set up and electrotyped. Published November, 1922. + + + + +LIST OF ILLUSTRATIONS + + + HOW THE WIND RUFFLES THE TOP + OF A FOG BANK _Frontispiece_ + + PAGE +FIG. 1. THE TOWER OF THE WINDS 13 + + " 2. BOREAS--THE NORTH WIND 19 + + " 3. KAIKIAS--THE NORTHEAST WIND 23 + + " 4. APHELIOTES--THE EAST WIND 29 + + " 5. EUROS--THE SOUTHEAST WIND 33 + + " 6. NOTOS--THE SOUTH WIND 37 + + " 7. LIPS--THE SOUTHWEST WIND 41 + + " 8. ALL STORMS LEAD TO NEW ENGLAND 45 + + " 9. ZEPHYROS--THE WEST WIND 49 + + " 10. PATHS OF HIGH AND LOW, JANUARY, 1922 55 + + " 11. SKIRON--THE NORTHWEST WIND 59 + + " 12. THE IDEALIZED STORM 63 + + " 13. TURNING OF WIND WITH ALTITUDE 67 + + " 14. VELOCITY OF SUMMER AND WINTER WINDS 73 + + " 15. BLUE HILL OBSERVATORY IN AN ICE STORM 79 + + + + +WIND AND WEATHER + + + + +THE TOWER OF THE WINDS + + +In Athens on the north side and near the base of the hill on which the +upper city--the Acropolis--is built, there is a small temple still +standing, altho its walls were completed twenty-two centuries ago. It is +known as the Tower of the Winds; but as a matter of fact, the citizens +of Athens used it to tell the hour of the day and the seasonal position +of the sun. It was a public timepiece. It served as a huge sun dial. +Water from a spring on the hillside filled the basins of a water clock +in the basement of the Tower. And so, whether the day was clear or +cloudy the measure of the outflow of water indicated the time elapsed. +Also there were markings or dials on each of the eight walls of the +temple, and the position of the shadow of a marker indicated the +seasonal advance or retreat of the sun as it moved north from the time +of the winter solstice and then south after the summer solstice. + +The sun is not an accurate time keeper and no one to-day runs his +business or keeps engagements on sun time. But the old Athenians were +quite content to do so; and their Tower served excellently for their +needs. And they did what we moderns fail to do, namely, give distinctive +names to the winds. They represented figuratively the characteristics of +the weather as the wind blew from each of the eight cardinal directions. + +[Illustration: FIG. 1. THE TOWER OF THE WINDS + +Erected in Athens, on the north side of the Acropolis, B. C. 150] + +The allegorical figures of the winds used in this little book are +reproductions of the eight bas-reliefs in the library of the Blue Hill +Observatory, placed there by the late Professor A. Lawrence Rotch. They +are copied from the frieze of the Tower of the Winds at Athens. + + + + +THE NAMES OF THE WINDS + + +Boreas, the north wind, is perhaps the most important of all winds. At +Athens this a cold, boisterous wind from the mountains of Thrace. The +noise of the gusts is so loud that the Greek sculptor symbolized the +tumult by placing a conch shell in the mouth of Boreas. His modern +namesake, the Bora of the Adriatic, is the same noisy, blustering, cold +wind-rush from the north. + +The northeast wind Kaikias is a trifle more pleasant looking than +Boreas, but still not much to brag about. Master of the squall and +thunderstorm, he carries in his shield an ample supply of hailstones, +ready to spill them on defenseless humanity. He might well serve as the +patron saint of air raiders dropping their bombs on helpless humans +below. + +Apheliotes, the east wind, is a graceful youth, with arms full of +flowers, fruit and wheat. Naturally this was a favorite wind, blowing in +from the sea, with frequent light showers. Some of us who dwell on the +Atlantic Coast, in more northern latitudes than Athens, do not always +regard with favor the east wind, associating it with chilly, damp and +sombre weather. Yet it is the harbinger of good--tempering the cold of +winter and the heat of summer. It is an angel of mercy in mid-summer +when the temperature is above the nineties and there is no air stirring. +Then it is, that we all welcome the refreshing wind from the sea. + +Euros, the southeast wind, and neighbor to Apheliotes, is a cross old +fellow, intent on the business of cloud making. He alone of all the +winds carries nothing in his hands. In the New Testament he becomes +Euroclydon, wind of the waves. He is no friend of the sailor; and the +seasick traveler prays to be rid of his company. + +The figure on the south face of the tower, Notos, is the master of the +warm rain. He carries with him a water jar which has just been emptied. +Compare his light flowing robes and half-clad neck and arms with the +close fitting jacket of old Boreas. At his shrine, hydraulic engineers +well might worship. + +Next, the Mariner's wind, Lips, the southwest favoring breeze bringing +the ships speedily into harbor; yes, into that Piraeus, famed in classic +history. Incidentally it is the southwest wind which differentiates the +climate of Great Britain from that of Labrador. This wind makes +Northwest Europe habitable; while on the other side of the Atlantic, in +similar latitudes, but under the influence of prevailing northwest +winds, we find Labrador--a section certainly misnamed, for it is not the +abode of farmers, as the name implies--but barren and bleak. What a +difference it would make thruout this region if the Gulf Stream +continued north, close to the shore, and the prevailing winds were _from +the east_. Our North Atlantic Coast would then be _the land of zephyrs_, +using the word in the sense of pleasant, gentle winds. + +[Illustration: FIG. 2. BOREAS--THE NORTH WIND] + +Zephyros, the west wind, is represented as a graceful youth, scantily +clad, with his arms filled with flowers. In Greece this wind traversed +the Ionian Sea and the Gulf of Corinth before reaching Athens. It is +quite unlike our west wind which blows across a continent, and is +continuously robbed of its water vapor on the long passage. The Ionian +wind is pleasantly moist and refreshing. + +Last of all, but by no means least important, is Skiron, lord of gusty +northwest gales. Freezing in winter, parching in summer, he carries with +him a brazen fire basket and spills a generous stream of hot air on all +below. His husky Highness might not inappropriately adorn legislative +halls and editorial sanctums. He would displace the blindfolded lady +holding scales very much out of balance. Think of the deep significance +of his presence. + +In our country the northwest is of all winds, except the west, most +persistent. For 1600 hours in a year, this wind is with us. Joining +forces with the west wind, these directions prevail one third of the +time. These northwest-west winds also have the greatest speed and +gustiness. The climate of the United States is essentially determined by +the prevalence of the north, northwest and west winds. + + + + +FORECASTING THE WEATHER + + +In old days, the _haruspices_ (for this is what the Romans called +weather men in the days of Caesar) proclaimed the will of the gods by +consulting the entrails of some freshly killed animal. Evidently these +haruspices did not always make correct forecasts; for there were some +Romans who openly questioned their worth. Cato, the Censor, is on record +as saying "that he wondered how one haruspex could look another in the +face without laughing!" + +[Illustration: FIG. 3. KAIKIAS--THE NORTHEAST WIND] + +The modern professional forecaster would scorn to consult the entrails. +There are however many amateur forecasters who foretell weather by their +aches and rheumatic pains. Probably there is a high correlation factor +between body sensations and dampness; and some individuals are quite +sensitive to changes in both relative and absolute humidity. This, +however, does not always mean that a storm is approaching. Humidity or +dampness is only one factor and may be quite local, whereas most storms +are wide-spread. + + + + +THE WEATHER MAP + + +The official forecaster consults a daily weather map and certain +auxiliary maps which show changes in pressure and temperature for twelve +hours or more. He examines closely the contours of pressure as shown on +the map. The synoptic map, as it is called, because it is a glance at +weather conditions over a large area at one and the same moment, is a +map on which are plotted pressure, temperature, wind direction, velocity +and rainfall. The lines of equal pressure or isobars generally curve and +inclose what is known as a cyclonic centre, or depression or LOW. The +arrows point in, but not exactly toward the centre of the depression. + +On the map there will probably appear also an area of high pressure +where the surface air flows leisurely outward and away from the place of +highest pressure. Such an area is called an anticyclone, a word first +used by Sir Francis Galton in 1863 to designate not only high pressure, +but general flow of the air in a reversed or opposite direction to that +of the low area or cyclone. The word cyclone was first used by +Piddington in 1843 in describing the flow of the air in the typhoons of +the East Indian Seas. It is from the Greek and literally means the coils +of a serpent. The word cyclone must possess some special merit in the +minds of journalists for it is quite commonly misused for tornado in +descriptions of the smaller and more destructive storm. + + + + +THE LOW + + +Cyclone is simply the generic name for a large rotating air mass. It is +a barometric depression or LOW and is characterized by a flow of air +inward and around a moving centre. The air circulation is +counter-clockwise in the northern hemisphere and clockwise in the south. + +Perhaps if the earth stopped rotating and there was no planetary +circulation, with the great west-moving trades and east-moving +"westerlies," the arrows on the weather map would all point directly +toward the centre of the LOW; but, as things are, there are some very +good reasons why air can not move directly into a LOW, that is at right +angles to the isobars. + +Moreover, the weather map does not indicate the true flow of the air, +for observations of the wind made at the ground tell only a part of the +story of the balance which the flowing air must maintain under the +action of various forces, such as gravitation, rotational deflection, +centrifugal tendency, and the various expansion and compression forces. + +The winds near the ground are modified both in velocity and direction by +friction. The free flow is often interfered with by topography. + + + + +THE TRUE AIR FLOW + + +One must rise above the ground some distance to get the true air flow, +or what is known as the gradient wind, the flow which balances the +gradient, i.e. a flow along the isobars. The gradient velocity is found +about 300 metres above the ground, and the gradient direction a little +higher. The lower clouds as a rule indicate true wind values very well; +and so, it is desirable in studying winds to use cloud directions and +velocities rather than surface values. In cloud work a nephoscope is +essential. The unaided eye, unless properly shielded, suffers from the +glare of a sunlit sky; and moreover, there are no fixed points or +references. A black mirror, with suitable sighting rods and measuring +devices, enables an observer to follow the cloud, estimate its height +and determine with accuracy the direction from which it is moving. There +is an average difference of 30 degrees between the cloud direction and +the surface wind; the upper direction being more to the right. At times +the directions may be opposite. + +[Illustration: FIG. 4. APHELIOTES--THE EAST WIND] + +It may seem surprising but few of us, except at sunrise and sunset, +really see what is going on in cloud land. + +Some meteorologists hold that the circulation of air 3000 to 5000 +metres above the ground controls the path and perhaps the intensity of +storms. It is therefore important to know something of the flow at high +levels if we would improve the forecasts. + + + + +LIMITATIONS OF MAP + + +The weather map fails to indicate what shifts of direction and changes +in velocity are likely to occur. The forecaster tries to anticipate +these, but he bases his conclusions chiefly upon an expected movement of +the low area; using the accumulated records of the paths of past storms. +But each storm is in reality a law unto itself; and while we know +something of the relations between pressure and flow of the air; as yet +we know very little about the relations of wind and weather. The problem +is complicated by the behavior of the load of water vapor. + +[Illustration: FIG. 5. EUROS--THE SOUTHEAST WIND] + +The Chief Forecaster of one of the great national weather services +recently wrote: + + + "Despite the fact that maps have now been drawn day by day for over + half a century, we may safely say that no two maps have been + identical." + + +It is perhaps unfortunate that so much attention has been given to the +cyclone or depression or LOW, and comparatively little to the HIGH or +anticyclone. For we are now beginning to understand that while there may +seem at first to be nothing specially noteworthy about a mass of air +where the pressure varies from 1020 to 1040 kilobars, that is, 2 to 4 +per cent _above_ a standard atmosphere, with isobars irregularly curved +and feeble surface winds, yet the anticyclone is more important than the +cyclone in determining weather sequence; for the progressive motion of +the cyclone depends largely upon the strength of the anticyclone. + + + + +OCEAN STORMS + + +Sir Napier Shaw, who has written much on the weather of the British +Isles, may be quoted here. + + + "Anyone who is interested in the weather is always on the lookout + for 'lows' and is very keen to know whether he is going to be on + the south of the centre or the north of it. He is, of course, + interested in the anticyclone too, because as long as an + anticyclone is there, there cannot be a depression; but it is the + depression which has the life and movement about it, giving it a + claim to the attention of everybody who wants to know what the + weather and its changes are going to be. + + "This has been recognized from the very earliest days of weather + maps with isobars. The depressions which pass over our shores + (Great Britain) mostly come from the west. Some of them come all + the way from America; one or two have been traced from the west + coast of Africa and so have crossed the Atlantic twice, first to + the westward and then to the eastward. Some have come all the way + from a sort of parent 'low' in the North Pacific Ocean. So general + is the tendency for 'lows' to go eastward that it was thought at + one time, particularly by the 'New York Herald,' that their + departure from the American Coast and subsequent arrival on our own + shores could be notified by cable, and we (the British) might thus + be forewarned of their approach, some three or four days in + advance. The attempt was made by the 'New York Herald' acting in + co-operation with the Meteorological Offices of the United Kingdom + and France. But a depression keeps to no beaten track; it has as + many paths for its centre as there are lines in a bundle of hay. + Though groups can be picked out there are many strays, and, + moreover, the depression changes its shape and intensity while it + travels, so that if you lose sight of it for a day you cannot be at + all sure of its identity." + + +[Illustration: FIG. 6. NOTOS--THE SOUTH WIND] + + + + +TRANSCONTINENTAL STORMS + + +If there is so much uncertainty in forecasting the path of a disturbance +at sea, how much more uncertain must it be on land? Elaborate statistics +of the average daily movement of various types of storms have been +officially published. The average speed of storms (not wind speeds) +across the United States is 11 metres per second or 25 miles an hour. +Storms travel more rapidly in winter than in summer, about half again as +fast; that is, summer storms travel 20 miles, and winter storms 30 +miles, an hour. + +[Illustration: FIG. 7. LIPS--THE SOUTHWEST WIND] + +The paths vary widely; from the Gulf storms moving northeast and West +Indian hurricanes recurving on the southern coast, to the storms from +Alberta and the west which move south and east. Ten types of storms, +classified according to the place of origin, are recognized by the +official forecasters of the United States. These are North Pacific, +Alberta, Northern Rocky Mountain, Colorado, Central, South Pacific, +Texas, East Gulf, South Atlantic and West Indian Hurricanes. A better +nomenclature would be (1) Alberta, (2) Washington, (3) Kootenay, (4) +Utah, (5) Kansas, (6) California, (7) Texas, (8) Louisiana, (9) +Florida, and (10) Hurricanes. + + + + +HURRICANES + + +Type 10 is the general class of tropical storms occurring chiefly in the +summer and fall which, drifting west, slowly work northward. Similar +storms are the typhoons and baguios of the East Indian and China Seas. + +The path and point of recurvature will be determined by the position of +the Bermuda Hyperbar, that is, the seasonal anticyclone of the Atlantic. +This accounts for the swinging east and north of these tracks as the +season progresses; for the hyperbar is slowly displaced east, the +maximum displacement occurring in September. + +[Illustration: BASE MAP BY GOODE + +FIG. 8. ALL STORMS LEAD TO NEW ENGLAND] + +Individual anticyclones also influence individual hurricanes. Thus a +hurricane passing west over Havana, will go farther west if a vigorous +"high" is spreading southeast over the Gulf States. And when this "high" +passes seaward, the hurricane will work around the southwest quadrant of +the "high," recurving and moving northeast. + + + + +STORM RENDEZVOUS + + +Altho storms originate or are first detected in nine different sections, +it is a fact worth mentioning that they all leave the United States in +the vicinity of New England or Nova Scotia. Some of the southern +depressions starting near the coast, pass to sea south of New York, but +in general an observer standing on Plymouth Rock can virtually encompass +within a radius of 500 kilometres, 300 miles, the paths of ninety per +cent of the storms that traverse the country. + +Thus a storm that originates in Texas (7) will probably pass close to +Cape Cod. Likewise, types (3) and (5); while the other types may pass a +little to the north or south. See Chart, Paths of Storms. + + + + +STORM PATHS + + +Forecasting then would seem to be very easy; for one would only have to +know the place of origin of the storm and the rate of travel, to +foretell exactly the time of arrival. Unfortunately these are only the +average paths; and as with most mean values, represent a value not often +experienced in fact. These paths then are not paths which any given +storm will follow. One must recall the story of the operating surgeon +who gave the average age of his patients in the operating room as 35. +There were but two patients, one 69 years old and the other 1 year old. + +[Illustration: FIG. 9. ZEPHYROS--THE WEST WIND] + +As a matter of fact the path of any individual depression depends upon +several factors, some of which are:--the prevailing eastward drift of +the air; the extent and motion of some anticyclone advancing before the +"LOW"; the duration and speed of relatively dry cold tongues of air from +the north; and the supply of water vapor brought from southern waters by +south winds. A depression can make little headway if to the north or +east the normal path is blocked by what is known as a stagnant "HIGH." +So therefore, if the anticyclone is a slow mover, a Texas storm, which +would normally pass not far from southern New England, may be deflected +farther north than when the HIGH moved rapidly east. So too, with the +storms which originate in the western part of the country. A slow moving +HIGH will prevent the LOW following it, from moving east at a normal +rate along the usual path. + +Anticyclones then, are the real weather controls. There are various +types, but all drift from the north or west. Occasionally they enter the +country from the Pacific, but the great majority come from Alberta and +move leisurely southeast, often reaching the South Atlantic States; but +more frequently recurving and passing to the north. + + + + +STAGNANT HIGHS + + +HIGHS are sometimes reinforced and this results in what is called a +stagnant HIGH. A good illustration of such a slow moving HIGH and its +consequences occurred during the last week of January, 1922. + +A surge of cold air from Alberta or farther north reached the +international boundary January 21st and spread slowly eastward, reaching +the Great Lakes on the 24th and the St. Lawrence Valley two days later. +Then seemingly it halted or moved slowly westward, retrograding. In +three days, that is, on the 29th, the centre of the HIGH was apparently +500 miles _west_ of where it had been on the 27th. After the 29th it +followed a normal track, moving slowly southeast, reaching the Atlantic +near Long Island. + +Meanwhile a depression on the south coast of Texas on the 25th, moved +across the Gulf of Mexico, passing over Southern Florida on the 27th and +advanced steadily northeast, reaching Cape Hatteras in 24 hours. Owing +to the presence of the anticyclone referred to above, the depression +recurved off Hatteras. The result was a memorable snow storm in Northern +Virginia and Maryland. At 8 p.m. January 27th, there had been a fall of +5 cms. (2 inches). Within the following twenty hours the average depth +in the city of Washington was 66 cms. (26 inches). The weight of the +snow caused the collapse of the roof of the Knickerbocker Theatre and +the death of 97 persons. + +The total snowfall in various coast cities was: + + + Raleigh 24 cms.* + Richmond 48 " + Washington 71 " + Baltimore 67 " + Wilmington 46 " + Philadelphia 31 " + Trenton 27 " + New York 18 " + New Haven 8 " + Boston 1 " + + *Note: To convert to inches multiply by 0.4. + + +The table shows clearly how the snow was formed. On the east side of the +LOW a stream of air, relatively warm, carried a load of water vapor, +approximately 13 grams in each cubic metre. + +[Illustration: BASE MAP BY GOODE + +FIG. 10. PATHS OF HIGH AND LOW, GREAT SNOW STORM OF JANUARY 27-28, 1922] + +This current was steered around the north side of the LOW and met the +north-northeast wind. Under the new conditions the air saturated could +hold only 2 or 3 grams; and so condensation and heavy precipitation +resulted. The region of maximum snowfall was near Washington, and it +will be seen that there is a proportional decrease north and south. The +snowfall at Washington was the heaviest ever known at that city. + +Unlike most storms, there was no strong cold northwest wind blowing into +the depression. The temperature rose slowly. It was less a contrast of +winds than a steady slow outward push of the anticyclone, and the +consequent turning of the path of the cyclone eastward. + + + + +LAWS OF FORECASTING + + +Buys Ballot's Law. + +"If you stand with your back to the wind the pressure decreases toward +your left, and increases toward your right." + +For navigators, this law is more generally expressed in the words of the +Hydrographic Office on "Cyclonic Storms." + +"Since the wind circulates counter-clockwise in the northern hemisphere, +the rule in that hemisphere is to face the wind, and the storm centre +will be at the right hand. If the wind traveled in exact circles, the +centre would be eight points (90 degrees) to the right when looking +directly in the wind's eye. But the wind follows a more or less spiral +path inward which brings the centre from eight to twelve points (90 to +135 degrees), to the right of the wind. The centre will bear more nearly +eight points from the direction of the lower clouds than from the +surface wind." + +[Illustration: FIG. 11. SKIRON--THE NORTHWEST WIND] + +The law given on the preceding page is named after C. H. D. Buys +Ballott, a Dutch meteorologist. It was announced in a paper published in +the _Comptes rendus_ in 1857. Two American writers on the Winds, J. H. +Coffin and William Ferrell, had however earlier found the law to hold. + + * * * * * + +While most of us study storms from a window at home and are not called +upon to handle a ship in a storm, yet it may not be out of place to +include here the diagram of the winds in an ideal storm and give the +rules for maneuvering. See Figure 12. The Winds in an Idealized Storm. +The rules apply only to storms in the northern hemisphere. + +"_Right or dangerous semicircle_,--Steamers: Bring the wind on the +starboard bow, make as much way as possible, and if obliged to heave-to, +do so head to sea. Sailing vessels: Keep close-hauled on the starboard +tack, make as much way as possible, and if obliged to heave-to, do so on +the starboard tack. + +_Left or navigable semicircle_,--Steam and sailing vessels: Bring the +wind on the starboard quarter, note the course and hold it. If obliged +to heave-to, steamers may do so stern to sea; sailing vessels on the +port tack. + +_On the storm track in front of center_,--Steam and sailing vessels: +Bring the wind two points on the starboard quarter, note the course and +hold it, and run for the left semicircle, and when in that semicircle +manoeuvre as above. + +On the storm track, in rear of center,--Avoid the center by the best +practicable route, having due regard to the tendency of cyclones to +recurve to the southward and eastward." + +[Illustration: FROM HYDROGRAPHIC OFFICE + +FIG. 12. THE WINDS IN AN IDEALIZED STORM] + + + + +WIND AND ALTITUDE + + +The law of the turning of the wind with altitude. + +A casual observation of the lower clouds where no means of measuring +small angles is available will not usually show any difference between +the motion of the clouds and the surface wind; but with the upper clouds +the case is different, and one readily detects a difference. + +Several thousand observations with various agencies, such as kites and +pilot balloons and more especially measurements made with theodolites +and nephoscopes, show that there is a definite twist to the right with +elevation. The amount of the deflection is shown in Figure 13. Turning +of the Wind with Altitude. Here the average yearly values are given for +directions and velocities. Thus if the mean wind direction at Blue Hill +is from a point a little to the north of west, 306 grads or 275 degrees, +and the mean velocity 7 metres per second; the clouds at 1000 metres +elevation will move from 312 or 280 degrees and at a speed of +approximately 11 metres per second (24 miles an hour). + +These however, are average values. In individual cases the difference +between surface winds and stratus clouds may be considerably greater. It +may be as much as 180 degrees; that is, the cloud may move directly +opposite to the wind. In general there will be a difference of 10 to 20 +degrees. + + + + +WIND AND RAIN + + +The law of wind direction, approximate cooling and rain. + +When the lower clouds are moving from the north or northwest, without +sharply defined edges, the LOW is east or northeast of the observer; and +rain or snow is not likely unless there is a rapidly falling +temperature. + +[Illustration: TURNING OF WIND WITH ALTITUDE, BLUE HILL + +FIG. 13. TURNING OF WIND WITH ALTITUDE] + +When a stream of warm air with a high absolute humidity flows north on +the east side of a LOW, and a cold northwest wind follows quickly after +the LOW, rain or snow may be expected. + +Any rapid chilling of warm, moist air produces cloudiness and rain or +snow; but a cold stream blowing into a warm area will not produce as +much rain as a warm stream blowing into a cold area. + + + + +DURATION OF WIND + + +The average duration of wind from various directions is as follows: + +From the north about 16 hours each week; from the northeast, the same; +from the east, 11 hours; from the southeast, 10 hours; from the south, +24 hours; from the southwest, 27 hours; from the west, 33 hours; and +from the northwest 31 hours. + +During an individual disturbance lasting about 36 hours, we may have 8 +hours of southwest wind; 4 hours of west wind, backing during the next 4 +hours to south; 2 hours of south wind; 2 hours of southeast wind; 2 +hours of east wind; 8 hours northeast wind and 4 hours north wind, 2 +hours northwest, when it may be considered that a new pressure +distribution prevails. + +The above values hold only for a storm moving with normal velocity. LOWS +are often blocked by slow moving HIGHS in advance. In such cases the +duration of east winds is greater. + + + + +THE WINDS OF A YEAR + + +The following table shows the marked increase in the prevalence of +northwest and west winds during winter months, the decrease in north +winds during July, the increase in northeast winds in May, also in east +winds; the increase of south and southwest winds in July; and the +falling off of southeast winds in December. See Table, page 72. + +In cities near the Atlantic Coast, a continuance of northeast wind, +especially in the fall and winter months, results in frequent altho not +necessarily heavy rains. On the other hand a period of continued +northwest and west wind is a dry period. + +In summer, southeast and east winds bring fog and cooler weather; while +southwest winds are favorable for the development of thunderstorms. + + +WINDS OF A YEAR + +TABLE I.--Number of Hours the Wind Blows from Different Directions. + + -------------------------------------------------------------------- + Jan. Mar. May July Sept. Nov. Year + Feb. Apr. June Aug. Oct. Dec. + + Boreas (N) 98 74 71 70 60 40 59 59 67 80 82 96 850 + Kaikias (NE) 41 46 65 94 101 55 79 79 77 91 48 30 819 + Apheliotes (E) 34 37 52 58 63 48 51 51 52 58 34 31 576 + Euros (SE) 37 37 45 41 54 45 62 62 52 45 39 34 534 + Notus (S) 82 66 95 99 143 155 128 128 118 93 81 65 1245 + Lips (SW) 112 77 81 79 118 170 135 135 133 108 119 131 1402 + Zephyros (W) 180 177 155 125 107 137 125 125 108 131 169 194 1732 + Skiron (NW) 160 162 183 154 98 94 105 105 113 138 148 163 1607 + -------------------------------------------------------------------- + + +[Illustration: FIG. 14. VELOCITY OF SUMMER AND WINTER WINDS IN METRES +PER SECOND] + + + + +THE SEA BREEZE + + +When the weather has been clear and moderately warm for two or more +days, and the winds are light and variable, there may occur on the third +day a moderate wind from the east, known as the sea-breeze. This occurs +during anticyclonic conditions. Preceding the sea-breeze, the winds are +very light, there are no clouds, and the temperature rises rapidly +during the forenoon. This heating is due to a slow dynamic compression +as the air slowly descends and the surface air does not flow away. There +is no cooling because there is no evaporation due to air movement. The +absolute humidity is low, often less than ten grams per cubic metre. +Cumulus clouds do not form because there is no uplift of the lower air +and consequently no chance for condensation of whatever water vapor may +be present. No thunder-heads form notwithstanding the heat. The heat, +while dry, is nevertheless extremely trying to men and animals. Relief +comes in the early hours of the afternoon by the arrival of the +sea-breeze. + +The usual explanation of the origin of the sea-breeze is that the land +being excessively warm, the air over a relatively cool ocean moves in to +take the place of the warm and therefore lighter air, which it is +assumed has risen. Unfortunately for this explanation, the air over the +land has _not_ risen; but on the contrary is falling slowly. Again the +sea-breeze does not begin at the place where the temperature contrast is +greatest, namely, just inside the shore line; but comes in from the sea. +Nor does the flow extend far inland, which would be the case if there +were up-rising currents. The sea-breeze is very shallow, generally not +extending upward more than 200 metres, and often not above 100 metres. +It does not penetrate far inland, as a rule not more than 15 +kilometres, 9 miles. + +The sea-breeze is probably caused by a slow descent of dry, warm air, on +an incline sloping from northeast to southwest. As it reaches the +surface it is twisted more to the right; that is, becomes an east wind. +It carries inland with it some of the air over the ocean which is much +cooler and heavily saturated. + + + + +MUGGY DAYS + + +There are certain days, more noticeable in summer than at other times, +when the air is heavily laden with water vapor; and there is little or +no cooling of the body due to evaporation. We perspire freely but as the +sweat does not evaporate, there is a constantly increasing amount of +water on the skin. + +[Illustration: FIG. 15. BLUE HILL OBSERVATORY DURING ICE STORM, NOVEMBER +29-30, 1922] + +It is not altogether a question of temperature, for another day may have +as high or even higher temperature. It is essentially a matter of +ventilation. On muggy days we are somewhat in the condition of the +unfortunate prisoners in the Black Hole at Calcutta. They did not die by +poisoning, as has generally been accepted, that is, lack of sufficient +oxygen and an excess of carbon dioxide; but because they were unable to +keep the skin sufficiently cool. There was no ventilation; no movement +of the air and the body became over-heated and exhaustion followed. No +matter how much water there may be on the skin if the surrounding space +is saturated, one feels oppressed. A vigorous fanning of the air helps +evaporation and cools us. That is why a brisk northwest wind routs a +muggy condition. + + + + +CASTILIAN DAYS + + +John Hay wrote of such days spent in Spain. We who live in a land where +the winds are more boisterous, occasionally experience what we call a +perfect day. Such days have easterly winds of two metres per second or +less than five miles an hour. The temperature is midway between freezing +and normal body temperature or about 70 deg. F. The relative humidity is +approximately 75% and the absolute humidity 12 grams per cubic metre. +The table on page 72 explains the paucity of perfect days. The gusty, +boisterous winds, Skiron and Zephyros, blow too frequently. + +Perhaps certain of our national characteristics may be traceable to +this flow of the air and our climatic environment. + + + + + +End of the Project Gutenberg EBook of Wind and Weather, by Alexander McAdie + +*** END OF THIS PROJECT GUTENBERG EBOOK WIND AND WEATHER *** + +***** This file should be named 38072.txt or 38072.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/3/8/0/7/38072/ + +Produced by Chris Curnow, Martin Pettit and the Online +Distributed Proofreading Team at http://www.pgdp.net (This +file was produced from images generously made available +by The Internet Archive) + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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