All our surface-winds, except the light, peculiar W. S. W. wind which is felt where the counter-trade is in contact with the earth, and which is a part of it, and perhaps the genuine N. W. wind which is very peculiar, are incidents of the trade, and are due to its conditions and attractions.We have already said this was true of the easterly wind and scud of a storm—it is alike true of all. The storm winds east of the Alleghanies are usually, though not always, from the eastward. They are sometimes from the southward, as they doubtless are still more frequently in the interior of the continent.
There is occasionally a southerly afternoon wind, followed by short rains in spring and fall, or a succession of showers in summer, which is rather a precedent wind than a storm wind; blowing toward and under an advance portion of the storm at the north, and hauling to the eastward when the rain sets in, or to the westward when the showers reach us.
When there are no storms, or showers, or inducing electric action in the counter-trade, within influential distance to disturb the surface atmosphere, it is calm. If a storm approaches, or forms within inducing distance, the surface atmosphere isaffectedandattracted toward the storm, from one or more points, and “blows,” as we say, toward and under it. Itcommences blowing first nearest the storm, and extends as the storm travels, or becomes more intense and extends its inducing influence. I have repeatedly noticed this in traveling on steamboats and railroads runningtowardorfrom, and in several instancesthrougha storm, and telegraphic notices and other investigations prove it. The point from which the surface atmosphere is attracted and blows, depends very much upon the position of the storm in relation to bodies of water and the point of observation, and its shape; and the force with which it may blow will depend much upon its intensity.
Let us take an instance or two by way of illustration of all these points; and as I have given instances of summer in the introduction, we will take those of winter. It is January of an “old fashioned winter;” the snow is about three feet deep in Canada, about one foot in Southern New York, and a few inches in Philadelphia, and so extends west to the Alleghanies at least. For several days the sky has been clear, the thermometer rising in the day-time, in the vicinity of New York to about 25° Fahrenheit, falling at night to about 6°, with light airs from the N. W. during the middle and latter part of the day; the counter-trade and the barometer both running high; cold but pleasant, steady, winter weather. There is a warm south-east rain and thaw coming, as one or more such almost invariably occur in January. How coming? The sun is far south, and shines aslant, but through a pure and windless atmosphere; he has tried for several days to melt the snow fromthe roof; a few icicles are pendant from the eaves; but the body of the snow is still there. How can a thaw come? not from the sun, surely. No, indeed, not from the action of the sun directly, upon our country, nor from the Atlantic or the Gulf Stream which is off our coast. But a portion of the current of counter-trade is coming, heated by his rays and the warm water in the South Atlantic, in an intense magneto-electric state, capable of inducing an electro-thermal change in the surface atmosphere which it approaches, and of being reciprocally acted upon by the north polar terrestrial magnetism. It is now over Northern Texas and Western Louisiana, it will be here day after tomorrow. The day passes as the day previous had passed; the sleigh-bells jingle merrily in the evening; the moon shines clear all night; the storm is coming steadily on, but its influence has not reached us, and the morning and midday are like those which preceded it. As nightfall approaches, however, the thermometer does not fall as rapidly as on the day previous; the sun shines dimly and through lines of whitish cirrus cloud extending from the horizon at the west, appearing darker as the sun descends and shines morehorizontallythrough them—perhaps mainly in the N. W.—and which extend up and over toward the E. N. E. The air next the earth begins to feel raw; it is changing, not from warm to cold, butelectricallyfrom positive to negative; and dampening, from a tendency to condensation by induction, as we shall see—the same condensation which in warm weathermay be seen on flagging stones, and walls, and vessels containing cold water. The advance cirrus condensation of the storm is over us and affecting us; the earth too is affecting the adjacent atmosphere by action extended from beneath the storm. Still there is no wind, although sounds seem to be heard a little more distinctly from the east, and so ends the day. Evening comes, and the moon wades in a smooth bank of cirro-stratus haze, with a very large circle around her; the cirrus bands of haze have coalesced and formed a thin stratus. The storm is coming steadily on, its condensation is seen to be thicker as it approaches, it is now raining from one hundred to one hundred and fifty miles to the west, but we do not know it.
That it is about to storm all believe, for all are conscious of a change. The candle if extinguished will not relight as readily, if at all, on being blown; there is a crackling almost too faint for snow in the fire; the sun did not set clear; the old rheumatic joints complain, and the venerable corns ache.
Morning comes, and the storm is on. The wind is blowing from the S. E., the scud are running rapidly from the same quarter to the N. W., the thermometer continues rising, and it rains. The storm has reached us and the thaw has commenced. Gradually, as the densest portion of the storm cloud reaches us, it darkens; the scud are nearer the earth, and run with more rapidity; the rain falls more heavily and continuously, and by the middle of the day a thick fog has enveloped the earth; the wind isdying away, and the trade itself, with its southern tendency to fog, has settled near us; the barometer has fallen, the thermometer is up to fifty degrees, the water is running down the hills, the snow is saturated with water and is disappearing under the influence of the fog, the rain, and the warm air. Evening comes; the south-east wind and the rain have ceased; the rain clouds have passed off to the eastward; the fog has followed on and disappeared; there is a light trade air from the S. W.; the moon shines out, and a few patches of stratus, broken up into fragments and melting away, are following on in the trade: the storm is past.
Hark! to the tones of Boreas as he bursts forth from the N. W., and rushing, whistling, howling, dashes on between the trade and the earth, following the storm. Now the barometer rises rapidly, the thermometer falls, and in an incredibly short time all is congealed, and cold and wintery as before. The cold N. W. wind has again interposed between the trade and the earth; the trade is elevated a mile or more above it and is entirely free from its influence and from condensation; the deep blue of a sky “as pure as the spirit that made it” is over us, and steady winter reigns again.
It is obvious that there was nothing in the action of the sun upon our snow-clad country, to induce the thaw or the storm. It began, continued, approached, and passed off to the N. E. in the counter-trade. The S. E. wind which existed every where within its influence: in the interior States, Missouri,Illinois, Indiana, Ohio, Michigan, and in Canada, as well as upon the Atlantic coast, commencing in the former earlier than upon the last, was the result of its induction and attraction. Of the N. W. wind that followed we shall speak hereafter. If any one doubts whether this be a true sketch let him examine the investigation of a storm published by Professor Loomis, or observe for himself hereafter. If, however, the storm of Professor Loomis is referred to, it should be remembered that his notes show the occurrence of a slight distinct snow storm at the N. W. stations one day in advance of the principal storm. The latter appears first as rain at Fort Towson, on the nineteenth, moving north and curving to the east—its center passing near St. Louis, and south of Quebec, and the whole storm enlarging as it advanced.
Take another instance. Since the thaw it has not been quite as cold as before; but the rain-soaked snow is hard and solid, the ground, where the snow was blown or worn off, icy and slippery—the thermometer falls during the night to about 12°, and rises to about 30°; the sun makes no impression upon the snow; the firmament is of the deepest blue, the borealis at night vivid. “O, for a storm of some kind, to mitigate the still severe cold;” for the thaw has made us more sensitive, and storm winds do blow warm in their season. But patience, it will come. Another day, or two, perhaps, pass: the sun rises as usual, the thermometer has the same range still. “Long cold snap,” we exclaim; “how long will it last?”
A change is coming, but this time it will snow. About an hour or two aftersunrisethe cirrus threads are discoverable again in the west, but now they are most numerous in the S. W. As the day passes on they thicken and advance toward the E. N. E., the sun begins to be obscured, the thermometer rises, and it slowly “moderates.” There is a snow storm approaching from the S. W.
But the thermometer rises slowly; it must get up to 26° or 28° before it can snow much. I have known in one instance, at Norwalk, a considerable fall of snow, although much mingled with hail, when the thermometer stood at 13° above zero, and one, a moderate fall, some two inches, with it at 24°, but these were exceptions. The snow range of the thermometer on the parallel of 41° north latitude, and south of it, is from 26° to 30° above 0°; when colder or warmer it may snow to whiten the ground, or perhaps barely cover it, but usually rains or hails. We have seen that in the polar regions, according to Dr. Kane, it is about zero, but the rise of the thermometer there, previous to the snow, was about the same as here,i. e., from 15° to 25°. This fact is instructive. Since the foregoing was written, and on the 7th of February, 1855, a snow-storm of considerable length set in, with the thermometer at 5°, and continued more than twenty-four hours, the thermometer gradually rising. The snow was very fine, like that described by Arctic voyagers as falling in extreme cold weather.
As the dense and darker portions of the stormapproach, and although the sun is obscured, and the ground frozen, it continues to moderate, and at evening, when the thermometer is up to 28°, and the dense portion of the storm has reached us, gently and in calmness the snow begins to fall. Perhaps a light air following the storm, or the presence of the trade near the earth, at first inclines the snow-flakes to the eastward. This is frequently so at the commencement of snow storms. Ere long, however, the wind rises from the N. E., and the snow is driven against the windows, rounded and hardened by the attrition of its flakes upon each other, in their descent through the eddying and opposite currents. The next day we rise to witness a heavy fall of snow, perhaps, and a continued driving N. E. storm, in full blast; the snow whirling and settling in drifts under the lee of every fence or building.
Can it be, you ask, that this driving wind is but anincidentof the storm? the result ofattraction, while the storm clouds are sailing quietly and undisturbed on in the counter-trade above, directly over the gale which is blowing below? It is even so. Nor has it “backed up,” as it is termed by those who have ascertained that it has commenced snowing first, and cleared off first, at a point west of them. You saw, or might have seen, the cirro-stratus cloud passing to the E. N. E. in the afternoon, and until the snow-flakes filled the air, and the clouds became invisible. You may still see that the wind will die away before the storm breaks, and “come out” gently from the S. W., unless it should back into the northward andwestward, and in either event you may see the last of the storm clouds, as you did see, or might have seen the first of them, pass to the eastward. Toward night the wind dies away, and the storm passes off abruptly, or the sky becomes clear in the N. W. Now you may see the smooth stratus storm cloud, continuous, or breaking up into fragments and passing off to the east, even at the edge which borders the clear sky in the west or north-west, to be followed that evening or the next day, by the north-west wind and its peculiar fair-weather scud.
I have given these as instances illustrating the manner in which rain and snow storms originate the surface easterly winds in winter.
But it must not be supposed that they commence with precisely the same appearances in every case in winter; much less in summer. There is very great diversity in this respect, in different seasons, and in different storms during the same season. A great many different and accurate descriptions might be given, if time and space would permit, which all would recognize as truthful. Very frequently in summer, and sometimes in winter, the wind will set in from the eastward, and blow fresh toward a storm, before the condensation in the trade, which forms the eastern and approaching edge of the storm, has assumed the form of a distinct cloud. Not unfrequently, when it is calm next the surface, a narrow stratum of easterly wind, a half a mile or a mile above the earth, may be seen with a continuous fog, condensing, but not in considerable patches like theusual scud, running with great rapidity toward the storm. Such a stream of fog blew with great rapidity for thirty-six hours toward the storm which inundated Virginia and Pennsylvania, in 1852, and carried away the Potomac bridge at Washington. Such a stream of fog was visible the evening before the great flood of 1854, which inundated Connecticut, and curried away so many railroad and other bridges. I have also seen such a stream of fog running at about the same height, when it was calm at the surface, from the S. W. toward a violent storm which formed over central New England—and from the north toward a heavy storm passing south of us. Such strata form, as far as I have been able to discover, themiddle currentof storms which are accompanied with very heavy falls of rain. These double currents are much more common than is supposed. East of the Alleghanies, short and heavy rain storms, which commence north-east, hauling to the south and lighting up about mid-dayafter a very rainy forenoon, frequently have a S. E. or S. S. E. middle current of this character, which involves the whole surface atmosphere when the storm has nearly passed, and the N. E. wind dies away, and the wind seems to haul to the S. S. E. and S.; so that it is rather the prevalence of adifferentandcoexisting current, than a hauling of thesame wind, which marks the period of lighting up in the south.
Sometimes the easterly wind will set in and blow a day or two before the border of the storm reaches us. Sometimes the storm is passing, or will pass, inits lateral southern extension, south of us, and the condensation in the trade extends over us sufficiently dense to induce an easterly current beneath it, but not dense enough to drop rain, and then we have a dry north-easter. I can not, within the limits I have prescribed, allude to all the peculiarities attending the induction and attraction of an easterly wind, by the storm in the counter-trade. They are readily noticeable by the attentive and discriminating observer, and their existence and cause is all with which I have to do at present.
Winds from the north, or any point from N. N. E. to N. N. W., are comparatively infrequent in the United States, east of the Alleghanies—though it is otherwise in the vicinity of the great lakes.
Sometimes the wind “backs,” as sailors term it, during a N. E. storm, from the N. E. through the N. N. E., N., and N. N. W. to N. W. When this takes place, it is toward the close of the storm. Occasionally, though very rarely, it continues to storm after the wind has passed the point of N. N. E., and until it gets N. W. I have known a few instances in the course of thirty years, and but a few. They are exceptions—rare exceptions. When the wind thus backs from the N. E. to the N. W. through the N., you may be very certain that the body of the storm, or at least the point of greatest intensity and greatest attraction, is at the time passing to the southward of you. This is most commonly the course of the wind when the storm extends far south and lasts several days, and does not extend north far, or if so, withmuch intensity, beyond the point of observation. The change of the wind is explained by the situation of the focus of intensity and attraction, to the south of the observer, and its passage by on that side.
Probably in locations further north and (as I think I have observed) south of the lakes, it may be more frequent than upon the parallel of 44° east of the Alleghanies (which is as far north as I have observed), inasmuch as the further north the locality, the more likely storms and other disturbances in the counter-trade will be to pass to the southward of it.
Between the N. E. and S. E. the wind may blow from any point, before and during storms, and in a clear day in the morning, as a light variable breeze, or, after mid-day, toward approaching showers. I have known it blow all day during a storm from due east; to change back and forth between south-east and north-east, and to blow for hours from any intermediate point—as different portions of the storm were of different intensity, and exerted a more or less powerful inducing influence; and doubtless this often takes place at sea. It depends upon the situation of the focus of attraction of the storm, its shape relative to the particular locality, and with reference to the atmosphere east of it, and peculiar local magnetic action; or, as is sometimes the case in low latitudes, is owing to the fact that the storm is made up of many imperfectly connected showers, which have different force, and induce changeable and baffling winds.
The inducing and attracting influence of theapproaching storm is exerted sooner, and with most force, upon the surface atmosphere, over bodies of water like the ocean and the lakes. Thus, the wind will set from the eastward toward an approaching storm out upon Long Island Sound, for hours before it is felt upon either shore; and when all is calm in the evening on land, and often before the moon forms a halo or circle in the milky condensation of the approaching storm, or any sign of condensation is visible, the breaking of the waves upon the shores may be heard. Doubtless this may be observed on the shores of the Atlantic at other points.
This power of attracting the surface atmosphere from bodies of water like the ocean and the great lakes, will account for two apparent anomalies, mentioned by Mr. Blodget in a valuable and instructive article read to the Scientific Convention, in 1853, regarding the annual fall of rain over the United States.
First—the influence of mountains in extracting the water from the atmospheric currents which pass over them, is well known and readily explainable. Mr. Blodget, however, found that the source of our rains, whatever it might be, when it reached the Alleghanies, was so far exhausted of its moisture that those mountains extracted less from it than fell to the westward, by some five to ten inches annually; and that the fall of rain upon them was less than upon the Atlantic slope eastward of them, to the ocean. This does not accord with observation elsewhere, but is easily explained. As the storm approaches the ocean, it attracts in under it the surface atmosphereof the ocean, loaded with vapor, condensing in the form of fog and scud, as it becomes subject to the increasing influence of the storm. Although the scud and fog would not of itself make rain, it aids materially in increasing the quantity of that which falls through it. The drops, by attraction and contact, enlarge themselves as they pass through, in the same manner as a drop of water will do in running down a pane of glass which is covered with moisture. The small drop which starts from the upper portion of a fifteen-inch pane, will sometimes more than double its size before it reaches the bottom.It is by this power of attracting the surface atmosphere, which contains the moisture of evaporation, under it, and inducing condensation in it, that the moisture of evaporation which rarely rises very far in the atmosphere is made to fall again during storms and showers.This attraction of a moist atmosphere from the ocean accounts for the excess of rain on the east of the Alleghanies, compared with its fall upon them. So the great valley of the Mississippi is comparatively level, and less of its water runs off than of that which falls upon the Alleghanies. There is, therefore, more moisture of evaporation in the atmosphere of the former to be thus precipitated and add to the annual supply of rain upon that valley, and it exceeds that which falls upon the Alleghanies. Those mountains, too, are elevated but about 1,500 feet above the table-lands at their base, and exert little influence on the counter-trade. If they, were 6,000 or 8,000 feet high, a different state of things would exist.
Second—Mr. Blodget found the quantity of rain which fell in Iowa, and to the south and west of the lake region, to be greater than fell over the lake region itself. This is doubtless in part owing to the same cause. The counter-trade, in a stormy state, attracts the surface atmosphere from the lake region, with its evaporated moisture, before it arrives over it, and therefore more rain falls S. W. of the lake region than upon it. This power of attracting the surface wind of the ocean in under it, produces the heavy gales which affect our coast, and which are rarely felt west of the Alleghanies to any considerable degree; and a storm coming from the W. S. W., extending a thousand miles or more from S. S. E. to N. N. W., may have the wind set in violently at S. E. on thesouthern coast first, and at later periods, successively, at points further north, and thus induce the belief that the storm traveled from south to north.
Mr. Redfield finding that some of the gales which he investigated, particularly that of September 3d, 1821, did not extend far inland, and commenced at later periods regularly, at more northern points, concluded that the gale traveled along the line of the coast to the northward. In this, and in relation to the storm of 1821 (and perhaps some others), he has been deceived. My recollections of that storm are accurate and distinct. But I shall recur to this again when I come to speak of his theory.
Toward storms, or belts of showers which would be storms if it were not summer and the tropicaltendency to showers active in the trade, which pass mainly to the north of us, or commence north and pass over us, condensing south while progressing east, the wind may commence blowing before the body of the storm reaches us, from any point between south by west and south east, particularly in the summer season and in the afternoon. When the rain in a storm of this character sets in, in the night, it will sometimes haul into the S. E., if the focus of attraction be situated north of us, and so remain until just before the storm is to break.
There are, however, a class of southerly summer winds which deserve more particular notice. For two or three months in the year—say from the middle of June to the 20th of August—storms on the eastern part of the continent, except in wet seasons, are rare, and most of our rain is derived from showers. During these periods belts of drought are frequent, sometimes in one locality, and sometimes in another, extending with considerable regularity from W. S. W. to E. N. E. in the course of the counter-trade, while rain falls in frequent and almost daily showers to the northward or southward of them. If the daily rains are at the north, over the belt of drought, S. S. W. and S. W. by S. winds blow, sometimes with cumuli or scud, during the middle of the day and afternoon, to underlie the showery counter-trade on the north of the line of drought. Thus, sometimes nearly every day for several days, the evaporated moisture of the dry belt will be carried over to increase the store of those who have asufficient supply without. During the latter part of the afternoon the clouds in the west may look very much like a gathering shower, but the attractions of the counter-trade fifty or one or two hundred miles to the north, will absorb them all, and at nightfall the wind will haul to the S. W. on a line with the counter-trade, and die away.
If there be a drought on any given line of latitude, and frequent showers or heavy rains at the south of it, although there may not be a like surface-wind, with cumuli and fog, blowing from the north toward it, yet a general, gentle set of the atmosphere, from the N. N. W., or N. W., or other northerly point, toward the belt of rains, some distance above the earth, will often be observable, with a barometer continually depressed, and perhaps a cool atmosphere.
During set fair weather, when the attracting belt of rains is far north, on the north shore of Long Island Sound, the wind, like a sea breeze, will set in gently from about S. S. E. or S. by E. in the forenoon, blowing a gentle breeze through the day, and hauling to W. S. W. on a line with the trade at nightfall, and dying away. During a drought I have known this to happen for seventeen successive days. It is obvious to an attentive observer that this is the result of the influence of the sun in exciting the magnetic influence of the earth, and producing a state of the trade not unlike that which induces the formation of cumuli, and which attracts the surface atmosphere from the Sound in over the land: for thetendency to cumulus condensation precedes the breeze, and the breeze isoften wanting in the hottest days where no such tendency to the formation of cumuli exists. The same is true of sea breezes elsewhere. They do not blow in upon some of the hottest surfaces. Where they do exist, they do not always blow, but are wanting during the hottest days; and careful observers have identified their appearance with the formation of cumuli, or other condensation, upon the hills inland. They are not, therefore, the result of ascending currents of heated air.
The received theory regarding sea and land breezes is a mistaken one in another respect. There is no such thing as a land wind corresponding in force to, and the opposite of, the sea breeze—occasioned by the comparative warmth of the ocean. These breezes blow mainly within the trade-wind region. Of course they are either beneath the belt of rains or the adjoining trades. They are said to be, and doubtless are, most active and strongly marked on lines of coast, particularly the Malabar coast, and where the trade-winds are drawing usually from them. In the day-time, when the action of the sun increases the action of the magnetic currents upon the land, or there areelevations inlandwhich approach the counter-trade, and especially if it is elevated near the coast, as the Malabar coast is by the Ghauts, the attraction of this atmosphere over itreverses the trade, or inclines it in upon the land, and it blows in obliquely or perpendicularly, according to the relative trending of the coast and the direction of the surface-trade. Thus, whereislands are situated within the range of the trades, the latter will bereversedduring the day on theleewardside, but continue to blow as land winds during the night. So they are sometimes deflected in upon the land on the sides, during the day, and in like manner return to their course in the night. So, too, the north-east trades of Northern Africa, are occasionally (though feebly where the coast is flat) deflected during the day-time, and blow in as N. W. winds. Upon the southern coast of Africa the S. E. trade is deflected, and blows in as a S. W. wind. Upon the south-western coast of North America, the N. E. trades are deflected in like manner, and so are the S. E. trades upon the western coast of South America. Where the coast mountain ranges are very elevated, as upon the western coast of the American continent, this attracting influence and consequent deflection extends to a considerable distance seaward, and hence the westerly winds of California, etc. It must be understood that we are now speaking of the winds which blow within the range and during the existence of the trade-winds or the presence of the dry belt—for the trades are not always perceptible on the land. Captain Fitzroy thus describes the sea breezes of the western coast of Peru, at 23° south latitude. “The tops of the hills on the coast of Peru are frequently covered with heavy clouds. The prevailing winds are from S. S. E. to S. W., seldom stronger than a fresh breeze, and often very slight.Sometimes during the summer, for three or four successive days, there is nota breath of wind, the sky is beautifully clear, with a nearly vertical sun.On the days that a sea breeze sets in, it generally commences about ten in the morning, then light and variable, but gradually increasing till one or two in the afternoon. From that time a steady breeze prevails till near sunset, when it begins to die away, and soon after the sun is down there is a calm. About eight or nine in the eveninglight windscome off the land, and continue till sun-rise, when it again becomes calm until the sea breeze sets in as before.”
To illustrate this further, I take the following letter from Professor Espy’s Philosophy of Storms:
Clinton Hotel, N. Y., Dec. 20, 1839.To Professor Espy,Dear Sir,—Understanding you are desirous of collecting curious meteorological facts, I take the liberty of communicating to you what I saw in the month of December, 1815, at the Island of Owhyhee. I lay at that island in the Cavrico Bay,[3]in which Captain Cook was killed, three weeks, and every day during that time, very soon after the sea breeze set in, say about nine o’clock, a cloud began to form round the lofty conical mountain in that island, in the form of a ring, as the wooden horizon surrounds the terrestrial artificial globe, and it soon began to rain in torrents, and continued through the day. In the evening the sea breeze died away and the rain ceased, and the cloud soon disappeared, and it remained entirely clear till after the sea breeze set in next morning. The land breeze prevailed during the night, and was so cool as to render fires pleasant to the natives, which I observed they constantly kindled in the evening. I was particularly struck with the phenomena of the cloud surrounding the mountain, when none was ever seen in any other part of the sky, and none then till after the sea breeze set in, in the morning, which it did with wonderful regularity. The mountain stood in bold relief, and its top could always be seen from where theship lay, above the cloud, even when it was the densest and blackest, with the lightning flashing and the thunder rolling, as it did every day. I passed up through the cloud once, and I know, therefore, how violently it rains, especially at the lower side of the cloud. This rain never extends beyond the base of the mountain;[4]and all round the horizon there is eternally a cloudless sky. The dews, however, are very heavy, and there seems to be no suffering for want of rain. That this state of things continues all the year, I have no doubt, from what an American, by name Sears, who had spent four years there, told me; he had seen no change in regard to the rain.Caleb Williams.Providence, R. I.
Clinton Hotel, N. Y., Dec. 20, 1839.
To Professor Espy,
Dear Sir,—Understanding you are desirous of collecting curious meteorological facts, I take the liberty of communicating to you what I saw in the month of December, 1815, at the Island of Owhyhee. I lay at that island in the Cavrico Bay,[3]in which Captain Cook was killed, three weeks, and every day during that time, very soon after the sea breeze set in, say about nine o’clock, a cloud began to form round the lofty conical mountain in that island, in the form of a ring, as the wooden horizon surrounds the terrestrial artificial globe, and it soon began to rain in torrents, and continued through the day. In the evening the sea breeze died away and the rain ceased, and the cloud soon disappeared, and it remained entirely clear till after the sea breeze set in next morning. The land breeze prevailed during the night, and was so cool as to render fires pleasant to the natives, which I observed they constantly kindled in the evening. I was particularly struck with the phenomena of the cloud surrounding the mountain, when none was ever seen in any other part of the sky, and none then till after the sea breeze set in, in the morning, which it did with wonderful regularity. The mountain stood in bold relief, and its top could always be seen from where theship lay, above the cloud, even when it was the densest and blackest, with the lightning flashing and the thunder rolling, as it did every day. I passed up through the cloud once, and I know, therefore, how violently it rains, especially at the lower side of the cloud. This rain never extends beyond the base of the mountain;[4]and all round the horizon there is eternally a cloudless sky. The dews, however, are very heavy, and there seems to be no suffering for want of rain. That this state of things continues all the year, I have no doubt, from what an American, by name Sears, who had spent four years there, told me; he had seen no change in regard to the rain.
Caleb Williams.
Providence, R. I.
Similar citations might be made to show that the sea breeze is induced by the same cause which forms the clouds over the land—that it is frequently wanting for three or four days under a vertical sun, and that the land breeze blows gently and not with corresponding force where there is no surface trade, or where it is deflected, not reversed.
A succession of showers passing across the country to the north, within one hundred to one hundred and fifty miles, almost always produces a southerly wind to the southward of them. There is more that is peculiar about these belts of showers. Although they consist of large highly-electrified cumuli, there is a strong tendency to cirro-stratus condensation in the lower part of the trade over them; and it is that condensation rather than the cumuli, which attracts the surface atmosphere from the south. They would be storms, if the atmosphere had not a summer-tropical tendency toshowers. There is, too, a tendency in these belts to extend to the south, and it is generally, as far as I have observed, the extension southerly of those belts, by the formation of new showers which terminate the “hot spells” or “heated terms” of mid-summer. The very oppressive and fatal one of the summer of 1853, was, in character, a type of all—although exceeding them in severity. The first three or four days were calm, hot, and smoky—an appearance which attends all similar periods more or less, refracting the red ray of the light, and giving the sun a peculiar dry-weather, red appearance. (This smoky haze is usually atmospheric, and occasionally seen even in March, although not unfrequently fires in the woods fill the air with actual smoke, and very much increase it, and when this is so, the odor of the smoke is often perceptible.) Then we began to have a fresh south-west by south breeze in the day-time, hauling to the south-west, and dying away at nightfall. The next day, the tendency to condensation and consequent belt of showers having extended further south and approached nearer to us, the S. S. W. wind blewfreshertoward it, anddid not die away at nightfall. During the evening the reflection of the lightning playing upon the tops of the thunder clouds, just visible at the north (heat-lightning, it is termed, because supposed to be unaccompanied by thunder, but in reality lightning reflected from clouds at too great a distance for the thunder to be heard), and the continuance of the southerly wind after nightfall, gave sure evidence ofthe coming showers the next day, and an end of the excessive heat for that time. So ended both of those long-to-be-remembered “heated terms” of 1853.
The same is probably true of the interior of the country every where. Lieutenant Maury, in the course of his investigations, and in order to ascertain the direction of the winds in the Mississippi valley during rain, addressed a number of gentlemen, and received their replies, which are published with his wind and current charts. Several answered, among other things, that, “whenever the lightning appears to linger at the north at eventide, rain almost invariably follows speedily; not so in the south.” Thus it frequently is with us. If, during a hot, dry time, of a few days continuance, the lightning so lingers in the evening, and the wind continues to blowfreshfrom the southwardafter nightfall, showers will generally follow within forty-eight hours, most commonly the next day, and a cool N. N. W. or N. W. wind with a favorable change ensue. Such, at least, has been the result of my observation for many years.
Indeed this seems to be the general law in summer in the Mississippi valley, where the easterly winds are not so common as with us. To illustrate this further, I copy from a recent work by T. Bassnett, entitled the “Mechanical Theory of Storms,” two short extracts, showing the manner in which belts of showers extend southerly, while progressing north-eastwardly, at Ottawa. The first occurred in August, 1853; the last, December, 1852. The first was abelt of showers; the latter would have been in August, but the lateness of the season changed its character somewhat, though not entirely, to a more regular rain, especially toward the close.
“August6th.—Very fine and clear all day: wind from S. W.; a light breeze; 8P.M.frequent flashes of lightning in the northern sky; 10P.M., alow bank of dense clouds in north, fringed with cirri, visible during the flash of the lightning; 12P.M., same continues.“7th.—very fine and clear morning; wind S. W. moderate; noon, clouds accumulating in the northern half of the sky;wind fresher,S. W.; 3P.M., a clap of thunder over head, and black cumuli in west, north, and east; 4P.M., much thunder and scattered showers; six miles west rained very heavily; 6P.M., the heavy clouds passing over to the south; 10P.M., clear again in north.“8th.—Clear all day; wind the same (S. W.); a hazy bank visible all along onsouthern horizon.“December21st, 1852.—Wind N. E., fine weather.“22d.—Thick, hazy morning, wind east, much lighter in S. E. than in N. W.; 8A.M., a clear arch in S. E. getting more to south; noon,very black in W. N. W.; above, a broken layer of cirro-cumulus, the sun visible sometimes through the waves; wind around to S. E., and fresher; getting thicker all day; 10P.M.,wind south, strong; thunder, lightning, and heavy rain all night, with strong squalls from south.“23d.—Wind S. W., moderate, drizzly day; 10P.M., wind west, and getting clearer.”
“August6th.—Very fine and clear all day: wind from S. W.; a light breeze; 8P.M.frequent flashes of lightning in the northern sky; 10P.M., alow bank of dense clouds in north, fringed with cirri, visible during the flash of the lightning; 12P.M., same continues.
“7th.—very fine and clear morning; wind S. W. moderate; noon, clouds accumulating in the northern half of the sky;wind fresher,S. W.; 3P.M., a clap of thunder over head, and black cumuli in west, north, and east; 4P.M., much thunder and scattered showers; six miles west rained very heavily; 6P.M., the heavy clouds passing over to the south; 10P.M., clear again in north.
“8th.—Clear all day; wind the same (S. W.); a hazy bank visible all along onsouthern horizon.
“December21st, 1852.—Wind N. E., fine weather.
“22d.—Thick, hazy morning, wind east, much lighter in S. E. than in N. W.; 8A.M., a clear arch in S. E. getting more to south; noon,very black in W. N. W.; above, a broken layer of cirro-cumulus, the sun visible sometimes through the waves; wind around to S. E., and fresher; getting thicker all day; 10P.M.,wind south, strong; thunder, lightning, and heavy rain all night, with strong squalls from south.
“23d.—Wind S. W., moderate, drizzly day; 10P.M., wind west, and getting clearer.”
It is obvious that the showers at the north passed east on the evening of the 6th of August; that new showers, taking the same course, originated in the north, but more southerly next day, with S. W. wind, and that they passed east, and others formed successively further south, which passed over the place of observation late in the afternoon, and that others formed south and passed east during the night and next day, visible in a bank on the southern horizon.
Later or earlier in the spring and autumn, thesebrisk afternoon southerly winds continuing after nightfall, indicate moderate rains from a rainy belt extending in a similar manner, without the cumuli and thunder which attend those of mid-summer. I shall recur to this class of showers and storms when we come to their classification.
Light surface winds from south-west to west are not often storm-winds, and are usually those which the trade near the earth draws after it. Sometimes the trade seems to draw the surface wind from the S. W. and W. S. W. with considerable rapidity, and some scud a little distance above the earth. When this is so, it will be found that a storm has passed to the north of us, or a belt of rains is passing north, which may or may not have sufficient southern extension to reach us. When there have been heavy storms at the south in the spring, especially if of snow, the S. W. wind which the trade draws after it, and which comes from the snowy or chilled surface, is exceedingly “raw”—that is, damp and chilly, although not thermometrically very cold. Probably every one has noticed these “raw” S. W. winds of spring.
Usually, when storms and showers, which have not a southern lateral extension, pass off, the trade is very near the earth, and a light S. W. wind or calm follows for a longer or shorter period. Not unfrequently, however, our N. E. storms terminate with a S. W. wind, shifting suddenly, perhaps, just at the close of the storm, during what is sometimes called a “clearing-off-shower,” or, more frequently, dying gradually away as a N. E. wind, and coming outgently from the S. W., following the retreating cloud of the storm. In such cases it is said to “clear off warm.”
With us the wind rarely blows from the west, except while slowly hauling from some southerly point to the N. W. It is probably otherwise east of the lakes and in some other localities to the north-west.
Occasionally, and most frequently in March, a W. to W. N. W. wind follows storms, and blows with considerable severity, with large irregular, squally masses of scud, and sometimes a gale. Such was the character of the dry gale which crossed the country, particularly Northern New York, in March, 1854, doing great damage. These westerly winds are always accompanied by a continued depression of the barometer, and peculiar, foggy, scuddy, condensation, and should be distinguished with care from the regular and peculiar N. W. wind, as they may be, by the continued depression of the barometer, and the character of the scud. They are doubtless magnetic storms.
The remaining surface wind, the N. W., the genuine Boreas of our climate, the invariable fair-weather wind, is one of great interest. It is unique and peculiar. It is not the left-hand wind of a rotary gale, and has no immediate connection with the storm. I have known it blow moderately, fifteen successive days in winter; rising about tenA.M., and dying away at nightfall. Occasionally, but very rarely indeed, a light wind exists from the N. W. during a storm, owing probably to a focus ofintensity in relation to some surface the storm covers, like the focus which exhibits itself as a clearing-off shower near the close of a storm; but the real fair-weather Boreas is a different affair altogether. Let us observe with care its peculiarities; they are instructive.
1st. It rarely blows with any considerable force beneath the trade while there are storm clouds, or any considerable condensation in it. It does not interfere with that reciprocal action which takes place between the trade and the earth, during approaching or existing storms. I have frequently seen it with its peculiar scud clouds in the N. W., waiting for the storm condensation of the trade to pass by, that full of positive electricity it might commence its sports; rushing and eddying along the surface, licking up the warm, south polar, electric rain, which stood in pools upon the ground, or rose in steamy vapor from the surface, and with its cool breath dry up the muddy roads as no degree of heat can dry them.
The annexed figure (14) shows the appearance of the northern edge of a stratus storm cloud, passing off E. N. E. at the close of the storm, which was “clearing off from the north-west.” It is from a daguerreotype view, looking W. N. W., taken at eight o’clock in the morning, in the fall of the year. Near the horizon maybe seen the N. W. scud, forming in the N. W. wind, which is about to follow the retreating edge of the storm cloud.
Figure 15 is from a daguerreotype view, taken at eleven o’clock the same day, when the storm cloudhad passed off and its edge remained visible only south of the zenith, and the north-east scud had risen up and covered the northern half of the sky, and the wind was blowing a gale from that quarter.
Fig. 14.
Another view was taken about twoP.M.of the same day, when the scud had a very dark, gloomy appearance—asdarkandgloomyas those of a Mexican norther—too dark to represent by a cut.
Not unfrequently in a moist summer season, after a day of showers or rain, which have had an extending formation or lateral extension from north to south, it will commence blowing in the morning, and encourage the hay-maker with the hope of fine weather. But often before noon, the milky stratus condensation above with cumuli below, will appear in the trade;the N. W. wind die away and variable airs from the east or south appear, to be followed toward night by an enlargement of the cumuli and showers. It rarely, if ever, blows fresh till the storm condensation of the trade has passed; or continues to blow after that condensation reappears. When it commences blowing after a storm, and the northern edge of the storm is not over us, we may frequently see the latter low down in the S. E. passing eastward.
Fig. 15.
NORTH VIEW.
2d. Its scud are peculiar. Every one, probably, has noticed them. They are distinct, more or less disconnected, irregular, with every form between those of the easterly scud, cumulus, and stratus, according to the season. If large, withdark undersurfaces; formingrapidlyand asrapidly dissolving; rarely dropping any rain, sometimes dropping a flurry of snow, in November or March, oftener than at any other period; sailing away to the S. E., and casting a traveling shadow as they pass on over the surface of the earth. Their electricity, particularly when white, is probably always positive, as that of all whitish clouds is supposed to be.
3d.It is emphatically a surface wind.The incident storm winds, the N. E. and S. E., frequentlycommence blowingunder the storm, toward its point of greatest intensity,up near the line of cirro-stratus condensation, evidenced by the running scud; or blow there with most rapidity, and so continue for hours before the whole surface atmosphere from thence to the earth becomes involved in the movement; and sometimes without being felt below at all. Not so with the N. W. wind; itbegins at the surfaceand blows there with more rapidity than above; it seems to be attracted by the earth; it interposes between the earth and the trade, wedging the trade up and occupying its place. It blows under at all seasons of the year, but most readily and strongly from a surface of snow whose electricity is always positive. Hence it blows most strongly andcontinuouslywhen snow has fallen at the north, and prevails during winter very much in proportion to the extent and continuance of the covering of snow which invests the earth in that direction. It follows after storms, and particularly warm rains, during the autumn, winter, and spring months, which have a lateral southern extension.Whether it is increased by the snow from the surface from which it blows, or is caused by the same magnetic action which causes the great fall of snow, is a question we shall consider hereafter.
4th. It does not connect or mingle with the trade current in any way, or change or divert the course of that current; but interposes between it and the earth, elevating the trade in proportion to its own volume, above the influences of the earth (when the trade becomes free from condensation, and singularly, clear); and raisingproportionatelythe barometer. An experienced observer can frequently estimate, with considerable accuracy, the rise of the barometer, by measuring with his eye, (when the clouds will enable him to do so,) the depth of this interposed N. W. current. The barometer rarely rises after a storm, for twenty-four or forty-eight hours if the wind continues at any point from S. W. to W. N. W., but always rapidly as soon as the genuine N. W. current with any considerable depth interposes and elevates the trade.
It will be obvious to every one, I think, certainly, if they will hereafter study the subject and observe for themselves, that the N. W. wind does not blow away the storm; and that it follows after it, blowing over the surface which is uncovered by the storm; rarely, if ever, with any force when the body of the storm passed south of us; and that it is a purely surface wind, seemingly attracted by the peculiar magneto-electric state in which the surface of the earth is left, compared with a snow-clad surface to the north, by a recent storm, or that peculiar state of thetrade which is left by the action of the storm. It seems to follow that magnetic wave which, passing from north to south, acts in its course upon the counter-trade, producing the storm, or belt of showers, and giving them their southern lateral extension, and will well repay future telegraphic investigation. Its electricity is intensely positive—that of the earth by the action of the storm as intensely negative.
5th. This N. W. wind occurs in all parts of the northern hemisphere, so far as we have data to determine, and its corresponding wind from the S. W. occurs in the southern hemisphere. It is identical with a class of the northers of the Gulf of Mexico, as a brief analysis of the character of the latter will show.
1st. The fall and winternortheris a dry wind without rain or falling weather—so is our N. W. wind.
2d. It is preceded by a falling barometer; S. E. scud and rain at the point where it blows, or to the eastward of it. So is ours when it blows a gale in the fall and spring months, which bear the nearest resemblance in climatic character to the periods when the northers blow. With this distinction, however, that our precedent rains either pass over us or to the southward, the direction of storms being E. N. E.; their precedent storms passing over or to the eastward of them as they move more to the northward.
3d. It is often preceded by a copious dew; so is ours—such dews often following light fall rains in our climate, and preceding N. W. wind.
4th. The most peculiar characteristic, however, is that the barometer rises rapidly and invariably whilethe norther prevails, and very much in proportion to its violence. The same is true of our genuine N. W. wind, and is not trueof any other windon this continent which I have observed or read of.
5th. While they are thus alike in these respects, they are unlike in no respect.
Mr. Redfield has traced them insupposedconnection with storms which continue from that vicinity across the United States to the E. N. E., and endeavored to connect them with those storms, as the left-hand winds of a rotary gale. Obviously, I think, they are identical with our N. W. winds which alsofollow, indeed, butare distinct from the storms.
There are a class of northers in the Gulf of Mexico—the “Nortes del Muero Colorado”—sometimes occurring in the summer months, beginning at N. E., veering about and settling at N. N. W., and as they decline hauling round by the west to the southward. These winds correspond precisely with the hurricane winds of the West Indies, and are doubtless the incident winds of a storm traveling thence to the N. N. W. precisely as our N. E. or E. N. E gales are incident storm winds to the N. E. storms of our latitude.
In this connection we will look at the peculiarities of a West India hurricane.
“It is not a little remarkable,” says Mr. Espy, speaking of the storms and hurricanes of the West Indies, “that all these storms, andall others which have been traced to the West Indies, traveled N. W. almost at right angles to the direction of the trade-windin those latitudes, but very nearly, if not exactly, in the direction of an upper current of the air known to exist there toward the N. W.” Substantially the same facts have been repeated by Mr. Redfield, and demonstrated by his able investigations, both there and in the Eastern Pacific, and are confirmed by the observations of Edwards, Lawson, and others, while residents there. It is a matter of surprise that gentlemen like Messrs. Redfield and Espy, who have certainly displayed great ability in the investigations of meteorological phenomena, should fail to recognize a more intimate relation between this upper current and the storms they were investigating, and to detect the general laws which govern both. The storms and hurricanes of the West Indies are comparatively of small diameter, and have little advance condensation. When they pass on to the south-western portion of North America and curve to the N. E., as they frequently do, they enlarge in front and at the sides, and their advance condensation, which is not dense enough to drop rain, extends in some cases from one to three hundred miles; and the storm itself, by the time it reaches the Alleghanies, may extend one thousand to fifteen hundred miles, and perhaps in certain magnetic states of the surface, and occasionally, may cover the entire portion of the continent, from north to south. Such, probably, was very nearly the extension of the storm investigated by Professor Loomis. In the West Indies, however, at the commencement, they vary from twenty to one hundred miles, or possibly more, in width.
First, they are preceded by a hot, sultry and oppressive atmosphere—as are electric storms every where—a peculiar electric state of the earth and adjacent air.
Second, the black clouds and lightning which indicate the approaching hurricane are seen to the S., S. E., and E. S. E., according to the season of the year, as we see them at the westward. During the rainy season, and when the storm, as is usual at that period, is small, and the S. E. trade blows more eastwardly, the wind at the Windward Islands, possibly, may set in at the north, and back round by the east as it progresses. So Colonel Reid thinks it sometimes does, at Barbadoes. But when the belt of rains is south, and the hurricane comes from the south-east, and is larger and more violent in its action, and the north-east winds prevail, the first effect is an increase of these trades. Soon, however, the wind hauls to the north and north-west, in opposition to its course, bearing the same relation to it that our east and north-east winds bear to storms in the United States; and the wind hauls around during the passage of the storm to the west, south-west, and south-east, and at the latter point it clears off. Mr. Edwards in his History of Jamaica says—and as a resident, his authority should be decisive as to this Island—“that all hurricanes begin from the north, veer back to the W. N. W., W., and S. S. W., and when they get around to the S. E. the foul weather breaks up.” Doubtless the same is true of the class of northers of which we are speaking on the Gulf ofMexico.But with this class the barometer does not rise during the gale, and in proportion to its length and violence.With the other class of N. W. winds—the northers of winter—it does.
The following description of two winter northers, copied from Colonel Reid’s valuable work, will illustrate what has been said.Precisely such changes from S. E. rains to N. W. winds, with blue sky and detached dark clouds—fair-weather N. W. scud—occur every autumn in October and November, and the falling of the thermometer and rising of the barometer, after rain, and a change of the wind, are perfectly characteristic.