The Philosophy of the Weather Part 22

The following diagram ill.u.s.trates the course and gradual enlargement of a mid-autumn tropical storm, which induces a S. E. wind in front, and occasions a thaw.

[Ill.u.s.tration: Fig. 20.]

2. Another cla.s.s originate at the N. W., and extend gradually south easterly on the magnetic meridian. These are most frequent in summer, forming belts of showers, but occur, I believe, at all seasons of the year. They seem to be produced by magnetic waves pa.s.sing south, and are followed in autumn and winter, and sometimes in summer, by the peculiar N.

W. wind and scud, and a term of cooler weather.

Thus, it is believed that many, perhaps all of the alternating terms of heat and cold, are dependent on magnetic waves pa.s.sing over the country in a similar manner, with a greater or less belt of condensation between them, and depending on peculiar magnetic action traveling in the same way. The S. E. extension of showers and storms, and the cooler changes of temperature which immediately follow them; with light N. W. wind in mid-summer, and with it fresher at earlier and later periods, in the form of northers blowing violently, according to the season, are intimately connected, and indicate such waves. The indication is strengthened also by the frequent progress of auroras in like manner, occurring usually after the belt of condensation has pa.s.sed, and frequently following it. The clouds and currents of the atmosphere, so far as I have been able to discover, show no permanent current from the pole to the atmospheric equator, compensating for the counter-trade; and that compensation is furnished by the periodical but frequent atmospheric waves, connected with the periodical changes of storm, and cloud, and sunshine, which gradually extend from north to south, in or near the magnetic meridian. Perhaps such compensating currents are found west of the magnetic poles, as we have suggested, and make the N. E. and northerly dry winds of Western Europe and the Pacific; but, in the present state of our knowledge, it is impossible to say that they are. If it be so, the compensation they furnish must be small; for the volume of counter-trade which is not depolarized before it reaches the Arctic circle, and which pa.s.ses round the magnetic pole, must be very small. A majority of our periodical changes, during the northern transit, and I believe at all seasons, are of this character; and, I have reason to believe, from observation, in one or two cases, that where belts of rains and showers begin, over _any locality_ in the United States, they may a.s.sume this character. I have been in Saratoga when an easterly storm commenced _south of that place_; the condensation and mackerel sky being visible at the south, and no cloud formation or rain occurring there at the time, and have traced it afterward as a belt which had a lateral extension south-eastward. Leaving that place immediately after a belt had pa.s.sed south, I have overtaken it by railroad, and run into it again before arriving at New York; and witnessed its subsequent extension south-eastwardly, out over the Atlantic. I have witnessed the approach of such a belt in the spring, at Sandusky, upon Lake Erie, and its pa.s.sage over to the S. E., followed by the N. W. wind, as Mr. Ba.s.snett describes them at Ottawa, and run under the attenuated edge of the same belt, on the same day, on the way to Pittsburg, leaving the N. W. wind behind, but finding it present again with clear sky on the following morning. I have seen hundreds of them approach from the north, and pa.s.s to S. E., out over the Atlantic; followed by the N. W. wind in spring and autumn. This cla.s.s of storms pa.s.s off toward, and doubtless over the track, of our European steamers and packets. I know this, for I witness it nearly every month in the year. It is not a matter of speculation, but of actual, long-continued observation.

Probably, as one approaches the Gulf Stream, and when over it, its induced winds may be more violent. It is time our navigators understood this; and that all the gales of the North Atlantic, certainly, are not rotary; and do not approach from the S. W. in the same manner as the cla.s.s investigated by Mr. Redfield do. Where a fresh southerly or south-westerly wind is followed by any considerable cirro-stratus or stratus-condensation, it is usually of this character.

The following diagram exhibits the peculiarities of this cla.s.s of storms.

It is intended to represent the same storm or belt of showers, on _two successive_ days, and, of course, its usual rate of southerly extension:

[Ill.u.s.tration: Fig. 21.]

This cla.s.s of storms, or belts of showers, present the following succession of phenomena in summer:

1. Still warm weather, one or more days.

2. Fresh southerly wind, one or more days; if more than one, dying away at the S. W., at night-fall, but continuing into the evening of the day before the belt of condensation arrives.

3. Belt of condensation, with or without rain or showers, with the easterly wind blowing axially, if the condensation is heavy and the belt wide; westerly if the condensation is feeble or the belt narrow--the clouds moving about E. N. E.

4. Cooler air, light N. W. in summer, heavy N. W. in autumn, winter, and spring.

And, the next period--

5. Still warm weather or light airs.

6. Southerly wind, fresh.

7. Belt of condensation.

8. Cool northerly wind.

And so on, successively, unless broken in upon by some other cla.s.s.

Sometimes these periods are exceedingly regular, at other times the other cla.s.ses prevail. I have much reason to believe that this is the _normal, periodic_ provision for condensation of our portion of the northern hemisphere, and probably of every other where rain falls regularly in the summer season, and that the other cla.s.ses are exceptions, as the hurricanes are exceptions to the normal condition of the weather every where. Perhaps in some seasons, during the northern transit, the exceptions may equal the rule, but I do not now remember such a season. In other years nearly all the storms are of this character. Thus, Dr.

Hildreth (in Silliman's Journal for 1827), speaking of the year 1826, in a note to his register of that year, says: "There have been, this year, an unusual number of winds from N. or N. W. Nearly every rain the past summer has been followed with winds from the northward, when, in many previous summers, the wind continued to the southward after rain." The immediate occurrence of northerly wind after the pa.s.sage of the belt of condensation, is a peculiar feature of this cla.s.s of storms.

As this also will be new, and is of great practical interest, I shall be pardoned for referring to other evidence. Bermuda is in lat.i.tude 32 north. In the summer season they are within the range of the Calms of Cancer, as Lieutenant Maury terms them, and not subject to storms. From November to May, inclusive, they have successions of revolving wind.

Colonel Reid gave them much attention, and studied them barometrically: that is, he studied the changes of the wind during the successive periodic depressions. He found them revolving like ours, and hence inferred the truth of the gyratory theory in relation to all winds. But it is perfectly evident the same polar belts which pa.s.s over us reach them during the southern transit. The precedent southerly wind, the _central condensation_, the appearance of lightning, and the rotation of the wind by both the east and west, but most frequently by west, are the same. In his chapter on observations at the Bermudas, he gives us many examples.

Probably the existence of the Gulf Stream to the west and north has a modifying influence upon them, and their action becomes less intense in that lat.i.tude, but they are very similar. I copy a record of the weather, for a month, which may be found on pages 252, 253, and 254, and a portion of his remarks:

"The month of December, 1839, presents a continual succession of revolving winds pa.s.sing over the Bermudas, with scarcely an irregularity, as regards the fall and rise of the barometer accompanying the veering of the wind. One, however, occurred on the 10th and 11th. The S. W. wind abated, and changed to W. N. W., with the barometer still falling. But in the column of remarks it is noted that there was lightning seen in the N. and N. W., from 7 P.M., during the night. This irregularity may, therefore, have been occasioned by a gale pa.s.sing over the banks of Newfoundland, influencing the direction of the wind at Bermuda.

"REVOLVING WINDS.

+-----------------------------------------------------------------+ Date. Hour. Direction of Wind's Weather. Bar. Ther. Wind. Force. -------- --------- ------------ -------- ----------- ------ ----- 1839. Nov. 30 Midnight. S. S. E. 1 b. c. 3006 65 Dec. 1 Noon. S. S. W. 3 b. c. 3007 71 2 " S. W. 5 g. m. q. 2986 70 3 " S. S. W. 3 g. c. 2976 " 4 " S. W. 6 g. m. r. 2962 68 5 " W. N. W. 5 p. q. 2956 " 6 " N. W. 6 p. q. *2955 " 7 " N. N. W. 5 b. c. 2978 70 " Midnight. N. N. W. 3 b. c. 2989 68 8 Noon. W. N. W. 2 b. c. 2982 71 9 " S. S. W. 5 p. q. 2984 70 10 " S. W. 2 b. c. 2996 " 11 " W. N. W. 6 b. c. m. *2988 68 12 " S. S. W. " b. v. 2999 69 13 " N. N. by W. " b. v. 3001 66 14 " N. N. W. 5 b. c. v. 3006 64 " Midnight. N. W. 2 b. c. p. 3005 63 15 Noon. S. W. by S. 6 g. m. r. 2972 65 " P.M. 2 S. S. W. 7 m. q. r. 2992 64 " " 4 S. S. W. " g. m. q. r. 2955 " " " 6 W. S. W. " q. w. *2953 " " " 8 N. W. 6 b. c. q. 2954 " " " 10 N. N. W. " b. c. 2955 " 16 Noon. N. W. 7 b. c. m. 2953 62 17 " N. W. by N. " p. q. 2967 60 18 " N. W. 6 c. q. 2986 " 19 " N. W. by N. 7 m. q. r. *2973 59 20 " N. N. W. " p. q. c. 2989 58 21 " N. W. by N. 6 c. q. 2996 56 " Midnight. S. W. 1 b. c. 2995 55 22 Dawn. ---- 0 " Noon. S. S. W. 5 g. m. 2983 56 " P.M. 4 S. 7 g. m. 2979 " " " 6 S. S. E. " g. m. r. 2961 " " " 8 S. S. E. " w. r. 2952 " " " 10 S. E. " m. w. r. 2948 " 23 Noon. S. W. 6 b. c. m. *2944 57 24 " W. N. W. " b. m. 2971 59 25 " W. N. W. 5 b. c. 2988 56 26 " N. 3 c. 3009 62 27 " S. E. 5 c. q. r. 3007 61 28 " S. W. 6 c. q. 2988 66 " Midnight. S. S. W. " b. c. 2976 65 29 Noon. S. W. 7 c. b. *2948 64 30 " W. N. W. 6 b. c. q. 2983 55 31 " N. W. 5 b. c. 3012 58 +-----------------------------------------------------------------+

"_Remark printed in the Register._

"The changes of the wind during the December gales have been nearly the same in all: _i. e._, commencing with a southerly wind at first, the wind has veered by the west, toward the north-west, sometimes ending as far round as N. N. W."

These extracts show the pa.s.sage of several successive belts, each with the phenomena in regular order.

The first commences with blue sky and detached clouds, barometer up, thermometer down to 65, and nearly calm, on the 30th of November.

Dec. 1 (at noon). Wind freshens from S. S. W.; thermometer rises; barometer still up.

Dec. 2. Barometer has fallen; thermometer up; wind increasing from S. W., with gloomy, squally appearance.

Dec. 3. Wind S. S. W.; barometer slowly falling; thermometer slightly.

Dec. 4. Wind fresh; S. W.; condensation and rain has reached them, and it carries barometer and thermometer down.

Dec. 5. Wind shifting by the west, and squally.

Dec. 6. Winds gets N. W.; blows fresh; barometer at its minimum, probably at the time of the change of wind, although the register does not show the precise time.

Dec. 7. Wind N. N. W.; blue sky and detached clouds (N. W. scud), cleared off; barometer elevated by the N. W. wind, from 29.55 to 29.78. Midnight: blue sky; detached clouds (N. W. scud probably); barometer up to 29.89; thermometer fallen, from the cooler character of the northerly wind.

Dec. 8. Wind having lulled as a northerly wind has got round to S. W.

again; thermometer up; barometer falling, and another belt approaching, and so on.

The first and last part of December show each two regular occurrences of substantially the same phenomena. The middle is somewhat more irregular.

There were five distinctly-marked periods, and one squally, long-continued period, with a slight tendency to condensation, and a slight fall of barometer and rain on the 19th (N. W. squall probably), but not sufficient to reverse the wind to the south. In Colonel Reid's opinion there were five revolving gales which pa.s.sed over Bermuda during the month. In my opinion, there were five perfect polar waves of condensation, and one imperfect one, with as many successive southerly winds preceding the condensation, with or without rain in the center, followed by as many cold N. W. or N. N. W. winds, with squalls, in the rear, about five days apart.

(See the * in the barometric column.)

_We are at issue._ Let the question be determined by _actual observation_, and not by _speculation_. It is of fundamental and exceeding importance to the science.

Now, let us take a month in summer, from the observations of Mr. Ba.s.snett, at Ottawa. Here the climate differs somewhat from that east of the Alleghanies; the magnetic intensity is greater, and the action more violent and irregular. That part of the country, it should be remembered, has a greater fall of rain in summer, for reasons we have stated, and those periodic revolutions are more frequent.

"A brief abstract from a journal of the weather for one sidereal period of the moon, in 1853.

"_June_ 21st. Fine clear morning (S. fresh): noon very warm 88; 4 P.M., plumous _cirri in south_; ends clear.

"22d. Hazy morning (S. very fresh) arch of cirrus in west; 2 P.M., black in W. N. W.; 3 P.M., overcast and rainy; 4 P.M., a heavy gust from south; 4.30 P.M., blowing furiously (S. by W.); 5 P.M., tremendous squall, uprooting trees and scattering chimneys; 6 P.M., more moderate (W.).

"23d. Clearing up (N. W.); 8 A.M., quite clear; 11 A.M., bands of mottled cirri pointing N. E. and S. W., ends cold (W. N. W.); the cirri seem to rotate from left to right, or with the sun.

"24th. Fine clear, cool day, begins and ends (N. W.).

"25th. Clear morning (N. W. light); 2 P.M. (E.), calm; tufts of tangled cirri in north, intermixed with radiating streaks, all pa.s.sing eastward; ends clear.