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TEMPERATE ZONE OF NORTH AMERICA, EAST OF THE ROCKY MOUNTAINS.
This region has much in common with Arizona and New Mexico, as to the mean direction and percentage of its winds. In summer a strong current from the south sets in to supply the air which is rising on the interior plateaus. In the winter, on the contrary, the prevailing winds are N. W. and the mean direction generally between N. and W. In winter the winds are more variable than in summer, and even southerly winds are sometimes experienced. The boundaries of this region are the great axis of the continent on the W., the Rio Grande on the S.W., the Gulf of Mexico on the S. E., and the Mississippi on the E. The northern boundary is rather doubtful, but yet, as far as 45° N., winds from the S. E., S., and S. W. prevail in summer. (See also maps, Plates 5, 6, 8 and 11.)
4 12 6 2
21 7 25 22 4 | 18 8 12
10 4 | 15.
E. New Mexico.
5 5 7 13 41 18 6 4 W. Texas
15 16 15 13 14 9 Rio Grande Valley
1.1 4 13 61 19 1.1 0.3 0.9 Central Texas.
7 4 19 | 46 | 11 2
2 8. Central Texas
15 32 28 9 4 2 San Antonio, Texas, No. of ob. 1.2
7 76 5
0.7 5 17 52 16 8 1 1
4 5 12 31 37 5 2 3 Eastern Central Texas
12 19 43 6 N. Texas, E. of 98" W. long.
2 17 13 47 9 Arkansas, 349-35° N.
9 10 13 18 | 2013 10 N. E. Arkansas
17 8 11 11 21 9 12 11 S. E. Indian Territory
7 10 18 16 26 11 6 6 N. E. Indian Territory
5 7 10 28 27 13 4 Central and N. E. Kansas
7 5 4 12 49 12 S. W. and W. Cent. Kansas
9 9 23 26 14 S. E. Colorado
20 25 | 14 8 19 Central Colorado
4 13 4 37 | 21 14 N. E. Colorado.
6 9 13 19 201 12 9 11 N. E. Wyoming
18 5 0.5 10 24 21 6 15 8. Ceutrai and S. E. Dacotah 10 7
7 16 N. E. Nebraska
13 5 5 9 36 12 8 12 S. and 8. E. Nebraska
10 12 7 23 23 10 5 9 S. Iowa
8 4 11 11 25 | 11 18 12 N. and N. E. Iowa
18 2017 9 16 S. E, Iowa.
4 | 12 4 19 10 28 8 16 S. E. Minnesota
9 8 2 22 19 16 12 12 W. and Central Missouri 11 10 9 19 2515 4 7 E. and S. E. Missouri
9 10 7 13 21 15 13
OCA voor Soeros
27 10 30 4 27 4 13 10 16 6 22 11 18 11 14 6 20 12 7 8 4 7 4 8 13 4 19 7 20 5 20 5
9 7 10 8 4 10 8 7 16 11 15 9
8 4 8 9 10 19 9 7 6 15
8 12 3 3 10
6 10 6 9 20
9 10 10
12 23 7 7 14 27 9 9 8
9 16 12 21 22 11 20 7 11 8 8 12 13 9
14 20 16 13 16 10 11 12 18 11 17 | 25 7 4 40 21 20 8
23 24 10 10 19 8
12 23 17 9
1324 14 11 12 26 12 9 22 23 11 12 1280
8 20 12 29 12 16 14 21 15
22 16 12
In Texas the winds have nearly the same direction as in Arizona and New Mexico, but the percentage of southerly winds in summer and northerly in winter is much greater. The winds in Texas have very strong monsoon features. This is due in a great measure to the proximity of the Gulf of Mexico. The state, except its extreme western part, is wholly open to the winds from the Gulf, and they must be strongly drawn in towards the land in summer, as the continent is much warmer than the sea. We have seen that there is a monsoon drawn in from the small and narrow Gulf of California to supply the deficiency in the interior. We must expect a much more powerful monsoon from the Gulf of Mexico. Winds in Texas, other than S. and S. E., are all but excluded from April to September.
In winter the winds are more northerly, but not N. E. or E. N. E. as in the trade-wind regions of the same latitudes, but N. and N. W., i.e. winds blow from the Staked Plain and other continental areas towards the Gulf of Mexico. Yet the prevalence of these winds, if we take the number of observations only, is not so great as that of the S. E. in summer. But the N. winds are extremely violent in Texas; they are the famous northers so well known and dreaded by seamen navigating the Gulf of Mexico, and also by travellers in Texas, especially because of the suddenness of their appearance. They are especially frequent in Central Southern Texas, about San Antonio, while the north winds east of the Guadalupe River are not so sudden and violent, resembling in fact rather the northwesters of the eastern States.
The cause of the violence of these winds must be sought to the southward in eastern Mexico. This country has not as regular a climate, with small barometrical variations, as other tropical regions of the same latitude. From December to March there are frequent storm-centres, with low barometer, passing there, as also on the eastern coast of Central America. A barometrical depression in Mexico or southward of it must draw in the air from the interior of Texas and New Mexico, where the pressure is high in the winter months. In April and May, when the barometrical variations are less in Mexico, the northers are less frequent, and cease altogether from June to September during the tropical rainy season, when barometrical variation is at minimum in Mexico. To illustrate this I give the mean and extremes of the pressure of the air at Vera Cruz. (See also Plate 14.)
From the observations by Dr. Berendt, manuscript collection of the Smithsonian Institution.
In the extreme south of Texas, at the mouth and in the valley of the Rio Grande, the S. E. winds are much more frequent, even in winter, than in the rest of the State. This is an intermediate region, partaking of some of the features of the Mexican climate, where easterly winds prevail the whole year. Yet the lower Rio Grande region is subject to violent northers. This seems to lead to the conclusion that in the other regions of Texas, where northerly winds prevail in winter, they are not all northers, there being also north winds of moderate force blowing towards the Gulf.
The mean direction of the winds in the different portions of Texas, is as follows:
N. 81° W..29. S. 7° E. .15 N. 28° E. .06 N. 57° W..33
The summer, as is shown by these tables, and the maps Plates 8 and 11, is the season in which the wind is most constant, the mean direction at all stations being between S. 7° E., and S. 46° E., and the ratio of the resultant very great, except in Western Texas. In the three last regions, nearest to the Gulf, the direction is more S. E., while in the more northern part of the State it is rather S. or S. S. E. The influence of the earth's rotation is here clearly seen. The wind begins as S. E., but soon is deflected to the south, and in its further course passes to the W. of S.
The agreement is not as exact in winter, probably because we have only the number of observations, and not the force of the wind. As the N. and N. W. winds are known to be the strongest, the mean direction would be much nearer each other in the different parts of the State, if we knew the force of the winds. Yet in all cases it would be seen to be more easterly on the lower Rio Grande near the Mexican frontier.
Spring and autumn are transition seasons, and in a country with monsoon winds, as Texas, there is very little to say about them. Generally spring is more analogous to summer, and autumn to winter. (See Plate 8.)
I must further remark as to the S. E. winds of the summer, that it would be an error to consider them merely as sea-winds blowing only during the day. They are stronger in the afternoon, while about sunset there is generally a calm. But about 9 P. M. the S. E. springs up again and blows till morning, when there is a second calm. I had occasion to observe this, in the summer of 1873, in the country between the Nueces and Guadalupe, and old residents of San Antonio informed me this was the regular course. (See the figures showing the number of observations and the force of the wind at 7 A. M., 2 P. M., and 9 P. M., at the last
place for the year 1872. (Zone 13, No. 13.) Even at stations on the Gulf coast, there are scarcely any land winds (N., N. W. and W.) observed in summer, which would be the case if there was a regular alternation of land and sea breezes.
North of Texas, throughout the whole region between 34° and 44° N. and the Rocky Mountains and Mississippi, the winds have also monsoon features, but more subdued. The prevailing winds of this region are N. and N. W. in winter and S. in summer. The cause is the same as in Arizona, New Mexico, and Texas. There are some irregularities in the mountain region (Central Colorado) but east of the mountains, in Nebraska and Iowa, the general character is again strongly marked. It is less the case in S. E. Minnesota, but even there the winds are southerly in summer, and deflected to the S. E. by the direction of the Mississippi Valley. In N. E. Arkansas and in Missouri the difference between winter and summer is still less marked. This is an approach to the character of the region between the Mississippi and the Appalachian chain, where there is no difference whatever between the seasons, the mean direction being about W. S. W. the whole year round. (See Plate 8.)
The tables for this work were printed before the results of observations on two high peaks of the Rocky Mountains could be obtained, both over 14,000 feet high. A meteorological station was established on Pike's Peak in the end of 1873, by the United States Signal Service, and the “Report for 1874” contains the means of observations for the first twelve months. I have given them in percentages, adding the station of Colorado Springs, at the eastern base of Pike's Peak. On Mount Lincoln the observations were made under Professor Hayden's geological survey of the territories, from 21st July, 1871, to the end of January, 1874. Both Pike's Peak and Mount Lincoln are situated in the central part of Colorado,
The difference between Pike's Peak and Colorado Springs seems to give a much greater proportion of S. W. and W. winds at the higher station, and a smaller amount of N., especially in summer. This agrees with the generally entertained opinion as to the prevailing direction of the upper atmospheric current from the W. S. W. in the middle and northern latitudes. In any case more observations are necessary in this respect.
The mean direction of the wind in the region north of Texas is :
S. E. Indian Territory
S. 74° E. 201 | S. 34° E. .324 N. 70° E. .221 | N. 37° E. 18
S. 23 W. 1.05 N. 65 W. 1.16
Here, again, as also shown by the maps (Plates 8 and 11), summer is the season which exhibits more regularity, the mean direction being everywhere between S. E. and S. W. The ratio of the resultant is greatest in the Indian Territory and Kansas, i. e., due north of the Gulf coast of Texas, and far from the influence of mountains. It is least in Missouri and N. E. Arkansas.
In winter the winds incline much more to the west than in Texas, being even S. of west, in East Missouri, N. E. Arkansas, and in S. E. Minnesota, i. e., in the extreme east of this region. Except in these regions there is a tolerably good agreement between the other stations.
The greatest difference between this region and Texas is seen in spring, as shown in Plate 8, when the winds are everywhere more or less westerly, except in the Indian Territory. Probably the cause is this: Texas being situated in a lower latitude is earlier heated, and the air from the Gulf of Mexico is sooner drawn in. The region here considered being further to the north, ascending currents are not established as early. Besides, when the lowlands between 34° to 42° N. are already heated, and an ascending current established over them, the deficiency is partly supplied by the cold air from the plateaus lying westward, partly by southerly winds from the Gulf of Mexico, and partly by winds from the polar regions. It is necessary to remember that the distribution of pressure in April and May is not the same as in midsummer. In the region here considered, pressure is lowest in May, while in Utah, and probably also on the lower Colorado, it is lowest in July. In the spring the winds coming from the Gulf of Mexico will be more westerly than in summer, because their point of attraction is more easterly in the former season than in the latter,
To recapitulate: There is an extensive region in the southwest of the United States which has a common yearly period of winds, different as are its geographical features. It includes the extreme S. E. of California, Arizona, New Mexico, Southern Utah, Texas, Arkansas, the Indian Territory, Eastern Colorado, Eastern Wyoming, Southern Dacotah, Nebraska, Iowa, Kansas, and Missouri. The winds are S. E., S., or S. W. in summer, with a great ratio of the resultant in the south, diminishing