Fig. 87—Wind roses for La Joya for the period April, 1892, to December, 1895. Compare the strong afternoon indraught from the south with the same phenomenon at Mollendo, [Fig. 79]. Figures drawn from data in Peruvian Meteorology, 1892-1895, Annals of the Astronomical Observatory of Harvard College, Vol. 39, Pt. 2, Cambridge, Mass., 1906.
At La Joya, a station on the desert northeast of Mollendo at an elevation of 4,140 feet, cloudiness is always slight, but it increases markedly during the summer. Caraveli, at an altitude of 5,635 feet,[22] and near the eastern border of the pampa, exhibits a tendency toward the climatic characteristics of the adjacent zone. Data for a camp station out on the pampa a few leagues from the town, were collected by Mr. J. P. Little of the staff of the Peruvian Expedition of 1912-13. They relate to the period January to March, 1913. Wind roses for these months show the characteristic light northwesterly winds of the early morning hours, in sharp contrast with the strong south and southwesterly indraught of the afternoon. The daily march of cloudiness is closely coördinated. Quotations from Mr. Little’s field notes follow:
“In the morning there is seldom any noticeable wind. A breeze starts at 10 A. M., generally about 180° (i. e. due south), increases to 2 or 3 velocity at noon, having veered some 25° to the southwest. It reaches a maximum velocity of 3 to 4 at about 4.00 P. M., now coming about 225° (i. e. southwest). By 6 P. M. the wind has died down considerably and the evenings are entirely free from it. The wind action is about the same every day. It is not a cold wind and, except with the fog, not a damp one, for I have not worn a coat in it for three weeks. It has a free unobstructed sweep across fairly level pampas.... At an interval of every three or four days a dense fog sweeps up from the southwest, dense enough for one to be easily lost in it. It seldom makes even a sprinkle of rain, but carries heavy moisture and will wet a man on horseback in 10 minutes. It starts about 3 P.M. and clears away by 8.00 P. M..... During January, rain fell in camp twice on successive days, starting at 3.00 P. M. and ceasing at 8.00 P. M. It was merely a light, steady rain, more the outcome of a dense fog than a rain-cloud of quick approach. In Caraveli, itself, I am told that it rains off and on all during the month in short, light showers.” This record is dated early in February and, in later notes, that month and March are recorded rainless.
Fig. 88—Wind roses for a station on the eastern border of the Coast Desert near Caraveli during the summer (January to March) of 1913. Compare with [Fig. 87]. The diameter of the circle in each case represents the proportion of calm. Note the characteristic morning calm.
Chosica (elevation 6,600 feet), one of the meteorological stations of the Harvard Astronomical Observatory, is still nearer the border. It also lies farther north, approximately in the latitude of Lima, and this in part may help to explain the greater cloudiness and rainfall. The rainfall for the year 1889-1890 was 6.14 inches, of which 3.94 fell in February. During the winter months when the principal wind observations were taken, over 90 per cent showed noon winds from a southerly direction while in the early morning northerly winds were frequent. It is also noteworthy that the “directions of the upper currents of the atmosphere as recorded by the motion of the clouds was generally between N. and E.” Plainly we are in the border region where climatic influences are carried over from the plateau and combine their effects with those from Pacific sources. Arequipa, farther south, and at an altitude of 7,550 feet, resembles Chosica. For the years 1892 to 1895 its mean rainfall was 5.4 inches.