TABLE II. WINDS ABOVE THE TRADE-WIND REGION OF THE ATLANTIC, BETWEEN LAT. 37° AND 10° N, LONG. 15° AND 26° W OF GREENWICH. NE to 800 meters; NW to at least 4200 meters. WNW to 1800 m.; NW and SW to 11,500 m.; SW at 11,600 m. NE to 2900 m.; NW and NE to 4200 m.; WSW to at least 12,500 m. NE trade to 400 m.; NW to 3500 m.; WSW to at NE trade (variable) to 2000 m.; NNW to 4000 m.; NE trade to 3300 m.; SW and NW to 5200 m.; NE trade to 3200 meters; SE and S to 5300 m.; NE trade to 2300 m.; S and SSW to at least 3900 m. E, 1 m. per sec., to 1000 m.; N, 4 m. per sec., at 2000 m.; N, 7 m. per sec., at 2500 m.; E, 3 m. per sec., at 3000 m.; S, 4 m. per sec., at 3500 m.; S at 4000 m. (?) NE trade to 2600 m.; NW to 3400 m.; WSW at 3400-4200 m.; SW to at least 6500 m. NE trade (variable) to 4100 m.; variable to 5100 NE trade to 650 m.; NW (variable) to 1900 m.; E, 7-3 m. per sec., to 500 m.; NE, 6 m. per sec., at 1000 m.; N, 6 m. per sec., at 1500 m.; N, 5 m. per sec., at 2000 m.; ENE at 2500 m.; E at 3500 m. (?) NE, 4-3 m. per sec., to 1000 m.; E, 16 m. per sec., N, 3-5 m. per sec., to 1600 m.; E at 3000 m. (?) by cumulus and alto-stratus clouds were seen floating in it at a height of perhaps 4000 or 5000 meters, and from them light sprinkles of rain fell occasionally. On the Peak of Teneriffe, in passing into this upper current, a rise of temperature was noted, which was less than that encountered above the surface-trade. The winds at great heights in and near the trade-wind region are given in Table II. They were obtained by pilot-balloons launched from the islands, excepting the one from the yacht, and the last figures for each ascension show the maximum height at which the balloon was sighted. The means of direct observations of wind-direction and velocity at definite heights, obtained during the ascents and descents of the peaks on the tropical islands of Teneriffe and Fogo, and the drift of clouds passing at estimated heights above these mountains, are given. Observations of the direction and velocity of the wind, obtained in two kite-flights south of the trade-wind region, complete the table. In that portion of the Atlantic investigated by the Franco-American Expedition, the atmospheric circulation was found to be as follows: (1) North of Madeira, and near the Azores, the upper winds, as was already known by observations of clouds, are chiefly from west and northwest, this region being generally to the north of the barometric maximum over the ocean and beyond the zone of the trades. (2) The winds blowing towards the equator are from northeast to east in the lower region, and generally from northwest to northeast above 1000 meters. (3) The return currents from the equator, or anti-trades, are formed by winds having a southerly component, being generally southwest in the latitude of the Canaries, and southeast near the Cape Verdes, thus showing the influence of the earth's rotation. The law of the vertical succession of winds, as formulated by Abercromby, 5 namely, a shifting in the northern hemisphere of the upper winds to the left-hand, when one's back is towards the wind, is found not to hold true always, the right or left-handed rotation depending upon the origin of the wind, and, presumably, upon the distribution of the pressure at high levels. The vertical distribution of temperature and relative humidity revealed by these observations up to a height of 4000 meters is nearly the same as that found by Professor Hergesell during the cruises of the "Princesse-Alice," in 1904 and 1905. Most of his observations Nature, 36, 85. Comptes Rendus de l'Académie des Sciences, 30 janvier, 1905; Meteorologische Zeitschrift, November, 1905; Bulletin du Musée Océanographique de Monaco, 30 novembre, 1905. of direction of the upper currents differ radically, however, in showing no southerly component, although one balloon, launched west of the Canaries, gave the same direction as that obtained near these islands, meeting interlaced currents from the southeast and southwest, above the northeast trade. From the distribution of pressure on the earth's surface it would be supposed that the upper antitrade ought to be especially regular in the region between Cape Verde and the Canaries; but this idea is contrary to the belief of Professor Hergesell that the upper southeast and southwest winds observed near these islands, and long considered to furnish a demonstration of the return-trade, are due to local disturbing causes. To settle this question, Messrs. Teisserenc de Bort and the author again sent the "Otaria," during the winter of 1906, to the south and west of the region which had been explored by them the preceding summer. Since this paper was presented to the Academy, Messrs. Maurice and Nilsson, constituting the scientific staff of the "Otaria," have communicated the results of their atmospheric soundings, made from the vessel to the westward of the Canaries, and these results appear in Table III. The longitudes are from Greenwich. TABLE III. WINDS OBSERVED IN FEBRUAry, 1906, above THE ATLANTIC, SOUTHWEST OF THE CANARIES. Lat. 28° N, Long. 180 W. ENE to 2850 m., NW to 3680 m., SW to the culminating point of the balloon, 5300 m. N to Lat. 27° N, Long. 180 W. ENE to 1800 m., SSE to 2100 m., Lat. 26° N, Long. 19° W. NE changing to N up to 1350 m., NW to 2600 m., WSW and SW to 5100 m. Lat. 26° N, Long. 19° W. NE to 1300 m., NW and W to 3150 m., strong SW to 3300 m. Cirrus clouds (4 observations) from S 50° W. Lat. 25° N, Long. 20° W. NE to 2300 m., NW to 3000 m., SW to 3250 m., WNW changing to W up to 3950 m., SW to 4150 m. Alto-cumulus clouds from NE, cirrus (2 observations) from S 30° W. Cirrus clouds from S 45° W. It is seen that the upper anti-trade is shown both by the balloons and by the drift of the clouds, the stratified conditions giving place to the southerly wind between 3000 and 4000 meters. Therefore the classic observations of the return-trade, which were long ago made on the Peak of Teneriffe, indicate a general phenomenon, and agree with those obtained over the open ocean by the present expedition. |