Don or David Pacifico Pacifico

Meteorology.

Partly on account of its great extent, and partly because there is no wide opening to the Arctic regions, the normal wind circulation is on the whole less modified in the north Pacific than in the Atlantic, except in the west, where the south-west monsoon of southern Asia controls the prevailing winds, its influence extending eastwards to 145° E., near the Ladrones, and southwards to the Equator. In the south Pacific, during the winter months of the Northern Hemisphere, the north west monsoon of Australia affects a belt running east of New Guinea to the Solomon islands. In the east the north-east trade belt extends between 5° and 25° N., the south-east trade crosses the Equator, and its mean southern limit is 25° S. The trade winds are generally weaker and less persistent in the Pacific than in the Atlantic, and the intervening belt of equatorial calms is broader. Except in the east of the Pacific, the south-east trade is only fully developed during the southern winter; at other sea sons the regular trade-belt is cut across from north-west to south-east by a band 20°-30° wide, in which the trades alternate with winds from north-east and north, and with calms, the calms prevailing chiefly at the boundary of the monsoon region (5° N.– 15° S., i6o°-185° E.). This area, in which the south-east trade is interrupted, includes the Fiji, Navigator and Society groups, and the Paumotus. In the Marquesas group the trade-wind is fairly constant.

The great, warming and abundant rainfall of the island regions of the western south Pacific, and the low temperature of the surface water in the east, cause a displacement of the southern tropical maximum of pressure to the east; hence we have a permanent "south Pacific anti-cyclone" close to the coast of South America. The characteristic feature of the south-western Pacific is therefore the relatively low pressure and the existence of a true monsoon region in the middle of the trade-wind belt.

It is to be noted that the climate of the islands of the Pacific becomes more and more healthy the farther they are from the monsoon region. The island regions of the Pacific are every where characterized by uniform high air-temperatures; the mean annual range varies from I° to 9° F, and the diurnal range from 9° to 16°. In the monsoon region relative humidity is high, viz., 8o to 90%. The rainfall is abundant; in the western island groups there is no well-marked rainy season, but over the whole region the greater part of the rainfall takes place during the southern summer, even as far north as Hawaii.

The whole north Pacific from the tropic to the Bering sea has on its Asiatic side a monsoonal reversal of its prevailing winds, winter and summer. In winter exceedingly dry and cold north westerly winds, dependent on an air pressure maximum over Siberia and an air pressure minimum near the Aleutians, blow over the whole area; in summer, with low pressure over the Asiatic continent, warm and rainy south and south-easterly winds (in connection with the south-west monsoon of the China sea) prevail over the whole area of the Yellow sea, Japan sea, Okhotsk sea and Bering sea. On the American side of the Pacific this

complete change of wind direction is absent, and throughout the year moist, warm winds from the ocean; i.e., south-westerlies, prevail from Sitka to Vancouver, except for irregular changes in consequence of the passing of atmospheric depressions. These circumstances explain the great differences shown in the following table between the average air temperatures on the Australo Asiatic side of the Pacific and on the American : Air Temperature (° F) and Rainfall (mm.) in the Pacific Temperature.—The distribution of temperature in the waters of the Pacific ocean has been fully investigated, so far as is pos sible with the existing observations, by G. Schott. At the surface an extensive area of maximum temperature (over 82° F) occurs over o° on each side of the Equator to the west of the ocean. On the eastern side temperature falls to 72° F on the Equator and is slightly higher to north and south. In the north Pacific, beyond lat. 40°, the surface is generally warmer on the east than on the west, but this condition is, on the whole, reversed in cor responding southern latitudes. In the intermediate levels, down to depths not exceeding 1,000 metres, a remarkable distribution appears. A narrow strip of cold water runs between the Equator and 10° N., widest to the east and narrowing westward, and separates two areas of maximum which have their greatest in tensity in the western part of the ocean and have their central portions in higher latitudes as depth increases, apparently tend ing constantly to a position in about latitude 20° to 30° N. and S. A comparison of this distribution with that of atmospheric pressure is of great interest. High temperature in the depth may be taken to mean descending water, just as high atmospheric pressure means descending air; low temperature in the depth may be taken to mean ascending water, as low pressure means ascending air, and hence it would seem that the slow vertical movement of water in the Pacific reproduces to some extent the phenomena of the "doldrums" and "horse latitudes." The isothermal lines, in fact, suggest that in the vast area of the Pacific something correspond ing to a "planetary circulation" is established. In the greater depths of more than 2,o0o metres, temperature is extraordinarily uniform, 8o% of the existing observations falling within the limits of 34.8 and 35.5• In the enclosed seas of the western Pacific, temperature usually falls till a depth corresponding to that of the summit of the barriers which isolate them from the open ocean is reached, and below that point temperature is uni f orm to the bottom. In the Sulu sea, for example, a temperature of 50•4° F is reached at 700 metres, and this remains constant to the bottom in 4,66o metres.