General Circulation of the Atmosphere and Two Types of Mechanism of Falling Rain

[摘要] At present there are two dominant theories for the mechanism of falling rain. One is the polar front theory set forth by the Norwegian school, which considers the rain to occur along a front. In this theory the area of precipitation extends with the movement of the front, and so it may be concluded that the lower circulation of the atmosphere is primarily important for the mechanism of falling rain. The other is the “Steuerung” theory developed by H. v. Ficker and followed by the Central-European school, in which the area of rainfall is mostly influenced by upper air circulations.The present paper investigates these two typical examples of rainfall in the Far East. According to the report of the Shanghai Observatory, the first example of rainfall was observed on the afternoon of November 8, 1939 in the interior of a modified Tm air mass. This rain area started from somewhere near Formosa and extended towards the NE-direction, guided by upper air currents, as it was seen from the estimated 3000m isobars. The center of isallobaric low (the time interval was put as 24 hours) accompanying this rainfall also took the same direction. After some more detailed examinations, the essential cause of this rainfall may be reduced to the vertical instability of the air mass itself. Thus the “Steuerung” theory is important for this rainfall.The second example of rainfall occurred in the midnight of the same day, which was caused by the conspicuous cold front due to the outbreak of a modified Pc air mass from the Siberian High. The cold front moved towards the SE-direction across the 3000m isobars. Thus the second rainfall is well explained by the polar front theory, as is ordinarily the case in the Far East.

[学科分类] 大气科学