Once a rainstorm takes place, abundant local vapor which is the fundamental condition, merges with a steady flow of vapor to rainstorm area creating convergence are both necessary. There are many vapor channels to Northeast of China, which depends on flow field condition while the main factor is the location and shape of western Pacific subtropical high(WPSH). There are some primary channels in Northeast of China:
The belt areas which has features of WPSH lie in northwest of this region and its west part deeps into continent. Southwest air stream started from the west, mixes with mid-latitude front airflow of westerly trough, forming a southwest warm air current from the Bay of Bengal or South China Sea to Northeast of China, and sometimes, moisture of tropical ocean will be sent to mainland by the east flow on the southern of the sub-tropical high, and then it turns to the Northeast of China.
Southern moisture channel can be divided into south-southwest direction, which is related to Jianghuai cyclone and North China cyclone, and south-southeast direction that is connected with typhoon and inter tropical convergence zoon.
Southeast moisture channel often has a bearing on northward typhoon, especially those from Western Pacific towards northwest.
It is a distinctive passageway in Northeast of China, which seldom happens. When Yakutsk is high pressure and there is a vortex in the East Sea of Japan, the vapor from the Pacific to the sea of Okhotsk, will pass through the high pressure Yakutsk and low vortex sea, and then it could reach Northeast of China, Heilongjiang province and Jilin province in particular.
The first, second and third kind of channels, are the ways that transport vapor to Northeast of China directly, called primary water vapor channel, while as for those approaches that carriage vapor from the sea over southwest mainland ( like some ways in "southwestern moisture channel") or through the sea of Okhotsk( like Northeastern moisture channel ), known as two water vapor channel.
The information is provided from Disaster Risk Reduction Knowledge Service.
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