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Analysis of Physical Field of the Rainfall Process during Flood Season from August 2 to August 14,1998
2018-05-24  |   Editor : houguangbing  
Category : Natural Sciences
Vapor flux

Because the system that affected this rainfall process was different, so the source of water vapor was not the same. In the rain before August 6, the water vapor mainly came from the sea. The large value area of the water vapor flux near the Bohai Bay extended to the Nenjiang River Basin in August 2nd. Although the center of water vapor flux was in the two provinces of Liaoning and Jilin, the region of large water vapor flux gradient was still in the southern part of Heilongjiang province at 20 o 'clock on August 3rd. A large value area of water vapor extended from the sea of Japan to the middle of Heilongjiang Province that merged with the water vapor from the north of the Gulf of Bohai in the southern part of Heilongjiang Province. According to the actual rainfall data, the heavy rainfall area of August 3 and August 5 ~ 6 was in the middle part of the songhua river dry flow, which was the intersection of two large value areas of water vapor flux. After August 7, there was basically no water vapor supplement near the sea of Japan. Water vapor came mainly from Bohai Gulf and the west of Nenjiang river. The water vapor flux graph of 850pha from August 8 could clearly showed the two sources of water vapor in Bohai Gulf and the west of Nenjiang. The water vapor flux center was located in the middle and lower reaches of the nenjiang river basin. In the south, a strong water vapor flux center extended northward from the Bohai Gulf to the LiaoDong Peninsula as a supplementary source of water vapor. At this time, heavy rainfall in the middle and lower reaches of nenjiang began. After August 11th, the water vapor flux intensity began decreasing and moving to the East. Heavy rainfall in the lower reaches of Songhua River began, but the rainfall intensity was weaker than the nenjiang river basin.

Vorticity

On the vorticity field on August 1 ~ 2 days, the southern positive vorticity zone moved to northward and the center of the positive vorticity was located in the Songhua River basin, which was the area of greater rainfall in the future. The center of the positive vorticity was weakened and the negative vorticity was moved to the region on August 3 ~ 4 days. The middle of the Songhua River basin was controlled by the positive vorticity zone on August 4 ~ 5 days. The middle and lower reaches of Nenjiang and the middle and upper reaches of the Songhua River main stream were all strong positive vorticity zones at 20 o 'clock on August 5th. The vorticity advection was very obvious and the central intensity was relatively large, which resulting in heavy rainfall on August 5 ~ 6 days. After that, the vorticity center was transferred to the Nenjiang basin after August 6th and merged with the westward vorticity at 20 o'clock in August 8th. The center was located near the Tao'er River and Nenjiang was still in the vorticity gradient larger region. The intensity of the rain was great and this state lasted until August 11th. At 20 August 11th, the center of the positive vorticity moved eastward and weakened. At 20 August 11th, the center of the positive vorticity moved eastward and weakened. The change of the vorticity led to the eastward movement of the heavy rainfall center and the relative weakening of the rainfall intensity.

Divergence and vertical velocity

At this point, we first focused on the divergence field of August 8th before the heavy rainfall occurred. At low altitude, there were large areas of strong convergence zone over the Nenjiang Basin and the convergence zones were in the vicinity of Taoerhe River Center. The middle and lower reaches of the Nenjiang basin were at the edge of the center of the convergence zone. But at the height of the sky, there were large fields of radiation in the Nenjiang River Basin. Low altitude convergence and high altitude divergence brought up the rising movement of the atmosphere, which was beneficial to the low layer of water vapor and energy to transport to the high rise, resulting in larger rainfall.

From the vertical velocity field of 850pha at 20 August 8th, we could see there was a strong upward movement in the area of future heavy rainfall and the ascending motion center was located in the strong rainfall area, which met the dynamic conditions of the heavy rainfall.

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