Title: Process analysis of the extraordinarily torrential rainfall from Typhoon Krosa in Zhejiang
Abstract: No.0716 Typhoon Krosa landed near Xiaguan town, Cangnan County, Zhejiang adjacent to Fujian province at 15:30 on October 7, 2007, which brought torrential rain in Zhejiang province with the average rainfall of 163.0 mm during the typhoon. Extraordinarily torrential rain occurred in Wenzhou, Taizhou and Ningbo areas and the maximum rainfall occurred at Shibalong Town, Yongjia County, Wenzhou, where the rainfall was up to 545.8 mm.Based on NCEP/NCAR 1°×1° reanalyzed grid data, data from the automatic observation stations in Zhejiang, and Ki and Ky indices from MICAPS analysis system general circulation evolution, dynamic conditions, water vapor transportation and the characteristics of physical variables that brought torrential rain by Typhoon Krosa (0716) in Zhejiang are analyzed. The results show that when Krosa hit Zhejiang in October 6 to 9, the circulation was straight in middle and higher latitudes at 500 hPa; high-pressure ridge was to the west of Urals and there was a moving cold trough from Hexi Corridor to the Central Plains; the gradually intensified western Pacific subtropical high was in the shape of east-west belt, its northern part was stranger than normal; the area to the south of Jianghuai was covered by the subtropical high, the ridge was located near 30°N; in the middle and low levels of 700 hPa and 850 hPa of the troposphere, there was an apparent cold temperature tough passing though the Hexi Corridor, Hetao area, Jianghuai and the middle and lower reaches of the Changjiang River. The interaction between the surface cold front and the inverted trough of typhoon Krosa from 14pm, October 7 to 14pm, October 8 formed special environmental conditions of cold air invasion at the surroundings of the typhoon which favors the torrential rain in Zhejiang. Huge amount of vapor content in the spiral cloud band of Krosa was transported from the East China Sea to Zhejiang continent, which resulted in an area of great water vapor flux value from the East China Sea to the most part of Zhejiang with the maximum flux greater than 40 g/(s·hPa·cm) at the low level of 850 hPa at 02am, October 7 in East China Sea. The water vapor transportation at the low level from the East China Sea to the continent of Zhejiang lasted for 42 h, which provided water vapor for this torrential rain. Diagnosis shows that there could be torrential rain when the precipitable water in the atmospheric column is up to 65 kg/m2 and extraordinarily torrential rain when it is 70 kg/m2. The stream, divergence and vertical velocity fields show that not only the vigorous rising motion at the low level in the typhoon region provided a trigger of the rising motion of the torrential rain, the overlap of the upper and middle level divergence area and the strong convergence area at the north of the typhoon's inverted trough enhanced the convergence of the middle and lower levels, which favored the maintenance and strengthening of the torrential rain at the north of the typhoon. Besides, the area of vertically rising motion in the circulation area of the typhoon experienced a thickening process. The analysis of temperature advection shows that the warm air and cold air interacted below 550 hPa from October 6 to October 8 over Zhejiang, which is resulted from the meeting of the cold air inserted into the typhoon and the warm and wet air brought by typhoon. The typhoon circulation exhibited a western-eastern seesaw mode cold in the west and warm in the east. Together with the affection of the convergence mechanism at the low level, the baroclinic instability energy was further increased and maximum effective potential energy released, which made the 35℃ Ki index and 4~6 high value Ky index control the whole Zhejiang. These lead to vigorous ascend motion and more rainfall in typhoon inverted trough.
Publication Year: 2010
Publication Date: 2010-01-01
Language: en
Type: article
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