Analysis of Daily Extreme Rainfall Characteristics and Forecast Points of Typhoons in Wenzhou
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Abstract:
Based on the National Basic Meteorological Station observation data, European Centre for Medium-Range Weather Forecasts Reanalysis, and the typhoon best track data of Shanghai Typhoon Research Institute from 1951 to 2022, the characteristics of daily extreme rainfall events caused by typhoons and the points of daily extreme rainfall forecast in Wenzhou are studied and analysed using the percentile method and composite analysis. The results show that typhoons causing daily extreme rainfall in Wenzhou are all landing typhoons. Daily extreme rainfall is concentrated between July and October, with the most occurring in August and the strongest in September. According to similar rainfall patterns and paths, they are divided into four types: Southern Zhejiang, Eastern Guangdong, Middle, and Southwest types. The heavy rainfall centres of the Southern Zhejiang type and Eastern Guangdong type are located in the northeast of Wenzhou, and the corresponding typhoons land in the south of Zhejiang Province and the east of Guangdong Province, respectively. The heavy rainfall centre of the Middle type is located in the middle of Wenzhou, and the corresponding typhoons land in the area from the junction of Zhejiang and Fujian Provinces to the middle of Fujian Province. The heavy rainfall centre of the Southwest type is located in the southwest of Wenzhou, and the corresponding typhoons land in the middle and south of Fujian Province. Except for the Eastern Guangdong type, low-layer vorticity at 850 hPa reaches 8×10-5/s or above, which provides a good indication for daily extreme rainfall forecasts. The intensity differences of water vapour transport, water vapour convergence, vertical water vapour flux gradient between 850-925 hPa, and different types of low-layer jets correspond well with the intensity of extreme rainfall. The differences between the west boundary of the water vapour transport above 30 g/(s·hPa·cm) and the position of the strong water vapour convergence centre below -(2-4)×10-6 g/(cm2·hPa·s) correspond to the differences in extreme rainfall areas. The dense zone of water vapour flux and the convergence centre of water vapour flux at 925 hPa correspond well with the area of heavy rainfall, except for the Eastern Guangdong type. The differences in the development height and intensity of vertical ascending motion below -0.8 Pa/s correspond to the differences in extreme rainfall area and intensity. The characteristics of the low-layer convergence zone explain the distribution of vertical ascending motion. The uplift caused by sea-land terrain in the east and mountainous terrain in the west strengthens the ascending motion. The intensity difference of differential pseudo-equivalent potential temperature advection in the middle and lower levels corresponds with the difference in rainfall intensity. Cold air has a certain enhancement effect on the extreme rainfall events of the Eastern Guangdong, Middle and Southwest types.
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Supported by:Beijing E-Tiller Technology Development Co., Ltd.
Supported by:Beijing E-Tiller Technology Development Co., Ltd.