Abstract
Based on daily rainfall data and the NCEP/NCAR reanalysis data from 1961 to 2016, and according to the definition of regional persistent torrential rain (RPTR), features of typical circulation pattern of RPTR during the flood season in Hunan province and their relation to the distribution of first-day precipitation area were statistically analyzed. Results are as follows:①RPTR often occurs in six major circulation patterns, namely, two-trough-one-ridge, two-trough-two-ridge, two-ridge-one-trough, zonal fluctuation, typhoon depression and mutil-vortex;②RPTR occurs mainly in June, July, followed by May and August, and the probability of occurrence in April and September is small. Besides, the spatial distribution of RPTR cumulative frequency varies in different circulation patterns;③Similar characteristics of circulation at 500hPa are found in the middle-high latitude, which are conducive to the southwards moving of northern cold air to Hunan. However, due to the different intensities and morphological configurations of low latitude of the West Pacific subtropical high, the northern extension of southwest monsoon at 850hPa varies accordingly, resulting in significant difference in torrential rainfall area on the first day.
Abstract
Based on daily rainfall data and the NCEP/NCAR reanalysis data from 1961 to 2016, and according to the definition of regional persistent torrential rain (RPTR), features of typical circulation pattern of RPTR during the flood season in Hunan province and their relation to the distribution of first-day precipitation area were statistically analyzed. Results are as follows:①RPTR often occurs in six major circulation patterns, namely, two-trough-one-ridge, two-trough-two-ridge, two-ridge-one-trough, zonal fluctuation, typhoon depression and mutil-vortex;②RPTR occurs mainly in June, July, followed by May and August, and the probability of occurrence in April and September is small. Besides, the spatial distribution of RPTR cumulative frequency varies in different circulation patterns;③Similar characteristics of circulation at 500hPa are found in the middle-high latitude, which are conducive to the southwards moving of northern cold air to Hunan. However, due to the different intensities and morphological configurations of low latitude of the West Pacific subtropical high, the northern extension of southwest monsoon at 850hPa varies accordingly, resulting in significant difference in torrential rainfall area on the first day.
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