Available online: July 09, 2021 , DOI:
In this study, the key area of upstream southwest wind speed was established, which is closely associated with Spring Persistent Rains in Hunan (SPRH). The starting date, ending date, rainfall, rainy period and intensity index of SPRH were defined from 1980 to 2014. The temporal and spatial patterns of SPRH rainfall were analyzed. The anomaly of the atmospheric circulations during the strong/weak SPRH period and sea surface temperature (SST) during the early period were discussed. Results showed that: The climate average of SPRH occurred from the 13 pentads to the 27 pentads, whereas the starting date and ending date of SPRH varied in different years. The rainfall of SPRH was exceeded normal conditions during the periods of before the mid-1980s and after 2014, whereas it was lower than normal conditions during the periods of the mid-1980s to 2014. The strong years of SPRH in whole province were found in 1981, 1992, 2014 and 2016. By contrast, the weak years of SPRH in whole province occurred after 1990 including 1991, 1994, 2008 and 2011. In the strong SPRH years in whole province, the western pacific subtropical high (WPSH) remarkably became stronger and westward; the Indo-Burmese trough tended to become weaker; and an anomalous anticyclone existed in the southern Yangtze River regions in low-level wind field. Hunan was located in the center of anomalous anticyclone, which led to strong SPRH. However, in the weak SPRH years, WPSH evidently became weaker; the Indo-Burmese trough tended to become stronger; and an anomalous cyclone was found in southern China. Additionally, Hunan was located in the center of anomalous water vapor divergence, resulting in weaker SPRH in whole province. In the following year of the occurrence of El Nino events, SPRH started earlier, longer rainy period, more intensive rainfall amount compared with the normal years. On the contrary, during the following year of the occurrence of La Nina, SPRH started later, shorted rainy periods, lower rainfall amount and weaker rainfall intensity compared with the normal years.