CLIMATIC CHARACTERISTICS AND CAUSES OF HAIL IN GUIZHOU:1961-2021

LIU Tao; XIA Xiaoling; PENG Yuxiang; TANG Piru; LI Hao; WEN Jifen

doi:10.16032/j.issn.1004-4965.2023.075

Abstract：Based on the hail observational data from 84 national stations in Guizhou Province during 1961-2021,the temporal and spatial distribution of hail in Guizhou in recent 61 years were studied by using regression analysis,wavelet analysis and EOF decomposition.Anomalies of atmospheric circulation and external forcing factors were also adopted to analyze hail frequency.The results showed that hail can occur all year long in Guizhou with most in spring and least in autumn.On a daily scale,hail mainly occurred in the afternoon and evening from 14:00 to 01:00.The occurrence of hail in Guizhou showed oscillation cycles of 14 years and eight years,and the trend changed around 1995 with shorter oscillation and lower frequency.The central and western regions were more hail-prone,and the annual average hail frequency was positively correlated with altitude.After EOF decomposition,the first two modes of spatial distribution of hail in Guizhou were provincial consistent and east-west opposite in the spatial vector field.Hail caused by large-scale circulation and topography tended to decrease.After 1991,hail induced by terrain and local convection in the east of central Guizhou slightly increased,but its variance contribution rate was small.Therefore,the overall number of hail days in Guizhou exhibited a downward trend.Through the analysis of atmospheric circulation and external forcing factors,it was found that the anomaly of sea surface temperature in a La Niña year triggered abnormal cyclones in the tropical northwest Pacific,leading to a weaker Subtropical High in the region and further affected negative height anomalies in Guizhou and its surrounding areas,which was favorable for the occurrence of hail in Guizhou.By contrast,the number of hail events in Guizhou decreased in El Niño years.