Spatial And Temporal Distribution Characteristics And Formation Mechanism Of Heavy Precipitation In Hainan Island In Winter

In addition to typhoon rainstorm and autumn flood season rainstorm,some unique weather system configurations in Hainan Island in winter(December-next year's February)will also trigger extreme heavy precipitation.This kind of extreme weather process is sudden and strong,and the precipitation intensity is high,and the precipitation period is concentrated,which is more likely to cause local floods and lead to serious economic losses.Based on radar data,observation data and reanalysis data of European Center ERA5(0.25× 0.25),the temporal and spatial distribution characteristics of heavy precipitation in winter in Hainan Island are statistically analyzed,and the circulation characteristics of heavy precipitation in winter in Hainan Island and the formation mechanism of deep convection are deeply analyzed.The main conclusions are as follows:(1)Statistics show that winter rainstorms in Hainan Island occur in the whole winter,and December is the concentrated period.Tthere are great differences in the time distribution of rainstorm days and rainstorm stations,and the greater the rainfall magnitude,the more obvious the difference.There is also a significant regional feature in the spatial distribution,with the highest frequency in the eastern region,generally showing the distribution characteristics of less in the west and more in the east,stronger in the east and weaker in the west.(2)From the synthetic analysis of cases above the magnitude of heavy rain,it is concluded that the occurrence of heavy precipitation in Hainan Island in winter is closely related to the large-scale circulation anomaly.Compared with the average climate,the low-level jet to the east is stronger,the shape of the south branch trough of Indo-China Peninsula is more obvious,the subtropical high is fairly strong and more northerly,the outflow of the South Asian high to the northwest is relatively strong,and there is a significant positive SST anomaly in the South China Sea.(3)From the anomaly analysis of the extreme case,it is found that the occurrence of the extreme case in Hainan Island in winter is closely related to large-scale circulation anomalies.Compared with the synthetic field of individual cases above the magnitude of heavy rain,the low-level jet to the east is stronger,the south branch trough of Indo-China Peninsula is quite strong,the outflow of the South Asian high to the northwest is relatively strong,and subtropical high is weaker.(4)From the strength of different case analysis and comparison,it is found that they all have similar weather situation configuration,and the difference of precipitation intensity is mainly caused by the difference between southern trough and subtropical high position and intensity.(5)From the simulation analysis of the extreme case,cold pool,cold pad,wet neutral stratification and frontogenesis caused by horizontal movement are very important to the development of deep convection.Vertical wind shear with different heights can indicate the movement and structural change of convection.