Occurrence Time Characteristics Of Extreme Precipitation In Eastern China And Its Relationship With Atmospheric Circulation Anomalies

Under the background of global climate change,the frequency of extreme precipitation events is increasing.Previously,scholars mainly focused on the intensity,frequency and mechanism of extreme precipitation events,however,there is a lack of research on the spatial and temporal characteristics and influencing factors of the occurrence timing of extreme precipitation.Exploring the characteristics and influencing factors of extreme precipitation occurrence timing can help us further understand and predict the extreme precipitation events in the region and reduce the negative impacts of extreme precipitation events.In this paper,daily precipitation data from 419 meteorological stations in Eastern China(15°?54°N,105°?135°E)from 1961 to 2015 and NCEP/NCAR reanalysis data from the same period were used in the research.Firstly,the spatio-temporal evolution characteristics of each extreme precipitation occurrence timing were analyzed,while the occurrence timing of annual maximum seven-day precipitation(PX7D)was used to represent the extreme precipitation occurrence timing.Secondly,the EOF analysis of extreme precipitation occurrence timing was carried out,and the typical years of extreme precipitation occurrence timing was selected,based on which the meridional changes of circulation field,water vapor conditions,precipitation and wind speed were further investigated.Finally,based on the typical years of extreme precipitation occurrence,the influence of circulation anomalies such as the timing of the northward jump of the West Pacific subtropical high,the timing of the first appearance of the South Asian high on the Tibetan Plateau and its withdrawal from the plateau,the timing of the summer monsoon outbreak in the South China Sea,the timing of the first appearance of the cold vortex,and the influence of the heat source on the occurrence of extreme precipitation on the Tibetan Plateau were investigated in the early and late typical years,respectively.The conclusions of the study are as follows.(1)The characteristics of extreme precipitation occurrence timing based on the definition of maximum value method and the percentile threshold method.The occurrence timing of maximum seven-day precipitation is generally characterized by a latitudinal gradient of delaying from south to north,and its spatial distribution is more regular,which is consistent with the process of the south-to-north propagation of the summer rain belt in China.The average occurrence timing of maximum one-day precipitation and maximum seven-day precipitation advanced,and the median and average of the timing of extreme precipitation occurrence based on the 90% threshold also advanced.(2)In the typical year of early(late)occurrence of extreme precipitation,the position of South Asian high is eastward(westward)in May-June,and westward(eastward)in July-August;the position and area of the western Pacific subtropical high is westward(eastward)and large(small)in May and June,and eastward(westward)and small(large)in July and August;water vapor transport has a strong positive anomaly in eastern China in May-June(July-August).The intensity of precipitation center occurs in late May-early June(mid-June to early-mid July).(3)The timing of extreme precipitation occurrence in the early years is early relative to the late years for the northward jump of the West Pacific subtropical high,the first arrival and withdrawal of South Asia high on Tibetan Plateau the summer monsoon outbreak in the South China Sea and the first appearance of the cold vortex.From the vertical distribution of atmospheric heat sources,the maximum heating rate in May-June is greater in the early years than in the late years,and the maximum heating rate in July-August is greater in the late years than in the early years.In terms of spatial distribution,the intensity of atmospheric heat source for the early(late)typical years of extreme precipitation occurrence is the strongest in June(July)in the Tibetan Plateau region.The corresponding dynamic conditions are convergent at the low level and divergent at the high level with strong upward motion,thus favoring the formation of extreme precipitation.