Gaoyuan qixiang (Dec 2023)
Analysis of the Difference between Rainstorm Accompanied by Easterly Low-level Jet in Tarim and Rainstorm without Easterly Low-level Jet in Tarim in Southern Xinjiang
Abstract
Most of the regional heavy rain processes in the monsoon region of China are related to the low-level jet.However， in arid and semi-arid regions， the low-level jet stream is not necessarily associated with every rainstorm process.Based on the daily precipitation data from May to September from 1971 to 2020， hourly precipitation data from 2011 to 2020， and the radiosonde data from Ruoqiang Station twice a day， the observational characteristics of heavy rain with and without easterly low-level jet in southern Xinjiang in recent 40 years were analyzed by statistical methods.The results show that the number of rainstorm days accompanied by easterly low-level jet is slightly less than that without easterly low-level jet in southern Xinjiang in recent 40 years.Both of them showed an increasing trend in the past 40 years， but the increasing trend of the number of rainstorm days accompanied by the easterly low-level jet was more significant.In the past 40 years， the proportion of rainstorm days accompanied by easterly low-level jet to the total rainstorm days in southern Xinjiang showed an increasing trend， while the proportion of rainstorm days without easterly low-level jet showed a decreasing trend.In the warm season of southern Xinjiang， the number of rainstorm days accompanied by easterly low-level jet was the highest in May， while the number of rainstorm days without easterly low-level jet was the highest in July， and both of them were the least in September.From the 1970s to the 1990s， the heavy rain in the warm season in southern Xinjiang was mainly accompanied by the easterly low-level jet， and from the 2000s to the present， the heavy rain was mainly accompanied by the easterly low-level jet.The number of rainstorm days is relatively higher in the western part of southern Xinjiang， and the rainstorm is mainly accompanied by easterly low level jet stream.The proportion of short-time heavy precipitation events in the rainstorm without the easterly low-level jet in the warm season in southern Xinjiang is significantly higher than that in the rainstorm with the easterly low-level jet.The rainstorm accompanied by the easterly low-level jet is dominated by night rain， while the rainstorm without the easterly low-level jet is dominated by day rain.In the warm season of southern Xinjiang， the periods of maximum precipitation and maximum occurrence of the rainstorm with the easterly low-level jet mainly occurred around midnight， while the periods of maximum precipitation of the rainstorm without the easterly low-level jet mainly occurred from late afternoon to late afternoon.The maximum cumulative frequency of the rainstorm without the easterly low-level jet is similar to that of the rainstorm with the easterly low-level jet occurred around midnight.The maximum intensity of both types of torrential rain occurs from mid-afternoon to late afternoon.The peak value of rainstorm precipitation with easterly low-level jet in the warm season in southern Xinjiang was mainly caused by the frequency of precipitation in the early night， while the sub-peak value of rainstorm precipitation around evening was mainly caused by the intensity of precipitation.The diurnal variation characteristics of rainstorm precipitation without easterly low-level jet in the warm season in southern Xinjiang are similar to its precipitation intensity， and the difference between it and its precipitation frequency is great.There is a great difference between the rainstorm with easterly low level jet and the rainstorm without easterly low level jet in the warm season of southern Xinjiang.At present， the research on the formation mechanism of rainstorm in southern Xinjiang with the coordination of easterly low level jet from Tarim is relatively mature， while the formation mechanism of rainstorm without the coordination of easterly low level jet from Tarim is still unclear.
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