Moisture Source For Short-Time Heavy Rainfall In Xinjiang Based On Specific Humidity-Adjusted Lagrangian Model

Based on hourly observation data from China Ground Weather Station and GDAS meteorological data and NCEP/NCAR data in the period of 2016-2017,using Lagrangian Backward Trajectory Model,according to the change of specific humidity,temporal and spatial distribution characteristics and moisture source of short-time heavy rainfall in Xinjiang is adjusted,the change of meteorogical elements is studied.The results showed that:(1)The hourly precipitation and short-time heavy rainfall amount in summer are the largest in all regions of Xinjiang.Except that the peak time of hourly precipitation amount in Junggar Basin is concentrated in spring,and the peak time of short-time heavy rainfall in Hami-Turpan Desert Natural Area is concentrated in autumn,the hourly precipitation and short-time heavy rainfall in other areas are concentrated in summer.(2)The diurnal variation characteristics of hourly precipitation and short-time heavy rainfall in Xinjiang are different in different regions and seasons.In the area,the precipitation amount in the Altai-Tacheng Forest Grassland Natural Area is the highest,while that Hami-Turpan Desert Natural Area is the lowest.In the season,the summer precipitation smount in five regions of Xinjiang is the highest.Except for Middle Tianshan Natural Area in spring,except for Hami-Turpan Desert Natural Area in summer,except for Altai-Tacheng Forest Grassland Natural Area and Hami-Turpan Desert Natural Area in autumn,hourly precipitation in other areas mainly concentrates in the morning.In winter,hourly precipitation in Altai-Tacheng Forest Grassland Natural Area and Tarim Basin distributes evenly in all periods.Short-time heavy rainfall in spring,summer and the whole year in Altai-Tacheng Forest and Grassland Natural Area mainly concentrated in the latter half of the night,and in autumn in the first half of the night.The short-time heavy rainfall in the Middle Tianshan Natural Area in summer and the Hami-Turpan Desert Natural Area in the whole year concentrated in the afternoon and the first half of the night.Short-time heavy rainfall in the Tarim Basin and Junggar Basin in spring,summer,autumn and the whole year mainly concentrated in the morning.(3)The maximum hourly precipitation amount in spring,summer and autumn occur in the latter half of the night.Both spring and summer are distributed in the northern part of the Tarim Basin.In autumn,it is distributed in the western part of the Junggar Basin and theeastern part of the Tarim Basin.In winter,the daily and night precipitation amount is lower.The maximum short-time heavy rainfall in spring,summer and autumn occur mainly in the morning.It distributed in the south and west of Tarim Basin in spring and summer,and in the south of Junggar Basin in autumn.The spatial variations of precipitation frequency show a decreasing trend from north to south in spring,autumn,winter and the whole year in Xinjiang,and from northwest to southeast in summer.It has the highest precipitation frequency in summer and the lowest precipitation frequency in winter in Xinjiang.The high frequency areas of precipitation in spring and summer mainly distribute in Junggar Basin and Middle Tianshan Natural Area,the low value areas distribute in the west part of Tarim Basin and Hami-Turpan Desert Natural Area,the high frequency areas of precipitation in autumn and winter mainly distribute in Altai-Tacheng Natural Area,and the low value areas distribute in the middle and south of Tarim Basin.(4)Moisture source in Xinjiang was mainly in the Caspian Sea,the Black Sea,the Mediterranean Sea,the Atlantic Ocean,the Arctic Ocean and the nearby inland areas.Xinjiang was affected by the westerly wind all the year round,especially the westerly wind in the south.The vapor transport path in the Altai-Tacheng Forest Grassland Natural Area and the Desert Natural Area of the Junggar Basin were generally more northward,and the Yili-Bayinbulak(Middle Tianshan)Natural Area and Hami-Turpan Desert Natural Area were more affected by the land moisture source,while the vapor transport path in the extreme Arid Desert Natural Area of the Tarim Basin were generally southerly.The result of cluster analysis was that the moisture source in the Altai-Tacheng Forest Grassland Natural Area came from Europe,the moisture source in the Desert Natural Area of the Junggar Basin mainly came from Central Asia,the Caspian Sea and Mongolia.The moisture source of the Extreme Arid Desert Natural Area in the Tarim Basin mainly came from the Tarim Basin,Western Asia,Central Asia and the Black Sea.After the moisture source replenishment was adjusted by the specific humidity,the backtracking path was generally short,and the moisture source mainly came from Central Asia,the Black Sea,the Caspian Sea and nearby land.The adjusted correction method is not sensitive to different thresholds,the water vapor transport of the water source source tracked by the trajectory is related to the initial height.The water vapor transport in the upper atmosphere is smoother than that in the lower atmosphere.(5)The water vapor source of 197 precipitation process in different regions of Xinjiang are different.The water vapor mainly comes from inland,followed by westerly water vapor and northwest water vapor.The changes of meteorological elements in different water vapor sources are different.The cloud base height shows increasing trend,while the pressure shows decreasing trend.Before 72 hours of retrospect,the characteristics of relative humidity were relatively flat,and the specific humidity showed a decreasing trend.After the moisture source replenishment was adjusted by the specific humidity,the moisture source transmission from the main moisture source area need an average of 3.5 days.In the season,the moisture source was the closest in summer,while that was far in spring.In the area,the moisture source was the farthest in the Altai-Tacheng Forest Grassland Natural Area,and that was nearest in the Hami-Turpan Desert Natural Area.The precipitation at the initial heights in Xinjiang was mainly affected by the northward and southerly westward airflows,and the northward westward airflow contributed more than the southerly westward.