Mechanism and Water Vapor Transport Characteristics of a Regional Snowstorm in the North Slope of Middle Tianshan Mountains
Based on the conventional observation data at high altitude and ground,NCEP/NCAR reanalysis data,the characteristics and causes of snowstorm process in the north slope of middle Tianshan Mountains on February 2017 were diagnosed and analyzed.Combined with GDAS reanalysis data and HYSPLIT model,the water vapor source,main water vapor transport channels and their contribution to water vapor transport were simulated and tracked.The results show that the stable confrontation of warm and cold advection and strong frontal zone provide stable synoptic scale condition for the snowstorm when the regional snowstorm occurs.The continuous cold cushion uplift in the middle and lower layers is the main dynamic mechanism,the coupling of high and low jet streams stimulates the mesoscale vertical ascending branch and secondary circulation has an increasing effect on snowstorm.The main water vapor sources of snowstorm are located in the Red Sea on the west side of Arabian Peninsula and Persian Gulf to the north of Arabian Sea on the southwest side of Iranian Plateau.The water vapor channel is mainly concentrated in 500-850 hPa,and the water vapor convergence area is located in 700-850 hPa.There is southwest airflow in the middle and upper layers,westerly airflow in the middle layer and northwest jet stream in the lower layer to relay water vapor to snowstorm area.By use of HYSPLIT model,it is found that water vapor input in the west and north boundaries which plays an important role during the snowstorm.The main water vapor transport channels are westward path,southwestern path and local water vapor path,their contribution rates are roughly equal at 1 500 m height tracking,and local water vapor and westward path have greater contribution rates at 3 000 m height.
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