天山北坡一次区域性暴雪形成机制及水汽输送特征

Mechanism and Water Vapor Transport Characteristics of a Regional Snowstorm in the North Slope of Middle Tianshan Mountains

利用高空、地面常规观测资料、NCEP/NCAR再分析资料,诊断分析2017年2月天山北坡一次区域性暴雪过程的特征及成因,结合GDAS再分析资料并采用HYSPLIT模式,模拟追踪水汽源地、主要水汽输送通道及其对水汽输送的贡献。结果表明:天山北坡区域性暴雪发生时,冷暖空气持续对峙,锋区强度强,为暴雪的形成提供了稳定的天气尺度条件;中低层西北急流的冷垫抬升是形成暴雪的主要动力机制,高低空急流耦合激发中尺度垂直上升支和次级环流,对降雪有增幅作用;暴雪主要水汽源地位于阿拉伯半岛西侧的红海和伊朗高原西南侧的波斯湾至阿拉伯海北部一带,水汽通道主要集中在500~850 hPa,水汽辐合区位于700~850 hPa,中高层有西南气流、中层有偏西气流、低层有西北气流将水汽接力输送至暴雪区;利用HYSPLIT模式模拟发现,暴雪期间,西边界、北边界水汽输入均起重要作用,主要水汽输送通道分别为偏西路径、西南路径、局地水汽路径,在1 500 m高度,三者贡献率大致相当,在3 000 m高度,局地水汽和偏西路径水汽贡献率更大。

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 1500 m height tracking,and local water vapor and westward path have greater contribution rates at 3000 m height.