不同触发条件下吉林省一次极端暴雪大风天气过程诊断分析

Diagnostic analysis of an extreme blizzard and gale weather process under different triggering conditions over Jilin province

利用常规气象观测资料、区域自动气象站降水观测资料和NCEP(National Centers for Environmental Prediction)的1°×1°逐6 h再分析资料,对2015年2月21—22日吉林省一次极端暴雪大风天气过程进行诊断分析。结果表明:高空冷涡配合地面蒙古气旋东移发展为形成暴雪的重要因素,850 hPa温压场反位相叠加符合吉林省典型大风天气的形势。此次降雪过程可以分为暖区和冷区降雪两个阶段,第一个阶段降雪由低空南风急流触发,来源于渤海和黄海的水汽异常丰沛,动力条件相对较弱;第二个阶段降雪水汽条件弱于第一个阶段,水汽主要来源于低涡北部的偏东风急流和偏北风急流,汇集日本海的水汽集中向西输送,但动力条件强于第一个阶段降雪,强降雪期间伴随明显的干侵入及锋生过程,冷空气作用显著。强降雪发生时,回波强度一般为15—25 dBz,且回波高度≤4 km,同时冷区降雪强度还与切变线的加强和冷空气的入侵密切相关。

An extreme blizzard and gale weather process over Jilin province on February 21 to 22 in 2015 was diagnosed and analyzed using the conventional meteorological observation data, regional automatic station precipitation data and the NCEP（ National Centers for Environmental Prediction） 1° × 1° 6-hourly reanalysis data. The results show that a high-level cold eddy combining with eastern expansion of the ground Mongolia cyclone is a main factor influencing this blizzard weather event. Overlaying of temperature and pressure fields at 850 hPa in reverse phase is consistent with the typical gale weather situation over Jilin province. Corresponding snowfall process can be divided into two phases,namely, snowfall at warm and then cold areas. The first phase of snowfall is triggered by the low-level southerly jet with an abnormally abundant water vapor coming from Bohai and Yellow Sea. The dynamic conditions in this phase are relatively weak. In the second phase, the water vapor condition is weaker than in the first phase. It is mainly due to the westerly transport of water vapor converging at the Sea of Japan,which is controlled by the easterly and northerly jets in the north part of the low vortex. While its dynamic conditions are stronger than those of the first phase. During the heavy snowfall period, the dry intrusion and frontogenesis process are obvious,and the role of cold air is significant. When the heavy snowfall occurs, the echo intensity is general within 15-25 dBz,and the echo height is equal or less than 4 km. Meanwhile, the snowfall intensity in the cold area is closely related to the strengthening of shear line and the invasion of cold air.