南支槽影响下西藏高原南部3次暴雪天气特征分析

利用NCEP/NCAR再分析资料和常规观测资料,对2013年1-2月西藏高原南部3次暴雪天气的环流形势、动力、水汽条件等进行诊断对比分析。结果表明:3次暴雪天气中高纬度均以经向型环流形势为主,从长波槽脊配置可分为长波槽型和横槽型两大类;西太平洋副热带高压偏西偏强、伊朗高压东北发展对南支槽加深和缓慢东移起到关键作用。南支槽区560 dagpm线在30°N以南,并东移至70°E附近或以东时西藏高原南部开始出现暴雪天气;暴雪区附近涡度场变化反映了南支槽强度特征,中高层强辐散对南支槽发展起到重要作用;水汽主要源于阿拉伯海,孟加拉湾水汽对东部降雪起到补充作用,南支槽前高空西南急流对水汽输送起关键作用,同时喜马拉雅山脉的大地形抬升,有利于上升运动和水汽凝结成云;水汽通量、水汽通量散度等变化及中心的移动方向,对降雪的强度、落区和时段具有较好的预报指示意义。

Analysis of Three Snowstorms in Southern Tibetan Plateau Affected by Southern Branch Trough

Using the NCEP/NCAR reanalysis data and conventional observation data, this paper analyzes the circulation situation, dynamic and thermodynamic conditions of the three snowstorms in southwest of the Tibetan Plateau in 2013. The results show that, over the middle and high latitudes, there existed radial circulation situation. According to the ridge and trough positions, they can be divided into the long-wave trough and the horizontal trough. The Western Pacific subtropical high is by west and stronger, and Iran high developing to the northeast slowly plays a key role for the southern branch trough to deepen and move eastward. When the 560 dagpm line of southern branch trough area is south to 30°N, and moves eastward to 70°E near or to the east at the southern part of the Tibet Plateau, snowstorm begins to appear. The vorticity change in the vicinity of snowstorm area reflects the strength characteristics of the south branch trough. The vertical evolution of divergence field in mid-high levels plays an important role in the south branch trough development. Water vapor mainly comes from the Arabia Sea, and the water vapor in the Bay of Bengal plays a complementary role in the eastern snowfall. The southwest upper-level jet plays a key role in water vapor transport. At the same time, the Himalaya Mountain terrain uplift is conducive to the ascending motion and water vapor condensation. Water vapor flux, vapor flux divergence value changes and the center moving direction have better forecasting significances to the forecasting of snowfall intensity, falling area and time.