青藏高原近地层低压系统移动路径及其特征

Analysis of Trajectories and Characteristics of low-level Low Pressure Systems over Qingzang Plateau

利用ECMWF 600hPa高度场加密逐月再分析资料,分析了强、弱季风年高原近地层低压系统的移动路径及其特征。研究结果表明:低压系统于4月在青海省西南部形成,5月沿西南方向移入西藏地区,此后低压系统呈南北向波动西移,直至到达"西至点"后转向东退于10月衰减消散;强季风年低压系统中心强度总体上较弱季风年强。强季风年低压系统移动路径偏北,南北向波动振幅较小,弱季风年低压系统移动路径偏南,南北向波动振幅较大,呈"V"形分布;孕育初生阶段低压系统的形成过程在弱季风年出现"反复"现象;发展成熟阶段高原近地层低压系统南侧印度上空低压系统形成,并且强季风年较弱季风年形成时间偏迟,位置偏南;衰减消亡阶段高原近地层低压系统西北侧的高压系统减弱消散,10月东伸高压脊的脊点在弱季风年较强季风年偏东。

Based on the monthly 600 hPa ECMWF reanalysis data, the trajectories and characteristics of the lowlevel low pressure systems in active and weak monsoon years are analyzed, respectively. The results show that the low pressure system formed in April in the southwest of Qinghai Province and moved into Xizang along the southwest direction in May and then shifted westward with longitudinal fluctuations. After it reached the “farthermost west point,” it shifted back with attenuation and dissipated in October. The center intensities of the low pressure system in monsoon active years were stronger than those in monsoon weak years. The trajectories of the low pressure system were farther north than normal in active monsoon years and farther south with a Vshaped distribution in weak monsoon years with longitudinal fluctuations. The low pressure systems often formed repeatedly in monsoon weak years at the early stage. The low pressure systems over India formed later and more southslanting in active monsoon years than in weak monsoon years at the maturity stage. The high pressure system in the northwest of the low pressure system weakened at the later stage. In October, the eastern extension of the subtropical high ridge was farther east in weak monsoon years than in active monsoon years.