青藏高原东部重力波过程与西南涡活动的统计关系

Statistical Relationship between Gravity Waves over the Eastern Tibetan Plateau and the Southwest Vortex

本文利用2012~2015年西南涡加密观测大气科学实验的剑阁、金川、九龙和名山四站探空资料,统计分析了6~7月西南涡活动期间对流层中、高层(6~12 km)的重力波过程,结果表明:青藏高原东部川西高原南部的九龙站与其余三站不同,重力波源主要来自对流层上层,波能传播方向向上,剑阁、金川和名山三站重力的波源主要来自对流层下层,波能传播方向向下。重力波过程在不同类型的西南涡活动中有明显差异,在移出型西南涡活动初期,重力波水平传播方向主要为东北向,其上传概率远大于下传概率,波动的动能和潜能较大且变化剧烈;而对应源地型西南涡,初期主要呈西北-东南向传播且重力波上传与下传概率相当,动能和潜能较小且变化相对平缓同时本次研究表明,重力波水平传播方向对西南涡的移动方向也有一定指示作用。按照发生时刻本文将重力波分为日发型重力波和夜发型重力波,在夜发型西南涡初期,重力波活动夜发(北京时20:00~08:00)的概率较大,这表明重力波的夜发性与西南涡的夜发性可能存在一定关联。

This study statistically analyzes gravity waves activity in the middle and upper troposphere(6-12 km) based on radiosonde data obtained at four stations, i. e., Jiange, Jinchuan, Jiulong, Mingshan, in the Intensive Atmospheric Science Observational Experiment of Southwest China vortex during 2012-2015. The results reveal downward propagation of gravity waves energy at Jiulong station, suggesting that the gravity waves are generated in the upper troposphere at Jiulong station. The opposite is true at other three stations. Corresponding to different types of the southwest vortex, gravity waves activities are quite different. At the initial stage of the moving-out type of southwest vortex, gravity waves mainly propagate northeastward with larger probability of upward wave energy transport compared to downward transport. Meanwhile, kinetic and potential energy are large with significant variation. At the initial stage of source southwest vortex, however, gravity waves largely propagate along the northwest-southeast direction, while wave energy can be transported upward or downward with similar probability. Meanwhile, kinetic and potential energy are relatively small with weak variation. It is noted that the horizontal propagation direction of gravity waves are important for the moving direction of southwest vortex. Gravity waves are divided into nocturnal type and daytime type based on their generation time. It is found that more nocturnal-type gravity waves [2000 BT to 0800 BT(Beijing time)] are generated at the initial stage of nocturnal southwest vortex, indicating that there may exist a correlation between the generations of nocturnal gravity waves and southwest vortex.