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

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.