应用气象学报 (Mar 2023)
A Heavy Precipitation Process over the Tibetan Plateau Under the Joint Effects of a Tropical Cyclone and Vortex
Abstract
The plateau vortex and the tropical cyclone over the Bay of Bengal have common active periods but there are few studies on the influence of their interaction on the plateau precipitation. Therefore, a large scale heavy precipitation process over the Tibetan Plateau under the joint effects of a tropical cyclone over the Bay of Bengal and plateau vortex is analyzed which occurs during 26-31 May 2017, based on the Joint Typhoon Warning Center (JTWC) best-track data, hourly precipitation observation data and combined with hybrid single-particle lagrangian integrated trajectory (HYSPLIT) model. The results show that, with the cooperation of tropical cyclone over the Bay of Bengal and the India-Burma though, the water vapor transport jet from the Bay of Bengal to the southeast of the Tibetan Plateau is established, providing water vapor for the low vortex and shear line of the plateau. The cold air behind the India-Burma though forms a cold cushion on the steep slope of the southern Tibetan Plateau, and the warm water vapor from the Bay of Bengal first rises northward along the cold cushion, then sinks after ascending to the plateau, and rises northward again near the low vortex and shear line of the plateau, which increases the precipitable water between the plateau surface and the upper troposphere atmosphere. Meanwhile, frontogenesis is generated by the confluence of tropical cyclone southerly warm water vapor with the cold and dry air in the northern part of the plateau. In the process of frontogenesis, the atmospheric wet baroclinicity increases significantly and the wet isentropic line rises sharply, which promotes the sharp development of vertical vorticity and the enhancement of plateau low vortex. During the northward movement, the anticyclonic outflow from the upper layer of the tropical cyclone strengthens the southwest jet in front of the upper trough of the Tibetan Plateau, and the enhancement of divergence favors the development of the plateau shear line and the eastward movement of the plateau low vortex, resulting in a large-scale heavy precipitation. On the other hand, the positive feedback of the water vapor transportation of the tropical cyclone over the Bay of Bengal and the shear line of the plateau vortex provides continuous apparent heat source and apparent moisture sink for the precipitation area, which is favorable for the maintenance and development of the precipitation system on the plateau.
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