An Analysis of an Extreme Rainstorm caused by the Interaction of the Tibetan Plateau Vortex and the Southwest China Vortex from an Intensive Observation

Abstract A rainstorm caused by the coupling of the Tibetan Plateau vortex (TPV) and the Southwest China vortex (SWCV) in eastern Sichuan during 29 June–2 July 2013, is analyzed by using the conventional observed data and its time intensive observed data, the intensive observed data of SWCV scientific experiment during flood season. The results show that under the control of a large transverse trough in Eurasia region at mid-high latitude, the westerly flow in northern China leads TPV eastward movement. And SWCV moves northeastward. Finally, both of them merge to form a combined vortex (CBV) in Sichuan Basin resulting in heavy rainfall. The water vapor from both the Bay of Bengal and the South China Sea provides the sufficient humidity condition. The intensive observation clearly reveals the nascent states of TPV and SWCV, the movements and interactions, especially, the two vortices merging process, and the effects of cold and warm advection, as well as the rainstorm. When the two vortices merge into CBV, cold tongue and warm flow meet and produces frontogenesis around the center of CBV. A frontogenetical area exists deeply from lower troposphere to upper troposphere with the south-positive and north-negative vertical structure, which is similar to front. The positive PV evidently developed both in the range and in the intensity with the stronger center at upper level, and the positive PV center located at the front of CBV has indicative significance for the vortex's activities. And CBV has the same distributions of vorticity and temperature with SWCV and TPV, respectively. SWCV and TPV make different key contributions to the dynamic-thermodynamic property of CBV, but both of them have obvious influences on the divergence distribution of CBV. Furthermore，Rainfall mainly distributes in the high areas of averaged temperature deviation gradient, it is closely related to the joint influences of warm-moist air from the south and dry-cold air from the north. But, only using the conventional observed data, it is difficult to obtain the above useful understanding. So, augmenting intensive observation, improving scientific experiment and focusing on fine study are much conducive for the meso-scale and small-scale weather systems such as SWCV and TPV, as well as its weather influences.

Key words: Intensive observation, Tibetan Plateau vortex, Southwest China vortex, Coupling effect, Rainstorm