Vertical structure of Tibetan Plateau Vortex in boreal summer

Abstract

The Tibetan Plateau vortex (TPV) is a major rain-producing system over the Tibetan Plateau (TP) in summer. The vertical structure of TPV is critical in understanding the generation and development of TPV. In this paper, the ERA-Interim reanalysis data and an objective TPV detection and vertical tracing method are used to investigate the vertical structure of TPV in boreal summer (June–August). Most TPVs are shallow, with only 1/5 of them can reach 400 hPa. Among the TPVs that move off the TP, more than half are deep vortices. The tilting direction of TPV is related to its baroclinic structure. In general, TPVs tilt to the direction of the cold air from low to high isobaric levels, and the tilting direction depends on the relative positions of the warm pool and the cold air intruding into TPV. Deep TPVs inside the TP and those moving off the TP have different vertical structures. On the plateau, TPVs have convergence at the low levels (400–500 hPa) and divergence at the high levels (above 400 hPa), which can cause updrafts in the vortex and a tropical cyclone-like structure. For the TPVs moving off the TP, the updrafts are significantly weak due to the relatively low low-level convergence and the relatively low high-level divergence. These TPVs almost have positive vertical vorticity and present an extratropical cyclone-like structure. The vertical thickness of TPV is important in determining whether the TPV could move off the TP. The results show that the deep TPVs are more likely to move out than the shallow ones. Therefore, the vertical structure is a better predictor on the movement of TPV than its other properties.