Activity characteristics of the northeast moving Tibetan Plateau vortices in summer

Abstract

The Tibetan Plateau Vortex (TPV) is mainly divided into east moving (E-TPV), northeast moving (NE-TPV) and so on according to its moving path after moving off the Tibetan Plateau (TP). Based on the database of TPV from 1979 to 2018, this paper mainly makes statistical analysis on the NE-TPV in summer. According to its moving-off position, NE-TPV is subdivided into westward vortex (denoted as NEI-TPV) and eastward vortex (denoted as NEII-TPV). In terms of source, structure, circulation, moving speed, life history and influence on precipitation, the characteristics of two types of NE-TPVs were analyzed and compared with E-TPV to reveal the activity characteristics of the NE-TPVs and the similarities and differences between them. The results show that: (1) The NEI-TPV is mainly generated in the northwest of the TP, while the NEII-TPV and E-TPV are generated in the whole TP. There are mainly three centers of vortex sources: west, middle and east. The eastern sources of TPV with different paths differ greatly in north-south location and concentration. The eastern source of NEI-TPV is northward and concentrated, while the E-TPV is southward and dispersed, and NEII-TPV is between the former two. (2) The intensity of NEII-TPV is stronger than that of NEI-TPV before moving off, and the ascending motion of these two is located near the vortex center. After moving off, the relative vorticity and vertical velocity of both of them weakened significantly, and the maximum upward movement of NEI-TPV moved to the northeast of the vortex, while the NEII-TPV is similar to E-TPV, and its rising region is located in the southeast of the vortex. (3) The moving direction before moving off and moving-off position of TPV is mainly affected by the 200 hPa westerly fluctuations, while after moving off, the moving direction is mainly affected by 500 hPa troughs and ridges. Among them, the Hetao High-Pressure Ridge is particularly important in blocking NE-TPV. (4) Besides the influence of altitude difference, the moving speed of TPV is closely related to its moving direction, so the TPV moving eastward move faster. (5) NEII-TPV and E-TPV have longer mean life history than NEI-TPV, meanwhile, they often result in a wider range of precipitation and a higher proportion of rainstorms. The precipitation of NEI-TPV is mainly located in the Hexi Corridor. While the precipitation of NEII-TPV is mainly located in the eastern part of Northwest China.