The movement of southwest China vortex (SWV) and its heavy rainfall process in South China had been investigated during June 11–14, 2008. The results show that under the steering of upper-level jet (ULJ) and mid-level westerly trough, SWV moved eastward from southern Sichuan Plateau, across eastern Yunnan-Guizhou Plateau to South China, forming an obvious heavy rain belt. SWV developed in the large storm-relative helicity (SRH) environment, as environmental wind field continuously transferred positive vorticity to it to support its development. The thermodynamic structures of distinctive warm (cold) advections in front (rear) of the SWV movement are also important factors for the SWV evolutions with a southwest low-level jet (LLJ) and vertical wind shear. SWV development was associated with the distributions of negative MPV1 (the barotropic item of moist potential vorticity) and positive MPV2 (the baroclinic item of it). The MPV1 and MPV2 played the dominant role in the formation and the evolution of SWV, respectively. The mesoscale convective systems (MCSs) frequently occurred and persisted in water vapor convergence areas causing the severe heavy rainfall. The areas of high moist helicity divergence and heavy rainfall are consistent, and the moist helicity divergence could be a good indicator for heavy rainfall occurrence.

From 7 July to 11 July 2013, an extreme rainstorm occurred in the Sichuan Basin (SCB) of China, which is located at the eastern edge of the Tibetan Plateau, causing severe floods and huge economic losses. The rainstorm event was associated with mesoscale convection systems (MCSs). In this paper, we analyze the evolution characteristics and formation conditions of the MCSs, and the results show that: (1) the continuous activity of MCSs was a direct cause of the formation of extreme rainstorms. Under an “east high and west low” circulation mode, the MCSs formed a “cloud cluster wave train” phenomenon from the plateau to the basin; that is, the MCSs over the basin developed strongly in the process of the MCSs over the plateau area weakening. (2) The activities of MCSs over the rainstorm area was related to ascending branches of the two vertical circulations and topographic gravity wave. Under the influence of meridional vertical circulation, MCSs could move in the south–north direction in the western SCB, while under the influence of zonal circulation, it was difficult for MCSs to develop in the descending airflow east of 106°E. (3) In the mountainous area of the western part of the SCB, the gravity wave stress was obvious and its direction was opposite to the direction of the lower southeast warm–moist airflow. This configuration was able to form a drag effect in the low-level airflow, which was conducive to the convergence of the wind field and strengthening of the vertical ascending movement. These findings help in further understanding the effects of vertical circulation and terrain on MCSs and extreme rainstorms.

Tibetan Plateau vortices (TPVs) are mesoscale cyclones originating over the Tibetan Plateau (TP) during the extended summer season (April–September). Most TPVs stay on the TP, but a small number can move off the TP to the east. TPVs are known to be one of the main precipitation-bearing systems on the TP and moving-off TPVs have been associated with heavy precipitation and flooding downstream of the TP (e.g., in Sichuan province or over the Yangtze River Valley). Identifying and tracking TPVs is difficult because of their comparatively small horizontal extent (400–800 km) and the limited availability of soundings over the TP, which in turn constitutes a challenge for short-term predictions of TPV-related impacts and for the climatological study of TPVs. In this study k](i) manual tracking (MT) results using radiosonde data from a network over and downstream of the TP are compared with (ii) results obtained by an automated tracking (AT) algorithm applied to ERA-Interim data. Ten MT-TPV cases are selected based on method (i) and matched to and compared with the corresponding AT-TPVs identified with method (ii). Conversely k]ten AT-TPVs are selected and compared with the corresponding MT-TPVs. In general k]the comparison shows good results in cases where the underlying data are in good agreement k]but considerable differences are also seen in some cases and explained in terms of differences in the tracking methods k]data availability/coverage and disagreement between sounding and ERA-Interim data. Recommendations are given for future efforts in TPV detection and tracking k]including in an operational weather forecasting context.

The Tibetan Plateau Vortex (TPV) and Southwest China Vortex (SWCV) are important precipitation systems of the upper reaches of the Yangtze River in China in the warm half year (May–October). Sometimes, the vortices both move towards the Sichuan Basin, and encounter one other to merge into a deep vortex that induces mesoscale convective systems (MCSs) and heavy rainfall. In this paper, a formula for the depth of the positive vorticity column (PVC) in two extreme rainstorm events was constructed to reveal the dynamical characteristics of TPV–SWCV interaction. The results showed that: (a) One feature of TPV–SWCV interaction was to form a deep vortex with very deep positive vorticity in the vertical direction, and the occurrence of extreme rainstorms was closely related to the deep vortex. (b) The PVC depth can describe the thickness features of the deep vortex well: MCSs with low brightness temperature were observed in the area of >2 × 10² hPa PVC depth, and their frequent activities were the direct reason for the occurrence of extreme rainstorms. (c) The rainstorm areas were basically consistent with the area of large PVC depth, especially the area of 5–7 × 10² hPa PVC depth where 24‐hr accumulated precipitation reached 100 mm or more. The study indicates that the PVC depth can reflect the development of vortices in the vertical direction, and has the potential to be a valuable index for diagnosing heavy rainfall area.