Abstract
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.
Highlights
Generated by the complex terrain in the eastern edge of Tibetan Plateau (TP), Southwest China vortex (SWV), known as a meso-α scale low vortex, typically originates in Southwest China (98–108∘E, 26–33∘N) in the lower troposphere below 700 hPa
Numerous studies have been made in statistical analysis on the source region and movement path of low vortexes [7, 8], discussion on structural features of low vortexes and causes of their formation and development [1, 9,10,11,12,13], and case studies [14,15,16] and numerical simulations [17] on heavy rainfalls caused by SWV
The negative MPV1 center was still in Guangxi but moved northward slightly at 1800 UTC 12 (Figure 9(c)), compared with previous time point, MPV1 further increased, and positive vorticity of the low vortex reached maximum (Figure 1(b)), the values of MPV2 decreased (Figure 9(d)), to a certain extent, MPV1 had insignificant influence on the low vortex’s intensity, and a positive MPV2 center formed in Jiangxi-Hunan border area, indicating that the atmospheric baroclinicity was strong in the region and the SWV may develop towards the positive MPV2 area
Summary
Generated by the complex terrain in the eastern edge of Tibetan Plateau (TP), Southwest China vortex (SWV), known as a meso-α scale low vortex, typically originates in Southwest China (98–108∘E, 26–33∘N) in the lower troposphere below 700 hPa. Numerous studies have been made in statistical analysis on the source region and movement path of low vortexes [7, 8], discussion on structural features of low vortexes and causes of their formation and development [1, 9,10,11,12,13], and case studies [14,15,16] and numerical simulations [17] on heavy rainfalls caused by SWV. Few studies have been conducted on continuous heavy rainfall in South China caused by SWV. To analyze the eastward movement of SWV and the heavy rainfall-inducing physical process and reveal the physical causes of SWV’s formation and development as well as their mesoscale structure, the analysis is deeply performed in this study with a continuous severe heavy rainfall in South China during 11–14 June 2008. Physical process of the SWV inducing heavy rainfall is analyzed.
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