Diagnostic Analysis of the Quasi-Balanced Flow of a Mesoscale Vortex During the 12 June 2008 Guangxi Rainstorm |
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Authors: | Jingjing Ge Wei Zhong Hancheng Lu |
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Institution: | Institute of Meteorology, PLA University of Science and Technology, Nanjing 211101;Institute of Meteorology, PLA University of Science and Technology, Nanjing 211101;Institute of Meteorology, PLA University of Science and Technology, Nanjing 211101 |
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Abstract: | By using the high-resolution observation data and MM5 model simulation data, the analysis on the 12 June 2008 Guangxi flash-flood
rainstorm shows that the associated major mesoscale weather system of this event is a quasi-stationary mesoscale vortex, which
resulted from the interaction between the midlatitude synoptic-scale waves in the westerly belt and the low-latitude warm-moist
flow under the terrain effect. The genesis, development, and movement of the mesoscale vortex have significant impacts on
the intensity and persistence of the severe precipitation from the Guangxi flash-flood rainstorm. This vortex is characterized
by the coexistence of strong vorticity and divergence with the same order of magnitude. Well organized, deep, and moist convection
was observed for a long period of time, and was produced by the interaction between the mesoscale vortex and the gravity waves.
The latter was generated by the terrain effect and the ageostrophic effect of high winds in the low-level jet. According to
the quasi-balanced dynamical theory, quasi-balanced flow must have existed in the mesoscale motions with both divergent and
rotational winds. Thus, based on the diagnosis of the quasi-balanced flow, the PV-ω inversion method is employed to analyze the organized moist convection. The results show that 50%–70% of the vertical circulation
in the rainstorm areas was quasi-balanced, so the quasi-balanced flow could well reflect features of the strong vertical motions
associated with the coexistence of vorticity and divergence during this event. |
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Keywords: | |
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