Formation of Long-Lived Summertime Mesoscale Vortices over Central East China: Semi-Idealized Simulations Based on a 14-Year Vortex Statistic

Authors:

SHEN-MING FU

International Center for Climate and Environment Sciences, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China

JIAN-HUA SUN

Laboratory of Cloud-Precipitation Physics and Severe Storms, Institute of Atmospheric Physics, Chinese Academy of Sciences, and State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China

YA-LI LUO

State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences, Beijing, China

YUAN-CHUN ZHANG

Laboratory of Cloud-Precipitation Physics and Severe Storms, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China

Abstract:

Regions around Dabie Mountain (DBM) in the Yangtze River basin (YRB) are the source of a mesoscale vortex: the Dabie vortex (DBV). Based on a 14-yr statistical study, 11 long-lived heavy-rainproducing DBVs were composited for convection-permitting semi-idealized simulations. A control simulation, initialized 12 h before the composite vortex formation, successfully reproduced a DBV, with all the salient characteristics of the 11 events. Sensitivity experiments were designed to understand the impacts of large-scale environmental conditions, regional topography, and latent heating on DBV formation. The main results were as follows: (i) Supposition of a 500-hPa shortwave trough with an east–west-oriented lower-level transversal trough around the DBM is crucial for the formation of vortices. A nocturnal lower-level jet on the southern side of the transversal trough accelerates DBV formation by enhancing convergence, triggering/sustaining convection, and producing cyclonic vorticity. (ii) During the simulation period, the topography east of the second-step mountain ranges, including the DBM, significantly affects nearby precipitation and convective activity, whereas this is not crucial for DBV formation. (iii) Latent heating is not required forgenerating DBVs, but it enhances the intensity, longevity, and eastward progression of these vortices along the shear line associated with the transversal trough. (iv) The vorticity budget suggests the convergence-related (horizontal) shrinking and vertical transport dominate the cyclonic-vorticity increase associated with DBVs, whereas tilting and horizontal transport mainly act in the opposite manner.

Citation:

Fu, S.-M., J.-H. Sun, Y.-L. Luo, and Y.-C. Zhang, 2017: Formation of long-lived summertime mesoscale vortices over central east China: Semi-idealized simulations based on a 14-year vortex statistic. J. Atmos. Sci., DOI: 10.1175/JAS-D-16-0328.1.

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