Abstract
A torrential rainfall that occurred in Beijing during the period of 21–22 July 2012 is simulated by the Weather Research and Forecasting Model in order to investigate the probable mechanisms for the initiation and organization of warm-sector mesoscale convective systems (MCSs). The simulated results show that the cyclone, which formed in Hetao area, Inner Mongolia and moved eastward slowly, played a key role in the formation and development of warm-sector precipitation, although the favorable atmospheric environment and the configuration of weather systems are also important, which caused the trigger and organization of convective cells along Taihang Mountains. It is the interaction of the local terrain convergence line and the southerly airflows of Hetao cyclone that cause the continuous trigger of convective cells along Taihang Mountains. While, the triggers of convective cells in the plains are caused by the gravity waves, which is related to the development and eastward movement of Hetao cyclone. It must be pointed out that the merging and coupling between the cells that triggered in Taihang Mountains and moved southwesterly and the cells that triggered in plains and moved northeasterly are the key factors for the formation and development of MCSs during the warm-sector precipitation. In addition, the back-building processes and the cold pool forcing are also important for the formation and development of MCSs in this study.
Highlights
Warm-sector torrential rain (WSTR), which occurs in warm and moist air masses with small thermal gradients located in the warm section of a depression or cyclone (Nozumi and Arakawa, 1968 [1]; Kingsmill et al, 2006 [2]) is one of the most important precipitation types in China (Zhang et al., 2013 [3]; Wen et al, 2015 [4]; Zhong et al, 2015 [5]; Mao et al, 2018a [6])
Pointed out that warm-sector precipitation in Beijing is mainly produced by four meso-β-scale convective systems, which pass through Beijing one after another
The radar observations revealed that four convective systems initiated at the eastern foot of the Taihang Mountains at around (39° N, 114.5° E), and moved along the pointed out that warm-sector precipitation in Beijing is mainly produced by four meso-β-scale convective systems, which pass through Beijing one after another
Summary
Warm-sector torrential rain (WSTR), which occurs in warm and moist air masses with small thermal gradients located in the warm section of a depression or cyclone (Nozumi and Arakawa, 1968 [1]; Kingsmill et al, 2006 [2]) is one of the most important precipitation types in China (Zhang et al., 2013 [3]; Wen et al, 2015 [4]; Zhong et al, 2015 [5]; Mao et al, 2018a [6]). Studied a heavy precipitation process in eastern China based on observations and cloud-resolving simulation results, and found the combination of a convective convergence line and gravity waves was the main triggering mechanism of these convective systems. Research conducted by Schumacher and Johnson (2008, 2009) [15,16] revealed the interaction of a low-level jet, gravity waves, and a cold pool at the surface with the mid-level vortex to be the main reason for the initiation and organization of convective systems. It was found that during the dissipating stage of the MCSs, the downward movement of the mid-level vortex increased the potential vorticity in the lower troposphere, which coupled with the low-level jet and triggered the secondary convective system on the southeast side of the mesoscale convective vortex. Based on the simulation, the initiation and organization mechanism of the convective systems that produced the warm-sector rain was examined in detail.
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