Mechanisms for Torrential Rain Associated with the Mei-Yu Development during SCSMEX 1998

Abstract

A case of torrential precipitation associated with the mei-yu front, an Asian summer monsoon system east of the Tibetan Plateau, is studied using the coupled fifth-generation Pennsylvania State University-NCAR Mesoscale Model (MM5) and the NASA Goddard Space Flight Center Parameterization for Land-Atmosphere-Cloud Exchange model. The impact of both remote and local sources of water vapor on the location and intensity of mei-yu precipitation are studied by numerical experiments. The results demonstrate that the main source of water vapor for this heavy precipitation event over the Yangtze River Valley is the Bay of Bengal. Moisture is transported by a southwesterly low-level jet (LLJ) southeast of the Tibetan Plateau. Although the LLJ is largely manipulated by large-scale forcing, the mesoscale circulation that results from mei-yu condensational heating acts to increase the maximum wind speed of the jet. The condensation-induced local circulation strengthens the moisture transport in the LLJ, providing a positive feedback that sustains the mei-yu precipitation system. Precipitation recycling increases the total precipitation in the Yangtze River Valley only slightly, but it tends to shift the maximum rainfall center toward the warmer side of the mei-yu rain belt. This shift is due to the pronounced increase in atmospheric moisture and decrease in surface temperature over the warm side of the rain belt.

Mechanisms for concurrent low-latitude circulation anomalies responsible for persistent extreme precipitation in the Yangtze River Valley

“…This positive feedback render the southern cell self-maintaining. The importance of diabatic heating in maintaining such southern cell has been confirmed in both specific case study and model simulations (Chen et al 1998;Qian et al 2004;Jin et al 2013). …”

“…Coincidently, interaction between diabatic heating and circulations plays significant roles in modulating both the WPSH and the SAH, because varied spatial distribution of the anomalous diabatic heating can induce vorticity variations in both the lower and upper levels (Hong et al 2015;Ren et al 2015;Hsu and Weng 2001). Though phenomena concerning the anomalous WPSH and SAH were descriptively presented individually or simultaneously in some previous studies based on specific cases or composited results (Wang et al 2000;Wu and Liu 2003;Qian et al 2004;Ren et al 2007;Mao et al 2010;Yang et al 2010;Zhai 2014b, 2015), detailed mechanisms for the approach, maintenance, and departure of these two dominant systems related to PEPEs have hitherto been rarely systematically reported. This study therefore attempts to discuss the following issues.…”

Changes of Meiyu system in the future under A1B scenario simulated by MIROC_Hires model

“…In fact, there are several other thermal factors, e.g., the large-scale topography (Qian et al 2004;Zhu et al 2007;Xu et al 2010), the spatial heterogeneous warming over Tibet Plateau (TP) and Plain (Qing et al 2008;Zhao and Qian 2009;Zhao et al 2010), snow cover over TP (Zuo and Zhang 2012;Zuo et al 2013), and tropical central-eastern Pacific SST ). Nevertheless, a remaining question is why the heterogeneous warming appears over East Asia in the warmer future.…”

Simulation and Analysis of the Initiation of a Squall Line within a Meiyu Frontal System in East China

“…A deep understanding of the formation and evolution of these MCSs can help us better predict heavy rainfall and severe flooding in the Meiyu season. There have been many studies on the Meiyu frontal system and associated MCSs and heavy precipitation, including studies on the effects of the East Asian summer monsoon [3], large-scale moisture transport by the low-level jet (LLJ) typically found south of the Meiyu front [4][5][6], the eastward propagation of MCSs or mesoscale vortices along the Meiyu front [7,8], and diurnal cycle of precipitation [9][10][11][12]. The initiation of convective cells within the Meiyu frontal system that organizes into MCSs has been little studied, however.…”