Generation processes of mesoscale convective systems following midlatitude troughs around the Sichuan Basin

Abstract

[1] The generation processes of mesoscale convective systems (MCSs) that occurred over the Sichuan Basin in China were revealed in the early 2008 monsoon season. MCS occurrences detected in METEOSAT geostational satellite images are associated with the traveling of midlatitude troughs after the onset of the Indian monsoon. Three episodes of large-scale MCSs were generated under synoptic conditions of merging southwesterly low-level monsoon flows with a northerly midlatitude air mass following the trough in the leeward of the Tibetan Plateau without direct migration of the vortex generated from the plateau surface. Numerical simulations using a weather research and forecast (WRF) model showed that the MCS was triggered in the evening by strengthening of the low-level wind convergences with horizontal shear between the southerly monsoon flow, with large convective available potential energy, and the northerly dry intrusion. A sudden increase in the northerly winds was confirmed by sonde observation data in the western basin, and the winds were simulated as intrusions passing over the Qinling Mountains when the daytime clouds over the mountain were diminished. Sensitivity experiments by a WRF simulation revealed that the topography of the Sichuan Basin was able to capture the dry intrusion at the bottom to prevent the propagation of disturbances from the plateau and to cause the sudden onset of MCSs apart from the plateau with a heavy precipitation zone.Citation: Ueno, K., S. Sugimoto, T. Koike, H. Tsutsui, and X. Xu (2011), Generation processes of mesoscale convective systems following midlatitude troughs around the Sichuan Basin,

Role of Mesoscale Convective Systems Developed around the Eastern Tibetan Plateau in the Eastward Expansion of an Upper Tropospheric High during the Monsoon Season

“…The methods of the MCS extraction and tracking conformed to those of Evans and Shemo (1996). Their methods have been applied to the region around the Himalayas and TP by Barros et al (2004), Sugimoto and Ueno (2010), and Ueno et al (2011). First, a continuous area larger than 4,000 km 2 and with Tbb less than 219 K (hereafter, the target cloud area) was identified.…”

“…According to a numerical simulation of Sugimoto and Ueno (2010), cyclonic circulation induced by land surface heating in the dry western TP and its eastward propagation during the nighttime induce a low-level convergence over the wet eastern TP on the following daytime, and this convergence is a trigger for large MCS generation. Case studies of the early 2008 monsoon season by Ueno et al (2011) indicate that a large MCS is generated at the Sichuan Basin in the evening by strengthening of the low-level convergence between the southerly monsoon flow and northerly dry intrusion under conditions of a following mid-latitude trough. Xie and Ueno (2011) also clarifies that intensive generated areas of the MCSs in the Sicuan Basin overlap with areas recording heavy rains accompanying severe disasters.…”

A China-Japan Cooperative JICA Atmospheric Observing Network over the Tibetan Plateau (JICA/Tibet Project): An Overviews

“…The generation processes of mesoscale convective systems (MCSs), which often cause heavy rainfall over the Sichuan Basin in China were investigated by using the JICA/Tibet intensive radio sonde observation data held in the 2008 monsoon season, the METEOSAT geostational satellite images and the numerical simulations using a weather research and forecast (WRF) model (Ueno et al 2011). The MCS was generated under synoptic conditions of merging southwesterly low-level monsoon flows with a northerly midlatitude air mass following the trough in the leeward of the Tibetan Plateau.…”

Role of Patchy Snow Cover on the Planetary Boundary Layer Structure during Late Winter Observed in the Central Tibetan Plateau

“…To assess the albedo e¤ect for daytime PBL development, a numerical simulation was performed. The Weather Research and Forecast (WRF) model version 3.0.1.1 (Skamarock et al 2008) was used following the instructions in Ueno et al (2011). Four cases of three successive days were chosen, including a spin-up day without snow fall events, such as Case A: March 1-3, Case B: 5-7, Case C: 10-12, and Case D: 17-19.…”