Three-Dimensional Structure of a Mesoscale Convective System in a Baiu-Frontal Depression Generated in the Downstream Region of the Yangtze River

Abstract

A Baiu-frontal meso-a-scale depression was generated on 18 June 2001 in the mesoscale observational region, which was located in the downstream region of the Yangtze River. Based mainly on the data collected in this observation, we analyze the three-dimensional structure of a meso-a-scale convective system. We describe this structure and discuss the evolution of Baiu-frontal convective systems near the east coast of the continent.This convective system was composed of several meso-b-scale convective groups, which were bandshaped echoes located near the depression center, cellular echoes formed one after another ahead of the center, and a band-shaped echo extending more than 500 km in the rearward of the depression. There were three flows toward the convective system in the lower troposphere: moist southwesterly jet, dry west-to-northwesterly wind, and cold shallow easterly wind, which appeared near the coast. These convective groups were formed where the southwesterly wind, with convectively-unstable air, was lifted up to the free-convection level. This lifting resulted from low-level convergence, which was formed both by easterly and west-to-northwesterly wind in the central portion of the depression, by easterly wind at the forward portion, and by west-to-northwesterly wind at the rear portion.The system-relative speed of the southwesterly wind in the forward portion was larger than that in the rear. It is suggested that this strong inflow caused the formation of a deep convective structure in the forward portion, which reached the tropopause. The easterly wind played an important role in lifting such a strong inflow, and forming the deep convective groups in the meso-a-scale convective system, and then contributed to evolving the depression through the extension of the convective-updraft area. The Corresponding author: Hiroyuki Yamada, Frontier Observational Research System for Global Change, 3173-25, Shouwa-machi, Kanazawa-ku, Yokohama, 236-0001, Japan. E-mail: yamada@jamstec.go.jp ( 2003, Meteorological Society of Japan mechanism that the easterly wind was formed locally near the coastline is discussed. The enhancement of low-level convergence, due to the formation of such a local wind system, is suggested to be one of the causes for the development of a mesoscale convective system, near the east coast of the continent during Baiu seasons.

Environment and morphology of mesoscale convective systems associated with the Changma front during 9–10 July 2007

“…Shear at low-to-medium levels has been reported by Parker and Johnson (2004) as an important factor in the maintenance of convective systems, which may be a reason for the extended lifetime of NMαCS. Such a vertical wind shear was also observed in past studies on a convective system along Meiyu/Baiu frontal regions (Ogura et al, 1985;Ishihara et al, 1995;Yamada et al, 2003;Zhou, 2009). They described that convective systems formed on the shear line, a southwesterly jet was prevalent in the low troposphere.…”

“…This study utilised Doppler radar, which provides datasets with high spatial and temporal resolutions of the internal structure of precipitation. In the past, dual-Doppler radar observations have provided in-depth information on structures of the meso-α and meso-β scales, including their development in monsoon frontal systems (Yamada et al, 2003;Moteki et al, 2004;Geng et al, 2004). You et al (2010) proved that deep warm-air advection (WAA) supports the maintenance of a convective system for a longer time and results in greater rain intensity, producing drops of larger sizes.…”

Study on the Dynamic Characteristics of an Eastward-offshore Mesoscale Vortex along the Meiyu-Baiu Front

“…It should be noted that the severe weather events (such as strong wind and heavy rainfall) induced by these vortices in the East China Sea and Yellow Sea have become a significant problem for the shipping, fishing, and energy exploration industries of Northeast Asian countries, especially China. Although there are a certain number of studies focused on eastward-moving vortices (e.g., Yamada et al, 2003;Sun et al, 2010), the details of the move-off-shore vortices are still unclear due to the lack of observations at sea and the short lifespans of the vortices in general cases (Geng, 2008). Therefore, the purpose of this study is to investigate the evolution of the move-off-shore MBFMV and compare the maintenance mechanisms of the vortex under different environmental conditions.…”

Some Statistical Characteristics of Meiyu/Baiu Frontal Depressions

“…Previous studies have revealed large scale characteristics of MBFD (e.g., Yoshizumi 1977;Akiyama 1984), the evolution of MBFD from cloud clusters (e.g., Ninomiya and Akiyama 1971;Ninomiya et al 1981), precipitation features associated with MBFD (e.g., Ninomiya 1978;Ninomiya and Shibagaki 2003), and the internal kinematic structure of MBFD from the Doppler radar observation (e.g., Yamada et al 2003). Recently, a nonhydrostatic model has been used to illustrate processes related to the development of MBFD (Tagami et al 2007).…”