Synoptic conditions associated with propagating and nonpropagating cloud/rainfall episodes during the warm season over the East Asian continent

Chung Chieh Wang, George Tai Jen Chen, Hsiao Ling Huang, Richard E. Carbone, Sau Wa Chang

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

Using European Centre for Medium-Range Weather Forecasts (ECMWF) analyses, this study identifies common synoptic flow patterns associated with propagating (long lived) and nonpropagating (short lived) precipitation/cloud episodes in the warm season over East Asia (258-408N, 958-1258E). Among 123 initial cases during May-July 1997-2003, 86 were classified into three categories (propagating cases with strong and weak forcing, and nonpropagating ones with strong inhibition) consisting of 10 types based on their 500-hPa flow patterns. For each type, composites at various levels when episodes moved across 1008, 1058, 1108, 1158, and 1208E were made and discussed to elucidate the influence of synoptic conditions. For propagating episodes with strong 500-hPa forcing (46 cases), four types were identified. In their composites, favorable positive vorticity advection forcing from an approaching trough/short wave exists aloft, and concurrent development of southwest vortex and front/wind-shift line at low levels leads to enhanced southwesterly flow to provide vertical shear and moisture. For nonpropagating episodes with strong inhibition (25 cases), three types dominated by synoptic-scale subsidence from either negative vorticity advection or the subtropical high were identified. Thus, episodes weaken shortly after they move out from the Tibetan Plateau. There are also propagating episodes but with weak forcing (15 cases), for which another three types were found. The differences in their composites from nonpropagating types are mainly at low levels, where the southerly flow is stronger and can penetrate deeper inland. As stability conditions are similar for all type of episodes, the results suggest an important role of stronger low-level southwesterly winds in providing moisture and vertical wind shear to sustain episodes and their propagation.

Original languageEnglish
Pages (from-to)721-747
Number of pages27
JournalMonthly Weather Review
Volume140
Issue number3
DOIs
Publication statusPublished - 2012 Mar 1

Keywords

  • Convective storms
  • Orographic effects
  • Rainfall
  • Storm environments
  • Summer/warm season
  • Synoptic-scale processes

ASJC Scopus subject areas

  • Atmospheric Science

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