Organized Deep Cumulus Convection Over the South China Sea and its Interaction with Cold Surges

[摘要] This is an observational and diagnostic study exploring the interaction between the northeasterly cold surge from the Asian continent and deep cumulus convection over the South China Sea. Based on the data analyses (FGGE III-B), a physical mechanism, by which the cold surge affects deep cumulus convection, has been suggested. The northeasterly cold surge enhances deep cumulus convection in front of it by increasing the lower level convergence and weakens the deep cumulus convection afterwards by stabilizing the stratification through cooling and drying the lower-level air. As a response of deep cumulus convection to the cold surge, the upper level (200mb) outflow over the cluster area is clearly increased.It is also found that deep cumulus clouds always grow over the area where the stratification is conditionally unstable (θe5001000<-10°C), the lower levels large scale flow is convergent (Div. <-10-5s-1).The case study on 14 December reveals that there is a distinct local meridional circu-lation which cooperates with the cold surge and the deep cumulus convection. The circula-tion is enhanced due to the release of latent heat in cumulus clusters. The large-scale vertical velocity profile shows a similarity to the pattern occurring over the western Pacific. The diagnostic results show that the deep cumulus convection and its associated large-scale subsidence stabilizes the stratification in both the cumulus cloud clusters area and in the adjacent clnud-free area.

[学科分类] 大气科学