Diagnostic Analysis of Rate and Efficiency of Torrential Rainfall Associated with Bilis (2006)

By using high-resolution simulation data of Bilis (0604) and three-dimensional surface precipitation and precipitation efficiency (L_SPE) equations, precipitation rate (P_s) and L_SPE as well as their relations to macroscopic and microphysical factors were analyzed.The results show that L_SPE increases with P_s, but the relationship between them is not linear with one-to-one correspondence.With increased P_s, the increasing tendency of L_SPE slowed down gradually.Following the rapid development of the torrential rainfall system, both P_s and L_SPE increased distinctly, while temporal changes in the main source/sink terms of the surface rainfall were much more complicated.Physical processes associated with surface rainfall before the occurrence of the torrential rainfall differed a lot from those associated with the torrential rainfall.Before the occurrence, the water vapor convergence mainly moistened the local atmospheric column and also partially contributed to the development of the rainfall cloud system through microphysical processes.The convergence of liquid-phase hydrometeors contributed more to the rapid development of the rainfall cloud system compared to ice-phase hydrometeors.The strong microphysical process, i.e. "accretion of cloud water by rainwater (P_racw)", may be directly related to the distinct convergence of liquid-phase hydrometeors.The ratio of the microphysical processes, i.e. "melting of graupel (P_gmlt)" to P_racw, was about 27%.During the heavy rainfall period, the distinctly enhanced moisture convergence was still the primary water vapor source for surface rainfall, but the sink terms for surface rainfall changed a lot.Meanwhile, microphysical conversion processes became more vigorous, especially P_racw and P_gmlt.The ratio of P_gmlt to P_racw was nearly 50%.