Quantitative analysis of torrential rainfall associated with typhoon landfall: A case study of typhoon Haitang (2005)

A quantitative analysis of torrential rainfall associated with typhoon Haitang (2005) is carried out using a modified moist ageostrophic Q vector and data from Weather Research and Forecasting (WRF) model simulation. Four major factors determining the ascending motion associated with torrential rainfall have been studied: large-scale and convective condensational heating, topographic lifting and friction. The results show that the convective condensational heating plays a major role in the torrential rainfall process, and the large-scale condensational heating is secondary before the landfall of typhoon Haitang, and vice versa after the landfall. The topographic lifting affects the formation of rainfall, whereas the topographic friction has important impacts on torrential rainfall after the landfall. The rainfall amounts forced by the topographic friction and lifting have similar horizontal distributions, but the magnitudes of the former are 2–3 times larger than those of the latter. The rainfall amounts forced by topography (lifting and friction) and modified moist ageostrophic Q vector have different horizontal distributions, and the magnitudes of the former are 2–5 times larger than those of the latter. Synthetic analysis shows that the typhoon rainfall may be motivated by modified moist ageostrophic Q vector and enhanced further by the topographic effects.