The Impacts Of Land Surface Process On Sustention And Rainfall Associated With Tropical Cyclones

China, with its long coastline, is attacked by Tropical cyclones (TCs) frequently. SomeTCs usually move into inland and result in serious disaster. Complicated land surface processis an important factor for TCs’inland behaviors. However, the impacts of land surface processon TC activities are not understood until now. In this study, statistical features of TC activitieson China mainland are studied firstly based on CMA60-year TC Year Book data from1949to2008. And several typhoons moving into inland are selected to learn the changes of underlyingland surface and atmosphere under the influence of typhoons. Then typhoon Rananim (0414),a TC stagnated over Poyang Lake area after its landfall, is selected to explore the impacts ofland surface process on its track, intensity and rainfall based on mesoscale numerical modelWRF. Finally, a set of sensitivity experiments are employed to investigate the impacts ofinland water bodies on TC’s intensity and rainfall.Statistical analysis shows that Jiangxi and Anhui Provinces, where presentwell-developed water landscapes, are inland areas attacked by TCs with high frequency. Mostof TCs sustaining more than60hours over land passed though these areas in the past60years.It is found that a TC is likely to have a slow speed and maintain its intensity statistically whenpassing across Poyang Lake in inland China. Observations indicate that the temperature ofland surface is decreased with a less obvious diurnal variation while the atmosphere humidityin lower layer is increased under the influence of typhoon rainfall and cloud coverage.Numerical study on Typhoon Rananim suggests that land surface process have nosignificant impact on its track, intensity and large scale circulation, but can improvesimulations on typhoon mesoscale structure, rainfall rate and distribution. It is noted thattyphoon rainfall and cloud coverage lead to land surface cooling but expand the underlyingsaturated wetland area, which aggravates asymmetric distribution of surface heat fluxes.Accordingly, an energy frontal zone may genesis in the lower troposphere to enhanceascending motions and local convection, resulting in the change of rain rate and location. Sensitivity experiments on Poyang Lake demonstrate that inland water bodies arefavorable for the sustention of TC and associated rainfall. Compared to other surface covers,water bodies have less friction to increase wind speed near the underground, which enhancesconvergence over heavy rainfall area on one hand. On the other hand, water bodies mayrelease more surface heat fluxes to make air warmer and wetter in lower atmosphere, which isfavorable for TC sustention and its heavy rainfall.