Diagnostic analysis and high-resolution simulation of the typical hollow typhoon"Mulan"in the South China Sea in August 2022
A systematic diagnostic study was conducted to examine the characteristics and causes of the hollow typhoon"Mulan",which formed in the South China Sea in August 2022.The study applied on-site observation precipitation data,global analysis data,and merged precipitation data from multiple sources.The results indicated that typhoon"Mulan",originating from a monsoon depression in the South China Sea,exhibited typical features of depressions in the region.Satellite observations revealed that"Mulan"lacked typical typhoon characteristics,with no deep convection development near its center.Strong convection and rainstorms were primarily distributed in the typhoon's periphery,with precipitation significantly higher there than near the center.In terms of atmos-pheric circulation,"Mulan"featured multiple smaller vortices within its early-stage cyclonic circulation,with strong winds mainly concentrated in the periphery.Therefore,typhoon"Mulan"exhibited characteristics of a hol-low typhoon.Despite being weak,"Mulan"brought strong winds and heavy rainfall to regions of South China,in-cluding Guangdong,Guangxi,and southern Yunnan,due to a combination of factors including a northeastern low-level jet,ample water vaper supply from the South China Sea,and intense convective activity over land.The strong winds on the northeast side of the typhoon resulted from the convergence of the southwest monsoon from the South China Sea and the southeast monsoon from the northwest Pacific Ocean.Blocked by the zonal subtropi-cal high over the mid-latitudes of the Asian continent,the typhoon's direction of movement changed from north-west to westward as it approached land,following an inverted parabolic path shape.Using the Weather Research and Forecasting(WRF)model,a retrospective simulation of 84 hours was conducted,employing the nesting of two domains with horizontal grid spacings of 9 and 3 km.The model reasonably reproduced the circulation struc-ture and evolution process of"Mulan",although with some discrepancies,particularly in the simulated monsoon trough and typhoon track.Comparison with Final Operational Global Analysis(FNL)data showed significant im-provement in precipitation simulation with the WRF model,particularly at higher resolution.This study contributes to understanding the formation and characteristics of hollow typhoons in the South China Sea and highlight the potential of mesoscale models for enhancing typhoon simulation and forecasting.Future research will focus on the cloud microphysical characteristics of"Mulan"and evaluate different parameterization schemes of the WRF model to enhance the forecasting ability for weak typhoons with heavy precipitation.
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