Relation of the Second Type Thermal Helicity to Precipitation of Landfalling Typhoons:A Case Study of Typhoon Talim  

作　　者：喻自凤 余晖 

机构地区：[1]Shanghai Typhoon Institute/Laboratory of Typhoon Forecast Technique,CMA

出　　处：《Acta meteorologica Sinica》2011年第2期224-237,共14页

基　　金：Supported by the "973" Program of China (2009CB421505);National Natural Science Foundation of China (40405012,40830958, 40705024, and 40875039);Shanghai Meteorological Bureau (2009ST11)

摘　　要：This study utilized the MM5 mesoscale model to simulate the landfalling process of Typhoon Talim.The simulated typhoon track,weather patterns,and rainfall process are consistent with the observation.Using the simulation results,the relation of the second type thermal helicity（H2） to rainfall caused by the landfalling typhoon Talim was analyzed.The results show that H2 could well indicate the heavy inland rainfall but it did not perform as well as the helicity in predicting rainfall during the beginning stage of the typhoon landfall.In particular,H2 was highly correlated with rainfall of Talim at 1-h lead time.For 1-5-h lead time,it also had a higher correlation with rainfall than the helicity did,and thus showing a better potential in forecasting rainfall intensification.Further analyses have shown that when Talim was in the beginning stage of landfall,1） the 850-200-hPa vertical wind shear around the Talim center was quite small（about 5 m s-1）;2） the highest rainfall was to the right of the Talim track and in the area with a 300-km radius around the Talim center,exhibiting no obvious relation to low-level temperature advection,low-level air convergence,and upper-level divergence;3） the low-level relative vorticity reflected the rainfall change quite well,which was the main reason why helicity had a better performance than H2 in this period.However,after Talim moved inland further,1） it weakened gradually and was increasingly affected by the northern trough;2） the vertical wind shear was enhanced as well;3） the left side of the down vertical wind shear lay in the Lushan and Dabieshan mountain area,which could have contributed to triggering a secondary vertical circulation,helping to produce the heavy rainfall over there;hence,H2 showed a better capacity to reflect the rainfall change during this stage.This study utilized the MM5 mesoscale model to simulate the landfalling process of Typhoon Talim.The simulated typhoon track,weather patterns,and rainfall process are consistent with the observation.Using the simulation results,the relation of the second type thermal helicity（H2） to rainfall caused by the landfalling typhoon Talim was analyzed.The results show that H2 could well indicate the heavy inland rainfall but it did not perform as well as the helicity in predicting rainfall during the beginning stage of the typhoon landfall.In particular,H2 was highly correlated with rainfall of Talim at 1-h lead time.For 1-5-h lead time,it also had a higher correlation with rainfall than the helicity did,and thus showing a better potential in forecasting rainfall intensification.Further analyses have shown that when Talim was in the beginning stage of landfall,1） the 850-200-hPa vertical wind shear around the Talim center was quite small（about 5 m s-1）;2） the highest rainfall was to the right of the Talim track and in the area with a 300-km radius around the Talim center,exhibiting no obvious relation to low-level temperature advection,low-level air convergence,and upper-level divergence;3） the low-level relative vorticity reflected the rainfall change quite well,which was the main reason why helicity had a better performance than H2 in this period.However,after Talim moved inland further,1） it weakened gradually and was increasingly affected by the northern trough;2） the vertical wind shear was enhanced as well;3） the left side of the down vertical wind shear lay in the Lushan and Dabieshan mountain area,which could have contributed to triggering a secondary vertical circulation,helping to produce the heavy rainfall over there;hence,H2 showed a better capacity to reflect the rainfall change during this stage.

关 键 词：second type thermal helicity TYPHOON rainfall diagnosis 

分 类 号：P458.12[天文地球—大气科学及气象学]