Water Budget And Intensity Change Of Tropical Cyclones

Using the Tropical Rainfall Measuring Mission(TRMM)3B42 and 2A25 precipitation data,TRMM Microwave Imager(TMI)total precipitable water(TPW)data,Institut Francais de Recherche pour l’Exploitation de la Mer,version 3(IFREMER3)air-sea heat flux data,CloudSat cloud type data,the National Centers for Environmental Prediction(NCEP)Final analysis(FNL)and Joint Typhoon Warning Center(JTWC)best-track data during 2001-2015,this study compares spatial distribution of water budget components associated with Northwest Pacific tropical cyclones(TCs)with different vertical wind shear directions and intensity change and aims to investigate possible mechanisms for the impacts of water budget on TC intensity change.Results show that:(1)The maximum TC rainfall are all located in the downshear left quadrant regardless of shear direction,and TCs with easterly shear have greater magnitudes of rainfall than those with westerly shear.Rainfall amount of a TC is related to its relative position and proximity from the western Pacific subtropical high and the intensity of water vapor transport,and low-level jet is favorable for water vapor transport.The maximum of vertically integrated moisture flux convergence(MFC)are located on the downshear side regardless of shear direction.The cyclonic displacement of the maximum rainfall relative to the maximum MFC is possibly due to advection of hydrometeors by low-and middle-level cyclonic circulation of TCs.(2)Surface evaporation and TPW in the outer environment are vital to TC rapid intensification(RI)and the highest evaporation associated with rapidly intensifying TCs is associated with the highest sea surface temperature.The roles of surface evaporation and TPW in TC RI are related to the enhanced convective available potential energy(CAPE)by moistening and warming the boundary layer.In addition to boundary layer thermodynamics,midlevel thermodynamics also play a role in the large CAPE of RI storms.The largest amount of column-integrated MFC associated with weakening(W)TCs,which results in the heaviest precipitation,is because their strongest mean intensity promotes moisture transport.The results agree with the notion that TC intensity change results from a competition between surface moisture and heat fluxes and low-entropy downdrafts into the boundary layer.(3)TC rainfall decreases sharply with increasing distance in both horizontal and vertical directions regardless of TC intensity change.In the horizontal direction,heavy rainfall is mainly concentrated in one radius of maximum wind from the storm center,while in the vertical direction,it is mainly concentrated within 2 km.Within 2 km,W storms show the heaviest precipitation mainly due to their strongest mean intensity.The higher vertical extension of precipitation associated with RI stroms,which results in the heaviest precipitation beyond 2 km,is because of their relative deep convection.The maximum TC rainfall are located in the downshear left quadrant and TC rainfall is stronger and wider in the downshear side than that in the upshear side regardless of TC intensity change.(4)Cloud type is dominated by deep convective clouds near the TC center and the occurrence probability of deep convective clouds are always large,indicating that updrafts mainly occur in the deep convective clouds.RI storms have much higher occurrence probability of deep convective cloud than non-RI storms.The distribution of deep convective cloud changes obviously with quadrants and the quadrant with the highest occurrence probability changes with TC intensity change categories.The distribution of altostratus also shows some asymmetry,while the distribution of cirrus,altocumulus,stratocumulus and cumulus are more evenly and symmetric.