Modeling The Impact Of Deep Convection In Tropical Cyclone Saomai (2006) On The Stratospheric Water Vapor

Stratosphere water vapor plays an important role in regulating global climate,which has a significant source by overshooting deep convection vertical transporting.The aim of this study is to examine the effect and mechanism of overshooting convection in tropical cyclone(TC)on stratosphere water vapor by high resolution simulations of 0608 Typhoon Saomai,with the advanced research version of the Weather Research and Forecasting(ARW)model using different cloud microphysical parameterization schemes.The experiments show that the simulated tracks are not sensitive to microphysical parameterization schemes,but the intensity presents deviations.Lin and NSSL1 schemes produce the rapid intensification,and other schemes vary slowly,verified against the JTWC best track.NSSL1 scheme produces the strongest convergence causing the disappear of outer rainband,which result in lower amount of rainwater at lower levels.Lin scheme storm has the best performance in all experiments which double strong rainband in outer region with stronger reflectivity.The vertical profiles of hydrometeors with Lin scheme are also closed to observations.It is found that deep convection in TC continues nearly 60 h through the entire simulation.During the stage of slow development and rapid intensification,the deep convection horizontal coverage scale exceed 10 km arising near inner eyewall.Furthermore,20 dBZ echo top can reach 18 km with hot tower crossing tropopause and penetrating in lower stratosphere(LS).Meanwhile,large amount of ice particles freezes in cold trap near tropopause caused by a combination of adiabatic ascent of air.A large number of ice particles increasing rapidly in the LS are transported upward by deep convection before ice particles away from clouds.In the stage of steady intensity,convection become stronger but effect by upper-levels divergence without penetrating the stratosphere.Upward transport of ice particles correspondingly reduces due to decrease of freezing caused by cold trap dissipating.The impact of TC in stage of slow development and rapid intensification is greater than stage of steady and weak intensity.The analysis of stratosphere show that total amount of water increased during the 72 h in simulation via TC.The ice phase hydrometeors vary with the strength of deep convection but water vapor falls behind it.The amount of water vapor increased slowly even weaken deep convection.This suggests that the existence of deep convection in TC can cause a moistening of LS.However,the amount of water vapor is not completely dominated by strength of deep convection but also managed by microphysics.The results show that the moistening of LS has two principal ways:direct upward transport of water vapor by overshooting convection and sublimation of ice particles.Sublimation is the main mechanism of water vapor increasing in later period.In earlier period a few amount of water vapor was directly transported by strong deep convection due to ice particles dominating hydrometeors,which results in water vapor increasing slowly.In later period direct convective transport of water vapor into stratosphere was also less despite of vapor mixing ratio increasing with cold trap dissipating.The most of ice particles entering into stratosphere converted to graupel and snow with sedimentation.The other fraction staying at LS converted to water vapor by sublimation causing moistening of LS.