Hot Towers Detected By Satellites And Their Relationship With The Tropical Cyclone Intensities

Hot towers are the horizontally small but intense cumulonimbus convection cores that reach the tropopause via nearly undilute ascent in tropical regions.Based on the satellite data,the relationship between inner-core hot towers and rapid intensifications of the tropical cyclones(TCs)is verified,the large-scale conditions for hot towers occuring are studied,and a new TC current intensity retrieval method is proposed.The conclusions are summarized as follows:1.The indicative significance of inner-core hot towers for rapid intensification has been explained or verified in various numerical simulations and case observations.However,according to the existing literatures,the climate survey results didn't support this viewpoint.With the help of the Tropical Rainfall measuring Mission(TRMM)data,this study demonstrates that the inconsistency is due to ignoring the regional differences,especially differences of the latitude and the tropopause height TC locating at.In the North Atlantic(NA)and eastern and central Pacific(ECP)basin,the hot tower indeed has no skill in predicting the TC's rapid intensification without the help of other meteorological information.However,in the Southern Indian Ocean(SI),Southern Pacific(SP),and West Northern Pacific(WNP)basin,the hot tower can be used to the rapid intensification's prediction even when other information is absent.If the hot tower is used in conjunction with the TC previous 12-h intensity change(PER),Potential intensity(maximum potential intensity-current intensity)(POT)and 850-200-hPa vertical shear of the horizontal wind(SHRD),the forecast skill in SI and SP basin will be competitive with that of the rapid intensification index(RII)method that is considered as the most advanced prediction scheme.In NA,ECP and WNP basin,the skill score will be 0.24,0.34,and 0.48,respectively,when combining the hot towers with POT,PER,and SHRD.2.For the hot tower detection method using geostationary meteorological satellite infrared and visible channel,a new visible albedo normalization scheme,that is,the Quasi-Lambertian Surface Adjustment(QLSA),is developed.Taking the variation of relative locations between the sun,satellite and clouds into account,the QLSA effectively reduces the inconsistencies in the VIS image brightness caused by the Lambertian surface approximation to cloud tops(i.e.,the reflection characteristic is isotropic).The evaluation,using Chinese and Japanese geostationary satellite data,shows that the QLSA is more effective and accurate than three other albedo normalization methods currently in use.The new algorithm is applicable in regions with solar zenith angle and satellite zenith angle less than 60°,which,in the summertime,approximately corresponds to the time range from 0800 to 1600 local time.3.The TRMM observations and the statistical hurricane intensity prediction scheme(SHIPS)data are employed to examine the large-scale characteristics of TC with inner-core hot towers.By comparing the differences between the magnitudes of the TC with hot towers and TC without hot towers,six predictors are proposed for the inner-core hot towers.They are:latitude(LAT),the lasting time after the cyclonegenesis(HIST),the ocean heat content(RHCN),The average equivalent potential temperature difference between a parcel lifted from the surface and its environment(ENEG),the temperature difference between 1000 and 150 hPa(Tdiff),and the magnitude of the horizontal temperature gradient between 850 and 700 hPa(TGRD).A prediction test for the Atlantic hurricane Wilma(2005)demonstrates these six predictors are of significant usefulness to the prediction of inner-core hot towers.4.Due to the cirrus's obscuring effects and the incomplete understanding of the impacts caused by hot towers,little progress has been made in recent years to estimate TC current intensity based on geostationary satellite infrared window(IRW)and water vapor(WV)imagery.In this study,a WV-IRW to IRW Ratio(WIRa)-based indicator is proposed in the first place.This indicator can not only screen out thin cirrus and week convections,but also hot towers and hot tower-derived cirrus anvil and stratospheric WV anomaly from common deep convections.It is highly correlated with the best track minimum sea-level pressure(MSLP),and thus used for estimating the western North Pacific(WNP)TC current intensity.Detailed analyses have demonstrated that the WIRa-based indicator can significantly improve the estimation of TC current intensity.The WIRa-based indicator is designed based on the hypothesis that "hot towers may be not suitable to serve as an indicator of TC current intensity",and the satisfying results of the WIRa-based method perhaps provide indirect evidence to support this hypothesis in turn.