The Observational Study Of The Microphysical Characteristics For Rainbands In Typhoon Nida(2016) And The Evaluation Of The Microphysical Schemes

The landfalling Tropical cyclones(TCs)and heavy precipitation accompanying them is a disaster to the coastal area of China,and often induce severe casualties and financial lost.Most of the precipitation in a TC is produced by different rainbands which can be divided into inner-and outer-rainbands based on the distance to TC center.And the microphysical processes occurred in the rainbands have a direct impact on the precipitation intensity.Thus,the key to improving the quantitative prediction of the precipitation in TCs is to thoroughly understand the microphysical mechanism.Polarimetric radar is an important tool to observe the three-dimensional microphysical information of the TC precipitation.Recently the microphysical characteristics of the inner-rainband and the mechanisms for its heavy precipitation have been studied by some researchers using polarimetric radar observation.But the understanding of the microphysical characteristics of the outer-rainband is still quite limited.In this study,the recently updated polarimetric radar observations are used to analyze the microphysical characteristics and the mechanism for heavy precipitation in the outer-rainband of Typhoon Nida(2016).The differences between the inner-and outer-rainband are also compared.Then,the performance of three commonly-used microphysical parameterization schemes are evaluated by the observational results.The main conclusions are:First of all,the microphysical characteristics of the convective cells in the outer rainband of Typhoon Nida(2016)are analyzed based on polarimetric radar observation.The result shows that the growth of the hydrometeor in this outer rainband is mainly through ice-phased microphysical processes above the freezing level,including aggregation and riming.The ice particles in the mature convective cells may experience more active riming and finally have larger sizes.The melting of these large ice particles might cause much stronger surface precipitation with larger rain drops.Comparing with the outer rainband,the vertical extent of the convection in the inner rainband is lower.The updraft strength is also weaker.The liquid water content below the freezing level increases much faster and its value is also much larger than that of the ice water content above,indicating that the warm rain processes are dominant pathway for the particle growth in the inner rainband.Then,in order to assess the model performance regarding microphysics,three double-moment microphysics schemes(Morrison,Thompson and WDM6)are evaluated by performing a set of simulations.Sensitivity tests indicate that the microphysical characteristics of the simulated precipitation are primarily attributed to the different microphysics parameterizations,rather than the differences in large-scale environments after a long period of integration.While these simulations reproduce the outer rainband regarding its structure,the microphysics of the simulated precipitation are different from the observation.Further analysis shows that the surface rain rate is closely related to the simulated raindrop size distribution(DSD).The mass-weighted raindrop diameters are overestimated in Morrison and Thompson schemes and underestimated in WDM6 scheme;while the former two schemes produce less precipitation than WDM6 scheme.A comparison between the ice water content estimated by a new method and the output from the simulations shows that,the ice water content above the freezing level in all simulations is smaller than observation,especially above 12 km height where small ice particles are prevalent.This suggests that the improperly treatment of the ice phase processes is an important error source of DSD and thereby surface precipitation in all microphysics schemes.Another error source in WDM6 scheme is attributed to the more active warm-rain processes that produce much higher concentration of smaller raindrops.Finally,the performances of the three microphysical schemes for the precipitation in the TC inner rainband are also evaluated based on polarimetric radar observations.The simulated reflectivity is stronger than the observation.The size of the observed raindrops is small,and the signal of the warm rain processes is obvious in the inner rainband precipitation.Below the freezing level,although the Thompson and Morrison experiments have the same warm-rain feature,the efficiency in Morrison scheme is lower than observation.The efficiency of the ice particle transferring into liquid or accreting cloud water is higher than observation in the WDM6 scheme,and the efficiency of breakup or evaporation is also overestimated.