Comparison of two double-moment microphysics schemes in aspects of warm-rain droplet spectra and raindrop budget

两种双参数微物理方案暖云粒子谱及雨滴源汇模拟对比研究（英文）

Simulation results of the WDM6 scheme and the Thompson scheme,both of which are commonly-used double-moment bulkmicrophysics schemes,are compared within theWeather Research and Forecasting model.The purpose of the comparison is to study the difference in the aspects of the warm-rain hydrometeor number concentrations,the droplet size distributions,and the budgets of the rain mixing ratio and number concentration.It is found that the WDM6 scheme overestimates the ratio and the amount of large precipitation,and underestimates those of small precipitation,compared to the Thompson scheme.The cloud number concentration(CNC)predicted in the WDM6 scheme is one to three orders ofmagnitude smaller than that of the Thompson scheme,which is set to the specific valueof CNC.The cloud droplet spectra of the WDM6 scheme are broader.The WDM6 scheme produces a larger rain number concentration and smaller mass mean diameter of raindrops under the influence of both warm and cold rain processes—specifically,autoconversion and melting of snow and graupel.The WDM6 scheme produces a larger autoconversion rate and smaller total melting rate of snow and graupel than the Thompson scheme in the rain mixing ratio budget.The sign of the difference in the rain-cloud collection varieswith region,and the rain-cloud collection process together with evaporation of rain have a major influence on the sign of the surface precipitation difference between the two schemes.

本文对WRF模式中两种常用的雨滴双参数微物理方案,即Thompson方案和WDM6方案在华北地区‘7.20’暴雨中暖云粒子谱和雨滴源汇项的模拟差异,以及上述差异如何影响降水模拟进行了详细的分析。结果表明:WDM6方案模拟的云滴数浓度比Thompson方案中给定的云滴数浓度概量小1-3个量级,云滴谱较宽。云雨自动转换过程和雪、霰融化过程的共同导致WDM6方案雨滴粒子数浓度较大,平均尺度较小。本文着眼于微物理方案间的暖云粒子谱模拟差异,是以往研究关注较少的领域,有助于更好地理解微物理方案的模拟特征。