LAUSR

A 2-km resolution simulation using the Weather Research and Forecasting model with Morrison microphysics was employed to investigate the rainwater microphysical properties during different stages of Typhoon Usagi (2013) in the inner-core and outer region. The model reproduced the track, intensity, and overall structure of Usagi (2013) reasonably. The simulated raindrop size distribution showed a rapid increase in small-size raindrop concentration but an oscillated decrease in large-size ones in the inner-core region, corresponding well with the upward motion. It was found that there existed two levels (1.25 and 5.25 km) of maximum number concentration of raindrops. The ice-related microphysics at high levels was stronger than the warm-rain processes at low levels. The larger raindrops formed by self-collection in the inner-core suffered from significant breakup, but the raindrops outside the eyewall did not experience evident breakup. Model results indicated that the dominant terms in the water vapor budget were the horizontal moisture flux convergence (HFC) and local condensation and deposition. The evaporation from the ocean surface (PBL) was ∼10% of the HFC in the inner core, but up to 40% in the outer region as the air therein was far from saturation. Furthermore, water vapor in the outer region was obtained equally through evaporation from the cloud and inward transportation from the environment. An earlier start of cloud microphysical processes in the inner-core region was evident during the intensification stage, and the continuous decreasing of condensation in both the inner-core and outer regions might imply the beginning of the storm weakening.概要采用高分辨率(2km)的中尺度数值模式,对2013年台风“天兔”进行数值模拟, 研究该天气系统不同发展阶段, 不同区域内雨水的演变特征.模拟结果较好的重现了“天兔”的路径、强度和整体结构.系统内的雨滴谱型变化与上升运动紧密相关, 内核区域的小雨滴的数量显著增加而大雨滴的数量减少并伴有震荡.雨滴的数浓度存在两个极大值中心, 分布位于1.25km和5.25km的高度处.高层的冰相云微物理过程对雨滴数浓度的贡献大于低层的暖云微物理过程.内核区域低层的雨滴较大, 存在明显的自发破碎, 而外围雨带由于粒子较小, 没有明显的破碎发生.水汽收支分析进一步显示, 水平水汽通量辐合和局地的凝结(含凝华)是水汽的主要源、汇项.内核区域, 海表向上蒸发对局地水汽的贡献仅占水平辐合输送贡献的10%, 外围区域则高达40%.此外, 外围区域的局地蒸发对水汽的贡献等同于四周围水汽的水平辐合.系统增强阶段, 内核的云微物理过程先于外围区域启动.内核、外围区域, 凝结量的持续性减少可能预示着台风强度的减弱.