Macro- and Microphysical Characteristics of Extreme Rainfall Producing-convective Clouds Observed by the Nanjing Dual-polarimetric Radar During the 2020-2022 Warm Seasons
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摘要: 全球变暖背景下极端降水发生频次升高,但不同地区不同程度极端降水的对流云宏微观特征的认识仍然不清晰。利用2020—2022年5—9月南京地区S波段双偏振雷达观测数据,定义“极端降水对流体” (Extreme Precipitation Feature,EPF),根据雨强极端程度分为三组EPF (ER1、ER2、ER3),进一步分为强对流、中等强度对流和弱对流EPF,分析其对流云宏微观特征。结果表明,随着极端雨强强度增强,EPF的40 dBZ区域水平尺寸增大,20 dBZ区域尺寸变化较小;强对流EPF占比明显上升(11.4%~25.4%),弱对流EPF占比显著下降(36.6%~23.8%);强对流和中等强度对流EPF的液水和冰水含量均显著增加,混合相和液相微物理过程都更加活跃。三种雨强阈值下,强对流EPF的液相微物理过程均以尺度分选、蒸发为主(43.9%~50.8%),弱对流EPF的液相微物理过程以碰并为主(76.9%~75.3%),雨滴谱分布介于海洋性与大陆性之间、但偏向海洋性对流,数浓度与雨滴粒径频次峰值类属海洋性对流,数浓度平均值高于大陆性对流、雨滴直径平均值大于海洋性对流。随雨强极端程度的升高,液相微物理过程中雨滴碰并的占比仅略有减少、破碎的占比略有上升,雨滴平均粒子大小和数浓度变化不明显。Abstract: Despite global warming increases extreme precipitation frequency, the understanding of the macro-and microphysical characteristics of extreme precipitation-producing convective clouds in different regions remains incomplete. This study utilizes dual-polarization radar and rain gauges data (May-September 2020-2022) in the Nanjing area to compare three rainfall intensity-based Extreme Precipitation Features(EPFs) groups (ER1, ER2, ER3). Each group is further categorized into EPFs with intense, moderate and weak convection. It is found that, as the rainfall extremity increases, the horizontal extent of 40 dBZ region in EPFs increases, whereas 20 dBZ regions exhibit minimal changes. The proportion of intense convection EPFs rises from 11.4% to 25.4%, while the proportion of weak convection declines from 36.6% to 23.8%. The liquid and ice water contents in intense and moderate convection EPFs increase significantly with more extreme rainfall, while both mixed - and liquid-phase processes become more active. In EPFs with intense convection, liquid-phase processes are mainly dominated by size sorting and evaporation, while EPFs with weak convection are governed by coalescence. The raindrop size distributions resemble maritime-like convection, with characteristics between "maritime-like" and "continental-like" convection. The peak values of concentration and droplets size belong to "maritimelike" convection, with raindrop size distributions featuring a mean size large than "maritime-like" droplets and a concentration much higher than "continental-like" raindrops. As the rainfall extremity increases, liquid-phase processes show a slightly decrease in raindrop coalescence and a slight increase in raindrop breakup. The average raindrops size and concentration of ER1 to ER3 exhibit minimal variation.
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表 1 不同雨强以及不同对流强度的EPF数量(个)
对流强度 ER1 ER2 ER3 强对流 1 209 796 189 中等强度对流 5 523 2 046 378 弱对流 3 879 847 177 表 2 EPF第50百分位IWP和LWP的平均值(kg·m-2)
对流强度 ER1 ER2 ER3 IWP LWP IWP LWP IWP LWP 总体EPF 1.86 5.06 2.35 5.73 2.57 5.79 强对流EPF 3.9 7.25 4.06 7.36 4.35 7.58 中等强度对流EPF 1.56 5.31 1.73 5.71 1.81 5.69 弱对流EPF 0.77 3.95 0.73 4.16 0.71 4.01 -
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