江淮地区山区和非山区夏季降水雨滴谱特征

Characteristics of summer rainfall droplet spectra in mountainous and non-mountainous areas of the Jianghuai region

  • 摘要: 雨滴谱特征分析是研究降水微物理特征的重要方法,使用2011—2012年夏季(6—8月)安徽4个站的雨滴谱资料,根据雨强及其随时间的变化将降水划分为对流降水和层云降水,对比分析山区和非山区对流降水和层云降水的雨滴谱特征。主要结论是:山区地形对对流降水的雨滴谱影响较大,对层云降水的雨滴谱影响较小。当雨强相同时,山区对流降水的雨滴数浓度比非山区高,雨滴尺寸比非山区小。随着雨强增大,山区和非山区对流降水的雨滴数浓度和雨滴尺寸均在增大。比较了标准化参数(Nw)与雨滴数浓度的关系,发现Nw与雨滴数浓度有关,但不能完全反映雨滴数浓度的变化,并且对雨强的变化不敏感。当雨强相同时,山区与非山区对流降水的雨滴数浓度差别较小,Nw则差别明显,说明Nw更能体现山区和非山区降水机制的差异。对于雨强小于30 mm/h的弱对流降水,山区与非山区小雨滴数浓度比较接近,大雨滴数浓度明显低于非山区,对应山区雨滴谱谱宽更窄,此时地形对雨滴谱的影响较为明显。对于雨强超过30 mm/h的强对流降水,山区和非山区雨滴谱比较接近,此时地形对雨滴谱的影响显著减弱。山区降水类型对Z(雷达反射率)-R(雨强)关系的影响较小。

     

    Abstract: Analysis of raindrop spectrum characteristics is an important method to study the microphysical characteristics of precipitation. In this paper, raindrop spectrum data collected at four stations in Anhui province from June to August of 2011—2012 are used to investigate raindrop spectra of convective precipitation and stratiform precipitation in mountainous and non-mountainous areas and compare their similarities and differences. The precipitation is divided into convective precipitation and stratiform precipitation according to the rainfall rate and its variation with time. The main conclusions are as follows. The mountain terrain has a greater impact on the raindrop spectrum of convective precipitation, but a smaller impact on the raindrop spectrum of stratiform precipitation. When the rainfall intensity is the same, the concentration of raindrops in convective precipitation in mountainous areas is larger than that in non-mountainous areas, while the size of raindrops is smaller than that in non-mountainous areas. The raindrop number concentration and raindrop size of convective precipitation in mountainous and non-mountainous areas both increase with rainfall intensity. The relationship between Nw (standardization parameter) and raindrop number concentration is studied. It is found that Nw is related to raindrop number concentration, but it cannot fully reflect the change of raindrop number concentration, and is not sensitive to the change of rain intensity. When the rainfall intensity is the same, the difference in raindrop number concentration between mountainous and non-mountainous convective precipitation is small, yet the difference in Nw is obvious, which indicates that Nw can better reflect the difference of precipitation mechanism between mountainous and non-mountainous areas. For weak convective precipitation with rainfall intensity less than 30 mm/h, the concentration of small raindrops in mountainous areas is relatively close to that in non-mountainous areas, while the concentration of large raindrops is lower than that in non-mountainous areas, which corresponds to a narrower spectral width of raindrops, indicating that terrain impact on raindrop spectra is more obvious. For strong convective precipitation with rainfall intensity greater than 30 mm/h, the rainfall droplet spectra in mountainous and non-mountainous areas are relatively close, which indicates that terrain impact on the rainfall droplet spectra is significantly weakened. Precipitation type have little influence on the Z (radar reflectivity)-R (rainfall rate) relationship in mountainous area.

     

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