四川盆地与周边地区的降水垂直结构和宏微观差异研究

A study on vertical structure and macro- to micro-characteristics and differences of precipitation in Sichuan basin and the surrounding areas

  • 摘要: 为进一步认识地形对降水的影响,利用2014年3月—2020年12月全球降水测量卫星(GPM)星载双频雷达(DPR)探测资料研究了四川盆地(C1)及邻近山地(C2)和高原东坡(C3)降水的垂直结构及宏微观特征和差异。结果表明:(1)GPM/DPR与地面雨滴谱仪的测量结果有较好的一致性。(2)降水样本总数为C1>C3>C2,层性云降水频次远高于对流云降水。(3)两类降水的降水顶高度均为C3>C2>C1。层性云降水,C1能够发展到最强,垂直厚度最大、雨滴谱最宽。降水顶向下,回波强度、雨滴谱和降水强度均增大。0℃层以上,C3回波增强最快;0℃层以下,C1回波达到最强,降水强度增强最快。(4)对于对流云降水,C2和C3弱对流的回波较强、垂直尺度较大,粒径较小而数浓度较高。C1强对流的回波较强、垂直尺度较大,大粒子数浓度更高。降水顶往下,回波强度和降水强度均增强,降水强度廓线斜率最大的地区从C2转为C1,至近地面前斜率均为0。粒径和数浓度变化较复杂,C1以凝结和碰并占主导,C2和C3的凝结和碰并、蒸发和破碎都重要。(5)当近地面产生较小降水强度时,粒子的增长多发生在降水顶以下0.5—2 km;随后蒸发和破碎效应增强,尤其是C1。当近地面降水强度进一步增强时,凝结和碰并作用占主导。

     

    Abstract: To advance the understanding of terrain influences on precipitation physics, the GPM space-borne dual-frequency radar (DPR) products collected from March 2014 to December 2020 are used to study the differences and characteristics of precipitation vertical structure and macro- to micro-parameters in three different sub-regions, including the Sichuan basin (C1, the region with altitudes smaller than 1 km), its surrounding mountains (C2, the mountainous region surrounding C1 with altitudes greater than 1 km but smaller than 3.5 km) and the plateau region (C3, the eastern slope region of the Tibetan Plateau with altitudes greater than 3.5 km). Results indicate that: (1) Validation of GPM/DPR data indicate that they agree well with surface disdrometer measurements. (2) Total numbers of precipitation samples in the three subregions are C1>C3>C2, and stratiform precipitation in all the three sub-regions shows a much higher frequency than the convective precipitation. (3) For stratiform and convective precipitation, the rain top height indicates that C3>C2>C1. For stratiform precipitation, cloud-precipitation in C1 can develop to the strongest with widest raindrop spectrum and largest vertical scales. In the vertical direction, radar echo intensity, raindrop spectra and rain rate all increase with decreasing height. Above the 0℃ layer, the echo intensity increases most rapidly in C3; below the 0℃ layer, the echo intensity is the strongest and the rain rate is the fastest in C1. (4) For convective precipitation, weak convective precipitation has relatively strong echo intensity, large vertical scale, small raindrop diameters and high concentration in C2 and C3. On the contrary, deep convective precipitation has relatively strong echo intensity, large vertical scale and high concentration of large particles in C1. In the vertical direction, profiles of echo intensity and rain rate of the cloud-precipitation in the three sub-regions both increase with decreasing height, and the large slope of the rain rate profile is changed from C2 to C1. When closing to the surface, the slope of the rain rate profile is 0 in all the three subregions of C1, C2 and C3. However, the profiles of the raindrop diameter and concentration are more complicated. They are dominated by coagulation and collision-coalescence in C1, while coagulation and collision-coalescence as well as evaporation and shattering can be more critical in C2 and C3. (5) For small surface rain rate, the growth process of the particles more likely appears at 0.5–2 km, and evaporation and shattering can then become more important, especially in C1. When surface rain rate is increasing, collision-coalescence is dominant in all the three sub-regions.

     

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