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

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.