1.Key Laboratory for Cloud Physics, Chinese Academy of Meteorological Sciences;2.Gansu Weather Modification Office
Locating in the northeastern of the Tibetan Plateau, Qilian Mountains is an important ecological protective screen and conservation zone, as well as a key water source for Yellow River basin. However, studies on cloud and precipitation in this region are seriously lacking. Using the observations of 11 Parsivel2 disdrometers in Qilian Mountains, this paper studied the raindrop size distribution characteristics and orographic impact in a spring stratiform precipitation case over the Qilian Mountains. This precipitation process was initiated under the influence of a short wave trough and had significantly temporal and spatial variation. The disdrometer observations show that the mass equivalent diameter (D_m) was small, and the total number concentration of the raindrops (N_T) and D_m would increase and decrease as the elevation become higher. The relationship between 〖logN〗_w and D_m had featured stratiform precipitation characteristics, and in the same D_m there was higher N_w in Qilian Mountains. For lower elevation sites, there were less smaller raindrops (＜1 mm) and more larger raindrops because of the evaporation of small raindrops and the coalescence. Because the sites of higher elevation were close to the cloud base or in the cloud, the size scale of raindrops became smaller and D_m varied little with rain rate (R). The parameter values of the Γ distribution fit results were larger than other regions, so as to the N_0 of M-P distribution fit results. Γ distribution fits better for smaller raindrops, however, the Γ distribution and M-P distribution have underestimate and overestimate for larger raindrops, respectively. Influenced by the topography and the relative position between observational site and cloud base, the fit results of raindrop size distribution, the μ-Λ relationship, and the Z-R relationship all showed quite different characteristics with other regions or researches.