摘要
摘要:祁连山是青藏高原东北部重要的生态屏障和冰川与水源涵养生态功能区，是黄河流域重要水源产流地，但针对该地区的云和降水过程研究很少。本文利用祁连山地区11个Parsivel2雨滴谱仪的观测数据，研究了祁连山地区春季一次层状云降水过程的雨滴谱分布及地形影响特征。此次降水过程主要受短波槽影响，降水时空差异较大。雨滴谱观测数据表明，此次降水过程的雨滴等效直径（D_m）较小，雨滴谱数浓度（N_T）与D_m随海拔高度升高分别呈增加和减小的趋势，低海拔站点logN_w（N_w为雨滴谱截断参数）和D_m分布有着明显的层状云降水特征，而整个祁连山地区在同样D_m下有着更低的N_w。低海拔站点由于碰并和小雨滴的蒸发，有着更少的小雨滴（＜1 mm）和更多的大雨滴，而高海拔站点由于距离云底较近或位于云内，云滴尺度小且浓度大，D_m随R（R为降水强度）增大变化趋势不明显。M-P分布和Gamma分布在低海拔站点的拟合效果要优于高海拔站点，相较于Gamma分布，M-P分布对高海拔站点的小雨滴和大雨滴浓度有一定的高估和低估，因此更适用于高海拔站点雨滴谱的描述。对比于低海拔站点，高海拔站点的μ–Λ（μ、Λ分别为Gamma分布的形状参数和斜率参数）关系与相关研究的结果较为接近，但在Λ较小（＜40 mm^?1）时拟合结果较为接近。受海拔高度与云底的相对位置和地形的影响，祁连山地区的Z–R（Z为雷达反射率因子）关系与其他地区或研究有着较大的区别。
关键词:祁连山/
雨滴谱与降水特征/
地形高度影响/
雨滴谱仪观测
Abstract:Located northeast of the Tibetan Plateau, the Qilian Mountains is an important ecological protective screen and conservation zone, as well as a key water source for the Yellow River basin. However, studies on cloud and precipitation in this region are seriously lacking. Using the observations of 11 Parsivel2 disdrometers in the Qilian Mountains, this paper studied the raindrop size distribution characteristics and the 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 a significant temporal and spatial variation. Disdrometer observations show that the mass equivalent diameter ($ {D}_{\mathrm{m}} $) was small. The total number concentration of the raindrops ($ {N}_{\mathrm{T}} $) and $ {D}_{\mathrm{m}} $ would increase and decrease as the elevation becomes higher. The relationship between $ {\mathrm{l}\mathrm{o}\mathrm{g}N}_{\mathrm{w}} $ ($ {N}_{\mathrm{w}} $ is the intercept parameter of the rain drop size distribution) and $ {D}_{\mathrm{m}} $ had featured stratiform precipitation characteristics. In the same $ {D}_{\mathrm{m}} $, there was a higher $ {N}_{\mathrm{w}} $ in the Qilian Mountains. For lower elevation sites, there were fewer small raindrops (＜1 mm) than the large raindrops because of the evaporation of small raindrops and the coalescence. Because the sites with a higher elevation were close to the cloud base or in the cloud, the size scale of raindrops became smaller and $ {D}_{\mathrm{m}} $ varied little with the rain rate ($ R $). The M-P and Gamma distribution fit better for sites with a lower altitude. For sites with a higher altitude, the Gamma distribution describes the spectrum better, while the M-P distribution will overestimate/underestimate the concentrations of smaller/larger raindrops. The μ–Λ (μ and Λ are shape and slope parameters of the rain drop size distribution) relationship for sites with a higher altitude are similar to those in related researches. However, when the Λ is small (<40 mm^?1), results will be better for all sites. Influenced by the topography and the relative position between the observational site and cloud base, the Z–R (Z is the radar reflectivity factor) relationship all showed quite different characteristics with other regions or researches.
Key words:Qilian Mountains/
Characteristics of precipitation and raindrop size distribution/
Impact of orographic elevation/
Disdrometer observation



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