中国大陆降水日变化研究进展

Progress in studies of the precipitation diurnal variation over contiguous China

中文关键词:  降水日变化  区域差异  降水持续性  数值模拟

英文关键词:Rainfall diurnal variation  Regional differences  Rainfall duration  Numerical simulation

中文摘要:

      文章概述了中国大陆降水日变化的最新研究成果，给出了中国大陆降水日变化的整体图像，指出目前数值模式模拟降水日变化的局限性，为及时了解和掌握降水日变化研究进展、开展相关科学研究和进行降水预报服务提供了有价值的科学依据和参考。现有研究表明：（1）中国大陆夏季降水日变化的区域特征明显。在夏季，东南和东北地区的降水日峰值主要集中在下午；西南地区多在午夜达到降水峰值；长江中上游地区的降水多出现在清晨；中东部地区清晨、午后双峰并存；青藏高原大部分地区是下午和午夜峰值并存。（2）降水日变化存在季节差异和季节内演变。冷季降水日峰值时刻的区域差异较暖季明显减小，在冷季南方大部分地区都表现为清晨峰值；中东部地区暖季降水日变化随季风雨带的南北进退表现出清晰的季节内演变，季风活跃（间断）期的日降水峰值多发生在清晨（下午）。（3）持续性降水和局地短时降水的云结构特性以及降水日峰值出现时间存在显著差异。持续性降水以层状云特性为主，地表降水和降水廓线的峰值大多位于午夜后至清晨；短时降水以对流降水为主，峰值时间则多出现在下午至午夜前。（4）降水日变化涉及不同尺度的山-谷风、海-陆风和大气环流的综合影响，涉及复杂的云雨形成和演变过程，对流层低层环流日变化对降水日变化的区域差异亦有重要影响。（5）目前数值模式对中国降水日变化的模拟能力有限，且模拟结果具有很强的模式依赖性，仅仅提高模式水平分辨率并不能总是达到改善模拟结果的目的，关键是要减少存在于降水相关的物理过程参数化方案中的不确定性问题。

英文摘要:

      This paper summarizes the recent progress in studies of the diurnal variation of precipitation over contiguous China. The main results are as follows. (1) The rainfall diurnal variation over contiguous China presents distinct regional features. In summer, precipitation peaks in the late afternoon over southern inland China and northeastern China, while it peaks around midnight over southwestern China. In the upper and middle reaches of Yangtze River valley, precipitation occurs mostly in the early morning. Summer precipitation over the central eastern China (most regions of the Tibetan Plateau) has two diurnal peaks, one in the early morning (midnight) and the other in the late afternoon. (2) The rainfall diurnal variation experiences obvious seasonal and sub-seasonal evolutions. In cold seasons, the regional contrast of rainfall diurnal peaks decreases, with an early morning maximum over most of the southern China. Over the central eastern China, diurnal monsoon rainfall shows sub-seasonal variations with the movement of the summer monsoon system. The rainfall peak mainly occurs in the early morning (late afternoon) during the active (break) monsoon period. (3) Cloud properties and occurrence time of rainfall diurnal peaks are different for long- and short-duration rainfall events. Long-duration rainfall events are dominated by stratiform precipitation, with the maximum surface rain rate and the highest profile in the late night to early morning, while short-duration rainfall events are more related to convective precipitation, with the maximum surface rain rate and the highest profile occurring between late afternoon and early night. (4) The rainfall diurnal variation is influenced by multi-scale mountain-valley and land-sea breezes as well as large-scale atmospheric circulation, and involves complicated formation and evolution of cloud and rainfall systems. The diurnal cycle of winds in the lower troposphere also contributes to the regional differences in the rainfall diurnal variation. (5) Evaluation of the model performance shows that the present numerical models are weak in simulating the rainfall diurnal variation over contiguous China. The simulations are not significantly improved by increasing the model horizontal resolutions alone. The key is to reduce the uncertainty in physical parameterizations related to the rainfall processes.