青藏高原春季土壤湿度异常对我国夏季降水影响的模拟研究

利用耦合的全球海气模式（NCAR CCSM3）， 对青藏高原春季土壤湿度异常影响我国夏季7月降水的机制进行了数值模拟。结果表明， 高原6~62 cm深度的中层土壤湿度异常与表层土壤湿度异常有很好的一致性， 相对而言， 中层土壤湿度异常的持续性较好。若5月高原中层土壤偏湿， 则春末至夏初高原地面蒸发、 潜热通量增加， 而感热通量、 地面温度降低， 高原表面的加热作用减弱， 使得印度高压西撤偏晚， 环流系统的季节性转换偏晚， 东亚地区形成有利于我国夏季出现第I类雨型的环流分布形势， 使我国东部雨带偏北， 华北地区多雨， 江淮地区降水偏少， 华南地区降水偏多; 反之亦然。

Simulation of the Impacts of Spring Soil Moisture over the Tibetan Plateau on Summer Precipitation in China

Snow cover over the Tibetan Plateau (TP) in winter and spring can affect rainfall in China in the following summer,but the mechanism has been remained to be confirmed for a long time. The coupled model NCAR CCSM3 was employed in this study to investigate how the spring soil moisture resulted from anomalous snow cover over the TP influences summertime precipitation in China. The results indicate that the anomalies of top layer soil moisture and middle layer soil moisture have good consistency,but the anomaly of middle layer soil moisture persists longer. The wetter the middle soil moisture over the TP in May,the more surface evaporation and associated latent heat flux,leading to less surface sensible heat flux and lower surface temperature in early summer. The weaker surface heating over the TP results in a later westward withdraw of the mid-troposphere Indian High and a later seasonal transition of the circulation system over south and east Asia to its summer regime. All of these factors are in favor of the first spatial rainfall pattern of China in summer:More rainfall in North China and South China,but less rainfall in the Yangtze-Huaihe River Basin,and vice versa.