基于WRF模式的青藏高原斜坡和平台加热影响亚洲夏季风的模拟研究

Influences of thermal forcing over the slope/platform of the Tibetan Plateau on Asian summer monsoon:Numerical studies with the WRF model

青藏高原大地形的热力强迫作用对亚洲夏季风的形成和发展具有重要的影响.本文利用较高分辨率的WRF区域模式,探讨了高原不同区域(斜坡和平台)的地形加热分别对南亚夏季风和东亚夏季风的影响.结果表明:高原南部喜马拉雅山脉的斜坡地形加热对其周围局地的环流形势和降水影响十分明显,是南亚夏季风北支分量形成和维持的主导因子,也是斜坡上气流爬坡和降水发生的必要条件.斜坡加热对东亚夏季风也有明显的增强作用,它不仅加强了中国东部低空西南季风环流,还会造成北部南下的异常干冷空气的响应.斜坡上的地形加热作用也是对流层高层暖中心位置维持在斜坡上空的一个重要原因.而高原平台加热对季风环流和降水的影响虽然没有喜马拉雅山脉斜坡加热那么显著,但是对南亚夏季风的影响范围更广,对经向哈得来环流影响更明显,能够调控高原以外更远处热带洋面上的西南季风环流.通过比较高原不同区域地形加热条件下的多种季风指数,进一步表明了高原地形加热对南亚和东亚夏季风均有增强作用,但是高原不同区域的地形加热对两类夏季风子系统又会产生不一样的影响.

With global warming,the evolution of Asian summer monsoon（ASM）becomes more complicated,while the thermal effect of the Tibetan Plateau（TP）is an important forcing to the variability of weather and climate in ASM areas.The regional climate model（RCM）is a usefultool in research of the regional climate change and has higher resolutions that can represent topography and land surface processes more accurately compared with atmospheric general circulation models（AGCMs）.In this study,the impact of thermal forcing over different terrains of TP on ASM（including South and East ASM（SASM and EASM））is investigated using the Weather Research and Forecasting（WRF）models.Results indicate that the local circulation and precipitation around the Himalayas（HIM）are significantly influenced by the surface heating over the HIM′s southern slope,which is a dominant factor for the formation of the north branch of SASM.Meanwhile,the climbing moist airflow and precipitation over the southern slope of TP are mainly induced by HIM′s thermal forcing.Due to HIM′s slope heating,the upper-level troposphere warm center is steadily located over the HIM area and the EASM is also intensified obviously（characterized both by the enhanced low-level southwesterly over East China and the enhanced southward anomalous dry-cold northerly）.As to the surface heating over the TP′s platform region（PL）,although its influence on the summer monsoon circulation and precipitation is weaker than the HIM′s,it induces a wider response of SASM and a stronger influence on the meridional Hadley circulation.The PL′s heating is able to regulate low-level southwesterly over the remote tropical ocean.Furthermore,the comparison of multiple monsoon indices reveals that both HIM sloping heating and PL heating can intensify SASM or EASM,but the impacts of thermal forcing over different terrains on the two subsystems of ASM are distinct.