青藏高原冬春积雪影响南海季风爆发的数值研究

NUMERICAL STUDY OF EFFECTS OF WINTER-SPRING SNOW COVER OVER THE TIBETAN PLATEAU ON THE SOUTH CHINA SEA MONSOON ONSET

采用NCAR CAM3.0大气环流模式,研究了冬春季青藏高原积雪异常对南海夏季风爆发的可能影响机制。通过比较多雪年与少雪年试验中的热力场、环流场季节演变的差异得出,多雪年青藏高原感热加热偏弱、高原纬度的中上层大气温度偏低,导致大尺度经向温度梯度反转时间偏晚;同时,青藏高原感热加热偏弱将不利于Hadley环流的季节转换,使得中南半岛上空的下沉异常气流维持时间较长、副高在孟加拉湾断裂的时间偏晚、中南半岛对流爆发偏晚、中南半岛地表温度下降时间偏晚,从而造成中南半岛与南海局地纬向温度梯度反转时间也偏晚。在上述大尺度经向温度梯度以及中南半岛与南海局地纬向温度梯度的共同作用下,多雪年南海季风爆发偏晚。

Based on the NCAR CAM3.0 model,experiments were designed to investigate the possible mechanism for the effects of winter-spring snow cover over the Tibetan Plateau（TP） on the South China Sea（SCS） monsoon onset.By comparing the difference in the seasonal evolutions of thermal and atmospheric circulation between experiments with heavy and light snow cover,it is found that during heavy snow years,the sensible heating over the TP will weaken,and the mid-upper air temperature will decrease,thus leading to later reversion in large-scale longitudinal temperature gradients.Meanwhile,the seasonal evolution of Hadley circulation will take place later,with the abnormal descent airflow maintaining over the Indo-China Peninsula（ICP）,causing later break of the subtropical high over the Bay of Bengal and later outbreak of convective activities over the ICP,in such a way that the surface temperature over the ICP will decrease later,resulting in later reversion in local zonal temperature gradient between the ICP and the SCS.The SCS monsoon onset may be later in heavy snow years under the joint action of the above large-scale longitudinal and local zonal temperature gradients.