地表反照率的改变影响夏季北非副热带高压的数值模拟

A NUMERICAL SIMULATION STUDY OF THE IMPACTS OF SURFACE ALBEDO ON THE SUMMER TIME NORTH AFRICA SUBTROPICAL HIGH

利用 LASG L 9R1 5AGCM设计了两组不同地表反照率的数值试验。通过分析其夏季平均气候的差异来考察地表反照率改变对夏季北非副高的影响。结果表明 ,当北非地表反照率增大时 ,由于地面接收到的净辐射减少 ,地面温度降低 ,底层大气的感热加热减弱 ,抑制了局地的对流和降水 ,相应的对流层中层的凝结加热也减弱。这种中、低层的冷却强迫出高空的异常辐合与低空的异常辐散 ,导致北非地区下沉运动增强 ,从而加强了北非副高。另外 ,这种北非地区的环流异常 ,通过辐散风环流加强了南亚高空的辐散 ,在一定程度上加强了南亚高压。

Two sets of numerical experiments different in surface albedo were carried out by using of LASG L9R15 AGCM in this work. The impacts of surface albedo on the summer time North Africa subtropical high are investigated through comparative study of the July mean climate of these two sets of experiments. The results indicate that with the increase of surface albedo, especially at North Africa, the net radiation reaches the ground surface decreases (from 140W/m 2 to 101W/m 2), so do the surface temperature and the sensible heat flux transfered to the above atmosphere, therefore the convection and precipitation in North Africa reduce. The cooling of middle and lower troposphere in the aforementioned region results in more convergence at high level and more divergence at low level, hence stronger downward motion and the reinforcement of the North Africa subtropical high during summer time.Besides the aforementioned impacts of the changes of surface albedo on local climate in north Africa, the differential circulation in north Africa enhances the low level convergence and high level divergence in south Asia through divergent wind circulation which connects these two regions, therefore strengthens the South Asia high to some extent, and increases monsoon precipitation in southeast Asia.