青藏高原对非洲北部降水影响的模拟研究

利用耦合模式CESM1.0, 研究青藏高原地形对非洲北部降水的影响。敏感性试验结果表明, 去掉青藏高原地形后, 首先, 大气环流迅速做出调整, 出现自热带大西洋向东北方向至北非的水汽输送异常和自印度洋向西至北非的水汽输送异常, 造成北非大气水汽含量增加和水汽辐合增强, 降水增多。然后, 当海洋环流调整到准平衡态时, 北大西洋海表温度降低, 南大西洋海表温度升高, 地表大气温度也发生相应的变化。在南北温度梯度的影响下, 原本由热带大西洋向北非的水汽输送发生转向, 导致北非的水汽含量减少和水汽辐合减弱, 使得降水比前一阶段减少。即便如此, 在没有青藏高原的试验中, 当海洋环流调整到平衡态时, 北非大部分区域水汽辐合仍然强于有青藏高原的真实地形试验, 区域平均降水也增多。结果表明, 青藏高原的隆升可能在一定程度上加剧了北非的干旱化。

A Modeling Study of the Impact of Tibetan Plateau on the North African Precipitation

The impact of Tibetan Plateau (TP) on the North African precipitation is investigated using a fully coupled climate model (CESM1.0). Results from sensitivity experiments show that when the TP is removed, first of all the atmospheric circulation responds quickly and there are enhanced northeastward moisture transport from the tropical Atlantic Ocean to the North Africa and the westward moisture transport from the Indian Ocean to the North Africa. As a result, the atmospheric moisture content increases and moisture convergence enhances over the North Africa, leading to more precipitation. Later on, when the ocean circulation reaches the quasi-equilibrium (QE), the sea surface temperature (SST) in the North (South) Atlantic decreases (increases). The surface air temperature (SAT) changes synchronously with the SST. This temperature gradient anomaly leads to the moisture transport out of the North Africa, so that the atmospheric moisture content decreases and moisture convergence weakens over the North Africa. Consequently, the precipitation over there decreases. Even so, in the QE stage in the world without TP, the moisture convergence over the North Africa is still much stronger than that in the realistic topography experiment, and the precipitation still increases significantly. This study suggests that the uplift of TP may contribute to the aridification in the North Africa.