Wintertime Southern Hemisphere Jet Streams Shaped by Interaction of Transient Eddies with Antarctic Orography
Wintertime Southern Hemisphere Jet Streams Shaped by Interaction of Transient Eddies with Antarctic Orography
复制标题
冬季南半球急流由瞬变涡流与南极地形相互作用形成
作者：
M. Patterson;T. Woollings;T. Bracegirdle;N. Lewis
冬季南半球温带环流表现出相当大的纬向不对称性。我们使用半现实的仅大气气候模型研究了各种表面边界条件在形成平均状态中的作用。我们发现，与之前的文献一致，热带海面温度（SST）模式是平均状态的重要贡献者，而中纬度海表温度和海冰范围的作用较小。我们的主要发现是南极地形对中纬度环流结构具有一级影响。在没有南极地形的情况下，与地形相关的赤道涡动量通量被消除，因此中纬度地区涡动量的收敛性减少。这削弱了印度洋急流，使得罗斯贝波向下游传播到南太平洋变得不那么有利。因此，气流在南太平洋中高纬度地区停滞，典型的分裂急流模式被破坏。消除南极地形也会导致南极洲东部大幅变暖，部分原因是瞬变涡流能够向极地渗透得更远，从而增强了向极地的热传输。然而，应用高纬度冷却的实验表明，这些温度变化并不是中纬度地区环流变化的主要驱动因素。相反，我们调用一个简单的正压机制，其中地形坡度创建有效的位涡梯度，改变涡动量通量。
The wintertime Southern Hemisphere extratropical circulation exhibits considerable zonal asymmetries. We investigate the roles of various surface boundary conditions in shaping the mean state using a semi-realistic, atmosphere-only climate model. We find, in agreement with previous literature, that tropical sea surface temperature (SST) patterns are an important contributor to the mean state, while midlatitude SSTs and sea ice extent play a smaller role. Our main finding is that Antarctic orography has a first-order effect on the structure of the midlatitude circulation. In the absence of Antarctic orography, equatorward eddy momentum fluxes associated with the orography are removed and hence convergence of eddy momentum in midlatitudes is reduced. This weakens the Indian Ocean jet, making Rossby wave propagation downstream to the South Pacific less favorable. Consequently, the flow stagnates over the mid- to high-latitude South Pacific and the characteristic split jet pattern is destroyed. Removing Antarctic orography also results in a substantial warming over East Antarctica partly because transient eddies are able to penetrate farther poleward, enhancing poleward heat transport. However, experiments in which a high-latitude cooling is applied indicate that these temperature changes are not the primary driver of circulation changes in the midlatitudes. Instead, we invoke a simple barotropic mechanism in which the orographic slope creates an effective potential vorticity gradient that alters the eddy momentum flux.
影响因子：
4.4
作者：
Bracegirdle, Thomas J.;Shuckburgh, Emily;Wilcox, Laura J.
通讯作者：
Wilcox, Laura J.