Stratospheric Modulation of Tropical Upper-Tropospheric Warming-Induced Circulation Changes in an Idealized General Circulation Model
Stratospheric Modulation of Tropical Upper-Tropospheric Warming-Induced Circulation Changes in an Idealized General Circulation Model
复制标题
理想化大气环流模型中热带对流层上层变暖引起的环流变化的平流层调制
DOI：
10.1175/jas-d-21-0232.1
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发表时间：
2023
影响因子：
3.1
通讯作者：
T. Birner
中科院分区：
文献类型：
--
作者：
R. Walz;H. Garny;T. Birner
平流层极涡与对流层环流动态耦合。因此，更好地从机理上理解这一耦合系统，对于正确解释过去和未来的环流变化是很重要的。以前，用干燥动力核心大气环流模式和强迫的热带上对流层变暖(TUTW)进行的理想化模拟表明，存在一个临界变暖水平，在这个临界变暖水平上，极涡从一个弱而可变的区域转变为一个强而稳定的区域。在这里，我们通过在有极涡(REF)和无极涡(NPV)的情况下进行类似的理想化实验，研究了引起这种区域转变的动力学机制及其对对流层的影响。根据临界层控制机制，在两次实验中，副热带急流对TUTW的响应增强了上翼，导致了波驱动的剩余环流加速。对于REF实验，较强的剩余环流与平流层低层热结构的变化有关，这与极涡向赤道方向移动是一致的。在REF实验中，在一定的TUTW阈值下，对流层急流和平流层极涡形成了行星尺度波的受限波导，这可能有利于下行波耦合事件。与NPV实验相比，与NPV实验相比，极涡不断增强，同时对流层急流的极移增强。总体而言，这些理想化的实验表明，极地涡旋的加强可能是由温室气体通过修改波导引起的变暖引起的。这一机制也可能与在更复杂的模式中理解极涡变化有关。
The stratospheric polar vortex is dynamically coupled to the tropospheric circulation. Therefore, a better mechanistic understanding of this coupled system is important to interpret past and future circulation changes correctly. Previously, idealized simulations with a dry dynamical-core general circulation model and imposed tropical upper-tropospheric warming (TUTW) have shown that a critical warming level exists at which the polar vortex transitions from a weak and variable to a strong and stable regime. Here, we investigate the dynamical mechanism responsible for this regime transition and its influence on the troposphere by performing similar idealized experiments with (REF) and without a polar vortex (NPV). According to the critical-layer control mechanism, the strengthened upper flank of the subtropical jet in response to TUTW leads to an accelerated wave-driven residual circulation in both experiments. For the REF experiment, the stronger residual circulation is associated with changes in the lower-stratospheric thermal structure that are consistent with an equatorward shift of the polar vortex. At a certain threshold of TUTW in the REF experiment, the tropospheric jet and the stratospheric polar vortex form a confined waveguide for planetary-scale waves that presumably favors downward wave coupling events. Consistently, the polar vortex strengthens in combination with an enhanced poleward shift of the tropospheric jet compared to the NPV experiment. Overall, these idealized experiments suggest that a polar vortex strengthening can be caused by greenhouse gas–induced warmings via modifications of the waveguide. This mechanism might also be relevant to understand the polar vortex changes in more complex models.
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