On the Relative Importance of Stratospheric and Tropospheric Drivers for the North Atlantic Jet Response to Sudden Stratospheric Warming Events
On the Relative Importance of Stratospheric and Tropospheric Drivers for the North Atlantic Jet Response to Sudden Stratospheric Warming Events
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DOI：
10.1175/jcli-d-21-0680.1
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发表时间：
2022-10
影响因子：
4.9
通讯作者：
Hilla Afargan‐Gerstman;B. Jiménez-Esteve;D. Domeisen
中科院分区：
文献类型：
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作者：
Hilla Afargan‐Gerstman;B. Jiménez-Esteve;D. Domeisen
大约三分之二的观测到的平流层突然变暖（SSW）事件之后是北大西洋对流层急流向赤道移动，而其他事件通常表现出向极地移动。然而，尚不清楚哪些驱动因素导致了表面影响中事件间的巨大变化。使用中等复杂度的大气模型，我们分析了不同因素对下行响应的贡献：平流层下部的极冠位势高度异常、东北太平洋的下游影响以及初始响应时北大西洋的局部对流层条件。在重新分析中，发现模型中三分之二的南海风发生了北大西洋急流向赤道的移动。我们发现，SSW事件后对流层急流响应的大约40%的方差可以用平流层低层位势高度异常来解释，而大约25%可以用东北太平洋地区的纬向风异常来解释。研究发现，南西南风爆发时，大西洋当地的条件也会对地表响应产生影响。为了将平流层的作用与对流层变化分开，我们使用模型实验，将纬向平均平流层风推向气候学。当平流层变化受到抑制时，太平洋的影响就会减弱。这些发现揭示了平流层对 SSW 事件的多种向下影响的贡献，并可能有助于提高北大西洋对流层急流变率的可预测性。
Roughly two-thirds of the observed sudden stratospheric warming (SSW) events are followed by an equatorward shift of the tropospheric jet in the North Atlantic, while the other events generally show a poleward shift. It is however not resolved which drivers lead to the large inter-event variability in the surface impact. Using an intermediate complexity atmospheric model, we analyze the contribution of different factors to the downward response: polar cap geopotential height anomalies in the lower stratosphere, downstream influence from the northeastern Pacific, and local tropospheric conditions in the North Atlantic at the time of the initial response. As in reanalysis, an equatorward shift of the North Atlantic jet is found to occur for two-thirds of SSWs in the model. We find that around 40% of the variance of the tropospheric jet response after SSW events can be explained by the lower stratosphere geopotential height anomalies, while around 25% can be explained by zonal wind anomalies over the northeastern Pacific region. Local Atlantic conditions at the time of the SSW onset are also found to contribute to the surface response. To isolate the role of the stratosphere from tropospheric variability, we use model experiments where the zonal mean stratospheric winds are nudged toward climatology. When stratospheric variability is suppressed, the Pacific influence is found to be weaker. These findings shed light on the contribution of the stratosphere to the diverse downward impacts of SSW events, and may help to improve the predictability of tropospheric jet variability in the North Atlantic.