On the Linearity of the Stratospheric and Euro-Atlantic Sector Response to ENSO
On the Linearity of the Stratospheric and Euro-Atlantic Sector Response to ENSO
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DOI：
10.1175/jcli-d-18-0746.1
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发表时间：
2019-09
影响因子：
4.9
通讯作者：
Paloma Trascasa-Castro;A. Maycock;Y. Yiu;J. Fletcher
中科院分区：
文献类型：
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作者：
Paloma Trascasa-Castro;A. Maycock;Y. Yiu;J. Fletcher
利用HadGEM3模式研究了冬季平流层和欧洲-大西洋气候响应对ENSO振幅的依赖关系。实验采用与Niño-3.4±0.75、1.5、2.25和3.0 K异常对应的东太平洋海面温度扰动进行。在北太平洋，El Niño （EN）加深并使阿留申低压向东移动，而等效量级的La Niña （LN）扰动驱动相反符号的异常，弱约4倍。北太平洋对LN的弱响应可以追溯到热带对流和相关的异常罗斯比波源的弱响应。EN扰动使北极极涡减弱，冬季60°N和10 hPa纬向平均风与Niño-3.4距平呈近似线性减少，减少幅度约为−3.6 m s−1 K−1。在最强EN情况下（+ 3k），与对照实验相比，平流层突然变暖（SSWs）的频率增加了约60%。因此，结果不支持以往文献中提出的平流层路径饱和的强EN。与一些基于再分析的研究相反，等效振幅LN扰动导致极涡的微弱增强，并且SSW频率没有实质性变化。在整个北方冬季，EN诱发负北大西洋涛动（NAO）指数，该指数与Niño-3.4异常近似线性增加，约为- 0.6标准差K−1。只有对最强烈的热带气旋扰动的响应反映了11月一个弱的正的北大西洋涛动，这表明欧洲-大西洋对热带气旋的响应机制可能不同于EN。
The dependence of the winter stratospheric and Euro-Atlantic climate response on ENSO amplitude is investigated using the HadGEM3 model. Experiments are performed with imposed east Pacific sea surface temperature perturbations corresponding to Niño-3.4 anomalies of ±0.75, 1.5, 2.25, and 3.0 K. In the North Pacific, El Niño (EN) deepens and shifts the Aleutian low eastward, while the equivalent magnitude La Niña (LN) perturbations drive anomalies of opposite sign that are around 4 times weaker. The muted North Pacific response to LN can be traced back to the weaker response of tropical convection and the associated anomalous Rossby wave source. The EN perturbations weaken the Arctic polar vortex, with the winter mean zonal mean zonal wind at 60°N and 10 hPa decreasing approximately linearly with Niño-3.4 anomaly by around −3.6 m s−1 K−1. For the strongest EN case (+3 K), the frequency of sudden stratospheric warmings (SSWs) increases by ~60% compared to the control experiment. Hence the results do not support a saturation of the stratospheric pathway for strong EN as suggested in previous literature. The equivalent amplitude LN perturbations cause a weak strengthening of the polar vortex and no substantial change in SSW frequency, in contrast to some reanalysis-based studies. EN induces a negative North Atlantic Oscillation (NAO) index throughout boreal winter, which increases approximately linearly with the Niño-3.4 anomaly by around −0.6 standard deviations K−1. Only the response to the strongest LN perturbations projects onto a weak positive NAO in November, suggesting that the mechanism for the Euro-Atlantic response to LN may be distinct from EN.