Shen Xiaocen, Kretschmer Marlene, Shepherd Theodore G
Department of Meteorology, University of Reading, Reading, UK.
Institute for Meteorology, University of Leipzig, Leipzig, Germany.
Clim Dyn. 2025;63(8):305. doi: 10.1007/s00382-025-07802-9. Epub 2025 Aug 6.
The Barents-Kara Sea ice concentration (BKS) has undergone dramatic declines in recent decades, consistent with the overall reduction in sea ice across the Arctic region. There has been a long-standing scientific question whether this BKS loss significantly influences winter temperature extremes over mid-to-high latitudes. While there is ongoing debate on this point, it is generally acknowledged that BKS loss affects the stratospheric polar vortex (SPV) through the enhancement of upward propagating waves, which itself can subsequently influence surface weather and climate conditions. However, due to the large internal variability within the climate system and the limited observational data, the strength of the BKS-SPV linkage and its dependence on different background states remain unclear. In this work, we investigate the causal effect of BKS change on SPV using a climate model with large ensemble simulations. Consistent with previous literature, the results indicate that BKS loss significantly weakens the SPV, with the magnitude of the response varying with El Niño-Southern Oscillation (ENSO) and Quasi-Biennial Oscillation (QBO) phases, indicating a state-dependent causal effect. In particular, El Niño is found to suppress the causal effect of BKS change on the SPV, whereas La Niña and neutral ENSO strengthen it, which is consistent with what is found from observations. In contrast, the effect of QBO alone is relatively weak but becomes more pronounced when combined with ENSO. Dynamical analyses reveal that both tropospheric wave forcing and modulation of stratospheric wave propagation contribute to the state-dependent causal effects. By leveraging large ensemble simulations and combining statistical and physical analyses, this study provides an additional perspective on understanding the factors influencing the SPV response to BKS loss, which could ultimately impact surface climate.
近几十年来，巴伦支海-喀拉海冰浓度（BKS）急剧下降，这与整个北极地区海冰的总体减少情况一致。长期以来，一直存在一个科学问题，即这种BKS的减少是否会对中高纬度地区的冬季极端温度产生重大影响。尽管在这一点上仍存在争论，但人们普遍承认，BKS的减少通过增强向上传播的波来影响平流层极涡（SPV），而极涡本身随后又会影响地面天气和气候条件。然而，由于气候系统内部存在很大的变率，且观测数据有限，BKS与SPV之间联系的强度及其对不同背景状态的依赖性仍不明确。在这项工作中，我们使用一个具有大集合模拟的气候模型来研究BKS变化对SPV的因果效应。与之前的文献一致，结果表明BKS的减少会显著削弱SPV，响应的幅度随厄尔尼诺-南方涛动（ENSO）和准两年振荡（QBO）阶段而变化，这表明存在状态依赖的因果效应。特别是，发现厄尔尼诺会抑制BKS变化对SPV的因果效应，而拉尼娜和中性ENSO则会增强这种效应，这与观测结果一致。相比之下，单独的QBO效应相对较弱，但与ENSO结合时会变得更加明显。动力学分析表明，对流层波强迫和平流层波传播的调制都对状态依赖的因果效应有贡献。通过利用大集合模拟并结合统计和物理分析，本研究为理解影响SPV对BKS减少响应的因素提供了一个额外的视角，这最终可能会影响地面气候。
