Based on data diagnosis and numerical experiments, this study investigated the changes in the interannual properties of the May North Atlantic Oscillation (NAO) and their impact on summer (June–July) sea ice in the North Atlantic during 1979–2021. Results showed statistically significant increase in the interannual variability of the May NAO after the mid-2000s, which had remarkably enhanced impact on summer sea ice in the eastern Hudson Bay (EHB) and the western Labrador Sea (WLS). During 2005–2021, corresponding to a positive phase of the May NAO, anomalous surface westerly or northwesterly winds prevailed over the Hudson Bay and Labrador Sea in May. This led to statistically significant increase in sea ice in both the EHB and the WLS in May via dynamic processes (favoring southeastward movement of the sea ice) and thermal processes (changing surface turbulent heating and shortwave radiation). In comparison with the situation in May, the increase in sea ice in the EHB developed further during summer mainly via thermal processes (positive feedback between the increased sea ice and shortwave radiation). In contrast, amplitude of the increased sea ice in the WLS was comparable between May and summer. Dynamic processes (southeastward movement of sea ice), which was induced by a barotropic anomalous high in the troposphere centered over the Labrador Peninsula, favored the increase in sea ice in summer in the WLS. The tripole sea surface temperature anomalies in the North Atlantic and increased snowpack on the Labrador Peninsula in May, triggered by the positive phase of the May NAO, played an important role in the formation of the anomalous high. During 1979–2004, the surface wind, snowpack, and tripole sea surface temperature anomalies in May, triggered by the May NAO, were relatively weak, leading to statistically insignificant changes in summer sea ice in the EHB and WLS.

中文翻译：

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2000 年代中期后 5 月北大西洋涛动的年际变率增强及其对北大西洋夏季海冰的影响


本研究基于数据诊断和数值实验，调查了 1979—2021 年 5 月北大西洋涛动 （NAO） 年际特性的变化及其对北大西洋夏季（6 月至 7 月）海冰的影响。结果显示，在 2000 年代中期之后，5 月 NAO 的年际变化在统计学上显着增加，这显着增强了对哈德逊湾东部 （EHB） 和拉布拉多海西部 （WLS） 夏季海冰的影响。在 2005-2021 年期间，对应于 5 月 NAO 的正阶段，5 月哈德逊湾和拉布拉多海盛行了异常的表面西风或西北风。这导致 5 月份 EHB 和 WLS 中的海冰通过动态过程（有利于海冰向东南移动）和热过程（改变表面湍流加热和短波辐射）在统计学上显着增加。与 5 月的情况相比，EHB 中海冰的增加在夏季主要通过热过程（增加的海冰和短波辐射之间的正反馈）进一步发展。相比之下，WLS 中海冰增加的幅度在 5 月和夏季之间是相当的。由以拉布拉多半岛为中心的对流层气压异常高压引起的动力过程（海冰向东南移动）有利于 WLS 夏季海冰的增加。5 月 NAO 正相触发的北大西洋三极海面温度异常和 5 月拉布拉多半岛积雪增加，对异常高压的形成起了重要作用。 在 1979-2004 年期间，由 5 月 NAO 触发的 5 月表面风、积雪和三极海表温度异常相对较弱，导致 EHB 和 WLS 中夏季海冰的变化在统计学上不显著。