Northern Europe and Northeast Asia, which are climatologically mild and temperate in early summer, both witnessed record-breaking heat extremes in June 2023. With a focus on the subseasonal time scale, this study highlights a teleconnected relationship in historical early-summer heat extremes between Northern Europe and Northeast Asia. By diagnosing the thermal budget and wave activity flux, we show that over one third of historical Northeast Asian heat extremes are initialized by Eurasian mid-latitude Rossby wave packets. The wave packets manifest as strong anticyclonic anomalies over subpolar North Atlantic, cyclonic anomalies over Ural region and anticyclonic anomalies over Northeast Asia, which directly cause coexisting heat extremes in Northern Europe and Northeast Asia. Such wave packets are strongly modulated by the Eurasian jet stream. By carrying out numerical experiments, we further explain why the wave packet is significant in early summer. We find that the quasi-stationary response of the Eurasian midlatitude Rossby wave packets to a specified heating in subpolar North Atlantic is dependent on the background jet structure. In early summer, the double-jet state over Eurasia favors Rossby wave propagation. This is of great practical importance for accurate prediction of Northeast Asian heat extreme amplitude and location.

中文翻译：

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欧亚中纬度急流在极端高温下架起了大西洋与亚洲夏季遥相关的桥梁

北欧和东北亚初夏气候温和，在 2023 年 6 月都见证了破纪录的极端高温。这项研究重点关注次季节时间尺度，强调了历史上初夏极端高温与北欧和东北亚。通过诊断热收支和波浪活动通量，我们发现历史上超过三分之一的东北亚极端高温是由欧亚中纬度罗斯贝波包引发的。波包表现为北大西洋副极地的强反气旋异常、乌拉尔地区的气旋异常和东北亚的反气旋异常，直接导致北欧和东北亚极端高温并存。这种波包受到欧亚急流的强烈调制。通过数值实验，我们进一步解释了初夏波包显着的原因。我们发现欧亚中纬度罗斯贝波包对北大西洋副极地特定加热的准稳态响应取决于背景喷流结构。初夏，欧亚大陆上空的双喷流状态有利于罗斯贝波的传播。这对于准确预测东北亚高温极值振幅和位置具有重要的现实意义。