A seesawing temperature pattern occurred over northern mid-latitudes in December 2023, with cold anomalies over northern parts of Eurasia and warm conditions over North America. The recurrent dipole temperature pattern in boreal winter has been revealed to be associated with concurrent changes in atmospheric variability (e.g., Siberian high and Alaska ridge) and boundary forcing (e.g., Arctic sea ice and North Atlantic sea surface temperature), whereas its precursor features remain less clear. Based on reanalysis data and two sets of coupled simulations, this study revealed that strong blocking activity over the Greenland-Eurasia sector in November was an important precursor to the remarkable “colder North Eurasia, warmer North America” pattern in December 2023. Increased tropospheric blocking frequency in November favored vertically propagating planetary waves to weaken the stratospheric polar vortex. The stratospheric response that persisted into December was characterized as the shift of polar vortex towards Eurasia and away from North America, linked to the enhanced zonal wavenumber-1 planetary waves. Downward propagation of the amplified wavenumber-1 component into the troposphere in December contributed to stronger continental high pressure over Eurasia and weaker ridge over Alaska, causing the “colder North Eurasia, warmer North America” pattern. High consistency between the results of observations and two sets of numerical simulations confirms the critical role of preceding tropospheric blocking, which is valuable for sub-seasonal prediction of the dipole temperature pattern across northern mid-latitudes.

中文翻译：

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2023 年 12 月的“北欧亚大陆更冷，北美更暖”模式及其阻塞前兆


2023 年 12 月，中纬度北部地区出现跷跷板温度模式，欧亚大陆北部出现寒冷异常，北美出现温暖天气。北方冬季反复出现的偶极子温度模式已被证明与大气变率（例如，西伯利亚高压和阿拉斯加脊）和边界强迫（例如，北极海冰和北大西洋海面温度）的并发变化有关，而其前体特征仍然不太清楚。基于再分析数据和两组耦合模拟，本研究揭示了 11 月格陵兰-欧亚大陆部分的强烈阻塞活动是 2023 年 12 月显着的“北欧亚大陆更冷，北美更暖”模式的重要前兆。11 月对流层阻塞频率的增加有利于垂直传播的行星波以削弱平流层极涡。持续到 12 月的平流层响应被描述为极地涡旋向欧亚大陆并远离北美，这与增强的纬向波数 1 行星波有关。12 月放大的波数 1 分量向下传播到对流层，导致欧亚大陆上空的大陆高压增强，阿拉斯加上空的高压较弱，导致“北欧亚大陆更冷，北美更暖”的模式。观测结果和两组数值模拟之间的高度一致性证实了先前对流层阻塞的关键作用，这对于北部中纬度地区偶极子温度模式的亚季节预测很有价值。