Atmospheric rivers (ARs) are elongated areas of pronounced atmospheric water vapor transport that play an important role in the hydrological cycle over North America during winter. We investigate the sources of winter seasonal AR predictability over North America using average predictability time (APT) analysis. The skill of seasonal AR frequency predictions, in dynamical model forecasts provided by the Seamless System for Prediction and Earth System Research, is nearly entirely attributable to three physically interpretable APT modes that together represent about 19% of the total seasonal AR frequency variance. These three modes represent the AR response to the El Niño-Southern Oscillation, anthropogenic forcing and equatorial heating over the eastern flank of the western Pacific warm pool, respectively. We further show that these three modes, calculated from AR frequency, explain nearly all winter seasonal precipitation forecast skill over North America.

中文翻译：

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北美冬季季节性大气河流变化的可预测模式


大气河流 （ARs） 是显著大气水蒸气输送的细长区域，在冬季北美的水文循环中起着重要作用。我们使用平均可预测性时间 （APT） 分析调查了北美冬季季节性 AR 可预测性的来源。在无缝预测系统和地球系统研究提供的动态模型预测中，季节性 AR 频率预测的技能几乎完全归因于三种物理可解释的 APT 模式，它们合计约占季节性 AR 频率总方差的 19%。这三种模态分别代表了对西太平洋暖池东侧厄尔尼诺-南方涛动、人为强迫和赤道加热的 AR 响应。我们进一步表明，根据 AR 频率计算的这三种模式几乎可以解释北美所有冬季季节性降水预报技能。