The Pacific/North American (PNA) pattern is a major low-frequency variability in boreal winter. A recent modeling study suggested that PNA variability increases through extratropical atmosphere-ocean coupling, but the effect was not fully extracted due to a particular experimental design. By comparing coupled and two sets of uncoupled large-ensemble global model simulations, here we show that the PNA-induced horseshoe-shaped sea-surface temperature (SST) anomaly in the North Pacific returns a non-negligible influence on the PNA itself. Its magnitude depends on the presence or absence of atmosphere-ocean coupling. The coupling accounts for ∼16% of the PNA variance, while the horseshoe-shaped SST anomaly explains only 5% under the uncoupled condition. The coupling reduces the damping of available potential energy by modulating turbulent heat fluxes and precipitation, magnifying the PNA variance. Precipitation processes in the extratropics as well as tropics are therefore important for realistically representing PNA variability and thereby regional weather and climate.

中文翻译：

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温带海洋对 PNA 遥相关的影响：大气-海洋耦合的作用


太平洋/北美（PNA）模式是北半球冬季的主要低频变化。最近的一项建模研究表明，温带大气-海洋耦合会增加 PNA 的变异性，但由于特定的实验设计，该效应并未完全提取出来。通过比较耦合和非耦合的两组大集合全球模型模拟，我们发现PNA引起的北太平洋马蹄形海面温度（SST）异常对PNA本身产生了不可忽视的影响。其大小取决于大气-海洋耦合的存在与否。耦合解释了 PNA 方差的~16%，而马蹄形海温异常在非耦合条件下仅解释了 5%。耦合通过调节湍流热通量和降水来减少可用势能的阻尼，从而放大 PNA 方差。因此，温带地区和热带地区的降水过程对于真实地反映 PNA 变化以及区域天气和气候非常重要。