Abstract At least two main oceanic fronts (the subarctic and subtropical fronts) exist in the North Pacific. Especially in the subtropical frontal zone (STFZ), the sea subsurface temperature gradient is significantly larger than that of the surface layer in winter. Subseasonal interaction between the subsurface subtropical front and overlaying atmosphere is revealed by using empirical orthogonal function (EOF) analysis of oceanic temperature gradient. The first EOF mode mainly corresponds to the atmosphere-to-ocean influences. With the enhanced westerly wind, a cold sea surface temperature anomaly (SSTA) appears and then passes down to affect the subsurface ocean. However, the second EOF mode indicates the ocean-to-atmosphere forcing. For the second mode, cold oceanic temperature anomaly generates in the subsurface layer and passes up, which makes the SST gradient increasing. Due to the increasing atmospheric baroclinicity, the enhanced westerly wind leads to more heat fluxes from the ocean to the atmosphere, which results in a colder SSTA and a larger SST gradient in the STFZ. Therefore, a positive ocean-atmosphere feedback begins to maintain in the mid-latitude in winter.

中文翻译：

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冬季北太平洋次表层副热带锋与上覆大气的次季节耦合

摘要 北太平洋至少存在两条主要的洋锋（亚北极锋和亚热带锋）。特别是在副热带锋区（STFZ），冬季海面次表层温度梯度明显大于表层。通过对海洋温度梯度的经验正交函数 (EOF) 分析，揭示了次表层副热带锋与覆盖大气之间的次季节相互作用。第一种EOF模式主要对应于大气对海洋的影响。随着西风的增强，出现冷海面温度异常（SSTA），然后向下传递影响次表层海洋。然而，第二种 EOF 模式表示海洋对大气的强迫。对于第二种模式，冷海洋温度异常在地下层产生并向上传递，这使得 SST 梯度增加。由于大气斜压增加，增强的西风导致更多的热通量从海洋到大气，这导致 STFZ 的 SSTA 更冷和 SST 梯度更大。因此，冬季中纬度地区开始保持海洋-大气正反馈。