A regional perspective is taken to investigate the intriguing ∼25‐day periodicity in the Southern Hemisphere (SH) baroclinic annular mode (BAM) and the possible underlying mechanisms. Results show that the 25‐day periodicity exists not only in the zonal average but also in the regional average of eddy activity as long as the domain of the average is wide enough to accommodate a wave packet. The favorable domain for the ∼25 days periodicity is located downstream of the largest baroclinicity in midlatitudes. The wave activity developed there can travel circumglobally several times with a typical group velocity of 25 m s⁻¹, and reenter the domain every 12.5 days, setting the base periodicity. A slower oceanic oscillation at a time scale of ∼100 days in the same region appears to select and reinforce the multiples of 12.5 days, giving rise to a pronounced ∼25‐day periodicity in the wave activity.

中文翻译：

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南半球中纬度海洋与大气的次季节振荡之间耦合的证据

采取区域视角来研究南半球（SH）斜压环形模式（BAM）的有趣的〜25天周期及其可能的潜在机制。结果表明，涡旋活动的区域平均值和区域平均值中都存在25天的周期性，只要该平均值的范围足够宽以容纳波包。约25天周期的有利区域位于中纬度最大斜斜度的下游。在那里产生的波活动可以绕全球传播数次，典型群速度为25 m s ^-1，然后每12.5天重新输入一次域，并设置基本周期。在同一地区，在大约100天的时间尺度上，较慢的海洋振荡似乎会选择并加强12.5天的倍数，从而使海浪活动产生明显的〜25天周期性。