The Asian-Pacific Oscillation (APO), featuring a seesaw pattern in the upper-tropospheric temperatures between Asia and the North Pacific, plays profound roles in the Northern Hemispheric climate anomalies. So, its variability and associated physical mechanisms are of great interest. Although progress has been achieved for the APO variability at the interannual time scale, the understanding of its interdecadal variability remains relatively poor. Based on the twentieth-century reanalysis and the simulations of the preindustrial control, Pacific pacemaker, and large ensemble experiments, this study reports a salient contribution of the Pacific Decadal Oscillation (PDO) to the interdecadal variability of the APO during summer, featured as a warm (cold) PDO phase accompanying a negative (positive) APO polarity. During the warm PDO phase, the sea surface temperature (SST) warming over the eastern Pacific is conducive to local ascending anomalies, which teleconnect with descending anomalies over the Tibetan Plateau through zonal vertical circulations. The anomalous ascent (descent) over the eastern Pacific (Tibetan Plateau) tends to strengthen (weaken) the atmospheric heating, beneficial for a warming (cooling) of the troposphere in situ. In addition, the PDO-related meridional SST gradient anomalies favor a southward shift of the subtropical jet stream, weakening the South Asian high and the North Pacific trough in the upper troposphere, which corresponds to the atmospheric situation of a negative APO phase. Quantitative analysis from the large ensemble simulations indicates that the PDO may contribute to approximately 48% of recent APO interdecadal variation from the negative phase to the positive phase in the late 1990s.

中文翻译：

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太平洋年代际涛动与亚太涛动年代际变化的关系


亚洲太平洋涛动（APO）以亚洲和北太平洋之间对流层上层温度的跷跷板模式为特征，在北半球气候异常中发挥着深远的作用。因此，它的变异性和相关的物理机制引起了人们的极大兴趣。尽管在年际时间尺度上 APO 变异性已经取得了进展，但对其年代际变异性的了解仍然相对较少。基于二十世纪的再分析和对工业化前控制、太平洋起搏器和大型集合实验的模拟，本研究报告了太平洋年代际振荡（PDO）对夏季 APO 年代际变化的显着贡献，其特点是暖（冷）PDO 阶段伴随着负（正）APO 极性。在温暖的PDO阶段，东太平洋海表温度（SST）变暖有利于局部上升异常，并通过纬向垂直环流与青藏高原下降异常遥相关。东太平洋（青藏高原）的异常上升（下降）往往会加强（减弱）大气加热，有利于对流层原位变暖（变冷）。此外，与PDO相关的经向海温梯度异常有利于副热带急流南移，削弱了对流层高层的南亚高压和北太平洋槽，这对应了APO负位相的大气状况。大型集合模拟的定量分析表明，PDO 可能对 20 世纪 90 年代末近代 APO 从负位相到正位相的年代际变化贡献了约 48%。