[A-CG32] Climate Variability and Predictability on Subseasonal to Centennial Timescales

[ACG32-P04] Atlantic impacts on subdecadal variation over the tropical Pacific

*望月 崇¹、渡部 雅浩² (1.九州大学大学院理学研究院、2.東京大学大気海洋研究所)

キーワード：数年規模変動、海盆間相互作用、部分同化実験

A subdecadal variation over the tropical Pacific is very distinctively observed in the 2000s, and it may illustrate the low-frequency part and subdecadal modulation of the observed ENSO variability in the tropical Pacific rather than a specific mode independent on the ENSO. Here, we have demonstrated that sea surface temperature (SST) anomalies in the tropical Atlantic contribute to forming high ocean-temperature anomalies in the tropical Pacific in the early 2000s by performing partial data assimilation of a global climate model. Low SSTs over the equatorial Atlantic change the Walker circulation, and the associated weakening of the Pacific trade winds raises the equatorial SST on subdecadal timescales. At the same time, a high SST anomaly is also generated in the off-equatorial North Pacific through deepening of the upper ocean thermocline due to an accompanying anticyclonic surface wind anomaly aloft. While the subtropical North Atlantic SSTs may help the subdecadal warming in the equatorial Pacific, the resultant SST anomalies show a one-year delay in the phase transition and are modestly accompanied by ocean thermocline deepening. These partial data assimilation results exhibit the strong wavelet powers not only in the 2000s but also in the preceding decades, suggesting that the Atlantic impacts potentially work also in other periods.