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

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

*Takashi Mochizuki¹, Masahiro Watanabe² (1.Department of Earth and Planetary Sciences, Kyushu University, 2.Atmosphere-Ocean Research Institute, The University of Tokyo)

Keywords:subdecadal variability, interbasin interaction, partial data assimilation

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.