[A-CG45] [EE] Multi-scale ocean-atmosphere interaction in the tropical Indo-Pacific region

[ACG45-P02] Decadal variations in the tropical Indo-Pacific sea surface height based on a historical OGCM simulation

*Goro Yamanaka¹, Hiroyuki Tsujino¹, Hideyuki Nakano¹, Shogo Urakawa¹, Kei Sakamoto¹ (1.Meteorological Research Institute)

Keywords:decadal variability, sea surface height, ocean general circulation model, Indo-Pacific

We examine long-term sea surface height (SSH) variations in the tropical Indo-Pacific Oceans, using a historical OGCM simulation (1948-2006). It is known that the SSH pattern in the tropical Pacific is not a mirror image on decadal timescales. For example, it is north-south asymmetric during the positive phase (1977-1987), while it is north-south symmetric during the negative phase (1996-2006). EOF analysis of tropical Pacific SSH anomalies indicates four dominant modes: east-west seesaw pattern (1^st mode), north-south asymmetric pattern (2^nd mode), north-south symmetric pattern (3^rd mode) with longer time scales, and north-south symmetric pattern (4^th mode) with ENSO timescales. The SSH pattern during the positive phase is largely explained by the combination of the four modes including a north-south asymmetric pattern (2^nd mode), while the north-south symmetric 1^st and 4^th modes are dominant during the negative phase. This answers the question why the tropical Pacific SSH pattern is not a mirror image on decadal timescales. Overall, the tropical Indo-Pacific SSH decadal variability is correlated with the wind stress curl. The 1^st and 3^rd modes are associated with the tropical Indian Ocean SSH variability through the atmospheric bridge. We also discuss a possible reason for the enhancement of the trade winds over the tropical Pacific after the late 1990s, which leads to the enhanced negative phase hereafter.