On the dynamics of interdecadal thermocline depth and sea surface temperature variability in the low to mid-latitude Pacific Ocean

The role of upper ocean dynamics in generating interdecadal sea surface temperature (SST) variations is investigated with the help of the Australian Bureau of Meteorology Research Centre coupled general circulation model (CGCM) and a first baroclinic mode ("shallow-water'') ocean model (SWM). An empirical orthogonal function analysis is performed on the lowpass filtered SST and vertically averaged temperature in the upper 300 m anomaly data output from a 100-year CGCM simulation. The dominant mode SST spatial pattern and time variability is consistent with the Interdecadal Pacific Oscillation. The SWM is forced by wind stresses from the CGCM 100-year simulation to investigate the role of oceanic Rossby and Kelvin wave propagation on thermocline depth variations. The SWM produces variability similar to the CGCM interdecadal variability. We conclude that large scale wind forced upper ocean dynamics play a dominant role in generating interdecadal upper ocean temperature variations on decadal and longer timescales.