Decadal Variation of Mesoscale Eddy Activity in the South Pacific Subtropical Counter-current

The South Pacific Subtropical Counter-current (STCC), located in the western south Pacific (165°E-130°W, 21°-29°S), is a region characterized by enhanced mesoscale eddy activity. Previous work has examined baroclinic instabilities as a possible source of this eddy activity. This study expand upon that work, and will use ARGO float data to examine spatial patterns and long-term temporal variations in the zonal current shearing and density stratification – the dominant factors in determining the strength of the baroclinic instability.

A low-frequency warming of the upper ocean is found with widespread consistency throughout the STCC region. This warming increases stratification and causes the region to be less baroclinically unstable. However, there is found to be large spatial variation in the shearing of the system, with the eastern and western portions of the region following opposite trends. These spatial patterns in shearing show agreement with the spatial patterns of variability of the eddy kinetic energy, and is found to account for the largest contribution to long-term variations in the STCC mesoscale eddy activity since 2001.