Kinetic energy of coherent eddy features from sea surface altimetry.

Josué Martínez Moreno Sr, Andrew M Hogg, Andrew E Kiss, Navid Constantinou and Adele K Morrison, Australian National University, Research School of Earth Sciences, Canberra, ACT, Australia
Abstract:
The mesoscale eddy field plays a key role in the mixing, transport of physical and biological properties, and redistributes energy in the ocean. Eddy kinetic energy is commonly defined as the kinetic energy of the time-varying component of the velocity field.
However, this definition contains all processes that vary in time, including coherent mesoscale eddies, jets, waves, and large-scale motions. In this study, we focus on the transient kinetic energy contained in coherent mesoscale eddies (transient eddy kinetic energy).

We have investigated the trends of transient kinetic energy and transient eddy kinetic energy in the Southern Ocean (SO) using Satellite Sea Surface Height anomaly (AVISO+). The transient kinetic energy and transient eddy kinetic energy in the Indian and Pacific sectors of the SO exhibits a significant trend over the satellite altimetry era as a response to the strengthening of the SO wind stress, consistent with previous studies (Hogg et al., 2015).
Transient Kinetic Energy trends are explained by a combination of the changes in the coherent eddy field ( approximately 1/3 of the TKE ) and other non-coherent processes ( 2/3 of the TKE ). Therefore, it is clear that the contribution of non-coherent processes is fundamental to further understand the transient kinetic energy.

This trend in the transient eddy kinetic energy can been attributed with an increase of the coherent eddy amplitude and a decrease in eddy numbers in the SO since 1993. Additionally, there is a correlation between the 1-3 year lagged wind stress and the amplitude of the coherent eddy amplitude over the last two decades in the SO. These results suggest a response of the coherent eddy field to the intensification of westerly winds through the readjustment of coherent eddy amplitude, demonstrating a potential connection between the coherent eddy field and climate change in the SO.