Energy Loss from Transient Eddies due to Lee Wave Generation in the Southern Ocean

Luwei Yang,Andrew M Hogg,Bernadette M Sloyan,Maxim Nikurashin

doi:10.1175/jpo-d-18-0077.1

Abstract

ABSTRACTObservations suggest that enhanced turbulent dissipation and mixing over rough topography are modulated by the transient eddy field through the generation and breaking of lee waves in the Southern Ocean. Idealized simulations also suggest that lee waves are important in the energy pathway from eddies to turbulence. However, the energy loss from eddies due to lee wave generation remains poorly estimated. This study quantifies the relative energy loss from the time-mean and transient eddy flow in the Southern Ocean due to lee wave generation using an eddy-resolving global ocean model and three independent topographic datasets. The authors find that the energy loss from the transient eddy flow (0.12 TW; 1 TW = 1012 W) is larger than that from the time-mean flow (0.04 TW) due to lee wave generation; lee wave generation makes a larger contribution (0.12 TW) to the energy loss from the transient eddy flow than the dissipation in turbulent bottom boundary layer (0.05 TW). This study also shows that the energy loss from the time-mean flow is regulated by the transient eddy flow, and energy loss from the transient eddy flow is sensitive to the representation of anisotropy in small-scale topography. It is implied that lee waves should be parameterized in eddy-resolving global ocean models to improve the energetics of resolved flow.

Highlights

The importance of the Southern Ocean in the global circulation and climate is largely attributed to its energetic transient eddy field (Rintoul and Naveira Garabato 2013, and references therein)
The equilibration of the transient eddy field is important because the eddy kinetic energy (EKE) is often used as an indicator of how eddies respond to varying wind stress and regulate the Antarctic Circumpolar Current (ACC) transport and MOC strength
Our results show that the lee wave generation is potentially more important than the turbulent processes in the turbulent bottom boundary layer (TBBL) for the energy loss from the time-mean flow, albeit weaker than that associated with the total flow

Summary

Introduction

The importance of the Southern Ocean in the global circulation and climate is largely attributed to its energetic transient eddy field (Rintoul and Naveira Garabato 2013, and references therein). We estimate the relative energy loss from the time-mean and transient eddy field in the Southern Ocean (408–658S) due to lee wave generation by applying mean–eddy decomposition to modeled velocity fields.

Results

Conclusion