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- Title
Role of Frictional Processes in Mesoscale Eddy Available Potential Energy Budget in the Global Ocean.
- Authors
Yang, Peiran; Jing, Zhao; Wang, Hong; Wu, Lixin; Chen, Yuhu; Zhou, Shenghui
- Abstract
Mesoscale eddies in the global ocean are thought to be powered primarily through transfer from available potential energy stored in mean flows to eddy available potential energy (EAPE). Part of the EAPE is further converted to eddy kinetic energy (EKE) with the residue dissipated through diabatic processes. Currently, the effect of frictional processes on the EAPE budget has not been thoroughly analyzed. Using an eddy‐resolving (1/10°) global climate simulation, we demonstrate that frictionally driven mesoscale eddy flow plays an important role in the EAPE budget, accounting for more than 30% of the EAPE‐to‐EKE conversion in the global ocean and dominating its seasonal cycle. This role can be understood based on the turbulent thermal wind balance under which the frictional force induces an ageostrophic secondary circulation producing a prominent EAPE‐to‐EKE conversion in the winter surface boundary layer. Plain Language Summary: The swirling mesoscale (100–1,000 km) eddies are a prominent feature in the upper ocean. Their vigorous currents are powered primarily by releasing the potential energy stored in the tilting isopycnals (surface of constant density). To date, this release is prevailingly attributed to baroclinic instability, a process lowering the center of gravity by slumping isopycnals in a frictionless manner. However, based on a state‐of‐the‐art global climate simulation resolving mesoscale eddies, we demonstrate that frictional forces play an important role in converting the potential energy to kinetic energy of mesoscale eddies. It generates an overturning flow that is directed upwards on the buoyant side and downwards on the dense side, lowering the center of gravity. This frictionally driven overturning flow is stronger in winter than in summer as a result of active turbulent mixing induced by intense sea surface cooling and wind stirring in winter. Accordingly, the conversion of potential energy to kinetic energy of mesoscale eddies exhibits a distinct seasonal cycle in the global ocean. Key Points: Frictional processes make an important contribution to the conversion of eddy potential energy to kinetic energy and its seasonal changesThe effects of frictional processes on the eddy potential energy budget can be understood based on the turbulent thermal wind balance
- Subjects
MESOSCALE eddies; POTENTIAL energy; TURBULENT mixing; FRICTION; KINETIC energy; BAROCLINICITY; SWIRLING flow
- Publication
Geophysical Research Letters, 2022, Vol 49, Issue 13, p1
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2021GL097557