Abstract We use an interannually forced version of the Parallel Ocean Program, configured to resolve mesoscale eddies, to close the global eddy potential energy (EPE) budget associated with temperature variability. By closing the EPE budget, we are able to properly investigate the role of diabatic processes in modulating mesoscale energetics in the context of other processes driving eddy–mean flow interactions. A Helmholtz decomposition of the eddy heat flux field into divergent and rotational components is applied to estimate the baroclinic conversion from mean to eddy potential energy. In doing so, an approximate two-way balance between the “divergent” baroclinic conversion and upgradient vertical eddy heat fluxes in the ocean interior is revealed, in accordance with baroclinic instability and the relaxation of isopycnal slopes. However, in the mixed layer, the EPE budget is greatly modulated by diabatic mixing, with air–sea interactions and interior diffusion playing comparable roles. Globally, this accounts for ∼60% of EPE converted to EKE (eddy kinetic energy), with the remainder being dissipated by air–sea interactions and interior mixing. A seasonal composite of baroclinic energy conversions shows that the strongest EPE to EKE conversion occurs during the summer in both hemispheres. The seasonally varying diabatic processes in the upper ocean are further shown to be closely linked to this EPE–EKE conversion seasonality, but with a lead. The peak energy dissipation through vertical mixing occurs ahead of the minimum EKE generation by 1–2 months.
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The Global Sink of Available Potential Energy by Mesoscale Air‐Sea Interaction
The thermal component of oceanic eddy available potential energy (EPE) generation due to air‐sea interaction is proportional to the product of anomalous sea surface temperature (SST) and net air‐sea heat flux (SHF). In this study we assess EPE generation and its timescale and space‐scale dependence from observations and a high‐resolution coupled climate model. A dichotomy exists in the literature with respect to the sign of this term, that is, whether it is a source or a sink of EPE. We resolve this dichotomy by partitioning the SST and net heat flux into climatological mean, climatological seasonal cycle, and remaining transient contributions, thereby separating the mesoscale eddy variability from the forced seasonal cycle. In this decomposition the mesoscale air‐sea SST‐SHF feedbacks act as a 0.1 TW global sink of EPE. In regions of the ocean with a large seasonal cycle, for example, midlatitudes of the Northern Hemisphere, the EPE generation by the forced seasonal cycle exceeds the mesoscale variability sink, such that the global generation by seasonal plus eddy variability acts as a 0.8 TW source. EPE destruction is largest in the midlatitude western boundary currents due to mesoscale air‐sea interaction and in the tropical Pacific where SST variability is due mainly to the El Niño–Southern Oscillation. The EPE sink in western boundary currents is spatially aligned with SST gradients and offset to the poleward side of currents, while the mean and seasonal generation are aligned with the warm core of the current. By successively smoothing the data in space and time we find that half of the EPE sink is confined to timescales less than annual and length scales less than 2°, within the oceanic mesoscale band.
more » « less- PAR ID:
- 10375668
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Advances in Modeling Earth Systems
- Volume:
- 12
- Issue:
- 10
- ISSN:
- 1942-2466
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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