Jones, Ian

Leach, Harry

Ian Jones

Harry Leach

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Isopycnic modeling of the North Atlantic heat budget

A 2° resolution version of the Miami Isopycnic Coordinate Ocean Model is used within an idealized basin to examine the ocean heat budget. Simplified seasonal wind stress and thermohaline forcing, based on observational data of the North Atlantic, are used to drive the model. Following a 30‐year spin‐up, the model reaches a state of little annual heat content change, at which point a detailed study of the heat budget is performed. The heat budget is split into the components of surface forcing, diffusion, Ekman pumping, Ekman transport, and non‐Ekman advection. Both annual and seasonal results are obtained. Analysis of the heat budget reveals different annual balances to exist in different ocean regions. In the subpolar gyre the principal balance is between cooling caused by surface fluxes and warming due to geostrophic advection. However, in the subtropical gyre, where net surface fluxes are small, Ekman pumping balances geostrophic advection. As such, the Ekman pumping is seen to be important for supplying the necessary heat for subduction to take place. An investigation of the Ekman compensatory flow is undertaken. It is shown that the exact temperature and, consequently, the depth of this flow are important for determining the Ekman heat content change. The results here tentatively suggest this depth to be in the upper thermocline. Subduction rates are calculated and shown to be reasonable. The seasonal heat budget is dominated everywhere by surface fluxes. All other terms have negligible seasonal cycles, except for the Ekman terms, which exhibit a limited seasonal variation. In doing so the Ekman terms are seen to control the seasonal cycle of the transport of heat. This is due to their dependency on not only the time variation in wind stress but also the degree of stratification of the upper ocean.</jats:p

Isopycnic modeling of the North Atlantic heat budget

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