Mediterranean Sea heat budget

The Mediterranean Sea, being a semienclosed system, is an ideal test basin for the climate-research community, because it provides a good opportunity to investigate the closure of its hydrological and heat budgets. The closing of such budgets engenders more confidence that our understanding in many geophysical fields, such as sea air interactions, modelling and measuring solar and terrestrial fluxes and hydrological quantities, is adequate.

Evaporation losses from the Mediterranean Sea are larger than the freshwater gains, creating large salinity values. The effect of the above is: a) an inflow of warmer, less salty Atlantic water from Gibraltar at the surface; and b) an outflow of cooler, saltier Mediterranean water at a larger depth. The warm inflow adds to the Mediterranean heat budget between 5 and 7 W m~2. The outflow spreads across the Atlantic, with some of it moving northwards and affecting the thermohaline circulation of the Northern Atlantic. It has been argued that the greenhouse effect coupled with the damming of the Nile, will increase the Mediterranean outflow, displacing the North Atlantic Drift and creating conditions similar to the ones that triggered the last ice age. Therefore, a better understanding of the Mediterranean Sea heat and hydrological budgets would help us to better understand climate change on a regional scale.

8.9.1 The heat budget equation

The heat budget, Qt is determined from the radiative and turbulent energy components. The radiative ones are the net solar (shortwave) flux Qs absorbed by the sea and the net terrestrial (longwave) flux Qi emitted by the sea. The turbulent components are the latent Qe and the sensible heat flux, Qh corresponding to evaporative and convective energy losses of the sea, respectively,

Qt should balance the heat flux advected into the sea from Gibraltar, Ah, the heat flux entering the sea from the bottom surface G, and the change AH in the heat content H of the sea, so that

G can be assumed to be zero. Although on an annual basis AH can be neglected, on a monthly scale it is very important, as will be shown later. The advected heat fluxes from the Black Sea and freshwater influx via rivers are estimated to be less than 1 W m~2 each, and so are considered negligible.

The heat content H of the Mediterranean Sea has a strong seasonality and affects significantly the seasonal variation of the heat budget. To derive it, we need to divide the Mediterranean into J x L x K three-dimensional water cells, with J, L and K corresponding to the partition with respect to latitude, longitude and depth, respectively. H can then be estimated from (e.g. Krahmann et al. 2000)

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