The Heat and Freshwater Budgets of the Red Sea

Abstract

The heat and freshwater transports through the Strait of Bab el Mandab, connecting the Red Sea with the open ocean, are reviewed and used to test air?sea fluxes from a revised version of the Comprehensive Ocean?Atmosphere Data Set (UWM/COADS). Using historical data for the volume fluxes and water properties, the annual-mean net heat transport through the strait is found to require an average surface heat loss of 8 ± 2 W m?2, while the requirement for conservation of salt in the basin implies a net evaporation rate of 1.60 ± 0.35 m yr?1, lower than previously considered. The air?sea heat fluxes from UWM/COADS overestimate the total heat flux by nearly 100 W m?2; the discrepancy is attributed to systematic errors in the bulk formulas used to calculate the heat flux components. In particular, insolation appears to be overestimated by 36 W m?2, largely due to the neglect of aerosols. The effect of these is determined from ground stations and satellite data on the optical thickness index. The net longwave radiation appears to be underestimated by 21 W m?2 or more. The latent heat flux from UWM/COADS may also be underestimated as it corresponds to an evaporation rate of 1.60 m yr?1, less than the 1.75 ± 0.35 m yr?1 implied by the net evaporation defined from the water budget, plus an annual average precipitation rate of 0.15 m yr?1 from UWM/COADS. The net evaporation is the main contributor to the annual-mean buoyancy flux of approximately 2 ? 10?8 m2 s?3.