Eddy flux observations of evaporation and vapor advection in the Gulf of Aqaba (Eilat), Red Sea

There is a large uncertainty around the rates of evaporation from desert enclosed seas, and in particular the Red Sea. The Gulf of Aqaba is long and narrow and is partially isolated from the Red Sea and the Indian Ocean by shallow and narrow straits. The long fringing reef of the Red Sea has a large economic importance to the region's tourism. In the northern part of the Red Sea, vertical mixing of the water column, which is driven by evaporation, supplies nutrients to the shallow water and, at high levels, results in favorable conditions for algae over corals, and thus, will lead to the destruction of corals. The local weather and sea surface temperature are also affected by the rates of evaporation. There are two compounding phenomena that complicate the estimation of evaporation rate in this region: (1) Although the wind is mostly oriented along the long axis of the narrow Gulf, advection of water vapor towards the dry desert surrounding the Red Sea may account for large amounts of water. (2) In the summer, the mean sea surface temperature is colder than the warm, dry desert air, leading to a thin stable boundary layer above the sea that may suppress evaporation. Atmospheric and oceanic models of the Red Sea area have run into difficulties in estimating the evaporation rates. There are very few locations where the temperature and humidity are measured routinely. Direct measurements of evaporation or on-shore advection of water vapor were not previously conducted in this region. In March 2009 we set up two eddy flux towers at the Inter-University Institute for Marine Science in Eilat, Israel, at the north western shore of the Gulf of Aqaba. We conducted measurements of water vapor wind and other meteorological conditions. We used the eddy-covariance technique to calculate the mass balance of water in the atmosphere above the coral lagoon near the shore. Our measurements show that a combination of advection toward land and stability conditions of the boundary layer due to negative water-air temperature gradient in hot days significantly affects the evaporation rates.