Climatological evaporation seasonality in the northern Red Sea

[1] The dynamic and thermodynamic processes that underlie the exceptionally high evaporation over the northern Red Sea are examined. Through a combination of data analysis and a simple numerical model we show that the key boundary layer dehumidifier is ageostrophic cross-channel sea breezes. This circulation develops semidiurnally in response to thermal gradients across the Red Sea's coasts because of disparate land-ocean heat capacities. During the summer day the thermally induced high-pressure center over the Red Sea axis results in near-surface flows from the Red Sea toward the neighboring deserts. The strong divergence associated with these flows is maximized along the Red Sea axis and is accompanied by strong subsidence that suppresses boundary layer relative humidity by both reducing specific humidity and increasing temperatures. Because the summer nighttime reversed thermal gradients are smaller in magnitude, the daytime circulation dominates over the nighttime in summer and thus dominates over the daily and seasonal means. Following similar reasoning, we also devise a winter dehumidifier. We conclude by advancing a simple means of estimating Red Sea evaporation under diverse paleoinsolation regimes, and we show small but clear evaporation changes during the course of the Holocene. Our estimates represent lower bounds, and we plan to refine them in follow-up work.