Paleoceanography, Vol. 22 , PA4201, October 2007
Abstract
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
semi-diurnally in response to thermal gradients across the Red Sea's
coasts due to 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 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
paleo-insolation regimes, and show small but clear evaporation changes
during the course of the Holocene. Our estimates represent lower
bounds, and we plan to refine them in followup work.