Radar- and Model-Derived Mass Flux Profiles of a Sea-Breeze Circulation along a Complex Coastline

Sea breezes are perhaps the most widely recognized, and among the most studied examples of density currents in the atmosphere. In general, much of what is known about the vertical structure of sea-breeze circulations has been provided by two-dimensional modeling and theoretical efforts that have disregarded the intricate three-dimensional flow structure that is produced along regions of complex coastline. Studies of sea-breeze structure have generally used the term “return flow” to describe that part of the sea breeze that is returned toward the ocean above the sea-breeze inflow. The structure, strength, and even the existence of the sea-breeze return flow still remain controversial. With few exceptions, observational studies of sea-breeze circulations have been unable to provide the comprehensive analyses necessary to evaluate modeling results because of limited data above the surface. Our investigation addresses these unresolved issues by using dual-Doppler radar measurements collected during the Convection and Precipitation Electrification (CaPE) experiment in combination with idealized three-dimensional model simulations to examine the vertical structure and strength of the sea-breeze inflow and return flows.

Previous observational studies have found difficulties in identifying the depth and magnitude of the return flow because it typically occurs during time periods with shore-perpendicular ambient flow. To address this problem, three-dimensional mass flux profiles were determined using dual-Doppler radar and surface wind fields over a 150-km² region within the sea breeze along the Cape Canaveral, Florida shoreline. This approach allowed the influence of the ambient flow to be eliminated from our analyses. Our observational results show that the sea-breeze return flow had a depth approximately three times greater than the 500-m deep sea-breeze inflow. In addition, the magnitudes of the shore-parallel and shore-perpendicular mass flux profiles were nearly equivalent due to the evolution of the sea breeze in a region of complex coastline. The results from our idealized three-dimensional model simulations of a sea breeze developing along a complex coastline are in good agreement with the observed mass flux profiles retrieved from the CaPE dual-Doppler measurements. Our presentation will include discussion of results from the dual-Doppler radar analyses, mass flux profiles, and model simulations.