Onshore wind stress and buoyancy flux observed on a dissipative mediterranean beach

A five-month study was performed on an energetic, dissipative beach on a climatologically Mediterranean coastline to explore the wind stress and buoyancy flux. An eddy covariance system was deployed in the intertidal zone resulting in 1088 hours of quality-controlled flux observations at elevations of 1, 3, and 6m on a sandy beach in Monterey, CA. The wind stress angle relative to the mean wind direction varied as much as 31o, representing one standard deviation, with a range of ±151o. The variations were dependent on the wind angle relative to the swell direction and shoreline, which directed the stress vector to the left for winds approaching from 0o>θ>-45o and to the right for winds approaching from -45o>θ>-80o, where 0o is onshore. The stress angle was independent of stability, stress, and wind speed. Air-ocean temperature differences produced unstable conditions 88% of the time in contrast to the near neutral conditions that dominate the open ocean. Based on flux footprints, the surf zone was found to be a source of positive buoyancy and heat flux contributing to the unstable conditions. Minimum buoyancy fluxes were observed with the flux footprints that were farther offshore centered outside the surf zone, resulting in stable conditions.http://archive.org/details/onshorewindstres1094547980Lieutenant Commander, United States NavyApproved for public release; distribution is unlimited