Field Observations and Modeling of Surfzone Sensible Heat Flux

Abstract

AbstractSurfzone sensible heat flux (HS,SZ) obtained through direct eddy-covariance estimates was measured at four different sandy beach sites along Monterey Bay, California. The HS,SZ source region is estimated from a footprint probability distribution function (pdf) model and is only considered when at least 70% of the footprint pdf occupies the surfzone. The measured HS,SZ is 2 times the modeled interfacial sensible heat (HS,int) using COARE3.5. A formulation for estimating sensible heat flux from spray droplets (HS,spray) generated during depth-limited wave breaking is developed. The sea-spray generation function for droplet radii ranging over 0.1 < ro < 1000 μm is based on self-similar spectra of spray droplets measured from the surfzone forced by the average depth-limited breaking wave dissipation across the surfzone. However, it is shown that the size of the spume droplets that contribute to HS,spray is limited owing to the relatively short residence time in air as the droplets fall to the sea surface during wave breaking. The addition of the surfzone-modeled HS,spray to the COARE3.5 HS,int gives values similar to the observed surfzone HS,SZ, highlighting the importance of depth-limited wave-breaking processes to sensible heat flux. Measured HS,SZ values are an order of magnitude larger than simultaneous open ocean observations.