Field observations and modeling of surfzone sensible heat flux

Abstract

Surfzone sensible heat flux (H S,SZ ) obtained through direct eddy-covariance estimates was measured at four different sandy beach sites along Monterey Bay, California. The H S,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 H S,SZ is 2 times the modeled interfacial sensible heat (H S,int ) using COARE3.5. A formulation for estimating sensible heat flux from spray droplets (H S,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 H S,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 H S,spray to the COARE3.5 H S,int gives values similar to the observed surfzone H S,SZ , highlighting the importance of depth-limited wave-breaking processes to sensible heat flux. Measured H S,SZ values are an order of magnitude larger than simultaneous open ocean observations.