Mid- to Inner-Shelf Coupled ROMS–SWAN Model–Data Comparison of Currents and Temperature: Diurnal and Semidiurnal Variability

Accurately representing diurnal and semidiurnal internal variability is necessary to investigate inner-shelf to midshelf exchange processes. Here, a coupled Regional Ocean Model System (ROMS)–Simulating Waves Nearshore (SWAN) model is compared to observed diurnal and semidiurnal internal tidal variability on the mid and inner shelf (26–8 m water depth) near San Pedro Bay, California. Modeled mean stratification is about one-half of that observed. Modeled and observed baroclinic velocity rotary spectra are similar in the diurnal and semidiurnal band. Modeled and observed temperature spectra have similar diurnal and semidiurnal band structure, although the modeled is weaker. The observed and modeled diurnal and semidiurnal baroclinic velocity- and temperature-dominant vertical structures are similar and consistent with mode-one internal motions. Both observed and modeled diurnal baroclinic kinetic energy are strongly correlated to diurnal wind forcing and enhanced by subtidal vorticity-induced reduction in the inertial frequency. The mid- and inner-shelf modeled diurnal depth-integrated heat budget is a balance between advective heat flux divergence and temperature time derivative. Temperature–velocity phase indicates progressive semidiurnal internal tide on the midshelf and largely standing internal tide on the inner shelf in both observed and modeled. The ratio of observed to modeled inferred phase speed is consistent with the observed to modeled stratification. The San Pedro Bay modeled semidiurnal internal tide has significant spatial variability, variable incident wave angles, and multiple local generation sites. Overall, the coupled ROMS–SWAN model represents well the complex diurnal and semidiurnal internal variability from the mid to the inner shelf.