Evaluation of dynamical properties of the surface currents and sea surface heights in a coastal region

Abstract

We conduct statistical and spectral analyses of (1) observations of coastal radar-derived surface currents and altimeter-derived geostrophic currents and (2) forward regional circulation model simulations forced with realistic wind stress, tides, and boundary conditions off the Oregon coast in view of the geostrophy and ageostrophy and the balanced and unbalanced motions. The delineation of balanced and unbalanced motions was investigated with the Helmholtz decomposition in the physical and spectral spaces and wave-vortex spectral decomposition. The observed and simulated coastal surface currents do not exhibit a clear decomposition of the balanced motions and unbalanced motions because wave-vortex decomposition may not always work in the coastal regions where multiple sources of dominant variances are present. On the other hand, the stream functions obtained from the Helmholtz physical decomposition can be a proxy for the balanced motions when the variance in vertical currents is weak. The submesoscale ageostrophic currents account for up to 50$\%$ of the total variance and are primarily associated with near-inertial currents and internal tides, which can be missing components in the currents retrieved from only submesoscale sea surface heights (SSHs). As the pure SSHs may not constrain all submesoscale ageostrophic components, the missing variance in the submesoscale SSH observations is required to complement other highresolution {\it in-situ} observations, including HFR-derived surface velocities and surface drifter-derived tracks in view of constructive data integration to resolve submesoscale currents.