Relevance of Submesoscale Surface Currents and High-Resolution Sea Surface Heights in a Coastal Region

Abstract

This paper presents the relevance of submesoscale surface currents and high-resolution sea surface heights (SSHs) in a coastal region in a view of geostrophy and ageostrophy and the feasibility of retrieval of coastal surface currents from SSHs, based on statistical and spectral analyses of (1) observations of high-frequency radar (HFR)-derived surface currents and ltimeterderived geostrophic currents off the Oregon coast and (2) forward regional circulation model simulations forced with realistic wind stress and tides and boundary conditions. As anomalies from the geostrophic currents, which are the balanced currents between the Coriolis force and pressure gradients caused by the slope of SSHs, ageostrophic currents account for up to 50$\%$ of the total variance. The stream functions and SSHs and the stream function-derived currents and geostrophic currents show the high coherence in the low-frequency band ($|\sigma|$ $\leq$ 0.2 cycles per day). The submesoscale ageostrophic currents are primarily associated with near-inertial currents and internal tides, which can be missing components in the currents retrieved from solely submesoscale SSHs. A discussion on limitations to retrieve coastal submesoscale currents using in-situ observations is presented.