Baroclinic Tidal Energetics Inferred from Satellite Altimetry

Abstract

Abstract The energetics of baroclinic tides are analyzed using the High Resolution Empirical Tide (HRET) model. The HRET model consists of maps of the sea surface height (SSH) anomaly associated with that component of the tides’ baroclinic pressure fields, which are phase locked with the gravitational tidal potential. The dynamical assumptions underpinning the transformation of SSH into corresponding baroclinic velocity and energy flux are examined critically through comparisons with independent information and term balances in the equations of motion. It is found that the HRET-derived phase speed of the mode-1 baroclinic tide agrees closely with the phase speed predicted by the theory for long waves propagating through the observed climatological stratification. The HRET SSH is decomposed into contributions from separate vertical modes, and the energy, energy flux, and energy flux divergence of mode-1 (for M2, S2, K1, and O1) and mode-2 (for M2) tides are computed, with an emphasis on the most accurately determined mode-1 M2. The flux divergence of HRET mode-1 M2, computed as the contour integral of the outbound normal flux around strong generation regions, is found to correspond with independent estimates of the area-integrated barotropic-to-baroclinic-mode-1 conversion, although, there is considerable uncertainty in both the flux divergence and the barotropic-to-baroclinic conversion. Further progress on mapping the baroclinic tidal energetics from altimeter observations will require more dynamically complete descriptions of the baroclinic tides than can be provided by kinematic models of SSH, such as HRET.