Abstract:

In this presentation, I will review observations of trapped baroclinic wave energy in a range of ocean settings, focusing primarily on semidiurnal coastal trapped waves and their effects on flow variability in inner shelf environments.  Semidiurnal variability of alongshore currents for the inner shelf  of the Southern California Bight is investigated using a seven year velocity and pressure time series from three locations near San Diego. Analysis reveals that the M2-frequency alongshore current varies significantly over spatial scales of O(10km), inconsistent with a progressive surface tide. The observed variability is attributed to the influence of a northward-propagating, superinertial coastal trapped wave (CTW) that generates a quasi-barotropic (QBT) flow, defined as the portion of the depth-averaged alongshore current that not driven by the surface tide. A superinertial CTW model, forced by realistic bathymetry and stratification conditions, suggests that the dominant mode of variability is likely a mode-1 CTW with a wavelength of approximately 50 km. The observations and model also reveal that seasonal changes in stratification modulate the wavelength and phase speed of the CTW, leading to a seasonal pattern in the phasing of the quasi-barotropic alongshore flow. These findings shed light on the complex dynamics governing semidiurnal inner shelf variability in the Southern California Bight and on the importance of considering the effects of superinertial CTWs in interpreting coastal dynamics.