Diurnal Variability of Ocean Temperature Off Pt. Sal, Central California

Diurnal-band temperature (DU-T) variability is investigated over 30 days from measures of temperature over the vertical obtained by 78 moorings deployed in the Santa Monica Basin near Pt. Sal (PS), California. DU-T variability accounts for 3.6%-23% of the total variability. Vertical empirical orthogonal function mode-1 DU-T variability accounts for an average of 86% of the total vertical DU-T variability at each mooring, is greatest north of PS where its vertical structure is baroclinic, and weakest south of PS where its vertical structure is surface intensified. Spatial complex empirical orthogonal function mode-1 DU-T accounts for 73% of the total DU-T over the region, reveals an onshore baroclinic DU-T propagation of similar to 0.5 m/s, and a previously observed equatorward baroclinic DU-T propagation of similar to 1.9 m/s along the coast north of PS. Dominant vertical mode-1 diurnal-band baroclinic velocity (DU-w) variability at each mooring exhibits a two-layer structure that is 180 degrees out of phase with maxima near the surface and the bottom, and resembles the DU-T propagation. DU-T variability mechanisms include wind-forced deepening of the surface mixed layer, inertial motions, upwelling, and barotropic and baroclinic tides. Among these concomitant diurnal mechanisms, wind-driven inertial motions are likely the primary mechanism influencing DU-T variability during upwelling-favorable conditions owing to coherence between observed DU-w and the predicted inertial response to wind-forcing. Further, spatial mode-1 DU-T is correlated and coherent with spatial mode-1 DU-w and diurnal wind-forcing. In addition to describing predominant DU-T variability patterns, these findings have important implications regarding spatial patterns in biological recruitment, transport, and settlement.