Observations of the Central California Diurnal-Band Velocity and Temperature Field.

The vertical structure of the diurnal-band temperature and velocity fields is described using data from the extensive Santa Barbara Channel-Santa Maria Basin (SBCSMB) data set. The SBCSMB data consists of 10 years of high resolution temperature, velocity and pressure data taken from moorings in the Santa Barbara Channel and on the continental shelf, north of Point Conception. Despite the sub-inertial geographical location, the energetics of the diurnal band fluctuations observed in the area are commensurate with the semi-diurnal fluctuations. We interpret the observed diurnal band fluctuations as locally generated and non-propagating internal structures. Eigenfunction decomposition of the diurnal band temperature fluctuations indicates that three or fewer vertical modes account for greater than 90% of the variance at all mooring locations. These modes strongly resemble the theoretical internal wave modes at the diurnal frequency. Annual cycles in the amplitude of the internal modes correlate strongly with the annual stratification/ destratification cycle of the water column. The diurnal velocity variations correlate with the local diurnal-band tidal elevation. Depth variations in this coherence indicate a baroclinic structure to the diurnal velocity field.