Abstract:
Observational evidence of seasonal variability below the main thermocline
in the eastern North Atlantic is described, and a theoretical model
of oceanic response to seasonally varying windstress forcing is constructed
to assist in the interpretation of the observations. The observations are
historical conductivity-temperature-depth data from the Bay of Biscay
region (2° to 20°W, 42° to 52°N), a series of eleven cruises over the three
years 1972 through 1974, spaced approximately three months apart. The
analysis of the observations utilizes a new technique for identifying the
adiabatically leveled density field corresponding to the observed density
field. The distribution of salinity anomaly along the leveled surfaces is
examined, as are the vertical displacements of observed density surfaces
from the leveled reference surfaces, and the available potential energy.
Seasonal variations in salinity anomaly and vertical displacement occur
as westward propagating disturbances with zonal wavelength 390 (±50) km,
phase 71 (±30) days from 1 January, and maximum amplitudes of ±30 ppm and
±20 db respectively. The leveled density field varies seasonally with an
amplitude corresponding to a thermocline displacement of ±15 db.
The observations are consistent with the predictions of a model in
which an ocean of variable stratification with a surface mixed layer and
an eastern boundary is forced by seasonal changes in a sinusoidal windstress
pattern, when windstress parameters calculated from the observations
of Bunker and Worthington (1976) are applied.
