Dl. Rudnick, INTENSIVE SURVEYS OF THE AZORES FRONT .2. INFERRING THE GEOSTROPHIC AND VERTICAL VELOCITY-FIELDS, J GEO RES-O, 101(C7), 1996, pp. 16291-16303
The geostrophic and vertical velocity fields are inferred using densit
y and horizontal velocity data from three SeaSoar/acoustic Doppler cur
rent profiler surveys of the Azores Front. The analysis is a two-step
procedure consisting of (1) objective analyses to reflect the observed
length scales and (2) dynamical adjustments so that the density field
is statically stable and the velocity field is in geostrophic balance
. The vertical velocity is inferred using a version of the quasi-geost
rophic omega equation in which the stratification is allowed to vary i
n the horizontal. The resulting vertical velocity peaks at 2 x 10(-4)
m s(-1) at 200-300 m. There is a tendency for the denser water to the
north of the front to be downwelled, while the warmer water to the sou
th is up welled. The implied heat flux exceeds 10 W m(-2) near 100-m d
epth, so the upper 100 m is warmed while the lower water column is coo
led, tending to stratify the upper ocean. Ageostrophic horizontal flow
is toward the dense side of the front at the surface. The dominant te
rms in the density balance are time rate of change and horizontal adve
ction. The inferred circulation cells may be an important mechanism of
subduction in the upper ocean.