The response of the marine atmospheric boundary layer to the strong sea sur
face temperature (SST) gradient across the warm Agulhas Current was studied
in the Agulhas Current Air-Sea Exchange Experiment. south of Port Alfred,
South Africa. Shipboard meteorological and oceanographic measurements and r
adiosonde ascents are used to describe this response for wind regimes that
are approximately parallel to the current. Surface hear fluxes increased by
over 200 w m(-2) from the shelf to the current while the sensible heat flu
x reversed sign. A characteristically stable boundary layer over the cool s
helf waters was replaced by an unstable convective boundary layer over the
current. The mean specific humidity and potential temperature of the bounda
ry layer increased significantly over the current by 25% and 10% with a con
comitant boundary layer deepening of 40 m (degrees C)(-1) SST In the presen
ce of alongcurrent winds an atmospheric moisture and thermal front develope
d over the inshore SST front, This is attributed to the horizontal gradient
in the surface heat fluxes. The strong SST front owes its presence here to
the juxtaposition of the warm current and an inshore kinematically driven
subsurface upwelling cell whose surface expression is modulated by the wind
stress.