The heat budget in the North Atlantic subtropical frontal zone is exam
ined using moored measurements of horizontal velocity, temperature, an
d surface heat flux obtained during the Frontal Air-Sea interaction Ex
periment (FASINEX). The three moorings used in this calculation define
d a triangle with base of 19 km and height of 28 km, and were densely
instrumented from the surface to 160-m depth. Empirical orthogonal fun
ctions (EOFs) are employed to identify components of current and tempe
rature variability with scales that are resolved by the observations.
A least squares fit to the EOF-filtered data is used to derive maps of
velocity and temperature. The temperature field is dominated by the p
assage of fronts, with the highest variability at 160 m. Horizontal te
mperature gradients at 160 m peak at values approaching 1 x 10(-4) deg
rees-C m-1 and are indicative of a tilting of the seasonal thermocline
. Velocities are directed primarily along isotherms and are swifter at
the surface than at depth. The heat budget of the upper 160 m, for pe
riods longer than 48 hours, is essentially a balance between rate of c
hange of heat and horizontal advection; the correlation between these
terms is 0.7. A simple explanation is the northward advection by a mea
n current of a series of fronts. The effect of surface heating becomes
apparent in the upper 40 m, notably at the diurnal frequency and its
first harmonic. An imbalance in the mean (102 days) heat budget can be
rectified by a mean downwelling velocity of 5 x 10(-5) m s-1 at 160 m
.