Observations and Modelling of Fronts and Frontogenesis

tracer by a strain field, rather than a collection of
isolated patches of random temperature. The thermistor chain
tows are cross-sections of this field. On horizontal scales
of hundreds of kilometers, several large fronts, across which
the temperature change (roughly 1 °C or more) has the same
sign as the large-scale gradient, give a step-like appearance
to the temperature record.
The salinity-compensated temperature structure that
dominates Tow 1 is visible near 33° N in Figure 11.3.
Measured horizontal temperature gradients exceeded 0.25
°C/lOOm in the front near 110 km, the largest observed during
the experiment.
In Tow 2a, a large front was encountered at 200 km, near
300 N. The feature in Tow 2b near 70 km appears to be a
meander of the same front. This meander is visible in
infrared satellite imagery from 17 January 1980 (Figure 2a,
Van Woert, 1982).
Tow 3, made on 25 January, was contained in the region
covered by a CTD survey (Roden, 1981) during 24-31 January.
The tow is roughly perpendicular to the isotherms of the
surveyed front (Figure II.lb). The mean temperature gradient
is large over this entire tow. The sharp frontal boundary
near 18 °C observed a week earlier at the same location
during Tow 2a, does not appear in Tow 3. A tongue of warm
water was crossed at the southern end of the tow, with a
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