Observations and Modelling of Fronts and Frontogenesis

etween 50 and 75 km and in the warm tongue near 110 km.
These features and the associated vertical gradients are
evident as well in Tow 3b, which followed the same track on
the opposite course. In Tow 4, as in Tows 1 and 2, vertical
gradients are found consistently near frontal features.
Often the upper sections of individual fronts appear
displaced horizontally by several kilometers from the lower
sections. During Tow 2, particularly over the interval
125-300 km, 15 m temperatures have traces that are similar to
the 70 in temperatures but offset to the north. Winds (Table
11.2) during 17 January were from the south, and may have
displaced a shallow layer northward and eastward. Isotherm
cross-sections of the feature near 135 kin are shown in Figure
II.5b. (Note that the presence of a temperature inversion
implies an anomalous local T-S relation, according to which
the warmer, more saline water is denser.) The displacement
can only be estimated, since the angle of incidence of the
tow track across the front is unknown, but it appears to be a
few kilometers. This is an appropriate value for Ekman layer
flow in response to light winds whose direction varies on a
2-5 day time scale, and is typical of such features in the
data, most of which occurred after periods of light winds.
Estimates of daily average buoyancy flux, made from hourly
bulk estimates of surface fluxes, are shown in Table 2, and
Monin-Obukhov depths calculated from the flux estimates are
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