Observations and Modelling of Fronts and Frontogenesis

front at about 18.5 °C. There is frontal structure near 60
kin, at about 17.5 0C, in both Tows 3a and 3b. Note the
similarity of Tows 3a and 3b, which were made on the same
track (in opposing directions) but several hours apart.
The largest temperature front encountered during the
experiment, with horizontal gradient reaching 1.5 °C/3 km and
a temperature change of roughly 2 °C over 10 kin, occurred
near 27° N at 350 km in Tow 4. The salinity change across
this feature is small and in fact enhances the density
change, which is approximately 0.5 kg m3 over 10 km, most of
it occurring over 3 km. This is larger than the density
variability observed over the entire remainder of the
experiment. Isotherm cross-sections of this front are shown
in Figure II.5a. The geostrophic vertical shear across the
front is roughly 10-2 s- at the surface. Large amplitude
internal wave vertical displacements of the seasonal
thermocline are visible.
The vertical temperature gradient between 15 m and 70 m
was generally weak except in regions near frontal features.
During Tow 1, appreciable vertical gradients appear only
within 10-15 km of the fronts. During Tow 2, some vertical
gradients occur up to 25-30 km from fronts (though there may
be closer fronts that lie off the tow track). The upper 70 m
are nearly homogeneous in temperature over most of Tow 3a. A
small amount of stratification is evident near features
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