Observations and Modelling of Fronts and Frontogenesis

adiabatic meridional displacements of roughly 100 km, likely
arise from baroclinic instability of the geostrophic upper
ocean flow. They form a plateau in the temperature gradient
spectrum at wavelengths above 10 km (Figure 11.8).
(2) Strong temperature fronts are observed near 330 N, 310
N and 27° N, with density compensation by salinity increasing
northward (Figures 11.3,4). Maximum horizontal near-surface
gradients exceed 0.25 °C/l00 m (Figure 11.7). There is
evidence of vertically differential horizontal advection in
the surface layer by light winds (Figure II.5b), enhanced
vertical mixing during periods of strong winds, and shallow
(100-200 m depth) convection caused by wind-driven advection
of a dense layer over a deep less-dense layer.
(3) Temperature is roughly normally distributed around the
climatological mean (Figure 11.6). The near-surface
horizontal temperature gradient has high kurtosis (Figure
II . 7)
(4) The high horizontal wavenumber (0.1-1 cpkm) tail of the
near-surface temperature spectrum has the -3 power law form
(Figures 11.8,10) predicted by Charney (1971) for energetic
high wavenumber near-geostrophic motion above a baroclinic
production range. Horizontal temperature gradients have
significant vertical coherence over the upper 50 m at all
wavelengths and over the upper 70 m at wavelengths greater
than 5 km (Figure 11.12).
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