Observations and Modelling of Fronts and Frontogenesis

II. TOWED THERMISTOR CHAIN OBSERVATIONS OF FRONTS
IN THE SUBTROPICAL NORTH PACIFIC
Abstract
A thermistor chain was towed 1400 km through the Eastern
North Pacific Subtropical Frontal Zone in January 1980. The
observations resolve surface layer temperature features with
horizontal wavelengths between 200 m and several hundred
kilometers and vertical scales of 10 to 70 m. The dominant
features have horizontal wavelengths of 10-100 km, amplitudes
of 0.2 to 1.0 °C, and random orientation. Associated with
them is a plateau below 0.1 cpkm in the horizontal
temperature gradient spectrum that is coherent between 15 and
70 m depths. They likely arise from baroclinic instability.
Strong temperature fronts 0(1-2 °C/3-10 km) are observed near
330 N, 31° N and 27° N. Temperature variability is partially
density compensated by salinity, with the fraction of
compensation increasing northward. There is evidence of
vertically differential horizontal advection by light winds
in stable conditions, vertical mixing during high winds, and
shallow convection caused by wind-driven advection of denser
water over less dense water. Temperature at 15 m depth is
roughly normally distributed around the climatological
surface mean, with a standard deviation of approximately 0.7
°C, while its horizontal gradient has high kurtosis and
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