STRUCTURE AND DYNAMICS OF A COASTAL FILAMENT

Repeated microstructure transects across filaments in the coastal transition zone (CTZ) have revealed fundamental structure and dynamics of the complicated features. The measurements allow detailed momentum and vorticity analyses and provide a possible explanations for structural asymmetry of the fronts. Observations made between July 2 and July 23, 1988, along the central meridional CTZ survey line were used to estimate terms in the meridional momentum equation. The analysis indicates geostrophic flow along the axes of the fronts with the across-front pressure gradient explaining as much as 87% of the variance in the balance. Significant ageostrophic flow in the across-front coordinate was found, with the along-front pressure gradient explaining only 71% of the variance in the momentum balance. The fronts were found to be asymmetric in relative vorticity, with stronger positive vorticity on the cooler side of the front and weaker negative vorticity on the warm side. Mean vertical velocities were estimated from the repeated transects of acoustic Doppler current profiles and the rapid sampling vertical profiler hydrographic and turbulence measurements. Regions of upwelling and downwelling are likely associated with adjustments in the relative vorticity, resulting in maximum vertical velocities of 40 m d-1. Asymmetry in the near-surface temperature and salinity extrema are explained by cross-frontal exchange. This cross-frontal exchange modifies the relative roles of salinity and temperature in determining the density away from the coastal upwelling region, a dynamically important characteristic not revealed by advanced very high resolution radiometer imagery.