Meso- and Submesoscale Structure of a Convecting Field

Abstract

Intensive data collection in the region of the Labrador Sea northwest of former Ocean Weather Station Bravo during the winter of 1998 allowed examination of the meso- and submesoscale structure during active convection. Data used include shipboard CTDs, shipboard underway data, isobaric CTD profiling floats, and high-drag floats whose trajectories were approximately Lagrangian in the horizontal and vertical directions. On the mesoscale, O(20 km), horizontal variability was nearly 1°C and 0.1 psu. An anticyclonic eddy of 40-km diameter was found. On a smaller scale, O(5 km), variability of 0.04 psu and 0.3°C was found. By utilizing data from fully Lagrangian floats, this smaller-scale field was found to be organized into eddies of 1?12-km radius. Both cyclonic and anticyclonic features were found, with the anticyclones being larger. This observation may explain the excess of anticyclones reported in previous studies having lower spatial resolution. These features were unsteady, with an anticyclone doubling in size in less than a week. There was communication between eddies, with four of five floats escaping an anticyclone. This exchange produced horizontal diffusivities (250?350 m2 s?1) on the order of basin-scale values, implying these small-scale features could produce the majority of the stirring. The influence of these structures on convection was explored: convection occurred throughout the region sampled despite the presence of eddies, the deepest mixed layers were found within an anticyclone, and convective trajectories within small cyclones were found to be significantly tilted so as to avoid the surface centers of the cyclones.