Surface forcing on the southern flank of Georges Bank, February–August 1995

Abstract

Surface wind stress, heat, and freshwater fluxes were estimated over the southern flank of Georges Bank during February–August 1995 using moored measurements made at ST1 located on the 76‐m isobath, roughly halfway between the tidal mixing and shelf/slope fronts. Wind stress variability was dominated by a succession of atmospheric lows that passed Georges Bank during the deployment. A transition between frequent lows and strong wind stress events (“winter”) to less frequent lows and weaker wind stresses (“summer”) occurred in mid‐May. In winter, wind stress fluctuations tended to be omnidirectional, with maximum stresses above 0.5 N/m2 during four storms, one a classic “nor'easter”, while summer fluctuations were weaker but strongly polarized in the along‐bank direction. The ST1 surface heat flux was dominated by shortwave heating, which increased from a winter mean of 130 W/m2 to 230 W/m2 in summer. Long‐wave cooling decreased from 50 W/m2 (winter) to 30 W/m2 (summer), while mean sensible and latent fluxes increased from −20 and −40 W/m2 (winter) to +10 and 0 (summer) respectively. Overall, winter was characterized by weak net heating (30 W/m2) with shortwave gain offset by long‐wave, latent, and sensible heat loss. In summer, increased shortwave gain and reduced long‐wave loss and weak sensible and latent fluxes combined to produce strong net heating (210 W/m2). ST1 precipitation was highly episodic with little seasonality while evaporation occurred mostly during winter, resulting in a net evaporation of −15 cm and net freshwater flux of +48 cm over the deployment.