An Observation of Frontal Wave Development on a Shelf-Slope/Warm Core Ring Front Near the Shelf Break South of New England

Abstract

Small-scale waves have been observed near 40°N, 68°30′W in specially enhanced satellite imagery of a strong temperature front formed in May 1979, between the shelf/slope-water front and warm core ring 79-B. Thew frontal waves had a wavelength of 23±4 km, an eastward propagation speed of 32 ± 4 km day−1, and a growth rate (e-folding time) of 17.5 h (12–19 h). These satellite data plus current-velocity and hydro-graphical data gathered from the Nantucket Shoals Flux Experiment (NSFE79) allow comparison of the observed growth rate with theoretical predictions based on the assumption of a Margules front and the instability model of Orlanski (1968). This comparison suggests that the observed frontal waves were due primarily to horizontal-shear instability and derived their energy from the mean flow structure across the front in the presence of ring 79-B.