The space‐time structure and variability of the shelf water‐slope water and Gulf Stream surface temperature fronts and associated warm‐core eddies

Abstract

The space‐time structure and variability of three thermal features on the surface of the Northwest Atlantic—the shelf water‐slope water front; the Gulf Stream front; and warm‐core, anticyclonic eddies— were examined between September 1, 1975, and August 31, 1977, using weekly satellite‐derived charts of surface temperature fronts. The temporal and spatial correlation scales of both the shelf‐slope and Gulf Stream fronts were about 2 weeks and 80 km, respectively. The rms amplitude of both fronts increased from about 25 to 80 km in the first 1,000 km northeastward from Cape Hatteras. The dominant Gulf Stream meanders had wavelengths of about 320 km and periods of 7–8 weeks, and they propagated downstream jit a speed of about 6 cm/s. The warm‐core eddies averaged about 100 km in diameter and propagated southwestward from Georges Bank at an average speed of 6 cm/s; they decreased hi diameter from about 120 to 90 km and increased in speed from about 4 to 7 cm/s in moving from the Georges Bank‐to‐Hudson Canyon subdomain to the Hudson Canyon‐to‐Cape Charles subdomain. Some large Gulf Stream meanders induced perturbations of the shelf‐slope front. Eddies forced seaward perturbations of the front, which propagated southwestward with the eddies. (There were more rapidly propagating disturbances which also moved southwestward along the shelf‐slope front; they may have been due to coastally trapped waves.) There was significant interannual variation in the mean position of the Gulf Stream front and the number and intensity of warm‐core eddies shed by the Stream, though the correlation scales of its front did not change. Consequently, there were substantial interannual variations in the inferred entrainment of shelf waters by warm‐core eddies. Furthermore, the correlation scales of the shelf‐slope front had interannual variation. The results of this study agree with earlier, more limited estimates, and they extend the statistical analyses to the space‐time continuum of long waves and meanders with the aid of wave number‐frequency spectra and empirical orthogonal functions. These analyses quantify the broadbanded nature of the various perturbations and their interactions. Thus a holistic view of the principal surface thermal features of the Northwest Atlantic, and their interactions, is provided.