Subsurface energetics of the Gulf Stream cyclonic frontal zone off Onslow Bay, North Carolina

Abstract

It has been shown with the use of 4‐month‐long time series of velocity, temperature, and conductivity that fluctuating kinetic and potential energy was converted into kinetic and potential energy of the mean flow following a fluid particle in the subsurface Gulf Stream cyclonic frontal zone off Onslow Bay, North Carolina, during early 1979. This result agrees well with earlier measurements made in the surface layer off Onslow Bay. These flux calculations represent an important step in verifying the direction of the net cross‐stream energy flux within the stream off Onslow Bay. According to an hypothesis presented for the growth and decay of Gulf Stream meanders along the continental margin of the southeastern United States, Onslow Bay is an area of decreasing meander amplitude. The direction of the energy conversion from meanders to the mean flow, determined from our calculations, is consistent with this hypothesis. Relatively low velocity covariances were found to be associated with relatively small transfers of kinetic energy during a period of low meander activity. This finding supports the notion that meanders play a significant role in the energy transformation processes. The presence of such ‘quiet’ periods may indicate a low‐frequency modulation of Gulf Stream meander activity.