A discussion on ocean currents and their dynamics - Spectral characteristics of some deep current records from the eastern North Atlantic

Abstract

A brief resume is given of the work performed since 1967 by the National Institute of Oceanography in the collection of current meter records by the use of deep sea moorings and recording current meters. These records are, unlike most other current observations, accompanied by simultaneous observations of water temperature. It is possible from a knowledge of the vertical profile of temperature at or near to a mooring to derive from the temperature observations a time series which approximates to that of the vertical movement of the water. The object of this paper is to investigate the validity of equating the derived time series to that of the true vertical water motion. The spectra of potential energy of vertical motion derived from the temperature records are compared with the simultaneous spectra of horizontal kinetic energy derived from the measurements of horizontal velocities. It is concluded that under circumstances in which there are well-defined vertical gradients of temperature and density the derivation of vertical motion from a temperature record is valid and can be used with a good degree of confidence to investigate the frequency distribution of potential energy in the inertial subrange (extending from the local inertial frequency to the Brunt-Vaisala stability frequency). An idealized observational scheme is suggested which would in most cases fulfil the necessary requirements for a simple monitoring of vertical motions over long periods of time.