VERTICAL STRUCTURE OF TEMPERATURE FLUCTUATIONS WITHIN AN OCEANIC THERMOCLINE

A study has been made of the vertical structure of the temperature fluctuations present in an oceanic thermocline from 2 time-series of temperature profiles to 300 m depth, of duration 2 1/2 and 7 days, in the North Ocean. The maximum variation of temperature for both series (r.m.s. value 0.5[degree]C) occurred on the upper boundary of the thermocline. Within the frequency ranges considered for each series (i.e. 0.2-1 c/hr and 0.05-1 c/hr) the spectral intensity of the temperature fluctuations generally tended to decrease with increase in frequency and no predominant periodic components were found. The variation of coherence between the temperature components of a given frequency at 2 depth levels, separated by varying distances, gave an indication of the vertical scale of the fluctuations. Throughout most of the frequency range the fluctuations within the thermocline were significantly coherent for levels spaced by almost the whole thermocline layer. A level could be found at which the temperature fluctuations were most representative of the variation of the layer. The implications of the various spectral and coherence features on the nature of the fluctuations has been discussed.