Spectra and gross features of vertical temperature and salinity profiles off the central west coast of India

Abstract

Continuous vertical profiles of temperature and salinity recorded by a CTD-system  from the continental slope and the continental rise off Goa, west coast of India, were used for delineating the gross statistical features of the fine structure and to understand the underlying physical processes. Spectra of temperature and salinity fluctuations from the different stations showed similar patterns and trend of decrease to a wave length of about 10 m, generally with a crest like feature at 20 m wave length. The estimates of spectral density for temperature and salinity were comparatively very high for low wave numbers and showed a difference varying from 1.5 to 2 decades. The spectra for the range 0-0.11 cy /m computed using the perturbation series from a First Difference filter and corrected for the filter-response followed an average slope of -2.9 (range: -2.57 to -3.43 and std. dev. : .-0.3) and --2.6 (range: -2.05 to -3.15 and std. dev. : --0.36) with correlation coefficients -0.96 and -0.92 for temperature and salinity respectively. Coherency estimates were high (> 0.8) for the range 0-0.02 cy /m and were independent of the distance between stations showing the spatial homogeneity of low wave number processes.. Correlation coefficients between T` and S` and the individual standard deviations for different layers increased with increasing filter length and generally decreased with depth. Both horizontal and vertical mixing processes were very active in the upper water column (0-250 m). In the deeper layers, > 500 m. non-isopycnal mixing processes were found to be active.