INFERENCE OF DEEP-OCEAN STRUCTURE FROM UPPER-OCEAN MEASUREMENTS

Many in situ oceanographic measurements sample only the upper few hund red meters of the ocean. It is therefore important to understand to wh at extent these measurements may be used to infer the structure in the deep ocean. In this paper the use of empirical orthogonal functions ( EOFs), normal modes, and linear regression for vertical extrapolation are examined. Results of trials using historical data from the northwe st Atlantic are presented and compared with the predictions of a simpl e theory. When using EOFs or normal modes, the accuracy of the extrapo lation is dependent upon the structure of the basis functions used. In creasing the number of basis functions does not always improve the res ults. The most accurate extrapolation is obtained by using linear regr ession. Undulating conductivity-temperature-depth profilers typically measure down to 500-m depth. For the dataset used in this study, it is found that if a 500-m-deep profile is extrapolated to 700-m depth, th e expected errors are about one-third of the standard deviation of tem perature at that depth.