This study was supported in part by grants from the National Oceanographic and Atmospheric Administration NA46GP0244 and NA56GP0451 (BB and JDN) and NA66GP0195 (DG). During this study BB also received support from the Centre National de la Recherche Scientifique. Earlier versions of this work were presented at the American Geophysical Union conference in December 1993 and at the International TOGA Scientific Conference in April 1995.
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