Skill in an Inversion Solution: CONVEX-91 Hydrographic Results Compared with ADCP Measurements

Abstract

This paper demonstrates skill in simple linear inversion solutions in two ways: first, qualitatively, by showing that the inversion method can put in place a known feature of the deep circulation of the study region when initialized with nominally unbiased geostrophic reference currents (zero at the bottom); and second, quantitatively, a new technique is developed for comparing estimates of reference currents derived from acoustic Doppler current profiler (ADCP) data with the inversion solutions, whereby the ADCP estimates are projected onto the basis vectors produced by the singular-value decomposition of the hydrographic problem setup. This technique can be used as objective assistance in choosing a solution degree cutoff. The questions of tidal- and navigation-induced errors in the ADCP estimates are addressed together with the quality of matching between the ADCP current profiles and the computed geostrophic shear. The dataset consists of three approximately 500-km-sided boxes of CTD stations collected as the U.K. Control Volume Experiment (CONVEX-91) during summer 1991 in the northeast Atlantic between Greenland and the U.K. continental shelf.