AN OPTIMIZED DESIGN FOR A MOORED INSTRUMENT ARRAY IN THE TROPICAL ATLANTIC-OCEAN

This paper presents a series of observing system simulation experiment s (OSSEs) which are intended as a design study for a, proposed array o f instrumented moorings in the tropical Atlantic Ocean. Fields of TOPE X/Poseidon sea surface height anomalies are subsampled with the goal b eing reconstruction of the original fields through the use of reduced- space Kalman filter data assimilation at a restricted number of locati ons. Our approach differs from typical identical and fraternal twin ex periments in that real observed data (i.e., TOPEX/Poseidon data) are s ubsampled and used in place of synthetic data in all phases of the OSS Es. In this way the question of how closely a particular model-generat ed data set resembles nature is avoided. Several data assimilation run s are performed in order to optimize the location of a limited number of moorings for the proposed Pilot Research Moored Array in the Tropic al Atlantic (PIRATA). Results of experiments in which data are assimil ated at 2 degrees N, 2 degrees S and the equator and the longitude is systematically varied by 5 degrees show that the greatest impact of th e assimilated data occurs when the observations are taken between 15 d egrees W and 30 degrees W. Next, a more systematic technique is presen ted which allows us to determine optimal points in an objective fashio n by applying a least squares regression approach to reconstruct the e rrors on a dense array of points from the data misfits at any three se lected points. The forecast error structure from the Kalman filter is used in a novel way to assess the optimality of mooring locations. Fro m a large sample of triads of points, the optimal mooring locations ar e found to be along the equator at 35 degrees W, 20 degrees W, and 10 degrees W. Additional experiments are performed to demonstrate the eff icacy of the initial and final PIRATA configurations and the added val ue that can be expected from PIRATA observations beyond existing expen dable bathythermograph observations.