Basin-scale variability in the Labrador Sea from TOPEX/POSEIDON and Geosat altimeter data

摘要

The TOPEX/POSEIDON altimeter data and the Geosat altimeter data from the Exact Repeat Mission (ERM) have been analyzed to show the basin-scale features of annual sea surface height anomalies in the Labrador Sea. A complex empirical orthogonal function (CEOF) analysis is used to extract spatial and temporal patterns of altimetric sea surface height anomalies. The analysis of TOPEX/POSEIDON data has revealed that the first eigenmode has an annual variation with amplitudes of ∼5 cm, positive in summer and negative in winter. The Geosat data analysis implies similar results but shows only the sea surface height variabilities relative to those of the subtropical gyre circulation and the North Atlantic Current due to an orbit error correction. The steric height anomalies of the climatological monthly-mean Levitus data and the sea surface height anomalies of a wind-driven barotropic model are also analyzed using the CEOF technique. The annual cycle in the Levitus data, dominated by thermal expansion, has an amplitude of ∼4 cm and is nearly in phase with the TOPEX/POSEIDON data. The wind-driven annual signal is approximately in phase with the TOPEX/POSEIDON and Levitus data, but its amplitude is less than ∼1 cm. A correlation analysis suggests that the basin-scale features deduced from TOPEX/POSEIDON data are dominated by the steric height variability of the Levitus data, supplemented to much less extent by the wind-driven response of the barotropic model. The Geosat results are found to represent the steric effect only. It is modified by the orbit error correction so much that the phase changes by 180°.