Complex Singular Value Decomposition Analysis of Equatorial Waves in the Pacific Observed by TOPEX/Poseidon Altimeter

Abstract

The mean of the sea level deviation data derived from the TOPEX/Poseidon altimeter in the equatorial Pacific, between 10°S and 10°N, and between 120°E and 78°W, from cycles 2 to 136 (3 October 1992–2 June 1996), are extracted using a maximum–minimum average method. Then, two-dimensional (2D) sea level deviation time series are developed to visualize the dynamics of equatorial waves. The complex singular value decomposition (CSVD) method is applied to decompose these 2D time series into empirical orthogonal modes. Using this method, zonal and meridional structures, propagation directions, periods, and propagation speeds of these empirical modes are obtained. The first empirical mode is propagating westward, and its structure is asymmetric to the equator. It has an average phase speed c = −0.6 m s−1 within 4°–6°N and c = −0.4 m s−1 within 6°–8°S, respectively, and a period of 15 months, which is associated with an interannual Rossby wave. The second empirical mode is propagating eastward along the equator and has a phase speed of 2.5 m s−1 and a period of 7 months, which is associated with an equatorial Kelvin wave. The asymmetric feature of the empirical Rossby wave, which is also observed in the equatorial Pacific, may suggest that the background currents and wind fields in the equatorial Pacific Ocean affect its propagation. The amplitude of the empirical Kelvin mode increases as it propagates eastward. This is associated with an eastward shoaling of the thermocline depth along the equatorial Pacific Ocean. The results of both empirical modes are consistent with those predicted by the theory of Kelvin and Rossby waves and closely represent the actual features of both waves observed in the equatorial Pacific Ocean. Therefore, the CSVD is a suitable method for revealing the dynamics of equatorial waves.