Equatorial Pacific 1,000‐dbar Velocity and Isotherm Displacements From Argo Data: Beyond the Mean and Seasonal Cycle

Abstract

AbstractEquatorial Pacific zonal velocity at 1,000 dbar and vertical isotherm displacements from 0–2,000 dbar are analyzed using Argo data through February 2018. In agreement with previous studies, the mean 1,000‐dbar zonal velocity is characterized by alternating eastward and westward jets of amplitude 5–10 cm/s. Similarly, the seasonal cycle is dominated by an annual Rossby wave that is apparent in annual harmonic fits to both the isotherm displacement and velocity fields. Residual (mean, annual, and semiannual harmonics removed) zonal velocity and isotherm displacements are analyzed using Complex Empirical Orthogonal Functions (CEOFs) and their Principal Components. For the analysis at 1,000 dbar, the first velocity CEOF accounts for 28% of the variance and the first isotherm displacement CEOF 24%. Spatial patterns of the lead CEOFs are broadly consistent with Rossby waves, but only isotherm displacement CEOF1 can be clearly linked to known physical processes in the equatorial Pacific. This is true of the isotherm displacement CEOF1s across pressure surfaces, despite being estimated independently on each one. The Principal Component of isotherm displacement CEOF1 at 1,000 dbar is well correlated (r = –0.65) with the Niño3.4 index at a 12‐month lag, suggesting that El Niño signals propagate deep into the equatorial Pacific Ocean. The 3‐D structure of the isotherm displacement CEOF1s suggests that the deep isotherm displacement signals are consistent with a vertically propagating Rossby wave of vertical mode 3–4.