Equatorial Pacific 1000-dbar Velocity and Isotherm Displacements from Argo Data: Beyond the Mean and Seasonal Cycle
Abstract
We analyze equatorial Pacific zonal velocity and vertical isotherm displacements using Argo data. Zonal velocities are from the Yomaha'07 dataset (Lebedev et al. 2007), updated through February 2018 and isotherm displacements from the Roemmich and Gilson (2009) monthly Argo fields, also updated through February 2018. Zonal velocities are mapped using a Loess filter with 1° latitude and 8° longitude half-power points, with annual and semiannual harmonics added. We then map residual velocities (after removing the mean and annual/semiannual harmonics) using a Loess filter with half-power points at 1.5° latitude, 12° longitude, and 3 months. Next, we compute Complex Empirical Orthogonal Functions (CEOFs) for these maps. We also fit mean, annual, and semiannual harmonics to monthly isotherm vertical displacement fields, remove those fits, and then compute CEOFs for the residuals.
The first velocity CEOF accounts for 28% of the residual variance. It is Rossby wave-like with a zonal wavelength of basin scale and a period of 6 years, implying a high vertical mode (12-13). The second CEOF of the isotherm displacements at 1000 dbar corresponds to the first velocity CEOF. This correspondence occurs because the second CEOF isotherm displacement amplitudes (averaged from 850-1150 dbar) are larger than those of the first CEOF within a few degrees of the Equator. The first CEOF of the isotherm displacements exhibits a Rossby wave-like signature with symmetric components at 1000 dbar and is maximally correlated (r=0.71) to the Niño3.4 index at a 10-month lag. Its low vertical mode, implying relatively weak velocity anomalies, may explain why none of 1000-dbar velocity CEOFs 1-6 (accounting for 87% of the residual variance) are well correlated with it or Niño3.4.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMOS41E2066Z
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSESDE: 4522 ENSO;
- OCEANOGRAPHY: PHYSICALDE: 4532 General circulation;
- OCEANOGRAPHY: PHYSICALDE: 4576 Western boundary currents;
- OCEANOGRAPHY: PHYSICAL