A simple diagnostic based on sea surface height with application to Central Pacific ENSO.

Lai, Jufen, Greatbatch, Richard John and Claus, Martin (2023) A simple diagnostic based on sea surface height with application to Central Pacific ENSO. Open Access Ocean Science, 19 (2). pp. 421-430. DOI 10.5194/os-19-421-2023.

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We use output from a freely-running NEMO model simulation for the equatorial Pacific to investigate the utility of linearly removing the local influence of vertical displacements of the thermocline from variations in sea surface height. We show that the resulting time series of residual sea surface height, denoted ηnlti, measures variations in near-surface heat content that are independent of the local vertical displacement of the thermocline and can arise from horizontal advection, surface heat flux and diapycnal mixing processes. We find that the variance of ηnlti and its correlation with sea surface temperature, are focused on the Niño4 region. Furthermore, ηnlti averaged over the Niño4 region is highly correlated with indices of Central Pacific El Niño Southern Oscillation (CP ENSO), and its variance in 21 year running windows shows a strong upward trend over the past 50 years, corresponding to the emergence of CP ENSO following the 1976/77 climate shift. We show that ηnlti can be estimated from observations, using satellite altimeter data and a linear multi-mode model. The time series of ηnlti, especially when estimated using the linear model, show pronounced westward propagation in the western equatorial Pacific, arguing an important role for zonal advective feedback in the dynamics of CP ENSO, in particular for cold events. We also present evidence that the role of the thermocline displacement in influencing sea surface height increased strongly after 2000 in the eastern part of the Niño4 region, at a time when CP ENSO was particularly active. Finally, the diagnostic is easy to compute and can be easily applied to mooring data or couple climate models.

Document Type: Article
Keywords: sea surface height; ENSO; El Nino; SST
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-OD Ocean Dynamics
Main POF Topic: PT2: Ocean and Cryosphere
Refereed: Yes
Open Access Journal?: Yes
Publisher: Copernicus Publications (EGU)
Related URLs:
Date Deposited: 13 Jan 2023 10:58
Last Modified: 07 Feb 2024 15:25
URI: https://oceanrep.geomar.de/id/eprint/57740

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