Temporal and spatial characteristics of sea surface height variability in the North Atlantic Ocean

• Main Author: Cromwell, D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2006
• Subjects: Labrador Sea; North Atlantic; North Atlantic oscillation
• Online Access: https://eprints.soton.ac.uk/41997/; https://eprints.soton.ac.uk/41997/1/Cromwell_OS2006.pdf; http://www.copernicus.org/EGU/os/os/2/147/os-2-147.pdf

We investigate the spatial and temporal variability of sea surface height (SSH) in the North Atlantic basin using satellite altimeter data from October 1992–January 2004. Our primary aim is to provide a detailed description of such variability, including that associated with propagating signals. We also investigate possible correlations between SSH variability and atmospheric pressure changes as represented by climate indices. We first investigate interannual SSH variations by deriving the complex empirical orthogonal functions (CEOFs) of altimeter data lowpass-filtered at 18 months. We determine the spatial structure of the leading four modes (both in amplitude and phase) and also the associated principal component (PC) time series. Using wavelet analysis we derive the time-varying spectral density of the PCs, revealing when particular modes were strongest between 1992–2004. The spatial pattern of the leading CEOF, comprising 30% of the total variability, displays a 5-year periodicity in phase; signal propagation is particularly marked in the Labrador Sea. The second mode, with a dominant 3-year signal, has strong variability in the eastern basin. Secondly, we focus on the Azores subtropical frontal zone. The leading mode (35%) is strong in the south and east of this region with strong variations at 3- and 5-year periods. The second mode (21%) has a near-zonal band of low variance between 22–27 N, sandwiched between two regions of high variance. Thirdly, we lowpass filter the altimeter data at a cutoff of 30 days, instead of 18 months, in order to retain signals associated with propagating baroclinic Rossby waves and/or eddies. The leading mode is the annual steric signal, around 46% of the SSH variability. The third and fourth CEOFs, ~11% of the remaining variability, are associated with westward propagation which is particularly dominant in a “waveband” between 32–36N. For all three cases considered above, no significant crosscorrelation is found between the North Atlantic Oscillation index and the amplitude ...