Wednesday 24 August 2005

GP2
1000-1200 hours

249
Scale-based wavelet analysis of sea level observations in the North Atlantic from satellite altimetry and tide gauges
Barbosa, Susana¹, Fernandes, Joana¹, Silva, Eduarda¹
1 FCUP, Porto, Portugal
Author email: susana.barbosa@fc.up.pt
A comparative study of sea level observations from tide gauges (TG) and Topex/Poseidon (T/P) altimetry is carried out using the discrete wavelet transform for a scale-by-scale description. Monthly TG records from 12 stations in both sides of the North Atlantic covering the altimetry period January 1993 to December 2002 are analysed. Corrected sea surface heights are derived from T/P by applying the standard instrumental and geophysical corrections, except the inverse barometer (IB) correction. Only measurements for which the radiometer flag is not set are considered. Sea level anomalies (SLA) are obtained with respect to the GSFC00.1 model and are gridded onto a regular 1 by 1 degree grid. Time series of sea level anomalies at the gridpoints nearest each TG location are analysed. The correlation between TG and altimetry measurements is analysed for different frequency bands through a scale-by-scale decomposition of wavelet correlation based on the discrete wavelet transform. Correlation between TG and altimetry observations exhibits a clear pattern for all stations, with lower correlation (<0.6) at the smallest scale and highest correlation (>0.8) for the annual signals; within station variability increases with scale. The effect of forcing variables on sea level, measured both from TG and altimetry, is investigated through a wavelet scale-based analysis of the correlation between sea level observations at each station and climate variables from the NCEP reanalysis dataset: sea level pressure (SLP), air temperature, sea surface temperature, precipitation and wind speed. Dependence between sea level and SLP varies with scale and is different for TG and altimetry observations: for altimetry correlation with SLP is higher at the largest scale, while correlation between TG and SLP observations is larger at the smaller scale. For the other analysed variables, altimeter and gauge measurements exhibit a similar correlation pattern.

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