Tidal corrections for TOPEX altimetry in the Coral Sea and Great Barrier Reef Lagoon: Comparisons with long term tide gauge records

The well-known capability of TOPEX/Poseidon altimetry to map sea levels precisely in the deep oceans motivates its application to the topographically complex Coral Sea and NE Australian continental margin. We assess several global tidal models for correcting TOPEX altimetry in the Coral Sea and find CSR3.0 offers good overall performance, based on comparisons of model-predicted and tide gauge harmonic constituents. Using CSR3.0 tidal corrections, we evaluate residual Sea Surface Height (SSH) Root Mean Square (RMS) variability and residual M2 tidal alias errors. Away from large reefs and islands, CSR3.0 amplitude and phase errors for M2 are typically less than 5 cm and 8 deg, respectively, with RMS tidal errors of 5 cm or less and RMS SSH residuals approximating 10 cm. Since model deficiencies appear in the macro-tidal region of the Southern Great Barrier Reef Lagoon, near Broad Sound, we employ a high-resolution hydrodynamic model in this area to compute the tidal corrections. Predicted M2 amplitude and phase in this region are within 3 cm and 5 deg of observations, RMS errors are mostly under 4 cm and coastal RMS SSH residuals are as low as 15 cm, in spite of coastal trapped waves and submesocale eddies in the Lagoon. Daily and monthly smoothed SSH residual time series, respectively, yield optimal lagged correlations with in situ sea level data in the range 0.3-0.9 and 0.6-0.9 for locations spanning the Coral Sea and in the Lagoon. Lag correlations of monthly smoothed Geostrophic Current Anomalies derived from TOPEX SSH gradients with long-term currents from the continental slope yield optimal correlations of 0.5 and 0.8, respectively, near Jewell (lat 14 deg S) and Myrmidon Reef (19 deg S). Our results demonstrate that low-frequency sea level and geostrophic current variations can be reliably observed using altimetry over the Coral Sea and NE Australian continental slope, and for selected locations on the continental shelf, if appropriate tide correction models are employed.