CoAuthors

Richard Ray (NASA/GSFC, United States)

The multi-satellite mesoscale sea level anomaly (SLA) maps produced by Ssalto/Duacs, originally distributed through the ``Archiving, Validation and Interpretation of Satellite Oceanographic Data'' center - usually referred to as AVISO - and now distributed by the Copernicus Marine Environmental Monitoring Service, have been used in hundreds of diverse oceanographic studies. Changes to the Ssalto/Duacs objective analysis methodology in 2014 resulted in increased levels of aliased tidal sea level in the mesoscale maps, compared to the methodology employed prior to 2014. The present work investigates the magnitude and spatial distribution of these tidal signals, which are typically smaller than one centimeter in the open ocean, but which can reach tens of centimeters in the coastal ocean. In the open ocean, the signals are caused by a combination of phase-locked and phase-variable baroclinic tides. In the coastal ocean, the signals appear to be caused by a combination of aliased, high-frequency non-tidal variability and erroneous tidal corrections applied to the along-track altimetry prior to objective analysis. Experiments have been conducted with low-pass and band-pass filters to reduce the tidal signals in the SLA maps, using tide gauge data to provide an objective assessment of the performance of the filters. The filter which attenuates both the small-scale (less than 200~km) and high-frequency (period shorter than 108~d) components of SLA removes aliased baroclinic tidal variability and improves the accuracy of tidal analysis in the open ocean, while also performing
acceptably in the coastal ocean.