Seasonal and interannual variability in the Gulf of Cadiz: Validation of gridded altimeter products

Nine years of gridded multi-mission altimeter products have been validated in the Gulf of Cadiz. The comparison was performed using two tide gauges deployed in the mouths of two estuaries: the Tinto-Odiel system and Guadalquivir River. The averaged seasonal cycle of the sea-level - corrected for atmospheric pressure effect - obtained from the two tide gauges and their closest altimeter points showed good agreement, correlation coefficients being about 0.95 (at both stations). The variability about the mean seasonal cycle observed in the altimeter data is about half that obtained from the tide gauges. The year-to-year analysis of the seasonal cycle confirmed the level of agreement between the two datasets, and indicated lower amplitude errors in the estimate of the annual harmonic (only significant at 95% confidence level in most of the years) in the altimeter data. The estimation of the annual component is affected by sporadic heavy river discharges only observed in the tide-gauge records. In those cases the river flow explained more than 50% of the variance associated with the daily mean sea-level.