Richard Ray (NASA-GSFC, USA); Brian Beckley (SGT Inc/NASA-GSFC, USA)

Focus is on the recent changes in the seasonal cycle of mean sea level over the Gulf of Mexico observed in satellite altimetry using global gridded AVISO data. Altimetry is in a good agreement with tide gauge data confirming increased annual amplitude of sea level in recent years for a set of tide gauges distributed along the coastline of the Gulf of Mexico. Overall, there is a positive trend in the seasonal sea level cycle during recent altimeter years over different regions (confirmed by e.g., Wahl et al. 2014, Etcheverry et al. 2015). Historical tide gauge data give a neutral or slightly positive trend in the seasonal cycle of sea level along the coast of the Gulf of Mexico. Altimetry extends this observed signal in tide gauges over the coastal areas to deep open ocean regions. Temporal variability of annual amplitude of sea level shows a significant increase in the latest period (2007-2013) over most of the Gulf of Mexico region, especially over the north-eastern coastline waters and central of the Gulf of Mexico from 10 to 15 cm, and a trend higher than 1 mm/yr. Part of this increase appears to be due to changes in mean sea level pressure acting through the inverted barometer response of the sea level. To determine possible mechanisms responsible for observed recent changes in the seasonal sea level cycle, we also investigate relationship with other important parameters, such as sea surface temperature (SST), wind curl, circulation, mesoscale eddies, etc. Correlations between these parameters vary but the highest correlation seems to be with SST. Comparison between the altimetry and model-based (e.g., NASA’s GMAO) annual amplitude of sea level shows similar trend, with significant model underestimation of amplitude increase. Understanding these mechanisms responsible for observed variations in seasonal sea level cycle should offer better understanding of present and future climatic variations on seasonal, inter-annual to inter-decadal time-scales.