Seasonal Mode-1 M2 Internal Tides from Satellite Altimetry

Abstract

The seasonal variability of mode-1 M2 internal tides is investigated using 25 years of multisatellite altimeter data from 1992 to 2017. Four seasonal internal tide models are constructed using seasonally subsetted altimeter data and World Ocean Atlas seasonal climatologies. This work is made possible by a newly developed mapping procedure that can significantly suppress model errors. Seasonal-mean and seasonally variable internal tide models are derived from the four seasonal models. All of the models are intercompared and evaluated using independent CryoSat-2 data. The seasonal-mean model is overall the best model because averaging the four seasonal models further reduces model errors. The seasonally variable models are better in the tropical zone, where large seasonal signals may overcome model errors. Each seasonal model works best in its own season and worst in its opposite season. These internal tide models reveal that mode-1 M2 internal tides are subject to significant seasonal variability and that their seasonal variations are a function of location. Large seasonal variations dominantly occur in the tropical zone, where the World Ocean Atlas climatology shows strong seasonal variations in ocean stratification. Seasonal phase variations are obtained from the directionally decomposed internal tide components. They are dominantly 6608 at the equator and up to 61208 in the central Arabian Sea. Incoherence caused by seasonal phase variations is usually less than 10% but may be up to 40%–50% in the tropical zone.