Using Complex-Demodulation to Identify Non-Phase-Locked Tides from Reference-Mission Altimetry
Event: 2019 Ocean Surface Topography Science Team Meeting
Session: Tides, internal tides and high-frequency processes
Presentation type: Type Poster
Modulations of the internal tide are caused by both large-scale, seasonal-to-interannual, changes in ocean stratification and also by smaller-scale mesoscale currents and stratification. The magnitude and frequency spectrum of the tidal modulations is hardly known, but it is clear that this information may be crucial to the interpretation of ocean topography measured by SWOT and it may provide a useful record of climate statistics which are currently poorly measured by direct means. Complex-demodulation, which may be implemented with short-term harmonic analysis or other techniques, can be combined with spatial analyses of along-track altimetry data to reveal changes in internal tides and distinguish them from broadband mesoscale variability. In this talk I will show examples of these kinds of analysis which identify seasonal-to-interannual variability of internal tides. By looking at variability as a function of the demodulation window, it is possible to infer the total variance associated with the non-phase-locked internal tide. These results provide a view of internal tide variability which complements previous approaches based on analysis of the wavenumber spectrum.