Development of the yearly mode-1 M2 internal tide model in 2019
Event: 2022 Ocean Surface Topography Science Team Meeting
Session: Tides, internal tides and high-frequency processes
Presentation type: Type Forum only
This work is motivated to study the interannual variations of internal tides using observation-based yearly internal tide models from satellite altimetry. The yearly mode-1 M2 internal tide model in 2019 is constructed using sea surface height (SSH) measurements made by six concurrent altimetry missions: Jason-3, Sentinel-3A, Sentinel-3B, CryoSat-2, Haiyang-2A and SARAL/AltiKa. The model is developed following a three-step procedure consisting of two rounds of plane wave analysis with a spatial bandpass filter in between. Prior mesoscale correction is made on the altimeter data using AVISO gridded mesoscale fields. The model is labeled Y2019, because it represents the one-year-coherent internal tide field in 2019. In contrast, the model developed using altimeter data from 1993–2017 is labeled MY25, because it represents the multi-year-coherent field in 25 years. Thanks to the new mapping technique, model errors in Y2019 are as low as those in MY25. Evaluation using independent altimeter data confirms that Y2019 reduces slightly less variance (~6%) than MY25 does. Further analysis reveals that the altimeter data from five missions (without Jason-3) can yield an internal tide model of almost same quality. Comparing Y2019 and MY25 shows that mode-1 M2 internal tides are subject to significant interannual variability in both amplitude and phase, and their interannual variations are a function of location. For example, along southward internal tides from Amukta Pass (Alaska), the energy flux in Y2019 is two times large and the phase speed in Y2019 is about 1.1% faster. This work demonstrates that internal tides can be observed using yearly concurrent altimetry missions and thus their interannual variations can be quantified. This work confirms that non-repeat (e.g., geodetic, drifting) altimetry missions (phases) can be used to observe internal tides, whose feasibility has been debated in the altimetry community. This mapping technique has been applied successfully to other yearly altimeter datasets.