Internal tide model ZHAO23: A milestone achieved by 30 years of satellite altimetry sea surface height measurements from 1993 to 2022
Event: 2023 Ocean Surface Topography Science Team Meeting
Session: Tides, internal tides and high-frequency processes (ROUND TABLE)
Presentation type: Type Poster
Contribution: PDF file
A new-generation internal tide model ZHAO23 is constructed using 30 years of sea surface height (SSH) measurements made by 15 satellite altimetry missions (excluding HY-2C and -2D) from 1993 to 2022. The merged data record is about 120 satellite years long. Our mapping procedure consists of two rounds of plane wave analysis and a spatial bandpass filter in between. The mapping technique is developed utilizing the frequencies and theoretical wavelengths of the target internal tidal constituents. Prior mesoscale correction is made using the spatiotemporally gridded SSH fields. ZHAO23 contains eight tidal constituents (M2, S2, N2, K2, O1, K1, P1, Q1) for the first baroclinic mode, four tidal constituents (M2, S2, O1, K1) for the second baroclinic mode, and one tidal constituent (M2) for the third baroclinic mode. Model errors are estimated using background internal tides that are mapped using slightly different tidal frequencies. The resulting model is evaluated using the satellite altimetry SSH data in 2023 from both the traditional and SWOT nadir-looking altimeters. The temporal variation of internal tides is studied using the newly-developed model. We find that internal tides are subject to significant variability on seasonal, interannual, and decadal timescales. We also find that, in the past 30 years, the global mode-1 M2 internal tides strengthened in terms of both SSH amplitude and depth-integrated energy, and their propagation speeds increased, although the internal tide strengthening is spatially inhomogeneous. The performance of empirical internal tide models in making internal tide correction for SWOT is affected by internal tide strengthening.