Internal tides and waves in a high-resolution ocean general circulation model with data assimilation
- (University Of Michigan, Ann Arbor)
A group of US scientists proposes to examine the frequency-wavenumber spectra and predictability of internal tides and the internal gravity wave (IGW) continuum in global high-resolution simulations of the HYbrid Coordinate Ocean Model (HYCOM) with simultaneous atmospheric and tidal forcing, the Navy Coupled Ocean Data Assimilation (NCODA) scheme acting on the mesoscale eddies, and an Augmented State Ensemble Kalman Filter (ASEnKF) acting on the tides. The simulations therefore simultaneously contain barotropic tides, IGWs including internal tides, the general circulation, and mesoscale eddies. The eddies render internal tides and other internal waves non-stationary, hence reducing their predictability. The NCODA scheme helps to place mesoscale eddies in the correct locations, and also moves the model stratification towards observations, while the ASEnKF increases the accuracy of the modeled barotropic tides. This work has implications for both present-day nadir altimetry (e.g., the Jason-series) and for planned future generation wide-swath altimetry (e.g., the SWOT mission). We have shown in a 2012 paper that the high-wavenumber end of the sea surface height wavenumber spectrum is dominated by high-frequency motions in regions of strong internal tides. Over the last year we have recognized that the high-frequency motions include the IGW continuum as well as internal tides. New results included in this proposal demonstrate that the continuum contributes more to sea surface height (SSH) variance than internal tides, at least in our models.
For the Ocean Surface Topography Science Team,