WATER HM maating, Washington, DC 2007 Tidal corrections for the WATER mission F. Lyard LEGOS, CNRS, Toulouse

WATER HM maating, Washington, DC 2007 Rationales First years of water mission corrections will rely on pre-WATER tidal products Tidal corrections are again a challenge to exploit the wide swath observations: –Shelf/coastal sea tides issue –Surface signature of internal tides issue

WATER HM maating, Washington, DC 2007 Can we expect improved tidal corrections compared to present one? YES! But it will need subsequent efforts Either in deep and coastal oceans, the present tidal models are extremely well fitted close to available observations. WATER HM corrections will need to improve models between observational gaps… In addition: Deep ocean: 1.longer time series analysis will allow better tidal analysis/models 2.But (1) is true if we deal with the internal tide issue Shelf/coastal ocean: 1.longer time series analysis will allow better tidal analysis/models 2.But (1) is true if we develop enough regional models with assimilation

WATER HM maating, Washington, DC 2007 M 2 internal tide surface effects CCA Tuamotu ridge M2 internal tide effects M2 internal tide signal to noise ratio

WATER HM maating, Washington, DC 2007 Internal tides signature correction My suggestion: attempt to map those signatures Methodology: Re-analyse all the available data (T/P+Jason, T/P interlaced, GEOSAT+GFO, ERS1/2+ENVISAT). Focus on M 2, possibly S 2 Resolve propagation directions at cross-overs Filter the internal wave signature (with the help of 1st internal mode wavelength maps? ) Map the analysed signatures on 1/12° resolution satellite track Internal tide Ocean 1st baroclinic mode wavelength (km)

WATER HM maating, Washington, DC 2007 Shelf/coastal tides GOT00 M2 tide (amplitude in cm) against T/P (right) and T/P interlaced (left) Altimetry data inconsistency (drying ?) Single mission data have not enough resolution (compared to tidal distribution) and/or not long enough time series Loss of data in coastal regions induce an increased error budget in tidal analysis, thus models Harmonic analysis accuracy is limited by local effects such as drying We need all available techniques to improve the shelf/coastal tidal atlases (such as regional models->)

WATER HM maating, Washington, DC 2007 tidal correction IS an issue in shelf and coastal seas Methodology: 1)Fully re-process altimetry data for tidal analysis 2)Develop regional tidal models for all significant shelf and semi-enclosed seas (hydrodynamic + assimilation of tide gauge and altimetry data) Gather data (bathymetry, bottom rugosity,…), knowledge, assesments in progress 2)Merge regional models into existing global tidal atlases (OI to insure continuity) (within 2/3 years or more) 3) Integrate regional model in true global tidal models (within 5 years) Not yet good enough !!! lack of spatial resolution lack of accuracy, especially between satellite tracks missing compound tides

WATER HM maating, Washington, DC 2007 Regional modelling FE mesh usefull to properly describe the regional, estuary and river channels details

WATER HM maating, Washington, DC 2007 Bathymetry: 1st order error GEBCO (gridone) : lack of detailsSmith & Sandwell : noisy and unrealistic Amazon river shelf Large bathymetry errors are found in available database. Effects on tidal simulation are dramatic. There is an urgent need to improve regional bathymetries…

WATER HM maating, Washington, DC 2007 Re-creating regional bathymetries fastidious… Scan and digitize bathymetric and nautic charts Special cares devoted to estuarine channels Mapped and merged into global database improved model bathymetry Digitized data Re-worked channel path

WATER HM maating, Washington, DC 2007 Conclusions We need to improve tidal atlases: 1.In the T/P and Jason inter-tracks regions, both for the barotropic AND internal tides 2.In shelf and coastal seas Immediate actions to be taken: Assess the current atlases accuracy in WATER HM configuration Address internal tide issue Develop regional models for shelf and coastal seas Harmonic analysis is not well suited to take all the benefits of short missions (short in term of mission duration compared to tidal alias). Improved assimilation techniques (i.e. no more spectral, but sequential in time) are needed to fully benefit of existing and forthcoming data. Such an effort will also profit to atmospherically induce ocean HF.