water hm maating, washington, dc 2007 tidal corrections for the water mission f. lyard legos, cnrs,...

WATER HM maating, Washington, DC 2007

Tidal correctionsfor the WATER mission

F. LyardLEGOS, CNRS, Toulouse


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


Can we expect improved tidal corrections compared to present one?

YES! But it will need subsequent effortsEither 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/models2. 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/models2. But (1) is true if we develop enough regional models with

assimilation


M2 internal tide surface effects

CCATuamoturidge

M2 internal tide effects

M2 internal tide signal to noise ratio


Internal tides signature correctionMy 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 M2, possibly S2

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 trackInternal tide

Ocean 1st baroclinic mode wavelength (km)


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->)


tidal correction IS an issue inshelf 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 resolutionlack of accuracy, especially between satellite tracksmissing compound tides


Regional modelling

FE mesh usefull to properly describe the regional, estuary and river channels details


Bathymetry: 1st order error

GEBCO (gridone) : lack of details Smith & 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…


Re-creating regional bathymetriesfastidious…

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


ConclusionsWe need to improve tidal atlases:

1.In the T/P and Jason inter-tracks regions, both for the barotropic AND internal tides2.In shelf and coastal seas

Immediate actions to be taken:

Assess the current atlases accuracy in WATER HM configurationAddress internal tide issueDevelop 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.

water hm maating, washington, dc 2007 tidal corrections for the water mission f. lyard legos, cnrs,...

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