OCEAN TIDES

The FES2014b (MSf corrected) model is available for download as spherical harmonic coefficients.

The original FES2014b documentation and  1/16° x 1/16° grid files can be found on the AVISO web site.

The original amplitude and phase grids of FES2014b have been processed in the following way (in order to deliver products usable by orbit computation softwares):

  • adoption of the corrected MSf wave instead of the original one (in the original MSf wave, only the non-linear part of this wave was given, whereas in the corrected MSf wave the complete wave amplitude is given – non-linear and quasi-equilibrium parts)
  • setting tide amplitude to zero on the land areas
  • conversion to spherical harmonics (SH) up to degree and order 100 x 100 for each wave
  • application of an ellipsoidal correction to the SH coefficients in order to pin the water heights to the ellipsoidal surface of the Earth
  • addition of the long-period Om1 and Om2 waves (only the C20 coefficient)
  • removal (or not) of the S1 wave (depending on the ocean dealiasing model used)

Explanation: In the TUGO dealiasing product, the atmospheric S1 wave cannot be distinguished from the astronomic S1 wave, so the TUGO products include the S1 astronomic wave and therefore this wave should not be taken into account in the ocean tide model.

The load Love numbers used for the conversion from water heights to geopotential coefficients have been computed by Pascal Gégout up to SH degree 250. They are given HERE (the values in the file are SH degree, h’, l’ and k’).

The FES2014b (MSf corrected) ocean tide model in spherical harmonics therefore comes in two versions (with or without S1 wave).

 

  • FES2014b Spherical harmonics in water height:

FES2014b with S1 wave

FES2014b without S1 wave

Om1_wave_only_in_SH_up_to_degree_100

 

  • FES2014b Spherical harmonics in geopotential units (for the sake of compatibility with the files of FES2004 available from the IERS Conventions 2010 web site, the S1 wave alone is also provided):

FES2014b with S1 wave

FES2014b without S1 wave

S1 wave only from FES2014b

 

CAVEAT

For those who retrieved the files from this site before November 12, 2019, we recommend to discart these files and reload the new ones, which are correct at present.

Explanation:

Due to an unfortunate mistake in the original release of the files above, the version of the FES2014b tidal maps that was used for the conversion from water height grids to spherical harmonics was the one with an extrapolation of the tides over the continents. This choice was incorrect, leading to a product that cannot be used for gravity calculations. This error was particularly sensitive for the lowest flying satellites like GRACE, which experienced a 30% increase of the K-Band Range-Rate residuals compared to previous tide models.

An example of the difference between the extrapolated and non-extrapolated version of FES2014b is given below for the « O1 » wave:

This error has now been corrected by using the right version of FES2014b from the AVISO web site (ftp://ftp-access.aviso.altimetry.fr/auxiliary/tide_model/fes2014_elevations_and_load/), the one with no extrapolation over land. All the products in spherical harmonics have been recomputed and the files replaced by the correct ones.