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Combined mean dynamic topography

Types of dataset: auxiliary products
Contents: mean over the 1993-2012 period of the sea surface height above geoid. The MDT_CNES-CLS13 is an estimate of the ocean MDT for the 1993-2012 period. Since April 2014 (Duacs 2014, v15.0 version), the Ssalto/Duacs (M)SLA products are computed relative to 1993-2012 period that is consistent with this new MDT CNES-CLS13.
Use: ocean circulation, operational oceanography
Description: based on 2 years of GOCE data, 7 years of GRACE data, and 20 years of altimetry and in-situ data (hydrologic and drifters data). (More information)
Geographic coverage: global
Format: NetCDF
Distribution media: Authenticated  FTP
Condition of access: The MDT-CNES_CLS13 is delivered for scientific purposes only and non-commercial uses, as stated in the licence agreementAll auxiliary product users need an account, see Access to auxiliary productsTo get an acces to the last version of MDT product, please fill in, select the given product and valid the following form:

File weight: 5 MB (gzip NetCDF) 
How to cite Aviso data?
Copyright: 1992-ongoing Cnes-CLS

Compared to the previous MDT_CNES-CLS09 field, the main improvements of MDT_CNES-CLS13 are:

  • In the computation of the first-guess:

    • use of the geoid model EGM-DIR-R4 based on 2 years of reprocessed GOCE data and 7 years of GRACE data 
    • use of the CNES-CLS11 Mean Sea Surface
    • improvement of the filtering process
    • optimal filter at around 125 km (instead of about 400 km)

  • In the combination with oceanic in-situ data:

    • updated dataset of drifting buoy velocities (1993-2012) and carefully preprocessed to take into account drogue loss and corrected for wind slippage in this case
    • Improvement of Ekman model to extract the geostrophic component of the buoy velocities (parameters fitted over the 1993-2012 period, by longitude, latitude and month) and computation of an Ekman model at 0m (used for undrogued boys) and at 15m depth  (used for drogued boys)
    • updated dataset of dynamic heights (1993-2012) computed from Temperature/Salinity profiles from CORA3.4

Releases of previous MDT

March 2010: CNES-CLS09_v1.1

Contents: mean of the 1993-1999 period sea surface above geoid, corrected from geophysical effects. The MDT_CNES-CLS09 is an estimate of the ocean MDT for the 1993-1999 period. The MDT for a different time period P can be easily deduced using altimetric Sea Level Anomalies referenced to the 1993-1999 period with : MDTP=MDT93-99+<SLA93-99>P.  The Ssalto/Duacs multimisson (M)ADT products from the Duacs 2014 (V15.0) are computed with a new MDT referenced over a twenty-year period [1993-2012] which doesn't correspond to this MDT CNES-CLS09.
Description: based on 4.5 years of GRACE data, and 15 years of altimetry and in-situ data (hydrologic and drifters data). (More information).

The strongest changes with the CNES-CLS09_v1.0 concern the mean velocity estimate in the equatorial band: due to the failure of the geostrophic approximation near the equator, no velocity estimates were given in the CNES-CLS09_v1.0 release for the [-3°,3°] latitudinal band. A specific work has been done to estimate the mean velocities at the equator.

Figure 1: Mean velocity module (in cm/s) in the [-15°, 15°] latitudinal band in the CNES-CLS09_v1.0 release (top) and in the CNES-CLS09_v1.1 release (bottom).

The height differences between the two releases is small with a global mean difference of -0.02 cm and a rms difference of 0.05 cm.

Figure 2: Map of height differences (in cm) between the CNES-CLS09_v1.0 MDT and the CNES-CLS09_v1.1 MDT

October 2009: CNES-CLS09_v1.0.

Compared to the previous RIO05 field, the main improvements are:

  • The use of the recent EIGEN-GRGS.RL02.MEAN-FIELD based on 4,5 years of GRACE data
  • The use of an updated dataset of drifting buoy velocities(1993-2008)and dynamic heights(1993-2007)
  • The use of an improved Ekman model to extract the geostrophic component of the buoy velocities
  • The use of an improved processing method of the dynamic heights allowing to make use of T/S profiles to different reference depths.
  • Estimation was done on a 1/4° resolution grid(instead of 1/2° for RIO05).

2005: Rio05 MDT

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