Combined mean dynamic topography - MDT CNES-CLS22

Types of dataset: auxiliary products

DOI: 10.24400/527896/a01-2023.003 -  more metadata

Contents:  The Mean Dynamic Topography MDT-CNES-CLS22 is an estimate of the mean over the 1993-2012 period of the sea surface height above geoid. This is consistent with the reference time period also used in the SSALTO DUACS products.

Use: ocean circulation, operational oceanography

Description: use of the latest GOCO06S geoid model (based on the complete GOCE mission fully reprocessed and 14 years of GRACE data) and 30 years of altimetry and in-situ data (hydrologic, drifters and High Frequency radar on a limited area). (More information)

Geographic coverage: global, 1/8°

Distribution media: Authenticated FTP, gridded data extraction tool and Thredds Data Server (TDS).

Condition of access: The MDT-CNES-CLS22 is a standard product as stated in the licence agreement. Please see our FAQ to access this product (distinction if you are already an Aviso+ user or not).

Copyright: 1992-ongoing Cnes-CLS

References:
- Jousset S., Mulet S., Wilkin J., Greiner E., Dibarboure G. and Picot N.: “New global Mean Dynamic Topography CNES-CLS-22 combining drifters, hydrological profiles and High Frequency radar data”, OSTST 2022, https://doi.org/10.24400/527896/a03-2022.3292.
- Image of the month March 2022: a new mean dynamic topography released

to get access Aviso products and select the product "MDT_CNES_CLS (Global Mean Dynamic Topography)"

MDT

Product Authenticated access service type format File weight
MDT-CNES-CLS22 access via MY AVISO+ and select the product
"MDT_CNES_CLS (Global Mean Dynamic Topography)"		 gridded NetCDF4 48 Mb

Releases of previous MDT

MDT-CNES-CLS18

All information about this MDT can be found in a dedicated page.

MDT_CNES-CLS13 improvements 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

Comparison between MDT CNES-CLS13 and MDT09 can be found in a dedicated page.
Details about MDT CNES-CLS13 can be found here.

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

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).

Rio05 MDT