Assimilation of satellite altimetry referenced to the new GRACE geoid estimate

Birol, Florence; Brankart, Jean-Michel; Lemoine, Jean‐Michel; Brasseur, Pierre; Verron, Jacques

doi:10.1029/2004gl021329

Cited by 14 publications

(11 citation statements)

References 10 publications

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“…Our conclusion therefore is similar to the recent results from Birol et al (2005) in that existing geoids do show skill in improving ocean circulation estimates on the large scale.…”

Section: Discussionsupporting

confidence: 91%

Impact of Accurate Geoid Fields on Estimates of the Ocean Circulation

Stammer

Köhl

Wunsch

2007

Journal of Atmospheric and Oceanic Technology

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The impact of new geoid height models on estimates of the ocean circulation, now available from the Gravity Recovery and Climate Experiment (GRACE) spacecraft, is assessed, and the implications of far more accurate geoids, anticipated from the European Space Agency's (ESA) Gravity and Ocean Circulation Explorer (GOCE) mission, are explored. The study is based on several circulation estimates obtained over the period 1992-2002 by combining most of the available ocean datasets with a global general circulation model on a 1°horizontal grid and by exchanging only the EGM96 geoid model with two different geoid models available from GRACE. As compared to the EGM96-based solution, the GRACE geoid leads to an estimate of the ocean circulation that is more consistent with the Levitus temperature and salinity climatology. While not a formal proof, this finding supports the inference of a substantially improved GRACE geoid skill. However, oceanographic implications of the GRACE model are only modest compared to what can be obtained from ocean observations alone. To understand the extent to which this is merely a consequence of a not-optimally converged solution or if a much more accurate geoid field could in principle play a profound role in the ocean estimation procedure, an additional experiment was performed in which the geoid error was artificially reduced relative to all other datasets. Adjustments occur then in all elements of the ocean circulation, including 10% changes in the meridional overturning circulation and the corresponding meridional heat transport in the Atlantic. For an optimal use of new geoid fields, improved error information is required. The error budget of existing time-mean dynamic topography estimates may now be dominated by residual errors in time-mean altimetric corrections. Both these and the model errors need to be better understood before improved geoid estimates can be fully exploited. As is commonly found, the Southern Ocean is of particular concern.

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“…Our conclusion therefore is similar to the recent results from Birol et al (2005) in that existing geoids do show skill in improving ocean circulation estimates on the large scale.…”

Section: Discussionsupporting

confidence: 91%

Impact of Accurate Geoid Fields on Estimates of the Ocean Circulation

Stammer

Köhl

Wunsch

2007

Journal of Atmospheric and Oceanic Technology

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“…The changed vertical density structure in turn has a direct impact on the simulation of sea level. Some studies have shown that the sea level data assimilation helps to improve model's climatology (Parent et al, 2003;Birol et al, 2005;Fu et al, 2009a). Comparisons in this study show that the SLA assimilation was also helpful for improving the variability of the subsurface temperature and salinity, provided that the assimilation method is appropriately used.…”

Section: Discussionmentioning

confidence: 66%

“…This method takes into consideration vertical correlations for both temperature and salinity background errors and the nonlinear T -S relation. In addition to the 3DVAR, EnOI and other reduced forms of the ensemble Kalman filter (EnKF) such as Singular Evolutive extended Kalman (SEEK) filter, are also applied to assimilate sea level data in OGCMs Parent et al, 2003;Birol et al, 2005;Oke et al, 2008;Counillon and Bertino, 2009). The ensemble-based methods present a relatively straightforward method in altimetric data assimilation by utilizing the inherent multivariate relation.…”

Section: Introductionmentioning

confidence: 99%

Altimetric data assimilation by EnOI and 3DVAR in a tropical pacific model: Impact on the simulation of variability

2012

Adv. Atmos. Sci.

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When altimetric data is assimilated, 3DVAR and Ensemble Optimal Interpolation (EnOI) have different ways of projecting the surface information downward. In 3DVAR, it is achieved by minimizing a cost function relating the temperature, salinity, and sea level. In EnOI, however, the surface information is propagated to other variables via a stationary ensemble. In this study, the differences between the two methods were compared and their impacts on the simulated variability were evaluated in a tropical Pacific model.Sea level anomalies (SLA) from the TOPEX/Poseidon were assimilated using both methods on data from 1997 to 2001 in a coarse resolution model. Results show that the standard deviation of sea level was improved by both methods, but the EnOI was more effective in the central/eastern Pacific. Meanwhile, the SLA evolution was better reproduced with EnOI than with 3DVAR. Correlations of temperature with the reanalysis data increased with EnOI by 0.1-0.2 above 200 m. In the eastern Pacific below 200 m, the correlations also increased by 0.2. However, the correlations decreased with 3DVAR in many areas. Correlations with the independent TAO profiles were also compared at two locations. While the correlations increased by up to 0.2 at some depths with EnOI, 3DVAR generally reduced the correlations by 0.1-0.3. Though both methods were able to reduce the model-data difference in climatological sense, 3DVAR appears to have degraded the simulated variability, especially during El Niño-Southern Oscillation events. For salinity, similar results were found from the correlations. This tendency should be considered in future SLA assimilations, though the comparisons may vary among different model implementations.

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“…In a higher-resolution, North Atlantic system, Birol et al (2005) showed that using a GRACEderived MDT may locally improve the representation of current velocities but at the expense of a less accurate temperature field. ''Spurious'' temporal variability as a consequence of the abrupt jumps resulting from the use of external MDT information is not such a problem if there is no need for a continuous historical reanalysis, but mainly an estimation of the current ocean state.…”

Section: Mean Dynamic Topographymentioning

confidence: 99%

Assimilation of Altimeter Data in the ECMWF Ocean Analysis System 3

Vidard

Balmaseda

Anderson

2009

Monthly Weather Review

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The latest version of the ECMWF ocean analysis system was recently introduced into operational use. This not only provides initial conditions for the monthly and seasonal forecast systems but also creates a historical reanalysis. For the first time, altimeter data are used in the ECMWF operational ocean analysis. However, making good use of altimetric sea level information was not easy and several difficulties had to be overcome. Various strategies were tried and compared. Attempts to use mean sea level from gravimetric satellites were also tried, but no satisfactory method of using this data was found. The altimetric data used show a marked rising trend that cannot be directly represented in the model as the Boussinesq approximation is used. A strategy for dealing with the trend is given. Results of Observing System Experiments (OSEs) with and without altimeter data are described and results are compared to illustrate the benefits of using altimetry. Although the results are positive, further developments are needed to more fully utilize the data.

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Assimilation of satellite altimetry referenced to the new GRACE geoid estimate

Cited by 14 publications

References 10 publications

Impact of Accurate Geoid Fields on Estimates of the Ocean Circulation

Impact of Accurate Geoid Fields on Estimates of the Ocean Circulation

Altimetric data assimilation by EnOI and 3DVAR in a tropical pacific model: Impact on the simulation of variability

Assimilation of Altimeter Data in the ECMWF Ocean Analysis System 3

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