Mean dynamic topography estimates purely based on GOCE gravity field models and altimetry

Becker, S.; Brockmann, Jan Martin; Schuh, Wolf-Dieter

doi:10.1002/2014gl059510

Cited by 20 publications

(18 citation statements)

References 14 publications

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“…Several sophisticated approaches to optimal filtering of an altimetric MDT have recently been developed (e.g. Bingham et al 2011;Knudsen et al 2011;Slobbe et al 2012;Becker et al 2014), each of which has pointed to the deficiencies of simple low-pass spatial filtering of the MDT field to reduce noise. However, in the present case we believe that such a simple approach is adequate in describing the MDT's main features.…”

Section: Mdt From Altimetry Minus Geoidmentioning

confidence: 99%

The status of measurement of the Mediterranean mean dynamic topography by geodetic techniques

Woodworth

Gravelle

Marcos

et al. 2015

J Geod

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We review the measurement of the mean dynamic topography (MDT) of the Mediterranean using ellipsoidal heights of sea level at discrete tide gauge locations, and across the entire basin using satellite altimetry, subtracting estimates of the geoid obtained from recent models. This 'geodetic approach' to the determination of the MDT can be compared to the independent 'ocean approach' that involves the use of in situ oceanographic measurements and ocean modelling. We demonstrate that with modern geoid and ocean models there is an encouraging level of consistency between the two sets of MDTs. In addition, we show how important geodetic MDT information can be in judging between existing global ocean circulation models, and in providing insight for the development of new ones. The review makes clear the major limitations in Mediterranean data sets that prevent a more complete validation, including the need for improved geoid models of high spatial resolution and accuracy. Suggestions are made on how a greater amount of reliable geo-located tide gauge information can be obtained in the future. IntroductionThis paper discusses the mean dynamic topography (MDT) of the Mediterranean and its measurement by geodetic techniques. The MDT is the amount by which the Mean Sea Surface (MSS) is further from the centre of the Earth than a surface called the geoid, which is an equipotential surface resulting from the Earth's spatially-varying gravity field, and which would correspond to the MSS in the absence of an ocean circulation. An accurate measurement of the MDT can, therefore, provide oceanographers with insight into the circulation. Conversely, knowledge of the circulation, obtained by a number of oceanographic techniques can be used to infer the MDT. 2Much is already known about the mean circulation of the Mediterranean and its variability (e.g. Pinardi and Masetti 2000) and, therefore, also about the spatial variation of its MDT. This insight has largely been obtained using in situ oceanographic measurements and ocean modelling. However, in recent years major advances have been made in geodetic techniques that have enabled the MDT to be determined, for the first time, as the difference between MSS and geoid to the accuracy required for oceanographic research (e.g. Bingham et al. 2014). These techniques have primarily involved satellite altimetry to provide the MSS over the open ocean and space gravity to provide the geoid, complemented at the coast with the use of tide gauges equipped with Global Positioning System (GPS) equipment (Woodworth et al. 2012). By studying the Mediterranean, particular lessons can be learned in the use of these techniques, notably by pointing to missing infrastructure and data limitations, which can also be relevant to discussion of the MDT in other data-sparse regions around the world.Models of the MDT in the Mediterranean have already been made by previous authors in various ways (e.g. Rio et al. 2014a). Consequently, the present paper focuses on reviewing how an MDT model can be compa...

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Section: Mdt From Altimetry Minus Geoidmentioning

confidence: 99%

The status of measurement of the Mediterranean mean dynamic topography by geodetic techniques

Woodworth

Gravelle

Marcos

et al. 2015

J Geod

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“…This section summarizes some characteristics of the model and describes comparisons with independent gravity field models. The detailed and specific validation of the model is not part of this paper and will be performed in the future using independent methods and data sets as done for the previous GOCE models by Gruber et al [], Hirt et al [], Rexer et al [], Becker et al [], and Voigt and Denker [].…”

Section: The Solution Egm_tim_rl05mentioning

confidence: 99%

EGM_TIM_RL05: An independent geoid with centimeter accuracy purely based on the GOCE mission

Brockmann

Zehentner

Höck

et al. 2014

Geophysical Research Letters

145

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After more than 4.5 years in orbit, the Gravity field and steady‐state Ocean Circulation Explorer (GOCE) mission ended with the reentry of the satellite on 11 November 2013. This publication serves as a reference for the fifth gravity field model based on the time‐wise approach (EGM_TIM_RL05), a global model only determined from GOCE observations. Due to its independence of any other gravity data, a consistent and homogeneous set of spherical harmonic coefficients up to degree and order 280 (corresponding to spatial resolution of 71.5 km on ground) is provided including a full covariance matrix characterizing the uncertainties of the model. The associated covariance matrix realistically describes the model quality. It is the first model which is purely based on GOCE including all observations collected during the entire mission. The achieved mean global accuracy is 2.4 cm in terms of geoid heights and 0.7 mGal for gravity anomalies at a spatial resolution of 100 km.

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“…In both products, the geostrophic component is obtained by deriving altimeter maps of the ocean absolute dynamic topography, calculated as the sum of the altimeter Sea Level Anomalies (SLA) and an ocean Mean Dynamic Topography (MDT). A number of studies have demonstrated the importance of the recent GOCE (Gravity and Ocean Circulation Experiment) mission for calculating the ocean MDT [ Bingham et al ., ; Knudsen et al ., ; Mulet et al ., ; Becker et al ., ]. The resulting fields are accurate at the centimeter level at scales of around 100–150 km [ Mulet et al ., ], which is a significant improvement over the previous Gravity Recovery and Climate Experiment (GRACE)‐based geoid models.…”

Section: Introductionmentioning

confidence: 99%

Beyond GOCE for the ocean circulation estimate: Synergetic use of altimetry, gravimetry, and in situ data provides new insight into geostrophic and Ekman currents

Rio

Mulet

Picot

2014

Geophysical Research Letters

333

285

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Accurate estimate of ocean surface currents is both a challenging issue and a growing end-users requirement. In this paper ocean currents are calculated at two levels (surface and 15 m depth) as the sum of the geostrophic and Ekman components. First, a new, global, 1 4°M ean Dynamic Topography, called the CNES-CLS13 MDT, has been calculated and is now available for use by the oceanographic community. By exploiting information from surface drifters and Argo floats, the new MDT resolves spatial scales beyond the resolution permitted by the recent Gravity and Ocean Circulation Experiment (GOCE) geoid models (125 km). Associated mean geostrophic speeds in strong currents are increased by 200% on average compared to GOCE-based mean currents. In addition, for the first time, a two-level, monthly, empirical Ekman model that samples a spiral-like behavior is estimated. We show that combining both pieces of information leads to improved ocean currents compared to other existing observed products.

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Mean dynamic topography estimates purely based on GOCE gravity field models and altimetry

Cited by 20 publications

References 14 publications

The status of measurement of the Mediterranean mean dynamic topography by geodetic techniques

The status of measurement of the Mediterranean mean dynamic topography by geodetic techniques

EGM_TIM_RL05: An independent geoid with centimeter accuracy purely based on the GOCE mission

Beyond GOCE for the ocean circulation estimate: Synergetic use of altimetry, gravimetry, and in situ data provides new insight into geostrophic and Ekman currents

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