On the assimilation of absolute geodetic dynamic topography in a global ocean model: impact on the deep ocean state

Androsov, Alexey; Nerger, Lars; Schnur, Reiner; Schröter, Jens; Albertella, A.; Rummel, Reiner; Savcenko, R; Bösch, Wolfgang; Skachko, Sergey; Danilov, Sergey

doi:10.1007/s00190-018-1151-1

Cited by 14 publications

(14 citation statements)

References 66 publications

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“…However, inconsistencies due to the higher noise level of the observations, especially in sea-ice areas and the enhanced smoothing of the model are demonstrated. For example, an offset of about half a meter exists between the two datasets since the datum of FESOM is not defined with respect to a standard reference frame (Androsov et al, 2018). Moreover, the annual sea level variability observed by the two datasets differs by a few centimeters.…”

Section: Discussionmentioning

confidence: 99%

“…where u ≡ (u, v) is the velocity vector and H is the water depth. Water elevations are relative to a geopotential surface and therefore comparable to an altimetry derived dynamic ocean topography (Androsov et al, 2018). The upper limit in the in-10 tegration is set to zero, which corresponds to a linear free-surface approximation.…”

Section: Model Basis: Finite Element Sea-ice Ocean Model (Fesom)mentioning

confidence: 99%

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Dynamic Ocean Topography of the Greenland Sea: A comparison between satellite altimetry and ocean modeling

Müller

Wekerle

Dettmering

et al. 2018

Preprint

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Abstract. The dynamic ocean topography (DOT) in the polar seas can be described by satellite altimetry sea surface height observations combined with geoid information and by ocean models. The altimetry observations are characterized by an irregular sampling and seasonal sea-ice coverage complicating reliable DOT estimations. Models display various spatio-temporal resolutions, but are limited to their computational and mathematical context and introduced forcing models. In the present paper, ALES+ retracked altimetry ranges and derived along-track DOT heights of ESA's Envisat and water heights of the Finite Element Sea-ice Ocean Model (FESOM) are compared to investigate similarities and discrepancies. The study period covers the years 2003–2009. An assessment analysis regarding seasonal DOT variabilities shows good accordance and confirms the most dominant impact of the annual signal in both datasets. A comparison based on estimated regional annual signal components shows 2–3 times stronger amplitudes of the observations but good agreement of the phase. Reducing both datasets by constant offsets and the annual signal reveals small regional residuals and highly correlated DOT time series (correlation coefficient at least 0.67). The highest correlations can be found in areas that are ice-free and affected by ocean currents. However, differences are visible in sea-ice covered shelf regions. Furthermore, remaining constant artificial elevations in the observational data can be addressed to an insufficient representation of the used geoid. In general, the comparison results in good accordance between simulated and altimetry based description of the DOT in the Greenland Sea. Furthermore, the investigation shows that combining both datasets and exploiting the advantages of along-track altimetry observations and those of homogeneous modeled DOT representations leads to a deeper comprehension of the Arctic Ocean's DOT.

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Section: Discussionmentioning

confidence: 99%

Section: Model Basis: Finite Element Sea-ice Ocean Model (Fesom)mentioning

confidence: 99%

Dynamic Ocean Topography of the Greenland Sea: A comparison between satellite altimetry and ocean modeling

Müller

Wekerle

Dettmering

et al. 2018

Preprint

Self Cite

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“…bathymetry). The bathymetry acts as geopotential surface, which enables a linkage to the altimetry derived DOT heights (Androsov et al (2018)). FESOM is a global multiresolution circulation model with an included sea ice component resolving the major sea ice drift patterns.…”

Section: Simulation: Finite Element Sea Ice Ocean Model (Fesom)mentioning

confidence: 99%

Geostrophic Currents in the northern Nordic Seas from a Combination of Multi-Mission Satellite Altimetry and Ocean Modeling

Müller¹,

Dettmering²,

Wekerle³

et al. 2019

Preprint

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Abstract. A deeper knowledge about geostrophic ocean surface currents in the northern Nordic Seas supports the understanding of ocean dynamics in an area affected by sea ice and rapidly changing environmental conditions. Monitoring these areas by satellite altimetry results in a fragmented and irregularly distributed data sampling and prevents the computation of homogeneous and highly resolved spatio-temporal datasets. In order to overcome this problem, an ocean model is used to fill in data when altimetry observations are missing. The present study provides a novel dataset based on a combination of along-track satellite altimetry derived dynamic ocean topography (DOT) elevations and simulated differential water heights (DWH) from the Finite Element Sea ice Ocean Model (FESOM). This innovative dataset differs from classical assimilation methods because it substitutes altimetry data with the model output, when altimetry fails or is not available. The combination approach is mainly based on a Principal Component Analysis (PCA) after reducing both quantities by their constant and seasonal signals. In the main step, the most dominant spatial patterns of the modeled differential water heights as provided by the PCA are linked with the temporal variability of the estimated DOT from altimetry by performing a Principal Component Synthesis (PCS). After the combination, the by altimetry obtained annual signal and a constant offset are re-added in order to reference the final data product to the altimetry height level. Surface currents are computed by applying the geostrophic flow equations to the combined topography. The resulting final product is characterized by the spatial resolution of the ocean model around 1 km and the temporal variability of the altimetry along-track derived DOT heights. The combined DOT is compared to an independent DOT product resulting in a positive correlation of about 80 % to provide more detailed information about short periodic and finer spatial structures. The derived geostrophic velocity components are evaluated by in-situ surface drifter observations. Summarizing all drifter observations in equal-sized bins and comparing the velocity components shows good agreement in spatial patterns, magnitude and flow direction. Mean differences of 0.004 m/s in the zonal and 0.02 m/s in the meridional component are observed. A direct pointwise comparison between the drifter trajectories and to the drifter location interpolated combined geostrophic velocity components indicates that about 94 % of all residuals are smaller than 0.15 m/s. The dataset is able to provide surface circulation information within the sea ice area and can be used to support a deeper comprehension of ocean currents in the northern Nordic Seas affected by rapid environmental changes in the 1995–2012 time period. The data is available at https://doi.org/10.1594/PANGAEA.900691 (Müller et al., 2019).

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“…3) with respect to the ocean bottom topography (i.e., bathymetry). The bathymetry acts as geopotential surface, which enables a linkage to the altimetry-derived DOT heights (Androsov et al, 2018). FESOM is a global multi-resolution ocean circulation model with an included sea ice component resolving the major sea ice drift patterns.…”

Section: Simulation: Finite Element Sea Ice Ocean Model (Fesom)mentioning

confidence: 99%

“…Farrell et al, 2012) or to satellite altimetry missions dedicated to sea ice conditions (e.g., CryoSat-2; Kwok and Morison, 2015, and ICESat;Kwok and Morison, 2011). Nevertheless, monthly DOT estimates have been generated and published by Armitage et al (2016) using DOT observations derived from long-term satellite altimetry. Furthermore, Armitage et al (2017) presented a dataset based on a 12-year altimetry observation (from 2003 to 2014) of geostrophic currents at a monthly time frame on a 0.75 • × 0.25 • longitude-latitude regular data grid up to a latitudinal limit of 81.5 • N. The authors created a dataset which combines satellite-altimetry observations from icecovered and open-ocean regions.…”

Section: Introductionmentioning

confidence: 99%

Geostrophic currents in the northern Nordic Seas from a combination of multi-mission satellite altimetry and ocean modeling

Müller¹,

Dettmering²,

Wekerle

et al. 2019

Earth Syst. Sci. Data

Self Cite

View full text Add to dashboard Cite

Abstract. A deeper knowledge about geostrophic ocean surface currents in the northern Nordic Seas supports the understanding of ocean dynamics in an area affected by sea ice and rapidly changing environmental conditions. Monitoring these areas by satellite altimetry results in a fragmented and irregularly distributed data sampling and prevents the computation of homogeneous and highly resolved spatio-temporal datasets. In order to overcome this problem, an ocean model is used to fill in data when altimetry observations are missing. The present study provides a novel dataset based on a combination of along-track satellite-altimetry-derived dynamic ocean topography (DOT) elevations and simulated differential water heights (DWHs) from the Finite Element Sea ice Ocean Model (FESOM) version 1.4. This innovative dataset differs from classical assimilation methods because it substitutes altimetry data with the model output when altimetry fails or is not available. The combination approach is mainly based on a principal component analysis (PCA) after reducing both quantities by their constant and seasonal signals. In the main step, the most-dominant spatial patterns of the modeled differential water heights as provided by the PCA are linked with the temporal variability in the estimated DOT from altimetry by performing a principal component synthesis (PCS). After the combination, the annual signal obtained by altimetry and a constant offset are re-added in order to reference the final data product to the altimetry height level. Surface currents are computed by applying the geostrophic flow equations to the combined topography. The resulting final product is characterized by the spatial resolution of the ocean model around 1 km and the temporal variability in the altimetry along-track derived DOT heights. The combined DOT is compared to an independent DOT product, resulting in a positive correlation of about 80 %, to provide more detailed information about short periodic and finer spatial structures. The derived geostrophic velocity components are evaluated by in situ surface drifter observations. Summarizing all drifter observations in equally sized bins and comparing the velocity components shows good agreement in spatial patterns, magnitude and flow direction. Mean differences of 0.004 m s−1 in the zonal and 0.02 m s−1 in the meridional component are observed. A direct pointwise comparison between the combined geostrophic velocity components interpolated onto the drifter locations indicates that about 94 % of all residuals are smaller than 0.15 m s−1. The dataset is able to provide surface circulation information within the sea ice area and can be used to support a deeper comprehension of ocean currents in the northern Nordic Seas affected by rapid environmental changes in the 1995–2012 time period. The data are available at https://doi.org/10.1594/PANGAEA.900691 (Müller et al., 2019).

show abstract

On the assimilation of absolute geodetic dynamic topography in a global ocean model: impact on the deep ocean state

Cited by 14 publications

References 66 publications

Dynamic Ocean Topography of the Greenland Sea: A comparison between satellite altimetry and ocean modeling

Dynamic Ocean Topography of the Greenland Sea: A comparison between satellite altimetry and ocean modeling

Geostrophic Currents in the northern Nordic Seas from a Combination of Multi-Mission Satellite Altimetry and Ocean Modeling

Geostrophic currents in the northern Nordic Seas from a combination of multi-mission satellite altimetry and ocean modeling

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