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Discussion papers
https://doi.org/10.5194/essd-2019-102
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/essd-2019-102
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: data description paper 26 Jun 2019

Submitted as: data description paper | 26 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Earth System Science Data (ESSD).

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

Felix L. Müller1, Denise Dettmering1, Claudia Wekerle2, Christian Schwatke1, Marcello Passaro1, Wolfgang Bosch1, and Florian Seitz1 Felix L. Müller et al.
  • 1Deutsches Geodätisches Forschungsinstitut, Technische Universität München, Arcisstraße 21, 80333 Munich, Germany
  • 2Climate Dynamics, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bussestraße 24, 27570 Bremerhaven, Germany

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).

Felix L. Müller et al.
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Felix L. Müller et al.
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Geostrophic Currents in the northern Nordic Seas – A Combined Dataset of Multi-Mission Satellite Altimetry and Ocean Modeling (data) F. L. Müller, D. Dettmering, C. Wekerle, C. Schwatke, W. Bosch, and F. Seitz https://doi.org/10.1594/PANGAEA.900691

Felix L. Müller et al.
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Short summary
In polar regions by satellite altimetry derived geostrophic currents (GC) suffer from irregular and sparse data coverage. Therefore, a new dataset is presented, combining along-track derived dynamic ocean topography (DOT) heights with simulated differential water heights. For this purpose a combination method, based on Principal Component Analysis, is used. The results are combined and spatio-temporal consistent DOT and derived GC representations on unstructured, triangular formulated grids.
In polar regions by satellite altimetry derived geostrophic currents (GC) suffer from irregular...
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