Geostrophic currents in the northern Nordic Seas from a combination of multi-mission satellite altimetry and ocean modeling
Item
Title (Dublin Core)
Geostrophic currents in the northern Nordic Seas from a combination of multi-mission satellite altimetry and ocean modeling
Description (Dublin Core)
<p>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.</p>
<p>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.</p>
<p>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.</p>
<p>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 <span class="inline-formula">0.004</span> m s<span class="inline-formula"><sup>−1</sup></span> in the zonal and <span class="inline-formula">0.02</span> m s<span class="inline-formula"><sup>−1</sup></span> 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 <span class="inline-formula">0.15</span> m s<span class="inline-formula"><sup>−1</sup></span>.</p>
<p>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 <a href="https://doi.org/10.1594/PANGAEA.900691">https://doi.org/10.1594/PANGAEA.900691</a> <span class="cit" id="xref_paren.1">(<a href="#bib1.bibx18">Müller et al.</a>, <a href="#bib1.bibx18">2019</a>)</span>.</p>
<p>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.</p>
<p>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.</p>
<p>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 <span class="inline-formula">0.004</span> m s<span class="inline-formula"><sup>−1</sup></span> in the zonal and <span class="inline-formula">0.02</span> m s<span class="inline-formula"><sup>−1</sup></span> 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 <span class="inline-formula">0.15</span> m s<span class="inline-formula"><sup>−1</sup></span>.</p>
<p>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 <a href="https://doi.org/10.1594/PANGAEA.900691">https://doi.org/10.1594/PANGAEA.900691</a> <span class="cit" id="xref_paren.1">(<a href="#bib1.bibx18">Müller et al.</a>, <a href="#bib1.bibx18">2019</a>)</span>.</p>
Creator (Dublin Core)
F. L. Müller
D. Dettmering
C. Wekerle
C. Schwatke
M. Passaro
W. Bosch
F. Seitz
Subject (Dublin Core)
Environmental sciences
GE1-350
Geology
QE1-996.5
Publisher (Dublin Core)
Copernicus Publications
Date (Dublin Core)
2019-11-01T00:00:00Z
Type (Dublin Core)
article
Identifier (Dublin Core)
10.5194/essd-11-1765-2019
1866-3508
1866-3516
https://doaj.org/article/dae88c49324f43e6b482b3d969640d95
Source (Dublin Core)
Earth System Science Data, Vol 11, Pp 1765-1781 (2019)
Language (Dublin Core)
EN
Relation (Dublin Core)
https://www.earth-syst-sci-data.net/11/1765/2019/essd-11-1765-2019.pdf
https://doaj.org/toc/1866-3508
https://doaj.org/toc/1866-3516
Provenance (Dublin Core)
Journal Licence: CC BY