Improved statistics of sub-mesoscale eddies in the Baltic Sea retrieved from SAR imagery

Karimova, Svetlana; Gade, Martin

doi:10.1080/01431161.2016.1145367

Cited by 48 publications

(29 citation statements)

References 21 publications

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“…Upon the preprocessing step, every image was visually inspected at full resolution in search of eddy signatures described above and exemplified in Figure . Then by looking at eddy boundaries outlined due to accumulation of slicks, floating ice, or enhanced wave breaking, their location, diameter, vorticity sign, and manifestation type were defined manually, similarly as what was done, for example, in Dokken and Wahl (), Karimova (), Karimova and Gade (), and Atadzhanova et al (). All detected eddies were then split into two major groups—those identified over open‐water regions (hereinafter, open‐water (OW) eddies) and eddies manifested owing to spatial redistribution of drifting ice floes near the ice edge and in the marginal ice zone (hereinafter, MIZ eddies).…”

Section: Methodsmentioning

confidence: 99%

Eddies in the Western Arctic Ocean From Spaceborne SAR Observations Over Open Ocean and Marginal Ice Zones

et al. 2019

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The Western Arctic Ocean is a host to major ocean circulation systems, many of which generate eddies that can transport water masses and corresponding tracers over long distances from their formation sites. However, comprehensive observations of critical eddy characteristics are currently not available and are limited to spatially and temporally sparse in situ observations. Here we use high-resolution spaceborne synthetic aperture radar measurements to detect eddies from their surface imprints in ice-free sea surface roughness, and in sea ice patterns throughout marginal ice zones. We provide the first estimate of eddy characteristics extending over the seasonally ice-free and marginal ice zone regions of the Western Arctic Ocean, including their locations, diameters, and monthly distribution. Using available synthetic aperture radar data, we identified over 4,000 open ocean eddies, as well as over 3,500 eddies in marginal ice zones from June to October in 2007, 2011, and 2016. Eddies range in size between 0.5 and 100 km and are frequently found over the shelf and near continental slopes but also present in the deep Canada Basin and over the Chukchi Plateau. We find that cyclonic eddies are twice more frequent compared to anticyclonic eddies at the surface, distinct from the dominating anticyclonic eddies observed at depth by in situ moorings and ice-tethered profilers. Our study supports the notion that eddies are ubiquitous in the Western Arctic Ocean even in the presence of sea ice and emphasizes the need for improved ocean observations and modeling at eddy scales. Plain Language SummaryOcean eddies play an important role in the transport of heat, salt, and pollutants over long distances from their formation sites. However, their observations in the Arctic Ocean are complex due to severe weather and sea ice cover. Here we present results of high-resolution satellite observations over the ice-free ocean and in the marginal ice zones. Detailed eddy characteristics are for the first time presented for the Western Arctic Ocean. These results provide observational evidence that eddies are ubiquitous in this Arctic region even in the presence of sea ice and emphasize the need for improved ocean observations and modeling at eddy scales. Key Points: • First account of eddies in the Western Arctic Ocean is presented based on satellite observations over open ocean and marginal ice zones • Eddies range in size between 0.5 and 100 km and are ubiquitous over deep and shelf regions of the Western Arctic Ocean • Cyclonic eddies are twice more frequent compared to anticyclones

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Section: Methodsmentioning

confidence: 99%

Eddies in the Western Arctic Ocean From Spaceborne SAR Observations Over Open Ocean and Marginal Ice Zones

et al. 2019

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“…One way spiral eddies can form is through ageostrophic baroclinic instability associated with a background horizontal density gradient; and theoretical studies [21] show such eddies to have cyclonic vorticity and a spiral diameter D = 2 R d , where R d = (g ∆ρ/ρ H) 1/2 / f is the baroclinic deformation radius. Analysis of SAR spirals in the Baltic, Black, and Caspian seas shows that nearly all the spirals have a morphology consistent with cyclonic vorticity [19,20], a diameter proportional to R d [20], and are statistically associated with lateral density gradients [20]. Our analysis explicitly reveals the cyclonic vorticity, and based on the available measurements of water stratification, we estimate a value of R d~3 .7 km, which is close to a climatological value of 3.9 km near the study site [22].…”

Section: Spiral Pattern (Band 3 Data)mentioning

confidence: 99%

“…In synthetic aperture radar (SAR) imagery, at wind speeds of 0.2 to 5.6 m s −1 , the spiral arms would appear as relative dark streaks because of the wave-damping effect of algae-derived surface films. Sub-mesoscale eddies are thus manifested in SAR imagery as "black" spirals [19]. In the Baltic Sea, such black eddies have a mean diameter D = 6.4 km (s.d.…”

Section: Spiral Pattern (Band 3 Data)mentioning

confidence: 99%

Use of WorldView-2 Along-Track Stereo Imagery to Probe a Baltic Sea Algal Spiral

Marmorino

Chen

2019

Remote Sensing

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The general topic here is the application of very high-resolution satellite imagery to the study of ocean phenomena having horizontal spatial scales of the order of 1 kilometer, which is the realm of the ocean submesoscale. The focus of the present study is the use of WorldView-2 along-track stereo imagery to probe a submesoscale feature in the Baltic Sea that consists of an apparent inward spiraling of surface aggregations of algae. In this case, a single pair of images is analyzed using an optical-flow velocity algorithm. Because such image data generally have a much lower dynamic range than in land applications, the impact of residual instrument noise (e.g., data striping) is more severe and requires attention; we use a simple scheme to reduce the impact of such noise. The results show that the spiral feature has at its core a cyclonic vortex, about 1 km in radius and having a vertical vorticity of about three times the Coriolis frequency. Analysis also reveals that an individual algal aggregation corresponds to a velocity front having both horizontal shear and convergence, while wind-accelerated clumps of surface algae can introduce fine-scale signatures into the velocity field. Overall, the analysis supports the interpretation of algal spirals as evidence of a submesoscale eddy and of algal aggregations as indicating areas of surface convergence.

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“…His eddy definition is based on the detection of isolated anomalies in pressure. Karimova and Gade (2016) detected around 7000 sub-mesoscale eddies in the entire Baltic Sea based on SAR images between 2009 and 2010. However, even these Karimova and Gade (2016) cannot directly be compared to ours.…”

Section: Eddies In the Western Baltic Seamentioning

confidence: 99%

“…Additionally, features like the size of eddies, their sense of rotation, Rossby number or propagation distance can be important. Several studies investigated these features for the global ocean (e.g., Chelton et al, 2011;Petersen et al, 2013) as well as for smaller regions like the southern New England shelf (Kirincich, 2016), the California Bight (Kurian et al, 2011;Dong et al, 2012), the South China Sea (Xiu et al, 2010;Chen et al, 2011), the Mediterranean Outflow (Aguiar et al, 2013), or the Baltic Sea (Reißmann, 2005;Karimova and Gade, 2016). Yet, McGillicuddy (2016) addressed the effect of these features on biological processes.…”

Section: Introductionmentioning

confidence: 99%

Eddies: Fluid Dynamical Niches or Transporters?–A Case Study in the Western Baltic Sea

et al. 2019

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Improved statistics of sub-mesoscale eddies in the Baltic Sea retrieved from SAR imagery

Cited by 48 publications

References 21 publications

Eddies in the Western Arctic Ocean From Spaceborne SAR Observations Over Open Ocean and Marginal Ice Zones

Eddies in the Western Arctic Ocean From Spaceborne SAR Observations Over Open Ocean and Marginal Ice Zones

Use of WorldView-2 Along-Track Stereo Imagery to Probe a Baltic Sea Algal Spiral

Eddies: Fluid Dynamical Niches or Transporters?–A Case Study in the Western Baltic Sea

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