Baroclinic instability and the mesoscale eddy field around the Lofoten Basin

Isachsen, Pål Erik

doi:10.1002/2014jc010448

Cited by 57 publications

(80 citation statements)

References 43 publications

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“…This is in line with Benilov [], who showed that bottom depressions stabilize ACEs, which can reduce breakups and reformation of ACEs. The larger eddy generation in the eastern Lofoten Basin near the continental slope and along the northern part of the slope current (above 70°N) is associated with the eddy shedding in these regions from the slope current [ Rossby et al ., ; Isachsen , ; Raj et al ., ]. Indications of ACEs being shed from the Norwegian Atlantic Front Current along the Mohn Ridge can also be seen in Figure c.…”

Section: Resultsmentioning

confidence: 99%

Quantifying mesoscale eddies in the Lofoten Basin

Raj¹,

Johannessen

Eldevik

et al. 2016

JGR Oceans

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The Lofoten Basin is the most eddy rich region in the Norwegian Sea. In this paper, the characteristics of these eddies are investigated from a comprehensive database of nearly two decades of satellite altimeter data (1995–2013) together with Argo profiling floats and surface drifter data. An automated method identified 1695/1666 individual anticyclonic/cyclonic eddies in the Lofoten Basin from more than 10,000 altimeter‐based eddy observations. The eddies are found to be predominantly generated and residing locally. The spatial distributions of lifetime, occurrence, generation sites, size, intensity, and drift of the eddies are studied in detail. The anticyclonic eddies in the Lofoten Basin are the most long‐lived eddies (>60 days), especially in the western part of the basin. We reveal two hotspots of eddy occurrence on either side of the Lofoten Basin. Furthermore, we infer a cyclonic drift of eddies in the western Lofoten Basin. Barotropic energy conversion rates reveals energy transfer from the slope current to the eddies during winter. An automated colocation of surface drifters trapped inside the altimeter‐based eddies are used to corroborate the orbital speed of the anticyclonic and cyclonic eddies. Moreover, the vertical structure of the altimeter‐based eddies is examined using colocated Argo profiling float profiles. Combination of altimetry, Argo floats, and surface drifter data is therefore considered to be a promising observation‐based approach for further studies of the role of eddies in transport of heat and biomass from the slope current to the Lofoten Basin.

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Section: Resultsmentioning

confidence: 99%

Quantifying mesoscale eddies in the Lofoten Basin

Raj¹,

Johannessen

Eldevik

et al. 2016

JGR Oceans

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“…9) may alter the stability characteristics of the flow leading to enhanced baroclinic instability (Isachsen 2011). The steeper topography associated with these conditions also tends to make the flow more baroclinically unstable (Spall 2010;Isachsen 2015). This in turn will impact the cross-stream eddy fluxes of heat and salt from the NIIC into the interior, which is an important component of the local overturning cell in the Iceland Sea (Våge et al 2011).…”

Section: Pathway Of the Nijmentioning

confidence: 99%

The North Icelandic Jet and its relationship to the North Icelandic Irminger Current

Pickart¹,

Spall²,

Torres³

et al. 2017

j mar res

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Shipboard hydrographic and velocity sections are used to quantify aspects of the North Icelandic Jet (NIJ), which transports dense overflow water to Denmark Strait, and the North Icelandic Irminger Current (NIIC), which imports Atlantic water to the Iceland Sea. The mean transports of the two currents are comparable, in line with previous notions that there is a local overturning cell in the Iceland Sea that transforms the Atlantic water to dense overflow water. As the NIJ and NIIC flow along the north side of Iceland, they appear to share a common front when the bottom topography steers them close together, but even when they are separate there is a poleward flow inshore of the NIJ. The interannual variability in salinity of the inflowing NIIC is in phase with that of the outflowing NIJ. It is suggested, however, that the NIIC signal does not dictate that of the NIJ. Instead, the combination of liquid and solid freshwater flux from the east Greenland boundary can account for the observed net freshening of the NIIC to the NIJ for the densest half of the overturning circulation in the northwest Iceland Sea. This implies that the remaining overturning must occur in a different geographic area, consistent with earlier model results. The year-to-year variability in salinity of the NIJ can be explained by applying annual anomalies of evaporation minus precipitation over the Iceland Sea to a one-dimensional mixing model. These anomalies vary in phase with the wind stress curl over the North Atlantic subpolar gyre, which previous studies have shown drives the interannual variation in salinity of the inflowing NIIC.

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“…Figure a) is significantly reduced downstream of the Lofoten slope. We hypothesize that this reduction may be due, but not limited (reasons to be discussed later), to the vigorous cross‐slope eddy shedding here [ Isachsen , ; Raj et al ., ; Jakobsen et al ., ]. To support this conjecture, the slope‐to‐basin propagation of temperature anomaly is studied.…”

Section: Poleward Propagating Warm Temperature Anomaliesmentioning

confidence: 99%

“…This indicates that mesoscale eddies account for a large fraction of the total EKE. These eddies are shed persistently from the slope current and drift into the LB interior (see the supporting information animation) [ Isachsen , ; Raj et al ., ; Søiland and Rossby , ; Koszalka et al ., ; Rossby et al ., ; Köhl , ].…”

Section: Poleward Propagating Warm Temperature Anomaliesmentioning

confidence: 99%

On the flow of Atlantic water and temperature anomalies in the Nordic Seas toward the Arctic Ocean

et al. 2015

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The climatic conditions over the Arctic Ocean are strongly influenced by the inflow of warm Atlantic water conveyed by the Norwegian Atlantic Slope Current (NwASC). Based on sea surface height (SSH) data from altimetry, we develop a simple dynamical measure of the NwASC transport to diagnose its spatio‐temporal variability. This supports a dynamical division of the NwASC into two flow regimes; the Svinøy Branch (SvB) in the southern Norwegian Sea, and the Fram Strait Branch (FSB) west of Spitsbergen. The SvB transport is well correlated with the SSH and atmospheric variability within the Nordic Seas, factors that also affect the inflow to the Barents Sea. In contrast, the FSB is influenced by regional atmospheric conditions around Svalbard and northern Barents Sea. Using a composite analysis, we further relate anomalous strong SvB flow events to temperature fluctuations along the core of Atlantic water. A warm composite anomaly is found to propagate northward, with a tendency to amplify enroute, after these events. A roughly 12 months delayed temperature signal is identified in the FSB. However, also in the Lofoten Basin interior a delayed temperature signal is found, which appears to originate from the NwASC. This study suggests that hydrographic anomalies both upstream from the North Atlantic, and locally generated in the Norwegian Sea, are important for the oceanic heat and salt transport that eventually enters into the Arctic.

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Baroclinic instability and the mesoscale eddy field around the Lofoten Basin

Cited by 57 publications

References 43 publications

Quantifying mesoscale eddies in the Lofoten Basin

Quantifying mesoscale eddies in the Lofoten Basin

The North Icelandic Jet and its relationship to the North Icelandic Irminger Current

On the flow of Atlantic water and temperature anomalies in the Nordic Seas toward the Arctic Ocean

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