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  • 1
    Publication Date: 2019-02-01
    Description: The parameterization of sub-grid scale processes is one of the key challenges towards improved numerical simulations of the atmospheric and oceanic circulation. Numerical weather prediction models as well as climate models would benefit from more sophisticated turbulence closures that allow for less spurious dissipation at the grid-scale and consequently higher and more realistic levels of eddy kinetic energy (EKE). Recent studies propose to use a hyperviscous closure in combination with an additional deterministic forcing term as a negative viscosity to represent backscatter of energy from unresolved scales. The sub-grid EKE is introduced as an additional prognostic variable that is fed by dissipation at the grid scale, and enables recycling of EKE via the backscatter term at larger scales. This parameterization was previously shown to work well in zonally re-entrant channel configurations. Here, a generalization in the form of a Rossby number-dependent scaling for the strength of the backscatter is introduced to represent the emergence of a forward energy-cascade in unbalanced flows near the boundaries. We apply the parameterization to a shallow water model of a double gyre basin and provide evidence for its general applicability. In terms of mean state and variability, a low resolution model is considerably improved towards a high resolution control run at low additional computational cost.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 2
    Publication Date: 2019-05-04
    Type: Dataset
    Format: text/tab-separated-values, 502017 data points
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  • 3
    Publication Date: 2016-12-05
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 4
    Publication Date: 2014-10-08
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 5
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    In:  [Poster] In: EGU General Assembly 2014, 27.04.-02.05.2014, Vienna, Austria .
    Publication Date: 2015-01-15
    Description: The formation of an anticyclonic mode water eddy in Jan/Feb 2013 within the Peru-Chile Undercurrent is presented based on a multi-platform observational study. Two consecutive research cruises, a glider swarm experiment and moored measurements were conducted as part of the interdisciplinary "SFB 754 Climate-Biogeochemistry Interactions in the Tropical Ocean" project within the Peruvian upwelling regime at 12°S. The dataset allows a detailed investigation of the eddy generation process and its impacts on the near-coastal hydrography and biogeochemistry in space and time. The near-coastal horizontal circulation off Peru at 12°S changes significantly over the two months of observation. In early January, we observe a strong but clear Peru-Chile Undercurrent with maximal pole-ward velocities of ~25 cm/s in 100 - 200 m depth. A week later the vertical shear starts to increases and finally a mode water eddy forms. The eddy has a velocity maximum of ~0.3 m/s in 100 - 200 m depth and a radius of ~45 km. The eddy induced circulation strongly influences the near-coastal hydrography: Across-shore velocities result in an exchange of water masses between the shelf-break and the offshore ocean. At the eddy edge small scale salinity anomalies are found, which seem to be formed by mesoscale stirring. Energetic near-inertial oscillations are observed in the deeper water column during eddy generation that appear to be associated with this feature. After its generation close to the shelf break the eddy propagates westwards.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 6
    Publication Date: 2019-03-01
    Type: Dataset
    Format: text/tab-separated-values, 261961 data points
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  • 7
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    PANGAEA
    In:  GEOMAR - Helmholtz Centre for Ocean Research Kiel
    Publication Date: 2019-02-12
    Type: Dataset
    Format: text/tab-separated-values, 358477 data points
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  • 8
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    In:  (Doctoral thesis/PhD), Christian-Albrechts-Universität Kiel, Kiel, Germany, 110 pp
    Publication Date: 2019-02-01
    Description: The role of meso- and submesoscale processes for the near-coastal circulation, physical and biogeochemical tracer distributions and oxygen minimum zone ventilation in the Peruvian upwelling regime is investigated in this thesis. A multi-platform four-dimensional observational experiment was carried out off Peru in early 2013 and is the basis for this thesis. Furthermore a high-resolution submesoscale permitting physical circulation model is used to study submesoscale frontal dynamics in more detail. The formation of a subsurface anticyclonic eddy and its impact on the near-coastal salinity, oxygen and nutrient distributions was captured by the observations. The eddy developed in the Peru-Chile Undercurrent downstream of a topographic bend, suggesting flow separation as the eddy formation mechanism. The eddy resulted in enhanced cross-shore exchange of physical and biogeochemical tracers due to along-isopycnal stirring and offshore transport of core waters. The core waters originated from the bottom boundary layer and were characterized by low potential vorticity and an enhanced nitrogen-deficit. The subduction of highly oxygenated surface water in a submesoscale cold filament is observed by glider-based measurements. The subduction ventilates the upper oxycline but does not reach into oxygen minimum zone core waters during the summer observations. Lagrangian floats are used to study the pathways of newly upwelled water in a regional submesoscale permitting model. The model analysis suggests a gradual warming of the newly upwelled waters due to surface heat fluxes. The associated density decrease prevents the floats to enter the density range of the oxygen minimum zone in summer. However, in winter a density increase is found due to surface cooling and thus it might be possible that submesoscale processes ventilate the oxygen minimum zone. In the model about 50 % of the newly upwelled floats leave the mixed layer within 5 days both in summer and winter emphazising a hitherto unrecognized importance of subduction for the ventilation of the Peruvian oxycline
    Type: Thesis , NonPeerReviewed
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  • 9
    Publication Date: 2012-10-09
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 10
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    American Meteorological Society
    In:  Journal of Physical Oceanography, 44 (2). pp. 445-463.
    Publication Date: 2018-04-12
    Description: Mooring observations and model simulations point to an instability of the Labrador Current (LC) during winter, with enhanced eddy kinetic energy (EKE) at periods between 2 to 5 days, and much less EKE during other seasons. Linear stability analysis using vertical shear and stratification from the model reveals three dominant modes of instability in the LC: - a balanced interior mode with along-flow wavelengths of about 30–45 km, phase velocities of 0.3 m/s, maximal growth rates of 1 d−1 and surface intensified, but deep reaching amplitudes, - a balanced shallow mode with along-flow wavelengths of about 0.3–1.5 km, about three times larger phase speeds and growth rates, but amplitudes confined to the mixed layer (ML), - and an unbalanced symmetric mode with largest growth rates, vanishing phase speeds and along-flow structure, and very small cross-flow wavelengths, also confined to the ML. Both balanced modes are akin to baroclinic instability, but operate at moderate to small Richardson numbers Ri with much larger growth rates as for the quasi-geostrophic limit of Ri ≫ 1. The interior mode is found to be responsible for the instability of the LC during winter. Weak stratification and enhanced vertical shear due to local buoyancy loss and the advection of convective water masses from the interior result in small Ri within the LC, and to three times larger growth rates of the interior mode in March compared to summer and fall conditions. Both the shallow and the symmetric mode are not resolved by the model, but it is suggested that they might also play an important role for the instability in the LC and for lateral mixing.
    Type: Article , PeerReviewed
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