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  • 1
    Buch
    Buch
    Zirkulation und Dynamik in der Agulhasregion anhand eines numerischen Modells (1998)
    Kiel : Inst. für Meereskunde, Abt. Theoretische Ozeanographie
    Details Verfügbarkeit
    Schlagwort(e): Report ; Dissertation ; Hochschulschrift ; Forschungsbericht
    Beschreibung / Inhaltsverzeichnis: Im Rahmen des World Ocean Circulation Experiment, WOCE, wurde ein Modell der Agulhasregion entwickelt. Ziele dieser Arbeit waren die Identifizierung der Quellregion des Agulhasstromes und die Bestimmung des Volumentransportes, die Untersuchung der Ablösungsprozesse und der Drift von Agulhasringen, sowie Schätzungen des interozeanischen Transportes von Masse, Wärme und Salz. (MOD)
    Materialart: Buch
    Seiten: 118 S. , Ill., graph. Darst., Kt.
    Serie: Berichte aus dem Institut für Meereskunde an der Christian-Albrechts-Universität 301
    Sprache: Deutsch
    Anmerkung: Literaturverz. S. 105 - 118 , Kiel, Univ., Diss., 1998
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  • 2
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    Tracking the Evolution of Water Flow Patterns Based on Spatio-Temporal Particle Flow Clusters (2022)
    Details
    Publikationsdatum: 2022-09-20
    Beschreibung: Marine scientists investigate the movement of oceanic water particles with floating measurement devices released in the real ocean, as well as with virtual particles released in numerical model simulations. The detection, visualization, and evolution of clustered particles is key for gaining a comprehensive understanding of the underlying processes in the oceans. Thereby, vast amounts of mobility data (3D coordinates of these particles over time) need to be analyzed using mobility data science methods. In this paper, we describe the application of data science techniques to detect particle clusters and, more importantly, to track the evolution of these clusters over time in order to support the analysis of oceanic flows. In particular, we apply a well-known concept for tracking the cluster evolution from the data mining community that relies on pair-counting and, thus, is rather inefficient. In order to be applicable to large amounts of particles, we further elaborate two heuristic solutions to compute the cluster transitions based on spatial approximations. Experiments on real world data show a considerable speed-up while sacrificing marginal accuracy drops. Our prototype is used by domain experts for the analysis of the large-scale ocean by virtual particle release experiments in ocean simulations.
    Materialart: Conference or Workshop Item , NonPeerReviewed
    Format: text
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    OceanRep: Artikel in Konferenzband
  • 3
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    Major sources of North Atlantic Deep Water in the subpolar North Atlantic from Lagrangian analyses in a high–resolution ocean model (2022)
    Copernicus Publications (EGU)
    Details
    Publikationsdatum: 2022-09-20
    Beschreibung: North Atlantic Deep Water (NADW) is a crucial component of the Atlantic Meridional Overturning Circulation and, therefore, is an important factor of the climate system. In order to estimate the mean relative contributions, sources and pathways of the three different deep water mass components (namely Labrador Sea Water, Northeast Atlantic Deep Water and Denmark Strait Overflow Water) at the southern exit of the Labrador Sea, Lagrangian particle experiments were performed. The particles were seeded according to the strength of the velocity field along the 53° N section and computed 40 years backward in time in the three-dimensional velocity and hydrography field. Water masses were defined within the model output in the central Labrador Sea and the subpolar North Atlantic. The resulting transport pathways, their sources and corresponding transit time scales were inferred. Our experiments show that the majority of NADW passing 53° N is associated with diapycnal mass flux, accounting for 14.3 Sv (48 %), where 6.2 Sv originate from the Labrador Sea, compared to 4.7 Sv from the Irminger Sea. The second largest contribution originates from the mixed layer with 7.2 Sv (24 %), where the Labrador Sea contribution (5.9 Sv) dominates over the Irminger Sea contribution (1.0 Sv). Another 5.7 Sv (19 %) of NADW cross the Greenland–Scotland Ridge within the NADW density class, where about 2/3 pass Denmark Strait, while 1/3 cross the Iceland Scotland Ridge. The NADW exported at 53° N is hence dominated by entrainment through diapycnal mass flux and the mixed layer origin in the Labrador Sea.
    Materialart: Article , NonPeerReviewed
    Format: text
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  • 4
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    The role of mesoscale eddies in the source regions of the Agulhas Current (1999)
    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 29 . pp. 2303-2317.
    Details
    Publikationsdatum: 2020-08-04
    Beschreibung: A primitive equation model to study the dynamics of the Agulhas system has been developed. The model domain covers the South Atlantic and the south Indian Ocean with a resolution of ⅓° in the Agulhas region while coarser outside. It is driven by a climatology of the European Centre for Medium-Range Weather Forecasts. It is shown that the model simulates the Agulhas Current, its retroflection, and the ring shedding successfully. The model results show baroclinic anticyclonic eddies in the Mozambique Channel and east of Madagascar, which travel toward the northern Agulhas Current. After the eddies reach the current they are advected southward with the mean flow. Due to the limited numerical resolution only a few eddies reach the retroflection region without much modification. These eddies are responsible for drastic enhancement of the heat transfer from the Indian Ocean to the South Atlantic and lead to periodicities in the interoceanic heat transport of about 50 days superimposed on the seasonal variability. Combined satellite data from TOPEX/Poseidon and ERS-1 show that the observed vortices in the Mozambique Channel are comparable to those seen in the model. In contrast to this the simulated eddies east of Madagascar seem not to be well reproduced. Analyses of the energy conversion terms between the mean flow and the eddies suggest that barotropic instability plays an important role in the generation of Mozambique Channel eddies. For the generation of Agulhas rings and other eddy structures in the model the barotropic instability mechanism seems to be minor, and baroclinic instability mechanisms are more likely.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1175/1520-0485(1999)029〈2303:TROMEI〉2.0.CO;2
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  • 5
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    Zirkulation und Dynamik in der Agulhasregion anhand eines numerischen Modells (1998)
    In:  (PhD/ Doctoral thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 105 pp . Berichte aus dem Institut für Meereskunde an der Christian-Albrechts-Universität Kiel, 301 . DOI 10.3289/ifm_ber_301 〈http://dx.doi.org/10.3289/ifm_ber_301〉.
    Details
    Publikationsdatum: 2018-09-12
    Materialart: Thesis , NonPeerReviewed
    Format: text
    DOI: 10.3289/ifm_ber_301
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    OceanRep: Hochschulschrift - nicht über Verlag veröffentlicht
  • 6
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    Stevens Open Boundary Conditions (1996)
    Geophysical Fluid Dynamics Laboratory (GFDL)
    In:  In: MOM 2 Version 2.0 (Beta) - Documentation User’s Guide and Reference Manual - Release date: Nov 7,1996. , ed. by Pacanowski, R. C. GDFL Ocean Technical Report, 3.2 . Geophysical Fluid Dynamics Laboratory (GFDL), Princeton, USA, pp. 141-150.
    Details
    Publikationsdatum: 2020-04-24
    Materialart: Book chapter , NonPeerReviewed
    Format: text
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    OceanRep: Buchkapitel
  • 7
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    Stevens Open Boundary Conditions (1999)
    Geophysical Fluid Dynamics Laboratory (GFDL)
    In:  In: MOM 3.0 Manual. , ed. by Pacanowski, R. C. and Griffies, S. M. GFDL Ocean Group Technical Report, 4 . Geophysical Fluid Dynamics Laboratory (GFDL), Princeton, USA, pp. 245-252.
    Details
    Publikationsdatum: 2020-03-24
    Materialart: Book chapter , NonPeerReviewed
    Format: text
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    OceanRep: Buchkapitel
  • 8
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    The Importance of flow in the Mozambique Channel to seasonality in the greater Agulhas Current system (1999)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 26 . pp. 3321-3324.
    Details
    Publikationsdatum: 2018-02-13
    Beschreibung: The temporal variability of the greater Agulhas Current system has important climatological consequences. Some recent results have suggested that this variability contains a large seasonal component, due to changes in the circulation at latitudes poleward of Madagascar only. A model simulation shows that the contribution of Tropical Surface Water to Agulhas Current waters, via the Mozambique Channel, also has a distinct seasonal characteristic that is brought about by the seasonal wind stress over the tropical Indian Ocean. This simulated flow through the Channel contributes substantially to the seasonality of the Agulhas Current. This model result is shown to be not inconsistent with available hydrographic observations.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1029/1999GL002349
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  • 9
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    Dynamics, estimation and impact of South Atlantic inter-ocean exchange (1999)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 104 (C9). pp. 20885-20910.
    Details
    Publikationsdatum: 2017-11-24
    Beschreibung: Interocean exchange of heat and salt around South Africa is thought to be a key link in the maintenance of the global overturning circulation of the ocean. It takes place at the Agulhas Retroflection, largely by the intermittent shedding of enormous rings that penetrate into the South Atlantic Ocean. This makes it extremely hard to estimate the inter ocean fluxes. Estimates of direct Agulhas leakage from hydrographic and tracer data range between 2 and 10 Sv (1 Sv = 106 m3 s−1). The average ring shedding frequency, determined from satellite information, is approximately six rings per year. Their associated interocean volume transport is between 0.5 and 1.5 Sv per ring. A number of Agulhas rings have been observed to cross the South Atlantic. They decay exponentially to less than half their initial size (measured by their available potential energy) within 1000 km from the shedding region. Consequently, most of their properties mix into the surroundings of the Benguela region, probably feeding directly into the upper (warm) limb of the global thermohaline circulation. The most recent observations suggest that in the present situation Agulhas water and Antarctic Intermediate Water are about equally important sources for the Benguela Current. Variations in the strength of these may lead to anomalous stratification and stability of the Atlantic at decadal and longer timescales. Modeling studies suggest that the Indian-Atlantic interocean exchange is strongly related to the structure of the wind field over the South Indian Ocean. This leads in the mean to a subtropical supergyre wrapping around the subtropical gyres of the South Indian and Atlantic Oceans. However, local dynamical processes in the highly nonlinear regime around South Africa play a crucial role in inhibiting the connection between the two oceans. The regional bottom topography also seems to play an important role in locking the Agulhas Currents' retroflection. State-of-the-art global and regional “eddy-permitting” models show a reasonably realistic representation of the mean Agulhas system; but the mesoscale variability and the local geometrical and topographic features that determine largely the interocean fluxes still need considerable improvement. In this article we present a review of the above mentioned aspects of the interocean exchange around South Africa: the estimation of the fluxes into the South Atlantic from different types of observations, our present level of understanding of the exchanges dynamics and forcing, its representation in state-of-the-art models, and, finally, the impact of the Indian-Atlantic fluxes on regional and global scale both within the Atlantic Ocean and in interaction with the overlying atmosphere.
    Materialart: Article , PeerReviewed
    Format: text
    DOI: 10.1029/1998JC900099
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  • 10
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    North Atlantic climate mean state and variability: Local effects of mesoscale ocean dynamics (2020)
    In:  [Talk] In: Ocean Sciences Meeting 2020, 16.-21.02.2020, San Diego, USA .
    Details
    Publikationsdatum: 2020-02-27
    Beschreibung: Western Boundary Currents, such as the Gulf Stream, are regions of vivid air-sea interaction. Mesoscale features of these currents play a fundamental role in global ocean heat transport and exchange with the atmosphere. Related processes and their interactions across scales have gained increasing attention in the last years, since high-resolution, mesoscale-resolving modeling became computationally feasible on climate time scales. Here, we show the impact of explicitly resolving the oceanic mesoscale in the coupled global climate model FOCI on North Atlantic and European climate. For this purpose, we use the ocean nesting capability in FOCI, which facilitates regional ocean grid refinement. We explore and compare pre-industrial simulations each extending over at least 150 years: a reference run without any grid refinement and an experiment with a nest in the North Atlantic. Technically, the regional ocean nest maintains frequent two-way exchange with the global host grid, which in turn is fully coupled to the atmosphere model. The ocean model NEMO has a global resolution of 1/2˚ model with 46 vertical levels and 1/10˚ refinement in the nest region, while the atmosphere model ECHAM6 has a 1.8˚ horizontal resolution (T63) and 95 vertical levels, including the strato- and mesosphere. Within the nest region, the increased resolution leads to a more eddy-rich simulation and an improved mean state. The North Atlantic Current is considerably better represented, which reduces the typical North Atlantic cold bias from -8˚C in the reference run without nest to -2˚C. Beyond local bias correction of the mean state, we will also discuss the impact of explicitly modeling ocean mesoscale dynamics on atmospheric variability on different time scales, such as the North Atlantic Oscillation or the Atlantic Multidecadal Variability.
    Materialart: Conference or Workshop Item , NonPeerReviewed
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