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  • 1
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    Over what area did the oil and gas spread during the 2010 Deepwater Horizon oil spill? (2016)
    The Oceanography Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © The Oceanography Society, 2016. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 29, no. 3 (2016): 96–107, doi:10.5670/oceanog.2016.74.
    Beschreibung: The 2010 Deepwater Horizon (DWH) oil spill in the Gulf of Mexico resulted in the collection of a vast amount of situ and remotely sensed data that can be used to determine the spatiotemporal extent of the oil spill and test advances in oil spill models, verifying their utility for future operational use. This article summarizes observations of hydrocarbon dispersion collected at the surface and at depth and our current understanding of the factors that affect the dispersion, as well as our improved ability to model and predict oil and gas transport. As a direct result of studying the area where oil and gas spread during the DWH oil spill, our forecasting capabilities have been greatly enhanced. State-of-the-art oil spill models now include the ability to simulate the rise of a buoyant plume of oil from sources at the seabed to the surface. A number of efforts have focused on improving our understanding of the influences of the near-surface oceanic layer and the atmospheric boundary layer on oil spill dispersion, including the effects of waves. In the future, oil spill modeling routines will likely be included in Earth system modeling environments, which will link physical models (hydrodynamic, surface wave, and atmospheric) with marine sediment and biogeochemical components.
    Beschreibung: This research was made possible by a grant from BP/The Gulf of Mexico Research Initiative to the CARTHE and Deep-C Consortia, and by contract M12PC00003 from the Bureau of Ocean Energy Management (BOEM).
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  • 2
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    Arctic decadal variability : an auto-oscillatory system of heat and fresh water exchange (2010)
    American Geophysical Union
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 31 (2004): L03302, doi:10.1029/2003GL019023.
    Beschreibung: This paper presents a mechanism of decadal variability in the Artic Ocean–GIN Sea (Greenland, Iceland and Norwegian Seas) atmosphere-ice-ocean system. We hypothesize that Arctic variability is regulated by heat and freshwater exchange between the Arctic Ocean and the GIN Sea. The interaction between basins is weak during anticyclonic circulation regimes (low AO/NAO) and strong during cyclonic circulation regimes (high AO/NAO). Regime shifts are controlled by the system itself through oceanic and atmospheric gradients (dynamic height and surface air temperature) that increase during the anticyclonic regime and decrease during the cyclonic regime. This conceptual mechanism for Arctic decadal variability has been reproduced in a model experiment. Both model results and observational data support the suggested mechanism.
    Beschreibung: This research has been supported by the National Science Foundation and by the International Arctic Research Center, University of Alaska Fairbanks, under auspices of the United States National Science Foundation and from the Alaska Sea Grant through the Center for Global Change, University of Alaska Fairbanks.
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  • 3
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    Arctic circulation regimes (2015)
    The Royal Society
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    Publikationsdatum: 2022-05-25
    Beschreibung: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Philosophical Transactions of the Royal Society A 373 (2015): 20140160, doi:10.1098/rsta.2014.0160.
    Beschreibung: Between 1948 and 1996, mean annual environmental parameters in the Arctic experienced a well-pronounced decadal variability with two basic circulation patterns: cyclonic and anticyclonic alternating at 5 to 7 year intervals. During cyclonic regimes, low sea-level atmospheric pressure (SLP) dominated over the Arctic Ocean driving sea ice and the upper ocean counterclockwise; the Arctic atmosphere was relatively warm and humid, and freshwater flux from the Arctic Ocean towards the subarctic seas was intensified. By contrast, during anticylonic circulation regimes, high SLP dominated driving sea ice and the upper ocean clockwise. Meanwhile, the atmosphere was cold and dry and the freshwater flux from the Arctic to the subarctic seas was reduced. Since 1997, however, the Arctic system has been under the influence of an anticyclonic circulation regime (17 years) with a set of environmental parameters that are atypical for this regime. We discuss a hypothesis explaining the causes and mechanisms regulating the intensity and duration of Arctic circulation regimes, and speculate how changes in freshwater fluxes from the Arctic Ocean and Greenland impact environmental conditions and interrupt their decadal variability.
    Beschreibung: Support was provided by US National Science Foundation PLR 1313614, 1203720, 1107277 and 0856531 to A.P., PLR-0804017 to D.D. and by the HYCOM consortium (no. N00014-09-1-0587) to D.D.
    Schlagwort(e): Arctic climate variability ; Circulation regimes ; Freshwater and heat content
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  • 4
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    Arctic decadal variability from an idealized atmosphere-ice-ocean model : 2. Simulation of decadal oscillations (2006)
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    Publikationsdatum: 2022-05-25
    Beschreibung: Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 111 (2006): C06029, doi:10.1029/2004JC002820.
    Beschreibung: A simple model of the Arctic Ocean and Greenland Sea, coupled to a thermodynamic sea ice model and an atmospheric model, has been used to study decadal variability of the Arctic ice-ocean-atmosphere climate system. The motivating hypothesis is that the behavior of the modeled and ultimately the real climate system is auto-oscillatory with a quasi-decadal periodicity. This system oscillates between two circulation regimes: the Anticyclonic Circulation Regime (ACCR) and the Cyclonic Circulation Regime (CCR). The regimes are controlled by the atmospheric heat flux from the Greenland Sea and the freshwater flux from the Arctic Ocean. A switch regulating the intensity of the fluxes between the Arctic Ocean and Greenland Sea that depends on the inter-basin gradient of dynamic height is implemented as a delay mechanism in the model. This mechanism allows the model system to accumulate the “perturbation” over several years. After the perturbation has been released, the system returns to its initial state. Solutions obtained from numerical simulations with seasonally varying forcing, for scenarios with high and low interaction between the regions, reproduced the major anomalies in the ocean thermohaline structure, sea ice volume, and fresh water fluxes attributed to the ACCR and CCR.
    Beschreibung: This publication is the result of research sponsored by Alaska Sea Grant with funds from the National Oceanic and Atmospheric Administration Office of Sea Grant, Department of Commerce, under grant no. NA 86RG0050 (project no. GC/01-02), and from the University of Alaska with funds appropriated by the state. This research has also been supported by the National Science Foundation and by the International Arctic Research Center, University of Alaska Fairbanks, under auspices of the United States National Science Foundation.
    Schlagwort(e): Arctic decadal variability ; Arctic simple model ; Greenland Sea convection
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  • 5
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    Skill metrics for evaluation and comparison of sea ice models (2015)
    John Wiley & Sons
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    Publikationsdatum: 2022-05-25
    Beschreibung: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Geophysical Research: Oceans 120 (2015): 5910–5931, doi:10.1002/2015JC010989.
    Beschreibung: Five quantitative methodologies (metrics) that may be used to assess the skill of sea ice models against a control field are analyzed. The methodologies are Absolute Deviation, Root-Mean-Square Deviation, Mean Displacement, Hausdorff Distance, and Modified Hausdorff Distance. The methodologies are employed to quantify similarity between spatial distribution of the simulated and control scalar fields providing measures of model performance. To analyze their response to dissimilarities in two-dimensional fields (contours), the metrics undergo sensitivity tests (scale, rotation, translation, and noise). Furthermore, in order to assess their ability to quantify resemblance of three-dimensional fields, the metrics are subjected to sensitivity tests where tested fields have continuous random spatial patterns inside the contours. The Modified Hausdorff Distance approach demonstrates the best response to tested differences, with the other methods limited by weak responses to scale and translation. Both Hausdorff Distance and Modified Hausdorff Distance metrics are robust to noise, as opposed to the other methods. The metrics are then employed in realistic cases that validate sea ice concentration fields from numerical models and sea ice mean outlook against control data and observations. The Modified Hausdorff Distance method again exhibits high skill in quantifying similarity between both two-dimensional (ice contour) and three-dimensional (ice concentration) sea ice fields. The study demonstrates that the Modified Hausdorff Distance is a mathematically tractable and efficient method for model skill assessment and comparison providing effective and objective evaluation of both two-dimensional and three-dimensional sea ice characteristics across data sets.
    Beschreibung: U.S. National Science Foundation (NSF) Grant Number: PLR-0804017, NASA JPL OVWST, Bureau of Ocean Energy Management (BOEM), FSU Grant Number: M12PC00003, NSF Grant Numbers: projects PLR-0804010 , PLR-1313614 , PLR-1203720, BP/The Gulf of Mexico Research Initiative Grant Number: SA12-12, GoMRI-008, DoD High Performance Computing Modernization Program
    Schlagwort(e): Sea ice model ; Sea ice model validation ; Model skill assessment
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  • 6
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    Arctic decadal variability from an idealized atmosphere-ice-ocean model: 1. Model description, calibration, and validation (2006)
    American Geophysical Union
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    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 111 (2006): C06028, doi:10.1029/2004JC002821.
    Beschreibung: This paper describes a simple “multibox” model of the Arctic atmosphere-ice-ocean system. The model consists of two major modules (an Arctic module and a Greenland Sea module) and several sub-modules. The Arctic module includes a shelf box model coupled with a thermodynamic sea ice model, and an Arctic Ocean model coupled with a sea ice model and an atmospheric box model. The Greenland Sea module includes an oceanic model coupled with a sea ice model and a statistical model of surface air temperature over the Greenland Sea. The full model is forced by daily solar radiation, wind stress, river runoff, and Pacific Water inflow through Bering Strait. For validation purposes, results from model experiments reproducing seasonal variability of the major system parameters are analyzed and compared with observations and other models. The model reproduces the seasonal variability of the Arctic system reasonably well and is used to investigate decadal Arctic climate variability in Part 2 of this publication.
    Beschreibung: This publication is the result of research sponsored by Alaska Sea Grant with funds from the National Oceanic and Atmospheric Administration Office of Sea Grant, Department of Commerce, under grant no. NA 86RG0050 (project no. GC/01-02), and from the University of Alaska with funds appropriated by the state. This research has also been supported by the National Science Foundation and by the International Arctic Research Center, University of Alaska Fairbanks, under auspices of the United States National Science Foundation.
    Schlagwort(e): Arctic decadal oscillations ; Idealized Arctic model ; Arctic–Greenland Sea interaction
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  • 7
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    Role of Greenland freshwater anomaly in the recent freshening of the subpolar North Atlantic (2019)
    American Geophysical Union
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    Publikationsdatum: 2022-05-26
    Beschreibung: The cumulative Greenland freshwater flux anomaly has exceeded 5,000 km3 since the 1990s. The volume of this surplus freshwater is expected to cause substantial freshening in the North Atlantic. Analysis of hydrographic observations in the subpolar seas reveals freshening signals in the 2010s. The sources of this freshening are yet to be determined. In this study, the relationship between the surplus Greenland freshwater flux and this freshening is tested by analyzing the propagation of the Greenland freshwater anomaly and its impact on salinity in the subpolar North Atlantic based on observational data and numerical experiments with and without the Greenland runoff. A passive tracer is continuously released during the simulations at freshwater sources along the coast of Greenland to track the Greenland freshwater anomaly. Tracer budget analysis shows that 44% of the volume of the Greenland freshwater anomaly is retained in the subpolar North Atlantic by the end of the simulation. This volume is sufficient to cause strong freshening in the subpolar seas if it stays in the upper 50–100 m. However, in the model the anomaly is mixed down to several hundred meters of the water column resulting in smaller magnitudes of freshening compared to the observations. Therefore, the simulations suggest that the accelerated Greenland melting would not be sufficient to cause the observed freshening in the subpolar seas and other sources of freshwater have contributed to the freshening. Impacts on salinity in the subpolar seas of the freshwater transport through Fram Strait and precipitation are discussed.
    Beschreibung: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Dukhovskoy, D. S., Yashayaev, I., Proshutinsky, A., Bamber, J. L., Bashmachnikov, I. L., Chassignet, E. P., Lee, C. M., & Tedstone, A. J. Role of Greenland freshwater anomaly in the recent freshening of the subpolar North Atlantic. Journal of Geophysical Research-Oceans, 124(5), (2019): 3333-3360, doi:10.1029/2018JC014686.
    Schlagwort(e): Greenland ice sheet melting ; freshwater anomaly ; subpolar North Atlantic ; subpolar gyre ; passive tracer numerical experiment ; freshwater budget
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  • 8
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    Assessment of numerical simulations of deep circulation and variability in the Gulf of Mexico using recent observations (2020)
    American Meteorological Society
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    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © American Meteorological Society, 2020. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 50(4), (2020): 1045-1064, doi:10.1175/JPO-D-19-0137.1.
    Beschreibung: Three simulations of the circulation in the Gulf of Mexico (the “Gulf”) using different numerical general circulation models are compared with results of recent large-scale observational campaigns conducted throughout the deep (〉1500 m) Gulf. Analyses of these observations have provided new understanding of large-scale mean circulation features and variability throughout the deep Gulf. Important features include cyclonic flow along the continental slope, deep cyclonic circulation in the western Gulf, a counterrotating pair of cells under the Loop Current region, and a cyclonic cell to the south of this pair. These dominant circulation features are represented in each of the ocean model simulations, although with some obvious differences. A striking difference between all the models and the observations is that the simulated deep eddy kinetic energy under the Loop Current region is generally less than one-half of that computed from observations. A multidecadal integration of one of these numerical simulations is used to evaluate the uncertainty of estimates of velocity statistics in the deep Gulf computed from limited-length (4 years) observational or model records. This analysis shows that the main deep circulation features identified from the observational studies appear to be robust and are not substantially impacted by variability on time scales longer than the observational records. Differences in strengths and structures of the circulation features are identified, however, and quantified through standard error analysis of the statistical estimates using the model solutions.
    Beschreibung: This work was supported by the Gulf Research Program of the National Academy of Sciences under Awards 2000006422 and 2000009966. The content is solely the responsibility of the authors and does not necessarily represent the official views of the Gulf Research Program or the National Academy of Sciences. The authors acknowledge the GLORYS project for providing the ocean reanalysis data used in the ROMS simulation. GLORYS is jointly conducted by MERCATOR OCEAN, CORIOLIS, and CNRS/INSU. Installation, recovery, data acquisition, and processing of the CANEK group current-meter moorings were possible because of CICESE-PetróleosMexicanos Grant PEP-CICESE 428229851 and the dedicated work of the crew of the B/O Justo Sierra and scientists of the CANEK group. The authors thank Dr. Aljaz Maslo, CICESE, for assistance with analysis of model data. The Bureau of Ocean Energy Management (BOEM), U.S. Dept. of the Interior, provided funding for the Lagrangian Study of the Deep Circulation in the Gulf of Mexico and the Observations and Dynamics of the Loop Current study. HYCOM simulation data are available from the HYCOM data server (https://www.hycom.org/data/goml0pt04/expt-02pt2), MITgcm data are available from the ECCO data server (http://ecco.ucsd.edu/gom_results2.html), and the ROMS simulation data are available from GRIIDC (NA.x837.000:0001).
    Schlagwort(e): Ocean circulation ; Abyssal circulation ; Bottom currents/bottom water ; Eddies ; Ocean models
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  • 9
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    Greenland freshwater pathways in the sub-Arctic Seas from model experiments with passive tracers (2016)
    John Wiley & Sons
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    Publikationsdatum: 2022-05-26
    Beschreibung: Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 121 (2016): 877–907, doi:10.1002/2015JC011290.
    Beschreibung: Accelerating since the early 1990s, the Greenland Ice Sheet mass loss exerts a significant impact on thermohaline processes in the sub-Arctic seas. Surplus freshwater discharge from Greenland since the 1990s, comparable in volume to the amount of freshwater present during the Great Salinity Anomaly events, could spread and accumulate in the sub-Arctic seas, influencing convective processes there. However, hydrographic observations in the Labrador Sea and the Nordic Seas, where the Greenland freshening signal might be expected to propagate, do not show a persistent freshening in the upper ocean during last two decades. This raises the question of where the surplus Greenland freshwater has propagated. In order to investigate the fate, pathways, and propagation rate of Greenland meltwater in the sub-Arctic seas, several numerical experiments using a passive tracer to track the spreading of Greenland freshwater have been conducted as a part of the Forum for Arctic Ocean Modeling and Observational Synthesis effort. The models show that Greenland freshwater propagates and accumulates in the sub-Arctic seas, although the models disagree on the amount of tracer propagation into the convective regions. Results highlight the differences in simulated physical mechanisms at play in different models and underscore the continued importance of intercomparison studies. It is estimated that surplus Greenland freshwater flux should have caused a salinity decrease by 0.06–0.08 in the sub-Arctic seas in contradiction with the recently observed salinification (by 0.15–0.2) in the region. It is surmised that the increasing salinity of Atlantic Water has obscured the freshening signal.
    Beschreibung: NSERC. Grant Numbers RGPIN 227438-09, RGPIN 04357 and RGPCC 433898; RFBR. Grant Number 13-05-00480, 14-05-00730, and 15-05-02457; NSF Grant Number: PLR-0804010, PLR-1313614, and PLR-1203720
    Beschreibung: 2016-07-25
    Schlagwort(e): Greenland Ice Sheet melting ; Greenland freshwater ; Thermohaline circulation ; Nordic Seas ; Sub-Arctic seas ; Baffin Bay ; Labrador Sea
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  • 10
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    Time scales of the Greenland freshwater anomaly in the subpolar North Atlantic (2022)
    American Meteorological Society
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    Publikationsdatum: 2022-06-03
    Beschreibung: Author Posting. © American Meteorological Society, 2021. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 34(22), (2021): 8971–8987, https://doi.org/10.1175/JCLI-D-20-0610.1.
    Beschreibung: The impact of increasing Greenland freshwater discharge on the subpolar North Atlantic (SPNA) remains unknown as there are uncertainties associated with the time scales of the Greenland freshwater anomaly (GFWA) in the SPNA. Results from numerical simulations tracking GFWA and an analytical approach are employed to estimate the response time, suggesting that a decadal time scale (13 years) is required for the SPNA to adjust for increasing GFWA. Analytical solutions obtained for a long-lasting increase of freshwater discharge show a non-steady-state response of the SPNA with increasing content of the GFWA. In contrast, solutions for a short-lived pulse of freshwater demonstrate different responses of the SPNA with a rapid increase of freshwater in the domain followed by an exponential decay after the pulse has passed. The derived theoretical relation between time scales shows that residence time scales are time dependent for a non-steady-state case and asymptote the response time scale with time. The residence time of the GFWA deduced from Lagrangian experiments is close to and smaller than the response time, in agreement with the theory. The Lagrangian analysis shows dependence of the residence time on the entrance route of the GFWA and on the depth. The fraction of the GFWA exported through Davis Strait has limited impact on the interior basins, whereas the fraction entering the SPNA from the southwest Greenland shelf spreads into the interior regions. In both cases, the residence time of the GFWA increases with depth demonstrating long persistence of the freshwater anomaly in the subsurface layers.
    Beschreibung: D. S. Dukhovskoy and E. P. Chassignet were funded by the DOE (Award DE-SC0014378) and HYCOM NOPP (Award N00014-19-1-2674). The HYCOM-CICE simulations were supported by a grant of computer time from the DoD High-Performance Computing Modernization Program at NRL SSC. G. Platov was funded by the RSF N19-17-00154. P. G. Myers was funded by an NSERC Discovery Grant (Grant RGPIN 04357). A. Proshutinsky was funded by FAMOS project (NSF Grant NSF 14-584).
    Schlagwort(e): North Atlantic Ocean ; Lagrangian circulation/transport ; Ocean circulation ; Differential equations ; Ocean models
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