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Bernard Barnier - One of the best experts on this subject based on the ideXlab platform.
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contributions of Atmospheric Forcing and chaotic ocean variability to regional sea level trends over 1993 2015
Geophysical Research Letters, 2018Co-Authors: William Llovel, Thierry Penduff, Benoit Meyssignac, Jean-marc Molines, Laurent Terray, Laurent Bessières, Bernard BarnierAbstract:A global ¼° ocean/sea-ice 50-member ensemble simulation is analyzed to disentangle the imprints of the Atmospheric Forcing and the chaotic ocean variability on regional sea level trends over the satellite altimetry period. We find that the chaotic ocean variability may mask Atmospherically forced regional sea level trends over 38% of the global ocean area from 1993 to 2015, and over 47% of this area from 2005 to 2015. These regions are located in the western boundary currents, in the Southern Ocean and in the subtropical gyres. While these results do not question the anthropogenic origin of global mean sea level rise, they give new insights into the intrinsically oceanic versus Atmospheric Forcing of regional sea level trends and provide new constraints on the measurement time required to attribute regional sea level trends to the Atmospheric Forcing or to climate change.
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Contributions of Atmospheric Forcing and Chaotic Ocean Variability to Regional Sea Level Trends Over 1993–2015
Geophysical Research Letters, 2018Co-Authors: William Llovel, Thierry Penduff, Benoit Meyssignac, Jean-marc Molines, Laurent Terray, Laurent Bessières, Bernard BarnierAbstract:A global ¼° ocean/sea-ice 50-member ensemble simulation is analyzed to disentangle the imprints of the Atmospheric Forcing and the chaotic ocean variability on regional sea level trends over the satellite altimetry period. We find that the chaotic ocean variability may mask Atmospherically forced regional sea level trends over 38% of the global ocean area from 1993 to 2015, and over 47% of this area from 2005 to 2015. These regions are located in the western boundary currents, in the Southern Ocean and in the subtropical gyres. While these results do not question the anthropogenic origin of global mean sea level rise, they give new insights into the intrinsically oceanic versus Atmospheric Forcing of regional sea level trends and provide new constraints on the measurement time required to attribute regional sea level trends to the Atmospheric Forcing or to climate change.
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A global probabilistic study of the ocean heat content low-frequency variability: Atmospheric Forcing versus oceanic chaos
Geophysical Research Letters, 2017Co-Authors: Guillaume Sérazin, William Llovel, Thierry Penduff, Jean-marc Molines, Laurent Bessières, Bernard Barnier, Alexandre Jaymond, Stephanie Leroux, Laurent TerrayAbstract:A global 1/4° ocean/sea ice 50‐member ensemble simulation is used to disentangle the low‐frequency imprints of the Atmospherically forced oceanic variability and of the chaotic intrinsic oceanic variability (IOV) on the large‐scale (10° × 10°) ocean heat content (OHC) between 1980 and 2010. The IOV explains most of the interannual‐to‐decadal large‐scale OHC variance over substantial fractions of the global ocean area that increase with depth: 9%, 22%, and 31% in the 0–700 m, 700–2000 m and 2000 m bottom layers, respectively. Such areas concern principally eddy‐active regions, mostly found in the Southern Ocean and in western boundary current extensions, and also concern the subtropical gyres at intermediate and deep levels. The oceanic chaos may also induce random multidecadal fluctuations so that large‐scale regional OHC trends computed on the 1980–2010 period cannot be unambiguously attributed to the Atmospheric Forcing in several oceanic basins at various depths. These results are likely to raise detection and attribution issues from real observations.
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Sensitivity of coastal polynyas and high-salinity shelf water production in the Ross Sea, Antarctica, to the Atmospheric Forcing
Ocean Dynamics, 2012Co-Authors: Pierre Mathiot, Jean-marc Molines, Bernard Barnier, Nicolas C. Jourdain, Hubert Gallée, Julien Le Sommer, Thierry PenduffAbstract:Coastal polynyas around Antarctica are the place of intense air–sea exchanges which eventually lead to the formation of high-salinity shelf waters (HSSW) over continental shelves. Here, the influence of Atmospheric Forcing on coastal polynyas in the Ross Sea is studied by contrasting the response of a regional ocean/sea-ice circulation model to two different Atmospheric Forcing sets. A first Forcing (DFS3) is based on ERA40 Atmospheric surface variables and satellite products. A second Forcing (MAR) is produced on the basis of ERA40 with a dynamical downscaling procedure. As compared to DFS3, MAR Forcing is shown to improve substantially the representation of small-scale patterns of coastal winds with stronger katabatic winds along the coast. The response of the ocean/sea-ice model to the two Forcing sets shows that the MAR Forcing improves substantially the geographical distribution of polynyas in the Ross Sea. With the MAR Forcing, the polynya season is also shown to last longer with a greater ice-production rate. As a consequence, a greater flow of dense water out of the polynyas is found with the MAR Forcing and the properties of HSSW are notably improved as compared to the DFS3 Forcing. The factors contributing to the activity of Terra Nova Bay and Ross Ice Shelf polynyas in the model are studied in detail. The general picture that emerges from our simulations is that the properties of HSSW are mostly set by brine rejection when the polynya season resume. We found that coastal polynyas in the Ross Sea export about 0.4 Sv of HSSW which then flows along three separate channels over the Ross Shelf. A 6-month time lag is observed between the peak of activity of polynyas and the maximum transport across the sills in the channels with a maximum transport of about 1 Sv in February. This lag corresponds to the time it takes to the newly formed HSSW to spread from the polynya to the sills (at a speed of nearly 2 cm s−1).
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Controlling Atmospheric Forcing parameters of global ocean models: sequential assimilation of sea surface Mercator-Ocean reanalysis data
Ocean Science, 2009Co-Authors: C. Skandrani, J.-m. Brankart, N. Ferry, Jacques Verron, Pierre Brasseur, Bernard BarnierAbstract:Abstract. In the context of stand alone ocean models, the Atmospheric Forcing is generally computed using Atmospheric parameters that are derived from Atmospheric reanalysis data and/or satellite products. With such a Forcing, the sea surface temperature that is simulated by the ocean model is usually significantly less accurate than the synoptic maps that can be obtained from the satellite observations. This not only penalizes the realism of the ocean long-term simulations, but also the accuracy of the reanalyses or the usefulness of the short-term operational forecasts (which are key GODAE and MERSEA objectives). In order to improve the situation, partly resulting from inaccuracies in the Atmospheric Forcing parameters, the purpose of this paper is to investigate a way of further adjusting the state of the atmosphere (within appropriate error bars), so that an explicit ocean model can produce a sea surface temperature that better fits the available observations. This is done by performing idealized assimilation experiments in which Mercator-Ocean reanalysis data are considered as a reference simulation describing the true state of the ocean. Synthetic observation datasets for sea surface temperature and salinity are extracted from the reanalysis to be assimilated in a low resolution global ocean model. The results of these experiments show that it is possible to compute piecewise constant parameter corrections, with predefined amplitude limitations, so that long-term free model simulations become much closer to the reanalysis data, with misfit variance typically divided by a factor 3. These results are obtained by applying a Monte Carlo method to simulate the joint parameter/state prior probability distribution. A truncated Gaussian assumption is used to avoid the most extreme and non-physical parameter corrections. The general lesson of our experiments is indeed that a careful specification of the prior information on the parameters and on their associated uncertainties is a key element in the computation of realistic parameter estimates, especially if the system is affected by other potential sources of model errors.
Thierry Penduff - One of the best experts on this subject based on the ideXlab platform.
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contributions of Atmospheric Forcing and chaotic ocean variability to regional sea level trends over 1993 2015
Geophysical Research Letters, 2018Co-Authors: William Llovel, Thierry Penduff, Benoit Meyssignac, Jean-marc Molines, Laurent Terray, Laurent Bessières, Bernard BarnierAbstract:A global ¼° ocean/sea-ice 50-member ensemble simulation is analyzed to disentangle the imprints of the Atmospheric Forcing and the chaotic ocean variability on regional sea level trends over the satellite altimetry period. We find that the chaotic ocean variability may mask Atmospherically forced regional sea level trends over 38% of the global ocean area from 1993 to 2015, and over 47% of this area from 2005 to 2015. These regions are located in the western boundary currents, in the Southern Ocean and in the subtropical gyres. While these results do not question the anthropogenic origin of global mean sea level rise, they give new insights into the intrinsically oceanic versus Atmospheric Forcing of regional sea level trends and provide new constraints on the measurement time required to attribute regional sea level trends to the Atmospheric Forcing or to climate change.
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Contributions of Atmospheric Forcing and Chaotic Ocean Variability to Regional Sea Level Trends Over 1993–2015
Geophysical Research Letters, 2018Co-Authors: William Llovel, Thierry Penduff, Benoit Meyssignac, Jean-marc Molines, Laurent Terray, Laurent Bessières, Bernard BarnierAbstract:A global ¼° ocean/sea-ice 50-member ensemble simulation is analyzed to disentangle the imprints of the Atmospheric Forcing and the chaotic ocean variability on regional sea level trends over the satellite altimetry period. We find that the chaotic ocean variability may mask Atmospherically forced regional sea level trends over 38% of the global ocean area from 1993 to 2015, and over 47% of this area from 2005 to 2015. These regions are located in the western boundary currents, in the Southern Ocean and in the subtropical gyres. While these results do not question the anthropogenic origin of global mean sea level rise, they give new insights into the intrinsically oceanic versus Atmospheric Forcing of regional sea level trends and provide new constraints on the measurement time required to attribute regional sea level trends to the Atmospheric Forcing or to climate change.
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A global probabilistic study of the ocean heat content low-frequency variability: Atmospheric Forcing versus oceanic chaos
Geophysical Research Letters, 2017Co-Authors: Guillaume Sérazin, William Llovel, Thierry Penduff, Jean-marc Molines, Laurent Bessières, Bernard Barnier, Alexandre Jaymond, Stephanie Leroux, Laurent TerrayAbstract:A global 1/4° ocean/sea ice 50‐member ensemble simulation is used to disentangle the low‐frequency imprints of the Atmospherically forced oceanic variability and of the chaotic intrinsic oceanic variability (IOV) on the large‐scale (10° × 10°) ocean heat content (OHC) between 1980 and 2010. The IOV explains most of the interannual‐to‐decadal large‐scale OHC variance over substantial fractions of the global ocean area that increase with depth: 9%, 22%, and 31% in the 0–700 m, 700–2000 m and 2000 m bottom layers, respectively. Such areas concern principally eddy‐active regions, mostly found in the Southern Ocean and in western boundary current extensions, and also concern the subtropical gyres at intermediate and deep levels. The oceanic chaos may also induce random multidecadal fluctuations so that large‐scale regional OHC trends computed on the 1980–2010 period cannot be unambiguously attributed to the Atmospheric Forcing in several oceanic basins at various depths. These results are likely to raise detection and attribution issues from real observations.
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Sensitivity of coastal polynyas and high-salinity shelf water production in the Ross Sea, Antarctica, to the Atmospheric Forcing
Ocean Dynamics, 2012Co-Authors: Pierre Mathiot, Jean-marc Molines, Bernard Barnier, Nicolas C. Jourdain, Hubert Gallée, Julien Le Sommer, Thierry PenduffAbstract:Coastal polynyas around Antarctica are the place of intense air–sea exchanges which eventually lead to the formation of high-salinity shelf waters (HSSW) over continental shelves. Here, the influence of Atmospheric Forcing on coastal polynyas in the Ross Sea is studied by contrasting the response of a regional ocean/sea-ice circulation model to two different Atmospheric Forcing sets. A first Forcing (DFS3) is based on ERA40 Atmospheric surface variables and satellite products. A second Forcing (MAR) is produced on the basis of ERA40 with a dynamical downscaling procedure. As compared to DFS3, MAR Forcing is shown to improve substantially the representation of small-scale patterns of coastal winds with stronger katabatic winds along the coast. The response of the ocean/sea-ice model to the two Forcing sets shows that the MAR Forcing improves substantially the geographical distribution of polynyas in the Ross Sea. With the MAR Forcing, the polynya season is also shown to last longer with a greater ice-production rate. As a consequence, a greater flow of dense water out of the polynyas is found with the MAR Forcing and the properties of HSSW are notably improved as compared to the DFS3 Forcing. The factors contributing to the activity of Terra Nova Bay and Ross Ice Shelf polynyas in the model are studied in detail. The general picture that emerges from our simulations is that the properties of HSSW are mostly set by brine rejection when the polynya season resume. We found that coastal polynyas in the Ross Sea export about 0.4 Sv of HSSW which then flows along three separate channels over the Ross Shelf. A 6-month time lag is observed between the peak of activity of polynyas and the maximum transport across the sills in the channels with a maximum transport of about 1 Sv in February. This lag corresponds to the time it takes to the newly formed HSSW to spread from the polynya to the sills (at a speed of nearly 2 cm s−1).
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Stochastic study of the temperature response of the upper ocean to uncertainties in the Atmospheric Forcing in an Atlantic OGCM
Ocean Modelling, 2008Co-Authors: Marc Lucas, Thierry Penduff, Bernard Barnier, Nadia Ayoub, Pierre De Mey-frémauxAbstract:The impact of errors in Atmospheric Forcing on the behaviour of ocean models is a fundamental issue for ocean modellers and data assimilation and one that has yet to be fully addressed. In this study, we use a stochastic modelling approach with 50 7-months (September-March) primitive equation eddy permitting (1/4°) integrations. We investigate the response of the oceanic circulation to Atmospheric uncertainties, focusing principally on their impact on the upper oceanic temperature field. The ensemble is generated by perturbing the wind, Atmospheric temperature and incoming solar radiation of the ERA40 reanalysis. Each perturbation consists of a random combination of the 20 dominant EOFs of the difference between the ERA40 and NCEP/CORE reanalysis datasets. The ensemble standard deviation of various interfacial and oceanic quantities is then examined in the upper 200 m of three distinct regions of the North Atlantic: in the Gulf Stream, in the Northern Tropical band and in the North East Atlantic. These show that even a very small perturbation of the Atmospheric variables can lead to significant changes in the ocean properties and that regions of oceanic mesoscale activity are the most sensitive. The ocean response is driven by vertical diffusivity and eddy activity. The role of subsurface currents is also crucial in carrying the eddy signal away from the regions of mesoscale activity. Finally, the decorrelation time scale of the mesoscale activity is critical in determining the amplitude of the oceanic response.
Pierre De Mey-frémaux - One of the best experts on this subject based on the ideXlab platform.
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Stochastic study of the temperature response of the upper ocean to uncertainties in the Atmospheric Forcing in an Atlantic OGCM
Ocean Modelling, 2008Co-Authors: Marc Lucas, Thierry Penduff, Bernard Barnier, Nadia Ayoub, Pierre De Mey-frémauxAbstract:The impact of errors in Atmospheric Forcing on the behaviour of ocean models is a fundamental issue for ocean modellers and data assimilation and one that has yet to be fully addressed. In this study, we use a stochastic modelling approach with 50 7-months (September-March) primitive equation eddy permitting (1/4°) integrations. We investigate the response of the oceanic circulation to Atmospheric uncertainties, focusing principally on their impact on the upper oceanic temperature field. The ensemble is generated by perturbing the wind, Atmospheric temperature and incoming solar radiation of the ERA40 reanalysis. Each perturbation consists of a random combination of the 20 dominant EOFs of the difference between the ERA40 and NCEP/CORE reanalysis datasets. The ensemble standard deviation of various interfacial and oceanic quantities is then examined in the upper 200 m of three distinct regions of the North Atlantic: in the Gulf Stream, in the Northern Tropical band and in the North East Atlantic. These show that even a very small perturbation of the Atmospheric variables can lead to significant changes in the ocean properties and that regions of oceanic mesoscale activity are the most sensitive. The ocean response is driven by vertical diffusivity and eddy activity. The role of subsurface currents is also crucial in carrying the eddy signal away from the regions of mesoscale activity. Finally, the decorrelation time scale of the mesoscale activity is critical in determining the amplitude of the oceanic response.
Milan Curcic - One of the best experts on this subject based on the ideXlab platform.
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Atmospheric Forcing of the upper ocean transport in the Gulf of Mexico: From seasonal to diurnal scales
Journal of Geophysical Research: Oceans, 2016Co-Authors: Falko Judt, Shuyi S. Chen, Milan CurcicAbstract:The 2010 Deepwater Horizon oil spill in the Gulf of Mexico (GoM) was an environmental disaster, which highlighted the urgent need to predict the transport and dispersion of hydrocarbon. Although the variability of the Atmospheric Forcing plays a major role in the upper ocean circulation and transport of the pollutants, the air-sea interaction on various time scales is not well understood. This study provides a comprehensive overview of the Atmospheric Forcing and upper ocean response in the GoM from seasonal to diurnal time scales, using climatologies derived from long-term observations, in situ observations from two field campaigns, and a coupled model. The Atmospheric Forcing in the GoM is characterized by striking seasonality. In the summer, the time-average large-scale Forcing is weak, despite occasional extreme winds associated with hurricanes. In the winter, the Atmospheric Forcing is much stronger, and dominated by synoptic variability on time scales of 3–7 days associated with winter storms and cold air outbreaks. The diurnal cycle is more pronounced during the summer, when sea breeze circulations affect the coastal regions and nighttime wind maxima occur over the offshore waters. Realtime predictions from a high-resolution atmosphere-wave-ocean coupled model were evaluated for both summer and winter conditions during the Grand LAgrangian Deployment (GLAD) in July–August 2012 and the Surfzone Coastal Oil Pathways Experiment (SCOPE) in November–December 2013. The model generally captured the variability of Atmospheric Forcing on all scales, but suffered from some systematic errors.
Marc Lucas - One of the best experts on this subject based on the ideXlab platform.
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Stochastic study of the temperature response of the upper ocean to uncertainties in the Atmospheric Forcing in an Atlantic OGCM
Ocean Modelling, 2008Co-Authors: Marc Lucas, Thierry Penduff, Bernard Barnier, Nadia Ayoub, Pierre De Mey-frémauxAbstract:The impact of errors in Atmospheric Forcing on the behaviour of ocean models is a fundamental issue for ocean modellers and data assimilation and one that has yet to be fully addressed. In this study, we use a stochastic modelling approach with 50 7-months (September-March) primitive equation eddy permitting (1/4°) integrations. We investigate the response of the oceanic circulation to Atmospheric uncertainties, focusing principally on their impact on the upper oceanic temperature field. The ensemble is generated by perturbing the wind, Atmospheric temperature and incoming solar radiation of the ERA40 reanalysis. Each perturbation consists of a random combination of the 20 dominant EOFs of the difference between the ERA40 and NCEP/CORE reanalysis datasets. The ensemble standard deviation of various interfacial and oceanic quantities is then examined in the upper 200 m of three distinct regions of the North Atlantic: in the Gulf Stream, in the Northern Tropical band and in the North East Atlantic. These show that even a very small perturbation of the Atmospheric variables can lead to significant changes in the ocean properties and that regions of oceanic mesoscale activity are the most sensitive. The ocean response is driven by vertical diffusivity and eddy activity. The role of subsurface currents is also crucial in carrying the eddy signal away from the regions of mesoscale activity. Finally, the decorrelation time scale of the mesoscale activity is critical in determining the amplitude of the oceanic response.