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  • 1
    Online Resource
    Online Resource
    Is the observed NAO variability during the instrumental record unusual? (2008)
    Associated volumes
    Details Availability
    In: Geophysical research letters, Hoboken, NJ : Wiley, 1974, 35(2008), 1944-8007
    In: volume:35
    In: year:2008
    In: extent:5
    Description / Table of Contents: Observed multidecadal variability (30 yr running means, trends, and moving standard deviations) of the North Atlantic Oscillation (NAO) during the instrumental record is compared to that simulated by two different coupled general circulation models in extended-range control experiments. Simulated NAO exhibits strong low frequency fluctuations, even on multi-centennial time scale. Observed multi-decadal NAO variations agree well with the model variability. Trend probability distribution functions, observed and simulated, were not found to be different with statistical significance. Thus, multi-decadal NAO changes similar to those observed during the instrumental record, including the recent increase in 1965-1995, may be internally generated within the coupled atmosphere-ocean system without considering external forcing.
    Type of Medium: Online Resource
    Pages: 5 , graph. Darst
    ISSN: 1944-8007
    DOI: 10.1029/2008GL033273
    Language: English
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  • 2
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    Three time-slice simulations of the Eemian (eem), the mid-Holocene (hol), and a pre-industrial (pri) control run with the coupled atmosphere-ocean-model ECHAM5/MPI-OM (2010)
    PANGAEA
    In:  Supplement to: Fischer, Nils; Jungclaus, Johann H (2010): Effects of orbital forcing on atmosphere and ocean heat transports in Holocene and Eemian climate simulations with a comprehensive Earth system model. Climate of the Past, 6, 155-168, https://doi.org/10.5194/cp-6-155-2010
    Details
    Publication Date: 2023-11-22
    Description: Orbital forcing does not only exert direct insolation effects, but also alters climate indirectly through feedback mechanisms that modify atmosphere and ocean dynamics and meridional heat and moisture transfers. We investigate the regional effects of these changes by detailed analysis of atmosphere and ocean circulation and heat transports in a coupled atmosphere-ocean-sea ice-biosphere general circulation model (ECHAM5/JSBACH/MPI-OM). We perform long term quasi equilibrium simulations under pre-industrial, mid-Holocene (6000 years before present – yBP), and Eemian (125 000 yBP) orbital boundary conditions. Compared to pre-industrial climate, Eemian and Holocene temperatures show generally warmer conditions at higher and cooler conditions at lower latitudes. Changes in sea-ice cover, ocean heat transports, and atmospheric circulation patterns lead to pronounced regional heterogeneity. Over Europe, the warming is most pronounced over the north-eastern part in accordance with recent reconstructions for the Holocene. We attribute this warming to enhanced ocean circulation in the Nordic Seas and enhanced ocean-atmosphere heat flux over the Barents Shelf in conduction with retreat of sea ice and intensified winter storm tracks over northern Europe.
    Keywords: Abbreviation; Experiment; File format; File name; File size; Integrierte Analyse zwischeneiszeitlicher Klimadynamik; INTERDYNAMIK; Parameter; Uniform resource locator/link to model result file; Unit
    Type: Dataset
    Format: text/tab-separated-values, 100 data points
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    DATA PANGAEA
  • 3
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    Holocene experiment with coupled atmosphere-ocean-model ECHAM5/MPI-OM (2012)
    PANGAEA
    In:  Supplement to: Fischer, Nils; Jungclaus, Johann H (2011): Evolution of the seasonal temperature cycle in a transient Holocene simulation: orbital forcing and sea-ice. Climate of the Past, 7, 1139-1148, https://doi.org/10.5194/cp-7-1139-2011
    Details
    Publication Date: 2023-11-22
    Description: Changes in the Earth's orbit lead to changes in the seasonal and meridional distribution of insolation. We quantify the influence of orbitally induced changes on the seasonal temperature cycle in a transient simulation of the last 6000 years – from the mid-Holocene to today – using a coupled atmosphere-ocean general circulation model (ECHAM5/MPI-OM) including a land surface model (JSBACH). The seasonal temperature cycle responds directly to the insolation changes almost everywhere. In the Northern Hemisphere, its amplitude decreases according to an increase in winter insolation and a decrease in summer insolation. In the Southern Hemisphere, the opposite is true. Over the Arctic Ocean, decreasing summer insolation leads to an increase in sea-ice cover. The insulating effect of sea ice between the ocean and the atmosphere leads to decreasing heat flux and favors more "continental" conditions over the Arctic Ocean in winter, resulting in strongly decreasing temperatures. Consequently, there are two competing effects: the direct response to insolation changes and a sea-ice insulation effect. The sea-ice insulation effect is stronger, and thus an increase in the amplitude of the seasonal temperature cycle over the Arctic Ocean occurs. This increase is strongest over the Barents Shelf and influences the temperature response over northern Europe. We compare our modeled seasonal temperatures over Europe to paleo reconstructions. We find better agreements in winter temperatures than in summer temperatures and better agreements in northern Europe than in southern Europe, since the model does not reproduce the southern European Holocene summer cooling inferred from the paleo reconstructions. The temperature reconstructions for northern Europe support the notion of the influence of the sea-ice insulation effect on the evolution of the seasonal temperature cycle.
    Keywords: Abbreviation; File format; File name; File size; Integrierte Analyse zwischeneiszeitlicher Klimadynamik; INTERDYNAMIK; Parameter; Uniform resource locator/link to model result file; Unit
    Type: Dataset
    Format: text/tab-separated-values, 77 data points
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    DATA PANGAEA
  • 4
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    The PMIP4 contribution to CMIP6 – Part 3: The last millennium, scientific objective, and experimental design for the PMIP4 past1000 simulations (2017)
    Copernicus Publications (EGU)
    In:  Geoscientific Model Development, 10 (11). pp. 4005-4033.
    Details
    Publication Date: 2020-02-06
    Description: The pre-industrial millennium is among the periods selected by the Paleoclimate Model Intercomparison Project (PMIP) for experiments contributing to the sixth phase of the Coupled Model Intercomparison Project (CMIP6) and the fourth phase of the PMIP (PMIP4). The past1000 transient simulations serve to investigate the response to (mainly) natural forcing under background conditions not too different from today, and to discriminate between forced and internally generated variability on interannual to centennial timescales. This paper describes the motivation and the experimental set-ups for the PMIP4-CMIP6 past1000 simulations, and discusses the forcing agents orbital, solar, volcanic, and land use/land cover changes, and variations in greenhouse gas concentrations. The past1000 simulations covering the pre-industrial millennium from 850 Common Era (CE) to 1849 CE have to be complemented by historical simulations (1850 to 2014 CE) following the CMIP6 protocol. The external forcings for the past1000 experiments have been adapted to provide a seamless transition across these time periods. Protocols for the past1000 simulations have been divided into three tiers. A default forcing data set has been defined for the Tier 1 (the CMIP6 past1000) experiment. However, the PMIP community has maintained the flexibility to conduct coordinated sensitivity experiments to explore uncertainty in forcing reconstructions as well as parameter uncertainty in dedicated Tier 2 simulations. Additional experiments (Tier 3) are defined to foster collaborative model experiments focusing on the early instrumental period and to extend the temporal range and the scope of the simulations. This paper outlines current and future research foci and common analyses for collaborative work between the PMIP and the observational communities (reconstructions, instrumental data).
    Type: Article , PeerReviewed
    Format: text
    Format: archive
    DOI: 10.5194/gmd-10-4005-2017
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    OMIP contribution to CMIP6: experimental and diagnostic protocol for the physical component of the Ocean Model Intercomparison Project (2016)
    Copernicus Publications (EGU)
    In:  Geoscientific Model Development, 9 (9). pp. 3231-3296.
    Details
    Publication Date: 2019-02-01
    Description: The Ocean Model Intercomparison Project (OMIP) is an endorsed project in the Coupled Model Intercomparison Project Phase 6 (CMIP6). OMIP addresses CMIP6 science questions, investigating the origins and consequences of systematic model biases. It does so by providing a framework for evaluating (including assessment of systematic biases), understanding, and improving ocean, sea-ice, tracer, and biogeochemical components of climate and earth system models contributing to CMIP6. Among the WCRP Grand Challenges in climate science (GCs), OMIP primarily contributes to the regional sea level change and near-term (climate/decadal) prediction GCs. OMIP provides (a) an experimental protocol for global ocean/sea-ice models run with a prescribed atmospheric forcing; and (b) a protocol for ocean diagnostics to be saved as part of CMIP6. We focus here on the physical component of OMIP, with a companion paper (Orr et al., 2016) detailing methods for the inert chemistry and interactive biogeochemistry. The physical portion of the OMIP experimental protocol follows the interannual Coordinated Ocean-ice Reference Experiments (CORE-II). Since 2009, CORE-I (Normal Year Forcing) and CORE-II (Interannual Forcing) have become the standard methods to evaluate global ocean/sea-ice simulations and to examine mechanisms for forced ocean climate variability. The OMIP diagnostic protocol is relevant for any ocean model component of CMIP6, including the DECK (Diagnostic, Evaluation and Characterization of Klima experiments), historical simulations, FAFMIP (Flux Anomaly Forced MIP), C4MIP (Coupled Carbon Cycle Climate MIP), DAMIP (Detection and Attribution MIP), DCPP (Decadal Climate Prediction Project), ScenarioMIP, HighResMIP (High Resolution MIP), as well as the ocean/sea-ice OMIP simulations
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.5194/gmd-9-3231-2016
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Cyclogenesis in the Denmark Strait Overflow Plume (2001)
    AMS (American Meteorological Society)
    In:  Journal of Physical Oceanography, 31 (11). pp. 3214-3229.
    Details
    Publication Date: 2018-04-06
    Description: A densely spaced hydrographic survey of the northern Irminger Basin together with satellite-tracked near-surface drifters confirm the intense mesoscale variability within and above the Denmark Strait overflow. In particular, the drifters show distinct cyclonic vortices over the downslope edge of the outflow plume. Growing perturbations such as these can be attributed to the baroclinic instability of a density current. A primitive equation model with periodic boundaries is used to simulate the destabilization of an idealized dense filament on a continental slope that resembles the northeastern Irminger Basin. Unstable waves evolve rapidly if the initial temperature profile is perturbed with a sinusoidal anomaly that exceeds a certain cutoff wavelength. As the waves grow to large amplitudes isolated eddies of both signs develop. Anticyclones form initially within the dense filament and are rich in overflow water. In contrast, cyclones form initially with their center in the ambient water but wrap outflow water around their center, thus containing a mixture of both water types. The nonlinear advection of waters that were originally located within the front between both water masses contributes most significantly to the stronger intensification of the cyclones in comparison with anticyclones. The frontal waters carry positive relative vorticity into the center of the cyclone. The process bears therefore some resemblance to atmospheric frontal cyclogenesis. After saturation there is a bottom jet of overflow water that is confined by counterrotating eddies: anticyclones upslope and cyclones downslope of the overflow core. The parameter dependence of the maximum growth rate is studied, and the implications of eddy-induced mixing for the water mass modification is discussed.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1175/1520-0485(2001)031〈3214:CITDSO〉2.0.CO;2
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Heat and salt intrusions in the pycnocline from sinking plumes. Test cases for the entrainment in the Black Sea (1997)
    Kluwer
    In:  In: Sensitivity to Change: Black Sea and North Sea. , ed. by Özsoy, E. and Mikaelyan, A. Kluwer, -, pp. 417-438.
    Details
    Publication Date: 2012-01-27
    Type: Book chapter , PeerReviewed
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    OceanRep: Book chapter
  • 8
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    Modelling the Overflows Across the Greenland–Scotland Ridge (2008)
    Springer
    In:  In: Arctic–Subarctic Ocean Fluxes. , ed. by Dickson, R. R., Meincke, J. and Rhines, P. Springer, Heidelberg, Germany, pp. 527-549. ISBN 978-1-4020-6773-0
    Details
    Publication Date: 2015-09-23
    Description: The Atlantic Meridional Overturning Circulation (AMOC) is part of a global redistribution system in the ocean that carries vast amounts of mass, heat, and freshwater. Within the AMOC, water mass transformations in the Nordic Seas (NS) and the overflows across the Greenland-Scotland Ridge (GSR) contribute significantly to the overturning mass transport. The deep NS are separated by the GSR from direct exchange with the subpolar North Atlantic. Two deeper passages, Denmark Strait (DS, sill depth 630 m) and Faroe Bank Channel (FBC, sill depth 840 m), constrain the deep outflow. The outflow transports are assumed to be governed by hydraulic control (Whitehead 1989, 1998). According to the circulation scheme by Dickson and Brown (1994), there is an overflow of 2.9 Sv (1 Sv = 1 Sverdrup = 106 m3 s–1) through DS, 1.7 Sv through FBC and another 1 Sv from flow across the Iceland%Faroe Ridge (IFR). To the south of the GSR, the overflows sink to depth and then spread along the topography, eventually merging to form a deep boundary current in the western Irminger Sea. During the descent, the dense bottom water flow doubles its volume by entrainment of ambient waters (e.g. Price and Baringer 1994) so that there is a deep water transport of 13.3 Sv once the boundary current reaches Cape Farvel (Dickson and Brown 1994). Thus the overflows and the overflow-related part of the AMOC account for more than 70% of the maximum total overturning, which is estimated from observations to be about 18 Sv (e.g. Macdonald 1998)
    Type: Book chapter , NonPeerReviewed
    Format: text
    DOI: 10.1007/978-1-4020-6774-7_23
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    OceanRep: Book chapter
  • 9
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    Clarifying the Relative Role of Forcing Uncertainties and Initial-Condition Unknowns in Spreading the Climate Response to Volcanic Eruptions (2019)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 46 (3). pp. 1602-1611.
    Details
    Publication Date: 2022-01-31
    Description: Radiative forcing from volcanic aerosol impacts surface temperatures; however, the background climate state also affects the response. A key question thus concerns whether constraining forcing estimates is more important than constraining initial conditions for accurate simulation and attribution of posteruption climate anomalies. Here we test whether different realistic volcanic forcing magnitudes for the 1815 Tambora eruption yield distinguishable ensemble surface temperature responses. We perform a cluster analysis on a superensemble of climate simulations including three 30-member ensembles using the same set of initial conditions but different volcanic forcings based on uncertainty estimates. Results clarify how forcing uncertainties can overwhelm initial-condition spread in boreal summer due to strong direct radiative impact, while the effect of initial conditions predominate in winter, when dynamics contribute to large ensemble spread. In our setup, current uncertainties affecting reconstruction-simulation comparisons prevent conclusions about the magnitude of the Tambora eruption and its relation to the “year without summer.”
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1029/2018GL081018
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    Variability in the northern North Atlantic and Arctic oceans across the last two millennia: A review (2019)
    AGU (American Geophysical Union) | Wiley
    In:  Paleoceanography and Paleoclimatology, 34 (8). pp. 1399-1436.
    Details
    Publication Date: 2022-01-31
    Description: The climate of the last two millennia was characterised by decadal to multi‐centennial variations which were recorded in terrestrial records and had important societal impacts. The cause of these climatic events is still under debate but changes in the North Atlantic circulation have often been proposed to play an important role. In this review we compile available high‐resolution paleoceanographic datasets from the northern North Atlantic and Nordic Seas. The records are grouped into regions related to modern ocean conditions and their variability is discussed. We additionally discuss our current knowledge from modelling studies, with a specific focus on the dynamical changes that are not well inferred from the proxy records. An illustration is provided through the analysis of two climate model ensembles and an individual simulation of the last millennium. This review thereby provides an up‐to‐date paleo‐perspective on the North Atlantic multidecadal to multi‐centennial ocean variability across the last two millennia.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2018PA003508
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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