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  • 1
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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
  • 2
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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
  • 3
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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
  • 4
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    Developments in the MPI‐M Earth System Model version 1.2 (MPI‐ESM1.2) and Its Response to Increasing CO2 (2019)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2023-01-03
    Description: A new release of the Max Planck Institute for Meteorology Earth System Model version 1.2 (MPI-ESM1.2) is presented. The development focused on correcting errors in and improving the physical processes representation, as well as improving the computational performance, versatility, and overall user friendliness. In addition to new radiation and aerosol parameterizations of the atmosphere, several relatively large, but partly compensating, coding errors in the model's cloud, convection, and turbulence parameterizations were corrected. The representation of land processes was refined by introducing a multilayer soil hydrology scheme, extending the land biogeochemistry to include the nitrogen cycle, replacing the soil and litter decomposition model and improving the representation of wildfires. The ocean biogeochemistry now represents cyanobacteria prognostically in order to capture the response of nitrogen fixation to changing climate conditions and further includes improved detritus settling and numerous other refinements. As something new, in addition to limiting drift and minimizing certain biases, the instrumental record warming was explicitly taken into account during the tuning process. To this end, a very high climate sensitivity of around 7 K caused by low-level clouds in the tropics as found in an intermediate model version was addressed, as it was not deemed possible to match observed warming otherwise. As a result, the model has a climate sensitivity to a doubling of CO2 over preindustrial conditions of 2.77 K, maintaining the previously identified highly nonlinear global mean response to increasing CO2 forcing, which nonetheless can be represented by a simple two-layer model.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    No Consistent Simulated Trends in the Atlantic Meridional Overturning Circulation for the Past 6,000 Years (2023)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-02-07
    Description: The Atlantic Meridional Overturning Circulation (AMOC) is a key feature of the North Atlantic with global ocean impacts. The AMOC's response to past changes in forcings during the Holocene provides important context for the coming centuries. Here, we investigate AMOC trends using an emerging set of transient simulations using multiple global climate models for the past 6,000 years. Although some models show changes, no consistent trend in overall AMOC strength during the mid-to-late Holocene emerges from the ensemble. We interpret this result to suggest no overall change in AMOC, which fits with our assessment of available proxy reconstructions. The decadal variability of the AMOC does not change in ensemble during the mid- and late-Holocene. There are interesting AMOC changes seen in the early Holocene, but their nature depends a lot on which inputs are used to drive the experiment.
    Type: Article , PeerReviewed
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Polar-lower latitude linkages and their role in weather and climate prediction (2015)
    AMER METEOROLOGICAL SOC
    In:  EPIC3Bulletin of the American Meteorological Society, AMER METEOROLOGICAL SOC, ISSN: 0003-0007
    Details
    Publication Date: 2015-06-11
    Description: International Workshop on Polar-lower Latitude Linkages in Weather and Climate Prediction What: Eighty experts from twenty different countries met to assess recent progress in, and new directions for, our understanding of the mechanisms governing polar-lower latitude linkages and their role in weather and climate prediction including services. When: 10–12 December 2014 Where: Barcelona, Spain
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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    PAPER (OA)
  • 7
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    Ocean Model Formulation Influences Transient Climate Response (2021)
    Wiley
    In:  EPIC3Journal of Geophysical Research-Oceans, Wiley, 126(12), pp. e2021JC017633, ISSN: 0148-0227
    Details
    Publication Date: 2022-06-29
    Description: The transient climate response (TCR) is 20% higher in the Alfred Wegener Institute Climate Model (AWI-CM) compared to the Max Planck Institute Earth System Model (MPI-ESM) whereas the equilibrium climate sensitivity (ECS) is by up to 10% higher in AWI-CM. These results are largely independent of the two considered model resolutions for each model. The two coupled CMIP6 models share the same atmosphere-land component ECHAM6.3 developed at the Max Planck Institute for Meteorology (MPI-M). However, ECHAM6.3 is coupled to two different ocean models, namely the MPIOM sea ice-ocean model developed at MPI-M and the FESOM sea ice-ocean model developed at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). A reason for the different TCR is related to ocean heat uptake in response to greenhouse gas forcing. Specifically, AWI-CM simulations show stronger surface heating than MPI-ESM simulations while the latter accumulate more heat in the deeper ocean. The vertically integrated ocean heat content is increasing slower in AWI-CM model configurations compared to MPI-ESM model configurations in the high latitudes. Weaker vertical mixing in AWI-CM model configurations compared to MPI-ESM model configurations seems to be key for these differences. The strongest difference in vertical ocean mixing occurs inside the Weddell and Ross Gyres and the northern North Atlantic. Over the North Atlantic, these differences materialize in a lack of a warming hole in AWI-CM model configurations and the presence of a warming hole in MPI-ESM model configurations. All these differences occur largely independent of the considered model resolutions.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
    Format: application/pdf
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