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  • 1
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    The role of subpolar deep water formation and Nordic Seas overflows in simulated multidecadal variability of the Atlantic meridional overturning circulation (2014)
    Copernicus Publications (EGU)
    In:  Ocean Science, 10 . pp. 227-241.
    Details
    Publication Date: 2019-09-23
    Description: We investigate the respective role of variations in subpolar deep water formation and Nordic Seas overflows for the decadal to multidecadal variability of the Atlantic meridional overturning circulation (AMOC). This is partly done by analysing long (order of 1000 years) control simulations with five coupled climate models. For all models, the maximum influence of variations in subpolar deep water formation is found at about 45° N, while the maximum influence of variations in Nordic Seas overflows is rather found at 55 to 60° N. Regarding the two overflow branches, the influence of variations in the Denmark Strait overflow is, for all models, substantially larger than that of variations in the overflow across the Iceland–Scotland Ridge. The latter might, however, be underestimated, as the models in general do not realistically simulate the flow path of the Iceland–Scotland overflow water south of the Iceland–Scotland Ridge. The influence of variations in subpolar deep water formation is, on multimodel average, larger than that of variations in the Denmark Strait overflow. This is true both at 45° N, where the maximum standard deviation of decadal to multidecadal AMOC variability is located for all but one model, and at the more classical latitude of 30° N. At 30° N, variations in subpolar deep water formation and Denmark Strait overflow explain, on multimodel average, about half and one-third respectively of the decadal to multidecadal AMOC variance. Apart from analysing multimodel control simulations, we have performed sensitivity experiments with one of the models, in which we suppress the variability of either subpolar deep water formation or Nordic Seas overflows. The sensitivity experiments indicate that variations in subpolar deep water formation and Nordic Seas overflows are not completely independent. We further conclude from these experiments that the decadal to multidecadal AMOC variability north of about 50° N is mainly related to variations in Nordic Seas overflows. At 45° N and south of this latitude, variations in both subpolar deep water formation and Nordic Seas overflows contribute to the AMOC variability, with neither of the processes being very dominant compared to the other.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.5194/os-10-227-2014
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    A multi-model assessment of last interglacial temperatures (2013)
    Copernicus Publications (EGU)
    In:  Climate of the Past, 9 (2). pp. 699-717.
    Details
    Publication Date: 2019-09-23
    Description: The last interglaciation (~130 to 116 ka) is a time period with a strong astronomically induced seasonal forcing of insolation compared to the present. Proxy records indicate a significantly different climate to that of the modern, in particular Arctic summer warming and higher eustatic sea level. Because the forcings are relatively well constrained, it provides an opportunity to test numerical models which are used for future climate prediction. In this paper we compile a set of climate model simulations of the early last interglaciation (130 to 125 ka), encompassing a range of model complexities. We compare the simulations to each other and to a recently published compilation of last interglacial temperature estimates. We show that the annual mean response of the models is rather small, with no clear signal in many regions. However, the seasonal response is more robust, and there is significant agreement amongst models as to the regions of warming vs cooling. However, the quantitative agreement of the model simulations with data is poor, with the models in general underestimating the magnitude of response seen in the proxies. Taking possible seasonal biases in the proxies into account improves the agreement, but only marginally. However, a lack of uncertainty estimates in the data does not allow us to draw firm conclusions. Instead, this paper points to several ways in which both modelling and data could be improved, to allow a more robust model–data comparison.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: archive
    DOI: 10.5194/cp-9-699-2013
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Effects of the Changjiang river discharge on sea surface warming in the Yellow and East China Seas in summer (2011)
    Elsevier
    In:  Continental Shelf Research, 31 . pp. 15-22.
    Details
    Publication Date: 2017-12-12
    Description: This study explores the effects of the Changjiang (also called the Yangtze River) river discharge (CRD) on the density stratifications and associated sea surface temperature (SST) changes using a global ocean general circulation model with regional focus on the Yellow and East China Seas (YECS). It is found that CRD increases the SST in summer through a barrier layer (BL) formation that tends to enhance stratification at the mixed layer base, and thus reduces both vertical mixing and entrainment. This process is effective, particularly in August, after the CRD reaches its maximum in July. The SST difference between the composites of flood and drought years confirms that the surface warming is related to surface freshening by the CRD. This result suggests that the BL induced by the CRD is an important contributor to the surface heat budget in the YECS.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.csr.2010.10.012
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Bi-decadal variability excited in the coupled ocean–atmosphere system by strong tropical volcanic eruptions (2012)
    Springer
    In:  Climate Dynamics, 39 (1/2). pp. 419-444.
    Details
    Publication Date: 2016-09-13
    Description: Decadal and bi-decadal climate responses to tropical strong volcanic eruptions (SVEs) are inspected in an ensemble simulation covering the last millennium based on the Max Planck Institute—Earth system model. An unprecedentedly large collection of pre-industrial SVEs (up to 45) producing a peak annual-average top-of-atmosphere radiative perturbation larger than −1.5 Wm−2 is investigated by composite analysis. Post-eruption oceanic and atmospheric anomalies coherently describe a fluctuation in the coupled ocean–atmosphere system with an average length of 20–25 years. The study provides a new physically consistent theoretical framework to interpret decadal Northern Hemisphere (NH) regional winter climates variability during the last millennium. The fluctuation particularly involves interactions between the Atlantic meridional overturning circulation and the North Atlantic gyre circulation closely linked to the state of the winter North Atlantic Oscillation. It is characterized by major distinctive details. Among them, the most prominent are: (a) a strong signal amplification in the Arctic region which allows for a sustained strengthened teleconnection between the North Pacific and the North Atlantic during the first post-eruption decade and which entails important implications from oceanic heat transport and from post-eruption sea ice dynamics, and (b) an anomalous surface winter warming emerging over the Scandinavian/Western Russian region around 10–12 years after a major eruption. The simulated long-term climate response to SVEs depends, to some extent, on background conditions. Consequently, ensemble simulations spanning different phases of background multidecadal and longer climate variability are necessary to constrain the range of possible post-eruption decadal evolution of NH regional winter climates.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s00382-011-1167-1
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Aerosol size confines climate response to volcanic super-eruptions (2010)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 37 . L24705.
    Details
    Publication Date: 2017-07-27
    Description: Extremely large volcanic eruptions have been linked to global climate change, biotic turnover, and, for the Younger Toba Tuff (YTT) eruption 74,000 years ago, near-extinction of modern humans. One of the largest uncertainties of the climate effects involves evolution and growth of aerosol particles. A huge atmospheric concentration of sulfate causes higher collision rates, larger particle sizes, and rapid fall out, which in turn greatly affects radiative feedbacks. We address this key process by incorporating the effects of aerosol microphysical processes into an Earth System Model. The temperature response is shorter (9–10 years) and three times weaker (−3.5 K at maximum globally) than estimated before, although cooling could still have reached −12 K in some midlatitude continental regions after one year. The smaller response, plus its geographic patchiness, suggests that most biota may have escaped threshold extinction pressures from the eruption.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2010GL045464
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Magnetic moments of the first excited 2^{+} states in the semi-magic ^{112,114,116,122,124}Sn isotopes (2011)
    American Physical Society (APS)
    Details
    Publication Date: 2011-07-20
    Description: Author(s): J. Walker, A. Jungclaus, J. Leske, K.-H. Speidel, A. Ekström, P. Boutachkov, J. Cederkäll, P. Doornenbal, J. Gerl, R. Gernhäuser, N. Goel, M. Górska, I. Kojouharov, P. Maier-Komor, V. Modamio, F. Naqvi, N. Pietralla, S. Pietri, W. Prokopowicz, H. Schaffner, R. Schwengner, and H.-J. Wollersheim The g factors of the first excited 2 + states in the 112,114,116,122,124 Sn isotopes have been measured with high accuracy using the transient field technique in combination with Coulomb excitation in inverse kinematics. The experimental results are discussed in a qualitative way on the basis of empir... [Phys. Rev. C 84, 014319] Published Tue Jul 19, 2011
    Keywords: Nuclear Structure
    Print ISSN: 0556-2813
    Electronic ISSN: 1089-490X
    Topics: Physics
    Published by American Physical Society (APS)
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    PAPER CURRENT
  • 7
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    Forecast skill of multi-year seasonal means in the decadal prediction system of the Max Planck Institute for Meteorology (2012)
    Wiley-Blackwell
    Details
    Publication Date: 2012-11-30
    Description: We examine the latest decadal predictions performed with the coupled model MPI-ESM as part of the Coupled Model Intercomparison Project Phase 5 (CMIP5). We use ensembles of uninitialized and yearly initialized experiments to estimate the forecast skill for surface air temperature. Like for its precursor, the initialization of MPI-ESM improves forecast skill for yearly and multi-yearly means, predominately over the North Atlantic for all lead times. Over the tropical Pacific, negative skill scores reflect a systematic error in the initialization. We also examine the forecast skill of multi-year seasonal means. Skill scores of winter means are predominantly positive over northern Europe. In contrast, summer to autumn means reveal positive skill scores over central and south-eastern Europe. The skill scores of summer means are attributable to an observed pressure-gradient response to the North Atlantic surface temperatures.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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    PAPER CURRENT
  • 8
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    Evolution of the seasonal temperature cycle in a transient Holocene simulation: orbital forcing and sea-ice (data supplement) (2011)
    Cimate of the Past, 7, 1139-1148
    In:  EPIC3Bremerhaven, Cimate of the Past, 7, 1139-1148
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: PANGAEA Documentation , notRev
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    PAPER (OA)
  • 9
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    The effect of ocean tides on a climate model simulation (2010)
    In:  Ocean Modelling
    Details
    Publication Date: 2020-02-12
    Description: We implemented an explicit forcing of the complete lunisolar tides into an ocean model which is part of a coupled atmosphere–hydrology–ocean–sea ice model. An ensemble of experiments with this climate model shows that the model is significantly affected by the induced tidal mixing and nonlinear interactions of tides with low frequency motion. The largest changes occur in the North Atlantic where the ocean current system gets changed on large scales. In particular, the pathway of the North Atlantic Current is modified resulting in improved sea surface temperature fields compared to the non-tidal run. These modifications are accompanied by a more realistic simulation of the convection in the Labrador Sea. The modification of sea surface temperature in the North Atlantic region leads to heat flux changes of up to 50 W/m2. The climate simulations indicate that an improvement of the North Atlantic Current has implications for the simulation of the Western European Climate, with amplified temperature trends between 1950 and 2000, which are closer to the observed trends.
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
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