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  • AGU (American Geophysical Union)  (8)
  • Hamburg : Max-Planck-Institut für Meteorologie
  • 2010-2014  (9)
  • 1
    Book
    Book
    Climate variability in a coupled GCM (1991-)
    Hamburg : Max-Planck-Institut für Meteorologie
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    Type of Medium: Book
    Series Statement: Report / Max-Planck-Institut für Meteorologie ...
    Language: English
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  • 2
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    Potential of Equatorial Atlantic Variability to Enhance El Nino Prediction (2013)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 40 . pp. 2278-2283.
    Details
    Publication Date: 2017-05-24
    Description: Extraordinarily strong El Niño events, such as those of 1982/83 and 1997/98, have been poorly predicted by operational seasonal forecasts made before boreal spring, despite significant advances in understanding, improved models, and enhanced observational networks. The Equatorial Atlantic Zonal Mode – a phenomenon similar to El Niño but much weaker and peaking in boreal summer – impacts winds over the Pacific, and hence affects El Niño, and also potentially its predictability. Here we use a climate model to perform a suite of seasonal predictions with and without SST in the Atlantic restored to observations. We show for the first time that knowledge of Equatorial Atlantic sea surface temperature (SST) significantly improves the prediction across boreal spring of major El Niño events and also weaker variability. This is because Atlantic SST acts to modulate El Niño variability, rather than triggering events. Our results suggest that better prediction of major El Niño events might be achieved through model improvement in the Equatorial Atlantic.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
    DOI: 10.1002/grl.50362
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Pacific and Atlantic Multidecadal Variability in the Kiel Climate Model (2010)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 37 . L24702.
    Details
    Publication Date: 2019-09-23
    Description: Pacific Decadal Variability (PDV) and Atlantic Multidecadal Variability (AMV), the two leading decadal modes of observed Northern Hemisphere sea surface temperature (SST) variability, are investigated in a multi-millennial control integration of the Kiel Climate Model (KCM). It is shown that the two phenomena are independent modes in the model and can be easily separated by Principal Oscillation Pattern (POP) analysis of model SST. PDVrelated variability covers the whole North Pacific with strong signals in both the mid-latitude North Pacific and the western Tropical Pacific. Strong signals are also simulated in the eastern Indian Ocean Sector. PDV’s memory, however, resides in the North Pacific and is linked to the subtropical gyre. The AMV mechanism is related to the Atlantic Meridional Overturning Circulation (AMOC). A stochastic mechanism applies to both PDV and AMV.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2010GL045560
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Tropical circulation and hydrological cycle response to orbital forcing (2012)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 39 . L15708.
    Details
    Publication Date: 2019-09-23
    Description: The intensity of the two major atmospheric tropical circulations, the Hadley and Walker circulation, has been analyzed in simulations with the Kiel Climate Model (KCM) of the early Eemian and the early Holocene, both warmer climate epochs compared to the late Holocene, or pre-industrial era. The KCM was forced by changes in orbital parameters corresponding to the early and late Holocene (9.5kyr BP and pre-industrial) and the early Eemian (126kyr BP). An intensification of the Southern Hemisphere (SH) winter Hadley cell and a northward extension of its rising branch, the Intertropical Convergence Zone, relative to pre-industrial are simulated for both warm periods. The Walker circulation's rising branch is shifted westward towards the Indian Ocean due to an increased zonal tropical sea surface temperature (SST) gradient across the Indo-Pacific Ocean, which drives enhanced easterlies over this region. The simulated vertically-integrated water vapor transport across the Equator shows the strongest response for the SH winter (boreal summer) Hadley cell over the Pacific Ocean due to an enhanced cross-equatorial SST gradient in the tropical Pacific during the early Holocene and the early Eemian. The orbitally-induced increase of the cross-equatorial insolation gradient in the tropical Pacific leads to a strengthening (weakening) of the wind speed and enhanced (reduced) evaporative cooling over the southern (northern) tropical Pacific, which reinforces the initial radiatively-forced meridional SST gradient change. The increased cross-equatorial insolation gradient in combination with the strong wind-evaporation-SST feedback and changing humidity are important mechanisms to enhance the SH winter Hadley circulation response to orbital forcing. Key Points: Intensification of the SH winter Hadley cell for the early Holocene and Eemian. Walker circulation's rising branch is shifted westward towards the Indian Ocean. WES feedback plays key role in intensification of the Hadley circulation.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2012GL052482
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Response of the Hydrological Cycle to Orbital and Greenhouse Gas Forcing (2010)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 37 . L19705.
    Details
    Publication Date: 2019-09-23
    Description: The sensitivity of the hydrological cycle to changes in orbital forcing and atmospheric greenhouse gas (GHG) concentrations is assessed using a fully coupled atmosphere-ocean-sea ice general circulation model (Kiel Climate Model). An orbitally-induced intensification of the summer monsoon circulation during the Holocene and Eemian drives enhanced water vapor advection into the Northern Hemisphere, thereby enhancing the rate of water vapor changes by about 30% relative to the rate given by the Clausius-Clapeyron Equation, assuming constant relative humidity. Orbitally-induced changes in hemispheric-mean precipitation are fully attributed to inter-hemispheric water vapor exchange in contrast to a GHG forced warming, where enhanced precipitation is caused by increased both the moisture advection and evaporation. When considering the future climate on millennial time scales, both forcings combined are expected to exert a strong effect.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2010GL044377
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Modeling the ENSO impact of orbitally induced mean state climate changes (2012)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Oceans, 117 (C5).
    Details
    Publication Date: 2019-09-23
    Description: The sensitivity of the El Niño–Southern Oscillation (ENSO) phenomenon to changes in the tropical Pacific mean climate is investigated with a coupled atmosphere-ocean-sea ice general circulation model (AOGCM), the Kiel Climate Model (KCM). Different mean climate states are generated by changing the orbital forcing that causes a redistribution of solar energy, which was a major driver of both the Holocene and the Eemian climates. We find that the ENSO amplitude is positively correlated with both the Equatorial Pacific sea surface temperature (SST) and the equatorial zonal SST contrast. The latter is controlled by the upwelling-induced damping of the SST changes in the Eastern Equatorial Pacific (EEP), and by the vertical ocean dynamical heating and zonal heat transport convergence in the Western Equatorial Pacific. The ENSO amplitude also correlates positively with the seasonal SST amplitude in the EEP and negatively with the strength of the easterly Trades over the Equatorial Pacific. However, the ENSO period is rather stable and stays within 3–4 years. Enhanced ENSO amplitude is simulated during the late-Holocene, in agreement with paleoproxy records. The tight positive correlation (r = 0.89) between the ENSO strength and the Western Pacific Warm Pool (WPWP) SST suggests that the latter may provide an indirect measure of the ENSO amplitude from proxy data that cannot explicitly resolve interannual variability. Key Points: - ENSO amplitude enhances as mean SST & west-east SST gradient rise in tropical Pacific - The broad range frequency peaks at periods of 3-4 years over Holocene and Eemian - The Pacific's warm pool SST is a suitable indicator to monitor ENSO variability
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2011JC007742
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Natural variability of the central Pacific El Niño event on multi-centennial timescales (2011)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 38 . L02704.
    Details
    Publication Date: 2017-06-20
    Description: There is an evidence of the increasing intensity as well as occurrence frequency of the so-called central Pacific (CP) El Niño events since the 1990s. We examine whether such an increase in the frequency of CP El Niño may be a manifestation of natural climate variability. A control simulation of the Kiel Climate Model, run for 4200 years with the present values of greenhouse gases, exhibit large variations of the occurrence frequency of the CP El Niño versus the eastern Pacific (EP) El Niño. A model simulates to some extent changes in the occurrence ratio of CP and EP El Niño in comparison with the observations. Therefore, we can not exclude the possibility that an increasing of occurrence frequency of CP El Niño during recent decades in the observation could be a part of natural variability in the tropical climate system.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2010GL045886
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Equatorial Atlantic interannual variability: the role of heat content (2010)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Atmospheres, 115 . C09020.
    Details
    Publication Date: 2019-09-23
    Description: The dynamics of the Equatorial Atlantic zonal mode are studied using observed sea surface height (SSH), sea surface temperature (SST), and heat flux and reanalysis wind stress and upper ocean temperature. Principal oscillation pattern (POP) analysis shows that the zonal mode is an oscillatory normal-mode of the observed coupled system, obeying the delayed-action/recharge oscillator paradigm for ENSO. Variations in equatorial averaged SSH, a proxy for upper ocean heat content, precede SST anomalies in the cold tongue by 4-5 months, about a quarter of the POP period. Positive subsurface temperature anomalies appear in the west, as a delayed response to the preceding cold event. These propagate eastward, where due to the shallow thermocline they can influence SST, leading to the next warm event. Although SST variations exhibit weak westward propagation during some zonal mode events, POP analysis indicates that to first order there is no zonal propagation in SST. Net surface heat flux anomalies generally act to damp SST anomalies. The zonal mode explains a large amount (70%) of SST variability in the east and a significant fraction (19%) of equatorial variability. Thus, the predictability potential in the Equatorial Atlantic on seasonal time scales may be considerably higher than currently thought.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2010JC006304
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Rising Arctic Ocean temperatures cause gas hydrate destabilization and ocean acidification (2011)
    AGU (American Geophysical Union)
    Details
    Publication Date: 2023-01-31
    Description: Vast amounts of methane hydrates are potentially stored in sediments along the continental margins, owing their stability to low temperature – high pressure conditions. Global warming could destabilize these hydrates and cause a release of methane (CH 4) into the water column and possibly the atmosphere. Since the Arctic has and will be warmed considerably, Arctic bottom water temperatures and their future evolution projected by a climate model were analyzed. The resulting warming is spatially inhomogeneous, with the strongest impact on shallow regions affected by Atlantic inflow. Within the next 100 years, the warming affects 25% of shallow and mid-depth regions containing methane hydrates. Release of methane from melting hydrates in these areas could enhance ocean acidification and oxygen depletion in the water column. The impact of methane release on global warming, however, would not be significant within the considered time span.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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