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  • 1
    Electronic Resource
    Electronic Resource
    Time-dependent greenhouse warming computations with a coupled ocean-atmosphere model (1992)
    Springer
    Climate dynamics 8 (1992), S. 55-69 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Climate changes during the next 100 years caused by anthropogenic emissions of greenhouse gases have been simulated for the Intergovernmental Panel on Climate Change Scenarios A (“business as usual”) and D (“accelerated policies”) using a coupled ocean-atmosphere general circulation model. In the global average, the near-surface temperature rises by 2.6 K in Scenario A and by 0.6 K in Scenario D. The global patterns of climate change for both IPCC scenarios and for a third step-function 2 x CO2 experiment were found to be very similar. The warming delay over the oceans is larger than found in simulations with atmospheric general circulation models coupled to mixed-layer models, leading to a more pronounced land-sea contrast and a weaker warming (and in some regions even an initial cooling) in the Southern Ocean. During the first forty years, the global warming and sea level rise due to the thermal expansion of the ocean are significantly slower than estimated previously from box-diffusion-upwelling models, but the major part of this delay can be attributed to the previous warming history prior to the start of present coupled ocean-atmosphere model integration (cold start).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00209163
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  • 2
    Electronic Resource
    Electronic Resource
    On the cold start problem in transient simulations with coupled atmosphere-ocean models (1993)
    Springer
    Climate dynamics 9 (1993), S. 53-61 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Finite computer resources force compromises in the design of transient numerical experiments with coupled atmosphere-ocean general circulation models which, in the case of global warming simulations, normally preclude a full integration from the undisturbed pre-industrial state. The start of the integration at a later time from a climate state which, in contrast to the true climate, is initially in equilibrium then induces a cold start error. Using linear response theory a general expression for the cold start error is derived. The theory is applied to the Hamburg CO2 scenario simulations. An attempt to estimate the global-mean-temperature response function of the coupled model from the response of the model to a CO2 doubling was unsuccessful because of the non-linearity of the system. However, an alternative derivation, based on the transient simulation itself, yielded a cold start error which explained the initial retardation of the Hamburg global warming curve relative to the IPCC results obtained with a simple box-diffusion-upwelling model. In the case of the sea level the behaviour of the model is apparently more linear. The cold start error estimations based on a CO2 doubling experiment and on an experiment with gradually increasing CO2 (scenario A) are very similar and explain about two thirds of the coupled model retardation relative to the IPCC results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00210008
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  • 3
    Electronic Resource
    Electronic Resource
    Techniques for asynchronous and periodically synchronous coupling of atmosphere and ocean models (1996)
    Springer
    Climate dynamics 12 (1996), S. 313-323 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Asynchronous and periodically-synchronous schemes for coupling atmosphere and ocean models are presented. The performance of the schemes is tested by simulating the climatic response to a step function forcing and to a gradually increasing forcing with a simple zero-dimensional non-linear energy balance model. Both the initial transient response and the asymptotic approach of the equilibrium state are studied. If no annual cycle is allowed the asynchronous coupling technique proves to be a suitable tool. However, if the annual cycle is retained, the periodically synchronous coupling technique reproduces the results of the synchronously coupled runs with smaller bias. In this case it is important that the total length of one synchronous period and one ocean only period is not a multiple of 6 months.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231105
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  • 4
    Electronic Resource
    Electronic Resource
    Techniques for asynchronous and periodically synchronous coupling of atmosphere and ocean models Part I: general strategy and application to the cyclo-stationary case (1996)
    Springer
    Climate dynamics 12 (1996), S. 313-323 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract. Asynchronous and periodically-synchronous schemes for coupling atmosphere and ocean models are presented. The performance of the schemes is tested by simulating the climatic response to a step function forcing and to a gradually increasing forcing with a simple zero-dimensional non-linear energy balance model. Both the initial transient response and the asymptotic approach of the equilibrium state are studied. If no annual cycle is allowed the asynchronous coupling technique proves to be a suitable tool. However, if the annual cycle is retained, the periodically synchronous coupling technique reproduces the results of the synchronously coupled runs with smaller bias. In this case it is important that the total length of one synchronous period and one ocean only period is not a multiple of 6 months.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820050111
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  • 5
    Electronic Resource
    Electronic Resource
    Techniques for asynchronous and periodically synchronous coupling of atmosphere and ocean models (1996)
    Springer
    Climate dynamics 12 (1996), S. 605-614 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A periodically synchronous scheme suitable for coupling atmosphere and ocean models with high internal variability is presented. The performance of the scheme is tested by means of a simple zero-dimensional non-linear energy balance model with stochastic forcing. The equilibrium behaviour and the response to changes in the model parameters are analysed. The response experiments are similar to CO2 doubling and transient CO2 experiments. The best results are obtained using a method with weighted means of the air-sea fluxes which are calculated during the synchronously coupled periods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00216269
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  • 6
    Electronic Resource
    Electronic Resource
    Techniques for asynchronous and periodically synchronous coupling of atmosphere and ocean models Part II: impact of variability (1996)
    Springer
    Climate dynamics 12 (1996), S. 605-614 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract. A periodically synchronous scheme suitable for coupling atmosphere and ocean models with high internal variability is presented. The performance of the scheme is tested by means of a simple zero-dimensional non-linear energy balance model with stochastic forcing. The equilibrium behaviour and the response to changes in the model parameters are analysed. The response experiments are similar to CO2 doubling and transient CO2 experiments. The best results are obtained using a method with weighted means of the air-sea fluxes which are calculated during the synchronously coupled periods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00216269
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  • 7
    Electronic Resource
    Electronic Resource
    Time-dependent greenhouse warming computations with a coupled ocean-atmosphere model (1993)
    Springer
    Climate dynamics 9 (1993), S. 165-165 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00209752
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  • 8
    Electronic Resource
    Electronic Resource
    Climate simulations with the global coupled atmosphere-ocean model ECHAM2/OPYC Part I: present-day climate and ENSO events (1996)
    Springer
    Climate dynamics 12 (1996), S. 195-212 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract In this study the global coupled atmosphere-ocean general circulation model ECHAM2/OPYC and its performance in simulating the present-day climate is presented. The model consists of the T21-spectral atmosphere general circulation model ECHAM2 and the ocean general circulation model OPYC with a resolution corresponding to a T42 Gaussian grid, with increasing resolution towards the equator. The sea-ice is represented by a dynamic thermodynamic sea-ice model with rheology. Both models are coupled using the flux correction technique. With the coupled model ECHAM2/OPYC a 210-year integration under present-day greenhouse gas conditions has been performed. The coupled model simulates a realistic mean climate state, which is close to the observations. The model generates several ENSO events without external forcing. Using traditional and advanced (POP-technique) methods these ENSO events have been analyzed. The results are consistent with the “delayed action oscillator” theory. The model simulates both a tropical and an extra-tropical response to ENSO, which are in good agreement with observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00211618
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  • 9
    Electronic Resource
    Electronic Resource
    Climate simulations with the global coupled atmosphere-ocean model ECHAM2/OPYC Part I: present-day climate and ENSO events (1996)
    Springer
    Climate dynamics 12 (1996), S. 195-212 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract. In this study the global coupled atmosphere-ocean general circulation model ECHAM2/OPYC and its performance in simulating the present-day climate is presented. The model consists of the T21-spectral atmosphere general circulation model ECHAM2 and the ocean general circulation model OPYC with a resolution corresponding to a T42 Gaussian grid, with increasing resolution towards the equator. The sea-ice is represented by a dynamic thermodynamic sea-ice model with rheology. Both models are coupled using the flux correction technique. With the coupled model ECHAM2/OPYC a 210-year integration under present-day greenhouse gas conditions has been performed. The coupled model simulates a realistic mean climate state, which is close to the observations. The model generates several ENSO events without external forcing. Using traditional and advanced (POP-technique) methods these ENSO events have been analyzed. The results are consistent with the "delayed action oscillator" theory. The model simulates both a tropical and an extra-tropical response to ENSO, which are in good agreement with observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820050103
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  • 10
    Electronic Resource
    Electronic Resource
    The impact of sub-grid scale sea-ice inhomogeneities on the performance of the atmospheric general circulation model ECHAM3 (1996)
    Springer
    Climate dynamics 12 (1996), S. 477-496 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract. Leads and polynyas have a great impact on the energy budget of the polar ocean and atmosphere. Since atmospheric general circulation models are not able to resolve the spatial scales of these inhomogeneities, it is necessary to include the effect of fractional sub-grid scale sea-ice inhomogeneities on climate by a suitable parametrization. In order to do this we have divided each model grid-cell into an ice-covered and an ice-free part. Nevertheless, a numerical model requires effective transports representative for the whole grid-box. A simple procedure would be to use grid averages of the surface parameters for the calculation of the surface fluxes. However, as the surface fluxes are non-linearly dependent on the surface properties, the fluxes over ice and open water should be calculated separately according to the individual surface-layer structure of each surface type. Then these local fluxes should be averaged to obtain representative fluxes. Sensitivity experiments with the Hamburg atmospheric general circulation model ECHAM3 clearly show that a subgrid scale distribution of sea ice is a dominant factor controlling the exchange processes between ocean and atmosphere in the Arctic. The heat and water vapour transports are strongly enhanced leading to a significant warming and moistening of the polar troposphere. This affects the atmospheric circulation in high- and mid-latitudes; e.g. the stationary lows are modified and the transient cyclonic activity over the subpolar oceans is reduced. A pronounced impact of sub-grid scale sea-ice distribution on the model climate can only be obtained when the non-linear behaviour of the surface exchange processes is considered by a proper, physically based, averaging of the surface fluxes. A simple linear averaging of surface parameters is not sufficient.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820050122
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