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  • 1
    Electronic Resource
    Electronic Resource
    Impact of a simple parameterization of convective gravity-wave drag in a stratosphere-troposphere general circulation model and its sensitivity to vertical resolution (1998)
    Springer
    Annales geophysicae 16 (1998), S. 238-249 
    Details
    ISSN: 0992-7689
    Keywords: Meteorology and atmospheric dynamics ; Convective processes ; Waves and tides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Systematic westerly biases in the southern hemisphere wintertime flow and easterly equatorial biases are experienced in the Météo-France climate model. These biases are found to be much reduced when a simple parameterization is introduced to take into account the vertical momentum transfer through the gravity waves excited by deep convection. These waves are quasi-stationary in the frame of reference moving with convection and they propagate vertically to higher levels in the atmosphere, where they may exert a significant deceleration of the mean flow at levels where dissipation occurs. Sixty-day experiments have been performed from a multiyear simulation with the standard 31 levels for a summer and a winter month, and with a T42 horizontal resolution. The impact of this parameterization on the integration of the model is found to be generally positive, with a significant deceleration in the westerly stratospheric jet and with a reduction of the easterly equatorial bias. The sensitivity of the Météo-France climate model to vertical resolution is also investigated by increasing the number of vertical levels, without moving the top of the model. The vertical resolution is increased up to 41 levels, using two kinds of level distribution. For the first, the increase in vertical resolution concerns especially the troposphere (with 22 levels in the troposphere), and the second treats the whole atmosphere in a homogeneous way (with 15 levels in the troposphere); the standard version of 31 levels has 10 levels in the troposphere. A comparison is made between the dynamical aspects of the simulations. The zonal wind and precipitation are presented and compared for each resolution. A positive impact is found with the finer tropospheric resolution on the precipitation in the mid-latitudes and on the westerly stratospheric jet, but the general impact on the model climate is weak, the physical parameterizations used appear to be mostly independent to the vertical resolution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s00585-998-0238-z
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  • 2
    Electronic Resource
    Electronic Resource
    Study of the influence of katabatic flows on the Antarctic circulation using GCM simulations (1990)
    Springer
    Meteorology and atmospheric physics 43 (1990), S. 187-195 
    Details
    ISSN: 1436-5065
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Summary A one dimensional analytical model of katabatic wind over the Antarctica has been developed. This parametric model is derived from the bulk two-layer model of Ball including the surface friction and taking into account the Earth's rotation and the geostrophic wind in the upper layer. This model is validated using the data set (70 soundings) collected during IAGO experiment at D47 (67°24′S, 138°43′E, altitude 1 564m), 110 km inland from the coast of Adélie Land. The parameteric model is then introduced into a GCM which is a spectral global version of the operational numerical weather prediction model used by the French weather service. The most significant effect of the parameterization is a 50 m increase of the geopotential height over the South Pole. The surface temperature at the South Pole increases (2°C) reducing the pole-midlatitude thermal gradient. The westerly circulation at 50° S is slowed down (4m/s at 850 hPa), and the surface pressure at the South Pole increases (4hPa). These results, consistent with an increase of katabatic winds, would however be improved by a better coupling between the parameterization and the GCM boundary layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01028121
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  • 3
    Electronic Resource
    Electronic Resource
    Climatology and interannual variability simulated by the ARPEGE-OPA coupled model (1995)
    Springer
    Climate dynamics 11 (1995), S. 487-505 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A 10-year simulation with a coupled ocean-atmosphere general circulation model (CGCM) is presented. The model consists of the climate version of the Météo-France global forecasting model, ARPEGE, coupled to the LODYC oceanic model, OPA, by the CERFACS coupling package OASIS. The oceanic component is dynamically active over the tropical Pacific, while climatological time-dependent sea surface temperatures (SSTs) are prescribed outside of the Pacific domain. The coupled model shows little drift and exhibits a very regular seasonal cycle. The climatological mean state and seasonal cycle are well simulated by the coupled model. In particular, the oceanic surface current pattern is accurately depicted and the location and intensity of the Equatorial Undercurrent (EUC) are in good agreement with available data. The seasonal cycle of equatorial SSTs captures quite realistically the annual harmonic. Some deficiencies remain including a weak zonal equatorial SST gradient, underestimated wind stress over the Pacific equatorial band and an additional inter-tropical convergence zone (ITCZ) south of the equator in northern winter and spring. Weak interannual variability is present in the equatorial SST signal with a maximum amplitude of 0.5°C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00207197
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  • 4
    Electronic Resource
    Electronic Resource
    Climatology and interannual variability simulated by the ARPEGE-OPA coupled model (1995)
    Springer
    Climate dynamics 11 (1995), S. 487-505 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract. A 10-year simulation with a coupled ocean-atmosphere general circulation model (CGCM) is presented. The model consists of the climate version of the Météo-France global forecasting model, ARPEGE, coupled to the LODYC oceanic model, OPA, by the CERFACS coupling package OASIS. The oceanic component is dynamically active over the tropical Pacific, while climatological time-dependent sea surface temperatures (SSTs) are prescribed outside of the Pacific domain. The coupled model shows little drift and exhibits a very regular seasonal cycle. The climatological mean state and seasonal cycle are well simulated by the coupled model. In particular, the oceanic surface current pattern is accurately depicted and the location and intensity of the Equatorial Undercurrent (EUC) are in good agreement with available data. The seasonal cycle of equatorial SSTs captures quite realistically the annual harmonic. Some deficiencies remain including a weak zonal equatorial SST gradient, underestimated wind stress over the Pacific equatorial band and an additional inter-tropical convergence zone (ITCZ) south of the equator in northern winter and spring. Weak interannual variability is present in the equatorial SST signal with a maximum amplitude of 0.5°  C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820050090
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  • 5
    Electronic Resource
    Electronic Resource
    The ARPEGE/IFS atmosphere model: a contribution to the French community climate modelling (1994)
    Springer
    Climate dynamics 10 (1994), S. 249-266 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A new atmospheric model has been developed jointly by Météo-France, and the European Centre for Medium-range Weather Forecasts (ECMWF) under the acronyms ARPEGE (action de recherche petite echelle grande echelle, which means research project on small and large scales) and IFS (integrated forecast system). This model includes, inter alia, an atmospheric general circulation model (GCM) which is intended by the French climate modelling community to be used for studying the anthropogenic climate impact. A preliminary version of this model has been available since 1992. This paper describes its main characteristics. Three 10-year integrations of this model having spectral horizontal resolutions of T21, T42, and T79 have been performed using prescribed monthly mean sea surface temperatures (SST) observed from 1979 until 1988. The results of these integrations are presented and compared with the observed climatology. The comparison is made for the winter (DJF) and summer (JJA) periods. It is shown that the model is capable of reproducing the observed climatology in a generally successful manner.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00208992
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  • 6
    Electronic Resource
    Electronic Resource
    High resolution climate simulation over Europe (1995)
    Springer
    Climate dynamics 11 (1995), S. 321-339 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Three AMIP-type 10 year simulations have been performed with climate versions of the ARPEGE-IFS model in order to simulate the European climate. The first one uses the standard T42 truncation. The second one uses a high resolution T106 truncation. The horizontal resolution of the third one varies between about T200 over Europe and T21 over the southern Pacific. The winter time general circulation improves in the Atlantic sector as the resolution increases. This is true for the time-mean pattern and for the transient and low-frequency variability. In summer time and in the southern hemisphere, the 3 versions of the model produce reasonable climatologies. When restricted to the European continent, the model verification against the observed climatology shows a reduction of the biases in temperature and, to a lesser extent, in precipitation with the increase in resolution. The use of a variable resolution GCM is a valid alternative to model nesting. The model is too warm in winter and too cold in summer, too wet in northern Europe and too dry in southern Europe.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00215735
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  • 7
    Electronic Resource
    Electronic Resource
    Simulation of climate change over Europe using a global variable resolution general circulation model (1998)
    Springer
    Climate dynamics 14 (1998), S. 173-189 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract  This study presents results from a downscaling simulation of the impact of a doubling of CO2 concentration. A multidecadal coupled simulation of a 1% per year increase of CO2 concentration with the Hadley Centre ocean-atmosphere model provides its sea-surface temperatures and deep soil climatological temperatures as a boundary condition to two 10-year integrations with a version of the ARPEGE-IFS atmosphere model. This global spectral model has a horizontal resolution varying between 60 km in the Mediterranean Sea and 700 km in the southern Pacific. The global impact as well as the regional impact over Europe in this time slice are examined and compared with results from other studies. Over Europe, our main focus, the model impact consists of a warming of about 2 °C, relatively uniform and with little seasonal dependence. There are precipitation increases of about 10% over the northern part in winter and spring, and 30% over the southern part in winter only. Precipitation decreases by 20% in the southern part in autumn. The day-to-day variability of the precipitation increases, except over the southern area in summer. No strong impact is found on the soil moisture. Budgets of physical fluxes are examined at the top of the atmosphere and at the land-atmosphere interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820050216
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  • 8
    Electronic Resource
    Electronic Resource
    A sensitivity experiment for the removal of Arctic sea ice with the French spectral general circulation model (1990)
    Springer
    Climate dynamics 5 (1990), S. 1-17 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Sea ice has a major influence on climate in high latitudes. In this paper we analyzed the impact of removal of Arctic sea-ice cover on the climate simulated by a T42 20-level version of the French spectral model “Emeraude”. The control experiment was the second winter of an annual cycle simulation of the present climate. In the perturbed simulation the Arctic sea-ice cover was replaced by open ocean maintained at the freezing temperature of sea water. The zonal mean patterns of the model response were found to be in good agreement with earlier simulations of Fletcher et al. and Warshaw and Rapp. The atmospheric warming, caused by the increase of upward fluxes of sensible and latent heat and of longwave radiation from the ice-free ocean surface, is largely limited to the high latitudes poleward of 70° N and the lower half of the troposphere and leads to a surface pressure decrease and a precipitation increase over this area. We also analyze the geographical distribution of the response and the mechanisms that can explain the simulated cooling over Eurasia in relation to the energy budget at the surface. Finally, we discuss the reduction of cloud cover over the ice-free Arctic, which was an unexpected result of our simulation, and conclude that further studies are necessary to resolve the question of cumulus convection and cloud process parameterization in high latitudes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00195850
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  • 9
    Electronic Resource
    Electronic Resource
    Validation of an annual cycle simulation with a T42-L20 GCM (1991)
    Springer
    Climate dynamics 5 (1991), S. 189-200 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract An annual cycle of an atmospheric general circulation model (AGCM) is presented. The winter and summer zonal averages of the atmospheric fields are compared with an observed climatology. The main features of the observed seasonal means are well reproduced by the model. One of the main discrepancies is that the simulated atmosphere is too cold, particularly in its upper part. Some other discrepancies might be explained by the interannual variability. The AGCM surface fluxes are directly compared to climatological estimates. On the other hand, the calculation of meridional heat transport by the ocean, inferred from the simulated energy budget, can be compared to transport induced from climatologies. The main result of this double comparison is that AGCM fluxes generally are within the range of climatological estimates. The main deficiency of the model is poor partitioning between solar and non-solar heat fluxes in the tropical belt. The meridional heat transport also reveals a significant energy-loss by the Northern Hemisphere ocean north of 45° N. The possible implications of model surface flux deficiencies on coupling with an oceanic model are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00210004
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  • 10
    Electronic Resource
    Electronic Resource
    High resolution climate simulation over Europe (1995)
    Springer
    Climate dynamics 11 (1995), S. 321-339 
    Details
    ISSN: 1432-0894
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract. Three AMIP-type 10 year simulations have been performed with climate versions of the ARPEGE-IFS model in order to simulate the European climate. The first one uses the standard T42 truncation. The second one uses a high resolution T106 truncation. The horizontal resolution of the third one varies between about T200 over Europe and T21 over the southern Pacific. The winter time general circulation improves in the Atlantic sector as the resolution increases. This is true for the time-mean pattern and for the transient and low-frequency variability. In summer time and in the southern hemisphere, the 3 versions of the model produce reasonable climatologies. When restricted to the European continent, the model verification against the observed climatology shows a reduction of the biases in temperature and, to a lesser extent, in precipitation with the increase in resolution. The use of a variable resolution GCM is a valid alternative to model nesting. The model is too warm in winter and too cold in summer, too wet in northern Europe and too dry in southern Europe.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003820050079
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