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  • 1.
    Doescher, Ralf
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Rutgersson, Anna
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    The development of the coupled ocean-atmosphere model RCAO2001In: Third study conference on BALTEX / [ed] J. Meywerk, 2001, p. 45-46Conference paper (Other academic)
  • 2.
    Doescher, Ralf
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Willen, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Rutgersson, Anna
    SMHI, Research Department, Climate research - Rossby Centre.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Graham, Phil
    SMHI, Research Department, Climate research - Rossby Centre.
    The development of the regional coupled ocean-atmosphere model RCAO2002In: Boreal environment research, ISSN 1239-6095, E-ISSN 1797-2469, Vol. 7, no 3, p. 183-192Article in journal (Refereed)
    Abstract [en]

    A regional coupled ocean-atmosphere-ice general circulation model for northern Europe is introduced for climate study purposes. The Baltic Sea is interactively coupled. The coupled model is validated in a 5-year hind-cast experiment with a focus on surface quantities and atmosphere-ocean heat fluxes. The coupled sea surface temperature matches observations well. The system is free of drift, does not need flux corrections and is suitable for multi-year climate runs. With flux forcing from the atmospheric model the regional ocean model gives sea surface temperatures statistically equivalent to the uncoupled ocean model forced by observations. Other oceanic surface quantities do not reach this quality in combination with the current atmosphere model. A strong dependence of sea ice extent on details of the atmospheric radiation scheme is found. Our standard scheme leads to an overestimation of ice, most likely due to a negative bias of long-wave radiation. There is indication that a latent heat flux bias in fall contributes to the ice problem. Other atmosphere-ocean heat fluxes are generally realistic in the long term mean.

  • 3.
    Jones, Colin
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Willen, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    The Rossby Centre Regional Atmospheric Climate Model part 1: Model climatology and performance for the present climate over Europe2004In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 33, no 4-5, p. 199-210Article in journal (Refereed)
    Abstract [en]

    The Rossby Centre Atmospheric Regional Climate Model (RCA2) is described and simulation results, for the present climate over Europe, are evaluated against available observations. Systematic biases in the models mean climate and climate variability are documented and key parameterization weaknesses identified. The quality of near-surface parameters is investigated in some detail, particularly temperature, precipitation, the surface energy budget and cloud cover. The model simulates the recent, observed climate and variability with a high degree of realism. Compensating errors in the components of the surface radiation budget are highlighted and the fundamental causes of these biases are traced to the relevant aspects of the cloud, precipitation and radiation parameterizations. The model has a tendency to precipitate too frequently at small rates, this has a direct impact on the simulation of cloud-radiation interaction and surface temperatures. Great care must be taken in the use of observations to evaluate high resolution RCMs, when they are forced by analyzed boundary conditions. This is particularly true with respect to precipitation and cloudiness, where observational uncertainty is often larger than the RCM bias.

  • 4.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Bärring, Lars
    SMHI, Research Department, Climate research - Rossby Centre.
    Gollvik, Stefan
    Meterologi.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Samuelsson, Patrick
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    A 140-year simulation of European climate with the new version of the Rossby Centre regional atmospheric climate model (RCA3)2005Report (Other academic)
    Abstract [en]

    This report presents the latest version of the Rossby Centre regional atmospheric model, RCA3, with focus on model improvements since the earlier version, RCA2. The main changes in RCA3 relate to the treatment of land surface processes. Apart from the changes in land surface parameterizations several changes in the calculation of radiation, clouds, condensate and precipitation have been made. The new parameterizations hold a more realistic description of the climate system.Simulated present day climate is evaluated compared to observations. The new model version show equally good, or better, correspondence to observational climatologies as RCA2, when forced by perfect boundary conditions. Seasonal mean temperature errors are generally within ±1oC except during winter in north-western Russia where a larger positive bias is identified. Both the diurnal temperature range and the annual temperature range are found to be underestimated in the model. Precipitation biases are generally smaller than in the corresponding reanalysis data used as boundary conditions, showing the benefit of a higher horizontal resolution.The model is used for the regionalization of two transient global climate change projections for the time period 1961- 2100. The radiative forcing of the climate system is based on observed concentrations of greenhouse gases until 1990 and on the IPCC SRES B2 and A2 emissions scenarios for the remaining time period. Long-term averages as well as measures of the variability around these averages are presented for a number of variables including precipitation and near-surface temperature. It is shown that the changes in variability sometimes differ from the changes in averages. For instance, in north-eastern Europe, the mean increase in wintertime temperatures is followed by an even stronger reduction in the number of very cold days in winter. This kind of performance of the climate system implies that methods of inferring data from climate change projections to other periods than those actually simulated have to be used with care, at least when it comes to variables that are expected to change in a non-linear way. Further, these new regional climate change projections address the whole 21st century.

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  • 5.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Bärring, Lars
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    An ensemble of regional climate change simulations2009In: / [ed] Rockel, B., Bärring, L and Reckermann, M., 2009, p. 134-135Conference paper (Other academic)
  • 6.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    21st century changes in the European climate: uncertainties derived from an ensemble of regional climate model simulations2011In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 63, no 1, p. 24-40Article in journal (Refereed)
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    fulltext
  • 7.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    21st century changes in the Nordic climate: 8ncertainties derived from an ensemble of regional climate model simulations2010Conference paper (Other academic)
  • 8.
    Kjellström, Erik
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Seasonal mean temperature, precipitation and wind speed in Europe from an ensemble of 16 transient RCM simulations for 1961-21002010In: Geophysical Research Abstracts, 2010, Vol. 12, article id EGU2010-10229Conference paper (Refereed)
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    fulltext
  • 9.
    Nikulin, Grigory
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Nordic weather extremes as simulated by the Rossby Centre Regional Climate Model: model evaluation and future projections2010Conference paper (Other academic)
  • 10.
    Nikulin, Grigory
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    European weather extremes as simulated by the Rossby Centre Regional Climate Model2010In: Geophysical Research Abstracts, 2010, Vol. 12, article id EGU2010-4204Conference paper (Refereed)
    Download full text (pdf)
    fulltext
  • 11.
    Nikulin, Grigory
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Evaluation and future projections of temperature, precipitation and wind extremes over Europe in an ensemble of regional climate simulations2011In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 63, no 1, p. 41-55Article in journal (Refereed)
    Download full text (pdf)
    fulltext
  • 12. Rana, Arun
    et al.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Kupiainen, Marco
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Kolax, Michael
    SMHI, Research Department, Climate research - Rossby Centre.
    Contrasting regional and global climate simulations over South Asia2020In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894Article in journal (Refereed)
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    fulltext
  • 13.
    Rummukainen, Markku
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Graham, Phil
    SMHI, Professional Services.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Räisänen, Jouni
    SMHI, Research Department, Climate research - Rossby Centre.
    Samuelsson, Patrick
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    PRUDENCE-related regional climate modeling at the SMHI/Rossby Centre2002In: PRUDENCE kick-off meeting / [ed] Jens Hesselbjerg Christensen, Danish Climate Centre DMI, Ministry of Transport , 2002, p. 40-41Conference paper (Other academic)
  • 14.
    Rummukainen, Markku
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Räisänen, Jouni
    SMHI, Research Department, Climate research - Rossby Centre.
    Bringfelt, Björn
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Omstedt, Anders
    SMHI, Research Department, Oceanography.
    Willen, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    A regional climate model for northern Europe: model description and results from the downscaling of two GCM control simulations2001In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 17, no 5-6, p. 339-359Article in journal (Refereed)
    Abstract [en]

    This work presents a regional climate model, the Rossby Centre regional Atmospheric model(RCA1), recently developed from the High Resolution Limited Area Model (HIRLAM). The changes in the HIRLAM parametrizations, necessary for climate-length integrations, are described. A regional Baltic Sea ocean model and a modeling system for the Nordic inland lake systems have been coupled with RCA1. The coupled system has been used to downscale 10-year time slices from two different general circulation model (GCM) simulations to provide high-resolution regional interpretation of large-scale modeling. A selection of the results from the control runs, i.e. the present-day climate simulations, are presented: large-scale free atmospheric fields, the surface temperature and precipitation results and results for the on-line simulated regional ocean and lake surface climates. The regional model modifies the surface climate description compared to the GCM simulations, but it is also substantially affected by the biases in the GCM simulations. The regional model also improves the representation of the regional ocean and the inland lakes, compared to the GCM results.

  • 15.
    Rummukainen, Markku
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Räisänen, Jouni
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Bringfelt, Björn
    SMHI.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Graham, Phil
    SMHI, Professional Services.
    RCA - Rossby Centre regional Atmospheric climate model: model description and results from the first multi-year simulation1997Report (Other academic)
    Abstract [en]

    The first version of the Rossby Centre regional climate model (RCA) has now been developed. The RCA model is based on a parallel coding of the operational weather forecast model HIRLAM. Some modifications have been done on the model formulation, especially in its surface/snow/soil scheme, in an attempt to include the regional and local scale climate-modifying forcing up to time scales of several years. The physical parameterization choices in HIRLAM and in RCA are discussed in some detail. One of the notable features in RCA is that the regional sea ice climate, as well as ice on the numerous lakes in the region, has been included in a crude, but time-efficient fashion. It appears that realistic modeling of the sea/lake ice is most important for modeling the regional climate in the Nordic region.

    The RCA model has been run fora ten-year period, focusing on the Nordic region, using results from a coupled ocean-atmosphere general circulation model. In this first multi-year simulation, the regional resolution was 44 km.  Several results are illustrated from this regional simulation and they are compared to the driving global model data, to analyzed observations and to Swedish station data for the 1961-90 period. The apparent model development needs are also discussed briefly.

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  • 16.
    Räisänen, Jouni
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Graham, Phil
    SMHI, Professional Services.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Samuelsson, Patrick
    SMHI, Research Department, Climate research - Rossby Centre.
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    GCM driven simulations of recent and future climate with the Rossby Centre coupled atmosphere - Baltic Sea regional climate model RCAO2003Report (Other academic)
    Abstract [en]

    A series of six general circulation model (GCM) driven regional climate simulations made at the Rossby Centre, SMHI, during the year 2002 are documented. For both the two driving GCMs HadAM3H andECHAM4/OPYC3, a 30-year (1961-1990) control run and two 30-year (2071-2100) scenario runs have been made. The scenario runs are based on the IPCC SRES A2 and B2 forcing scenarios. These simulations were made at 49 km atmospheric resolution and they are part of the European PRUDENCE project.Many aspects of the simulated control climates compare favourably with observations, but some problems are also evident. For example, the simulated cloudiness and precipitation appear generally too abundant in northern Europe (although biases in precipitation measurements complicate the interpretation), whereas too clear and dry conditions prevail in southern Europe. There is a lot of similarity between the HadAM3Hdriven (RCAO-H) and ECHAM4/OPYC3-driven (RCAO-E) control simulations, although the problems associated with the hydrological cycle and cloudiness are somewhat larger in the latter.The simulated climate changes (2071-2100 minus 1961-1990) depend on both the forcing scenario (the changes are generally larger for A2 than B2) and the driving global model (the largest changes tend to occur in RCAO-E). In all the scenario simulations, the warming in northern Europe is largest in winter or autumn. In central and southern Europe, the warming peaks in summer and reaches in the RCAO-E A2 simulation locally 10°C. The four simulations agree on a general increase in precipitation in northern Europe especiallyin winter and on a general decrease in precipitation in southern and central Europe in summer, but the magnitude and the geographical patterns of the change differ a lot between RCAO-H and RCAO-E. Thisreflects very different changes in the atmospheric circulation during the winter half-year, which also have a large impact on the simulated changes in windiness. A very large increase in the lowest minimumtemperatures occurs in a large part of Europe, most probably due to reduced snow cover. Extreme daily precipitation increases even in most of those areas where the mean annual precipitation decreases.

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    FULLTEXT01
  • 17.
    Räisänen, Jouni
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Rummukainen, Markku
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Bringfelt, Björn
    SMHI.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    The First Rossby Centre Regional Climate Scenario - Dynamical Downscaling of CO2-induced Climate Change in the HadCM2 GCM1999Report (Other academic)
    Abstract [en]

    Results of the first 10-year climate change experiment made with the Rossby Centre regional climate model (RCA) are described. The boundary data for this experiment were derived from two simulations with the .global HadCM2 ocean-atmosphere GCM, a control run anda scenario run with 150% higher equivalent CO2 and 2.6°C higher global mean surface air temperature.

    Some of the climate changes (scenario run - control run) simulated by RCA are substantial. The annual mean temperature in the Nordic region increases by roughly 4°C, with largest warming in winter. Annual absolute minimum temperatures increase even more than the winter mean temperature, presumably due to greatly reduced snow and ice cover. Precipitation is also simulated to increase in northern Europe, locally by 40% in the annual mean in Swedish Lappland. The larger time mean precipitation is accompanied by a marked increase in the number of days with heavy precipitation.

    The large-scale temperature and precipitation changes simulated by RCA are similar to those in HadCM2. Unlike HadCM2, however, RCA simulates a strong local maximum of wintertime warming over the northern parts of the Baltic Sea. This is caused by radically reduced ice cover, but the crude treatment of the Baltic Sea and its ice even in RCA complicates the interpretation. Large differences between the models occur in the simulated changes of winter mean total cloudiness and near-surface wind speed, demonstrating the sensitivity of these to differences in resolution and/or physical parameterizations.

    The significance of the simulated climate changes against interannual variability depends on the parameter considered. Of highest statistical significance are changes in surface air temperature and strongly temperature-related variables such as snow and ice cover. In general, changes in annual means are more commonly significant than those in seasonal means. The impact of the limited averaging period is also studied by comparing the 10-year mean climate changes simulated by the driving HadCM2 mode! with climate changes inferred from much longer HadCM2 integrations.

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  • 18.
    Samuelsson, Patrick
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Gollvik, Stefan
    SMHI, Research Department, Meteorology.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Jansson, Christer
    SMHI, Research Department, Climate research - Rossby Centre.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    The Rossby Centre Regional Climate model RCA3: model description and performance2011In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, no 1, p. 4-23Article in journal (Refereed)
  • 19.
    Samuelsson, Patrick
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Gollvik, Stefan
    SMHI, Research Department, Meteorology.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    The Rossby Centre Regional Climate Model RCA3: Model description and performance2011In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 63A, no 1, p. 4-23Article in journal (Refereed)
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  • 20. Soerensson, Anna A.
    et al.
    Menendez, Claudio G.
    Samuelsson, Patrick
    SMHI, Research Department, Climate research - Rossby Centre.
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Soil-precipitation feedbacks during the South American Monsoon as simulated by a regional climate model2010In: Climatic Change, ISSN 0165-0009, E-ISSN 1573-1480, Vol. 98, no 3-4, p. 429-447Article in journal (Refereed)
    Abstract [en]

    We summarize the recent progress in regional climate modeling in South America with the Rossby Centre regional atmospheric climate model (RCA3-E), with emphasis on soil moisture processes. A series of climatological integrations using a continental scale domain nested in reanalysis data were carried out for the initial and mature stages of the South American Monsoon System (SAMS) of 1993-92 and were analyzed on seasonal and monthly timescales. The role of including a spatially varying soil depth, which extends to 8 m in tropical forest, was evaluated against the standard constant soil depth of the model of about 2 m, through two five member ensemble simulations. The influence of the soil depth was relatively weak, with both beneficial and detrimental effects on the simulation of the seasonal mean rainfall. Secondly, two ensembles that differ in their initial state of soil moisture were prepared to study the influence of anomalously in subtropical South America as well. Finally, we calculated the soil moisture-precipitation coupling strength through comparing a ten member ensemble forced by the same space-time series of soil moisture fields with an ensemble with interactive soil moisture. Coupling strength is defined as the degree to which the prescribed boundary conditions affect some atmospheric quantity in a climate model, in this context a quantification of the fraction of atmospheric variability that can be ascribed to soil moisture anomalies. La Plata Basin appears as a region where the precipitation is partly controlled by soil moisture, especially in November and January. The continental convective monsoon regions and subtropical South America appears as a region with relatively high coupling strength during the mature phase of monsoon development dry and wet soil moisture initial conditions on the intraseasonal development of the SAMS. In these simulations the austral winter soil moisture initial condition has a strong influence on wet season rainfall over feed back upon the monsoon, not only over the Amazon region but in subtropical South America as well. Finally, we calculated the soil moisture-precipitation coupling strength through comparing a ten member ensemble forced by the same space-time series of soil moisture fields with an ensemble with interactive soil moisture. Coupling strength is defined as the degree to which the prescribed boundary conditions affect some atmospheric quantity in a climate model, in this context a quantification of the fraction of atmospheric variability that can be ascribed to soil moisture anomalies. La Plata Basin appears as a region where the precipitation is partly controlled by soil moisture, especially in November and January. The continental convective monsoon regions and subtropical South America appears as a region with relatively high coupling strength during the mature phase of monsoon development.

  • 21.
    Strandberg, Gustav
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Bärring, Lars
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Jansson, Christer
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Kupiainen, Marco
    SMHI, Research Department, Climate research - Rossby Centre.
    Nikulin, Grigory
    SMHI, Research Department, Climate research - Rossby Centre.
    Samuelsson, Patrick
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    CORDEX scenarios for Europe from the Rossby Centre regional climate model RCA42015Report (Other academic)
    Abstract [en]

    This report documents Coordinated Regional Downscaling Experiment (CORDEX) climate model simulations at 50 km horizontal resolution over Europe with the Rossby Centre regional atmospheric model (RCA4) for i) a ERA-Interim-driven (ERAINT) simulation used to evaluate model performance in the recent past climate, ii) historical simulations of the recent decades with forcing from nine different global climate models (GCMs) and iii) future scenarios RCP 4.5 and RCP 8.5 forced by the same nine different GCMs. Those simulations represent a subset of all CORDEX simulations produced at the Rossby Centre and a general conclusion drawn at the Rossby Centre is that such large ensembles could not have been produced without the establishment of an efficient production chain as outlined here. The first part of this report documents RCA4 and its performance in a perfect boundary simulation where ERAINT was downscaled. RCA4 is to a large extent replicating the large-scale circulation in ERAINT, but some local biases in mean sea level pressure appear. In general the seasonal cycles of temperature and precipitation are simulated in relatively close agreement to observations. Some biases occur, such as too much precipitation in northern Europe and too little in the south. In winter, there is also too much precipitation in eastern Europe. Temperatures are generally biased low in northern Europe and in the Mediterranean region in winter while overestimated temperatures are seen in southeastern Europe in winter and in the Mediterranean area in summer. RCA4 performs generally well when simulating the recent past climate taking boundary conditions from the GCMs. A large part of the RCA4 simulated climate is attributed to the driving GCMs, but RCA4 creates its own climate inside the model domain and adds details due to higher resolution. All nine downscaled GCMs share problems in their representation of the large-scale circulation in winter. This feature is inherited in RCA4. The biases in large-scale circulation induce some biases in temperature and precipitation in RCA4. The climate change signal in the RCP 4.5 and RCP 8.5 ensembles simulated by RCA4 is very similar to what has been presented previously. Both scenarios RCP 4.5 and RCP 8.5 project Europe to be warmer in the future. In winter the warming is largest in northern Europe and in summer in southern Europe. The summer maximum daily temperature increases in a way similar to summer temperature, but somewhat more in southern Europe. The winter minimum daily temperature in northern Europe is the temperature that changes the most. Precipitation is projected to increase in all seasons in northern Europe and decrease in southern Europe. The largest amount of rainfall per day (and per seven day period) is projected to increase in almost all of Europe and in all seasons. At the same time the longest period without precipitation is projected to be longer in southern Europe. Small changes in mean wind speed are generally projected. There are, however, regions with significant changes in wind. The ensemble approach is a way to describe the uncertainties in the scenarios, but there are other possible ensembles using other models which would give other results. Still, the ensemble used here is found to be similar enough to these other possible ensembles to be representative of the whole set of GCMs. Dynamical downscaling using RCA4 changes the climate change signal, and the ensemble spread is sometimes reduced, but the ensemble of nine RCA4 simulations, using different GCMs, is considered to be representative of the full ensemble. All scenarios agree on a climate change pattern; the amplitude of the change is determined by the choice of scenario. The relative importance of the chosen scenario increases with time.

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  • 22.
    Thomas, Manu Anna
    et al.
    SMHI, Research Department, Air quality.
    Kahnert, Michael
    SMHI, Research Department, Air quality.
    Andersson, Camilla
    SMHI, Research Department, Air quality.
    Kokkola, H.
    Hansson, Ulf
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Langner, Joakim
    SMHI, Research Department, Air quality.
    Devasthale, Abhay
    SMHI, Research Department, Atmospheric remote sensing.
    Integration of prognostic aerosol-cloud interactions in a chemistry transport model coupled offline to a regional climate model2015In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 8, no 6, p. 1885-1898Article in journal (Refereed)
    Abstract [en]

    To reduce uncertainties and hence to obtain a better estimate of aerosol (direct and indirect) radiative forcing, next generation climate models aim for a tighter coupling between chemistry transport models and regional climate models and a better representation of aerosol-cloud interactions. In this study, this coupling is done by first forcing the Rossby Center regional climate model (RCA4) with ERA-Interim lateral boundaries and sea surface temperature (SST) using the standard cloud droplet number concentration (CDNC) formulation (hereafter, referred to as the 'stand-alone RCA4 version' or 'CTRL' simulation). In the stand-alone RCA4 version, CDNCs are constants distinguishing only between land and ocean surface. The meteorology from this simulation is then used to drive the chemistry transport model, Multiple-scale Atmospheric Transport and Chemistry (MATCH), which is coupled online with the aerosol dynamics model, Sectional Aerosol module for Large Scale Applications (SALSA). CDNC fields obtained from MATCH-SALSA are then fed back into a new RCA4 simulation. In this new simulation (referred to as 'MOD' simulation), all parameters remain the same as in the first run except for the CDNCs provided by MATCH-SALSA. Simulations are carried out with this model setup for the period 2005-2012 over Europe, and the differences in cloud microphysical properties and radiative fluxes as a result of local CDNC changes and possible model responses are analysed. Our study shows substantial improvements in cloud microphysical properties with the input of the MATCH-SALSA derived 3-D CDNCs compared to the stand-alone RCA4 version. This model setup improves the spatial, seasonal and vertical distribution of CDNCs with a higher concentration observed over central Europe during boreal summer (JJA) and over eastern Europe and Russia during winter (DJF). Realistic cloud droplet radii (CD radii) values have been simulated with the maxima reaching 13 mu m, whereas in the stand-alone version the values reached only 5 mu m. A substantial improvement in the distribution of the cloud liquid-water paths (CLWP) was observed when compared to the satellite retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) for the boreal summer months. The median and standard deviation values from the 'MOD' simulation are closer to observations than those obtained using the stand-alone RCA4 version. These changes resulted in a significant decrease in the total annual mean net fluxes at the top of the atmosphere (TOA) by -5 W m(-2) over the domain selected in the study. The TOA net fluxes from the 'MOD' simulation show a better agreement with the retrievals from the Clouds and the Earth's Radiant Energy System (CERES) instrument. The aerosol indirect effects are estimated in the 'MOD' simulation in comparison to the pre-industrial aerosol emissions (1900). Our simulations estimated the domain averaged annual mean total radiative forcing of -0.64 W m(-2) with a larger contribution from the first indirect aerosol effect (-0.57 W m(-2)) than from the second indirect aerosol effect (-0.14 W m(-2)).

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