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  • 1. Bennartz, Ralf
    et al.
    Hoschen, Heidrun
    Picard, Bruno
    Schroder, Marc
    Stengel, Martin
    Sus, Oliver
    Bojkov, Bojan
    Casadio, Stefano
    Diedrich, Hannes
    Eliasson, Salomon
    SMHI, Research Department, Atmospheric remote sensing.
    Fell, Frank
    Fischer, Jurgen
    Hollmann, Rainer
    Preusker, Rene
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    An intercalibrated dataset of total column water vapour and wet tropospheric correction based on MWR on board ERS-1, ERS-2, and Envisat2017In: Atmospheric Measurement Techniques, ISSN 1867-1381, E-ISSN 1867-8548, Vol. 10, no 4, 1387-1402 p.Article in journal (Refereed)
  • 2.
    Devasthale, Abhay
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Karlsson, Karl-Göran
    SMHI, Research Department, Atmospheric remote sensing.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Quantifying the clear-sky temperature inversion frequency and strength over the Arctic Ocean during summer and winter seasons from AIRS profiles2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 12, 5565-5572 p.Article in journal (Refereed)
    Abstract [en]

    Temperature inversions are one of the dominant features of the Arctic atmosphere and play a crucial role in various processes by controlling the transfer of mass and moisture fluxes through the lower troposphere. It is therefore essential that they are accurately quantified, monitored and simulated as realistically as possible over the Arctic regions. In the present study, the characteristics of inversions in terms of frequency and strength are quantified for the entire Arctic Ocean for summer and winter seasons of 2003 to 2008 using the AIRS data for the clear-sky conditions. The probability density functions (PDFs) of the inversion strength are also presented for every summer and winter month. Our analysis shows that although the inversion frequency along the coastal regions of Arctic decreases from June to August, inversions are still seen in almost each profile retrieved over the inner Arctic region. In winter, inversions are ubiquitous and are also present in every profile analysed over the inner Arctic region. When averaged over the entire study area (70 degrees N-90 degrees N), the inversion frequency in summer ranges from 69 to 86% for the ascending passes and 72-86% for the descending passes. For winter, the frequency values are 88-91% for the ascending passes and 89-92% for the descending passes of AIRS/AQUA. The PDFs of inversion strength for the summer months are narrow and right-skewed (or positively skewed), while in winter, they are much broader. In summer months, the mean values of inversion strength for the entire study area range from 2.5 to 3.9 K, while in winter, they range from 7.8 to 8.9 K. The standard deviation of the inversion strength is double in winter compared to summer. The inversions in the summer months of 2007 were very strong compared to other years. The warming in the troposphere of about 1.5-3.0K vertically extending up to 400 hPa was observed in the summer months of 2007.

  • 3.
    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, 183-192 p.Article 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.

  • 4. Hazeleger, Wilco
    et al.
    Severijns, Camiel
    Semmler, Tido
    Stefanescu, Simona
    Yang, Shuting
    Wang, Xueli
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    Dutra, Emanuel
    Baldasano, Jose M.
    Bintanja, Richard
    Bougeault, Philippe
    Caballero, Rodrigo
    Ekman, Annica M. L.
    Christensen, Jens H.
    van den Hurk, Bart
    Jimenez, Pedro
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Kållberg, Per
    SMHI, Research Department, Meteorology.
    Koenigk, Torben
    SMHI, Research Department, Climate research - Rossby Centre.
    McGrath, Ray
    Miranda, Pedro
    Van Noije, Twan
    Palmer, Tim
    Parodi, Jose A.
    Schmith, Torben
    Selten, Frank
    Storelvmo, Trude
    Sterl, Andreas
    Tapamo, Honore
    Vancoppenolle, Martin
    Viterbo, Pedro
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    EC-Earth A Seamless Earth-System Prediction Approach in Action2010In: Bulletin of The American Meteorological Society - (BAMS), ISSN 0003-0007, E-ISSN 1520-0477, Vol. 91, no 10, 1357-1363 p.Article in journal (Other academic)
  • 5.
    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, 199-210 p.Article 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.

  • 6.
    Jones, Colin
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Willen, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    The Rossby Centre regional atmospheric climate model part II: Application to the Arctic climate2004In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 33, no 4-5, 211-220 p.Article in journal (Refereed)
    Abstract [en]

    The Rossby Centre regional climate model (RCA2) has been integrated over the Arctic Ocean as part of the international ARCMIP project. Results have been compared to observations derived from the SHEBA data set. The standard RCA2 model overpredicts cloud cover and downwelling longwave radiation, during the Arctic winter. This error was improved by introducing a new cloud parameterization, which significantly improves the annual cycle of cloud cover. Compensating biases between clear sky downwelling longwave radiation and longwave radiation emitted from cloud base were identified. Modifications have been introduced to the model radiation scheme that more accurately treat solar radiation interaction with ice crystals. This leads to a more realistic representation of cloud-solar radiation interaction. The clear sky portion of the model radiation code transmits too much solar radiation through the atmosphere, producing a positive bias at the top of the frequent boundary layer clouds. A realistic treatment of the temporally evolving albedo, of both sea-ice and snow, appears crucial for an accurate simulation of the net surface energy budget. Likewise, inclusion of a prognostic snow-surface temperature seems necessary, to accurately simulate near-surface thermodynamic processes in the Arctic.

  • 7.
    Karlsson, Karl-Göran
    et al.
    SMHI, Research Department, Atmospheric remote sensing.
    Willen, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    Evaluation of regional cloud climate simulations over Scandinavia using a 10-year NOAA advanced very high resolution radiometer cloud climatology2008In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 113, no D1, D01203Article in journal (Refereed)
    Abstract [en]

    A satellite-derived (NOAA Advanced Very High Resolution Radiometer) cloud climatology over the Scandinavian region covering the period 1991 - 2001 has been used to evaluate the performance of cloud simulations of the Swedish Meteorological and Hydrological Institute Rossby Centre regional climate model (RCA3). Several methods of adapting the satellite and model data sets to allow a meaningful comparison were applied. RCA3-simulated total cloud cover was shown to agree within a few percent of the satellite-retrieved cloud amounts on seasonal and annual timescales. However, a substantial imbalance between the respective RCA3 contributions from low-, medium- and high-level clouds was seen. The differences from satellite-derived contributions were +2.4% for high-level clouds, -5.2% for medium-level clouds and +4.0% for low- level clouds. In addition, an overrepresentation of cloud categories with high optical thicknesses was seen for all vertical cloud groups, particularly during the summer season. Some specific features of the geographical distribution of cloudiness were also noticed. Most pronounced were the excess of cloud amounts over the Scandinavian mountain range and a deficit leeward of the mountains. The overall results imply problems with the RCA3-modeled surface radiation budget components by causing reduced incoming solar radiation and increased downwelling longwave radiation.

  • 8.
    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.

  • 9.
    Koenigk, Torben
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Brodeau, Laurent
    Graversen, Rune Grand
    Karlsson, Johannes
    Svensson, Gunilla
    Tjernstrom, Michael
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    Arctic climate change in 21st century CMIP5 simulations with EC-Earth2013In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 40, no 11-12, 2719-2743 p.Article in journal (Refereed)
    Abstract [en]

    The Arctic climate change is analyzed in an ensemble of future projection simulations performed with the global coupled climate model EC-Earth2.3. EC-Earth simulates the twentieth century Arctic climate relatively well but the Arctic is about 2 K too cold and the sea ice thickness and extent are overestimated. In the twenty-first century, the results show a continuation and strengthening of the Arctic trends observed over the recent decades, which leads to a dramatically changed Arctic climate, especially in the high emission scenario RCP8.5. The annually averaged Arctic mean near-surface temperature increases by 12 K in RCP8.5, with largest warming in the Barents Sea region. The warming is most pronounced in winter and autumn and in the lower atmosphere. The Arctic winter temperature inversion is reduced in all scenarios and disappears in RCP8.5. The Arctic becomes ice free in September in all RCP8.5 simulations after a rapid reduction event without recovery around year 2060. Taking into account the overestimation of ice in the twentieth century, our model results indicate a likely ice-free Arctic in September around 2040. Sea ice reductions are most pronounced in the Barents Sea in all RCPs, which lead to the most dramatic changes in this region. Here, surface heat fluxes are strongly enhanced and the cloudiness is substantially decreased. The meridional heat flux into the Arctic is reduced in the atmosphere but increases in the ocean. This oceanic increase is dominated by an enhanced heat flux into the Barents Sea, which strongly contributes to the large sea ice reduction and surface-air warming in this region. Increased precipitation and river runoff lead to more freshwater input into the Arctic Ocean. However, most of the additional freshwater is stored in the Arctic Ocean while the total Arctic freshwater export only slightly increases.

  • 10. Lauer, Axel
    et al.
    Eyring, Veronika
    Righi, Mattia
    Buchwitz, Michael
    Defourny, Pierre
    Evaldsson, Martin
    SMHI, Research Department, Climate research - Rossby Centre.
    Friedlingstein, Pierre
    de Jeu, Richard
    de Leeuw, Gerrit
    Loew, Alexander
    Merchant, Christopher J.
    Mueller, Benjamin
    Popp, Thomas
    Reuter, Maximilian
    Sandven, Stein
    Senftleben, Daniel
    Stengel, Martin
    Van Roozendael, Michel
    Wenzel, Sabrina
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Benchmarking CMIP5 models with a subset of ESA CCI Phase 2 data using the ESMValTool2017In: Remote Sensing of Environment, ISSN 0034-4257, E-ISSN 1879-0704, Vol. 203, 9-39 p.Article in journal (Refereed)
  • 11. Ning, T.
    et al.
    Elgered, G.
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Johansson, J. M.
    Evaluation of the atmospheric water vapor content in a regional climate model using ground-based GPS measurements2013In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 118, no 2, 329-339 p.Article in journal (Refereed)
    Abstract [en]

    Ground-based GPS measurements can provide independent data for the assessment of climate models. We use the atmospheric integrated water vapor (IWV) obtained from GPS measurements at 99 European sites to evaluate the regional Rossby Centre Atmospheric climate model (RCA) driven at the boundaries by the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data (ERA Interim). The GPS data were compared to the RCA simulation and the ERA Interim data. The comparison was first made using the monthly mean values. Averaged over the domain and the 14 years covered by the GPS data, IWV differences of about 0.47 kg/m(2) and 0.39 kg/m(2) are obtained for RCA-GPS and ECMWF-GPS, respectively. The RCA-GPS standard deviation is 0.98 kg/m(2) whereas it is 0.35 kg/m(2) for the ECMWF-GPS comparison. The IWV differences for RCA are positively correlated to the differences for ECMWF. However, this is not the case for two sites in Italy where a wet bias is seen for ECMWF, while a dry bias is seen for RCA, the latter being consistent with a cold temperature bias found for RCA in that region by other authors. Comparisons of the estimated diurnal cycle and the spatial structure function of the IWV were made between the GPS data and the RCA simulation. The RCA captures the geographical variation of the diurnal peak in the summer. Averaged over all sites, a peak at 17 local solar time is obtained from the GPS data while it appears later, at 18, in the RCA simulation. The spatial variation of the IWV obtained for an RCA run with a resolution of 11 km gives a better agreement with the GPS results than does the spatial variation from a 50 km resolution run. Citation: Ning, T., G. Elgered, U. Willen, and J. M. Johansson (2013), Evaluation of the atmospheric water vapor content in a regional climate model using ground-based GPS measurements, J. Geophys. Res. Atmos., 118, 329-339, doi: 10.1029/2012JD018053.

  • 12. Ning, T.
    et al.
    Haas, R.
    Elgered, G.
    Willen, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Multi-technique comparisons of 10 years of wet delay estimates on the west coast of Sweden2012In: Journal of Geodesy, ISSN 0949-7714, E-ISSN 1432-1394, Vol. 86, no 7, 565-575 p.Article, review/survey (Refereed)
    Abstract [en]

    We present comparisons of 10-year-long time series of the atmospheric zenith wet delay (ZWD), estimated using the global positioning system (GPS), geodetic very long baseline interferometry (VLBI), a water vapour radiometer (WVR), radiosonde (RS) observations, and the reanalysis product of the European Centre for Medium-Range Weather Forecasts (ECMWF). To compare the data sets with each other, a Gaussian filter is applied. The results from 10 GPS-RS comparisons using sites in Sweden and Finland show that the full width at half maximum at which the standard deviation (SD) is a minimum increases with the distance between each pair. Comparisons between three co-located techniques (GPS, VLBI, and WVR) result in mean values of the ZWD differences at a level of a few millimetres and SD of less than 7 mm. The best agreement is seen in the GPS-VLBI comparison with a mean difference of -3.4 mm and an SD of 5.1 mm over the 10-year period. With respect to the ZWD derived from other techniques, a positive bias of up to similar to 7 mm is obtained for the ECMWF reanalysis product. Performing the comparisons on a monthly basis, we find that the SD including RS or ECMWF varies with the season, between 3 and 15 mm. The monthly SD between GPS and WVR does not have a seasonal signature and varies from 3 to 7 mm.

  • 13.
    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, Climate research - Rossby Centre.
    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, 339-359 p.Article 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.

  • 14.
    Räisänen, Jouni
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Hansson, U
    Ullerstig, Anders
    SMHI, Research Department, Climate research - Rossby Centre.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Graham, Phil
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Meier, Markus
    SMHI, Research Department, Oceanography.
    Samuelsson, Patrick
    SMHI, Research Department, Climate research - Rossby Centre.
    Willen, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    European climate in the late twenty-first century: regional simulations with two driving global models and two forcing scenarios2004In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 22, no 1, 13-31 p.Article in journal (Refereed)
    Abstract [en]

    A basic analysis is presented for a series of regional climate change simulations that were conducted by the Swedish Rossby Centre and contribute to the PRUDENCE (Prediction of Regional scenarios and Uncertainties for Defining EuropeaN Climate change risks and Effects) project. For each of the two driving global models HadAM3H and ECHAM4/OPYC3, a 30-year control run and two 30-year scenario runs (based on the SRES A2 and B2 emission scenarios) were made with the regional model. In this way, four realizations of climate change from 1961-1990 to 2071-2100 were obtained. The simulated changes are larger for the A2 than the B2 scenario (although with few qualitative differences) and in most cases in the ECHAM4/OPYC3-driven (RE) than in the HadAM3H-driven (RH) regional simulations. In all the scenario runs, the warming in northern Europe is largest in winter or late autumn. In central and southern Europe, the warming peaks in summer when it locally reaches 10 degreesC in the RE-A2 simulation and 6-7 degreesC in the RH-A2 and RE-B2 simulations. The four simulations agree on a general increase in precipitation in northern Europe especially in 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 markedly between RH and RE. This reflects very different changes in the atmospheric circulation during the winter half-year, which also lead to quite different simulated changes in windiness. All four simulations show a large increase in the lowest minimum temperatures in northern, central and eastern Europe, most likely due to reduced snow cover. Extreme daily precipitation increases even in most of those areas where the mean annual precipitation decreases.

  • 15.
    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.

  • 16.
    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)
  • 17. Schroeder, Marc
    et al.
    van Lipzig, Nicole P. M.
    Ament, Felix
    Chaboureau, Jean-Pierre
    Crewell, Susanne
    Fischer, Juergen
    Matthias, Volker
    van Meijgaard, Erik
    Walther, Andi
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Model predicted low-level cloud parameters Part II: Comparison with satellite remote sensing observations during the BALTEX Bridge Campaigns2006In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 82, no 1-2, 83-101 p.Article in journal (Refereed)
    Abstract [en]

    A pressing task in numerical weather prediction and climate modelling is the evaluation of modelled cloud fields. Recent progress in spatial and temporal resolution of satellite remote sensing increases the potential of such evaluation efforts. This paper presents new methodologies to compare satellite remote sensing observations of clouds and output of atmospheric models and demonstrates their usefulness for evaluation. The comparison is carried out for two MODerate resolution Imaging Spectrometer (MODIS) scenes from the BALTEX Bridge Campaigns. Both scenes are characterised by low-level clouds with a substantial amount of liquid water. Cloud cover and cloud optical thickness of five different models, LM, Wso-NH, MM5 (non-hydrostatic models), RACMO2, and RCA (regional climate models) as well as corresponding retrievals from high resolution remote sensing observations of MODIS onboard the Terra satellite form the basis of a statistical analysis to compare the data sets. With the newly introduced patchiness parameters it is possible to separate differences between the two scenes on the one hand and between the models and the satellite on the other hand. We further introduce a new approach to spatially aggregate cloud optical thickness. Generally the models overestimate cloud optical thickness which can in part be ascribed to the lack of subgrid-scale variability. However, UM underestimates the frequency of occurrence of cloud optical thickness at values around 25. Furthermore, we compare the standard operational output of the non-hydrostatic models to simulations of the same models including parameterised shallow convection. However, clear improvements in the representation of low-level clouds are not found for these models. A change of the coefficients for autoconversion in RCA shows that LWP and precipitation strongly depend on this parameter. Refined vertical resolution, implemented in RACMO2, leads to a better agreement between model and satellite but still leaves room for further improvements. In general, this study reveals deficiencies of the models in representing low-level clouds, in particular for a stratiform cloud. (c) 2006 Elsevier B.V. All rights reserved.

  • 18. Soerensson, Anna A.
    et al.
    Menendez, Claudio G.
    Ruscica, Romina
    Alexander, Peter
    Samuelsson, Patrick
    SMHI, Research Department, Climate research - Rossby Centre.
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Projected precipitation changes in South America: a dynamical downscaling within CLARIS2010In: Meteorologische Zeitschrift, ISSN 0941-2948, E-ISSN 1610-1227, Vol. 19, no 4, 347-355 p.Article in journal (Refereed)
    Abstract [en]

    Responses of precipitation seasonal means and extremes over South America in a downscaling of a Climate change scenario are assessed with the Rossby Centre Regional Atmospheric Model (RCA). The anthropogenic warming under A1B scenario influences more on the likelihood of occurrence of severe extreme events like heavy precipitation and dry spells than on the mean seasonal precipitation. The risk of extreme precipitation increases in the La Plata Basin with a factor of 1.5-2.5 during all seasons and in the northwestern part of the continent with a factor 1.5-3 in summer, while it decreases in central and northeastern Brazil during winter and spring. The maximum amount of 5-days precipitation increases by up to 50% in La Plata Basin, indicating risks of flooding. Over central Brazil and the Bolivian lowland, where present 5-days precipitation is higher, the increases are similar in magnitude and could cause less impacts. In southern Amazonia, northeastern Brazil and the Amazon basin, the maximum number of consecutive dry days increases and mean winter and spring precipitation decreases, indicating a longer dry season. In the La Plata Basin, there is no clear pattern of change for the dry spell duration.

  • 19. 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, 429-447 p.Article 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.

  • 20. Stengel, Martin
    et al.
    Stapelberg, Stefan
    Sus, Oliver
    Schlundt, Cornelia
    Poulsen, Caroline
    Thomas, Gareth
    Christensen, Matthew
    Henken, Cintia Carbajal
    Preusker, Rene
    Fischer, Juergen
    Devasthale, Abhay
    SMHI, Research Department, Atmospheric remote sensing.
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Karlsson, Karl-Göran
    SMHI, Research Department, Atmospheric remote sensing.
    McGarragh, Gregory R.
    Proud, Simon
    Povey, Adam C.
    Grainger, Roy G.
    Meirink, Jan Fokke
    Feofilov, Artem
    Bennartz, Ralf
    Bojanowski, Jedrzej S.
    Hollmann, Rainer
    Cloud property datasets retrieved from AVHRR, MODIS, AATSR and MERIS in the framework of the Cloud_cci project2017In: Earth System Science Data, ISSN 1866-3508, E-ISSN 1866-3516, Vol. 9, no 2, 881-904 p.Article in journal (Refereed)
  • 21. van Lipzig, Nicole P. M.
    et al.
    Schroeder, Marc
    Crewell, Susanne
    Ament, Felix
    Chaboureau, Jean-Pierre
    Loehnert, Ulrich
    Matthias, Volker
    van Meijgaard, Erik
    Quante, Markus
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Yen, Wenchieh
    Model predicted low-level cloud parameters - Part I: Comparison with observations from the BALTEX Bridge Campaigns2006In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 82, no 1-2, 55-82 p.Article in journal (Refereed)
    Abstract [en]

    The BALTEX Bridge Campaigns (BBC), which were held in the Netherlands in 2001 and 2003 around the Cabauw Experimental Site for Atmospheric Research (CESAR), have provided detailed information on clouds. This paper is an illustration of how these measurements can be used to investigate whether 'state-of-the-art' atmospheric models are capable of adequately representing clouds. Here, we focus on shallow low-level clouds with a substantial amount of liquid water. In situ, ground-based and satellite remote sensing measurements were compared with the output of three non-hydrostatic regional models (Lokal-Modell, LM.- M&so-NH: fifth-generation Mesoscale Model, MM5) and two hydrostatic regional climate models (Regional Atmospheric Climate Model version 2, RACMO2; Rossby Centre Atmospheric Model, RCA). For the two selected days, Meso-NH and MM5 reproduce the measured vertical extent of the shallow clouds, but the liquid water content of the clouds is generally overestimated. In LM and the climate models the inversion is too weak and located at a level too close to the surface resulting in an overestimation of the vertical extent of the clouds. A sensitivity integration with RACM02 shows that the correspondence between model output and measurements can be improved by a doubling of the vertical resolution; this induces an increase in the modelled inversion strenath and cloud top pressure. LM and Meso-NH underestimate the lifetime of clouds. A comparison between model output and cloud cover derived from the Moderate Resolution Imaging Spectrometer (MODIS) indicates that this deficiency is not due to advection of too small cloud systems,- it is rather due to an overestimation of the variability in the vertical velocity. All models overestimate the specific humidity near the surface and underestimate it at higher atmospheric levels, indicating that the models underestimate the mixing of moisture in the boundary layer. This deficiency is slightly reduced by inclusion of parameterised shallow convection in the non-hydrostatic models, which enhances the mixing of heat and moisture in the boundary layer. Consequently, the explicitly resolved updrafts weaken resulting in reduced condensation rates and lower liquid water path. The temporal variability of cloud occurrence is hardly affected by inclusion of parameterised shallow convection. (c) 2006 Elsevier B.V. All rights reserved.

  • 22.
    Willén, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Preliminary use of CM-SAF cloud and radiation products for evaluation of regional climate simulations: Visiting Scientist Report Climate Monitoring SAF (CM-SAF)2008Report (Other academic)
    Abstract [en]

    We have compared monthly mean cloud and radiation fields from the EUMETSAT Climate Monitoring SAF (CM-SAF, http://www.cmsaf.eu) data base with the clouds and radiation simulated by the Rossby Centre regional climate model (RCA) and by the European Centre Medium range Weather Forecast model (ECMWF) over Europe and North Africa for the time period January 2005 to December 2006.ECMWF and RCA overestimate the cloud fraction by 20% over snow covered regions in the north east of Europe and overestimate the surface downwelling longwave radiation (SDL) by 20-40W/m2 and surface outgoing longwave radiation by 10-30W/m2. The RCA-simulated clouds have too much cloud water in northern Europe in summer and in autumn and they therefore reflect too much shortwave radiation at the TOA (TRS) and this also leads to an underestimation of the incoming shortwave radiation (SIS) at the surface. Over most of Europe and over sea ECMWF (all year) and RCA (in winter-spring) underestimate the cloud fraction which could explain a corresponding underestimate of TRS, overestimate of SIS and underestimate of SDL. The satellites overestimate cloud cover over sea due to problems in the treatment of sub-pixel cloudiness and therefore the models underestimates are larger over sea. Mainly RCA but also ECMWF overestimate cloud fraction on top of mountains and underestimate it along mountain ranges and have corresponding differences in the TOA and surface radiation fluxes compared to the CM-SAF data.Over North Africa RCA underestimates TRS by -11W/m2 and overestimates the TOA emitted thermal radiation (TET) by 8W/m2. ECMWF underestimates TRS by -28W/m2 and overestimates TET by 14W/m2. These errors are similar to what has been found for many other global models and are attributed to clear sky errors either due to too high surface temperatures, errors in emissivity, albedo or lack of aerosols. Adding clear and cloudy skies radiation fluxes to the CM-SAF data base would help us to understand the reasons for ECMWF and RCA errors. The polar orbiting satellite retrieval for 2005-2006 erroneously overestimated cloud fraction over North Africa, which also affects the CM-SAF derived surface radiation fluxes.

  • 23.
    Willén, Ulrika
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Crewell, S
    Baltink, H K
    Sievers, O
    Assessing model predicted vertical cloud structure and cloud overlap with radar and lidar ceilometer observations for the Baltex Bridge Campaign of CLIWA-NET2005In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 75, no 3, 227-255 p.Article in journal (Refereed)
    Abstract [en]

    The cloud vertical distribution and overlap of four large-scale models operating at different horizontal and vertical resolutions have been assessed using radar and lidar observations from the Baltex Bridge Campaign of CLIWA-NET. The models range from the global European Centre for Medium range Weather Forecast (ECMWF) model, to the Regional Atmospheric Climate Model (RACMO) and the Rossby Centre Atmospheric (RCA) regional climate model, to the non-hydrostatic meso-scale Lokal Model (LM). Different time averaging periods for the radar data were used to estimate the uncertainty of the point-to-space transformations of the observations. Relative to the observations, all models underestimated the height of the lowest cloud base. Clouds occurred more frequently in the models but with smaller cloud fractions below 7 km. The findings confirm previous cloud radar studies which found that models overestimate cloud fractions above 7 km. Radar-observed clouds were often thinner than the model vertical resolutions, which can have serious implications on model cloud overlap and radiation fluxes. The radar-derived cloud overlap matrix, which takes into account the overlap of all vertical layers, was found to be close to maximum-random overlap. Using random overlap for vertically continuous clouds with vertical gradients in cloud fraction larger than 40-50% per kilometre gave the best fit to the data. The gradient approach could be improved by making it resolution- and cloud system-dependent. Previous cloud radar overlap studies have considered the overlap of two cloud layers as a function of maximum and random overlap. Here, it was found that the two-layer overlap could be modelled by a mixture of maximum and minimum overlap. (c) 2005 Elsevier B.V. All rights reserved.

  • 24.
    Wyser, Klaus
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Du, P.
    Girard, E.
    Willen, Ulrika
    SMHI, Research Department, Climate research - Rossby Centre.
    Cassano, J.
    Christensen, J. H.
    Curry, J. A.
    Dethloff, K.
    Haugen, J. -E
    Jacob, D.
    Koltzow, M.
    Laprise, R.
    Lynch, A.
    Pfeifer, S.
    Rinke, A.
    Serreze, M.
    Shaw, M. J.
    Tjernstrom, M.
    Zagar, M.
    An evaluation of Arctic cloud and radiation processes during the SHEBA year: simulation results from eight Arctic regional climate models2008In: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 30, no 2-3, 203-223 p.Article in journal (Refereed)
    Abstract [en]

    Eight atmospheric regional climate models (RCMs) were run for the period September 1997 to October 1998 over the western Arctic Ocean. This period was coincident with the observational campaign of the Surface Heat Budget of the Arctic Ocean (SHEBA) project. The RCMs shared common domains, centred on the SHEBA observation camp, along with a common model horizontal resolution, but differed in their vertical structure and physical parameterizations. All RCMs used the same lateral and surface boundary conditions. Surface downwelling solar and terrestrial radiation, surface albedo, vertically integrated water vapour, liquid water path and cloud cover from each model are evaluated against the SHEBA observation data. Downwelling surface radiation, vertically integrated water vapour and liquid water path are reasonably well simulated at monthly and daily timescales in the model ensemble mean, but with considerable differences among individual models. Simulated surface albedos are relatively accurate in the winter season, but become increasingly inaccurate and variable in the melt season, thereby compromising the net surface radiation budget. Simulated cloud cover is more or less uncorrelated with observed values at the daily timescale. Even for monthly averages, many models do not reproduce the annual cycle correctly. The inter-model spread of simulated cloud-cover is very large, with no model appearing systematically superior. Analysis of the co-variability of terms controlling the surface radiation budget reveal some of the key processes requiring improved treatment in Arctic RCMs. Improvements in the parameterization of cloud amounts and surface albedo are most urgently needed to improve the overall performance of RCMs in the Arctic.

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