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  • 1. Christensen, J H
    et al.
    Räisänen, Jouni
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Iversen, T
    Bjorge, D
    Christensen, O B
    Rummukainen, Markku
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    A synthesis of regional climate change simulations - A Scandinavian perspective2001Inngår i: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 28, nr 6, s. 1003-1006Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Four downscaling experiments of regional climate change for the Nordic countries have been conducted with three different regional climate models (RCMs). A short synthesis of the outcome of the suite of experiments is presented as an ensemble, reflecting the different driving atmosphere-ocean general circulation model (AOGCM) conditions, RCM model resolution and domain size, and choice of emission scenarios. This allows the sources of uncertainties in the projections to be assessed. At the same time analysis of the climate change signal for temperature and precipitation over the period 1990-2050 reveals strong similarities. In particular, all experiments in the suite simulate changes in the precipitation distribution towards a higher frequency of heavy precipitation.

  • 2. Hellstrom, C
    et al.
    Chen, D L
    Achberger, C
    Räisänen, Jouni
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Comparison of climate change scenarios for Sweden based on statistical and dynamical downscaling of monthly precipitation2001Inngår i: Climate Research (CR), ISSN 0936-577X, E-ISSN 1616-1572, Vol. 19, nr 1, s. 45-55Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two dynamically and statistically downscaled precipitation scenarios for Sweden are compared with respect to changes in the mean, The dynamically downscaled scenarios are generated by a 44 km version of the Rossby Centre regional climate model (RCM). The RCM is driven by data from 2 global greenhouse gas simulations sharing a 2.6degreesC global warming, one made by the HadCM2 and the other by the ECHAM4 general circulation model (GCM). The statistical downscaling model driven by the same GCMs is regression-based and incorporates large-scale circulation indices of the 2 geostrophic wind components (u and v), total vorticity (xi) and large-scale humidity at 850 hPa (q850) as predictors. The precipitation climates of the GCMs, RCMs and statistical models from the control runs are compared with respect to their ability to reproduce the observed seasonal cycle. Great improvements in the simulation of the seasonal cycle by all the downscaling models compared to the GCMs significantly increase the credibility of the downscaling models, The precipitation changes produced by the statistical models result from changes in all predictors, but the change in 4 is the greatest contributor in southern Sweden followed by q850 and u, while changes in q850 have greater effects in the northern parts of the country. The temporal and spatial variability of precipitation changes are higher in the statistically downscaled scenarios than in the dynamically downscaled ones. Comparisons of the 4 scenarios show that the spread of the scenarios created by the statistical model is on average larger than that between the RCM scenarios. The relatively large average spread is mainly due to the large differences found in summer. The seasonally averaged difference of the dynamical and statistical scenarios for the ECHAM4-based downscaled scenarios is 12%, and for the HadCM2 downscaled scenarios 21%. The differences in annual precipitation change are smaller, on average 4.5% among the HadCM2-based downscaled scenarios, and 6.9% among the ECHAM4-based downscaling scenarios.

  • 3. Palmer, T N
    et al.
    Räisänen, Jouni
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Quantifying the risk of extreme seasonal precipitation events in a changing climate2002Inngår i: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 415, nr 6871, s. 512-514Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Increasing concentrations of atmospheric carbon dioxide will almost certainly lead to changes in global mean climate(1). But because-by definition-extreme events are rare, it is significantly more difficult to quantify the risk of extremes. Ensemble-based probabilistic predictions(2), as used in short- and medium-term forecasts of weather and climate, are more useful than deterministic forecasts using a 'best guess' scenario to address this sort of problem(3,4). Here we present a probabilistic analysis of 19 global climate model simulations with a generic binary decision model. We estimate that the probability of total boreal winter precipitation exceeding two standard deviations above normal will increase by a factor of five over parts of the UK over the next 100 years. We find similar increases in probability for the Asian monsoon region in boreal summer, with implications for flooding in Bangladesh. Further practical applications of our techniques would be helped by the use of larger ensembles (for a more complete sampling of model uncertainty) and a wider range of scenarios at a resolution adequate to analyse average-size river basins.

  • 4. Rasmus, S
    et al.
    Räisänen, Jouni
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Lehning, M
    Estimating snow conditions in Finland in the late 21st century using the SNOWPACK model with regional climate scenario data as input2004Inngår i: ANNALS OF GLACIOLOGY, VOL 38 2004, 2004, s. 238-244Konferansepaper (Fagfellevurdert)
    Abstract [en]

    An assessment of possible snow changes in a changing climate for Finland is presented. The snowpack structure model SNOWPACK (developed at the Swiss Federal Institute for Snow and Avalanche Research) was used for calculating snow conditions at six different locations in Finland for the decades 1980-89 and 2080-89. Regional climate model (RCAO) data from the Rossby Centre, Sweden, were used as input to the SNOWPACK model. Ten years from the RCAO control run and scenario run Were chosen, and the snow conditions for different snow zones were calculated for these winters. The snow-cover depth and duration decreased at all locations in the scenario run cases, and the snow-cover quality also changed between the control and scenario runs: grains were bigger, snow was warmer and denser, and the fraction of faceted snow decreased while the fraction of icy or melting snow increased, even in mid-winter. Finally, the variability between different global climate predictions was analyzed. Significant differences were found between different climate-model outputs. The inter-model variable is comparable to the interannual variability of a single model. The qualitative Conclusions from the scenario run do not critically depend oil the climate-model variability.

  • 5.
    Rummukainen, Markku
    et al.
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Doescher, Ralf
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Graham, Phil
    SMHI, Affärsverksamhet.
    Hansson, Ulf
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Jones, Colin
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Meier, Markus
    SMHI, Forskningsavdelningen, Oceanografi.
    Räisänen, Jouni
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Samuelsson, Patrick
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Ullerstig, Anders
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Willén, Ulrika
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    PRUDENCE-related regional climate modeling at the SMHI/Rossby Centre2002Inngår i: PRUDENCE kick-off meeting / [ed] Jens Hesselbjerg Christensen, Danish Climate Centre DMI, Ministry of Transport , 2002, s. 40-41Konferansepaper (Annet vitenskapelig)
  • 6.
    Rummukainen, Markku
    et al.
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Räisänen, Jouni
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Bjorge, D
    Christensen, J H
    Christensen, O B
    Iversen, T
    Jylha, K
    Olafsson, H
    Tuomenvirta, H
    Regional climate scenarios for use in Nordic water resources studies2003Inngår i: Nordic Hydrology, ISSN 0029-1277, E-ISSN 1996-9694, Vol. 34, nr 5, s. 399-412Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    According to global climate projections, a substantial global climate change will occur during the next decades, under the assumption of continuous anthropogenic climate forcing. Global models, although fundamental in simulating the response of the climate system to anthropogenic forcing are typically geographically too coarse to well represent many regional or local features. In the Nordic region, climate studies are conducted in each of the Nordic countries to prepare regional climate projections with more detail than in global ones. Results so far indicate larger temperature changes in the Nordic region than in the global mean, regional increases and decreases in net precipitation, longer growing season, shorter snow season etc. These in turn affect runoff, snowpack, groundwater, soil frost and moisture, and thus hydropower production potential, flooding risks etc. Regional climate models do not yet fully incorporate hydrology. Water resources studies are carried out off-line using hydrological models. This requires archived meteorological output from climate models. This paper discusses Nordic regional climate scenarios for use in regional water resources studies. Potential end-users of water resources scenarios are the hydropower industry, dam safety instances and planners of other lasting infrastructure exposed to precipitation, river flows and flooding.

  • 7.
    Rummukainen, Markku
    et al.
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Räisänen, Jouni
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Bringfelt, Björn
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Ullerstig, Anders
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Omstedt, Anders
    SMHI, Forskningsavdelningen, Oceanografi.
    Willen, Ulrika
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Hansson, Ulf
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Jones, Colin
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    A regional climate model for northern Europe: model description and results from the downscaling of two GCM control simulations2001Inngår i: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 17, nr 5-6, s. 339-359Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 8.
    Rutgersson, Anna
    et al.
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Omstedt, Anders
    SMHI, Forskningsavdelningen, Oceanografi.
    Räisänen, Jouni
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Net precipitation over the Baltic Sea during present and future climate conditions2002Inngår i: Climate Research (CR), ISSN 0936-577X, E-ISSN 1616-1572, Vol. 22, nr 1, s. 27-39Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    By using a process-oriented ocean model forced with data from a gridded synoptic database, net precipitation values (precipitation minus evaporation) over the Baltic Sea are obtained. For a range of realistic meteorological forcing the average annual value obtained from an 18 yr (1981-1998) simulation ranges between 1100 and 2500 m(3) s(-1). The monthly variations are significant with the highest values occurring in early summer and even negative values in late autumn. Ice is an important factor, and the net precipitation is close to zero in the southern basins with no ice. Calculated net precipitation for a 98 yr period (1901-1998) using river runoff and maximum ice extent indicates that the investigated 18 yr period was wetter than the almost 100 yr climate mean. A realistic climate estimate of net precipitation during the 20th century is estimated to be 1500 +/-1000 m(3) s(-1). The evaluation of 2 present day regional climate simulations indicated high precipitation, low evaporation, and thus excessive net precipitation compared to the climate estimate from this investigation. When simulating the effect of increased greenhouse gases, the change in net precipitation was positive but small due to the compensating effects of increased precipitation and increased evaporation associated with increased temperature and reduced ice.

  • 9.
    Räisänen, Jouni
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    CO2- and aerosol-induced changes in vertically integrated zonal momentum budget in a GCM experiment1998Inngår i: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 11, nr 4, s. 625-639Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The German Climate Computing Center recently conducted a model experiment in which separate runs simulate the climatic response to increasing CO2 alone and to increasing CO2 together with direct radiative forcing by sulfate aerosols. One of the variables that shows interesting differences between the different runs is the nearsurface zonal-mean zonal wind. As compared with the control run, the midlatitude surface westerlies intensify and shift poleward in the CO2-only run in both hemispheres in both the northern winter (DJF) and summer (JJA). However, the aerosol forcing moderates these changes in general and, in particular, reverses the pattern of change in the Northern Hemisphere in JJA. Consistent differences between the various runs occur in the meridional distribution of sea level pressure. The origin of these simulated changes is studied by using the vertically integrated zonal-mean zonal momentum budget, utilizing the intimate linkage between the low-level wind and the surface stress and the close time-mean balance between the surface stress and the other terms in the budget. Regardless of the forcing used, momentum convergence in transient eddies is found to be the dominant agent of change in the extratropical Southern Hemisphere and in the Northern Hemisphere midlatitudes in JJA, In particular, the changes in the contribution of high-pass transients are relatively large and they seem to be qualitatively traceable to the changes in the tropospheric meridional temperature gradient. In the northern extratropics in DJE stationary eddies make an even larger contribution than the transients.

  • 10.
    Räisänen, Jouni
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    CO2-induced changes in atmospheric angular momentum in CMIP2 experiments2003Inngår i: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 16, nr 1, s. 132-143Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The response of atmospheric angular momentum to a gradual doubling of CO2 is studied using 16 model experiments participating in the second phase of the Coupled Model Intercomparison Project (CMIP2). The relative angular momentum associated with atmospheric zonal winds increases in all but one of the models, although the magnitude of the change varies widely. About 90% of the 16-model mean increase comes from increasing westerly winds in the stratosphere and the uppermost low-latitude troposphere above 200 hPa. This increase in westerly winds reflects a steepening of the meridional temperature gradient near the tropopause and in the upper troposphere. The simulated temperature gradient at this height increases partly as an indirect consequence of the poleward decrease in the tropopause height, and partly because convection induces a maximum in warming in the tropical upper troposphere. The change in the omega angular momentum associated with the surface pressure distribution is in most models smaller than the change in the relative angular momentum, although its exact value is sensitive to the method of calculation.

  • 11.
    Räisänen, Jouni
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    CO2-induced changes in interannual temperature and precipitation variability in 19 CMIP2 experiments2002Inngår i: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 15, nr 17, s. 2395-2411Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    CO2-induced changes in the interannual variability of monthly surface air temperature and precipitation are studied using 19 model experiments participating in the second phase of the Coupled Model Intercomparison Project (CMIP2). The magnitude of variability in the control runs appears generally reasonable, but it varies a great deal between different models, almost all of which overestimate temperature variability on low-latitude land areas. In most models the gradual doubling of CO2 leads to a decrease in temperature variability in the winter half-year in the extratropical Northern Hemisphere and over the high-latitude Southern Ocean. Over land in low latitudes and in northern midlatitudes in summer, a slight tendency toward increased temperature variability occurs. The standard deviation of monthly precipitation increases, on average, where the mean precipitation increases but also does so in some areas where the mean precipitation decreases slightly. The coefficient of variation of precipitation (i.e., the ratio between the standard deviation and the mean) also tends to increase in most areas, especially where the mean precipitation decreases. However, the changes in variability are less similar between the 19 experiments than the changes in mean temperature and precipitation, at least partly because they have a much lower signal-to-noise ratio. In addition, the changes in the standard deviation of monthly temperature are generally much smaller than the time-mean warming, which suggests that future changes in the extremes of interannual temperature variability will be largely determined by the latter.

  • 12.
    Räisänen, Jouni
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    CO2-induced climate change in CMIP2 experiments: Quantification of agreement and role of internal variability2001Inngår i: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 14, nr 9, s. 2088-2104Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    CO2-induced changes in surface air temperature, precipitation, and sea level pressure are compared between model experiments participating in the second phase of the Coupled Model Intercomparison Project (CMIP2). A statistical formalism is applied, in which the average squared amplitude of the simulated climate changes is divided into a common signal and variances associated with internal variability and model differences. In the 20-yr period centered at the doubling of CO2 and for a set of 14-15 models, the dimensionless global relative agreement on gridbox-scale annual mean climate changes is 0.89 for surface air temperature but only 0.22 for precipitation and 0.46 for sea level pressure. A majority of the interexperiment differences are attributed to model differences; the contribution of internal variability to the differences in change is estimated as 16% for temperature, 34% for precipitation, and 32% for sea level pressure. For seasonal rather than annual climate changes, the agreement is lower and the contribution of internal variability to the interexperiment variance larger. Likewise, the relative agreement is worse and internal variability in relative terms more important earlier during the transient experiments than around the doubling of CO2. Conversely, when climate changes are averaged over larger areas than individual grid boxes, the relative agreement improves with increasing averaging domain (especially with precipitation and temperature) and the impact of internal variability decreases.

  • 13.
    Räisänen, Jouni
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Internal variability as a cause of qualitative intermodel disagreement on anthropogenic climate changes1999Inngår i: Journal of Theoretical and Applied Climatology, ISSN 0177-798X, E-ISSN 1434-4483, Vol. 64, nr 1-2, s. 1-13Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The qualitative agreement of two climate models, HADCM2 and ECHAM3, on the response of surface climate to anthropogenic climate forcing in the period 2020-2049 is studied. Special attention is paid to the role of internal climate variability as a source of intermodel disagreement. After illustrating the methods in an intermodel comparison of simulated changes in June-August mean precipitation, some global statistics are presented. Excluding surface air temperature, the four-season mean proportion of areas in which the two models agree on the sign of the climatic response is only 53-60% both for increases in CO2 alone and for increases in CO2 together with direct radiative forcing by sulphate aerosols, but somewhat larger, 59-70% for the separate aerosol effect. In areas where the response is strong (at least twice the standard error associated with internal variability) in both models, the agreement is better and the contrast between the different forcings becomes more marked. The proportion of agreement in such areas is 57-75% for the response to increases in CO2 alone, 64-84% for the response to combined CO2 and aerosol forcing, and as high as 88-94% for the separate aerosol effect. The relatively good intermodel agreement for aerosol-induced climate changes is suggested to be associated with the uneven horizontal distribution of aerosol forcing.

  • 14.
    Räisänen, Jouni
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Model-simulated CO2-induced changes in seasonal precipitation extremes2002Inngår i: INTERGOVERNMENTAL PANEL ON CLIMATE CHANGE, 2002, s. 66-Konferansepaper (Annet vitenskapelig)
  • 15.
    Räisänen, Jouni
    et al.
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Alexandersson, Hans
    SMHI.
    A probabilistic view on recent and near future climate change in Sweden2003Inngår i: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 55, nr 2, s. 113-125Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The decade 1991-2000 was warm and wet in Sweden, with 10-station mean temperature 0.8 degreesC above and 20-station mean precipitation 6% above the mean for 1961-1990. Here we study the question if such changes should be seen as a symptom of anthropogenic climate change or if they might be of purely natural origin. Using the control simulations of 19 atmosphere-ocean general circulation models and taking into account difference's between the simulated and observed interannual variability, we estimate that the recent increase in temperature and that in precipitation had both about a 6-7% chance to occur solely as a result of natural variability. Using the corresponding simulations with increasing CO2, we further estimate that the anthropogenic forcing raised the probability of the observed changes to occur to 23% for the increase in temperature and to 14% for the increase in precipitation. About half of the warming and about 30% of the increase in precipitation appear to be explained by anthropogenic forcing. The seasonal aspects of observed and simulated climate change are also discussed, with special emphasis on winter, when the observed warming has been much larger than expected from the model simulations. Finally, a probabilistic forecast for the Swedish climate in the first decade of the 21st century suggests a 95% (87%) possibility of warmer (wetter) annual mean conditions than in 1961-1990 on the average. One of the caveats in our analysis is that the model simulations exclude variations in solar and volcanic activity, the effects of which might not be fully covered by our resealing of interannual variability.

  • 16.
    Räisänen, Jouni
    et al.
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Hansson, U
    Ullerstig, Anders
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Doescher, Ralf
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Graham, Phil
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Jones, Colin
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Meier, Markus
    SMHI, Forskningsavdelningen, Oceanografi.
    Samuelsson, Patrick
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Willen, Ulrika
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    European climate in the late twenty-first century: regional simulations with two driving global models and two forcing scenarios2004Inngår i: Climate Dynamics, ISSN 0930-7575, E-ISSN 1432-0894, Vol. 22, nr 1, s. 13-31Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 17.
    Räisänen, Jouni
    et al.
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Joelsson, Rune
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Changes in average and extreme precipitation in two regional climate model experiments2001Inngår i: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 53, nr 5, s. 547-566Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two regional climate model experiments for northern and central Europe are studied focussing on greenhouse gas-induced changes in heavy precipitation. The average yearly maximum one-day precipitation P-max shows a general increase in the A hole model domain in both experiments, although the mean precipitation P-mcan decreases in the southern part of the area, especially in one of the experiments. The average yearly maximum six-hour precipitation increases even more than the one-day P-max suggesting a decrease in the timescale of heavy precipitation. The contrast between the P-max, and P-max changes in the southern part of the domain and the lack of such a contrast further north are affected by changes in wet-day frequency that stem, at least in part. from changes in atmospheric circulation. However, the yearly extremes of precipitation exhibit a larger percentage increase than the average wet-day precipitation. The signal-to-noise aspects of the model results are also studied in some detail. The 44 km grid-box-scaie changes in P-max are very heavily affected by inter-annual variability, with an estimated standard error ;of about 20% for the 10-year mean changes. However. the noise in P-max decreases sharply toward larger horizontal scales, and large-area mean changes in P-max can be estimated with similar accuracy to those in P-mcan Although a horizontal averaging of model results smooths out the small-scale details in the true climate change signal as well, this disadvantage is, in the case of P-max changes, much smaller than the advantage of reduced noise.

  • 18.
    Räisänen, Jouni
    et al.
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Palmer, T N
    A probability and decision-model analysis of a multimodel ensemble of climate change simulations2001Inngår i: Journal of Climate, ISSN 0894-8755, E-ISSN 1520-0442, Vol. 14, nr 15, s. 3212-3226Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Because of the inherent uncertainties in the computational representation of climate and because of unforced chaotic climate variability, it is argued that climate change projections should be expressed in probabilistic form. In this paper, 17 Coupled Model Intercomparison Project second-phase experiments sharing the same gradual increase in atmospheric CO2 are treated as a probabilistic multimodel ensemble projection of future climate. Tools commonly used for evaluation of probabilistic weather and seasonal forecasts are applied to this climate change ensemble. The probabilities of some temperature- and precipitation-related events defined for 20-yr seasonal means of climate are first studied. A cross-verification exercise is then used to obtain an upper estimate of the quality of these probability forecasts in terms of Brier skill scores, reliability diagrams, and potential economic value. Skill and value estimates are consistently higher for temperature- related events (e.g., will the 20-yr period around the doubling of CO2 be at least 1 degreesC warmer than the present?) than for precipitation-related events (e.g., will the mean precipitation decrease by 10% or more?). For large enough CO2 forcing, however, probabilistic projections of precipitation-related events also exhibit substantial potential economic value for a range of cost-loss ratios. The treatment of climate change information in a probabilistic rather than deterministic manner (e.g., using the ensemble consensus forecast) can greatly enhance its potential value.

  • 19.
    Räisänen, Jouni
    et al.
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Rummukainen, Markku
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Ullerstig, Anders
    SMHI, Forskningsavdelningen, Klimatforskning - Rossby Centre.
    Downscaling of greenhouse gas induced climate change in two GCMs with the Rossby Centre regional climate model for northern Europe2001Inngår i: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 53, nr 2, s. 168-191Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two 2 x 10-year climate change experiments made with the Rossby Centre regional Atmospheric climate model(RCA) are reported. These two experiments are driven by boundary data from two global climate change simulations, one made with HadCM2 and the other with ECKAM4/OPYC3, in which the global mean warming is virtually the same, 2.6 degreesC. The changes in mean temperature and precipitation show similarities (including broadly the same increase in temperature and in northern Europe a general increase in annual precipitation) as well as differences between the two RCA experiments. These changes are strongly governed by the driving GCM simulations. Even on the RCA grid box scale, the differences in change between RCA and the driving GCM are generally smaller than the differences between the two GCMs. Typically about a half of the local differences between the two RCA simulations are attributed to noise generated by internal variability, which also seems to explain a substantial part of the RCA-GCM differences particularly for precipitation change. RCA includes interactive model components for the Baltic Sea and inland lakes of northern Europe. The simulated changes in these water bodies are discussed with emphasis on the wintertime ice conditions. Comparison with an earlier RCA experiment indicates that a physically consistent treatment of these water bodies is also of importance for the simulated atmospheric climate change.

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