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  • 51.
    Wyser, Klaus
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Jones, Colin
    SMHI, Research Department, Climate research - Rossby Centre.
    Modeled and observed clouds during Surface Heat Budget of the Arctic Ocean (SHEBA)2005In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 110, no D9, article id D09207Article in journal (Refereed)
    Abstract [en]

    [1] Observed monthly mean cloud cover from the SHEBA site is found to differ by a substantial amount during winter depending on cloud observing instrument. This makes it difficult for climate modelers to evaluate modeled clouds and improve parameterizations. Many instruments and human observers cannot properly detect the thinnest clouds and count them as clear sky instead, resulting in too low cloud cover. To study the impact from the difficulties in the detection of thin clouds, we compute cloud cover in our model with a filter that removes the thinnest clouds. Optical thickness is used as a proxy to identify thin clouds as we are mainly interested in the impact of clouds on radiation. With the results from a regional climate model simulation of the Arctic, we can reproduce the large variability in wintertime cloud cover between instruments when assuming different cloud detection thresholds. During winter a large fraction of all clouds are optically thin, which causes the large sensitivity to filtering by optical thickness. During summer, most clouds are far above the optical thickness threshold and filtering has no effect. A fair comparison between observed and modeled cloud cover should account for thin clouds that may be present in models but absent in the observational data set. Difficulties with the proper identification of clouds and clear sky also has an effect on cloud radiative forcing. The derived clear-sky longwave flux at the surface can vary by some W m(-2) depending on the lower limit for the optical thickness of clouds. This impacts on the "observed'' LW cloud radiative forcing and suggests great care is needed in using satellite-derived cloud radiative forcing for model development.

  • 52.
    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, p. 203-223Article 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.

  • 53.
    Wyser, Klaus
    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.
    Modelling clouds and radiation in the Arctic2005In: Extended abstracts of a WMO/WCRP-sponsored Regional-Scale Climate Modelling Workshop [Elektronisk resurs] : high-resolution climate modelling : assessment, added value and applications / [ed] Lars Bärring & René Laprise, Lund: Department of Physical Geography & Ecosystems Analysis, Lund University , 2005, p. 128-Conference paper (Other academic)
  • 54.
    Wyser, Klaus
    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.
    Modelling clouds and radiation in the ARctic.2004In: 14th International conference on clouds and precipitation, 2004, p. 1442-1445Conference paper (Other academic)
  • 55.
    Wyser, Klaus
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Kjellström, Erik
    SMHI, Research Department, Climate research - Rossby Centre.
    Koenigk, Torben
    SMHI, Research Department, Climate research - Rossby Centre.
    Martins, Helena
    SMHI, Research Department, Climate research - Rossby Centre.
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    Warmer climate projections in EC-Earth3-Veg: the role of changes in the greenhouse gas concentrations from CMIP5 to CMIP62020In: Environmental Research Letters, E-ISSN 1748-9326, Vol. 15, no 5, article id 054020Article in journal (Refereed)
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    fulltext
  • 56.
    Wyser, Klaus
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Koenigk, Torben
    SMHI, Research Department, Climate research - Rossby Centre.
    Fladrich, Uwe
    SMHI, Research Department, Climate research - Rossby Centre.
    Fuentes Franco, Ramon
    SMHI, Research Department, Climate research - Rossby Centre.
    Karami, Pasha
    SMHI, Research Department, Climate research - Rossby Centre.
    Kruschke, Tim
    SMHI, Research Department, Climate research - Rossby Centre.
    The SMHI Large Ensemble (SMHI-LENS) with EC-Earth3.3.12021In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 14, no 7, p. 5781-5796Article in journal (Refereed)
    Download full text (pdf)
    fulltext
  • 57.
    Wyser, Klaus
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    Rummukainen, Markku
    SMHI, Research Department, Climate research - Rossby Centre.
    Strandberg, Gustav
    SMHI, Research Department, Climate research - Rossby Centre.
    Nordic regionalisation of a greenhouse-gas stabilisation scenario2006Report (Other academic)
    Abstract [en]

    The impact of a CO2 stabilisation on the Swedish climate is investigated with the regional climate model RCA3 driven by boundary conditions obtained from a global coupled climate system model (CCSM3). The global model has been forced with observed greenhouse gas concentrations from pre-industrial conditions until today’s, and with an idealised further increase until the stabilisation level is reached. After stabilisation the model integration continues for another 150+ years in order to follow the delayed response of the climate system over a period of time.Results from the global and regional climate model are compared against observations and ECMWF reanalysis for 1961-1990. For this period, the global model is found to be too cold over Europe and with a zonal flow from the North Atlantic towards Europe that is too strong. The climate of the driving global model controls the climate of the regional model and the same deviations from one are thus inherited by the other. We therefore analyse the relative climate changes differences, or ratios, of climate variables between future's and today's climate.Compared to pre-industrial conditions, the global mean temperature changes by about 1.5oC as a result of the stabilisation at 450 ppmv equivalent CO2. Averaged over Europe, the temperature change is slightly larger, and it is even larger for Sweden and Northern Europe. Annual mean precipitation for Europe is unaffected, but Sweden receives more precipitation under higher CO2 levels. The inter-annual and decadal variability of annual mean temperature and precipitation does not change with any significant degree.The changes in temperature and precipitation are not evenly distributed with the season: the largest warming and increased precipitation in Northern Europe occurs during winter months while the summer climate remains more or less unchanged. The opposite is true for the Mediterranean region where the precipitation decreases mostly during summer. This also implies higher summer temperatures, but changes in winter are smaller. No substantial change in the wind climate over Europe is found.

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    FULLTEXT01
  • 58.
    Wyser, Klaus
    et al.
    SMHI, Research Department, Climate research - Rossby Centre.
    van Noije, Twan
    Yang, Shuting
    von Hardenberg, Jost
    O'Donnell, Declan
    Doescher, Ralf
    SMHI, Research Department, Climate research - Rossby Centre.
    On the increased climate sensitivity in the EC-Earth model from CMIP5 to CMIP62020In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 13, no 8, p. 3465-3474Article in journal (Refereed)
    Download full text (pdf)
    On the increased climat sensitivity in the EC-Earth model from CMIP5 to CMIP6
  • 59. Zhang, Qiong
    et al.
    Berntell, Ellen
    Axelsson, Josefine
    Chen, Jie
    Han, Zixuan
    de Nooijer, Wesley
    Lu, Zhengyao
    Li, Qiang
    Zhang, Qiang
    Wyser, Klaus
    SMHI, Research Department, Climate research - Rossby Centre.
    Yang, Shuting
    Simulating the mid-Holocene, last interglacial and mid-Pliocene climate with EC-Earth3-LR2021In: Geoscientific Model Development, ISSN 1991-959X, E-ISSN 1991-9603, Vol. 14, no 2, p. 1147-1169Article in journal (Refereed)
    Download full text (pdf)
    Simulating the mid-Holocene, last interglacial and mid-Pliocene climate with EC-Earth3-LR
12 51 - 59 of 59
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