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  • 1. Bromwich, David H.
    et al.
    Wilson, Aaron B.
    Bai, Le-Sheng
    Moore, George W. K.
    Bauer, Peter
    A comparison of the regional Arctic System Reanalysis and the global ERA-Interim Reanalysis for the Arctic2016In: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 142, no 695, p. 644-658Article in journal (Refereed)
    Abstract [en]

    The Arctic System Reanalysis version 1 (ASRv1), a high-resolution regional assimilation of model output, observations and satellite data across the mid- and high latitudes of the Northern Hemisphere, and the global European Centre for Medium Range Forecasting Interim Reanalysis (ERAI) are compared with atmospheric observations for the period December 2006 to November 2007. Results throughout the troposphere show observations to be well assimilated in the ASRv1, as monthly and annual near-surface (upper-level) temperature, dew-point (relative humidity), pressure (geopotential height) and wind-speed biases compared with surface stations and radiosondes are very small. These results are similar to the ERAI, although wind-speed biases are significantly smaller in the ASRv1. Despite the ASRv1’s use of a 3D-variational (Var) assimilation compared with the ERAI’s 4D-Var, similar results suggest that a regional approach with higher-resolution terrain and a detailed land-surface description forced by a global reanalysis may improve the assimilation of observations and help offset temporal information lost by the 3D-Var compared with the 4D-Var. However, the ASRv1 forecast field results compared with the ERAI are mixed. The ASRv1 and ERAI show negative precipitation biases during cool months compared with gauge observations, and too much precipitation falls in the ASRv1 during summer in the midlatitudes. Stations north of 60°N demonstrate smaller precipitation biases in the ASRv1 than the ERAI except during the summer, when the ASRv1 is very dry. Short-wave radiation compared with observations is much too large in the ASRv1, and both reanalyses show long-wave radiation deficits during most months. These results point to inadequacies in model physics in the ASRv1 (e.g. convective and radiation schemes) that will continue to be refined in subsequent versions of the ASR.

  • 2.
    Sotiropoulou, Georgia
    et al.
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Sedlar, Joseph
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Forbes, Richard
    Tjernström, Michael
    Stockholms universitet, Meteorologiska institutionen (MISU).
    Late Summer Arctic clouds in the ECMWF forecast model: an evaluation of cloud parameterization scheme2016In: Quarterly Journal of the Royal Meteorological Society, ISSN 0035-9009, E-ISSN 1477-870X, Vol. 142, no 694, p. 387-400Article in journal (Refereed)
    Abstract [en]

    Mixed-phase clouds are an integral part of the Arctic climate system, for precipitation and for their interactions with radiation and thermodynamics. Mixed-phase processes are often poorly represented in global models and many use an empirically based diagnostic partition between the liquid and ice phases that is dependent solely on temperature. However, increasingly more complex microphysical parametrizations are being implemented allowing a more physical representation of mixed-phase clouds.

    This study uses in situ observations from the Arctic Summer Cloud Ocean Study (ASCOS) field campaign in the central Arctic to assess the impact of a change from a diagnostic to a prognostic parametrization of mixed-phase clouds and increased vertical resolution in the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecast System (IFS). The newer cloud scheme improves the representation of the vertical structure of mixed-phase clouds, with supercooled liquid water at cloud top and ice precipitating below, improved further with higher vertical resolution. Increased supercooled liquid water and decreased ice content are both in closer agreement with observations. However, these changes do not result in any substantial improvement in surface radiation, and a warm and moist bias in the lowest part of the atmosphere remains. Both schemes also fail to capture the transitions from overcast to cloud-free conditions. Moreover, whereas the observed cloud layer is frequently decoupled from the surface, the modelled clouds remain coupled to the surface most of the time. The changes implemented to the cloud scheme are an important step forward in improving the representation of Arctic clouds, but improvements in other aspects such as boundary-layer turbulence, cloud radiative properties, sensitivity to low aerosol concentrations and representation of the sea-ice surface may also need to be addressed.

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