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  • 1.
    Gustafsson, Nils
    et al.
    SMHI, Research Department, Meteorology.
    Huang, Xiang-Yu
    Yang, Xiaohua
    Mogensen, Kristian
    Lindskog, Magnus
    SMHI, Research Department, Meteorology.
    Vignes, Ole
    Wilhelmsson, Tomas
    Thorsteinsson, Sigurdur
    SMHI, Research Department, Meteorology.
    Four-dimensional variational data assimilation for a limited area model2012In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 64, article id 14985Article in journal (Refereed)
    Abstract [en]

    A 4-dimensional variational data assimilation (4D-Var) scheme for the HIgh Resolution Limited Area Model (HIRLAM) forecasting system is described in this article. The innovative approaches to the multi-incremental formulation, the weak digital filter constraint and the semi-Lagrangian time integration are highlighted with some details. The implicit dynamical structure functions are discussed using single observation experiments, and the sensitivity to various parameters of the 4D-Var formulation is illustrated. To assess the meteorological impact of HIRLAM 4D-Var, data assimilation experiments for five periods of 1 month each were performed, using HIRLAM 3D-Var as a reference. It is shown that the HIRLAM 4D-Var consistently out-performs the HIRLAM 3D-Var, in particular for cases with strong mesoscale storm developments. The computational performance of the HIRLAM 4D-Var is also discussed.

  • 2.
    Gustafsson, Nils
    et al.
    SMHI, Research Department, Meteorology.
    Källén, Erland
    SMHI, Research Department, Meteorology.
    Thorsteinsson, Sigurdur
    SMHI, Research Department, Meteorology.
    Sensitivity of forecast errors to initial and lateral boundary conditions1998In: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 50, no 2, p. 167-185Article in journal (Refereed)
    Abstract [en]

    The adjoint of a limited area model has been used to study the sensitivity of 12 h forecast errors to initial and lateral boundary conditions. Upper troposphere potential vorticity and mean sea level pressure verification scores for 1 month of operational forecasts from the Swedish Meteorological and Hydrological Institute were used to select 2 cases with particularly poor forecast performance. The sensitivity experiments show that errors in initial data is the most likely explanation for one of the forecast failures, while errors in initial as well as lateral boundary data can explain the 2nd forecast failure. Results from the sensitivity experiments with respect to the lateral boundary conditions indicate that poor quality lateral boundary conditions may be improved by utilizing subsequent downstream observations within the model integration area. This result is of great significance with regard to the possibilities for applying 4-dimensional variational data assimilation (4DVAR) for limited area forecast models. Results from the sensitivity experiments also reveal, however, that the lateral boundary treatment in operational limited area models needs to be improved with regard to the mathematical formulation. It is furthermore shown that modifications to be applied to the lateral boundary conditions need to be determined with appropriate time resolution and that some filtering of these lateral boundary modifications has to be introduced to avoid enhanced high-frequency gravity wave noise in the vicinity of the lateral boundaries.

  • 3. Sanchez Arriola, Jana
    et al.
    Lindskog, Magnus
    SMHI, Research Department, Meteorology.
    Thorsteinsson, Sigurdur
    SMHI, Research Department, Meteorology.
    Bojarova, Jelena
    Variational Bias Correction of GNSS ZTD in the HARMONIE Modeling System2016In: Journal of Applied Meteorology and Climatology, ISSN 1558-8424, E-ISSN 1558-8432, Vol. 55, no 5, article id UNSP 1259Article in journal (Refereed)
1 - 3 of 3
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