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Four-dimensional variational data assimilation for a limited area model

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Author(s): Nils Gustafsson | Xiang-Yu Huang | Xiaohua Yang | Kristian Mogensen | Magnus Lindskog | Ole Vignes | Tomas Wilhelmsson | Sigurdur Thorsteinsson

Journal: Tellus A
ISSN 0280-6495

Volume: 64;
Start page: 1;
Date: 2012;
Original page

Keywords: data assimilation | analysis | numerical weather prediction

ABSTRACT
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.The review process was handled by Subject Editor Abdel Hannachi
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