Four-dimensional variational data assimilation for a limited area model

• Published in: Tellus. Series A, Dynamic meteorology and oceanography Vol. 64; no. 1; pp. 14985 - 29
• Main Authors: Gustafsson, Nils, Huang, Xiang-Yu, Yang, Xiaohua, Mogensen, Kristian, Lindskog, Magnus, Vignes, Ole, Wilhelmsson, Tomas, Thorsteinsson, Sigurdur
• Format: Journal Article
• Language: English
• Published: Taylor & Francis 01.12.2012; Stockholm University Press
• Subjects: analysis; data assimilation; numerical weather prediction
• ISSN: 1600-0870; 0280-6495; 1600-0870
• DOI: 10.3402/tellusa.v64i0.14985

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