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Variational data assimilation is an advanced technique to provide correct and high quality initial fields for the numerical model. Digital filter is not restricted to initialization; it may also be implemented as a weak constraint penalizing the analysis towards a balanced state in a preoperational 4D-Var system. The constraint is imposed only on the analysis increments to damp spurious fast oscillations associated with gravity–inertia waves. The influence of DFI as a weak constraint on 4D-Var forecast is assessed by assimilation experiments with the recently occurring severe snow weather. It is shown that the weak constraint imposed only on the increments manages to control efficiently the emergence of fast oscillations in the resulting forecast while maintaining a closer fitting to the observations.
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Keywords:
- variational data assimilation /
- initial imbalance /
- digital filter initialization /
- weak constraint
[1] Huang S X, Han W, Wu R S 2004 Chin. Science D 47 630
[2] Huang S X, Sheng Z 2006 Acta Phys. Sin. 55 6720 (in Chinese)[黄思训、盛 峥 2006 55 6720]
[3] Huang S X, Cai Q F, Xiang J 2007 Acta Phys. Sin. 56 2607 (in Chinese)[黄思训、蔡其发、项 杰 2007 56 2607]
[4] Cao X Q, Huang S X, Du H D 2008 Acta Phys. Sin. 57 1984 (in Chinese)[曹小群、黄思训、杜华栋 2008 57 1984]
[5] Courtier P, Thépaut J N 1994 Q. J. R. Meteorol. Soc. 120 1367
[6] Miyakoda K, Moyer R 1968 Tellus 20 115
[7] Machenhauer B 1977 Atmos. Phys. 50 253
[8] Baer F, Tribbia J 1977 Mon. Wea. Rev. 105 1536
[9] Lynch P, Huang X Y 1992 Mon. Wea. Rev. 120 1019
[10] Courtier P, Talagrand O 1990 Tellus. 42 A 531
[11] Gustafsson N 1992 Proc. Workshop on Variational Assimilation with Special Emphasis on Three-dimensional Aspects. United Kingdom: Reading, European Centre for Medium-Range Weather Forecasts.
[12] Polavarapu S, Tanguay M, Fillion L 2000 Mon. Wea. Rev. 128 2491
[13] Gauthier P, Thépaut J N 2001 Mon. Wea. Rev. 129 2089
[14] Wee T K, Kuo Y H 2004 Mon. Wea. Rev. 132 543
[15] Dee D P 1995 Mon.Wea.Rev. 123 1128
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[1] Huang S X, Han W, Wu R S 2004 Chin. Science D 47 630
[2] Huang S X, Sheng Z 2006 Acta Phys. Sin. 55 6720 (in Chinese)[黄思训、盛 峥 2006 55 6720]
[3] Huang S X, Cai Q F, Xiang J 2007 Acta Phys. Sin. 56 2607 (in Chinese)[黄思训、蔡其发、项 杰 2007 56 2607]
[4] Cao X Q, Huang S X, Du H D 2008 Acta Phys. Sin. 57 1984 (in Chinese)[曹小群、黄思训、杜华栋 2008 57 1984]
[5] Courtier P, Thépaut J N 1994 Q. J. R. Meteorol. Soc. 120 1367
[6] Miyakoda K, Moyer R 1968 Tellus 20 115
[7] Machenhauer B 1977 Atmos. Phys. 50 253
[8] Baer F, Tribbia J 1977 Mon. Wea. Rev. 105 1536
[9] Lynch P, Huang X Y 1992 Mon. Wea. Rev. 120 1019
[10] Courtier P, Talagrand O 1990 Tellus. 42 A 531
[11] Gustafsson N 1992 Proc. Workshop on Variational Assimilation with Special Emphasis on Three-dimensional Aspects. United Kingdom: Reading, European Centre for Medium-Range Weather Forecasts.
[12] Polavarapu S, Tanguay M, Fillion L 2000 Mon. Wea. Rev. 128 2491
[13] Gauthier P, Thépaut J N 2001 Mon. Wea. Rev. 129 2089
[14] Wee T K, Kuo Y H 2004 Mon. Wea. Rev. 132 543
[15] Dee D P 1995 Mon.Wea.Rev. 123 1128
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