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Ensemble initial conditions through 4D‐Var assimilation
Author(s) -
Goswami P.,
Gouda K. C.,
Talagrand O.
Publication year - 2005
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2005gl022542
Subject(s) - data assimilation , amplitude , perturbation (astronomy) , assimilation (phonology) , computer science , mathematics , meteorology , physics , philosophy , linguistics , quantum mechanics
The methodology to generate members of an ensemble is an important issue in operational forecasting; currently a number of procedures are followed at different operational centres. In the present work we propose and evaluate a methodology where a dynamically consistent set of initial conditions is generated through 4D‐Var assimilation procedure. The perturbations are generated through 4D‐Var assimilation with different information (observation) content, either through a variation in the frequency of observations or a variation in the length of assimilation window. We adopt a representative non‐linear system, viz. the three‐variable Lorenz system and show that ensemble forecasts generated through 4D‐Var assimilation show less error than those generated from initial conditions (with similar amplitude of perturbation) adopted arbitrarily. Another advantage of the procedure is that it provides a (variable‐specific) estimate of the maximum allowed amplitude and spread of perturbations.