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Journal of Meteorological Research

, Volume 32, Issue 6, pp 974–984 | Cite as

Conjugate Gradient Algorithm in the Four-Dimensional Variational Data Assimilation System in GRAPES

  • Yongzhu LiuEmail author
  • Lin Zhang
  • Zhihua Lian
Regular Article
  • 171 Downloads

Abstract

Minimization algorithms are singular components in four-dimensional variational data assimilation (4DVar). In this paper, the convergence and application of the conjugate gradient algorithm (CGA), which is based on the Lanczos iterative algorithm and the Hessian matrix derived from tangent linear and adjoint models using a non-hydrostatic framework, are investigated in the 4DVar minimization. First, the influence of the Gram-Schmidt orthogonalization of the Lanczos vector on the convergence of the Lanczos algorithm is studied. The results show that the Lanczos algorithm without orthogonalization fails to converge after the ninth iteration in the 4DVar minimization, while the orthogonalized Lanczos algorithm converges stably. Second, the convergence and computational efficiency of the CGA and quasi-Newton method in batch cycling assimilation experiments are compared on the 4DVar platform of the Global/Regional Assimilation and Prediction System (GRAPES). The CGA is 40% more computationally efficient than the quasi-Newton method, although the equivalent analysis results can be obtained by using either the CGA or the quasi-Newton method. Thus, the CGA based on Lanczos iterations is better for solving the optimization problems in the GRAPES 4DVar system.

Key words

numerical weather prediction Global/Regional Assimilation and Prediction System four-dimensional variation conjugate gradient algorithm Lanczos algorithm 

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Copyright information

© The Chinese Meteorological Society and Springer-Verlag GmbH Germany, part of Springer Nature 2018

Authors and Affiliations

  1. 1.National Meteorological CenterBeijingChina

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