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2000 - Realization of a simplified, differentiable and realistic physical parametrization for incremental four-dimensional variational data assimilation
Article published on June 2000
last modification on 25 October 2005

A complete set of the simplified physical parametrizations has been developed for incremental 4D-Var assimilation system. It contains a simplified computation of radiative fluxes, vertical turbulent diffusion, orographic gravity waves, deep convection and stratiform precipitation fluxes. The validation of the whole direct simplified physical package has been done.

To include the described simplified physical parametrizations into assimilating model, their tangent linear and adjoint have been developed. The accuracy of the linearization of the simplified physical parametrizations has been investigated. The problem of additional regularization, i.e. smoothing modifications of some discontinuities in the parametrizations, arose during this validation and some smoothing modifications had to be developed.

To investigate the sensitivity of a 4D-Var assimilation system to physical processes, 4D-Var experiments using the adjoint model with simplified physical parametrizations have been performed. FASTEX (Fronts and Atlantic Storm Track Experiments) situations have been selected as test cases. The potential of including the physical processes in the assimilating model for the representation of the cyclogenesis has been demonstrated.

This document was written by Marta Janiskova from her PhD thesis in June 2000.
It presents :

  • Position of the problem
  • Standard formulation of 4D-Var
  • Incremental approach of 4D-Var
  • Importance of including physics in the assimilating model
  • Surface processes
  • Stratiform precipitation
  • Vertical diffusion
  • Radiation
  • Solar radiation
  • TL and AD models
  • validation of TL model
  • Importance of the regulation of the TL model
  • regularization of the vertical diffusion scheme
  • Regularization of the radiation & convection schemes
  • 4D-Var experiments
  • Perspectives
  • One-week assimilation cycle