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Horizontal diffusion Scientific documentation : design and scaling of ARPEGE diffusions (2002)
Article published on 11 July 2002
last modification on 3 November 2005

This document written by Pierre Bénard summarizes the principles for implementing an horizontal diffusion in a stretched model and lists the problems encountered in the development and validation of HDF scheme, and its current status. One of the goals is to have a written material in order to avoid further errors. Lack of formalization can sometimes be a source of problems with very serious consequences.

Contents :

  • Introduction
  • HD coefficients in non-stretched models
  • "Target" diffusion operator for stretched models
  • Notations for the ARPEGE stretched geometry
  • Graphical examination of the spatial behaviour of diffusion operators in ARPEGE
  • The HDU diffusion in ARPEGE
    • The "pure" current HDU operator
    • The "practical" current HDU operator
    • Proposal for a "new" HDU operator
  • The HDF diffusion in ARPEGE
    • The "pure" current HDF operator
    • The "practical" current HDF operator
    • Alternative HDF operator
  • Spatial comparison of current HDU and HDF operators
  • Initial error in the specification of the hybrid character of the HDF
  • Definition of the pertinent parameter for the diffusion in stretched models
    • space-independent pertinent parameter
    • space- and resolution-independent pertinent parameter
    • space-, resolution-, and stretching-independent pertinent parameter
    • Comparison of the constraints linked to the global balance vs. the non-dependence of the pertinent parameter
  • Comments on the time-discretization of diffusion schemes
    • Current fully-implicit discretization
    • Proposal for a new time-discretization of spectral diffusions
    • Extension to HDF diffusion
  • Choice of the diffusion parameter(s) in the current HDU
  • Choice of the diffusion parameter in new HDU
  • Choice of the diffusion parameter in HDF
  • Choice of the diffusion parameter in proposed new-HDF
  • Comparison of operational diffusion absolute intensities
    • Damping-time in operational ALADIN
    • Damping-time in operational HDU
    • Damping-time in "reference" ALADIN
    • Damping-time in the "reference" IFS
    • Damping-time in HDF
    • Spectral comparison of operational HDU vs. reference IFS
    • summary
  • Conclusion
    • Recommendations
    • Comparison of new-HDU vs. HDF advantages
    • Absolute intensity of ARPEGE diffusion

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