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Semi-Lagrangian computations in the cycle 46t1r1 of ARPEGE/IFS.
Article published on 12 February 2019

by Karim Yessad

Abstract:

The general purpose of this documentation is to describe the set of equations used, and also the way to integrate the dynamics of the model with the semi-Lagrangian method currently implemented in ARPEGE/IFS. The following points will be described: semi-Lagrangian formulation and discretisation for different sets of equations, semi-Lagrangian trajectory research, horizontal and vertical interpolations done in the semi-Lagrangian scheme, specific geometric problems met in this type of discretisation. An organigramme is provided. An introduction to tangent linear and adjoint code is provided.


RESUME:

LE BUT GENERAL DE CETTE DOCUMENTATION EST DE DECRIRE LE JEU D’EQUATIONS UTILISE, ET EGALEMENT LA FACON DE DISCRETISER CES EQUATIONS AVEC UN SCHEMA D’ADVECTION SEMI-LAGRANGIEN TEL QU’IL EST UTILISE DANS ARPEGE/IFS. ON DECRIT LES POINTS SUIVANTS: FORMULATION LAGRANGIENNE DES EQUATIONS, LEUR DISCRETISATION AVEC UN SCHEMA SEMI-LAGRANGIEN, RECHERCHE DE TRAJECTOIRE, INTERPOLATIONS HORIZONTALES ET VERTICALES FAITES DANS LE SCHEMA SEMI-LAGRANGIEN, PROBLEMES DE GEOMETRIE SPECIFIQUES. ON FOURNIT UN ORGANIGRAMME. UNE INTRODUCTION AU CODE TANGENT LINEAIRE ET ADJOINT EST EGALEMENT PROPOSEE.


Contents:

 01/ Introduction.
 02/ Definition of Eulerian and semi-Lagrangian schemes.
 03/ The 2D equations.
 04/ The 3D equations in spherical geometry (ARPEGE/IFS).
 05/ Discretisation of the equations: general aspects.
 06/ Computation of medium and origin points.
 07/ The SL discretisation of the 2D shallow-water system of equations (spherical geometry).
 08/ The SL discretisation of the 3D primitive equation model.
 09/ The SL discretisation of the fully elastic non hydrostatic (NHEE) model.
 10/ The SL discretisation of the quasi elastic non hydrostatic (NHQE) model.
 11/ "R" operator.
 12/ Computation of longitudes and latitudes on the computational sphere.
 13/ Computation of "etadot" at full levels.
 14/ Interpolations and weights computations.
 15/ Lateral boundary conditions.
 16/ 2D shallow water and 3D models organigrammes.
 17/ Tangent linear and adjoint codes.
 18/ Some distributed memory features.
 19/ Specific SL variables in pointer modules, modules and namelists.
 20/ Bibliography.

 Appendix 1/ Description of treatment of NHX for semi-Lagrangian advection.
 Appendix 2/ Description of dataflow for option LGWADV=T.


Documents
Version cycle 42 642.1 kb / PDF

Version cycle 43 642.5 kb / PDF

Version cycle 44 632.5 kb / PDF

Version cycle 45 632.6 kb / PDF

Version cycle 46 593.1 kb / PDF

Version cycle 46t1 607.2 kb / PDF

Version cycle 46t1r1 611 kb / PDF