Spectral transforms in the cycle 46t1r1 of ARPEGE/IFS.

ARPEGE/IFS, ALADIN and AROME are spectral models, so this documentation has for purpose to describe the spectral transforms done. The present note has for aim to give a brief summary of the spectral method (how to compute Legendre polynomials, spectral transforms) and to describe parts of the code performing spectral transforms (organigramme).

ARPEGE/IFS, ALADIN ET AROME SONT DES MODELES SPECTRAUX, EN CONSEQUENCE CETTE DOCUMENTATION A POUR BUT DE DECRIRE LES TRANSFORMEES SPECTRALES NECESSAIRES POUR PASSER DE L’ESPACE SPECTRAL VERS L’ESPACE POINT DE GRILLE. ON Y FAIT UN BREF RAPPEL DE LA METHODE SPECTRALE (COMMENT CALCULER LES POLYNOMES DE LEGENDRE ET LES TRANSFORMEES SPECTRALES). ON Y DECRIT LES PARTIES DE CODE FAISANT DES TRANSFORMEES SPECTRALES, AVEC FOURNITURE DE QUELQUES ORGANIGRAMMES.

• 1/ Introduction.
• 2/ Theoretical aspects.
• 3/ Set-up routines.
• 4/ Spectral transforms routines: the general routines (E)DIR_TRANS and (E)INV_TRANS.
• 5/ Spectral transforms routines for general application.
• 6/ Spectral transforms used in the model under routine STEPO and for specific applications.
• 7/ Some distributed memory features.
• 8/ Specific variables in modules and namelists.
• 9/ Bibliography.

• A1/ Expression of the laplacian in spectral space (spherical geometry).
• A2/ Computation of Gaussian latitudes and Gaussian weights (spherical geometry).
• A3/ Computation of the normalized Legendre polynomials (spherical geometry).
• A4/ Fair numbers between 1 and 50000 writing 2**(1+p) 3**q 5**r.