This note gives a detailed description of the algorithmic part, for the benefit of phasing, remote installations and development. A theoretical overview is recalled for completeness with the technical section. A "User’s guide" is added for the general users of 3dvar.

• Formalism of incremental variational analysis
  • 3dvar
  • Background error covariance matrix B
  • Preconditioning
  • 4dvar
• Data flow and code organisation
  • Screening
  • 3dvar minimisation
  • 4dvar minimisation
• User’s guide : scripts and namelists
  • Sequences of execution and Input/Output
  • Most important namelist parameters
  • How to check for the execution ?
  • Frequently encountered ... crashes
• Domain definitions in ALADIN
• Aspects of the data distribution on MPP machines

The 3dvar ALADIN was also presented during the 1st ALADIN phasing and maintenance workskop, Budapest, November 2002.