Cycle 23r1 summary of changes

12 September 2000 The data assimilation procedure moved from 6-hour to 12-hour cycling. 4D-Var now processes the observations in 12-hour sets, spanning 03 -15 UTC for the 12 UTC analysis, and 15 - 03 UTC for the 00 UTC analysis. Surface analyses still run every six hours. Analysis fields are still archived every six hours. Other changes included in this model version are :

  • use of more accurate background trajectory in 4D-Var, thanks to an improved interpolation procedure, the use of the prognostic cloud scheme and first-guess cloud fields;
  • change to the 4D-Var incremental formulation by which the low-resolution increment is added to the high-resolution trajectory at analysis time (00 UTC and 12 UTC), instead of at the start of the 4D-Var window;
  • new quality-control step that prevents the use of observations that the incremental formulation of 4D-Var cannot handle correctly;
  • resetting of the stratospheric ozone and switching off of the multivariate coupling between ozone and vorticity;
  • monitoring of TOVS radiances in cloudy areas.


Cycle changes

Please note

Prior to 2006 information on cycle upgrades has been migrated from the old website to the new website "as is". The information has not been reviewed during the migration.