Description of the upgrade

  • Revised convection scheme numerics and calling of the cloud scheme
  • Use of tangent linear and adjoint of vertical diffusion in the 1st minimization of 4D-Var
  • Reduction of radiation frequency to 1 hour in the high-resolution forecasts
  • Improved numerics of surface tile coupling
  • Post-processing of total- column liquid water and ice.
  • RTTOV-8
  • Minor revisions to ATOVS and AIRS usage
  • Assimilation of MSG clear-sky radiances and GOES 9 BUFR AMVs
  • Assimilation of SCIAMACHY ozone products from KNMI
  • Correct error in AMSU-B usage over land
  • Activate EARS data.
Data assimilation:
  • Blacklist SYNOP humidity data at local night time (solar elevation SOE less than zero)
  • Increased use of radiosonde humidity: use RS90 to -80C, RS80 to -60C, other sensors to -40 C
  • Proper cycling of the information from the wave altimeter and the surface data analyses (FG forecasts moved from 00 and 12 UTC to 06 and 18 UTC)
  • Gaussian sampling for extra-tropical singular vectors (instead of selection and rotation)
  • Revision of initial condition perturbations for tropical cyclones (TC)
    • Initial condition perturbations extended to latitude belt 40 S 40 N (from 25 S 25 N)
    • Tropical singular vectors are computed in the subspace orthogonal to the leading 25 extra-tropical singular vectors
    • New algorithm to determine optimisation regions based on predicted TC tracks from previous EPS run
    • The Caribbean remains an optimisation region if no TC in the vicinity
    • Ortho-normalisation applied to set of all tropical SVs
Verification results gathered to date from the experimental suite and from several months of research experiments in winter and summer indicate that, in general, the impact of the new cycle is neutral to slightly positive in the extra-tropical troposphere in the deterministic forecasting system for the total sample of experiments. Wind and temperature scores in the tropical troposphere show small improvements, but stratospheric temperature biases are slightly larger. This issue is being addressed.
There are, however, noticeable changes in the EPS. The revision of initial condition perturbations for TCs, including the use of tropical cyclone tracks from the previous EPS run, improves the TC track forecasting giving a better spread and skill in the strike probability. The revised numerics in the convection scheme and calling of the cloud scheme has reduced the performance differences between the T511 forecast and the T255 control.
The previously experienced tendency in the EPS to develop spuriously deep lows has been reduced, providing better synoptic guidance with a smaller spread without affecting the overall skill of the EPS. Users also need to be aware of the changes in the generation of initial EPS perturbations. With the introduction of the Gaussian sampling the one to one positive and negative perturbations will no longer be present.
  • archive and disseminate step 0 for the deterministic forecast (as this is used in the generation of weather parameter products)
  • omit production of step 0 for BC project forecasts (was available in FDB only)
  • omit production of step 3 and 9 for eps control forecasts (to overcome a inconsistency between the control forecast and the perturbed forecasts and allow comparison of cumulative and mean fields)
  • archive tropical cyclone tracks in BUFR format in MARS
The change to the new cycle is transparent for users apart from a change in the atmospheric model identification number in GRIB headers, which will be set to 124.

Implemented: 28 September 2004