Revisions during 1992

7 January 1992 In model cycle 41 the horizontal diffusion was increased and the time-stepping for cumulus momentum transfer was changed. The diffusion was modified again on 15 January 1992.

20 February 1992 PAOB surface data from the Australian Bureau of Meteorology re-introduced for use in the analysis.

13 May 1992 Cycle 42

2 June 1992 A change to the determination of sea ice in the SST analysis was introduced, leading to an improved description of the ice edge.

9 June 1992 Two changes were introduced in the analysis:

1. humidity data from SYNOP observations were excluded from the analysis, to reduce excessive convective precipitation in short and early medium-range forecasts;



2. a redundancy check on aircraft data was introduced so that new high density data (ACARS) can be correctly used in the O1 scheme.

23 June 1992 The temperature data from the NOAA satellites used in the analysis of the Northern Hemisphere are now derived from cloud cleared radiance data received from NESDIS, using a 1D-variational inversion technique.

17 August 1992 A change was made to the forecast model (cycle 43), to include:

• introduction of vertically non-interpolating semi-Lagrangian scheme and smaller time filter;



• suppression of inversion clouds at the lowest three model levels rather than just the lowest level;



• introduction of a prognostic equation for sea-ice temperature to replace the use of climatological values;



• other minor parametrization changes.

1 September 1992 Cycle 44

7 December 1992 A modification to the model post-processing was implemented (model cycle 45) to improve the extrapolation of temperature and MSL pressure under model orography. The resulting extrapolated fields better continue the free atmosphere distribution of fields and show much less dependence on the overlying orography.