Description of the upgrade

1. a stability check of the temperature profiles deduced from the TOVS. As large errors in the lowest layer of TOVS data tend to be compensated aloft by errors of opposite sign, incorrect data are spotted by checking the difference in temperature between two layers, namely 1000/700 and 500/300 hPa, against the first-guess. The first guess check is also tightened for certain layers.
2. a revision of the observation error statistics for thicknesses: the horizontal correlation function is flattened and the error variances are distributed more evenly to the different layers.
3. a change to the SATOB OI-check: as introduced for SATEM in July 1988, SATOB are now checked without influence from neighbouring data of the same type.
4. modifications to the use of Precipitable Water Content data (PWC) from NOAA-10 and NOAA-11. The PWC are not used over land, nor when no thickness data are available in the same report; their observation error has been increased.