Tests with Separated Tables for Water Vapor Saturation Pressure over Ice and Water

A modiied water vapor saturation pressure table, containing both water vapor saturation pressure over ice and over water have been introduced in HIRLAM and compared to the reference table, where one single mixed table is used. Diierent aspects of how to use this new vapor saturation pressure table are treated in this report and two tests with it are presented. The best result is obtained when the water vapor saturation pressure for calculation of stratiform precipitation is somewhat diierent from that used for the cloud cover calculation. The most remarkable improvement is for the humidity analysis and for some of the near surface parameters in winter. The veriication against soundings shows that the temperature and the dewpoint temperature are somewhat better in both summer and winter, but the eeects of the quality of geopotential height and wind speed are small. The improvement of the dewpoint analysis is assumed be an eeect of that the treatment of dewpoint is fully consistent in both the analysis and the postprocessing.