* Geostationary Observing System Simulation Experiment: Four experimental simulations have been completed that compare the impact of assimilating retrievals from a geostationary radiometer (GR) to retrievals from a geostationary interferometer (GI). A 'no observation' (NO) simulation and a 'perfect observation' (PO) simulation were also generated to provide a range of expected performance. GR and GO temperature/dew point profiles were simulated by mapping expected errors onto the PO profiles. All profiles (approximately 5000) were assimilated at one hour intervals, for a period of 12 hours, into the Rapid Update Cycle (RUC) forecast model. A 12 hour forecast was generated after the assimilation period. The root-mean-square fit of each simulation was computed against 'perfect observations from the 'nature' run. The results for 700hPa relative humidity and 300hPa temperature are shown in the attached images. The GI simulation is able to retain more information than the GR simulation. (R. Aune, E/R2, 608-264-5325)