Observing System Experiments Using the AFGL Four-Dimensional Data Assimilation System

Abstract

Abstract Five observing system experiments have been performed with the Air Force Geophysics Laboratory (AFGL) global data assimilation system (GDAS). Each experiment includes one week of data assimilation during each of the two special observing periods of the First GARP Global Experiment (FGGE) of 1979, and three 4-day forecasts. The first experiment (STATSAT) provides a baseline for comparison. It uses all the available level II-b FGGE data, except surface observations. Comparisons with the National Meteorological Center (NMC) level III-A analyses show that the AFGL GDAS performs adequately. In the second experiment (NOSAT) all satellite data are removed from the dataset, showing the sensitivity of the AFGL GDAS to satellite data. As expected the impact on the analysis is small in the Northern Hemisphere, but large in the Southern Hemisphere. In the third experiment (GLASAT), the effect of a physical satellite retrieval method is tested by using the temperature profiles provided by NASA Goddard laborat...