Global Observing System Experiments on Operational Statistical Retrievals of Satellite Sounding Data

We report an observing system experiment on satellite sounding data during a 15.5-day period in January–February 1987, using the operational European Centre for Medium Range Weather Forecasts (ECMWF) system as it was in late July 1988. The forecast results show a negative impact of the satellite sounding data (SATEM) in the Northern Hemisphere, and a strong positive impact in the Southern Hemisphere. The model and analysis developments implemented between July 1987 and July 1988 led to forecast improvements whether or not SATEM data were used. Improvements were larger in the NoSATEM context. Consequently, the neutral Northern Hemisphere impact of SATEM data with the 1987 system became a negative impact with the 1988 system. Thus, recent changes in the analysis–forecast system have made the system more sensitive to data, and therefore more vulnerable to bad data. We show that the statistical retrievals have serious errors and biases. The biases are airmass-dependent and so have strong regional variations.