Simulation Experiments for Determining Wind Data Requirements in the Tropics

Abstract

Numerical simulation experiments are performed with a 9-level global general circulation model to help determine how much wind data in the tropics are needed for the reconstruction of meteorological fields. Prediction runs are updated every 12 hr with hypothetical data generated from the same model. It is found that the asymptotic root mean square (rms) wind errors in the tropics, particularly in the 11S-IIN “equatorial” latitude belt, fail to meet the GARP data requirements for the FGGE if surface pressure and temperature data alone are used for updating. The addition of tropical wind data at just two vertical levels leads to a significant, but insufficient, reduction of rrns wind errors within “tropics” (26S-26N); the largest errors remain near the equator. However, these errors become acceptably small if wind data are inserted at all 9 levels within the equatorial region. Another result is that insertion of tropical wind data at just two levels has a sizable influence upon wind errors even in the extratropics. A critique of some implicit assumptions made in simulation experiments of the type we have performed is included.