DOPPLER WIND LIDAR MEASUREMENTS SCENARIOS IN THE TROPICS

This study compares dynamical aspects of the assimilation of space-borne wind observations from several scenarios with two Doppler wind lidars (DWL) in space. The impact is measured with respect to ADM-Aeolus, a DWL satellite built by the European Space Agency with launch scheduled for 2009. In particular, the role of the background-error covariances in the tropics is studied in the context of “identical twin ” observing system simulation experiments. The assimilation model describes the horizontal structure of potential temperature and wind fields in regions of deep tropical convection. The background-error covariances are derived from the tropical forecast errors of the ECMWF model. The difficulty with making use of balance relationships in tropical three-dimensional variational assimilation is illustrated. Results show that for large-scale tropical conditions and using reliable background-error statistics, differences among various scenarios are not large. As the background-error covariances becomes less reliable, horizontal scales become smaller and the flow becomes less zonal, importance of observing information on the wind vector increases