Impact of variational assimilation of MODIS thermodynamic profiles in the simulation of western disturbance

The present study was carried out to examine the impact of temperature and humidity profiles from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the numerical simulation of western disturbance (WD) using the three-dimensional variational (3D-Var) assimilation technique in the nonhydrostatic version of the Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) fifth-generation Mesoscale Model (MM5). The WD that affected northwest India during 8-11 February 2007 was chosen for the numerical simulations. The results show that there are large differences between the initial meteorological fields from the National Center for Environmental Prediction (NCEP) analysis (without satellite data; control experiment (CNT)) and the optimal initial conditions (with MODIS data; experiment (EXP)). The optimal initial condition showed that MM5 3D-Var had produced an analysis that fit the MODIS observations very well. The assimilation of the MODIS temperature and moisture profiles did not show much impact on the track of the WD but, more importantly, it showed evidence of impacting the rainfall intensity prediction by retarding the incorrect prediction of intense rainfall. The root mean square difference (RMSD) in predicted rainfall from EXP was lower than from CNT. The assimilation of MODIS data also showed a positive impact on the temperature prediction.