A Radar Data Assimilation System for Nowcasting and Very Short Range NWP

A radar data assimilation system is under development at the Naval Research Laboratory (NRL) and is being added to the NRL Atmospheric Variational Data Assimilation System (NAVDAS) to enhance the NAVDAS capability to assimilate high-resolution Doppler radar data into the Navy's Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®). This system improves the COAMPS capability and accuracy in very short range (0 – 6 hour) prediction of hazardous weather for nowcasting and has been recently upgraded with new capabilities to assimilate not only the Doppler radial velocities but also reflectivity data. Several storm cases are selected to test the upgraded system and to study the impact of radar data assimilation on model forecasts. Improvements in very short range prediction of severe weather have been made with this system. As expected, the system performs best when Doppler radial-wind and reflectivity observations are both assimilated and the analysis incremental fields are adequately constrained by the COAMPS dynamics and properly adjusted to satisfy the thermodynamical balance. The detailed results will be presented at the conference. Several challenge issues, however, still remain regarding the assimilation of radar observations of storms characterized by strong nonlinearities and discontinuities. These issues will also be discussed.