Advancements in the Assimilation of Spaceborne Radar Observations

Conventional passive instruments encounter limitations in capturing vertical cloud and precipitation distributions, a gap addressed by active radar instruments. However, integrating these active radar measurements into data assimilation systems introduces challenges, driven by the lack of efficient forward radiative transfer models and complexities in error characterization. This presentation discusses the evolution, systematic evaluation, and comprehensive sensitivity analysis of an innovative forward radar model seamlessly incorporated within the CRTM framework.

The forward model relies on the hydrometeor scattering properties generated using the discrete dipole approximation technique. The model can compute reflectivity and attenuated reflectivity across diverse radar instruments and zenith angles as long as the instrument-specific coefficients for CRTM are available. Rigorous evaluation utilizing CloudSat measurements reveals substantial agreement between simulations and observations, contingent upon consistency between hydrometeor input profiles and measured reflectivity profiles.

Current efforts include the integration of the forward radar simulator into the Joint Effort for Data assimilation Integration (JEDI) framework. This integration not only includes generating new observation formats for spaceborne radars, but also adapting the Unified Forward Operator to effectively process radar measurements. This ongoing initiative provides new capabilities for the assimilation of spaceborne radar measurement, which can lead to improving the representation of precipitation and clouds in the NWP models.