Assimilation of radar reflectivity via a full-hydrometeor assimilation scheme based on the WSM6 microphysics scheme in WRF 4D-Var

We found that the nonlinearity of the radar operator in the two direct reflectivity assimilation experiments requires more iterations for cost function reduction than in the indirect assimilation method. The hydrometeor fields were reasonably analyzed using the full-hydrometeor assimilation scheme, particularly improving the simulation of ice-phase hydrometeors and reflectivity above the melting layer. The assimilation of radar reflectivity led to improvements in short-term (0-3 h) precipitation forecasting with the full-hydrometeor assimilation scheme.

Assimilation experiments across multiple case studies reaffirmed that assimilating radar reflectivity observations with the full-hydrometeor assimilation scheme accelerated model spinup and yielded enhancements in 0-3-h total accumulate precipitation forecasts for a range of precipitation thresholds.