Abstract. In this work, a new forward
polarimetric radar operator for the COSMO numerical weather prediction (NWP)
model is proposed. This operator is able to simulate measurements of radar
reflectivity at horizontal polarization, differential reflectivity as well as
specific differential phase shift and Doppler variables for ground based or
spaceborne radar scans from atmospheric conditions simulated by COSMO. The
operator includes a new Doppler scheme, which allows estimation of the full
Doppler spectrum, as well a melting scheme which allows representing the very
specific polarimetric signature of melting hydrometeors. In addition, the
operator is adapted to both the operational one-moment microphysical scheme
of COSMO and its more advanced two-moment scheme. The parameters of the
relationships between the microphysical and scattering properties of the
various hydrometeors are derived either from the literature or, in the case
of graupel and aggregates, from observations collected in Switzerland. The
operator is evaluated by comparing the simulated fields of radar observables
with observations from the Swiss operational radar network, from a high
resolution X-band research radar and from the dual-frequency precipitation
radar of the Global Precipitation Measurement satellite (GPM-DPR). This
evaluation shows that the operator is able to simulate an accurate Doppler
spectrum and accurate radial velocities as well as realistic distributions of
polarimetric variables in the liquid phase. In the solid phase, the simulated
reflectivities agree relatively well with radar observations, but the
simulated differential reflectivity and specific differential phase shift
upon propagation tend to be underestimated. This radar operator makes it
possible to compare directly radar observations from various sources with
COSMO simulations and as such is a valuable tool to evaluate and test the
microphysical parameterizations of the model.
From model to radar variables: a new forward polarimetric radar operator for COSMO
