Evaluation of the COSMO model (v5.1) in polarimetric radar space – impact of uncertainties in model microphysics, retrievals and forward operators

Abstract

Abstract. Sensitivity experiments with a numerical weather prediction (NWP) model and polarimetric radar forward operator (FO) are conducted for a long-duration stratiform event over northwestern Germany to evaluate uncertainties in the partitioning of the ice water content and assumptions of hydrometeor scattering properties in the NWP model and FO, respectively. Polarimetric observations from X-band radar and retrievals of hydrometeor classifications are used for comparison with the multiple experiments in radar and model space. Modifying the critical diameter of particles for ice-to-snow conversion by aggregation (Dice) and the threshold temperature responsible for graupel production by riming (Tgr), was found to improve the synthetic polarimetric moments and simulated hydrometeor population, while keeping the difference in surface precipitation statistically insignificant at model resolvable grid scales. However, the model still exhibited a low bias (lower magnitude than observation) in simulated polarimetric moments at lower levels above the melting layer (−3 to −13 ∘C) where snow was found to dominate. This necessitates further research into the missing microphysical processes in these lower levels (e.g. fragmentation due to ice–ice collisions) and use of more reliable snow-scattering models to draw valid conclusions.

Combining Triple‐Moment Ice With Prognostic Liquid Fraction in the P3 Microphysics Scheme: Impacts on a Simulated Squall Line

“…Although this study only examined a single case, the changes to reflectivity structure and the bright band with predicted liquid fraction are consistent with expected behavior, and likely to be general. A more in‐depth analysis of the simulated bright band (e.g., Shrestha et al., 2022) could include changing the options for the parameterization of particle properties (e.g., mixture and inclusion) in the equivalent reflectivity calculations of P3. While there is evidence from this case study that the reflectivity structure is generally improved, no claims can be made that the overall model performance is improved or deteriorated.…”

Evaluation of cloud and precipitation processes in regional and global models with ULTIMATE (ULTra-sIte for Measuring Atmosphere of Tokyo metropolitan Environment): A case study using the dual-polarization Doppler weather radars

“…For evaluations of numerical models using data from polarimetric radars, the use of observation simulators is becoming a standard approach (Matsui et al 2019b(Matsui et al , 2020Shrestha et al 2022). Bringi et al (2020) proposed how to improve rain and riming processes of cloud microphysics schemes using polarimetric radar observations.…”

A New Melting Model and Its Implementation in Parameterized Forward Operators for Polarimetric Radar Data Simulation With Double Moment Microphysics Schemes

“…This was extended to include dual-polarization variables in the Bonn Polarimetric Radar forward Operator (B-PRO) based on the T-matrix method for calculating scattering amplitudes (Xie et al, 2021). Shrestha, Mendrok and Brunner (2022), Shrestha, Mendrok, Pejcic et al (2022), and Shrestha, Tromel, et al (2022) used the B-PRO to reproduce the polarimetric features observed in convective storms and stratiform events. Wolfensberger and Berne (2018) proposed a polarimetric radar forward operator for the COSMO model which allows estimation of the full Doppler spectrum.…”

“…Shrestha, Mendrok and Brunner (2022), Shrestha, Mendrok, Pejcic et al. (2022), and Shrestha, Tromel, et al. (2022) used the B‐PRO to reproduce the polarimetric features observed in convective storms and stratiform events.…”