EGU22-12147
https://doi.org/10.5194/egusphere-egu22-12147
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Evaluation of the COSMO model in polarimetric radar space – impact of uncertainties in model microphysics, retrievals and forward operators

Prabhakar Shrestha1, Jana Mendrok2, Velibor Pejcic1, Silke Trömel1,3, Ulrich Blahak2, and Jacob Carlin4,5
Prabhakar Shrestha et al.
  • 1Bonn University, Institute for Geosciences, Department of Meteorology, Bonn, Germany
  • 2Deutscher Wetterdienst, Offenbach, Germany
  • 3Laboratory for Clouds and Precipitation Exploration, Geoverbund ABC/J, Bonn, Germany
  • 4Cooperative Institute for Mesoscale Meteorological Studies, University of Oklahoma, Oklahoma, USA
  • 5NOAA/OAR National Severe Storms Laboratory, Norman, Oklahoma, USA

Polarimetric observation operators generate virtual observations from the models, which enable a direct comparison of observed and simulated radar signatures of microphysical processes. However, differences in polarimetric fingerprints between observations and models may result both from model deficiencies and faulty assumptions in observation operators. Using the Bonn Polarimetric Radar forward Operator (B-PRO), the evaluation of the German weather forecast model COSMO in radar observation space revealed deficiencies in the ice-snow partitioning and spurious graupel production near the melting layer. Follow-up sensitivity experiments with the model and forward operator (FO) guided the improvement of model parameters, namely the critical diameter of particles for ice-to-snow conversion by aggregation (Dice) and the threshold temperature responsible for graupel production by riming (Tgr), pushing the synthetic radar variables closer to the observations. 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. Sensitivity experiments with the FO also could not explain this bias indicating shortcoming in the FO or missing cloud microphysical processes in the 2-moment cloud microphysical scheme of the model.

How to cite: Shrestha, P., Mendrok, J., Pejcic, V., Trömel, S., Blahak, U., and Carlin, J.: Evaluation of the COSMO model in polarimetric radar space – impact of uncertainties in model microphysics, retrievals and forward operators, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12147, https://doi.org/10.5194/egusphere-egu22-12147, 2022.

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