Thomas Schwitalla Institute of Physics and Meteorology University of Hohenheim

1. A Radar Data Assimilation Experiment for COPS IOP 10 with the WRF 3DVAR System in a Rapid Update Cycle Configuration. Thomas Schwitalla Institute of Physics and Meteorology University of Hohenheim

2. Motivation 13th WRF Users Workshop 2012

3. Outline • WRF model setup • Radar data assimilation in the WRF model • First radar assimilation experiment over France • Summary • Outlook 13th WRF Users Workshop 2012

4. WRF model setup • Convection permitting resolution of 3.6km • No cumulus scheme applied! • 550*550*50 grid boxes • Two-Moment microphysics • DFI initialization • Focus is set on events coming from in from the Western Europe • Direct initialization from ECMWF forecast or analysis on model levels • CV6 Background error Matrix 13th WRF Users Workshop 2012

5. 29.07.2012 Rapid Update Cycle approach with WRF Lateral boundary conditions from ECMWF analyses/forecast T 00Z 03Z 06Z 09Z 12Z Forecast Forecast Forecast Forecast Obs Obs Obs Obs T+0h T+3h T+6h T+9h T+12h T + xx hours 3DVAR 3DVAR 3DVAR 3DVAR Free forecast ECMWF analysis + DFI Update lateral boundary conditions Update low boundary 13th WRF Users Workshop 2012

6. Radar data coverage during COPS • 15 Doppler radar in total • 10 from France • 5 from Germany • S- and C-Band radars • Scanning radius up to 250km • Range resolution 1km • Rumax= 60m/s and 32m/s • 3D volume data 13th WRF Users Workshop 2012

7. Assimilation of radar data in WRF Radial velocity assimilation: Terminal velocity vT represents the fall speed of rain. It depends on the rain water mixing ratio qr under the assumption of a laminar flow (Re ≈ 300). Reflectivities (dBZ) are assimilated applying the following operator: Derived from a Marshall-Palmer distribution with N0 = 8*106m-4 13th WRF Users Workshop 2012

8. Quality control and data thinning Raw observations amount is too large and data are noisy Data thinning and filtering prior to its use in a data assimilation scheme Applied filtering procedure for e.g. German radar data: According to quality flags, the raw observation is set to missing value Calculation of a 3x3 average value Calculation of variance for every raw observation Variance rejection threshold 50dBZ² for reflectivity and 60m²/s² for radial velocity (Xiao, WRF Workshop 2008) Additional smoothing along the ray and azimuth Radial wind observation error = f(range) Reflectivity error set to 5dBZ Reflectivities are discarded above 4000m AGL and below 0°C 13th WRF Users Workshop 2012

9. Assimilation of radial velocities only 03Z (second last RUC step) 06Z, last RUC step Good agreement throughout the complete RUC 13th WRF Users Workshop 2012

10. Assimilation of radial velocities only No radar With radar winds Observation Small but positive influence on the 3h precipitation forecast (Reduction of RMSE ~6%, correlation slightly improved) 13th WRF Users Workshop 2012

11. Looks promising, but…. Assimilation of radial velocities only Last RUC step at 06UTC 13th WRF Users Workshop 2012

12. Looks promising, but…. Assimilation of reflectivities in addition Last RUC step at 06UTC Can you spot the difference? 13th WRF Users Workshop 2012

13. Looks promising, but…. Horizontal distribution of ZTD O-A No reflectivities 13th WRF Users Workshop 2012

14. Looks promising, but…. Horizontal distribution of ZTD O-A With reflectivities 13th WRF Users Workshop 2012

15. Looks promising, but…. • Model imbalances despite DFI? - Hopefully not! • Relative humidity set to 100% in the model? – Yes, set to 100% • Deficits in cloud microphysics in 3DVAR scheme? – possible • Too many observations used (approx. 5000)? 13th WRF Users Workshop 2012

16. Looks promising, but…. • Overestimation of IWV • Assimilation of reflectivities leads to larger errors in the first few hours 13th WRF Users Workshop 2012

17. Summary • Setup of a unique WRF Rapid Update Cycle over central Europe applying a convection permitting resolution • First steps to assimilate 3D volume radar data from two different networks with WRF over Europe • Results are promising, but still deficiencies due to model imbalances, deficits in clear air dynamics • Quality issues of reflectivities – bias correction required? • Problems with the humidity control variable qt in combination with the applied microphysics schemes? 13th WRF Users Workshop 2012

18. Outlook • Harmonize radar data quality and interpolation procedures  OPERA European radar data base • Statistical evaluation of assimilating radar reflectivities • Check short-term forecasts inside RUC • Utilize polarization radar data ( CAOS) • Comparison of 3DVAR-RUC and 4DVAR (challenging….) • Testing (hybrid) ensemble data assimilation methods (EnKF, 3DVAR-ETKF, Ensemble-3DVAR) • Incorporate GPS slant total delays and/or more ZTD data if available to further improve the water vapor fields 13th WRF Users Workshop 2012

19. Acknowledgements • WRF team (especially Wei, Cindy, Xin and John) • Galina Dick from GFZ Potsdam • Klaus Stephan from the German Meteorological Service • Olivier Caumont from Météo France • ECMWF • High Performance Computing Center Stuttgart (HLRS) 13th WRF Users Workshop 2012

20. Thanks for your attention! 13th WRF Users Workshop 2012

21. Results for COPS IOP10 performing a 3h RUC for 18 hours starting at 12Z, July 22, 2007 13th WRF Users Workshop 2012

22. Radar data assimilation experiment for COPS IOP 10 13th WRF Users Workshop 2012

23. Looks promising, but…. 16.04.2012 13th WRF Users Workshop 2012 Institut für Physik und Meteorologie