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Stefan Klink Data Assimilation Section stefan.klink@dwd.de

Early results with rainfall assimilation at DWD RADVOR-OP, supported by LAWA. Stefan Klink Data Assimilation Section stefan.klink@dwd.de. Early results with rainfall assimilation at DWD. Radar data Real case study Humidity adjustment Filtering of vertical profiles

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Stefan Klink Data Assimilation Section stefan.klink@dwd.de

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  1. Early results with rainfall assimilation at DWDRADVOR-OP, supported by LAWA Stefan Klink Data Assimilation Section stefan.klink@dwd.de 08.10.2003 - 1 -

  2. Early results with rainfall assimilation at DWD Radar data Real case study Humidity adjustment Filtering of vertical profiles Influence of convective parameterisation scheme Influence of mesh size Summary 08.10.2003 - 2 -

  3. Radar data Input data currently used • radar reflectivity at the ground (int. Composite: Germany and surrounding countries) • pixel size: 4km  4km • time resolution: 15 minutes (data from volume scan) • conversion: reflectivity to precipitation rate by simple Z-R-relation • problems: clutter, only 7 reflectivity classes 08.10.2003 - 3 -

  4. Radar data „new“ radar data • input data: reflectivities from precipitation scan, mesh: 1km  1°, time resolution: 5 minutes • correction of orographic attenuation • variable Z-R-relation • compositing • still incomplete clutter correction 08.10.2003 - 4 -

  5. operational domain (7 km) experimental domain (2.8 km) evaluation domain Real case study: experimental setup • Convective event on 28. Aug. 2002 over western Germany • LM runs on the operational domain: • mesh size 7 km • LM runs on an experimental domain: • covering almost Germany • mesh size 2.8 km • convective parameterisation scheme switched off • laterally driven by GME • 6h Nudging + LHN starting at 6 UTC • adjustment of humidity during LHN • 6h free forecast starting at 12 UTC 08.10.2003 - 5 -

  6. Real case study: humidity adjustment • Increased heating  increase q to reach f=100% over nudging timescale  • Reduced heating  decrease q (maintain f) 08.10.2003 - 6 -

  7. Real case study: humidity adjustment LM runs on the experimental domain: • mesh size 2.8 km • without humidity adjustment during LHN • with humidity adjustment during LHN 08.10.2003 - 7 -

  8. Hourly sums of modeled and radar-observed precipitation in mm/h Nudging 08-09 UTC Nudging11-12 UTC Real case study: humidity adjustment 08.10.2003 - 8 -

  9. free forecast14-15 UTC Real case study: humidity adjustment 08.10.2003 - 9 -

  10. Real case study: filtering of vertical profiles vertical cross section W-E, t = 11 UTC, with humidity adjustment specific cloud liquid water content in g/kg no filtering filtering 08.10.2003 - 10 -

  11. Real case study: influence of convective parameterisation scheme LM runs on the operational domain: • mesh size 7 km • no adjustment of humidity during LHN • without convective parameterisation scheme • with convective parameterisation scheme 08.10.2003 - 11 -

  12. Hourly sums of modeled and radar-observed precipitation in mm/h Nudging 08-09 UTC Nudging 09-10 UTC Real case study: influence of convective parameterisation scheme 08.10.2003 - 12 -

  13. Nudging 11-12 UTC free forecast 12-13 UTC Real case study: influence of convective parameterisation scheme 08.10.2003 - 13 -

  14. free forecast 14-15UTC Real case study: influence of convective parameterisation scheme 08.10.2003 - 14 -

  15. Case Studies: comparison: mesh sizes 7 km and 2.8 km LM runs: • CTRL 7 km: • mesh size 7km (operational domain) • LHN 7 km: • mesh size 7 km (operational domain) • LHN 2.8 km: • mesh size 2.8 km (smaller model domain) 08.10.2003 - 15 -

  16. Hourly sums of modeled and radar-observed precipitation in mm/h Nudging06- 07 UTC Nudging 08-09 UTC Case Studies: comparison: mesh sizes 7 km and 2.8 km 08.10.2003 - 16 -

  17. Nudging 11-12 UTC free forecast 12-13 UTC Case Studies: comparison: mesh sizes 7 km and 2.8 km 08.10.2003 - 17 -

  18. free forecast 14-15 UTC free forecast 17-18 UTC Case Studies: comparison: mesh sizes 7 km and 2.8 km 08.10.2003 - 18 -

  19. Summary • Results: • adjustment of humidity supports the assimilation of precipitation and leads to more exact free forecasts • explicit simulation of convection produces more realistic patterns and amounts of precipitation than the corresponding model run with a parameterisation scheme • model with 2.8 km mesh size shows potential for further improvements of precipitation forecast • sporadical occurrence of spurious precipitation • influence of the assimilation lasts for several hours 08.10.2003 - 19 -

  20. Summary • Future work: • numerical problems with noisy profiles of latent heat (2 z-structures) • quality of radar data • improvements to extend the influence of assimilation during free model run • prognostic precipitation 08.10.2003 - 20 -

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