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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 1 - Stefan Klink Data Assimilation Section stefan.klink@dwd.de Early results with rainfall assimilation at DWD RADVOR-OP, supported by LAWA
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 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
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 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
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 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
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 5 - 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 operational domain (7 km) experimental domain (2.8 km) evaluation domain
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 6 - Real case study: humidity adjustment Increased heating increase q to reach f=100% over nudging timescale Reduced heating decrease q (maintain f)
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 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
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 8 - Real case study: humidity adjustment Hourly sums of modeled and radar- observed precipitation in mm/h Nudging 08-09 UTC Nudging 11-12 UTC
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 9 - Real case study: humidity adjustment free forecast 14-15 UTC
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 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
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 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
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 12 - Real case study: influence of convective parameterisation scheme Hourly sums of modeled and radar- observed precipitation in mm/h Nudging 08-09 UTC Nudging 09-10 UTC
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 13 - Real case study: influence of convective parameterisation scheme Nudging 11-12 UTC free forecast 12-13 UTC
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 14 - Real case study: influence of convective parameterisation scheme free forecast 14-15 UTC
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 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)
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 16 - Case Studies: comparison: mesh sizes 7 km and 2.8 km Hourly sums of modeled and radar- observed precipitation in mm/h Nudging 06- 07 UTC Nudging 08- 09 UTC
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 17 - Case Studies: comparison: mesh sizes 7 km and 2.8 km Nudging 11-12 UTC free forecast 12-13 UTC
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 18 - Case Studies: comparison: mesh sizes 7 km and 2.8 km free forecast 14-15 UTC free forecast 17-18 UTC
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 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
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Joint SRNWP/COST-717 WG-3 session, Lisbon 08.10.2003 - 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
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