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Martin Weissmann, Andreas Dörnbrack,

Improved Water Vapour and Wind Initialisation for Precipitation Forecasts: Impact Studies with the ECMWF IFS. Martin Weissmann, Andreas Dörnbrack, Gerhard Ehret, Christoph Kiemle, Stephan Rahm, Oliver Reitebuch Institut für Physik der Atmosphäre, DLR Oberpfaffenhofen, Germany

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Martin Weissmann, Andreas Dörnbrack,

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  1. Improved Water Vapour and Wind Initialisation for Precipitation Forecasts: Impact Studies with the ECMWF IFS Martin Weissmann, Andreas Dörnbrack, Gerhard Ehret, Christoph Kiemle, Stephan Rahm, Oliver Reitebuch Institut für Physik der Atmosphäre, DLR Oberpfaffenhofen, Germany Carla Cardinali, Elias Holm European Centre for Medium-Range Weather Forecasts (ECMWF), Reading, UK

  2. AMSU-A: 50-55 GHz Motivation above oceans: hardly any radiosondes aircraft at cruise level height errors of AMVs low accuracy of passive instruments low vertical and horizontal resolution lidars can measure various atmospheric quantities in remote regions with high accuracy and high resolution either from satellites or aircraft goal: estimate benefit with impact studies

  3. dropsondes, u, v, t, rh, p DLR lidar instruments Doppler lidar DIAL lidar Differential Absorption Lidar (DIAL) nadir or zenith pointing profile of water vapour molecule number horiz. resolution: 2 - 40 km vert. resolution: 500 - 2000 m scanning coherent 2 µm Doppler lidar conical scans with 24 azimuth positions vertical profile of 3-D wind vector horiz. resolution 5 - 40 km vert. resolution 100 m

  4. Wind data - Atlantic THORPEX Regional Campaign (A-TReC) DLR Falcon: 14 - 28 Nov. 2003 4 flights in "sensitive areas" (targeting) 1 flight for Greenland Tip Jet 1 flight for intercomparison ASAR and lidar 2 transfer flights ======================================= 8 flights, 1600 wind profiles, 40 000 lidar measurements, 49 dropsondes 5 million operational measurements used per day lidar = 0.005% additional measurements

  5. Observations on 25 November 2003 Iceland Ireland http://www.sat.dundee.ac.uk/ ECMWF sensitivity plot and 500 hPa

  6. Dropsonde (2000 times enlarged) Instrumental and representativeness errors Error lidar 1-1.5 m/s Error drops/raso 2-3 m/s Background departures: (Std(bg-dep))2 = (Stdobs)2 + (Stdbg)2 Error AMV 2-5 m/s

  7. Observation influence (22 November 2003) observation influence (Cardinali et al. 2004): 0 --> no influence of observations 1 --> no influence of background mean global observation influence = 0.15

  8. area: 17 x 10-6 km2 Reduction of forecast error at 500 hPa - 72 h (gpdm)

  9. Reduction of forecast error - 500 hPa Mean reduction over Europe, averaged over 29 forecasts (~2 weeks) black: experiments with lidar, gray: experiment with 100 dropsondes

  10. Simmons and Hollingsworth 2002: 72 h: 10 m in 10 years Comparison to mean reduction of NWP error Reduction of forecast error of 500 hPa geopotential height: Lidar 72 h: ~ 1 m (3.5%)

  11. Reduction of forecast error - 48, 72, 96 h

  12. Relative reduction of RH forecast error - 48, 72, 96 h • Reduction of u, v, z, rh, and t forecast errors

  13. DLR NOAA A-TReC targeting campaigns 20031115 at 18 Step42 20031120 at 18 Step54 Cut off low; heavy precipitation in SE-Spain Heavy rain/strong wind in Portugal and NW-Spain 20031125 at 18 Step30 20031122 at 18 Step66 Strong winds –northwest Europe Heavy rain, Scotland and Norway

  14. The influence of targeted observations ­ ­ + + statistical problem --> larger sample 63 - 90% of total impact outside of verification area --> larger areas improved sensitivity predictions better structure functions practical restrictions --> better planning

  15. DIAL lidar water vapour observations Transfer flights to 4 field campaigns during 2002 - 2005

  16. Latitude 60 W 20 W 20 E Longitude Impact of lidar H2O-observations (preliminary) WV mixing ratio [mg/kg] Reduction of TCWV first guess error (lidar - control)

  17. Conclusions first assimilation of "real" Doppler lidar measurements in global NWP model lidar measurements have a smaller error than all other operational wind observations --> high analysis influence and information content lidar wind measurements reduce the average forecast error of u, v, z, rh, and t over Europe average reduction of the 48 - 96h forecast error over Europe ~3% limitations of targeted observations: need for more cases, larger verification area, systematic decisions, better structure functions... ongoing water vapour studies emphasizes the potential of airborne and spaceborne lidars (ADM-Aeolus, possible future water vapour DIAL satellite) future campaigns: COPS 2007, IPY 2008, T-PARC 2008 www.pa.op.dlr.de/na-trec/

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