Eidgenssisches Departement des Innern EDI Bundesamt fr Meteorologie

Eidgenössisches Departement des Innern EDI Bundesamt für Meteorologie und Klimatologie Meteo. Schweiz Institut für Physik der Atmosphäre On the Value of Radar-Derived Rainfall Assimilation on High-Resolution QPF Daniel Leuenberger 1, Christian Keil 2 and George Craig 2 1 Meteo. Swiss, Zurich, Switzerland 2 DLR, Oberpfaffenhofen, Germany COSMO GM 2008, Cracow

Introduction • Convective-scale assimilation of radar rainfall data • Latent Heat Nudging (LHN) • Results of a 7 month test suite at Meteo. Swiss • What determines the impact of LHN on QPF? Value of Radar Assimilation for QPF daniel. leuenberger@meteoswiss. ch COSMO GM 2008, Cracow 2

Meteo. Swiss Model Setup ECMWF IFS COSMO-7 • 6. 6 km, 60 levels • Param. deep convection • Assimilation of conv. obs. COSMO-2 • 2. 2 km, 60 levels • Explicit deep convection • Assimilation of conv. obs. and radar rainfall Radar ~600 km Value of Radar Assimilation for QPF daniel. leuenberger@meteoswiss. ch COSMO GM 2008, Cracow 3

Setup of Experiments • 2. 2 km assimilation cycle with/without LHN • Forecasts out to +12 h, initialized at 00 and 12 UTC • 11. June 2007 – 15. January 2008 (346 forecasts) Value of Radar Assimilation for QPF daniel. leuenberger@meteoswiss. ch COSMO GM 2008, Cracow 4

Examples of Improvement 0 -6 h Precipitation forecast (12. 06. 2007) LHN NOLHN 6 -12 h Precipitation Forecast (19. 06. 2007) LHN Value of Radar Assimilation for QPF NOLHN daniel. leuenberger@meteoswiss. ch Verifying Radar COSMO GM 2008, Cracow 5

Verification against Radar 346 Forecasts, 11. June 2007 - 15. January 2008, hourly sums Value of Radar Assimilation for QPF daniel. leuenberger@meteoswiss. ch COSMO GM 2008, Cracow 6

Verification against Radar (Summer) 9 Forecasts, 11. June - 19. July 2007, hourly sums Value of Radar Assimilation for QPF daniel. leuenberger@meteoswiss. ch COSMO GM 2008, Cracow 7

Verification of other Variables RMS of 74 12 UTC Forecasts (Reference: ca. 60 Swiss Sfc. Stations) Wind direction 10 m Wind speed 2. 25 66 330 2. 20 64 325 deg 335 m/s Pa Surface Pressure 2. 15 62 60 2. 10 320 NOLHN 315 12 13 18 00 Time UTC Value of Radar Assimilation for QPF 2. 05 12 13 18 00 Time UTC daniel. leuenberger@meteoswiss. ch 58 12 18 00 13 Time UTC COSMO GM 2008, Cracow 8

Verification of other Variables RMS of 74 12 UTC Forecasts (Reference: ca. 60 Swiss Sfc. Stations) 2. 6 32 2. 8 2. 4 30 2. 6 2. 2 K NOLHN 2. 4 28 26 12 K 3. 0 34 % 2 m Temperature 2 m Dewp. Temperature Cloud cover 18 00 13 Time UTC Value of Radar Assimilation for QPF 2. 0 2. 2 12 13 18 00 Time UTC daniel. leuenberger@meteoswiss. ch 1. 8 12 13 18 00 Time UTC COSMO GM 2008, Cracow 9

What determines the impact of LHN? • Use high-resolution NWP ensemble (2. 8 km mesh size) • Driven by regional COSMO-LEPS ensemble • 10 members with LHN, 10 members without • Different mesoscale environment in each member • 3 differently forced convection cases 31. July 2006 28. June 2006 12. July 2006 forced frontal non-forced frontal airmass Value of Radar Assimilation for QPF daniel. leuenberger@meteoswiss. ch COSMO GM 2008, Cracow 10

Example: Airmass convection Timelines of observed and simulated area-averaged surface rainfall LHN NOLHN mm 1. 0 Assimilation 0. 8 0. 6 Radar 0. 4 NWP Ensemble 0. 2 0. 0 06 Forecast 09 12 18 15 Time UTC Value of Radar Assimilation for QPF 21 00 06 09 daniel. leuenberger@meteoswiss. ch 12 18 15 Time UTC COSMO GM 2008, Cracow 00 21 11

Definition of Time Scales • LHN impact factor FLHN 1 0. 5 t. LHN time • LHN time scale t. LHN • Convective time scale • Done et al. (QJ 2006) Value of Radar Assimilation for QPF daniel. leuenberger@meteoswiss. ch COSMO GM 2008, Cracow 12

Stratification of Simulations • equilibrium situation: • short tc • precipitation only redistributed • short-lived impact of LHN • non-equilibrium situation: • long tc • LHN triggers convection • long lasting impact of LHN 100 t. LHN [h] Results suggest 2 different regimes: forced frontal, non-forced frontal airmass 10 1 0. 1 Value of Radar Assimilation for QPF daniel. leuenberger@meteoswiss. ch 1 tc [h] 10 COSMO GM 2008, Cracow 100 13

Findings • LHN improves high-resolution NWP forecasts • QPF improvement in the first 3 -12 h (dependent on score and rainfall intensity) • Other variables slightly improved, particularly in summer • More realistic rainfall input for soil moisture • Impact on QPF dependent on • Precipitation forcing (equilibrium vs. non-equilibrium) • Life time of precipitation system • Mesoscale environment of convection (e. g. stability) • Extent of NWP model domain and radar data coverage Value of Radar Assimilation for QPF daniel. leuenberger@meteoswiss. ch COSMO GM 2008, Cracow 14

What Next at Meteo. Swiss? • Introduce quality control • Based on statistics of radar data, can handle e. g. • visibility • non-rain echoes • foreign radar data (unknown specifications) • => quality weight for each pixel • Add foreign radar data • France, Germany, Italy, Austria Value of Radar Assimilation for QPF daniel. leuenberger@meteoswiss. ch COSMO GM 2008, Cracow 15

Thank you for your attention Value of Radar Assimilation for QPF daniel. leuenberger@meteoswiss. ch COSMO GM 2008, Cracow 16