Eidgenössisches Departement des Innern EDI Bundesamt für Meteorologie und Klimatologie MeteoSchweiz Statistics of COSMO Forecast Departures in View of Data Assimilation Priority Project KENDA Daniel Leuenberger MeteoSwiss, Zurich, Switzerland COSMO GM 2008, Cracow

2 COSMO Forecast Departure COSMO GM 2008, Cracow Introduction I General assumption in Data Assimilation: „Errors are of Gaussian Nature and bias-free“ Prerequisite for „optimal“ combination of model fc and observations or easily finding a minimum of the cost function Background term Observation term

3 COSMO Forecast Departure COSMO GM 2008, Cracow Introduction II How valid is this assumption for forecast departures of the COSMO model? Question 1: Distribution of departures from a short-range COSMO forecast? Question 2: Change of distribution with forecast range?

4 COSMO Forecast Departure COSMO GM 2008, Cracow Data COSMO-DE forecast departures at +3-6h and +9-12h Dec 2007 – Feb 2008 (91 days, 364 forecasts) Observations in COSMO-DE domain SYNOP (Ps,T,U/V,RH,PP) TEMP (T,U/V,RH) Aircraft data (T,U/V)at 940,850,500 and 300hPa Windprofiler (U/V)

5 COSMO Forecast Departure COSMO GM 2008, Cracow Evaluation Method PDF (qualitative) Normal Probability Plot (more quantitative) good fit bad fit „normrange“

6 COSMO Forecast Departure COSMO GM 2008, Cracow SYNOP: Surface pressure Bias

7 COSMO Forecast Departure COSMO GM 2008, Cracow SYNOP

8 COSMO Forecast Departure COSMO GM 2008, Cracow SYNOP: Precipitation

9 COSMO Forecast Departure COSMO GM 2008, Cracow Aircraft:

10 COSMO Forecast Departure COSMO GM 2008, Cracow Windprofiler:

11 COSMO Forecast Departure COSMO GM 2008, Cracow Radiosondes:

12 COSMO Forecast Departure COSMO GM 2008, Cracow Summary Generally good fit around median, „fat tails“ Normrange around 80% Good fit (>80%) Wind, Temperature Aircraft measurements, windprofiler Less good fit (<80%) Relative Humidity, Precipitation Radiosondes (however: less reliable statistics!) No clear decrease with lead time No clear dependency on height

13 COSMO Forecast Departure COSMO GM 2008, Cracow Outlook Summer months COSMO-EU Stratify results by weather type Other forms of humidity and precipitation Specific humidity Normalized relative humidity (Holm et al., 2002) Log(precipitation) Radar precipitation (convection) Write report to finish this task

14 COSMO Forecast Departure COSMO GM 2008, Cracow Thank you for your attention