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Verification of SYNOP, TEMP, and GPS data

This study examines the verification scores of SYNOP, TEMP, and GPS data, focusing on the availability of SYNOP data, errors in pressure and temperature measurements, bias in temperature and wind speed, and the relationship between relative humidity and dew point. The study also explores the impact of forecast range and surface type on verification results.

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Verification of SYNOP, TEMP, and GPS data

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  1. Verification with SYNOP, TEMP,and GPS data P. Kaufmann, M. Arpagaus, MeteoSwiss P. Emiliani., E. Veccia., A. Galliani., UGM U. Pflüger, DWD

  2. Surface Verification with SYNOP Verification scores neglecting a diurnal cycle

  3. Availability of SYNOP data on GTS PMSL • Red dots: all “main” SYNOPS (6-hourly) available • GB: Sea level pressure but no pressure at station height • Spain, Italy, Balkans: Many stations do not report during the night (not even the automatically measured parameters) PS Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate

  4. SYNOP Pressure: Standard Deviation of Errors • Standard deviation of errors (STDE) is considerably larger in winter than in summer • In winter much larger in the north than in the south Winter 2003/4, 42 – 48 h Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate Summer 2004, 42 – 48 h

  5. SYNOP Pressure • Dependence of mean error (ME) on forecast range • Winter: Increase • Summer: Decrease Winter 2003/4 Summer 2003 Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate but …

  6. SYNOP Pressure • … decrease in summer disappeared in summer 2004 • Effect of ECMWF-IFS boundary conditions? • Supported by results of IFS test chain summer 2003 Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate Summer 2004

  7. Model Grid Points over Water on Coasts and Lakes • Winter 2003/4, forecast range 42 – 48 h • Coasts and lakes: Large bias if model grid points over water are used! • but: small bias for small islands and oil platforms – not all water points need to be eliminated Land points preferred Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate Nearest grid point regardless of surface type

  8. SYNOP Temperature • Strong cold bias in winter (see verification of daily cycle), pronounced in Alps • Weak cold bias in summer • Standard deviation high in complex terrain ME ME Summer 2004, 42 – 48 h Winter 2003/4, 42 – 48 h Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate STDE

  9. Verification with TEMPs Vertical profiles

  10. TEMP Geopotential Summer 2004 (JJA) LM ME STDE aLMo ME • Sharp increase of mean error in stratosphere, reason unclear • Standard deviation largest around tropopause • LM only: negative bias below 600 hPa at +48 h Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate

  11. TEMP Geopotential aLMo – LAMI aLMo ME • “South of the Alps” • aLMo 6 stations • LAMI 7 stations • LAMI only July, August • Bias differences to aLMo below 500 hPa: • Bias at +12 h more positive • Negative bias at +48 h • LAMI and LM both driven by GME, aLMo by IFS aLMo ME Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate

  12. TEMP Temperature Summer 2004 (JJA) LM ME aLMo ME STDE • Cold bias up to 0.7 K between 1000 and 750 hPa • Warm bias 750 – 500 hPa, increase with forecast time up to 0.6 K • Weak cold (LM: no) bias 500 – 250 hPa • aLMo only: Strong cold bias in the stratosphere (150 hPa) • Analysis (+00) h far better than all others – effect of nudging • Standard deviation largest spread around tropopause (200 hPa) Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate

  13. TEMP Temperature aLMo – LAMI • LAMI only July, August • Smaller cold bias near surface • Warm bias extends higher up, up to 200 hPa level Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate aLMo ME

  14. TEMP Relative humidity Summer 2004 (JJA) aLMo ME LM ME STDE • Bias of varying sign, 5 – 8%, related to bias of temperature? • Moist below 850 hPa • Dry between 850 hPa and 500 hPa • Moist between 500 hPa and 200 hPa • Dry above 200 hPa • Clear distinction between analysis and forecasts • Standard deviation nearly uniform over large part of troposphere Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate

  15. TEMP Humidity aLMo – LAMI ? Relative humidity bias Dew point bias aLMo ME • Relative humidity and dew point temperature are not directly comparable Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate

  16. Long term evolution of RH RMSE LM RMSE of relative humidity • Decrease of RMSE for LM in 2004 • Effect of prognostic ice scheme and assimilation of pseudo-TEMPS from ECMWF into GME Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate

  17. TEMP Wind speed aLMo Summer 2004 (JJA) LM ME aLMo ME STDE • Mean error well below 1 m/s • Slightly increasing with forecast time • Largest in boundary layer and near or above tropopause • Boundary layer: Different sign of bias for LM and aLMo • Standard deviation largest at tropopause, consistent with strongest winds Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate

  18. TEMP Wind speed aLMo – LAMI • Only stations south of the Alps • Largest bias at 700 hPa Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate

  19. Verification with GPS Vertically Integrated Water Vapour

  20. GPS Integrated Water Vapour • Path delay (W – W0) caused by refraction • Error for geodesy • Signal for meteorology • Refractivity index depends on • Dry-air density (hydrostatic delay) • Humidity (wet delay) • Wet delay = total delay – hydrostatic delay • Integrated water vapour: • Need of surface pressure and temperature from nearby SYNOP • Currently calculated by KNMI Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate

  21. GPS data availability • Three processing centers deemed most reliable • Each covers primarily its home country • Time series have many gaps • Processing centers are not WMO members LPT Switzerland Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate GFZ Germany GOP Czechia

  22. GPS IWV BIAS • Weak dry bias outside complex topography • Bias (or mean error) is largest • In summer • In the mountains • Possible explanations • Larger specific humidity contents in summer than in winter • Height differences GPS antenna – SYNOP station – model surface are largest in mountainous terrain Winter 2002/3 Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate Summer 2003

  23. GPS IWV Standard Deviation • STDE largest in summer • Homogeneous in whole model domain • Problem in mountains only affect bias, i. e. values are shifted by constant offset Winter 2002/3 Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate Summer 2003

  24. Summary and Outlook • Model verification often stops at national boundaries: Model comparison difficult • Surface verification with SYNOP • Pressure increase/decrease with forecast range • Strong cold bias in winter • Need for continuous, quality-controlled data for the whole of Europe! • Model comparison even for TEMP difficult. Differences: • Set of stations • Time (definition of a season) • Statistical measures used: Only two out of ME, MAE, STDE, RMSE • GPS • Data availability problem (currently only available through European project; each centre provides subset only ) • Zenith total delay (ZTD) verification in the future to avoid interpolation problems between SYNOP and GTS locations Pirmin.Kaufmann@MeteoSwiss.ch 6th COSMO General Meeting, 22-24 Sept 2004, Linate

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