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FORECASTING WEATHER RADAR PROPAGATION CONDITIONS USING NWP MESOSCALE MODEL DATA

25th EWGLAM and 10th SRNWP Meetings. Joint SRNWP/COST 717 Session. Lisbon 8th October 2003. FORECASTING WEATHER RADAR PROPAGATION CONDITIONS USING NWP MESOSCALE MODEL DATA. Joan Bech 1 , Bernat Codina 2 and Jeroni Lorente 2 1 Servei Meteorològic de Catalunya 2 Universitat de Barcelona.

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FORECASTING WEATHER RADAR PROPAGATION CONDITIONS USING NWP MESOSCALE MODEL DATA

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  1. 25th EWGLAM and 10th SRNWP Meetings. Joint SRNWP/COST 717 Session. Lisbon 8th October 2003 FORECASTING WEATHER RADAR PROPAGATION CONDITIONS USING NWP MESOSCALE MODEL DATA Joan Bech1, Bernat Codina2 and Jeroni Lorente2 1Servei Meteorològic de Catalunya 2Universitat de Barcelona

  2. Index1. Introduction. 2. Methodology: Vertical Refractivity Gradients & Ducting Index 3. NWP Forecasts vs. Observations. Modified Forecasts. 4. Final remarks.

  3. Sub refraction Standard refraction Super refraction ANOMALOUS PROPAGATION (ANAPROP) “ANOMALOUS PROPAGATION (ANAPROP) OF THE WEATHER RADAR BEAM OCCURS WHEN MOISTURE AND TEMPERATURE PROFILES VARY SIGNIFICANTLY FROM NORMAL” SOME OBSERVED EXTREME ANAPROP CASES: MEDITERRANEAN SEA (Battan,1973) INDIC OCEAN (UKMO, 1994) US WEST COAST (Babin,1995) BALTIC SEA (Anderson et al, 1997) . .

  4. REFRACTIVITY & VRG REFRACTIVITY N & MODIFIED REFRACTIVITY M (Bean and Dutton, 1968) : VERTICAL REFRACTIVITY GRADIENT (VRG) SUB REFRACTIVE NORMAL SUPER REFRACTIVE (“DUCT”)

  5. (Turton et al., 1988)

  6. PROPAGATION CONDITIONS AND RADAR BEAM HEIGHT (1) • Anaprop leads to differences in expected radar beam heights. • Example for PBE radar beam height (0º elevation) with observed subrefractive and superrefractive VRG.

  7. PROPAGATION CONDITIONS AND RADAR BEAM HEIGHT (2) PBE radar PPI (0.7º elevation) with observed superrefractive VRG (-106 N units/km).

  8. VRG & DUCTING INDEX VRG = N / z ITU (1997) ID = 78 z - M Johson et al. (1999) November 2002 to February 2003 (183 cases) MASS model refractivity profiles 00 & 12 Z RAOB

  9. Vertical profile of modified refractivity on 13th Novembre 2002 at 12 Z over Barcelona: observation (OBS, thick solid line) and model forecast (FOR, crosses, dotted line). REFRACTIVITY VERTICAL PROFILE (OBS & FOR)

  10. VRG & DUCTING INDEX (OBS & FOR)

  11. DUCTING INDEX (OBS & FOR AVERAGES)

  12. OBSERVED VRG AUTOC., MAE, ME & RMSE

  13. DUCTING INDEX MODIFIED FORECASTS

  14. Final Remarks1. Four months of NWP derived VRG and ID forecasts have been compared with RAOB diagnosed VRG and ID. 2. Original model forecasts were biased towards subrefraction (specially ducting index). 3. Considering model tendency and previous OBS, new forecasts produced better verification scores. 4. Model forecasts were useful to anticipate anaprop conditions but in some aspects RAOB persistency was better.

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