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NWP models. Strengths and weaknesses.

NWP models. Strengths and weaknesses. Morten Køltzow, met.no NOMEK 22.04.2010. Outline. Models employed at met.no Models ability to forecast: Precipitation. 2m air temperature. Extreme weather (wind). Models employed at met.no. Hirlam, 12km, 8km, 4km (NOR)LAMEPS 12km UM, 4km -> 1km

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NWP models. Strengths and weaknesses.

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  1. NWP models. Strengths and weaknesses. Morten Køltzow, met.no NOMEK 22.04.2010

  2. Outline • Models employed at met.no • Models ability to forecast: • Precipitation. • 2m air temperature. • Extreme weather (wind).

  3. Models employed at met.no • Hirlam, 12km, 8km, 4km • (NOR)LAMEPS 12km • UM, 4km -> 1km • ECMWF (approximately 16km) • Simra, turbulence model, 100m -> 50m • AirQUIS, urban air quality model • Wave and ocean models • SNAP, (nuclear accident) transport model • EMEP, chemical transport model

  4. Hirlam - hydrostatic model. • Assumes that the vertical acceleration is much smaller than g. The vertical velocity is found by diagnostics. Good approximation for coarse models. • UM – non hydrostatic model. Non-hydrostatic models are important when features with large vertical velocities is resolved (i.e. convection or flow around steep orography).

  5. H12, H08, H4, UM4: 4km H08 H12

  6. Precipitation

  7. Seasonal mean, 24h precipitation: HIRLAM 8km JJA SON UM4km

  8. Precipitation from a fine scale model (left), a global model (mid) and observations (right). From Ebert (2009).

  9. Verification of precipitation DJF:(models ability to forecast correctly 24h precipitation above a certain threshold) HIT RATE FALSE ALARM RATIO

  10. At what spatial scales show the models useful information? • Binary approach: • Each coloured grid cell precipitation > 0.0mm • Compare fraction of occurences from forecast and radar for different areas. On which spatial scales are the fractions similar? Forecast Radar

  11. JJA Spin-up, cloud cover. 9months june - February HIRLAM 4 HIRLAM 8 HIRLAM 12 UM4 DJF

  12. Spin-up of precipitation (mm/h) 9mnd June - Februay JJA DJF HIRLAM 4 HIRLAM 8 HIRLAM 12 UM4

  13. Near surface temperature (T2m). • Coastlines. • Heightcorrection of T2m.

  14. T2m bias, coastal stations. BIAS BIAS SUMMER WINTER Warm bias in winter and cold bias in summer due to too high influence by the sea surface temperature on T2m.

  15. Coast “coarse model” ECMWF. B

  16. B Interpolation: bi-linear Nearest grid point Nearest land grid point (B is a ocean grid point in the model)

  17. Bi-linear interpolation: 22°

  18. Nearest land point “interpolation” Observed 28.7°

  19. Difference in topography 8km and 500m horizontal resolution Blue – real topo less than model topo

  20. HIRLAM8 T2m Height corrections of T2m is necessary! BIAS Model topography – real topography

  21. HAKADAL KJELLER BJØRNHOLT TRYVANN ALNA BLINDERN

  22. Variasjon i tid og rom: Sort – mean Stiplet – stdev Varsel;T+0->T+48 Nov. Dec. Jan. Feb.

  23. Modelling wind in Norway

  24. Low pressure system 1000 hPa, Newfoundland 31.12.91 kl. 00 Utc. From Karsten Eitrheim, VpV, met.no

  25. Analysis 18 Utc 31.12.91. From Karsten Eitrheim, VpV, met.no

  26. Analysis 00 UTC 01.01.92 From Karsten Eitrheim, VpV, met.no

  27. Analysis Kl. 06 UTC 01.01.92 From Karsten Eitrheim, VpV, met.no

  28. From Trygve Aspenes

  29. Maksvind ~33.5m/s From Karsten Eitrheim, VpV, met.no

  30. The new year storm, observed wind strength: Færder to Bodø: More than strong gale (>20.8m/s). Hardangerfjorden to Sklinna Fyr: More than violent storm (>28.5m/s). Stad to Vikna: More than hurricane force (>32.6m/s). Maximum wind strength (10min average) at Svinøy and Skalmen Fyr. Most probably the most severe storm in Norway the last 110 years. Skalmen Svinøy

  31. A rerun with a state of the art NWP model (HIRLAM, 8km) valid: 09UTC 1.1.1992 +21h +45h Green > 20m/s, Yellow > 24m/s, Red > 30m/s Maximum 35m/s Initial and lateral boundaries from ERA-interim.

  32. NORLAMEPS Probability based on the Norwegian Ensemble Prediction System (NORLAMEPS) +60h valid 06UTC 1.1.1992 Probabilities for more than 25m/s (green) Probabilities for more than 30m/s (red)

  33. Ulrik, 2008 Black: Analysis HIRLAM 00UTC 26.October. Red : HIRLAM forecast +48h

  34. Ulrik, 2008 Black: Analysis HIRLAM8 00UTC 26.October Red: HIRLAM forecast +24h

  35. Vera, Polar low, November 2008:

  36. Vera – “offshore”: Observations - black curve

  37. Vera – “outer coast line”: ECMWF Observations - black curve

  38. Vera – “inner coast line”: Observations - black curve

  39. Verification of wind (+0 to +60) at 6 Norwegian offshore stations December 2009 - February 2010 Model Observation Observations are originally taken approximately 100masl and reduced to 10masl assuming neutral conditions.

  40. Verification of wind (+0 to +60) at 28 Norwegian coast stations (lighthouses). December 2009 - February 2010. Model Observation

  41. Verification of wind (+0 to +60) at 9 Norwegian mountain stations (>930masl) December 2009 - February 2010 Model Observation

  42. Thank you for your attention!

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