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Evaluating Dissipation in NWP Models Using Kinetic Energy Spectra

Evaluating Dissipation in NWP Models Using Kinetic Energy Spectra. Bill Skamarock (NCAR/MMM) Mike Baldwin (NOAA/NSSL) Wei Wang (NCAR/MMM). Nastrom and Gage (1985) Spectra computed from GASP observations (commercial aircraft). Global Models: Koshyk and Hamilton (2001).

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Evaluating Dissipation in NWP Models Using Kinetic Energy Spectra

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  1. Evaluating Dissipation in NWP Models Using Kinetic Energy Spectra Bill Skamarock (NCAR/MMM) Mike Baldwin (NOAA/NSSL) Wei Wang (NCAR/MMM) Nastrom and Gage (1985) Spectra computed from GASP observations (commercial aircraft)

  2. Global Models: Koshyk and Hamilton (2001)

  3. Cloud Models: Vallis, Shutts and Gray (1997)

  4. What can we do with NWP model spectra? • Evaluate model resolution: Where does the spectra deviate from its expected behavior? • Tune model dissipation (and physics) to maximize resolution within a given model formulation. • Examine model spin-up: How long does it take to fill the spectra with energy at the fine scales.

  5. What should the kinetic energy spectra look like in an NWP model?

  6. NWP Model Resolution and Spectral Tails

  7. 10 km WRF forecast domain 4 km WRF forecast domain WRF mass coordinate model, BAMEX forecasts BAMEX Goal: Study the lifecycles of mesoscale convective vortices and bow echoes in and around the St. Louis MO area Field program conducted 20 May – 6 July 2003

  8. Observed Forecast Preliminary BAMEX Forecast Verification Number of MCSs for each 36 h forecast initialized at 00 UTC. (Done, Davis, and Weisman)

  9. Real-time WRF 4 km BAMEX Forecast Valid 6/10/03 12Z 4 km BAMEX forecast 36 h Reflectivity 4 km BAMEX forecast 12 h Reflectivity Composite NEXRAD Radar

  10. Real-time 12h WRF Reflectivity Forecast Valid 6/10/03 12Z 4 km BAMEX forecast 10 km BAMEX forecast 22 km CONUS forecast Composite NEXRAD Radar

  11. Spectra for WRF-mass BAMEX Forecasts, 1 – 3 June 2003 Average over approx. 4 – 9 km height, on model surfaces. 22 km conus WRF-mass: 24 - 48 h forecast avg. 10 km WRF-mass: 24 - 48 h forecast avg. 4 km WRF-mass: 12 - 36 h forecast avg.

  12. Spectra for WRF-mass BAMEX Forecasts, 1 – 3 June 2003 Nastrom and Gage GASP Spectra

  13. WRF-mass BAMEX Forecasts, 1 – 3 June 2003, Effective Resolutions

  14. Numerical Dissipation and Spectra WRF-mass BAMEX forecast 1 June 2003 Filters: 5th order horz. upwind advection in the RK3 scheme

  15. Numerical Dissipation and Spectra WRF-mass BAMEX forecast 1 June 2003 Filters: 5th order horz. adv. (solid green) 5th order horz. adv., 3rd order vert. adv., 2nd order horz. filter scaled to horz. def. (dashed green)

  16. Numerical Dissipation and Spectra WRF-mass BAMEX forecast 1 June 2003 Filters: 5th order horz. adv., 3rd order vert. adv., 2nd order horz. filter scaled to horz. def. (dashed green) 2nd order horz. filter with constant eddy viscosity equal to 17,000 m**2/s (solid red)

  17. Numerical Dissipation and Spectra WRF-mass BAMEX forecast 1 June 2003 Filters: 2nd order horz. filter using eddy viscosity 17,000 m**2/s (solid red) As above with horizontal divergence damping using an eddy viscosity of 74,000 m**2/s (dashed red)

  18. Numerical Dissipation and Spectra WRF-mass BAMEX forecast 1 June 2003 Filters: 4th order horz. filter using eddy viscosity 4,250 x 10**8 m**4/s (solid blue) 4th order horz. filter using eddy viscosity 17,000 x 10**8 m**4/s (dashed blue)

  19. WRF-mass BAMEX Forecasts, 2 June 2003 Spectra Evolution (model spin-up)

  20. NWP Forecast Spectra: Conclusions Uses for Spectra: • Evaluate model resolution. • Evaluate model dissipation (and physics) to maximize resolution. • Examine model spin-up. • Verification?

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