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Moist Convection and Mesoscale Predictability*

Moist Convection and Mesoscale Predictability*. Rich Rotunno NCAR. *based on work / C. Snyder, NCAR F. Zhang, Texas A&M. Agenda. Predictability Theory Idealized Predictability Experiments / Mesoscale Model / Moist Convection

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Moist Convection and Mesoscale Predictability*

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  1. Moist Convection and Mesoscale Predictability* Rich Rotunno NCAR *based on work / C. Snyder, NCAR F. Zhang, Texas A&M

  2. Agenda • Predictability Theory • Idealized Predictability Experiments / Mesoscale Model / Moist Convection 3. High-Resolution Numerical Forecasts of Moist Convection

  3. Predictability is… Range of Predictability Certain fluid systems “…have a intrinsic finite range of predictability, which cannot be lengthened by bettering the observations.” (Lorenz Tellus 1969)

  4. For example… limited if

  5. The Predictability of Flows with Many Scales of Motion Energy Spectrum Error Energy Spectrum Lorenz (Tellus 1969)

  6. A Dimensional Argument Energy Spectrum Error Growth Time Scale Lilly (Geo. Fluid Dyn. 1972)

  7. Predictability of Turbulence / EDQNM* Limited Predictability Unlimited Predictability Leith and Kraichnan (JAS 1972) *Métais and Lesieur (JAS 1986)

  8. Predictability of Turbulence / Lorenz (1969)* Limited Predictability SQG Unlimited Predictability 2DV *SQG=Surface QG , Blumen(JAS 1982) Pierrehumbert, Held and Swanson (CSF 1994) *Rotunno and Snyder (JAS In press)

  9. In physical space… SQG 2D Limited Predictability Unlimited Predictability

  10. Implications for Atmosperic Predictability?

  11. Observed Energy Spectra Nastrom and Gage (1985) spectra computed from GASP observations (commercial aircraft) Lindborg (1999) functional fit from MOZAIC observations (aircraft) Skamarock (MWR 2004)

  12. Time Scale

  13. Day 1,2 Error Doubling Time Decreased with Improved ECMWF Modeling System QJRMS 2002

  14. Estimate of Predictability Limit Lilly (QJRMS 1990)

  15. 1 .5

  16. Forecast Experiments / Idealized Initial Perturbations 12 h 6 h 3 h 0 h Zhang, Snyder, Rotunno (JAS 2003)

  17. Forecast Sensitivity for “Surprise” Snowstorm MM5 Simulated (dx=3.3km) MSLP and Reflectivity, t=30h Control Perturbed 30h Lp Lc Lc • Rapid Initial Error Growth in Regions of Moist Instability • Upscale Error Growth Modifies Position of Surface Low Zhang, Snyder, Rotunno (JAS 2003)

  18. Baroclinic Waves / Moist Convection white noise added to D2 at t = 36h Zhang et al. (JAS 2007)

  19. Evolution of Difference Field 500 hPa height (solid), v’ (color, c.i.=2m/s), 3h precip (shaded > 3mm) CAPE > 50J/Kg Zhang et al. (JAS 2007)

  20. Evolution of Difference Field 500 hPa height (solid), v’ (color, c.i.=2m/s), 3h precip (shaded > 3mm) CAPE > 50J/Kg Zhang et al. (JAS 2007)

  21. Evolution of Difference Field 500 hPa height (solid), v’ (color, c.i.=2m/s), 3h precip (shaded > 3mm) CAPE > 50J/Kg Zhang et al. (JAS 2007)

  22. Evolution of Difference Field 500 hPa height (solid), v’ (color, c.i.=2m/s), 3h precip (shaded > 3mm) CAPE > 50J/Kg Zhang et al. (JAS 2007)

  23. Evolution of Difference Field 500 hPa height (solid), v’ (color, c.i.=2m/s), 3h precip (shaded > 3mm) CAPE > 50J/Kg Zhang et al. (JAS 2007)

  24. Evolution of Difference Field 500 hPa height (solid), v’ (color, c.i.=2m/s), 3h precip (shaded > 3mm) CAPE > 50J/Kg Zhang et al. (JAS 2007)

  25. Difference Energy of Band-Pass Filtered Fields Zhang et al. (JAS 2007)

  26. Idealized Predictability Experiments

  27. Idealized Predictability Experiments

  28. High Res. Numerical Forecasts

  29. Real-time WRF 4 km Forecast Initialized 23 July 2005 00 UTC Reflectivity forecast Composite NEXRAD Radar Weisman et al. (WAF 2007 In review)

  30. Real-time WRF 4 km Forecast Initialized 04 June 2005 00 UTC Composite NEXRAD Radar Reflectivity forecast Weisman et al. (WAF 2007 In review)

  31. June 5, 2005 Radar 03 GMT 4 km WRF-ARW 12 km ETA 06 GMT prec. 30 hr 03 GMT 27 hr Weisman et al. (WAF 2007 In review)

  32. Summary Lorenz (1969)  Limited predictability for flows with decreasing with scale Describes predictability of various idealized turbulent flows (2D, 3D, SQG) Atmospheric spectrum suggests  Large scale (> 200-300km) independent of scale Mesoscale (<200-300km) decreases with scale Idealized Predictability Experiments / Mesoscale Models / Moist Convection  Predictability Limited Experience with Real-Time High-Resolution Convective Weather Forecasts Indicates Improvement is Still Possible through Reduction of Initial Mesoscale Error http://www.mmm.ucar.edu/people/rotunno/

  33. Spectra for WRF-ARW BAMEX Forecasts, 5 May – 14 July 2003 Average over approx. 4 – 9 km height, on model surfaces. 4 km WRF-ARW: 12 - 36 h forecast avg. Skamarock (MWR, 2004)

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