1. Numerical Simulation and Prediction of Supercell Tornadoes Ming Xue School of Meteorology and Center for Analysis and Prediction of Storms University of Oklahoma mxue@ou.edu February 2008

2. Outline of Talk LES-resolution simulation of supercell tornado Prediction of real tornados with radar data assimilation Sensitivity of tornado prediction to microphysics

3. Tornadogenesis and Tornado Dynamics as Revealed by LES-resolution Numerical Simulations of Supercell Storm

4. Numerical Simulation of Supercell Tornado using up to 12.5 m Grid Spacing Using the Advanced Regional Prediction System (ARPS, Xue et al 2000, 2001, 2003) of CAPS 1977 Del City, OK sounding (~3300 J/kg CAPE) 2000 x 2000 x 83 point uniform resolution covering 50 x 50 km 2.  x = 25 m,  z min = 20 m, dt = 0.125 s.  x = 12.5 m in a 20 x 20 km subdomain, dt = 0.05 s. Warmrain microphysics with surface friction at the later stage Simulations up to 5 hours Using 2048 Alpha Processors at Pittsburgh Supercomputing Center 60TB of data generated by one 25m simulation over 30 minutes, output at 1 second intervals

5. Sounding for May 20, 1977 Del City, Oklahoma tornadic supercell storm CAPE=3300J/kg

6. Full Domain Surface Fields of 50m simulation t =3 h 44 min Red – positive vertical vorticity

7. Near surface vorticity, wind, reflectivity, and temperature perturbation from 25-m run 2 x 2 km Vort ~ 2 s -1 Movie

8. Near surface vorticity, wind, reflectivity, and temperature perturbation from 12.5 m grid 1.5 x 1 km domain Vort > 4 s -1 Movie

9. Near surface vorticity, wind and p' felds - evolution from single to multiple vortices t=13447 s t=13661s Vort_max=3.27 /s Vort_max=3.28 /s

10. Movie of Cloud Water Field 25 m, 7.5x7.5km domain, 30 minutes Movie of Cloud Water Field. dx=25m 7.5x7.5km domain, 30 min.

11. 130m/s -100mb >120m/s max surface winds >90mb p drop +60m/s speed increase in ~2min 220min 236min Max sfc wind speed Min. sfc perturb. p 220min 236min Maximum surface wind speed and pressure drop in 12.5 m simulation

12. What is the main source of air parcel and vorticity feeding the tornado? Trajectory calculations based on 1-s model output

13. View from South t=13250s beginning of vortex intensification z = 3 km

14. View from Northeast 3km RFD of 1 st cell RFD of 2 nd cell Inflow from east Low-level jump flow East West

15. Diagnostics along Trajectories

16. Orange portion t=13250-500s – 13250+200s t=13250s Beginning of low-level spinup 14km

17. X Y Z 8km WVhWVh Streamwise Vort. Cross-stream Vort. Horizontal Vort. Vertical Vort. Total Vort. 13250 12750 13450 Vorticity components along trajectory

18. Force along trajectory Buoyancy Vert. Pgrad Sum of the two Perturbation pressure -76mb 5 -5 13250 ~2 m s -2 +b' due to -p' Forces along trajectory

19. Can we numerically predict real tornadoes?

20. May 8 th, 2003 OKC tornado OKC tornado 2210-2238 UTC 30 km long path F4 (Hu 2005; Hu and Xue 2007)

21. DA cycles on 1-km Grid 3DVAR+Cloud Analysis Forecast 2030 UTC 2140 UTC 4 nested grids

22. Observed v.s. Predicted Z and Vr at 1.45° of the supercell storm Observation 1 km Forecast From 2140 to 2240 UTC every 5-min Reflectivity Radial velocity

23. What about the prediction of embedded tornado?

24. 50-m Grid Forecast v.s. Observation Forecast Low-level Reflectivity Observed Low-level Reflectivity Movie 43 minute forecast

25. 50-m Grid Forecast v.s. Observation Forecast Low-level Reflectivity Observed Low-level Reflectivity Movie 43 minute forecast 43 min. forecast on 100m grid

26. t=34 min t=40 min Sfc vert. vort., and p’ E-W x-sections of vert. vort. and w

27. A case from CASA 2007 Spring Experiment CASA – an NSF ERC for Collaborative Adaptive Sensing of Atmosphere - Low cost, high density, adaptively scanning radars

28. © KSWO TV © Patrick Marsh May 8-9, 2007 A series of low-level circulations. NWS Tornado Warnings: 7:16pm, 7:39pm, 8:29pm 7:21pm (0021Z) 8:30pm (0130Z) 9:54pm 10:54pm (0354 Z) Minco Tornado A Case from 2007 CASA Spring Experiment

29. dx = 400 m 115-min. prediction of sfc winds, Z (color), and vertical vorticity at 0355 UTC. Both WSR-88D and CASA IP1 data were assimilated very 5 min. for 1 h. The black triangle indicates the location of observed Minco tornado. Predicted sfc Vort. max 115-min sfc forecast Minco tornado

30. Importance and/or Uncertainties of Microphysics? Daniel Dawson’s Poster Yesterday using multi-moment microphysics

31. Impact of Microphysics on Prediction of Tornadic Supercell Storm May 3, 1999 Moore – OKC F-5 Tornado Case Daniel Dawson’s Poster Yesterday using multi-moment microphysics

32. Surface  ’  gray shading), Z (blue contours), vertical vorticity (color shading), and wind vectors at the time of largest vertical vorticity using 100 m resolution and with MY1 (a) and MY2 (b) schemes. HP storm LP storm 100 m simulations with MY1 and MY2 schemes

33. Vis5D visualization of the cloud field (gray surface), and 0.3 s -1 vertical vorticity iso-surface (yellow) from the 100 m simulations using MY1 (left) and MY2 (right) schemes. MY Single-moment MY two-moment

34. Greensburg, Kansas Tornado, 5 May 2007 Numerical prediction of tornados - has its time come? What is the predictability of tornadoes?