1. Test of Supercell Propagation Theory Using Data from VORTEX 95 Huaqing Cai NCAR/ASP/ATD

2. Test of Supercell Propagation Theory Using Data from VORTEX 95 n Research Motivation and Objectives n Data and Methodology n Results n Summary

3. Schematic Visual Appearance of a Supercell Thunderstorm

4. Why Supercells Rotate ?

5. Schematic Plan View of an Idealized Supercell as Viewed by Radar Hook Echo

6. A Typical Supercell Viewed by Doppler Radar

7. Which direction is the storm moving ? Mean Wind Pure Advection

9. Burgess, Master Thesis, 1974 Storm Split & Propagation Hodograph Left Mover Right Mover

10. Illustration of Hodograph u V u V Straight Hodograph Curved Hodograph Surface Upper Level

11. Newton(1963), Obstacle Flow Analogy P+ P-

12. ADV VPGF BUOY Linear Nonlinear Buoyancy

13. Hodograph Environmental Wind Motion Produced by the Storm

14. Illustration of Linear Effect UpshearDownshear W>0 W<0

15. Illustration of Nonlinear Effects

16. Rotunno and Klemp, MWR, 1982 Mesocyclones X X + - Shear Vector -

17. Hane and Ray, JAS, 1985 Shear Vector Linear Effect H L 40 dBz Storm Relative Flow

18. LeMone et al, MWR, 1988 P’(hpa) H L W max Shear Vector

19. Findings and Limitations of Past Studies n The pressure pattern predicted by the linear theory appears to be confirmed n No vertical pressure gradient was obtained by earlier retrievals or aircraft observations n The aircraft observations can only be obtained near the cloud base, there was no direct measurement inside the storm

20. Research Objectives n There has been no comprehensive observational test of supercell propagation theory n Try to decompose nonlinear perturbation pressure into nonlinear cyclostrophic and nonlinear shear terms and determine which term is more important for the rightward movement of supercells

21. Data and Methodology n The Garden City storm during VORTEX on May 16, 1995 n Dual-Doppler technique n Pressure-buoyancy retrieval technique

22. Dual-Doppler Technique Radar 1 Radar 2 3D wind fields can be reconstructed through dual-Doppler technique

23. ELDORA Airborne Doppler Radar

25. Pressure-buoyancy Retrievals

26. Linear and Nonlinear Perturbation Pressure Retrievals

28. ELDORA Fly Track and Overall Storm Evolution

29. What is Special about the Garden City Data Set ? n High space resolution (300 m along track) n High time resolution ( ~5 minute) n Full coverage of the whole life cycle of the storm

30. Analysis Procedure of the Garden City Storm n A total of 11 legs were carefully edited using NCAR software SOLO (~2800 scans) n 3D wind field was obtained using NCAR software REORDER and CEDRIC n Pressure-buoyancy retrievals were performed for each leg using a modified retrieval routine

31. Hodograph From Sounding and Dual-Doppler Syntheses

32. Perturbation Pressure Vertical Vorticity Shear Vector

33. Linear and Nonlinear Perturbation Pressure Vertical Pressure Gradient Shear Vector

34. Linear and Nonlinear Perturbation Pressure Gradient Buoyancy and Advection Shear Vector

35. Vertical Velocity Tendency Using Forward Time Difference Vertical Velocity Tendency Using Vertical Momentum Eq Observed Calculated

36. Nonlinear Cyclostrophic Perturbation Pressure Nonlinear Shear Perturbation Pressure

37. Nonlinear Cyclostrophic Perturbation Pressure Gradient Nonlinear Shear Perturbation Pressure Gradient

38. Shear Vector

39. Summary and Future Work n This is the first comprehensive analysis of the perturbation pressure in a severe storm n The nonlinear terms in the pressure equation are important for the straight hodograph case, consistent with past numerical simulations. The importance of the nonlinear shear term has not been shown in the past, this study has shown that the horizontal circulation is as important as the vertical circulation associated with the mesocyclones.

40. Summary and Future Works (Continued) n More data will be needed for further verification of supercell propagation theory, especially in a curved- hodograph case