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Test of Supercell Propagation Theory Using Data from VORTEX 95

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  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 • Research Motivation and Objectives • Data and Methodology • Results • 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 ? Pure Advection Mean Wind

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

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

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

  11. ADV VPGF BUOY Linear Nonlinear Buoyancy

  12. Environmental Wind Motion Produced by the Storm Hodograph

  13. Illustration of Linear Effect W>0 W<0 Upshear Downshear W<0 W>0

  14. Illustration of Nonlinear Effects

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

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

  17. LeMone et al, MWR, 1988 L P’(hpa) Wmax H Shear Vector

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

  19. Research Objectives • There has been no comprehensive observational test of supercell propagation theory • 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

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

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

  22. ELDORA Airborne Doppler Radar

  23. ELDORA Airborne Doppler Radar

  24. Pressure-buoyancy Retrievals

  25. Linear and Nonlinear Perturbation Pressure Retrievals

  26. Linear and Nonlinear Perturbation Pressure Retrievals

  27. ELDORA Fly Track and Overall Storm Evolution

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

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

  30. Hodograph From Sounding and Dual-Doppler Syntheses

  31. Shear Vector Vertical Vorticity Perturbation Pressure

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

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

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

  35. Nonlinear Cyclostrophic Perturbation Pressure Nonlinear Shear Perturbation Pressure

  36. Nonlinear Cyclostrophic Perturbation Pressure Gradient Nonlinear Shear Perturbation Pressure Gradient

  37. Shear Vector

  38. Summary and Future Work • This is the first comprehensive analysis of the perturbation pressure in a severe storm • 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.

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