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Mike Leduc Sudesh Boodoo Cloud Physics and Severe Weather Research King City ON

Examination of the low level polarimetric radar parameters associated with the Aug 20 2009 southern Ontario tornadic supercells . Mike Leduc Sudesh Boodoo Cloud Physics and Severe Weather Research King City ON. Outline.

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Mike Leduc Sudesh Boodoo Cloud Physics and Severe Weather Research King City ON

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  1. Examination of the low level polarimetric radar parameters associated with the Aug 20 2009 southern Ontario tornadic supercells Mike Leduc Sudesh Boodoo Cloud Physics and Severe Weather Research King City ON

  2. Outline • Introduce Conceptual Model of Supercell at Low levels as Seen by Polarimetric Radar. • Compare features of 5 Aug 20 Supercells to this Model.

  3. Polarimetric Conceptual Model of Supercells Low levels of Storm

  4. ZDR and KDP • ZDR compares Z(H) and Z(V) can distinguish big drops from small drops • KDP rainfall estimates proportional to D**3 • Compared with Z (D**6) can provide valuable information

  5. Romine et al 2008 (Arc)

  6. ZDR arc • Ryzkhov – size sorting due to environmental shear. • Area nearer inflow ends up with fewer but larger drops hence higher zdr • Not only hypothesis for this effect. • Claim it’s measure of strength of circulation of supercell. (?)

  7. KDP foot • Seems to correspond to development of FFD. Does this help increase low level mesocyclone circulation? • Why increase in KDP • Descending air below freezing level –hail melts large drops break up into smaller drops . KDP proportional to D**3. while Z is D**6. • At low levels in this situation KDP values would increase relative to Z • In OK storm higher values of KDP accompanied by hail at surface

  8. Evolution of Kdp Foot as tornado develops May 8 2003 OK tornadic supercell

  9. TOR -18 min

  10. TOR-12min

  11. TOR-6min

  12. TOR touchdown

  13. TOR +6

  14. How Does Aug 20 compare at Low Levels • Look for “sharpness” of zdr shield • Relationship of kdp foot to zdr shield • Can we see expansion of kdp foot and cyclonic rotation as touchdown approaches • 3 tornadic supercells • 2 Non tornadic supercells

  15. Tornado 1 The Newmarket Storm

  16. R T(1)-34 MIN

  17. R T(1)-34MIN

  18. R T(1)-34MIN

  19. R T(1)-14MIN

  20. R T(1)-14MIN

  21. R T(1)-14MIN

  22. R T(1)-4MIN

  23. R T(1)-4MIN

  24. R R (T1)-4MIN

  25. Woodbridge Tornado

  26. R T(3)-0 MIN

  27. T(3)-0MIN

  28. R T(3)-0MIN

  29. Time Series of KDP with Woodbridge Storm

  30. New Lowell

  31. T-17 MIN

  32. KDP foot and FFD An example

  33. Comparing Tornadic and Non tornadic storms

  34. KDP foot conclusions • Subjectively appears that foot does expand and that cyclonic curvature of foot occurs with tornadic storms. • Again subjectively foot corresponds with FFD as defined by Doppler (divergent signature tripping micro algorithm)

  35. Hook Echoes • Indicative of RFD. • Higher Values of ZDR • Smaller particles have evaporated • stronger cold pool greater chance of gusting out. • Ryzhkov hypothesized tornadic supercells would have lower values of ZDR in hooks. • His study 4 tornadic 5 non tornadic storms looking just prior to touchdown. • Slight evidence for hypothesis but not statistically significant.

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