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Tornado powerpoint

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Tornado powerpoint

  1. 1. What’s Left to Learn About Tornadoes? Erik Rasmussen, Rasmussen Systems Jerry Straka, OU Kathy Kanak, CIMMS …and our students!
  2. 2. “ There are known knowns. These are things we know that we know. There are known unknowns. That is to say, there are things that we now know we don’t know. But there are also unknown unknowns. These are things we do not know we don’t know. ” —United States Secretary of Defense Donald Rumsfeld
  3. 3. n ct io Deep shear,adequate CAPE o nve e ep c ar-sid De f re o m ent Supercell lop ion Deve itat p ec i pr next gence, RFD to C onver near- of tilting H nd SR Updraft grou Baroclinic ; gene ration Tornado g archin Cyclone nStates cont ractio VortexProcesses Tornado
  4. 4. n ct io Deep shear,adequate CAPE o nve e ep c ar-sid De f re o m ent Supercell lop ion Deve itat p ec i pr next gence, RFD to C onver near- of tilting H nd SR Updraft grou E oclinic ER Bar ; H ration E gene Tornado AR g archin U Cyclone YO nStates cont ractio VortexProcesses Tornado
  5. 5. tornado—1. A violently rotating column ofair, in contact with the ground, eitherpendant from a cumuliform cloud orunderneath a cumuliform cloud, and often(but not always) visible as a funnel cloud.
  6. 6. tornado—1. A violently rotating column ofair, in contact with the ground, eitherpendant from a cumuliform cloud orunderneath a cumuliform cloud, and often(but not always) visible as a funnel cloud.
  7. 7. tornado—1. A violently rotating column ofair, in contact with the ground, eitherpendant from a cumuliform cloud orunderneath a cumuliform cloud, and often(but not always) visible as a funnel cloud.
  8. 8. tornado—1. A violently rotating column ofair, in contact with the ground, eitherpendant from a cumuliform cloud orunderneath a cumuliform cloud, and often(but not always) visible as a funnel cloud.
  9. 9. tornado—1. A violently rotating column ofair, in contact with the ground, eitherpendant from a cumuliform cloud orunderneath a cumuliform cloud, and often(but not always) visible as a funnel cloud.
  10. 10. tornado—1. I know one when I see one.
  11. 11. n ct io Deep shear,adequate CAPE o nve e ep c ar-sid De f re o m ent Supercell lop ion Deve itat p ec i pr next gence, RFD to C onver near- of tilting H nd SR Updraft grou E RER oclinic HE Bar EE ; ration ERH gene Tornado UUARA g archin YO Cyclone YO nStates cont ractio VortexProcesses Tornado
  12. 12. The Tornado Cyclone isroughly 10 times the diameterof the visible Tornado B A A B
  13. 13. Angular momentum M=Vr = tangential, swirling velocitytimes radius. Dimmitt tornado, 2 June 1995. From single-Doppler analysis. M=14000 contour
  14. 14. Approximate swirling windspeed and angular momentum in theDimmitt tornado early in mature stage about 200 m above the ground.
  15. 15. This flow would evolve from the previous in < 5 minutes witha modest inflow of (e.g.) about 5 m/s at 500 m radius
  16. 16. As the high-M air penetrates closer to the axis, maximumswirling wind speed ~doubles for each halving of the radiusof penetration of the large M region.
  17. 17. Early: In-upLate: Down-Out
  18. 18. Early: ~307 K, least precip, warmest airnear the tornado Late: ~305 K, most precip, cooler
  19. 19. Thoughts...• Most supercells probably have tornado cyclones*. Nomenclature isnt so important as understanding that...• A tornado, whatever wind speed or appearance criteria being used, is the inner portion of a tornado cyclone where enough angular momentum has been transported toward the center to give tornadic windspeeds.
  20. 20. Thoughts...• Tornadogenesis failure is possibly generally a failure of contraction of the tornado cyclone.• Strength of the inner portion of the vortex (the tornado) depends partially on angular momentum in the outer portion, and the removal of mass upward through the vortex (and hence convergence below).
  21. 21. Thoughts...• Hence we seek to understand why most supercells are not conducive to transporting sufficient air upward through the tornado cyclone to increase the vortex to tornado strength.• Operationally, even if tornado cyclones are close enough to the 88D for detection, the differences between tornadic and non-tornadic TCs may almost always be ~unresolvable.
  22. 22. Thoughts...• Tornado life cycle appears to be related to the changes of the secondary flow (in- up vs. down-out) in the tornado cyclone.• Conjecture: long-lived tornadoes occur in tornado cyclones that (for reasons unknown) have a very slow transition from in-up to down-out.
  23. 23. n ct io Deep shear,adequate CAPE o nve e ep c ar-sid De f re o m ent lop ion E Supercell eve itat ER D H p ec i RE pr next ence, UA g RFD to C onver near- YO of tilting H nd SR Updraft grou Baroclinic ; gene ration Tornado g archin Cyclone nStates cont ractio VortexProcesses Tornado
  24. 24. So how did the TornadoCyclone come into existence?• Does the Rear-Flank Downdraft have a role?• Here are some historically validated observations about the supercell:
  25. 25. • Updraft acquires horseshoe shape.• Counter-rotation is observed.• A Rear-Flank Downdraft is present in the interior of the horseshoe pattern.• The tornado cyclone is centered in strong vertical velocity gradient on the interior left edge of the horseshoe.• A gust front is present below the rear edge of the updraft.
  26. 26. A simulation...Vortexstraddlesup/downdraf Horseshoe-t shapedCounter- updraftrotatingvorticesRear-FlankDowndraft*
  27. 27. Initial conditions
  28. 28. Mechanism 1: ArchingIn a nutshell, vortex rings about the RFD aretugged upward at the leading edge in thelow-level updraft, giving rise to vortex linearches and counter-rotating vortices.See Straka et al. In the Electronic Journal ofSevere Storms Meteorology, Vol 2.(EJSSM.org)
  29. 29. Mechanism 2: Tilting/stretching of inflow streamwise vorticity
  30. 30. Mechanism 3: Agglomeration of shear vortices
  31. 31. Real mechanism: All threeacting together (others?)
  32. 32. RFD Genesis• Different forcings for different parts?• One example showing evidence that precipitation plays a role...
  33. 33. Rear-side precipitation...
  34. 34. 0050 UTC• From airborne DRC Doppler• 40 dBZ Western tip of forward-flank precipitation North
  35. 35. Western tip of forward-flank precipitation• From airborne Doppler• Away• To North DRC
  36. 36. Crowther video frame…0050 UTC (north-northwest)
  37. 37. • 500 m Gust AGL front 21 m/s C 21 m/s DRC A
  38. 38. The Blob Blobette BWER A C North
  39. 39. Bobby Eddins video frames ~0053 UTC (N-W)
  40. 40. Gust• 500 m front AGL 21 m/s Blobette C 18 m/s Blob A
  41. 41. A C North
  42. 42. Bobby Eddins video ~0055 UTC (north)
  43. 43. Tornado Forms
  44. 44. Ian Wittmeyer photo ~0106 UTC (northwest)
  45. 45. In summary….• The descent of a DRC is associated with… • Locally stronger outflow; • A gust front that surges; • Counter-rotating vortices to the ground.• A locally intense downdraft embedded in the RFD is the key feature, and the DRC is associated with this downdraft.
  46. 46. n ct io Deep shear,adequate CAPE o nve e E p c sid ER De e ar- H f re RE o ent UA m lop ion YO Supercell Deve itat p ec i pr next gence, RFD to C onver near- of tilting H nd SR Updraft grou Baroclinic ; gene ration Tornado g archin Cyclone nStates cont ractio VortexProcesses Tornado
  47. 47. Role of the Mesocyclone and Supercell• It creates the precipitation structure needed to facilitate all those neato mechanisms of Tornado Cyclone formation (heretical, hyperbolic, etc.)• And thats all I have to say about that (F. Gump, 1994).
  48. 48. E ER H RE n UA ct io Deep shear, nve YOadequate CAPE o e ep c ar-sid De f re o m ent Supercell lop ion Deve itat p ec i pr next gence, RFD to C onver near- of tilting H nd SR Updraft grou Baroclinic ; gene ration Tornado g archin Cyclone nStates cont ractio VortexProcesses Tornado
  49. 49. The supercell environment• Issues from being in the field again with VORTEX2.... • You dont need no Shtinkin CAPE • You DO need upper-tropospheric storm- relative flow • You VERY MUCH need good low-level shear, low-level humidity, and adequate (?) low-level CAPE.
  50. 50. The supercell environment• High-CAPE days • Very subjectively: • You DO need upper-trop storm-relative flow • You VERY MUCH need good low-level shear, low-level humidity, and adequate (?) low-level CAPE.
  51. 51. Finally, my latest quasi-eccentric perspective change... • Cloud models initialized with a warm bubble and a supercell sounding love to produce Tornado Cyclones (or tornadoes if they have enough resolution)
  52. 52. Finally, my latest quasi-eccentric perspective change...• Watching storms in VORTEX2, I felt that many storms would produce tornadoes “if only...”
  53. 53. Finally, my latest quasi-eccentric perspective change...• Hypothesis: Most supercells would be tornadic if something did not interrupt the series of processes leading to tornado formation.
  54. 54. 45-120 min 30 min 20 min 5-20 min n ct io Deep shear,adequate CAPE o nve e ep c ar-sid De f re o m ent Supercell lop ion Deve itat p ec i pr next gence, RFD to C onver near- of tilting H nd SR Updraft grou Baroclinic ; gene ration Tornado g archin Cyclone nStates cont ractio VortexProcesses Tornado
  55. 55. So if... the typical supercell needs to go through a 1.5-3 hour sequence of processes to produce a tornado, and there are a plethora of ways to interrupt and interfere with these processes,then warning and research emphases really should be on... identifying the physics and probabilities of these interfering mechanisms,not on... identifying the right most-special environments supportive of supercell tornadoes.
  56. 56. Thank you!This research is supported by you through the National Science Foundation erik@rasmsys.com http://rasmsys.com

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