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AOSC 200 Lesson 10

AOSC 200 Lesson 10. Visible image of super thunderstorm from GEO satellite. Fig. 11.2a. IR image of the same super thunderstorm. Fig. 11.2b. Fig. 11-1, p. 312. THUNDERSTORM. IS A CLOUD OR CLUSTER OF CLOUDS THAT PRODUCES THUNDER, LIGHTNING, HEAVY RAIN, AND SOMETIMES HAIL AND TORNADOS

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AOSC 200 Lesson 10

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  1. AOSC 200Lesson 10

  2. Visible image of super thunderstorm from GEO satellite Fig. 11.2a

  3. IR image of the same super thunderstorm Fig. 11.2b

  4. Fig. 11-1, p. 312

  5. THUNDERSTORM • IS A CLOUD OR CLUSTER OF CLOUDS THAT PRODUCES THUNDER, LIGHTNING, HEAVY RAIN, AND SOMETIMES HAIL AND TORNADOS • CAN DIVIDE THUNDERSTORMS INTO TWO MAIN TYPES ISOLATED THUNDERSTORMS PRODUCED WITHIN A WARM HUMID AIR MASS SEVERE THUNDERSTORMS PRODUCED BY FORCEFUL LIFTING • IN THE USA, AIRMASS THUNDERSTORMS GENERALLY OCCUR IN WARM MOIST AIR - mT • LIFTING CAN BE BY FRONTS OR OROGRAPHICALLY

  6. Lifted Index • A parcel of air will not rise unless it is unstable. • The lifted index follows a parcel of air as it is lifted from the surface and cools at the dry adiabatic lapse rate until saturation occurs, and then cools at the wet adiabatic lapse rate. • The lifted index is defined as: The environmental temperature at 500 mb minus the temperature of the parcel of air when lifted to 500 mb • If the lifted index is negative then the atmosphere is unstable. • Severe thunderstorms require a lifting index less than -3

  7. Stepped Art Fig. 7-6, p. 175

  8. Life cycle of an ordinary thunderstorm cell Fig. 11.7

  9. THUNDERSTORM CUMULUS STAGE • CUMULUS STAGE • REQUIRES CONTINUOUS SOURCE OF WARM MOIST AIR • EACH NEW SURGE OF WARM AIR RISES HIGHER THAN THE LAST • STRONG UPDRAFTS • FALLING PRECIPITATION DRAGS AIR DOWN - DOWNDRAFT • ENTRAINMENT

  10. THUNDERSTORM MATURE STAGE • SHARP COOL GUSTS AT SURFACE SIGNAL DOWNDRAFTS • UPDRAFTS EXIST SIDE BY SIDE WITH DOWNDRAFTS • IF CLOUD TOP REACHES TROPOPAUSE UPDRAFTS SPREAD LATERALLY - ANVIL SHAPE • TOP OF ICE LADEN CIRRUS CLOUDS • GUSTY WINDS, LIGHTNING, HEAVY PRECIPITATION, HAIL

  11. THUNDERSTORM DISSIPATING STAGE • DOWNDRAFT AND ENTRAINMENT DOMINATE • NO UPDRAFT • THUNDERSTORM LOSES ENERGY SOURCE

  12. An ordinary airmass thunderstorm Fig. 11.8

  13. Table 11-1, p. 315

  14. THUNDERSTORM GROWTH AND DEVELOPMENT • AIR NEEDS TO BE UNSTABLE • DRYLINE - LINE BETWEEN cT AND mT AIR MASSES-LEADS TO UNSTABLE AIR • LIFTED INDEX IS NEGATIVE, AIR IS UNSTABLE • VERTICAL WIND SHEAR CAN ‘SPIN UP’ THUNDERSTORM • SEVERE THUNDERSTORMS - mT MEETS Cp. • GREATEST CONTRAST - SPRING AND EARLY SUMMER

  15. A climatology of the average number of thunderstorm days in a year Fig. 11-3, p. 314

  16. Fig. 11-4, p. 315

  17. Schematic of a multicell thunderstorm. Red arrows represent the warm updraft, blue arrows the cool downdraft Fig. 11-10, p. 320

  18. Squall Line • Is a set of individual intense thunderstorm cells arranged in a line. • They occur along a boundary of unstable air – e.g. a cold front. • Strong environmental wind shear causes the updraft to be tilted and separated from the downdraft. • The dense cold air of the downdraft forms a ‘gust front’.

  19. Pre-frontal squall lines may form ahead of an advancing cold front as the air aloft forms wavesdownwind from the cold front

  20. Squall line associate with a cold front. Fig. 11.10a

  21. Fig. 11.13

  22. Mesoscale Convective Complex • A Mesoscale Convective Complex is composed of multiple single-cell storms in different stages of development. • The individual thunderstorms must support the formation of other convective cells • In order to last a long time, a good supply of moisture is required at low levels in the atmosphere.

  23. Infrared image of a mesoscale convective complex over Kansas, July 8 1997. Fig. 11-13, p. 322

  24. SUPERCELL THUNDERSTORM • SINGLE CELL THUNDERSTORM THAT PRODUCES DANGEROUS WEATHER • REQUIRES A VERY UNSTABLE ATMOSPHERE AND STRONG VERTICAL WIND SHEAR - BOTH SPEED AND DIRECTION • UNDER THE INFLUENCE OF THE STRONG WIND SHEAR THE ENTIRE THUNDERSTORM ROTATES • FAVORED REGION IS THE SOUTHERN GREAT PLAINS IN THE SPRING

  25. TYPE OF THUNDERSTORM • SINGLE-CELL THUNDERSTORM • MULTICELL THUNDERSTORM • MESOSCALE CONVECTIVE C0MPLEX • SUPERCELL THUNDERSTORM

  26. Tornado over College Park, 10/23/01

  27. Box 11-1, p. 329

  28. http://www.youtube.com/watch?v=43VoMesUd2Qhttp://www.youtube.com/watch?v=43VoMesUd2Qhttp://www.youtube.com/watch?v=43VoMesUd2Qhttp://www.youtube.com/watch?v=43VoMesUd2Q

  29. Geographic distribution of the month of maximum tornado threa.t Fig. 11-30, p. 337

  30. TORNADO • DERIVED FROM SPANISH WORD ‘TORNADA’ – THUNDERSTORM • TORNADOS ARISE FROM SEVERE THUNDERSTORMS • MOST TORNADOS IN CENTRAL US • ON AVERAGE ABOUT 770 TORNADOS ARE REPORTED ANNUALLY • OCCUR MAINLY FROM APRIL TO JUNE BUT ALL YEAR ROUND

  31. Fig. 11.18

  32. TORNADO • LESS THAN 1.6 KM WIDE, AND SHORT LIVED • NO ONE REALLY KNOWS HOW THEY ARE FORMED • MOST DROP DOWN FROM SUPERCELL THUNDERSTORMS - ROTATING • HOWEVER THIS ROTATION CANNOT EXPLAIN THE FAST ROTATION OF A TORNADO • THE HORIZONTAL ROTATION OF THE THUNDERSTORM IS CONVERTED INTO VERTICAL ROTATION OF THE TORNADO

  33. TORNADO • TRAVELS AT ABOUT 45 KM PER HOUR AND CUTS A PATH OF ABOUT 26 KM LONG • BUT REALLY NO SUCH THING AS AN AVERAGE TORNADO • PRESSURE AT CENTER OF VORTEX AS MUCH AS 30% LOWER THAN SURROUNDINGS. • AIR RUSHES IN FROM SURROUNDINGS AND IS SPIRALED UPWARD. • CONSERVATIONOF ANGULAR MOMENTUM • BECAUSE OF TREMENDOUS PRESSURE GRADIENT WINDS CAN REACH 400 KM (250 MILES) PER HOUR.

  34. Fig. 11-23, p. 331

  35. STAGES OF A TORNADO • ORGANIZING STAGE - FUNNEL CLOUD DROPS DOWN TO THE SURFACE • MATURE STAGE - TORNADO AT PEAK INTENSITY AND WIDTH • SHRINKING STAGE • ROPE STAGE

  36. Table 11-3, p. 333

  37. Fig. 11-25, p. 333

  38. Fig. 11-33, p. 342

  39. http://www.youtube.com/watch?v=ToY11hHpAJkhttp://www.youtube.com/watch?v=ToY11hHpAJkhttp://www.youtube.com/watch?v=ToY11hHpAJkhttp://www.youtube.com/watch?v=ToY11hHpAJk

  40. LIGHTNING • .LARGE ELECTRICAL DISCHARGE THAT RESULTS FROM RISING AND SINKING MOTIONS IN A THUNDERSTORM • .SEQUENCE IS AS FOLLOWS; • . CHARGE SEPARATION - REALLY DO NOT UNDERSTAND WHY • . GROUND BECOMES POSITIVELY CHARGED • . LIGHTNIING FORMATION BEGINS - LEADERS • . LIGHTNING FLASH OCCURS

  41. Lightning formation: Charge separation. Fig. 11.28

  42. Fig. 11-37, p. 346

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