aosc 200 lesson 10
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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 - PowerPoint PPT PresentationTRANSCRIPT
AOSC 200Lesson 10
Fig. 11.2a
Visible image of super thunderstorm from GEO satellite
Fig. 11.2b
IR image of the same super thunderstorm
Fig. 11-1, p. 312
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
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
Fig. 7-6, p. 175
Stepped Art
Fig. 11.7
Life cycle of an ordinary thunderstorm cell
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
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
THUNDERSTORM DISSIPATING STAGE
• DOWNDRAFT AND ENTRAINMENT DOMINATE
• NO UPDRAFT• THUNDERSTORM LOSES ENERGY SOURCE
Fig. 11.8
An ordinary airmass thunderstorm
Table 11-1, p. 315
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
Fig. 11-3, p. 314
A climatology of the average number of thunderstorm days in a year
Fig. 11-4, p. 315
Fig. 11-10, p. 320
Schematic of a multicell thunderstorm. Red arrows represent the warm updraft, blue arrows the
cool downdraft
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’.
Pre-frontal squall lines may form ahead of an advancing cold front as the air aloft forms waves downwind from the cold front
Fig. 11.10a
Squall line associate with a cold front.
Fig. 11.13
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.
Fig. 11-13, p. 322
Infrared image of a mesoscale convective complex over Kansas, July
8 1997.
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
TYPE OF THUNDERSTORM
• SINGLE-CELL THUNDERSTORM
• MULTICELL THUNDERSTORM
• MESOSCALE CONVECTIVE C0MPLEX
• SUPERCELL THUNDERSTORM
Tornado over College Park, 10/23/01
Box 11-1, p. 329
http://www.youtube.com/watch?v=43VoMesUd2Qhttp://www.youtube.com/watch?v=43VoMesUd2Q
Fig. 11-30, p. 337
Geographic distribution of the month of maximum tornado threa.t
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
Fig. 11.18
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
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.
Fig. 11-23, p. 331
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
Table 11-3, p. 333
Fig. 11-25, p. 333
Fig. 11-33, p. 342
http://www.youtube.com/watch?v=ToY11hHpAJk http://www.youtube.com/watch?v=ToY11hHpAJk
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
Fig. 11.28
Lightning formation: Charge separation.
Fig. 11-37, p. 346
Fig. 11-38, p. 346
Life cycle and path of a hailstone in a supercell
thunderstorm
HAIL• LARGE CLUMPS OR BALLS OF ICE
• START OF AS A SMALL ICE PARTICLE
• DUE TO UPDRAFT THE ICE PARTICLE DOES NOT FALL TO GROUND BUT IS RECYCLED INTO THE FREEZING PORTION OF THE THUNDERSTORM,
• EACH TIME IT IS TAKEN UPWARD IT ACCUMULATES MORE ICE
• CAN END UP AS LARGE AS A GRAPEFRUIT
Fig. 11.33
Number of days per year with Hail > .75 inch