THUNDERSTORMS Convective heavy rain accompanied by lightning and - - PowerPoint PPT Presentation

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THUNDERSTORMS Convective heavy rain accompanied by lightning and - - PowerPoint PPT Presentation

Dec 28, 2023 331 likes •1.01k views

THUNDERSTORMS Convective heavy rain accompanied by lightning and thunder Ahrens Thunderstorms About 1,800 T-storms occur around the world at any instant Where do they occur the most? National Lightning Safety Institute Satellite lightning

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THUNDERSTORMS

  • Convective heavy rain accompanied by lightning and thunder

Ahrens

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Thunderstorms

About 1,800 T-storms occur around the world at any instant Where do they occur the most?

National Lightning Safety Institute

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Satellite lightning frequency: flashes per km2 per year

National Lightning Safety Institute

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Where do Thunderstorms occur the most often?

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Supercell thunderstorms on a visible satellite image

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CUMULUS STAGE

  • Dr. M. Pidwirny, Dep. of Geography, Okanagan University College

UPDRAFTS An “Air Mass” Thunderstorm, caused by heated surface parcels

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MATURE STAGE

  • Dr. M. Pidwirny, Dep. of Geography, Okanagan University College

Glaciated anvil top of a mature air-mass thunderstorm

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DISSIPATING STAGE

DOWNDRAFTS OCCUR IN THE SAME AREA AS THE UPDRAFTS

DISSIPATING STAGE (DOWNDRAFTS)

Microburst in the region of cold, precipitation laden downdrafts

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Microbursts and aviation dangers

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Development of the sea breeze and formation of convection

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Satellite and Radar images of the Florida Sea Breeze Front

How can the front be “seen” by radar?

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Lightning facts:

  • Breakdown potential: 3 MV/meter
  • For a 1000 m strike, how much Voltage needed?
  • Can carry 30-40 kA
  • The channel can reach 30000 degrees C
  • The channel can be seen for over 100 mi.
  • Thunder results from shockwave of exploding hot air channel
  • Sound travels at ~330 m/s in air
  • …one thousand one, one thousand two, one thousand three:
  • Cloud to cloud, Intracloud, Cloud to ground (10%)
  • Sprites and Jets
  • Positive (10%) or negative charge (90%)
  • Process leading to charge separation is complex
  • People still don’t really understand how lightning rods work
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Lightning

Charge separation:

  • Charges reside on the ice-crystal

surfaces

  • During collision between particles,

charges get transferred

  • Small ice crystals tend to acquire net

positive charge and then get carried toward the cloud top

  • Typical distribution of charges shown,

but it can be much more complex

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The lightning process

1: Stepped Leader A series of steps about 50 meters (160 ft) in length and 1 microsecond (0.000001 seconds) in duration. Studies of individual strikes have as many as10,000 steps! 2: Upward streamer Induction causes positive charges to trace an upward path from high, sharp points until channels meet 3: Connection Ionized path allows easy-flow of charge downward from cloud to surface 4: Return stroke Positive charge from the ground flows back upward along the path. This is where most of the current is: 30000 Amps produces heat, glow, and thunder

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Lightning and the rumbling thunder: an issue of path distance

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Red Sprites discharging from the top of a thunderstorm

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HAIL

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1970 Coffeyville KA hailstone

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Thunderstorms

HAIL DAMAGE

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Thunderstorms

HAIL DAMAGE

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  • Hail 3/4" or larger, or basically the size of any coin or larger

(a dime is 11/16" which the NWS accepts as 3/4")

  • Fallen tree limbs with a minimum diameter of an average adult's wrist
  • Living trees uprooted or blown down
  • Any part of a permanent, well-built structure damaged or destroyed
  • Measured wind gust from a calibrated anemometer of 58 MPH (50 knots) or greater

NWS definition of a severe thunderstorm

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SEVERE THUNDERSTORMS

THREE MAIN TYPES: 1) SQUALL LINE THUNDERSTORMS 2) MESOSCALE CONVECTIVE COMPLEX (MCC) 3) SUPERCELL THUNDERSTORMS All three types last much longer than

  • rdinary thunderstorms.

All three types need warm air and other factors in order to form.

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SQUALL LINE ON RADAR

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SQUALL LINE THUNDERSTORMS

*Develop ahead of cold fronts *Multi-cell storms *Often produce wind damage (DOWNBURSTS)

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Squall Line Thunderstorms

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Squall Line Thunderstorms L

North, Northwest winds Cold air Clearing skies South, Southwest winds Warm air Clearing skies behind warm front Until cumulus clouds and thunderstorms ahead of the cold front Cooler air Stratus clouds Snow, sleet, rain ahead of warm front

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Squall Line Thundestorms

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Mesoscale Convective Complex

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MCC

Nebraska MCC moving Southeast, July 1997 – 7 hour difference between satellite images CIMMS, WISC U *MCC must live more than 6 hrs *MCC high cloud cover must be larger than 18,000 square miles (size of CT, RI, MA) *MCC high cloud cover must be circular in shape

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MCC

Minnesota MCC moving Southeast, June 1994 NCDC

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MCC The Great USA Flood of 1993

1993 Mississippi River, Grafton IL Flooding, USGS – the “500-year” flood

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SUPERCELL THUNDERSTORMS

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SUPERCELL THUNDERSTORMS

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SUPERCELL THUNDERSTORMS

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SUPERCELL THUNDERSTORMS

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SUPERCELL THUNDERSTORMS

*Vertical Wind Shear *Two Downdrafts

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SUPERCELL THUNDERSTORMS

Chaseday.com

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Supercell Thunderstorms

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Tornados

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Tornados

A rotating column of air

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Tornados

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Tornados

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Tornados

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Tornados

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http://esminfo.prenhall.com/science/geoanimations/animations/Tornadoes.html

Development of Spin in a thunderstorm: Divergence and Wind Shear

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Tornado Tracks: Width, length, and intensity vary widely

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The New Fujita Scale

http://www.spc.noaa.gov/faq/tornado/ef-scale.html http://whyfiles.org/013tornado/3.html http://www.pbs.org/wgbh/nova/tornado/dam age.html

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Tornado Damage

NSSL

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Tornado Facts

Tornadoproject.com

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Area most likely to find favorable conditions for tornados

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Tornado Facts

NSSL

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Size of Tornados

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DOPPLER RADAR

NWS

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May 3, 1999 Oklahoma City Tornado Outbreak

NWS Norman

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May 3, 1999 Oklahoma City Tornado Outbreak

NWS Norman

Doppler on Wheels: 301 mph record measured wind speed

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May 3, 1999 Oklahoma City Tornado Outbreak

NWS Norman

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May 3, 1999 Oklahoma City Tornado Outbreak

NWS Norman

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Multiple Vortex Tornado

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Tornados

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Sideways Tornado

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Rope Tornado

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Rope Tornado

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Tornado damage

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Suction Vortices Signatures

SPC

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Other Rotating Columns of Air: Waterspout

  • Miss. Sound July 2005
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Other rotating columns of air: Dust-devil

BOM Australia