Transcript Downbursts and dust storms

Downbursts and dust storms
Review of last lecture
1. 2 types of mesoscale convective systems
2. Structure of MCCs
3. Structure of squall lines: four components
4. Derechos
Downbursts: Introduction
• Downbursts are gusts of wind
that can reach speeds in
excess of 270km/hr (165mph),
and are potentially deadly.
• Three common types:
• Derechos (1000 km)
• Haboobs (10-100 km)
• Microbursts (1 km)
Video: Microburst
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http://www.youtube.com/watch?v=NT3Ybu
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Microburst
• is a very localized column of
downdraft (sinking air) in a
thunderstorm that is less than 2.5
miles in scale.
• produces damaging divergent and
straight-line winds at the surface
as high as 150mph
• is similar to, but distinguishable
from, tornadoes, which generally
have convergent damage.
• can produce dangerous situations
at airports, as they impede air
travel.
• 3 types: dry, wet, hybrid
Development of microburst
Three stages: Contact, Outburst, Cushion
Structure of a microburst
Dry microburst
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Very dry boundary layer topped by a moist layer
Primarily driven by cooling beneath the thunderstorm cloud base
due to rain evaporation and ice sublimation
Little or no rain. Often associated with high-based thunderstorms.
Sometimes associated with fair weather
Dry microburst: visual identification
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Virga in the sky: defined as
wisps or streaks of water or
ice particles falling out of a
cloud but evaporating before
reaching the earth's surface
as precipitation. (NOAA 2001)
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Blowing dust/dust rings at
surface
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Very good indicators of dry
microburst potential
Wet microburst
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A nearly saturated layer topped by an elevated dry layer
primarily driven by entrainment of mid-level dry air and
precipitation loading.
accompanied by heavy precipitation at the surface.
Wet microburst: visual identification
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A rain foot may be a visible
sign of a wet microburst.
Fatal crashes or aircraft incidents due
to microbursts
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A BOAC Canadair C-4 (G-ALHE), Kano Airport - 24 June 1956.
A Malév Ilyushin Il-18 (HA-MOC), Copenhagen Airport – 28 August 1971.
Eastern Air Lines Flight 66 Boeing 727-225(N8845E), John F. Kennedy
International Airport – 24 June 1975
Pan Am Flight 759 Boeing 727-235 (N4737), New Orleans International Airport
– 9 July 1982
Delta Air Lines Flight 191 Lockheed L-1011 TriStar (N726DA), Dallas/Fort
Worth International Airport – 2 August 1985
Martinair Flight 495 McDonnell Douglas DC-10 (PH-MBN), Faro Airport – 21
December 1992
USAir Flight 1016 Douglas DC-9 (N954VJ), Charlotte/Douglas International
Airport – 2 July 1994
Goodyear Blimp GZ-20A (N1A, "Stars and Stripes"), Coral Springs, Florida –
16 June 2005
Bhoja Air Flight 213 Boeing 737-200 (AP-BKC), Islamabad International
Airport, Islamabad, Pakistan- April 20 2012
Causes of atmospheric turbulence
1.
2.
3.
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Thermals - Heat from the sun
makes warm air masses rise and
cold ones sink.
Jet streams - Fast, high-altitude air
currents disturb the air nearby.
Mountains - Air passes over
mountains and causes wave and
turbulence on the other side.
Wake turbulence - Near the
ground a passing plane or
helicopter sets up small, chaotic air
currents, or Microbursts – dry,
wet and hybrid.
Video: Haboobs
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http://www.youtube.com/watch?v=LGDvBk
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Haboobs
• Very strong horizontal winds over desert regions create sandstorms
called haboobs (from the Arabic word meaning “wind”).
• Occur regularly in arid regions throughout the world.
Global distribution of aerosols
Global impact of dust storms
Factors contributing to dust storms
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Desertification
Drying of global soil moisture
Desertification
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Caused mainly be
human activities and
climate change
Is one of the most
significant global
environmental problems
About a billion people
are under threat
Global desertification vulnerability
Drying of global soil moisture
PDSI: Palmer drought
severity index
Summary
1. 3 types of downbursts (derechos, haboobs,
microbursts)
2. 3 types of microbursts (wet, dry, hybrid).
3. 4 causes of atmospheric turbulence.
4. Haboobs (dust storms). Global
desertification. Drying of global soil moisture
Works cited
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http://www-frd.fsl.noaa.gov/mab/microburst/
http://www.cimms.ou.edu/~doswell/microbursts/Handboo
k.html