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Downbursts and dust storms. Review of last lecture. 2 types of mesoscale convective systems Structure of MCCs Structure of squall lines: four components Derechos. Downbursts: Introduction.

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Review of last lecture

  • 2 types of mesoscale convective systems
  • Structure of MCCs
  • Structure of squall lines: four components
  • Derechos
downbursts introduction
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
Video: 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
Development of microburst

Three stages: Contact, Outburst, Cushion

dry microburst
Dry microburst

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
Dry microburst: visual identification
  • 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)
  • Blowing dust/dust rings at surface
  • Very good indicators of dry microburst potential
wet microburst
Wet microburst

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
Wet microburst: visual identification
  • A rain foot may be a visible sign of a wet microburst.
fatal crashes or aircraft incidents due to microbursts
Fatal crashes or aircraft incidents due to microbursts

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
Causes of atmospheric turbulence

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
Video: Haboobs

h aboobs
  • 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.
factors contributing to dust storms
Factors contributing to dust storms


Drying of global soil moisture

  • Caused mainly be human activities and climate change
  • Is one of the most significant global environmental problems
  • About a billion people are under threat
drying of global soil moisture
Drying of global soil moisture

PDSI: Palmer drought severity index



  • 3 types of downbursts (derechos, haboobs, microbursts)
  • 3 types of microbursts (wet, dry, hybrid).
  • 4 causes of atmospheric turbulence.
  • Haboobs (dust storms). Global desertification. Drying of global soil moisture
works cited
Works cited