Downbursts and dust storms
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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

http://www.youtube.com/watch?v=NT3YbuGHfC4


Microburst
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

http://www.youtube.com/watch?v=LGDvBk4knF0


H aboobs
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.




Factors contributing to dust storms
Factors contributing to dust storms

Desertification

Drying of global soil moisture


Desertification
Desertification

  • 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


Summary

  • 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

http://www-frd.fsl.noaa.gov/mab/microburst/

http://www.cimms.ou.edu/~doswell/microbursts/Handbook.html


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