1. Downbursts and dust storms

2. Review of last lecture 2 types of mesoscale convective systems
Structure of MCCs
Structure of squall lines: four components
Derechos

3. 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 ( km)
Microbursts (1 km)

4. Video: Microburst

5. 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
Chapter 11, Forcasting Labeled

6. Development of microburst
Three stages: Contact, Outburst, Cushion

7. Structure of a microburst

8. 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

9. 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

10. 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.

11. Wet microburst: visual identification
A rain foot may be a visible sign of a wet microburst.

12. 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 (N8845E), John F. Kennedy International Airport – 24 June 1975
Pan Am Flight 759 Boeing (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 (AP-BKC), Islamabad International Airport, Islamabad, Pakistan- April

13. 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.

14. Video: Haboobs

15. 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.

16. Global distribution of aerosols

17. Global impact of dust storms

18. Factors contributing to dust storms
Desertification
Drying of global soil moisture

19. 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

20. Global desertification vulnerability

21. Drying of global soil moisture
PDSI: Palmer drought severity index

22. 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

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