Downbursts and dust stormsDownbursts and dust storms

Review of last lectureReview of last lecture

1.1. 2 types of mesoscale convective systems2 types of mesoscale convective systems

2.2. Structure of MCCs Structure of MCCs

3.3. Structure of squall lines: four componentsStructure of squall lines: four components

4.4. DerechosDerechos

Downbursts: IntroductionDownbursts: 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: MicroburstVideo: Microburst

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

MicroburstMicroburst

• 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 microburstDevelopment of microburstThree stages: Contact, Outburst, Cushion

Structure of a microburstStructure of a microburst

Dry microburstDry microburst Very dry boundary layer topped by a moist layerVery dry boundary layer topped by a moist layer Primarily driven by cooling beneath the thunderstorm cloud base Primarily driven by cooling beneath the thunderstorm cloud base

due to rain evaporation and ice sublimation due to rain evaporation and ice sublimation Little or no rain. Often associated with high-based thunderstorms. Little or no rain. Often associated with high-based thunderstorms.

Sometimes associated with fair weatherSometimes associated with fair weather

Dry microburst: visual identificationDry microburst: visual identification

Virga in the skyVirga in the sky: defined as : defined as wisps or streaks of water or wisps or streaks of water or ice particles falling out of a ice particles falling out of a cloud but evaporating before cloud but evaporating before reaching the earth's surface reaching the earth's surface as precipitation. (NOAA 2001)as precipitation. (NOAA 2001)

Blowing dust/dust rings at Blowing dust/dust rings at surfacesurface

Very good indicators of dry Very good indicators of dry microburst potentialmicroburst potential

Wet microburstWet microburst A nearly saturated layer topped by A nearly saturated layer topped by an elevated dry layeran elevated dry layer primarily driven by entrainment of mid-level dry air and primarily driven by entrainment of mid-level dry air and

precipitation loading.precipitation loading. accompanied by heavy precipitation at the surface. accompanied by heavy precipitation at the surface.

Wet microburst: visual identificationWet microburst: visual identification

A rain foot A rain foot may be a visible may be a visible sign of a wet microburst. sign of a wet microburst.

Fatal crashes or aircraft incidents due Fatal crashes or aircraft incidents due to microburststo microbursts

A BOAC Canadair C-4 (G-ALHE), Kano Airport - 24 June 1956.A BOAC Canadair C-4 (G-ALHE), Kano Airport - 24 June 1956. A Malév Ilyushin Il-18 (HA-MOC), Copenhagen Airport – 28 August 1971.A Malév Ilyushin Il-18 (HA-MOC), Copenhagen Airport – 28 August 1971. Eastern Air Lines Flight 66 Boeing 727-225(N8845E), John F. Kennedy Eastern Air Lines Flight 66 Boeing 727-225(N8845E), John F. Kennedy

International Airport – 24 June 1975International Airport – 24 June 1975 Pan Am Flight 759 Boeing 727-235 (N4737), New Orleans International Airport Pan Am Flight 759 Boeing 727-235 (N4737), New Orleans International Airport

– 9 July 1982– 9 July 1982 Delta Air Lines Flight 191 Lockheed L-1011 TriStar (N726DA), Dallas/Fort Delta Air Lines Flight 191 Lockheed L-1011 TriStar (N726DA), Dallas/Fort

Worth International Airport – 2 August 1985Worth International Airport – 2 August 1985 Martinair Flight 495 McDonnell Douglas DC-10 (PH-MBN), Faro Airport – 21 Martinair Flight 495 McDonnell Douglas DC-10 (PH-MBN), Faro Airport – 21

December 1992December 1992 USAir Flight 1016 Douglas DC-9 (N954VJ), Charlotte/Douglas International USAir Flight 1016 Douglas DC-9 (N954VJ), Charlotte/Douglas International

Airport – 2 July 1994Airport – 2 July 1994 Goodyear Blimp GZ-20A (N1A, "Stars and Stripes"), Coral Springs, Florida – Goodyear Blimp GZ-20A (N1A, "Stars and Stripes"), Coral Springs, Florida –

16 June 200516 June 2005 Bhoja Air Flight 213 Boeing 737-200 (AP-BKC), Islamabad International Bhoja Air Flight 213 Boeing 737-200 (AP-BKC), Islamabad International

Airport, Islamabad, Pakistan- April 20 2012Airport, Islamabad, Pakistan- April 20 2012

Causes of atmospheric turbulenceCauses of atmospheric turbulence

1.1. ThermalsThermals - Heat from the sun - Heat from the sun makes warm air masses rise and makes warm air masses rise and cold ones sink.cold ones sink.

2.2. Jet streamsJet streams - Fast, high-altitude - Fast, high-altitude air currents disturb the air nearby.air currents disturb the air nearby.

3.3. MountainsMountains - Air passes over - Air passes over mountains and causes wave and mountains and causes wave and turbulence on the other side.turbulence on the other side.

4.4. Wake turbulenceWake turbulence - Near the - Near the ground a passing plane or ground a passing plane or helicopter sets up small, chaotic air helicopter sets up small, chaotic air currents, orcurrents, orMicroburstsMicrobursts – dry, wet – dry, wet and hybrid.and hybrid.

Video: HaboobsVideo: Haboobs

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

HaboobsHaboobs• 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 aerosolsGlobal distribution of aerosols

Global impact of dust stormsGlobal impact of dust storms

Factors contributing to dust stormsFactors contributing to dust storms

DesertificationDesertification Drying of global soil moisture Drying of global soil moisture

DesertificationDesertification

Caused mainly be Caused mainly be human activities and human activities and climate changeclimate change

Is one of the most Is one of the most significant global significant global environmental problemsenvironmental problems

About a billion people About a billion people are under threatare under threat

Global desertification vulnerabilityGlobal desertification vulnerability

Drying of global soil moistureDrying of global soil moisture

PDSI: Palmer drought severity index

SummarySummary

1.1. 3 types of downbursts (derechos, haboobs, 3 types of downbursts (derechos, haboobs, microbursts)microbursts)

2.2. 3 types of microbursts (wet, dry, hybrid). 3 types of microbursts (wet, dry, hybrid).

3.3. 4 causes of atmospheric turbulence.4 causes of atmospheric turbulence.

4.4. Haboobs (dust storms). Global Haboobs (dust storms). Global desertification. Drying of global soil moisturedesertification. Drying of global soil moisture

Works citedWorks cited

http://www-frd.fsl.noaa.gov/mab/microburst/ http://www.cimms.ou.edu/~doswell/microbursts/Handboo

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