Downbursts and dust stormsDownbursts and dust storms

Review of last lectureReview of last lecture

1.1. 3 stages of supercell tornado formation. 3 stages of supercell tornado formation.

2.2. 2 types of non-supercell tornado formation. 2 types of non-supercell tornado formation.

3.3. Tornado outbreak (number>6) Tornado outbreak (number>6)

4.4. Which state has the largest number of tornadoes in Which state has the largest number of tornadoes in U.S.?U.S.?

5.5. Tornado outlookTornado outlook

6.6. 2 types of mesoscale convective systems2 types of mesoscale convective systems

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 • Haboobs• Microbursts

Different downburstsDifferent downbursts

620 miles or 1000 km620 miles or 1000 km

62 miles or 100 km62 miles or 100 km

6.2 miles or 10 km6.2 miles or 10 km

0.62 mile or 1 km0.62 mile or 1 km

DerechosDerechos• A derecho (spanish word meaning “straight ahead”) is a widespread,

long-lived wind storm that is associated with a band of rapidly moving showers or thunderstorms (often a squall line).

• By definition, the wind damage swath extends more than 240 miles and wind speed > 57 mph. Can produce destruction similar to that of tornadoes. The damage typically is directed in one direction along a relatively straight swath.

From NOAA SPC Derecho website

Video: DerechoVideo: Derecho

http://www.youtube.com/watch?http://www.youtube.com/watch?v=K61qGvKltL8 v=K61qGvKltL8

Development of a derechoDevelopment of a derecho

Thunderstorm stageThunderstorm stage

Bow echo stageBow echo stage

Comma or line echo stageComma or line echo stage

Clouds associated with a derechoClouds associated with a derecho

From NOAA SPC Derecho website

"The Line Storm," by John Steuart "The Line Storm," by John Steuart Curry, 1897-1946Curry, 1897-1946

Different types of derechosDifferent types of derechos

Serial derechosSerial derechos Progressive derechosProgressive derechos Hybrid derechosHybrid derechos Low dewpoint derechosLow dewpoint derechos

Serial derechoSerial derecho typically is associated with an typically is associated with an

extensive extensive squall line or squall line or quasi-linear convective quasi-linear convective systemsystem with multiple with multiple embedded bow echoes. embedded bow echoes.

usually occur in conjunction usually occur in conjunction with well-defined, migratory with well-defined, migratory low pressure system. low pressure system.

Overall convective system Overall convective system (and, therefore, derecho) (and, therefore, derecho) motion is dominated by motion is dominated by advectionadvection --- the downstream --- the downstream movement of individual movement of individual thunderstorm cells by the thunderstorm cells by the environmental wind. environmental wind.

From NOAA SPC Derecho website

Progressive derechoProgressive derecho

typically is associated with a typically is associated with a squall line of restricted length squall line of restricted length that may involve a single that may involve a single bow echo or multiple bows. bow echo or multiple bows.

usually are associated with a usually are associated with a stagnant large scale weather stagnant large scale weather pattern. pattern.

Overall convective system Overall convective system (and, therefore, derecho) (and, therefore, derecho) motion is dominated by motion is dominated by thunderstorm thunderstorm propagationpropagation --- that is, the development of --- that is, the development of new storm cells downstream new storm cells downstream from existing ones. from existing ones.

June 2012 derecho over the Midwest and Ohio Valley

From NOAA SPC Derecho website

Annual number of derecho eventsAnnual number of derecho events

Timing of derecho eventsTiming of derecho events

From NOAA SPC Derecho website

MicroburstMicroburst• Downbursts with diameteres of less than 4km (2.5mi) called

microbursts• Two types: wet and dry• can produce dangerous situations at airports, as they impede air

travel.• Three stages of development: Contact, Outburst, Cushion

Microburst and air travelMicroburst and air travel

HaboobsHaboobs• Very strong horizontal winds over desert regions create sandstorms

called haboobs (from the Arabic word meaning “wind”).

Video: HaboobsVideo: Haboobs

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

A movie’s depiction:A movie’s depiction: http://www.youtube.com/watch?http://www.youtube.com/watch?

v=B4sNGmDBLWg v=B4sNGmDBLWg （（ at 1at 1 ：： 3333 ：： 59-59-1:35:001:35:00））

Global distribution of aerosolsGlobal distribution of aerosols

Global impact of dust stormsGlobal impact of dust storms

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

Palmer drought severity index (PDSI)Palmer drought severity index (PDSI) was developed by Wayne Palmer in the 1960s was developed by Wayne Palmer in the 1960s

and uses and uses temperature and rainfall temperature and rainfall information in information in a model to determine dryness of soil moisture.a model to determine dryness of soil moisture.

is most effective in determining long term is most effective in determining long term droughtdrought ( (a matter of several monthsa matter of several months) ) and is not and is not as good with short-term forecasts (a matter of as good with short-term forecasts (a matter of weeks). weeks).

It uses a 0 as normal, and drought is shown in It uses a 0 as normal, and drought is shown in terms of minus numbers; for example, minus 2 is terms of minus numbers; for example, minus 2 is moderate drought, minus 3 is severe drought, moderate drought, minus 3 is severe drought, and minus 4 is extreme drought.and minus 4 is extreme drought.

PDSI for US in December 2011PDSI for US in December 2011

Change of PDSI in the last 100 yearsChange of PDSI in the last 100 years

SummarySummary

1.1. 3 types of downbursts.3 types of downbursts.

2.2. 4 types of derechos. Which U.S. state has the largest 4 types of derechos. Which U.S. state has the largest annual mean number of derecho events? Which season annual mean number of derecho events? Which season has the largest occurrence of derechos?has the largest occurrence of derechos?

1.1. Haboobs. Haboobs.

2.2. Global desertification.Global desertification.

3.3. What is PDSI? Which two variables is PDSI dependent What is PDSI? Which two variables is PDSI dependent on? How has the PDSI been changing in the last on? How has the PDSI been changing in the last century?century?