Thunderstorms, Tornadoes, and Hurricanes

October 27/28 2010

Extreme Weather

Hurricane Ivanover Gulf, Sept. 2004

Source: NOAA

Definitions

*Climate Change: * Changes in climate of the past, present or future

associated with natural or anthropogenic (human) factors

*Global Warming:* Warming of the 20th and 21st century associated with

anthropogenic activities.

Weather VS Climate *Weather describes whatever is

happening outdoors in a given place at a given time.

*Weather is what happens from minute to minute.

*can change a lot within a very short time

*Weather includes daily changes in precipitation, barometric pressure, temperature, and wind conditions in a given location.

*Climate describes the total of all weather occurring over a period of years in a given place.

*Climate tells us what it's usually like in the place where you live

Climate is what you expect, weather is what you get!

Thunderstorms*Begin in cumulus stage*Warm, moist air rises, cools.*Water condenses out of air, releasing heat*Updrafts develop*Precipitation occurs when weight of

precipitation overcomes updrafts

Thunderstorms*Cloud draws in drier air which

evaporates some moisture, causes cooling. *This cool, dense air sinks,

creating downdrafts*Downdrafts mark mature

thunderstorms*Downdrafts and updrafts make

the thunderstorm cell*Storm may extend to top of

tropopause (~12 km)*#1: Why doesn’t precipitation fall

right as condensation occurs?

Thunderstorms*A rush of cold air (downdraft) usually occurs

at onset of precipitation*Storms usually dissipate within 15-30 min.*Updrafts weaken, downdrafts dominate*Provide summer rainfall for much of the US*Cooling of up to 10˚C/18˚F on hot summer

days*Strong downdrafts can force more warm air

up, causing multi-cell storms.

Thunderstorm development time lapse (Florida)*http://vimeo.com/4806845

Severe Thunderstorms

*Stronger winds aloft than at surface vertical wind shear*Tips over top of storm, allows for prolonged

updrafts, longer storm life*Hail forms due to strong updrafts, falls when

heavy enough to overcome updrafts*Strong downdrafts called “microbursts” may

occur, winds up to 146 kt*Dangerous to aviation!

Source: Wikipedia

Microburst#2: How do you think it could be dangerous to aviation?

Distribution of Thunderstorms

# days per year thunderstorms observed. Do you think hail follows the same distribution?

Distribution of Hail #3: How are max/min different here? Why do you think more hail over Rockies, Great Plains?

Lightning*Lightning occurs to reduce a buildup of positive

and negative charges within a cloud. *+ charged ice crystals tend to be at top of

cloud, and - charged hailstones at bottom. *Area of positive charge on ground develops

below storm*When electrical potential gradient large

enough, the electrical current flows to surface as lightning!*Can have cloud-to-cloud, cloud-to-ground, or

lightning within a cloud.

http://apollo.lsc.vsc.edu/classes/met130/notes/chapter14/graphics/lightning.mpg

Lightning*Can heat the air rapidly to 30,000˚C/54,000˚F*This rapid heating causes air to expand and

makes a booming sound wave– thunder!*Sound takes 3 sec to go 1 km, (5 sec per mile)*#4: If you see lightning and hear thunder 15 sec

later, how far away is the lightning?*5 km/3 miles away!*Sometimes thunder is not heard due to the

atmosphere bending the sound waves upward

Lightning*100 people per year die of lightning

strikes*If about to strike, hair stands on end, skin

tingles, hear clicking sounds

Sept 2003, Carquinez Straits, CAAfter rare influx of moisture from SW

Cloud-to-ground lightning over Las Vegas during SW monsoon season

Source: www.goldengatephotos.com

Tornadoes*Rapidly rotating winds around intense low

pressure center*Start as funnel-shaped cloud*Diameter of 100-600 meters (300-2000 ft)*Move at 20-40 kt (23-46 mph)*Last only a few minutes*Travel up to 7 km (4 mi)

Source: http://www.cs.uwaterloo.ca

Tornadoes*Most violent event: April 3 and 4, 1974*148 tornadoes over a 16 hour period*Covered 13 states*307 people killed, 6000 injured*$600 million in damage

Trailer park destroyed in Huntsville, ALF4 tornado over Parker City, IN

Source: http://www.april31974.com

Tornadoes*Tri-state tornado event March 18, 1925*7 tornadoes across MO, IL, IN*695 people killed!*US has most tornadoes of all countries*Occur in all states, greatest number in

“Tornado Alley”*This is area where cool, dry air from Canada

meets warm, moist air from Gulf

Source: http://wximpact40-88.pbworks.com

Tornadoes*Tornado alley susceptible since warm, humid air

overlain by cool air aloft*If strong vertical wind shear occurs and

thunderstorms form, tornadoes likely*Usually occur March-July in late afternoon*Can pick up people, animals, appliances, railroad

cars*220 kt winds max, most < 125 kt*Can pop roofs off/collapse houses! (Bernoulli’s

principle)*#5: How can tornadoes “pop” a roof off a

structure?Tornadoes around the UShttp://www.youtube.com/watch?v=43VoMesUd2Q

Fujita Scale

Hurricanes*An intense storm, winds over 64 kt/74 mph*Generally form in tropics (23 1/2˚N/S of

equator)*Warm, humid areas*A “tropical” aka “Easterly” wave in

atmosphere disrupts usual wind flow*In western N Pacific (Asia/Japan), typhoon*In Indian Ocean/Australia, cyclone*Today we will use “hurricane” to refer to all

Hurricane and SST Change

(Webster et al, 2005, Science)

Webster et al. report that the number of category 4 and 5 hurricanes has almost doubled globally over the past three decades

Be careful

*Hurricanes are natural events, and are not linearly related to climate change

*Climate change, by increase SST, indeed makes it more possible to have strong hurricane occur

Anatomy of a hurricane

Hurricanes*Convergence at surface brings warm, moist air

up*Divergence aloft and sinking air outside the

hurricane, clear skies immediately surrounding

Hurricanes*Ingredients for Hurricane:*Winds light*Deep layer of high humidity, warm air*Water >80˚F

*Season lasts June-November*Need converging winds, so form in ITCZ*Take in heat at ocean surface, convert it to

kinetic energy as wind*Form between 5˚and 10˚N and S*#6: Why don’t they form over equator?*No Coriolis effect at equator to start “spin”!

Hurricanes

#7: Why do hurricanes move from East to West?

Hurricanes*Begins as tropical disturbance/wave*Tropical depression: winds 20-34 kts, closed

isobars*Tropical storm: winds 35-60 kts*Hurricane: winds >64 kts

Hurricane Katrina Source: NOAA

Atlantic and Pacific Storm tracks, 2010

Source: Washington Post

Source: Wikipedia

Hurricanes: Why so destructive?*High winds, can collapse structures

*Storm surge!*High wind-driven waves*Low pressure in storm center causes sea

level to rise up to 0.5 m (1.5 ft)! *Like water up a straw

*Strong downbursts*Heavy, sudden rains can cause flooding

Katrina damage in Mississippi

Source: www.katrinadestruction.com

Hurricane Andrew*August 21, 1992*Hit Louisiana with 120 kt winds*200,000 homes destroyed*$30 billion in damage*53 deaths*Most deaths in US from hurricane:*1900 Galveston, TX: more than 6,000 died!*Confused when calm eye hit, went out to

“check things out”, other side of storm hit suddenly!

Source: NOAA

Hurricanes and El Niño*#8: What is El Nino? What are signs it is

happening?*Trade winds over Pacific slacken and/or

reverse, warm water “sloshes” eastward towards coast of Peru. *Causes global climate shifts!*Atlantic: Fewer hurricanes because stronger

upper level winds do not allow formation*Pacific: More hurricanes possible because

more warm water over a larger area

Naming Hurricanes

Gets name when becomes TSIf major event (like Katrina) name retired for several years

Source: Farmer’s Almanac

Heat Waves*Definition: A period of several days with

temperatures 5’C (9’F) above average for a given location at a given time of year*Definition varies by region.*Cause 175 deaths a year in US! *During 1980 heat wave, 1250 people died!*Many more die due to secondary effects of heat*Most summers have heat waves*Heat Index- issued by NWS*Gives the “apparent temperature” combining

effects of temperature, humidity, and wind*Ex, “feels like” 104’, actual temp may be 98

Heat Effects on Body*Sweating dehydrates, causes dizziness and

fainting*In heat, heart pumps more blood*Blood vessels dilate*Body tries to cool blood by getting it closer to

surface- can’t cool if ambient temp too high!*In high humidity, sweat does not evaporate *No cooling of skin

*Also sunburn, stroke, heat exhaustionSource: NOAA/wikipedia

2010 Russian Heat Wave*Temperatures up to 104’F/40’C for several weeks

*Wildfires, cause poor air quality*Heat like this not seen in 1000 year Russian

climate archives*30% crop decrease expected, ban on crop

exports until 12/31/2010*2000 people drowned trying to escape heat by

bathing in rivers or lakes *Most of them were drunk…

Source: The Economist, Rianovosti

Global Warming to blame?*Specific weather events cannot be linked to

global warming*Warming and changing of Earth’s surfaces can

increase probability of extreme events*Many extreme events are attributed to normal

oscillations*Ex: Pakistan floods generally associated with La

Nina (ENSO) summer

Global Warming to blame?*More areas with high Urban Heat Index

*More heat waves*Warm temperatures cause more evaporation*More intense rainfall (in some areas)

*More evaporation*More drought/water shortages (in some areas)

*Warmer oceans*Provide more kinetic energy for stronger hurricanes

*Higher and denser population*Increased chance of fatalities and damage caused by

events*Especially in poorer regions without good

infrastructure