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 damageTrailer 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 US

http://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 ktsHurricane 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