Download Lecture 10: Extreme Weather

Hurricane Ivan
over Gulf, Sept. 2004
Source: NOAA
Thunderstorms, Tornadoes, and Hurricanes
October 27/28 2010
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
* Climate describes the total of all
* Weather is what happens from
* Climate tells us what it's usually like
happening outdoors in a given place
at a given time.
minute to minute.
weather occurring over a period of
years in a given place.
in the place where you live
* 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 is what you expect,
weather is what you get!
* 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
* 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?
* 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
* 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!
Microburst
#2: How do you think it
could be dangerous to
aviation?
Source: Wikipedia
# days per year thunderstorms observed.
Do you think hail follows the same distribution?
#3: How are max/min different here?
Why do you think more hail over Rockies, Great Plains?
* 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
* 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
* 100 people per year die of lightning strikes
* If about to strike, hair stands on end, skin
tingles, hear clicking sounds
Source: www.goldengatephotos.com
Sept 2003, Carquinez Straits, CA
After rare influx of moisture from SW
Cloud-to-ground lightning over
Las Vegas during SW monsoon season
* 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
* 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, AL
F4 tornado over Parker City, IN
Source: http://www.april31974.com
* 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
* 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
* 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. report
that the number of category 4 and 5
hurricanes has almost doubled globally
over the past three decades
(Webster et al, 2005, Science)
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
* Convergence at surface brings warm, moist air up
* Divergence aloft and sinking air outside the
hurricane, clear skies immediately surrounding
* 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”!
#7: Why do hurricanes move from East to West?
* 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: Wikipedia
Source: Washington Post
* 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
* 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
* #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
Gets name when becomes TS
If major event (like Katrina) name retired
for several years
Source: Farmer’s Almanac
* 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
* 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 exhaustion
Source: NOAA/wikipedia
* 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
* 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
* 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