GEO 101, March 19, 2013
Review:
Precipitable water vapor by latitude
weather maps
global wind and pressure belts
latitudinal precipitation
cm
http://www.weather.com/maps/news/forecasts
ummary/uscurrentweather_large.html
Capacity of air to hold moisture directly related to temperature
Function of available energy for evaporation
Atmospheric lifting leads to adiabatic cooling & condensation
Adiabatic processes
http://www.youtube.com/watch?v=XH_M4jItiKw
Frontal = warm goes up over cold air
Convective = bubbles of warm wet air
Orographic = up a mountainside
Convergent = air meets in a LOW
Latitudinal variation in precipitation
Severe Weather
Thunderstorms
Tornadoes
Hurricanes
Explain this pattern in terms of capacity of the air to hold
moisture and lifting mechanisms.
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Average annual number of days with thunderstorms
Generalized charge
distribution in a
thunderstorm. Most
lightning between
adjacent clouds
http://upload.wikimedia.org/wikipedia/commons/d/dc/Leaderlightnig.gif
Lightning is the #2 storm killer in the U.S., killing more
than hurricanes or tornadoes on average. Only floods
kill more.
No Place Outside is Safe During Thunderstorms!
When you see lightning, count the time until you hear
thunder. If this time is 30 seconds or less, seek proper
shelter = substantial building with wiring and plumbing
in walls.
MYTH:
Cars are safe because the rubber tires insulate them
TRUTH:
Cars are relatively safe because of their metal shell,
don’t touch anything metal
Electric current carries “+” charges back to the cloud
This is what we see as lightning
If are stuck outside, minimize your risk by avoiding
Higher elevations
Wide-open areas
Tall isolated objects like trees, poles
Water-related activities: boating, swimming
Golfing
Open vehicles like open riding lawnmowers
Unprotected open buildings like picnic pavilions
Metal fences and metal bleachers.
DO NOT GO UNDER TREES TO KEEP DRY
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Lightening crouch
Spread apart from friends
Thunder appears to rumble because sound waves from the
lower part of the lightning stroke reach the observer before
those from the upper part of the stroke.
Sound travels ≈ 1
mile in 5 seconds
Sequential development of a thunderstorm cell
Air flow & precipitation pattern beneath a thunderstorm cloud.
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Some large thunderstorms have anvil shaped tops
Air in the updraft reaches the stratosphere
Tornado Wind Patterns
Why does U.S. have so many tornadoes?
Shaded relief map of world
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ENHANCED FUJITA SCALE
Rating
EF0
EF1
EF2
EF3
EF4
EF5
Wind
Speed
65-85
86-110
110-135
136-165
166-200
Over 200
Damage
Minor roof damage, branches
Shingles off, broken glass
Roofs off, Large trees down
Homes damaged, trains derailed
Homes leveled, missiles hurled
Incredible damage
Fair-weather waterspouts, usually EF0,
tropical and sub-tropical coastal areas
http://www.youtube.com/watch?v=cFe0846RgWc&feature=endscreen&NR=1
Hurricane: cyclonic storm of tropical origin
Hurricanes form over warm oceans (25°C, 80°F, or higher),
at least 8° away from Equator (need Coriolis Force).
Cyclones
Typhoons
Winds at least
75 mph
Estimated return period in years for
hurricanes passing within 50 nautical
miles of locations on the U.S. Coast
Category 3,4,5
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Temporal distribution of hurricanes
Development of a hurricane
Cold air aloft
Cold air above tropical thunderstorms generates unstable air
(steep lapse rate) and large cumulonimbus clouds
Hurricane Wind Patterns
Release of latent heat warms upper troposphere creating
high pressure and divergence aloft. This causes surface
pressure to drop pulling more warm moist air in to fuel the
reaction.
Hurricane Ivan, September, 2004
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Factors affecting severity of hurricane impact:
1. Strength of the storm
2. Status of local tide
3. Angle of impact
4. Forward speed of storm
5. Your location in relation to eye
6. Local basin shape
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4
3
2
1
http://www.youtube.com/watch?v=0woOxPYJz1U&featu
re=related
Moral of the
story:
Be prepared !
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