Transcript of Geography 1700 Chapter 9 Part 2 of 4 “Super-Storm Sandy” in October, 2012 caused more than $55...
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- Geography 1700 Chapter 9 Part 2 of 4 Super-Storm Sandy in
October, 2012 caused more than $55 Billion in financial losses and
cost more than 300 lives. Most of these losses were preventable.
People living along the sea coast are gamblers - - hoping that a
big storm wont really affect them. As of October, 2013, some people
in New Jersey still do not have electricity and/or drinking water.
People in New Jersey can say the same thing about us: people in
Utah think that a big earthquake wont really be that bad.
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- Extra-tropical Cyclone Development Low pressure develops along
fronts. Cold front on southwest, warm front on east. Cold air
circulates counter-clockwise. Warm air rises on the southeast side.
Dry air aloft feeds the cyclone from behind the cold front.
Occluded front develops, trapping warm air aloft. Pressure gradient
weakens and storm dissipates. Air will flow when there is a
gradient or slope between high and low pressure. Air pressure
results from differences in temperature. High pressure flows to low
pressure. WIND.
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- Hurricanes in East and Gulf Coasts Figure 9.21 Usually takes
one of three paths Season starts June 1 and ends Nov 30
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- Geographic Regions at Risk for Cyclones But what about tornado
alley? Lets broaden our definition of cyclone
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- Geographic Regions at Risk for Cyclones, cont. What makes the
USA so unusual in severe storms? Because, we should have desert in
Alabama - - but we dont. Instead, we have fight club -- tornado
alley. Westerlies
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- Track of Extra-Tropical Storms Trade winds from east to west
collect ocean transfer ocean heat to air vapor where it can collide
with drier air further north. Hurricanes west of Mexico tend to
blow away from land because of the same trade winds that blow
hurricanes toward land in the Gulf and Atlantic. This red arrow is
probably wrong. Hurricanes do not reach Los Angeles.
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- Geographic Regions at Risk for Cyclones Our definition of
cyclones should include tornado alley. The coast is hurricane
country, but cyclones include tornadoes that occur across much of
the USA. Hurricane regions are also tornado regions. All together,
the United States collects more than 90% of the worlds
tornadoes.
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- Geographic Regions at Risk from Cyclones, Summary Tropical
cyclones East and Gulf Coasts Hawaii and Atlantic Canada Baja
California and West Coast Mexico Extra-tropical cyclones Winter
windstorms in Pacific Coast Winter snow Sierra Nevada, Rocky
Mountains, and east Spring and summer thunderstorms and tornadoes
in U.S. and Canada
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- A classic extra-tropical cyclone. In our hemisphere they are
called hurricanes. Notice the tall clouds, well- developed eye and
the counter-clockwise winds. Low air pressure inside these storms
(rising air) allows ocean levels to rise also, allowing taller sea
level during the storm. High winds and heavy rain then add much
more to storm surge. Flooding. 600+ miles wide
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- Looking down on a cyclonic storm, notice that the right side
probably exhibits higher wind speeds because the forward speed of
the storm adds to the wind speed inside the storm. Storm forward
track = 20 mph Higher wind speed If wind speed inside the storm
reaches 100 mph and if the entire storm is moving forward at 20
mph, then the combined speed of wind on the forward- moving side
should be 120 mph. Likewise, the back side of the storm subtracts
forward speed to yield just 80 mph winds. Higher wind means higher
storm surge flooding. Lower wind speed
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- Is it true that tropical storms can become stronger when they
take their energy (heat) into encounters with cooler/drier
air?
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- For the same reason a dust devil hit Mr. Allreds car twice.
Still, it is important that dry dust devils rise only until they
lose their heat source, such as a black asphalt parking lot. But
wet tornadoes contain their own source of heat latent heat in
invisible water vapor. They rise until they run out of water &
heat. Can you see why cyclonic storms can hit twice?
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- Trade winds flow east to west. After collision with westerlies,
storm fronts tend to flow SW to NE. Calculate net wind speed right
front vs left rear. Westerlies cooler/drier Easterly Trade Winds
warmer/wetter
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- Facing the on-coming storm, calculate the left vs right side
wind speed differential to show why the storm is often worse on one
side or the other. Wind speed 100 mph Storm track 20 mph. Can you
see why cyclonic storms can hit twice? What about a dust devil
hitting Mr. Allreds car?
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- Cyclone Effects: High Winds Described by Saffir-Simpson Scale
Decrease exponentially with landfall Strongest recorded winds in
U.S. from extra-tropical cyclone Responsible for strong winds in
blizzards and tornadoes Figure 9.28
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- Cyclone Effects: Storm Surge 1. Low atmospheric pressure allows
sea water to rise as much as three feet, like drawing soda up a
straw. 2. High winds can push storm water far upstream and inland,
adding perhaps 6-10 feet of flooding above normal sea level. 3.
High winds can cause severe damage even without water involved. 4.
High winds cause higher and faster wave crests that push inland. 5.
Heavy rain can cause downstream flooding even as sea water is
pushing upstream. People live in between and sometimes drown. 6.
Flooding is even worse if the storm coincides with high tide.
Spring tide would be worse yet = Super Storm Sandy had it all 20
feet of surge in some places. Combined total flooding in a
hurricane can even exceed 30 feet.
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- Links to Other Natural Disasters Coastal erosion Flooding Mass
wasting Other types of severe weather Tornadoes, severe
thunderstorms, snowstorms, and blizzards
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- Natural Service Functions of Cyclones Source of precipitation
-- Many places depend on severe storms to help meet annual water
budget. Redistribute warm air from tropics Maintain ecosystems
Winds carry plants, animals, and microorganisms. Waves stir up
deeper, nutrient-rich waters. Winds topple weak and diseased trees
in forests. Waves break apart some corals.
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- Human Interaction with Cyclones Urbanization of vulnerable
coastlines Destruction of sand dunes Construction of seawalls and
bulkheads Poor building materials and practices Global warming
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- Forecasting and Warnings Forecast includes: If it will make
landfall Where and when Wind strength Rainfall amount Storm surge
Monitored by U.S. Hurricane Center, Canadian Hurricane Center.
Hurricane watch means likely hurricane in 36 hrs. Hurricane warning
given when hurricane is likely within 24 hrs or less.
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- Forecasting Tools Weather satellites Detect early warning signs
Cannot show wind speed Aircraft U.S. Air Force, NOAA airplanes fly
into the storm to collect data Doppler radar Give information on
rainfall, wind speed, and direction of the storm
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- Forecasting Tools, cont. Weather buoys Automated weather
stations that give information at their locations Computer models
Predict and track hurricane progress Have vastly improved hurricane
information Still lacking in predicting storm intensity
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- Storm Surge Predictions Predict the time and elevation of
surge. Forecasters use wind speed, fetch, and average water depth.
Need detailed information on topography. Different elevations on
land affect the storm surge. Computer models use central pressure,
size, forward speed, track, wind speed, and seafloor topography.
Lets keep in mind that prediction is still an issue even though we
can see a hurricane coming, we dont know how each part of the storm
will match-up with a coastline and urban areas. The result is
sometimes widely varying differences in storm surge and people who
get caught by surprise. Allreds Note
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- Hurricane Prediction and the Future Deaths have decreased
dramatically because of better forecasting, improved education, and
greater public awareness. However, coastal populations are
increasing, causing an increasing risk.
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- Perception of and Adjustment to Cyclones Perception of hazard
depends on personal experience. More experienced people may take
hazard more precautions. More experienced people may also take less
precautions. Community adjustments to cyclone hazard: Warning
systems (Hurricane Katrina may have been the most advertised
disaster in human history. The whole world watched it develop).
Evacuation plans and shelters Insurance Building design
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- Tornado warnings in the United States used to be only 2-3
minutes before arrival. Tornado warnings now provide as much as 11
minutes of warning. How do tornado warnings compared to hurricane
warnings? Hurricanes are known well in advance tornadoes are often
too small and quick-moving for the forecast. Remember: - a watch
means that an event might happen - a warning means that something
IS happening take cover.
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- Perception of and Adjustment to Cyclones, cont. Personal
adjustments to cyclone hazard Be aware of hurricane season Prepare
homes and property for hazard Obtain flood insurance Install heavy
shutters that can be latched Learn evacuation route Make a family
emergency plan Collect emergency supplies