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Hazards Final


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What is an air mass?
A mass of air with the same temperature and humidity
What are the different types of air masses?
cP, mP, cT, mT
What direction does a midlatitude cyclone normally rotate? What is the pressure like in a cyclone?
Counterclockwise; low
What direction does the air travel in a cyclone?
What part of the jet stream is a cyclone associated with?
How does a cold front produce unstable air?
Cold air pushes warm air up and forms clouds
What is unstable air?
Air that does not resist vertical displacement
How does a nor'easter, blizzard, or icestorm move up the NE US coast?
The counterclockwise rotation comes from the north, the eastern side picks up moisture from the Atlantic which feeds the cyclone
What are the characteristics of a blizzard?
Cold winds, less than 20 degrees, zero visibility
Explain how thunderstorms work
Warm buoyant air rises and condenses to form clouds. As the vapor condenses, it releases latent heat which makes the air warmer and therefore it rises higher. Cool air then makes is dissipate
Where are straightline winds found? What are they called?
In front of the storm, gust front
Where do thunderstorms primarily occur?
Plains states and Florida
Where is hail most frequent?
The plains states
How does lightning work?
Areas of excess positive charge seek negative charges. Bottom of the storm cloud is negative, top is positive
Where is lightning most frequent?
Texas, Florida, North Carolina
List lightning safety points
Seek shelter as soon as you hear thunder or see lightning, don't touch anything electrical (plumbing, water, phone), get in a non-convert. car and dont touch anything, move to a low place and crouch on the balls of your feet
What 3 conditions do you need for a tornado?
Northerly flow of mT air from the Gulf that is humid and 75+ degrees, cold, dry air from Canada at 50+mph, easterly jet stream winds at 150+ mph
What time of the year do tornados form?
Spring and Summer
What does the F-scale measure?
Wind speed and damage
List tornado safety points
take shelter during a warning, dont open windows and stay away from them, go to a basement or bathtub, stay on the northeast side of the shelter, get in a ditch, stay out of cars and mobile homes
What is a hurricane?
Large tropical cyclones that convert ocean heat into wind and waves
Where do hurricanes come from?
West coast of Africa, 20 degrees above the equator
How does a hurricane develop?
Low pressure zones of thunderstorms and weak winds create a disturbance. Stronger winds turn it into a depression. Warm air rises, cools, condenses-latent heat. Extra heat increases updrafts. More than 39 mph, storm, >74=hurricane
What is the difference between a distrubance and a storm?
A storm has rotational value
Requirements for a hurricane
80 degrees in upper 200ft of ocean, atmosphere cool fast enough with high to make it unstable, thunderstorms maintained, 300mi away from equator, coriolis to maintain low pressure, pre existing near surface convergence of rotating moist air, weak upper level winds blowing the same direction as the storm
What is a hurricane called in Japan/China? India/Africa?
Typhoon, Cyclone
When and where do hurricanes occur?
May-Dec around the Bermuda high
What causes a hurricane to change its path?
Areas of high pressure, large air masses, upper level winds
Why are barrier islands dangerous?
Get hit by flood and ebb
How does damage occur?
intensity, duration, angle at which the hurricane approaches land, population density
How can damage be reduced?
warnings/evacuations, maintain beach width and dune height, floodwalls, construction code enforcement, zoning for land use
What do streams do?
Carry water from land to sea, carry sediment, dissolve materials into ions, erosion
How do streams balance variables it deals with?
Changes dischange, available sediment, gradient, and channel pattern accordingly
What does the cross-sectional shape have to do with discharge?
larger cross section=greater discharge
What causes meandering?
too much discharge-uses its energy by cutting the banks
What does too much load do to a stream?
Braided streams, levees
What is lag time?
time difference between heavy rains and peak discharge in stream draining area
regional floods
rainfall for days
landslide flood
landslide, log jam, or lahar dams fail
Why are flash floods dangerous primarily?
transport large items, erosion, water damage, death, health hazards
Secondary dangers
service disruption, polluted water, food shortage
Tertiary dangers
channel location change, farms destroyed, lost jobs, insurance rate increase, corruption w/relief funds, wildlife habitat destruction
Societal responses to floods
structural, non-structural
Effects of channelization
decreases cross section and increases flooding
effects of subsidence
compaction causes pooling water and changes drainage pattern
Effects of storm sewers
collect runoff and block infiltration, decrease lag time, increase peak discharge of collection streams
Effects of urbanization
reduction of infiltration, decreased lag time, increase in peak discharge (flash floods)

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