Tornadoes
Lindsay SchulzEducation 373Inquiry #3/4Tornadoes
TornadoesTornadoes are the most powerful, unpredictable and
destructive weather systems on Earth. The National Weather Service
defines a Tornado as a violently rotating column of air in contact
with the earths surface (land or water) and commonly associated
with a severe thunderstorm.
QuestionsWhat causes tornadoes?Are there different
severities?How do people track tornadoes?What are some jobs that
involve tornadoes?Where are tornadoes most likely to happen?What
are some safety precautions?
CausesA tornado generally occurs when high winds within a low
pressure system (such as a thunderstorm) cause water vapor in the
air to condense in to a condensation funnel cloud. Many less severe
tornadoes are not even visible to the human eye. Major tornadoes
usually become more visible when the strong winds within the funnel
lift up dirt and debris off the Earths surface. The average tornado
has maximum wind speeds of about 112 mph or less, measures around
250 feet in width and travels approximately one mile before falling
apart. Some of the most catastrophic tornadoes in recorded history
have had winds in excess of 300 miles an hour (twice that of a
category 5 hurricane), have measured more than 2 miles in girth,
and have carved devastating paths of destruction miles and miles in
length.
Types of Tornadoes
Tornadoes are generally classified as either aland spout -- a
tornado on landwater spout -- a tornado that forms over
watergustnado -- a small tornado caused by a strong downburst of
wind from a thunderstorm
How Tornadoes workTornadoes don't just pop into existence --
they develop out of thunderstorms, where there's already a steady,
upward flow of warm, low-pressure air to get things started. It's
kind of like when a rock concert erupts into a riot. Conditions
were already volatile; they merely escalated into something even
more dangerous.
ThunderstormsThunderstorms themselves form like many other
clouds: A warm, moist air mass rises and cools, causing the water
vapor to condense into clouds.However, if the updraft continues,
this cloud mass will continue to grow and rise 40,000 feet (12,192
m) or more up into the troposphere, the bottommost layer of the
atmosphere that we live in. A typical thunderstorm cloud can
accumulate an enormous amount of energy. If the conditions are
right, this energy creates a huge updraft into the cloud, but where
does the energy come from?
ThunderstormsCloudsClouds are formed when water vapor condenses
in the air. This change in physical state releases heat, and heat
is a form of energy. A good deal of a thunderstorm's energy is a
result of the condensation that forms the cloud. Every gram of
water condensed results in about 600 calories of heat -- and
another 80 calories of heat per gram of water results from freezing
in the upper atmosphere. This energy increases the updraft
temperature, as well as the kinetic energy of upward and downward
air movement. The average thunderstorm releases around 10,000,000
kilowatt-hours of energy -- the equivalent of a 20-kiloton nuclear
warhead.
ThunderstormsIn supercell thunderstorms, the updrafts are
particularly strong. If they are strong enough, a vortex of air can
develop just like a vortex of water forms in a sink.This precursor
to the tornado is called a mesocyclone, and is typically 2 to 6
miles wide. Once a mesocyclone forms, there's a roughly 50 percent
chance that the storm will escalate into a tornado in around 30
minutes.
TornadoesSome tornadoes consist of a single vortex, but other
times multiple suction vortices revolve around a tornado's center.
These storms-within-a-storm may be smaller, with a diameter of
around 30 feet, but they experience extremely powerful rotation
speeds.The tornado reaches down out of a thundercloud as a huge,
swirling rope of air. Wind speeds in the range of 200 to 300 mph
aren't uncommon. If the vortex touches ground, the speed of the
whirling wind (as well as the updraft and the pressure differences)
can cause tremendous damage, tearing apart homes and flinging
potentially lethal debris.
TornadoesThe tornado follows a path that is controlled by the
route of its parent thundercloud, and it will often appear to hop.
The hops occur when the vortex is disturbed. You've probably seen
that it is easy to disturb a vortex in the tub, but then it will
reform. The same thing can happen to a tornado's vortex, causing it
to collapse and reform along its path.Smaller tornadoes may only
thrive for a matter of minutes, covering less than a mile of
ground. Larger storms, however, can remain on the ground for hours,
covering more than 90 miles and inflicting near continuous damage
along the way.
TornadoesAt this point, you might be wondering just how
tornadoes eventually dissipate. Scientists still debate exactly how
these deadly storms die, but one of the prime suspects is none
other than the parent thunderstorm: the rotating mesocyclone.
Tornadoes need instability and rotation. Disrupt the airflow, take
away its moisture or destroy its unstable balance of hot and cold
air, and it can't function.Often, a tornado will die because the
cold outflow of air from falling precipitation upsets the
balance.
Tornado RatingsTornadoes are among the most dangerous storms on
Earth and, as meteorologists strive to protect vulnerable
populations through early warning, it helps to classify storms by
severity and potential damage.Tornadoes were originally rated on
the Fujita Scale, named for its inventor, University of Chicago
meteorologist T. Theodore Fujita. The meteorologist created the
scale in 1971 based on the wind speed and type of damage caused by
a tornado. There were six levels on the original scale.
ScaleF 0: Wind speed: 40 - 72 (64 - 116)Possible Damage: Light
damage: Tears branches from trees; rips shallow-rooted trees from
the ground; can damage signposts, traffic signals and chimneys.F
1:Wind speed: 73 112 (117 - 180)Possible Damage: Moderate damage:
Roofing materials and vinyl siding can be displaced; mobile homes
are highly vulnerable and can easily be knocked from the foundation
or toppled; motorists can be sent careening off road and possibly
flipped over.F 2:Wind speed: 113 - 157 (181 - 253)Considerable
damage: Well-established trees are easily uprooted; mobile homes
are decimated; entire roofs can be ripped off houses; train cars
and trucking hauls are knocked over; small objects become dangerous
missiles
ScaleCont. F 3: Wind speed: 158 - 206 (254 - 332)Possible
damage: Severe damage: Forests are destroyed as a majority of trees
are ripped from the ground; entire trains are derailed and knocked
over; walls and roofs are torn from housesF 4:Wind speed: 207 - 260
(333 - 418)Possible damage: Devastating damage: Houses and other
small structures can be razed entirely; automobiles are propelled
through the air.F 5:Wind speed: 261 - 318 (419 - 512)Incredible
damage: Cars become projectiles as they are hurled through the air;
entire houses are completely destroyed after being ripped from the
foundation and sent tumbling into the distance; steel-reinforced
concrete structures can be seriously damaged.
Storm ChasersStorm chasing isn't nonstop action and danger. It's
actually a very methodical practice that requires lots of time
spent studying weather data, driving, waiting and more driving.
Storm chasers can spend 12 hours or more driving around and still
not see a tornado of any kind. Byron Turk, navigator for the
Discovery Channel's Storm Chasers series, describes the process
like this:We find the storm hopefully before it gets dark, and
hopefully it produces a tornado, and hopefully there are roads to
it. Lots of decisions need to be made on how the supercell is
doing, whether another one is more worthwhile, more data comes in
and it's just a constant process of making the right decision over
and over again. Hopefully.
Storm Chaserscontd.Before bed and first thing in the morning,
storm chasers check weather reports from the National Weather
Service, looking for favorable tornado conditions. Cold air at high
altitudes with warm air close to the ground is a promising sign,
along with wind shear, or winds at different altitudes blowing in
different direct. Areas where cool air masses collide with warm air
masses are also tornado spawning grounds. After analyzing the
weather data, the chasers select a likely location. Then they hop
into their chase vehicle and start driving.
Safety TipsLook & Listen for ...large hail, heavy rain,
strong winds, frequent intense lightning ...bulge with a rotary
motion at the base of the thunderstorm cloud ...loud roar like the
sound of a jet or train. Seek Safe Shelter A basement is best.
Otherwise choose ground-floor center rooms surrounded by other
rooms. Never choose upstairs locations because tornadic wind speeds
increase with height above the ground.
Choose rooms on the north and east sides of your shelter if no
interior rooms are available. Stay near the innermost walls. Avoid
rooms on the south and west, because tornados usually travel from
southwest to northeast.
Choose a small closet or bathroom, because small rooms are less
susceptible to collapse. Take shelter within the bathtub if there
are no glass tub enclosures or large mirrors nearby. How to Protect
Yourself and Your Family Stay calm.Seek shelter IMMEDIATELY!Keep a
portable TV/radio and flashlight in your shelter.Wear shoes to
protect your feet from broken glass and other debris left by the
storm.Protect head and chest- crouch, face to floor, hands behind
head.Cover yourself with blankets, pillows or coats.Hide under
sturdy furniture.Avoid candles, gas lanterns and oil lamps.In
schools and offices: seek designated shelter in interior rooms or
hallway's on ground floor, or lowest floor possible. Avoid
auditoriums and gymnasiums.In shopping malls, seek the smaller
interior shops on the ground floor.In shopping centers, avoid large
open rooms as well as the south and west walls.Evacuate mobile
homes and vehicles! Seek shelter in substantial structure, ditch or
culvert.
Tornado WhereaboutsTornadoes are produced by large (supercell)
thunderstorms that often grow to over 40,000 feet. Mouse over the
different regions of the continental United States on the map below
to see the average number of tornadoes per year.
United States Map
Pictures
Resourceshttp://www.livescience.com/topic/tornadoeshttp://www.howstuffworks.com/tornado.htmhttp://www.fema.gov/kids/tornado.htmhttp://www.weatherwizkids.com/weather-tornado.htmhttp://eo.ucar.edu/webweather/tornado.html#tornadochaos
