Download How are tornadoes formed

Tornadoes
Storms of Destruction
Mrs. Heathcott’s 7th grade Navasota Jr. High December 8, 2005
Tornadoes are
extremely rapid,
rotating winds
that form
from
cumulonimbus clouds
that
touch the ground.
Cumulonimbus clouds –
reach high into the atmosphere,
and are much larger and more
vertically developed than
cumulus clouds.
May 3, 1999
One of the deadliest series of tornadoes in U.S. history.
66 tornadoes touched down in Oklahoma and Kansas
F-5 tornado that moved along a 38-mile path
killed 46 people, injured 800, damaging 8,000 buildings
Caused at least $1.5 billion in damage
Every year, dozens of tornadoes rip through the U.S. and
cause massive amounts of damage.
 Scientists work to understand where and how these
storms originate and what powers them.
Tornado Classification
• Tornadoes are ranked by the amount of
wind and damage they create.
• The Fujita Scale ranges from F0 to F5,
with F0 being the least violent and F5
being the most violent.
Fujita Scale
Fujita
scale
Wind speed
mph
Damage
F0
<72
F1
72-111
Moderate: roofs damaged, mobile
homes upturned
F2
112-157
Considerable: roofs torn off homes,
large trees uprooted
F3
158-205
Severe: trains overturned, roofs and
walls torn off
F4
206-259
Devastating: houses completely
destroyed, cars picked up and carried
elsewhere
F5
260-317
Incredible: total demolition
Light: broken branches and chimneys
Storm Mechanisms
How are tornadoes formed ?
What are the three major
storm mechanisms
that create tornadoes ?
Storm Mechanisms1
• Tornadoes have changes in
air pressure.
• Where are the high and low air
pressures found in a balloon ?
• Where are the high and low air
pressures found in a tornado ?
So………
• Do winds blow from
areas of low pressure
to high pressure or
from high pressure to
low pressure ?
Tornadoes are formed when a severe low
pressure develops.
They operate like a ‘backwards’ balloon,
air from high pressure rushes in to fill in
the low pressure area.
Meteorologists closely monitor changes
in air pressure (particularly decreases)
because they can spawn tornadoes.
Storm Mechanisms2
• Tornadoes,
hurricanes and
thunderstorms have
an ‘updraft’
mechanism.
• The upward
movement of air is
due to the process
of convection.
Convection
• The Earth is heated by radiation from the
sun (transporting energy via electromagnetic waves).
• Heating of earth's surface and atmosphere
by the sun drives convection within the
atmosphere and oceans, which produces
winds and ocean currents.
Convection
is the transfer of heat
by the flow of a material.
 Molecules move closer together, making
air more dense, and air pressure rises.
The process
 Cold air sinks,
 pushing up warm air,
 which then cools and sinks,
 pushing up more warm air.
Movin’ On Up
 As instability occurs in
the atmosphere, fronts
move in and lower air
layers break the upper
layer cap.
 Warm air can now rise.
 As the warm, moist air
rises, vapor condenses
and precipitation
occurs.
 Thunderstorms and hail
often occur with
tornadoes.
Tornado Formation
Heating Up
 As moisture condenses it releases
“latent” heat.
 Latent heat is released during phase
changes (such as…)
Evaporation, freezing, melting …
 The latent heat released helps the rising air
stay warmer.
 The air continues to rise and to gain speed
(occasionally up to 150 mph!)
Storm Mechanisms3
The Coriolis Effect
 Air and water turn left (CCW)
in the southern hemisphere
and right (CW) in the
northern hemisphere due to
the Earth’s rotation.
 This rotation of the Earth
also causes storm systems
to rotate.
Start the Spinning
 Varying wind speeds
at different levels
cause the warm air
to rotate and to gain
even more speed.
 This huge, rotating
air mass is called a
mesocyclone.
Touchdown!
 When a
mesocyclone
begins to move
downward, it
narrows and rotates
even faster.
But….
 Only when the
spinning air
touches the ground
does it officially
become classified
as a tornado.
Tornadoes’ damage path ranges
from less than 150 feet to more
than a mile.
Where do Tornadoes Form?
Thunderstorms (and tornadoes) form where warm
moist air clashes with cool dry air.
Tornadoes are common
in a region of the U.S.
called “Tornado Alley”.
What are some features
that may cause
tornadoes to be so
common here?
Rocky Mountains
Tornado
Alley
Gulf of Mexico
• Air from the western mountains produces winds that are cool and dry.
• Gulf of Mexico produces warm and moist air.
• The interaction of these 2 air masses can produce strong thunderstorms.
• Texas Interstate 35 roughly separates the dry west and humid east sides of
our state.
So, where are the most damaging, most frequent tornados,
where are the least damaging, least frequent
and WHY?
How are tornadoes and hurricanes
similar ?
Storm Similarities
Both have….
 Severe storms with vortex winds
 Circulating winds due to the Coriolis effect
 Updraft mechanisms due to convection
 Considerable air pressure gradients
How do Tornadoes
and Hurricanes differ?
Hurricanes are fueled by “heat of
evaporation” and must form over
warm oceans.
Tornadoes form (mostly) over land
from convection updrafts and air
pressure gradients.
Storm Mechanisms
• The interaction between temperature,
air density, air pressure and convection
currents are similar in thunderstorms,
hurricanes and tornadoes.
Simulator Vortex
• Within this model, where are the areas of high and
low pressure ?
• How are convection currents modeled ?
• How is the Coriolis Effect modeled?
• What limits this model from working like a real
tornado ?
• Mist is used to show the simulator’s vortex. What is
the visible vortex in a real tornado?
• The simulator’s vortex breaks up quickly. Describe
why real tornadoes vortexes might also be short
lived.
Simulator Vortex
• Predict what will happen when the
simulator is modified by:
– Columns are turned out
– Top, middle and/or upper holes are
plugged
– Fan speed adjusted
– Other alterations/modifications ?
A
Texas twister sized
Thank you to
Mr. Rushing for taking the time and
energy to build this
vortex simulator for NISD!