Transcript SEVERE WEATHER

EARTH SCIENCE
Geology, the Environment and the Universe
Chapter 13: The Nature of Storms
CHAPTER
13
Table Of Contents
Section 13.1 Thunderstorms
Section 13.2 Severe Weather
Section 13.3 Tropical Storms
Section 13.4 Recurrent Weather
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SECTION
13.1
Thunderstorms
Essential Questions
• How do thunderstorms form?
• What are the different types of thunderstorms?
• What is the life cycle of a thunderstorm?
Review Vocabulary
• latent heat: stored energy in water vapor that is
not released to warm the atmosphere until
condensation occurs
SECTION
13.1
Thunderstorms
• The intensity and duration of thunderstorms
depend on the local conditions that create
them.
New Vocabulary
air-mass thunderstorm
mountain thunderstorm
sea-breeze
thunderstorm
frontal thunderstorm
stepped leader
return stroke
SECTION
13.1
Thunderstorms
Up to 2000 thunderstorms are in progress around
the world
SECTION
13.1
Thunderstorms
• Both geography and air mass movements make
thunderstorms most common in the
southeastern United States.
SECTION
13.1
Thunderstorms
How thunderstorms form
• For a thunderstorm to form, three conditions
must exist: a source of moisture, lifting of the air
mass, and an unstable atmosphere.
SECTION
13.1
Thunderstorms
Limits to thunderstorm growth
TROPOPAUSE
SECTION
13.1
Thunderstorms
Types of Thunderstorms
• Thunderstorms are often classified according to
the mechanism that causes the air mass that
formed them to rise.
• There are two main types of thunderstorms: airmass and frontal.
SECTION
13.1
Thunderstorms
Types of Thunderstorms
Air-mass thunderstorms
• When air rises because of unequal heating of
Earth’s surface beneath one air mass, the
thunderstorm is called an air-mass
thunderstorm.
• There are two kinds of air-mass thunderstorms.
SECTION
13.1
Thunderstorms
Types of Thunderstorms
Air-mass thunderstorms
• Mountain thunderstorms occur when an air
mass rises by orographic lifting, which involves
air moving up the side of a mountain.
SECTION
13.1
Thunderstorms
Types of Thunderstorms
Air-mass thunderstorms
• Sea-breeze thunderstorms are local air-mass
thunderstorms that occur because land and
water store and release thermal energy
differently.
SECTION
13.1
Thunderstorms
Types of Thunderstorms
Frontal thunderstorms
• Frontal thunderstorms are produced by
advancing cold fronts and, more rarely, warm
fronts.
SECTION
13.1
Thunderstorms
Thunderstorm Development
• A thunderstorm usually has three stages: the
cumulus stage, the mature stage, and the
dissipation stage. The stages are classified
according to the direction the air is moving.
SECTION
13.1
Thunderstorms
Please click the image above to view the video.
SECTION
13.1
Thunderstorms
• Lightning is the transfer of electrical charge
caused by the rapid rushes of air in a
cumulonimbus cloud.
SECTION
13.1
Thunderstorms
Lightning Facts
• A lightning bolt heats the surrounding air to about
30,000C, about five times hotter than the
surface of the Sun.
• Lightning natural creates Ozone.
• Lightning kills 60 people a year.
• The thunder you hear is the sound produced as
this superheated air rapidly expands and
contracts.
SECTION
Section Check
13.1
Thunderstorms in the United States are
most common in the Midwest.
a. true
b. false
SECTION
Section Check
13.1
A mature thunderstorm has a region of
updraft and a region of downdraft.
a. true
b. false
SECTION
13.1
Section Check
What is the difference between air-mass
thunderstorms and frontal thunderstorms?
Answer: Air-mass thunderstorms form as
a result of uplift of air within one air mass. Frontal
thunderstorms form as a result of
uplift of air along frontal boundaries.
SECTION
13.2
Severe Weather
Essential Questions
• Why are some thunderstorms more severe than
others?
• What are the dangers of severe weather?
• How do tornadoes form?
SECTION
13.2
Severe Weather
• All thunderstorms produce wind, rain, and
lightning, which can have dangerous and
damaging effects under certain circumstances.
Review Vocabulary
• air mass: large body of air that takes on the
characteristics of the area over which it forms
SECTION
13.2
Severe Weather
New Vocabulary
supercell
downburst
tornado
Enhanced Fujita Tornado
Damage scale
SECTION
13.2
Severe Weather
Severe Thunderstorms
Supercells
• Severe thunderstorms can develop into selfsustaining, extremely powerful storms called
supercells.
• These furious storms can last for several hours
and can have updrafts as strong as 240 km/h.
SECTION
13.2
Severe Weather
Severe Thunderstorms
Supercells
• An anvil-shaped cumulonimbus cloud is
characteristic of many severe thunderstorms.
SECTION
13.2
Severe Weather
Strong Winds
• Violent downdrafts that are concentrated in a local
area are called downbursts.
• Based on the size of the area they affect,
downbursts are classified as either macrobursts or
microbursts.
SECTION
13.2
Severe Weather
Hail
• Hail is precipitation in the form of balls or lumps of
ice. It forms because of two characteristics
common to thunderstorms.
SECTION
13.2
Severe Weather
Hail
• For hail to form, water droplets rise to the heights
of a cumulonimbus cloud where the temperature
is below freezing, encounter ice pellets, and
freeze on contact with the pellets, which causes
the ice pellets to grow larger.
SECTION
13.2
Severe Weather
Hail
• The second characteristic that allows hail to
form is an abundance of strong updrafts and
downdrafts moving side by side within a cloud.
SECTION
13.2
Severe Weather
Tornadoes
• A tornado is a violent, whirling column of air in
contact with the ground.
• When a tornado does not reach the ground, it is
called a funnel cloud.
SECTION
13.2
Severe Weather
Tornadoes
Development of tornadoes
• A tornado forms when wind speed and direction
change suddenly with height, a phenomenon
called wind shear.
• Although tornadoes rarely exceed 200 m in
diameter and usually last only a few minutes,
they can be extremely destructive.
SECTION
13.2
Severe Weather
Please click the image above to view the video.
SECTION
13.2
Severe Weather
Tornadoes
Tornado classification
• The Enhanced Fujita Tornado Damage scale,
which ranks tornadoes according to their
destruction and estimated wind speed, is used to
classify tornadoes.
SECTION
13.2
Severe Weather
Please click the image above to view the interactive table.
SECTION
13.2
Severe Weather
Tornadoes
Tornado distribution
• Most tornadoes—especially violent ones—
form in the spring during the late afternoon
and evening, when the temperature contrasts
between polar air and tropical air are the
greatest. This type of large temperature
contrast occurs most frequently in the central
United States.
SECTION
13.2
Severe Weather
Tornadoes
Tornado distribution
• Many of the more than 1000 tornadoes that
touch down in the United States each year occur
in a region called “Tornado Alley,” which extends
from northern Texas through Oklahoma, Kansas,
and Missouri.
SECTION
13.2
Severe Weather
Tornadoes
Tornado safety
• If you are caught in a
tornado, take shelter in
the southwest corner
of a basement, a small
downstairs room or
closet, or a tornado
shelter.
SECTION
Section Check
13.2
The strongest thunderstorms develop
under highly stable atmospheric
conditions.
a. true
b. false
SECTION
Section Check
13.2
Which type of precipitation requires strong
updrafts and downdrafts to exist side by
side in a cloud?
a. rain
b. snow
c. hail
d. sleet
SECTION
13.2
Section Check
How do tornadoes form?
Answer: The rotation of a tornado begins
as a result of wind shear, wind at different levels
of the atmosphere blowing in different directions
or at different speeds. The horizontal rotation is
then tilted to a vertical position by thunderstorm
updrafts. A tornado forms if the rotating column
extends to the ground.
SECTION
13.3
Tropical Storms
Essential Questions
• How do tropical cyclones form?
• What is the life cycle of a tropical cyclone?
• What are the dangers associated with hurricanes?
SECTION
13.3
Tropical Storms
• Normally peaceful, tropical oceans are capable of
producing one of Earth’s most violent weather
systems—the tropical cyclone.
Review Vocabulary
• Coriolis effect: caused by Earth’s rotation,
moving particles, such as air, are deflected to the
right north of the equator, and to the left south of
the equator
SECTION
13.3
Tropical Storms
New Vocabulary
tropical cyclone
eye
eyewall
Saffir-Simpson
Hurricane Wind scale
storm surge
SECTION
13.3
Tropical Storms
Overview of Tropical Cyclones
• During summer and fall, the tropics experience
conditions ideal for the formation of large, rotating,
low-pressure tropical storms called tropical
cyclones.
SECTION
13.3
Tropical Storms
Overview of Tropical Cyclones
Cyclone location
• Favorable conditions for cyclone formation exist
in all tropical oceans except the South Atlantic
Ocean and the Pacific Ocean off the west coast
of South America.
SECTION
13.3
Tropical Storms
Please click the image above to view the video.
SECTION
13.3
Tropical Storms
Overview of Tropical Cyclones
Cyclone formation
• Tropical cyclones require two basic conditions to
form: an abundant supply of warm ocean water
and some sort of mechanism to lift warm air and
keep it rising.
SECTION
13.3
Tropical Storms
Overview of Tropical Cyclones
Cyclone formation
• The first indication of a building tropical cyclone
is a moving tropical disturbance. When a
disturbance over a tropical ocean acquires a
cyclonic circulation around a center of low
pressure, it has reached the developmental
stage and is known as a tropical depression.
SECTION
13.3
Tropical Storms
Overview of Tropical Cyclones
Cyclone formation
• When wind speeds around the low-pressure
center of a tropical depression exceed 62 km/h,
the system is called a tropical storm.
• If air pressure continues to fall and winds around
the center reach at least 119 km/h, the storm is
officially classified as a cyclone.
SECTION
13.3
Tropical Storms
Overview of Tropical Cyclones
Cyclone formation
• Once winds reach at least 119 km/h, another
phenomenon occurs—the development of a
calm center of the storm called the eye.
• The eye of the cyclone is often 30 to 60 km of
calm weather and blue sky.
SECTION
13.3
Tropical Storms
Overview of Tropical Cyclones
Cyclone formation
• The strongest winds in a hurricane are
usually concentrated in the eyewall—a tall
band of strong winds and dense clouds
that surrounds the eye.
SECTION
13.3
Tropical Storms
Overview of Tropical Cyclones
Cyclone formation
• A hurricane will last until it can no longer produce
enough energy to sustain itself. This usually
happens when the storm has moved either over
land or over colder water.
SECTION
13.3
Tropical Storms
Visualizing Cyclone Formation
• Like most storms, cyclones begin with warm moist
air rising.
SECTION
13.3
Tropical Storms
Please click the image above to view the video.
SECTION
13.3
Tropical Storms
Overview of Tropical Cyclones
Tropical cyclone movement
• Like all large-scale storms, tropical cyclones
move according to the wind currents that steer
them.
SECTION
13.3
Tropical Storms
Hurricane Hazards
• The Saffir-Simpson
Hurricane Wind
scale classifies
hurricanes according
to wind speed, which
implies potential for
flooding and potential
for property damage.
SECTION
13.3
Tropical Storms
Hurricane Hazards
Damage
• Hurricanes can cause extensive damage,
particularly along coastal areas, which tend to be
where human populations are the most dense.
SECTION
13.3
Tropical Storms
Hurricane Hazards
Winds
• Much of the damage caused by hurricanes is
associated with violent winds.
SECTION
13.3
Tropical Storms
Hurricane Hazards
Storm surge
• A storm surge occurs when hurricane-force
winds drive a mound of ocean water toward
coastal areas where it washes over the land.
SECTION
13.3
Tropical Storms
Hurricane Hazards
Hurricane advisories and safety
• The National Hurricane Center issues a
hurricane warning at least 36 hours before a
hurricane is predicted to strike.
• Awareness, combined with proper safety
precautions, has greatly reduced death tolls
associated with hurricanes in recent years.
SECTION
13.3
Section Check
At what latitudes do tropical cyclones
usually form?
a. between 0 and 5
b. between 5 and 30
c. between 30 and 50
d. between 50 and 70
SECTION
Section Check
13.3
What weather condition usually exists
within the eye of a hurricane?
a. high wind
b. calm wind
c. tornadoes
d. lightning
SECTION
13.3
Section Check
What is the source of a hurricane’s
energy?
Answer: A hurricane’s energy comes from
the warm water over which it develops. As
ocean water evaporates, some heat is taken
from the ocean. The water vapor then rises
high into the atmosphere. The heat that was
taken from the ocean is released to the
atmosphere as the water vapor condenses.
SECTION
13.4
Recurrent Weather
Essential Questions
• What are the problems associated with recurring
weather patterns?
• What atmospheric events cause recurring
weather patterns?
• How do heat waves and cold waves differ?
SECTION
13.4
Recurrent Weather
• Even a relatively mild weather system can
become destructive and dangerous if it persists
for long periods of time.
Review Vocabulary
• Fahrenheit scale: a temperature scale in
which water freezes at 32 and boils at
212
SECTION
13.4
Recurrent Weather
New Vocabulary
drought
heat wave
cold wave
windchill index
SECTION
13.4
Recurrent Weather
Floods
• An individual thunderstorm can unleash enough
rain to produce floods, and hurricanes also cause
torrential downpours, which result in extensive
flooding.
• Floods can also occur when weather patterns
cause even mild storms to persist over the same
area.
SECTION
13.4
Recurrent Weather
Floods
• Low-lying areas are most susceptible to flooding,
making coastlines particularly vulnerable to storm
surges during hurricanes.
• Rivers in narrow-walled valleys can rise rapidly,
creating high-powered and destructive walls of
water.
SECTION
13.4
Recurrent Weather
Droughts
• Droughts are extended periods of well-belowaverage rainfall.
• Droughts are usually the result of shifts in global
wind patterns that allow large, high-pressure
systems to persist for weeks or months over
continental areas.
SECTION
13.4
Recurrent Weather
Droughts
• Because the sinking air prevents humid air from
rising, condensation cannot occur, and drought
sets in until global patterns shift enough to move
the high-pressure system.
SECTION
13.4
Recurrent Weather
Droughts
Heat waves
• An unpleasant side effect of droughts often
comes in the form of heat waves, which are
extended periods of above-average
temperatures.
• Heat waves can be formed by the same highpressure systems that cause droughts.
SECTION
13.4
Recurrent Weather
Droughts
Heat waves
• Because of the dangers posed by a combination
of heat and humidity, the National Weather
Service (NWS) routinely reports the heat index.
• The heat index assesses the effect of the body’s
difficulty in regulating its internal temperature as
relative humidity rises.
SECTION
13.4
Recurrent Weather
Please click the image above to view the interactive table.
SECTION
13.4
Recurrent Weather
Cold Waves
• The opposite of a heat wave is a cold wave,
which is an extended period of below-average
temperatures.
• Cold waves are also brought on by large, highpressure systems. However, cold waves are
caused by systems of continental polar or arctic
origin.
SECTION
13.4
Recurrent Weather
Cold Waves
• Because of the location and the time of year in
which they occur, winter high-pressure systems
are much more influenced by the jet stream than
are summer high-pressure systems.
SECTION
13.4
Recurrent Weather
Cold Waves
• The winter location of the jet stream can remain
essentially unchanged for days or even weeks.
This means that several polar high-pressure
systems can follow the same path and subject the
same areas to continuous numbing cold.
SECTION
13.4
Recurrent Weather
Cold Waves
Windchill index
• The effects of cold air on the human body are
magnified by wind. Known as the windchill factor,
this phenomenon is measured by the windchill
index.
SECTION
13.4
Recurrent Weather
Cold Waves
Windchill index
• The windchill
chart was
designed to
show the
dangers of cold
and wind.
SECTION
Section Check
13.4
The temperature is 0F and the wind speed
is 30 miles per hour. What is the windchill?
a. –5F
b. –10F
c. –26F
d. –58F
SECTION
13.4
Section Check
What happens to air at the center of a
high-pressure system?
a. It sinks and water vapor condenses.
b. It sinks and water vapor resists condensation.
c. It rises and water vapor condenses.
d. It rises and water vapor resists condensation.
SECTION
13.4
Section Check
What conditions result in extensive
flooding?
Possible answer: The most extensive flooding
occurs as a result of heavy and persistent rain,
saturated soil, and low-lying ground.
CHAPTER
The Nature of Storms
13
Resources
Earth Science Online
Study Guide
Chapter Assessment Questions
Standardized Test Practice
SECTION
Thunderstorms
13.1
Study Guide
• The intensity and duration of thunderstorms
depend on the local conditions that create them.
• The cumulus stage, the mature stage, and the
dissipation stage comprise the life cycle of a
thunderstorm.
• Clouds form as water is condensed and latent
heat is released.
SECTION
Thunderstorms
13.1
Study Guide
• Thunderstorms can be produced either
within air masses or along fronts.
• From formation to dissipation, all
thunderstorms go through the same stages.
• Lightning is a natural result of thunderstorm
formation.
SECTION
Severe Weather
13.2
Study Guide
• All thunderstorms produce wind, rain, and
lightning, which can have dangerous and
damaging effects under certain circumstances.
• Intense rotating updrafts are associated
with supercells.
• Downbursts are strong winds that result in
damage associated with thunderstorms.
SECTION
Severe Weather
13.2
Study Guide
• Hail is precipitation in the form of balls or lumps of
ice that accompany severe storms.
• The worst storm damage comes from a vortex of
high winds that moves along the ground as a
tornado.
SECTION
Tropical Storms
13.3
Study Guide
• Normally peaceful, tropical oceans are capable of
producing one of Earth’s most violent weather
systems—the tropical cyclone.
• Tropical cyclones rotate counterclockwise in the
northern hemisphere.
• Tropical cyclones are also known as hurricanes
and typhoons.
SECTION
Tropical Storms
13.3
Study Guide
• Tropical cyclones go through the same stages of
formation and dissipation as other storms.
• Tropical cyclones are moved by various wind
systems after they form.
• The most dangerous part of a tropical cyclone is
the storm surge.
• Hurricane alerts are given at least 36 hours before
the hurricane arrives.
SECTION
Recurrent Weather
13.4
Study Guide
• Even a relatively mild weather system can
become destructive and dangerous if it
persists for long periods of time.
• Too much heat and too little precipitation
causes droughts.
• Too little heat and a stalled jet stream can
cause weeks of cold weather in an area.
SECTION
Recurrent Weather
13.4
Study Guide
• Heat index estimates the effect on the human
body when the air is hot and the humidity is high.
• Cold index tells how wind, humidity, and
temperature affect your body in winter.
• Windchill is a factor used to warn about the effect
of cold air and wind on the human body.
CHAPTER
The Nature of Storms
13
Chapter Assessment
Which weather event is often related to the
presence of persistent high pressure over a
region?
a. a flood
b. a drought
c. a tornado
d. a blizzard
CHAPTER
13
The Nature of Storms
Chapter Assessment
Which type of movement describes the air flow
in the eyewall of a hurricane?
a. counterclockwise upward spiral
b. clockwise upward spiral
c. counterclockwise downward spiral
d. clockwise downward spiral
CHAPTER
13
The Nature of Storms
Chapter Assessment
Why do people feel less comfortable on a hot
day when the humidity is high?
a. The air is less dense.
b. The air moves less.
c. Less evaporation occurs.
d. Less precipitation occurs.
CHAPTER
13
The Nature of Storms
Chapter Assessment
Which type of thunderstorm could form as a
result of the air circulation
shown?
a. mountain thunderstorm
b. sea-breeze thunderstorm
c. cold-front thunderstorm
d. warm-front thunderstorm
CHAPTER
13
The Nature of Storms
Chapter Assessment
What hazards do hurricanes cause when they
make landfall?
Possible answer: Hurricanes making landfall
bring high wind, tornadoes, and sometimes severe
lightning. Storm surge causes flooding along the
coast, and heavy rain causes flooding inland.
CHAPTER
The Nature of Storms
13
Standardized Test Practice
What forms as superheated air expands and
produces a shock wave?
a. lightning
b. thunder
c. tornado
d. microburst
CHAPTER
13
The Nature of Storms
Standardized Test Practice
What is the Saffir-Simpson scale?
a. a scale for classifying tornadoes
b. a scale for classifying hurricanes
c. a scale for classifying thunderstorms
d. a scale for classifying lightning
CHAPTER
13
The Nature of Storms
Standardized Test Practice
On which side of a northern hemisphere
tropical cyclone does the wind blow from the
south?
a. north side
b. west side
c. south side
d. east side
CHAPTER
13
The Nature of Storms
Standardized Test Practice
How is the life cycle of a supercell thunderstorm
similar to the life cycle of a hurricane?
Possible answer: Both storms form from
energy supplied by rising moist air, and both
storms dissipate when the supply of rising
moist air is cut off.
CHAPTER
13
The Nature of Storms
Standardized Test Practice
Why do hailstones consist of concentric layers?
CHAPTER
13
The Nature of Storms
Standardized Test Practice
Possible answer: The layers form as hailstones are
tossed in a thunderstorm by strong updrafts. A new
layer of ice is added each time the hailstone moves
into a level of supercooled water droplets. These
water droplets exist at temperatures that are well
below the normal freezing point of water and so
change to ice as soon as they come into contact with
the hailstone.