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EARTH SCIENCE LECTURE
CHAPTER 24
24.1 Air Masses
•A large body of air –
one with uniform temperature and moisture content – is called an
___________________________________.
–
An air mass is sometimes thousands of kilometers in diameter.
–A ________________________________, where air masses form, must
have a fairly uniform temperature and moisture content, such as occurs
over polar or desert land areas or the ocean.
•Air masses that form
•Air masses that form over
•
Air masses are classified according _____________________________________.
–The source regions also determine
–The source regions for cold air masses are polar areas; these air masses are labeled
“_____”.
–The source regions for warm air masses are tropical areas; these air masses are
“_____”.
–Air masses formed over the ocean are called maritime and are labeled “_____”.
–Air masses formed over land are called continental and are labeled “_____”.
–
Notice the “case” of the letters!!!
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labeled
•The combination of tropical or polar air and continental or maritime air results in four
main types of air masses.
– 1)
– 2)
– 3)
– 4)
–An air mass may remain over its source region for days or weeks.
–It will move into other regions because of the _________________________.
•North American Air Masses
•Air masses that strongly affect the weather of
North America come from seven regions.
–1)
–2)
–3)
–4)
–5)
–6)
–7)
24.2 Fronts
•When two unlike air masses meet, density differences usually keep the air masses
separate.
– The air of a cool air mass is dense and does not mix with the less-dense air of a warm
air mass.
– A boundary forms between air masses and is called a _______________________
•Changes in middle-latitude weather usually take place along the various types of
fronts.
•
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•In order for a front to form, one air mass _____________________________________.
–
1)
–If the warm air is moist, ______________________will form.
–______________________________ and ___________________________
typically form along a fast-moving cold front.
•Storms created along a cold front are usually __________________________________.
–
A long line of heavy storms, called a _______________________________, may
occur just ahead of a fast-moving cold front.
–
A slow-moving cold front lifts the warm air ahead of it more slowly than does a fastmoving front.
For that reason, a slow-moving cold front produces
–2)
–
–
The less dense warm air rises over the cooler air.
(__________________________________________________________)
Because of this gentle slope, clouds may extend far ahead of the surface location,
or base, of the front.
•A distinct pattern of clouds precedes the approaching base of a warm front:
–1)
–2)
–3)
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• A warm front generally produces ___________________________ over a large
area.
•A warm front may produce some violent weather if the body of warm air
advancing over the cooler air is very moist.
–3)
–
The two air masses move _____________________________ to the front between
them.
–
–4)
–
–
–
The advancing cold front then comes into contact with cool air that develops beneath
the lifted warm air.
The warm front is completely _________________________, or occluded, from the
ground by colder air.
The warm air is held above the ground high in the atmosphere.
•Over each of the earth's polar regions is a dome of cold air.
•The boundary at which the cold polar air meets the warmer air of the middle latitudes is
called a _____________________________________.
–A polar front circles the earth between ___________________________________
in each hemisphere.
–The polar fronts move
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•In the winter, the average position of the polar front in North America is across
_____________________________________________________.
•In the summer, it is __________________________________________________.
•A ____________________________ is a bend formed in a cold front or a stationary
front.
–
•The waves along the boundary of a polar front are the beginnings of
____________________________________centers called
__________________________________.
–
–
–
Large storms -- up to _____________________ in diameter.
Winds blow in circular paths spiraling upward around the low-pressure region at the
center.
They strongly influence weather patterns in the middle latitudes.
–A.K.A.
•
Stages of a Wave Cyclone
–1)
–2)
–3)
–4)
•Within 24 hours after the occlusion, the wave cyclone __________________________.
•A wave cyclone can last several days.
•During this time, air masses are in motion, and the disturbance moves with them.
–In North America, wave cyclones generally move in an easterly direction
at speeds of about __________________________________________, as they
spin ________________________________________________________.
•
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–
–
The air of an anticyclone sinks and flows outward from a center of high pressure
Anticyclones bring ________________________________, since their sinking air
does not promote cloud formation.
If an anticyclone stagnates over a region for many days, it can cause
•Hurricanes
– Some tropical storms behave like middle- latitude wave cyclones.
–
Tropical storms are:
–1)
–2)
–3)
•A severe tropical storm, with wind speeds starting at
–Hurricanes develop over
–Hurricane winds spiral rapidly in toward an intensely
–Seldom more than 700 km in diameter, hurricanes are much smaller than wave
cyclones but are much more powerful.
•These storms are
•The greatest number of hurricanes --an average of ________per year -- occurs in the
western _____________________________________, where they are called
___________________________________.
–An average hurricane has an energy content equal to the total
amount of electricity used in the United States in six months.
•A fully developed hurricane consists of ____________________________________
spiraling upward around the center of the storm.
–
Rain is _____________________.
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–
Winds increase in velocity toward the center, or _____________________________,
reaching speeds of up to _____________________ along the eyewall.
–The eye is a region of
•The most dangerous aspect of the hurricane is
–
Most deaths during hurricanes are due to ___________________________.
•____________________________ can also be a significant problem associated
with hurricane landfall
•Hurricane Classification:
•
–
–
–
1)
2)
3)
–Damage to mobile homes and small trees
•
–
–
–
1)
2)
3)
–Some damage to houses, small boats break moorings
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•
–
–
–
1)
2)
3)
–Mobile homes destroyed, devastating coastal flooding
•
–
–
–
1)
2)
3)
–Extensive damage to houses, major beach erosion
•
–
–
–
1)
2)
3)
–Many buildings destroyed, massive evacuation
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•Costly natural disasters (billions):
•1. Hurricane Andrew (27)
•2. Midwest Flooding (20)
•3. Hurricane Fran (7)
•4. Southeast U.S. Flooding (6)
•5. Hurricane Opal (3)
•Thunderstorms
– A storm accompanied by
– Thunderstorms often occur when a portion of air in a
________________________________________ is heated and rises.
–High surface temperatures on the ground or in the ocean influence the rising of
this warm, moist air.
–For that reason, thunderstorms occur most commonly in the late afternoon or
early evening.
•Air rapidly rising over mountains or in a cold front also forms severe thunderstorms.
•A thunderstorm develops in three distinct stages:
–
1)
–At this stage, warm, moist air rises until the water vapor within the air
condenses and forms a cumulus cloud.
–
2)
–
Violently rising warm, moist air swells higher and higher.
–
The cumulus cloud
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–
The cloud tops may reach heights of over _________________________________,
where the top spreads out in an anvil shape.
–
–This precipitation produces a ______________________________________.
–
–3)
–
The ______________________________________ stop air currents from rising.
–
The thunderstorm dies out as the supply of water vapor ______________________.
–
During a thunderstorm,
•
The released electricity ___________________________________________.
–The rapid expansion and collapse of the air produces the loud noise known as
__________________________________.
• For lightning to occur, the clouds must have areas with distinct electrical charges.
–The upper part of the cloud usually carries a ______________________ electrical
charge
–The lower part carries mainly _____________________________________.
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•
In fair weather there is a natural separation of charge in the atmosphere.
•Positive and negative charges within a thunderstorm cloud separate
–As a thunderstorm moves across the landscape positive charges congregate below the
thunderstorm at the Earth’s surface
–
–
When the potential becomes to large there must be a release
The cloud sends _________________________________ toward the Earth’s
surface
•When the step leader nears the ground
__________________________________ the
Earth will send a leader upward to make the connection
–
When a connection is made the clouds charge will be released
–
_____________________________________________at the Earth’s surface tend
to send leaders upward
–Examples:
•
–There is
•
The Bolt
–A lightning bolt is approx. _____________________________ in diameter
–The temperature of a lightning bolt can reach
____________________________________________ which is
______________________________________________________
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•UNSAFE places to be in a lightning storm:
–
–
–You could be hit directly or from a side flash
–You could be hit by debris from the tree as the lightning explodes the tree
(____________________________________________)
•Lightning Myths
–
1)
–Lightning can and does strike the same object more than once
–
2)
–Distant thunderstorm which illuminates the sky (thunder is not heard because of
the great distance)
Lightning
•
•
Lightning is a discharge of ______________________________________.
May occur:
–
–
–
–
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•Tornadoes
–
–A tornado
•A tornado forms
–These winds cause the rising air in the thunderstorm to rotate.
–One of the storm clouds may develop a narrow, funnel-shaped, rapidly spinning
extension.
–
The extension reaches downward and may or may not actually touch the ground.
•If the tip of the funnel does touch the ground, it generally moves in a wandering,
haphazard path.
•Frequently the funnel rises and touches down again a short distance away.
–
The tornado generally covers a path not more than ____________________
•The destructive power demonstrated by the rapidly spinning winds indicates that
they may reach speeds of up to ____________________________________.
•Tornadoes occur in many locations.
–
They are most common in "____________________________________", in the
–
Tornadoes the ocean are called ______________________________.
–Waterspouts are usually smaller and less powerful than tornadoes.
–If the waterspout reaches land it is classified as a Tornado.
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•Tornado Detection:
–
Most common detection methods:
–1)
–
–
A.
B.
–2)
•Tornado Intensity Scale
–
Strength of tornado is often assigned __________________________________
–Known as the __________________________________________
•
•
•
•
Named after Dr. Theodore T. Fujita (1920 – 1998) at the University of Chicago
Invented in _________________________
Used
Also known as the
•Fujita Intensity Scale
•
–Damage to chimneys and billboards, broken branches, shallow trees pushed
over
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•
–Surfaces peeled off roofs, mobile homes pushed off foundations, moving
cars pushed off road
•
–Roofs torn off frame houses, mobile home destroyed, large trees snapped,
light object missiles generated
•
–Roofs and some walls torn off well-constructed homes, trains overturned,
most trees downed, heavy cars lifted and thrown
•
–Well-constructed houses leveled, cars thrown considerable distances,
large missiles generated
•
–Strong frame houses lifted and carried great distances, automobile size
missiles fly farther than 100m (328 ft), trees debarked, incredible
phenomena will occur
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Enhanced Fujita (EF) Scale vs. Fujita Scale
24.3 Weather Instruments
1)
2)
3)
4)
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– Both the ________________________________________________ are
commonly used in the United States.
–
A.
–
This thermometer consists of a bar made up of two strips, each of a different
metal.
–The metals, such as brass and iron, expand different amounts when heated.
–The bar will curve when heated and straighten again when cooled.
•5)
–A typical anemometer consists of small cups attached by spokes to a shaft that
rotates freely.
–The wind pushes against the cups, causing them to rotate.
–This rotation triggers an electrical signal that registers the wind speed in
_____________________________________________
•6)
–Shaped like an arrow with a large tail
–The wind vane turn freely on a pole as the tail catches the wind.
–
•A wind is described __________________________________________________, so
that westerly describes a wind that blows from the west.
–Wind direction may be described by one of ____________________________,
on the compass.
–Wind direction also may be recorded in degrees, beginning with 0 at north
and moving clockwise to 360.
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•7)
•8)
–Objects that cross the beam reflect back to the transmitter, which receives the
returning beams.
–Radar can detect objects that are too small or too far away for the human eye to
see.
•The Doppler radar can indicate the precise location, movement, and extent of a
storm, as well as the intensity of precipitation and wind patterns within a storm.
•
9)
In ____________ the United States formed a weather-forecasting agency as part of the
_____________________________________.
–___________ years later the agency was organized into the
__________________________________.
–In ___________ it was renamed the ____________________________________.
•Because accurate weather forecasting is so important, all nations around the world
cooperate in gathering and exchanging weather data.
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•Every ____________________, weather observers at stations all over the world
report weather conditions.
•These observers record:
–1)
–2)
–3)
–4)
–5)
–6)
–7)
•On the map, clusters of symbols are plotted around each weather station showing the
conditions at that station.
–Such a cluster of symbols is called a _____________________________.
•Common weather symbols describe: (P.513)
–1)
–2)
–3)
–4)
–5)
–6)
–7)
•On a weather map, lines are drawn to connect points of equal atmospheric pressure.
–
These lines are called ______________________________.
–The spacing and shape of the isobars help meteorologists interpret their
observations about the speed and direction of the wind.
–Closely spaced isobars indicate
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–Widely spaced isobars generally indicate
– Isobars that
– Such centers are marked with an __________________________or with an
__________________________________
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