Download Section 25.1: Air Masses

Chapter 25:
Weather
Section 25.1: Air Masses

An air mass is a large body of air that
remains stationary or moves slowly over
a uniform area.

It takes up the characteristics of the
area such as humidity and temperature.
Section 25.1: Air Masses

The regions that these air masses form
are called source regions.

These regions usually occur over the
poles, deserts and tropical oceans.

What type of weather do you think air masses
over each of these regions would produce?
Section 25.1: Air Masses

The source regions for cold air masses
are labeled with a P and warm air
masses are labeled with a T.

Why?
Section 25.1: Air Masses

Air masses formed over the ocean are
called maritime and air masses formed
over land are called continental.
Section 25.1: Air Masses

So there are four large types of air
masses:

maritime polar, mP

What type of weather would this produce?

Met Office: Air masses
Section 25.1: Air Masses

maritime tropical, mT


continental polar, cP


What type of weather would this produce?
What type of weather would this produce?
continental tropical, cT

What type of weather would this produce?
Section 25.1: Air Masses
Air masses travel from their source
region to wherever the winds carry them
and they take the weather from their
source region with them.


Example: An air mass which forms over
the land may be dry and cooler and begins
to warm and gain humidity as it moves over
the ocean.
Section 25.1: Air Masses

There are three polar air masses which
influence weather over North America.

They are the continental polar
Canadian, maritime polar Pacific, and
maritime polar Atlantic.
Section 25.1: Air Masses

These air masses bring cool dry air in the
summer and in the winter they bring
bitter cold weather.

What type of weather are we experiencing
right now?

Are we experiencing one of these air
masses?
Section 25.1: Air Masses

There are four tropical air masses which
influence the weather over North
America.

They are the continental tropical,
maritime tropical gulf, maritime tropical
Pacific and maritime tropical Atlantic.
Section 25.1: Air Masses

These air masses usually bring warm
moist air in both the summer and winter.

What type of weather are we experiencing
right now?

Are we experiencing one of these air
masses?
Section 25.1: Air Masses

These air masses bring weather from
the north and south but the westerly
winds which blow across the United
States cause weather to come from the
west and move to the east.
Section 25.2: Fronts
The dense air of cold air masses and
less dense air of warm air masses DO
NOT mix well.


A buffer forms between air masses, this
boundary is called a front.
Section 25.2: Fronts

There are many
different types of
fronts that affect
weather patterns.

When a cold air
mass over takes a
warm air mass it is
called a cold
front.
Section 25.2: Fronts

Where the cold and warm air meet
clouds and precipitation will usually form
and a line of thunderstorms or snow
storms will form called a squall line.
Section 25.2: Fronts

When a warm air mass over takes a cold
air mass it is called a warm front.
Section 25.2: Fronts

If the warm air mass is high in precipitation
it may become a violent front full of
precipitation where it meets the cold front.
Section 25.2: Fronts

When two air
masses of equal
strengths and sizes
meet and neither
moves the front that
results is called a
stationary front,
which acts much
like a warm front.
Section 25.2: Fronts

An occluded front is caused when a
warm air mass is overtaken by a fast
moving cold air mass and the cold air
mass completely cuts off the warm air
mass from the ground.
Section 25.2: Fronts

The change of weather that
accompanies the changes in the
seasons is due to the movement of the
polar front.

Which is a cold air mass that moves
closer to the middle latitudes (area
around Virginia) in the winter and up
toward the poles in the summer.
Section 25.2: Fronts

At the edge of this polar front is a
turbulent area of air called a wave
cyclone, which is a large storm.

What type of storms do we see which exhibit
a spinning motion?
Section 25.2: Fronts

The wave cyclones also have
anticyclones which balance their
effects on the weather.

The meeting of these fronts causes
many different weather patterns that
affect the world in many ways.
Section 25.2: Fronts

A hurricane is a severe tropical storm
that has wind speeds that are over
120km/hr.
Section 25.2: Fronts

Hurricanes that occur in the western
North Pacific Ocean are called
typhoons.

Hurricanes have an area of calm air at
their centers which is a result of pressure
pulling away from the center.

This calm area is called the eye.
Section 25.2: Fronts

A thunderstorm is a rain storm
accompanied by thunder and lightning.
Section 25.2: Fronts

Thunderstorms occur when warm fronts
are heated and the humidity within them
builds up.

Lightning is electricity released by the
storm caused by static build up.

This is the same concept as rubbing your
feet on the carpet and then getting shocked.
Section 25.2: Fronts

The smallest, most violent and shortest
lived severe storm is a tornado.
Section 25.2: Fronts

A tornado forms when a rising
thunderstorm meets high altitude winds
which cause the storm to spin much like
a whirlpool.

The destructive power of a tornado is
due to the high speed winds associated
with the storm.
Section 25.2: Fronts

If a tornado forms over the ocean it is
called a water spout because the high
winds suck water up into the air.
Section 25.3: Weather
Instruments

The tool used for measuring air
temperature is a thermometer.
Section 25.3: Weather
Instruments

A bimetal thermometer is a type of
thermometer that measures the
expansion rates of two different metals
such as copper and iron.
Section 25.3: Weather
Instruments

A thermograph is a type of thermometer
that measures temperature change with
a pen to a bar which moves with
variations in temperature.
Section 25.3: Weather
Instruments

An electrical thermometer measures
the electrical current running through
certain substances which changes as
temperature changes.
Section 25.3: Weather
Instruments

An instrument called
an anemometer
measures wind
speed.

This instrument is
made up of a few
cups attached to
spokes on a shaft that
rotates freely and
records the speed of
rotation.
Section 25.3: Weather
Instruments

Wind direction is determined by a wind
vane which is usually shaped like a large
arrow that catches the wind and rotates
around to face away from it.
Section 25.3: Weather
Instruments

Weather in the upper atmosphere is
measured by a radiosonde which is a
bundle of meteorological tools carried
by a weather balloon.
Section 25.3: Weather
Instruments

Satellite and radar are used by
meteorologists to look at a large area in
the upper atmosphere.
Section 25.4: Forecasting the
Weather

Every six hours meteorologists at
weather stations all over the world
report weather conditions to the World
Meteorological Organization (WMO).
Section 25.4: Forecasting the
Weather
These stations report their data as
symbols on a map.


These maps are called station models.
Section 25.4: Forecasting the
Weather
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The symbols on these maps include
cloud coverage, wind speed, wind
direction and precipitation.

These maps also have lines called
isobars which help meteorologists
interpret wind direction and speed based
on the spacing and shape of these lines.
Section 25.4: Forecasting the
Weather
There are two types of forecasts, daily
and long term.


Daily forecasts report current weather
conditions and the effects of current air
masses.

Nanticoke Weather Forecast and
Conditions Pennsylvania
Section 25.4: Forecasting the
Weather
Long term forecasts predict weather by
examining movement of air masses and
winds.


Long term forecasts can only be considered
accurate between 3 to 5 days, anything
longer is done by computer and is far less
accurate.

Nanticoke 10 Day Forecast Pennsylvania
Section 25.4: Forecasting the
Weather

Cloud seeding is a way meteorologists
can control the weather by forcing
precipitation by adding extra
condensation nuclei to a cloud.

Is this a way to stop weather from
occurring?
Section 25.4: Forecasting the
Weather

Hurricanes can also be seeded with
frozen nuclei in an attempt to reduce the
temperature and in turn diminish the
intensity of the hurricane.
Section 25.4: Forecasting the
Weather

Attempts to control lightning have been
made by releasing large amounts of
charges particles near the ground to help
reduce the strength of lightning.