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Done by: Faisal Al Najem
8-3
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An air mass is a large volume of air in which temperature and humidity
are nearly the same in different locations at the same altitude.
An air mass forms when the air over a large region of earth sits in one
place for many days. When earth’s surface is cold, the air becomes moist.
When earth’s surface is dry the air become’s also dry.
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The characteristics of an air mass depend on the region where it forms. A
hot desert produces dry, hot air masses, while cool ocean waters
produces moist, cool air masses.
Scientists rate air masses into categories according to the characteristics
of regions.
Characteristics of air mass
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There are four types of Characteristics, and they are:
 Continental
 Maritime
 Tropical
 Polar
Continential air mass
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Continental: Air masses form over land. Air becomes
dry as it loses it’s moisture to the dry land below it.
Maritime air mass
 Maritime:
air masses form over land. Air
becomes moist as it gains water vapor from the
water below it.
Tropical air mass
 Tropical:
air masses from near the equator. Air
becomes warm as it gains energy from the
warm land or water.
Polar air mass
 Polar:
Air masses form far from the equator. Air
becomes cool as it loses energy to the cold
land or water.
Movement of an air mass
 Air
masses can travel away from the regions
where they form. They move with the global
pattern of winds.
Movement of an air mass
 When
air mass moves to a new region, it carries
along it’s characteristics moisture and
temperature. As air moves over earth’s surface,
the characteristics of the surface begin to
change.
Weather changes where air
masses meets
 When
a new air mass moves over your area,
you can expect the weather to change.
 Front: is a boundary between air masses
Fronts and weather
 Different
types of fronts produce different types
of weather.
 When a cold, dense air mass pushes warmer
air, it produces a cold front. When a warm air
mass pushes colder air, it produces a warmer
front.
Types of fronts
 Cold
Front forms when cold air mass pushes a
warm air mass and forces the warm air to rises,
 It’s moisture condenses and forms tall clouds
Types of fronts
 Warm
front forms when a warm air mass
pushes a cold air mass. The warm air rises
slowly over the cold air and its moisture
condenses into flat clouds.
Types of Fronts
 Stationary
Fronts occurs when two air masses
push against each other without moving. A
stationary front becomes a warm or cold front
when one air mass advances.
High pressure system
A
high pressure system is formed when air
moves all the way around a high pressure
center. Most high pressure system are large
and change slowly.
Low pressure system
A
low pressure system is a large weather
system that surrounds a center of low pressure.
It begins as air moves around and inward
toward the lowest pressure and then up to
highest altitudes.
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3.2 Low pressure
systems can
become storms
Hurricanes form over warm
ocean water
 Near
the equator, warm ocean water provides
the energy that can turn a low-pressure center
into a violent storm.
Hurricanes form over warm
ocean water
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Tropical storm is a low-pressure system that starts near
the equator and has winds that blow at 65 kilometers
per hour and 40 mi per h and more
Hurricane is a tropical low pressure system with winds
blowing at speeds of 120 kilometer per hour 74 mi/h or
more – strong enough to uproot trees
Formation of hurricanes
 Energy
from warm water is necessary for
a low-pressure center to build into a
tropical storm and then into a hurricane.
Effects of hurricanes
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A hurricane can pound a coast with huge waves and
sweep the land with strong winds and heavy rains. Also
hurricane wind can lift cars, uproot trees, and tear the
roofs of buildings.
Storm surge often pushes a huge mass of ocean water.
A storm surge can be destructive and deadly.
Winter storms produce storms
and ice
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Blizzards are strong winds that can blow so much snow into the air at once
that it becomes difficult to see and dangerous to travel. They are also
blinding snowstorms with winds of at least 56 kilometer per hour 35 mi/h
and low temperatures-usually below -7c 920f.
Lake-Effect Snowstorms is some of the heaviest snows fall in the area just
east and south of the great lakes.
Ice storms is when rain falls onto freezing-cold ground, conditions can
become dangerous.
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you
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