Download Weather 4 - SusanPuckett

Warm Up # 27
• 1. Define—jet stream
• 2. Define—Coriolis Effect
• 3. Define—air pressure
Weather 4
Air masses, fronts, pressure systems
Vocab to remember
air mass--large volume of air with "same" temperature and
humidity in locations at the same altitude
front--boundary between air masses
high pressure system--formed when air moves around
a high pressure center
low pressure system--large weather system that surrounds a
center of low pressure
DQ—How can pressure cause positive and
negative change?
• S of I—Patterns of movement within systems result in
interaction and exchange.
• Weather changes as air moves
• Weather changes as a new air mass moves into the area. An
air mass can sit for many days over an area. As it sits, it takes
on the characteristics of the land or water below it.
Characteristics of an air mass
Where did the air mass form?
•Continental--air mass formed over land,
becomes dry as it loses its moisture to dry land
below it
•Maritime--forms over water becomes moist as it
gains water vapor from water below it
Did it form near the equator?
•Tropical--air mass formed
near equator becomes warm
as it gains energy
•Polar--forms far from equator
becomes cool as it loses
energy
Movement of air masses
An air mass moves with global winds and can be
influenced by jet streams.
It carries its characteristics with it and changes the
weather as it moves.
If the air mass moves quickly, it changes the
weather as it moves in.
If the air mass moves slowly, the mass may change
its characteristics as it sits in a new area.
Movement of air masses
Fronts
Fronts are boundaries between air masses.
As one air mass pushes another, the boundary
(front) between them may be very different
from either air mass. Cloudy or stormy weather
can be expected as fronts pass over an area.
Cold Fronts
When a cold, dense air mass
pushes warmer air, it produces a cold front.
Cold fronts move in quickly and are steep.
The cold, dense air moves forward and pushes the warmer
air upward. Water vapor in the warm air condenses.
Tall, cumulonimbus clouds and brief, heavy storms are
likely. After the front moves through, the air is cooler and
often very clear.
Warm Front
When a warm air mass pushes colder air,
it produces a warm front.
Warm fronts move more slowly than cold fronts.
Warm air moves up gradually over the colder, denser air.
The slope is less steep.
High cirrus clouds, then stratus clouds form.
Warm fronts often bring hours of steady rain or snow,
then the air is warmer after the front moves.
Stationary Front
Stationary front forms when two air masses meet
and stop moving. They may last for days with clouds
that cover the sky. The front becomes either a warm
front or a cold front depending on which mass pushes
the other.
High pressure systems
High pressure centers have air that sinks slowly
and spread outward from the center.
It moves clockwise in the Northern Hemisphere
due to the Coriolis Effect.
It usually moves slowly bringing clear skies and
calm air.
Low pressure systems
Develop around a center of low pressure. Air moves around
and inward toward the lowest pressure and then up to higher
altitudes.
As the air moves upward it lowers the air pressure
further and makes the air move faster.
It moves in a counter clockwise direction in the Northern
Hemisphere.
It can develop along fronts between warm air masses
and colder air masses. It can become very strong.
Exit Ticket
• 1. Name the 2 ways we identify air masses.
• 2. Draw and label a cold front. (color)
• 3. Draw and label a warm front. (color)
Formative Assessment
• You will be completing a formative assessment based on your
knowledge of the atmosphere, differences in air pressure
which cause changes in weather, and global warming.
• I am giving you a study guide with most of the questions
from the assessment. Spend time preparing yourself.
• This test will consist of MOSTLY ESSAY questions.