Download Weather and Climate Chapter 3, Section 1 (pg 72

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Weather and Climate
Topic
Class/Subject
Chapter 3, Section 1 (pg 72-79)
Air Masses and Fronts
Define air mass.
A huge body of air that has similar temperature, humidity, and air
pressure at any given height is called an air mass.
What 2 characteristics do
scientists use to classify
air masses?
Temperature and humidity are used to classify air masses.
Name the 4 major types of
air masses that influence
the weather in North
America.
4 major types of air masses:
1. maritime tropical
2. continental tropical
3. maritime polar
4. continental polar
What determines the
characteristics of an air
mass?
The characteristics of an air mass depend on the temperatures
and moisture content of the region over which the air mass
forms.
Describe a tropical air
mass.
A tropical air mass is warm, forms in the tropics, and has low air
pressure.
Describe a polar air mass.
A polar air mass is cold, forms north of 50°N latitude and south of
50°S latitude, and has high air pressure.
Describe a maritime air
mass.
A maritime air mass forms over oceans and is humid.
Describe a continental air
mass.
A continental air mass forms over land and is dry.
What moves air masses in Air masses are commonly moved by the prevailing westerlies
the continental U.S.?
and jet streams.
Define front.
A front is the boundary where air masses meet. Storms and
changeable weather often develop along fronts, because 2 air
masses with a different temperature and humidity do not easily
mix when they collide.
Name the 4 types of
fronts.
4 types of fronts:
1. cold fronts
2. warm fronts
3. stationary fronts
4. occluded fronts
What is a cold front and
what type of weather is
associated with it?
In a cold front, a fast-moving cold air mass overtakes a warm air
mass. Cold fronts can cause abrupt weather changes, including
thunderstorms. After a cold front passes, colder, drier air moves
in, often bringing clear skies, a shift in wind, and lower
temperatures.
What is a warm front and
what type of weather is
associated with it?
In a warm front, a warm air mass overtakes a slow-moving cold
air mass. Because warm fronts move slowly, the weather may
be rainy or cloudy for several days. After a warm front passes,
the weather is likely to be warm and humid.
What is a stationary front
and what type of weather
is associated with it?
In a stationary front, cold and warm air masses meet, but neither
can move the other. If a stationary front remains stalled over an
area, it may bring many days of clouds and precipitation.
What is an occluded front
and what type of weather
is associated with it?
In an occluded front, a warm air mass is caught between 2 cooler
air masses. The warm air mass is cut off, or occluded, from the
ground. As the warm air cools and its water vapor condenses,
the weather may turn cloudy and rain or snow may fall.
What causes cyclones
and anticyclones?
Cyclones and anticyclones are caused by distorted front
boundaries resulting from surface features or strong winds.
What is a cyclone?
A cyclone is a swirling center of low air pressure. Winds spiral
inward towards the low pressure center. Warm air at the center
rises and the pressure decreases. Winds in a cyclone spin
counterclockwise in the Northern Hemisphere.
What type of weather is
associated with a
cyclone?
Cyclones and decreasing air pressure are associated with
clouds, wind, and precipitation.
What is an anticyclone?
An anticyclone is a high-pressure center of dry air. Winds spiral
outward from the center, moving toward areas of low pressure.
Cool air at the center falls, warms up, and its relative humidity
drops. Winds in an anticyclone spin clockwise in the Northern
Hemisphere.
What type of weather is
associated with an
anticyclone?
The descending air in an anticyclone generally causes dry, clear
weather.
Summary
4 major air masses influence the weather in North America: maritime tropical, continental
tropical, maritime polar, and continental polar. In the continental U.S., air
masses are commonly moved by the prevailing westerlies and jet streams.
Colliding air masses can form 4 types of fonts: cold fronts, warm fronts,
stationary fronts, and occluded fronts. Cyclones and decreasing air
pressure are associated with clouds, wind, and precipitation. The
descending air in an anticyclone generally causes dry, clear weather.