science ~ chapter 8 weather
DESCRIPTION
Science ~ chapter 8 weather. Miss Nelson. Section 3. Air Masses and Fronts. Anticipatory set. Which is denser… warm air, or cold air? What do you think happens when warm air and cold air collide?. standards. S 6.4.e – - PowerPoint PPT PresentationTRANSCRIPT
Miss Nelson
SCIENCE ~ CHAPTER 8
WEATHER
Air Masses and Fronts
SECTION 3
Which is denser… warm air, or cold air?
What do you think happens when warm air and cold air collide?
ANTICIPATORY SET
S 6.4.e –Students know differences in pressure, heat, air movement, and humidity result in change in weather
STANDARDS
What are the major types of air masses in North America, and how do they move?
What are the main types of fronts?
What type of weather is associated with cyclones and anticyclones?
THE BIG IDEA
Air mass – a huge body of air that has similar temperature, humidity, and air pressure throughout
Tropical – a warm air mass that forms in the tropics and has low air pressure
Polar – a cold air mass that forms north of 50 degrees latitude or south of 50 degrees latitude and has high air pressure
Maritime – a humid air mass that forms over oceans
Continental – a dry air mass that forms over land
KEY TERMS
Front – the boundary where unlike air masses meet but do not mix
Occluded – cut off, as in a front where warm air mass is caught between two cooler air masses
Cyclone – a swirling center of low air pressure
Anticyclone – a high-pressure center of dry air
KEY TERMS
Weather can be influenced by air from thousands of kilometers away
A huge body of air that has similar temperature, humidity, and air pressure at any given height is called an air mass
A single air mass may spread out over millions of square kilometers and be up to 10 kilometers deep
AIR MASSES AND FRONTS
Four major types of air masses influence the weather in North America:Maritime tropicalContinental tropicalMaritime polarContinental polar
TYPES OF AIR MASSES
The characteristics of an air mass depend on the temperatures and moisture content of the region over which the air mass forms
TYPES OF AIR MASSES
Temperatures affects pressure
Cold, dense air has a higher pressure
Warm, less dense air has a lower pressure
TYPES OF AIR MASSES
Tropical air masses:
Warm air masses
Form in the tropics
Have low air pressure
Polar air masses:
Cold air masses
Form north of 50° and south of 50°
Have high air pressure
TYPES OF AIR MASSES
Whether an air mass is humid or dry depends on whether it forms over water or land
TYPES OF AIR MASSES
Maritime air masses form over waterThe air can become very humid
Continental air masses form over landHave less exposure to moisture from water – are drier
TYPES OF AIR MASSES
Warm, humid air masses form over tropical oceansGulf of Mexico, Atlantic Ocean
In summer time, they bring hot, humid weatherSummer showers and thunderstorms
In winter, bring heavy rain or snow
MARITIME TROPICAL
Cool, humid air masses form over the icy cold North Pacific and North Atlantic Oceans
Affect the west coast more than the east coast
Even in summer, they bring fog, rain, and cool temperatures to the west coast
MARITIME POLAR
Hot, dry air masses form mostly in summer over dry areas of the Southwest and northern Mexico
Cover a smaller area than other air masses
Occasionally move northeast, bringing hot, dry weather to the southern Great Plains
CONTINENTAL TROPICAL
Form over central and northern Canada and Alaska
Can bring bitterly cold weather with very low humidity
In winter, bring clear, cold, dry air to much of North America
In summer, the air mass is milder
Storms may occur when continental polar air masses move south and collide with maritime tropical air masses moving north
CONTINENTAL POLAR
Read Types of Air Masses on pages 311-312 of your textbook
TYPES OF AIR MASSES
In the continental United States, air masses are commonly moved by the prevailing westerlies (winds) and jet streams
HOW AIR MASSES MOVE
The major wind belts over the continental United States
Generally push air masses from west to east
PREVAILING WESTERLIES
Embedded within the prevailing westerlies are jet streams
Bands of high speed winds about 10 kilometers above Earth’s surface
Blow from west to east
JET STREAMS
As huge air masses move across the land and the oceans, they collide with each otherThey do not easily mix
Think about oil and water!Less dense oil floats on top of the denser water
Something similar happens when two air masses with different temperatures and humilities collide
FRONTS
The boundary where these air masses meet is called a front
Storms and changeable weather often develop along fronts
View the picture on page 313 of your textbook
FRONTS
Read How Air Masses Move on page 313 of your textbook
HOW AIR MASSES MOVE
Colliding air masses can form four types of fronts:
Cold frontsWarm frontsStationary frontsOccluded fronts
TYPES OF FRONTS
The type of front that develops depends on the characteristics of the air masses and how they are moving
TYPES OF FRONTS
Cold air is dense and tends to sink
Warm air is less dense and tends to rise
When a rapidly moving cold air mass runs into a slowly moving warm air mass… The denser cold air slides under the lighter warm air The warm air is pushed upward along the leading
edge of the colder air
View figure 14 on page 314 of your textbook
COLD FRONT
As the warm air rises, it expands and cools
Warm air can hold move water vapor than cool air
The rising air reaches the dew point (the temperature at which water vapor in the air condenses into droplets of water)
Clouds form
If there is a lot of water vapor in the warm air, heavy rain or snow may fall
If the warm air mass contains only a little water vapor, then the cold front may be accompanied by only cloudy skies
COLD FRONT
Read Cold Fronts on page 314 of your textbook
COLD FRONT
Clouds and precipitation also accompany warm fronts
At a warm front, a fast-moving warm air mass overtakes a slowly moving cold air mass
Cold air is denser than warm air, the warm air moves over the cold air
If the warm air is humid, l ight rain or snow falls along the front
If the warm air is dry, scattered clouds form
Because warm fronts move slowly, the weather may be rainy or cloudy for several days
After a warm front passes through an area, the weather is l ikely to be warm and humid
WARM FRONTS
Read Warm Fronts on page 315 of your textbook
WARM FRONTS
View the diagram on page 315 of your textbook
Read Stationary Fronts on page 315 of your textbook
STATIONARY FRONTS
View the diagram on page 315 of your textbook
Read Occluded Fronts on page 315 of your textbook
OCCLUDED FRONTS
As air masses collide to form fronts, the boundary between the fronts sometimes becomes distorted
Can be caused by surface features such as mountains, strong winds, or jet streams
When this happens the air begins to swirl
Swirling air can cause a low pressure center to form
CYCLONES AND ANTICYCLONES
When you look at a weather map you will see areas marked with an L Stands for “low” pressure
Swirling center of low air pressure is called a cyclone From the Greek word meaning “wheel”
Cyclones play a large part in the weather of the United States
As air rises in the cyclone, the air cools, forming clouds and precipitation
CYCLONES
Cyclones and decreasing air pressure are associated with clouds, winds, and precipitation
CYCLONES
The opposite of a cyclone
High pressure centers of dry air
Called “highs” and marked with an H on a weather map
Winds spiral outward from the center of an anticyclone, moving toward areas of low pressure
ANTICYCLONES
The descending air in an anticyclone generally causes dry, clear weather
ANTICYCLONES
What two characteristics are used to classify air masses?
Of the four types of air masses, which are dry, and which are humid?
CHECK FOR UNDERSTANDING
What two characteristics are used to classify air masses?The two characteristics used to classify air masses are temperature and humidity.
Of the four types of air masses, which are dry, and which are humid?Maritime tropical and maritime polar air masses are humid, while continental tropical and continental polar air masses are dry.
CHECK FOR UNDERSTANDING
What type of air mass would form over the northern Atlantic Ocean?
What are the four types of fronts?
GUIDED PRACTICE
What type of air mass would form over the northern Atlantic Ocean?The type of air mass that would form over the northern Atlantic Ocean is a maritime polar air mass.
What are the four types of fronts?The four types of fronts are cold front, warm front, stationary front, and occluded front.
GUIDED PRACTICE
Complete Weather 8-3 Independent Practice
INDEPENDENT PRACTICE