2.1 The atmosphere's air pressure changes.
REVIEW:
- The distance above sea level is _________________.
- The amount of mass in a given volume of substance is ___________________.
- The whole layer of air that surrounds Earth is the ________________________.
Air molecules move constantly. As they move, they bounce off each other like rubber balls. They also bounce off every surface they hit. Each time an air molecule bounces off an object, it pushes, or exerts a force, on that object. When billions of air molecules bounce off a surface, the force is spread over the area of that surface. Air pressure is the force of air molecules pushing on an area. The greater the force, the higher the air pressure. Because air molecules move in all directions, air pressure pushes in all directions.
Air pressure decreases as you move higher in the atmosphere. Think of a column of air directly over your body. If you stood at sea level, this column would stretch from where you stood to the top of the atmosphere. The air pressure on your body would be equal to the weight of all the air in the column. But if you stood on a mountain the column of air would be shorter. With less air above you, the pressure would be lower. At an altitude of 5.5 kilometer (3.4 miles), air pressure is about half what it is at sea level.
Air pressure and density are related. Just as air pressure decreases with altitude, so does the density of air. The air at sea level is denser than air at high altitudes.
Answer the following questions after watching the video.
- What gives wind its mass?
- What 3 things make air pressure change?
- What is a convection cell?
- What is the Coriolis Effect?
- What causes wind?
Air pressure is measured by a barometer.
Types of global wind belts
Calm Regions:
The doldrums are a low-pressure zone near the equator. There warm air rises to the top of the troposphere. Then the air spreads toward the poles. The rising, moist air produces clouds and heavy rain. During the hottest months, heavy evaporation from warm ocean water in the region fuels tropical storms.
The Horse Latitudes:
are high pressure zones located about 30 degrees north and 30 degrees south of the equator. Warm air traveling away from the equator cools and sinks in these regions. The weather tends to by clear and dry.
Wind Belts:
Trade Winds
Blow from the east, moving from the horse latitudes toward the equator. These strong, steady winds die out as they come near the equator.
Westerlies:
Blow from the west, moving from the horse latitudes toward the poles. They bring storms across much of the United States.
Easterlies:
blow from the east moving from the polar regions toward the mid-latitudes. Stormy weather often occurs when the cold air of the easterlies meets the warmer air of the westerlies.
Calm Regions:
The doldrums are a low-pressure zone near the equator. There warm air rises to the top of the troposphere. Then the air spreads toward the poles. The rising, moist air produces clouds and heavy rain. During the hottest months, heavy evaporation from warm ocean water in the region fuels tropical storms.
The Horse Latitudes:
are high pressure zones located about 30 degrees north and 30 degrees south of the equator. Warm air traveling away from the equator cools and sinks in these regions. The weather tends to by clear and dry.
Wind Belts:
Trade Winds
Blow from the east, moving from the horse latitudes toward the equator. These strong, steady winds die out as they come near the equator.
Westerlies:
Blow from the west, moving from the horse latitudes toward the poles. They bring storms across much of the United States.
Easterlies:
blow from the east moving from the polar regions toward the mid-latitudes. Stormy weather often occurs when the cold air of the easterlies meets the warmer air of the westerlies.
What are jet streams?
Watch the video on jet streams and answer these questions.
How many miles up in the air is the jet stream found?
What is the top speed the jet stream can reach?
What time of year is the jet stream the strongest?
How many miles up in the air is the jet stream found?
What is the top speed the jet stream can reach?
What time of year is the jet stream the strongest?