Chapter 5 Earth’s Weather
Lesson 2: Air Currents and Wind - Notes
Main Idea:
When air is heated unevenly, it moves around causing wind and air currents
Vocabulary:
Convection (247) – transfer of heat through the movement of a gas or liquid
Global winds (248) – winds that are caused by the Earth’s rotation and the difference between
heat and cold in different areas of the Earth
Why are temperatures different around the world?
Main Idea:
The Sun heats Earth’s atmosphere unevenly.
Supporting Details
1. Differences in temperature due to Earth’s shape
a. Heat energy from the rays of the sun warms Earth’s surface
b. The sun unevenly heats the Earth’s surface
c. Earth is shaped like a sphere
d. Sunlight strikes most directly at the equator (90˚ angle) (a circle)
e. As you go north or south, the angle that the sunlight hits the Earth’s surface
become larger
i. 120˚at the Tropics (an oval)
ii. 150˚ at the US and Chile (a wider oval)
iii. 180 at the North and South Poles (a flat line)
f. The larger the angle, the less heat the Earth’s surface receives from the sun’s
rays as the heat energy is disbursed over a wider area
2. As a result, it is generally warmer at the equator and cooler as your head north or south
of the equator.
How do land and water temperature affect air pressure?
Main Idea:
Air moves from an area of high pressure to an area of low pressure.
Supporting Details
1. Air pressure in sea breezes
a. Lands heats up faster than water during the day.
i. Matter particles are closer together on land as it is a solid than it does in
water (a liquid).
ii. Heat transfers more easily the closer the particles are.
b. As the land heats up, the air above the land is warmed by the surface.
c. The warm air is less dense therefore it applies less pressure.
d. The warm air over the land rises and pushes the cold air up and out to sea.
e. As the cold air above the land is pushed out to sea by the warm air, it pushes the
cold air that is over the ocean towards the surface of the ocean.
f. The cold air above the surface of the ocean is pushed to the shore by the air
above it.
2. Air pressure in land breeze
a. The opposite occurs at night.
b. The ocean cools off slower than the land.
c. The direction of the cycle changes.
d. The air is blown from the land to the sea.
3. Convection
a. Changing temperatures cause differences in air pressure.
b. Air flows from an area of high pressure to an area of low pressure.
c. As air flows, it moves heat from one place to another.
d. Convection is the transfer of heat through the movement of gas or liquid
e. When convection happens, it causes a breeze or a wind.
What are global winds?
Main Idea:
Global winds are predictable, blow steadily, and blow over long distances
Supporting Details
1. Global winds are winds that blow steadily in predictable directions over long distances
2. Global winds impacted by Earth’s rotation from west to east.
3. Global winds also impacted by air moving from an area of high pressure (polar regions)
to low pressure (equatorial region).
4. Warm air near the equator rises and cold air from the polar regions moves in to fill in
the area.
5. Trade winds are winds that blow between 30˚ N latitude and 30˚ S latitude.