Air Pressure

Reminder:What makes the

weather?• Remember: Weather is the condition of the

atmosphere at a particular time with respect to its o Heat or Coldnesso Wetness or Drynesso Clearness or Cloudiness

• All of Earth’s many kinds of weather depend on two things:o 1. Heat from the suno 2. Water

Weather and the Sun• All weather, good and bad, is

the result of energy exchange from the sun. Every day, the Earth is bombarded by energy from the Sun. Nearly 40% of this energy is reflected back into space.

• As the earth surface is warmed, it radiates heat back into the air. The sun’s rays are absorbed by both land and sea on earth.

Sun’s Rays on Land in the Day

• Land surfaces usually heat up faster than water. This causes the air above land to be quite warm during the day while the sun is shining.

Sun’s Hot Rays beam down on Earth

They heat up the land

Which creates warm air that rises in our atmosphere

Sun’s Rays on Land in the Day

• Land surfaces that are barren and dry heat up very quickly, and radiate hot air back into our atmosphere.

• Land surfaces filled with vegetation also heat up, but slower than those that are barren.

Sun’s Hot Rays beam down on Earth

They heat up the land

Which creates hot air that rises in our atmosphere

Sun’s Rays on the Ocean

• Water heats up slower than land. However, it maintains a fairly constant temperature in the day and night.

Sun’s Hot Rays beam down on the ocean

They slowly heat up the ocean

Some warm air rises. This amount is much less than that over land. The air over the ocean is much cooler.

Land temperature at night

• When the sun sets, the earth cools off quickly since it is no longer being heated. Without heat to radiate into the atmosphere, the temperature drops.

Ocean temperature at night

• Since the ocean takes longer to heat up, it also takes longer to cool down. The air over the ocean at night is warmer than that over the land.

The Weather • As the air gets warmer in

the day, and cools down at night, it causes different temperatures, can create winds and clouds, and even lead to storms.

• Let’s learn more about this in the movie, What is weather?

What is a Low Pressure System?A low pressure system is a whirling

mass of warm, moist air that generally brings stormy weather with

strong winds. When viewed from above, winds spiral into a low-

pressure center in a counterclockwise rotation in the

Northern Hemisphere. A low pressure system is represented as a

big, red L.

L

COLD AIR