Lesson 1: How Does Uneven Heating of Earth Affect Weather?

California Fast Fact! What is unusual about the photo and the month in which it was taken? What clue do the trees give you about the height of the snow? Where and when would you expect to see other scenes like this? Why? Mount Lassen, California This picture was taken in June

California Fast Fact! The area usually gets about 1m (39in) of snow per month from December to March. Most of this snow melts in the spring and summer. Record snowfalls on the mountain one winter left these GIANT snowdrifts. Mount Lassen, California This picture was taken in June

CA State Standards 4.a – Students know uneven heating of Earth causes air movements (convection currents) 4.e – Students know that the Earth’s atmosphere exerts a pressure that decreases with distance above Earth’s surface and that at any point it exerts this pressure equally in all directions.

Valuable Vocabulary! Atmosphere – The blanket of air surrounding Earth.

Valuable Vocabulary! Weather – The condition of the atmosphere at a certain place and time.

Valuable Vocabulary Air Pressure – The weight of the atmosphere pushing on a given square unit area of the Earth’s surface.

Valuable Vocabulary Convection Current – The upward and downward movement of air in the atmosphere.

Valuable Vocabulary Local Wind – Wind that results from local changes in temperature.

Valuable Vocabulary Prevailing Wind – A global wind that blows constantly from the same direction.

The Atmosphere A blanket of air called the atmosphere surrounds Earth. It is very thin compared to the size of Earth. If Earth were a peach, it would be thinner than the fuzz on the peach! The atmosphere is made up of several layers. 1st layer – closest to the Earth’s surface: troposphere

The Atmosphere

The Atmosphere The Troposphere contains about 90% of the atmosphere’s gases. Most of the Earth’s weather happens in the troposphere. Weather is the condition of the atmosphere at a certain place and time.

The Atmosphere You can’t see, taste, or touch the air in the atmosphere, but you can feel it. Every time the wind blows, you feel the air. You can feel it because air has mass. Everything on Earth that has mass is pulled toward Earth’s center by gravity. This pull causes air to have weight. Air particles closer to Earth’s surface have more weight than the air higher up. This means that air pressure is greatest at sea level.

The Atmosphere Air density is another factor that causes air pressure to be greater at sea level. Gravity pulls most of the air in the atmosphere down to the surface. This causes the air closer to Earth’s surface to become much denser, or heavier, than the air farther away from the surface.

Show What You Know In which layer of the atmosphere does most weather occur?

Show What You Know In which layer of the atmosphere does most weather occur? The troposphere is the layer of the atmosphere where most weather occurs.

Show What You Know What is the relationship between position in the atmosphere and air pressure?

Show What You Know What is the relationship between position in the atmosphere and air pressure? The lower the position, the higher the air pressure.

Show What You Know Write your own summary of what you learned in class today about the atmosphere.

Summary The earth is covered with a blanket called the atmosphere. The atmosphere is very thin, and is made up of several layers. The layer closest to Earth’s surface is called the troposphere. This layer contains about 90% of of the atmosphere’s gases, and it also is where most of Earth’s weather happens. You can not see, taste or touch air, but you know it is there ever time the wind blows. You can feel air. This is because air has mass. Gravity pulls air particles down, and particles closer to the surface have more weight than the air higher in the atmosphere.

Air Pressure The higher you go into the atmosphere, the less air there is above you. Air does not only push downwards, but it actually pushes evenly in all directions. Gas molecules are constantly moving in all directions. When you blow up a balloon, the air pressure inside the balloon increases, and it expands in all directions.

Air Pressure Temperature also affects air pressure. Cold air is denser than warm air. It sinks towards Earth’s surface. The cold air forces warmer, less dense air to rise. As the warm air rises, it begins to cool. Since cold air is denser, it sinks back down to Earth. High Pressure = More dense, cold air sinks. Low Pressure = Less dense, warm air rises.

Show What You Know What factors affect air pressure?

Show What You Know What factors affect air pressure? Some factors that affect air pressure are: location in the atmosphere (altitude), temperature, and density.

Show What You Know How does the outside air pressure on the left and right side of a basketball compare?

Show What You Know How does the outside air pressure on the left and right side of a basketball compare? The air pressure is identical on all sides.

Summarize Summarize what you learned in class today about air pressure.

Uneven Heating and Local Winds How did the air feel when you left home this morning? Was it windy, or was it calm? If you were to go outside right now, would the air feel the same?

Uneven Heating and Local Winds THE BIG IDEA: Air is always moving and changing. When the sun’s energy reaches Earth, some of the energy bounces off objects, such as clouds. Earth absorbs the rest of the energy. Different types of surfaces absorb different amounts of energy.

Uneven Heating and Local Winds Soil heats up faster and cools off faster than an equal amount of water. During a hot day, soil is hotter than water. It gives off more heat. Because of this, the air over soil tends to be hotter too. Water is cooler than soil, so the air over water tends to be cooler.

Uneven Heating and Local Winds Cool air is denser than warm air, so it sinks. Air that is warm is less dense, so it is pushed upward by the cooler air, denser air. The upward and downward movement of air is called convection currents.

Uneven Heating and Local Winds Air in the troposphere moves horizontally. As cool, dense air sinks; it spreads out along the surface. Air at the surface moves from areas of higher pressure to areas of lower pressure. This horizontal movement of air is called wind.

Uneven Heating and Local Winds Winds can be local, affecting small areas, or global, affecting large parts of the Earth. Sometimes, places in the same general area have slightly different temperatures. This produces local wind, or wind that results from a local difference in temperature.

Uneven Heating and Local Winds Local winds often occur along lakeshores or seashores. During the day, the air over the land is warmer than the air over the water. The cooler air over the water has a higher pressure than the warmer air over the land. The result is a wind that blows from the water toward the land. This is called a sea breeze. Sea Breeze Explained

Uneven Heating and Local Winds At night, the wind usually blows in the opposite direction. Land cools off more quickly than water. Once the land becomes cooler than the water, a wind blows from the land toward the water. This is called land breeze.

Show What You Know How does the absorption of energy from the suns rays differ for land and for water?

Show What You Know How does the absorption of energy from the suns rays differ for land and for water? The land absorbs the sun’s energy more quickly than water does.

Show What You Know What happens to the temperature of the land compared to that of water?

Show What You Know What happens to the temperature of the land compared to that of water? The land becomes warmer during the day than water does.

Show What You Know What occurs when cold air sinks?

Show What You Know What occurs when cold air sinks? What is the horizontal movement of air called? It forces warm air up. The horizontal movement is called wind.

Show What You Know What is sea breeze? When Does it happen? What causes it?

Show What You Know What is sea breeze? When Does it happen? What causes it? A sea breeze is a wind from the sea toward the land. During the day, the land warms up faster than the sea. The cooler, denser sea air flows under the warmer air over the land.

Why is air always moving? Show What You Know Why is air always moving?

Show What You Know Why is air always moving? Earth’s surface is heated unevenly, causing some air to be hotter than other air. Hot air is forced upward by sinking colder air, leading to air movement.

Summarize Summarize what you learned in class today about uneven heating of the Earth’s surface.

Global Winds Global winds are prevailing winds that almost always blow from the same direction. Sailors relied heavily on prevailing winds to carry them across the oceans. Uneven heating of Earth’s surface causes prevailing winds. Unlike local winds, prevailing winds result from uneven heating of large parts of Earth’s surface

Global Winds An area’s distance from the equator, also known as latitude, affects the amount of heat that the area will receive from the sun. Earth’s poles receive indirect sunlight, or no sunlight at all, so they are always cold. Earth’s equator gets direct sunlight all year, so it’s always warm. As a result, cold air above the poles sinks and moves towards the equator.

Global Winds Air does not just move in one big circle. Air moves in curved paths, because of Earth’s rotation. This rotation causes prevailing winds. Winds moving north curve to the east. Winds moving south curve to the west. Around the equator this curving causes trade winds to blow from the east. In the United States, this curving causes the prevailing westerlies to blow from the west.

Global Winds

Global Winds The prevailing westerlies cause most of the weather systems in the United States to from west to east. This helps forecasters predict the weather, because weather in San Francisco today often moves toward Kansas City tomorrow and then toward Baltimore.

How does the air in the atmosphere vary with latitude? Show What You Know How does the air in the atmosphere vary with latitude?

How does the air in the atmosphere vary with latitude (distance)? Show What You Know How does the air in the atmosphere vary with latitude (distance)? In general, with increases in latitude come decreases in air temperature.

In what direction do winds that blow toward the poles curve? Show What You Know In what direction do winds that blow toward the poles curve?

In what direction do winds that blow toward the poles curve? Show What You Know In what direction do winds that blow toward the poles curve? EAST EAST EAST EAST EAST EAST

In what direction do winds that blow away from the poles curve? Show What You Know In what direction do winds that blow away from the poles curve?

In what direction do winds that blow away from the poles curve? Show What You Know In what direction do winds that blow away from the poles curve? WEST WEST WEST WEST WEST

Show What You Know In what direction do most of the prevailing winds in the United States curve?

Show What You Know In what direction do most of the prevailing winds in the United States curve? Most of the prevailing winds in the United States curve east.

Why do global winds move in curved paths? Show What You Know Why do global winds move in curved paths?

Show What You Know Why do global winds move in curved paths? Earth’s rotation causes winds to curve as they blow northward or southward.

What two factors cause prevailing winds? Show What You Know What two factors cause prevailing winds?

Show What You Know What two factors cause prevailing winds? Earth’s rotation and uneven heating of the atmosphere are two factors that cause prevailing winds.

Summarize Summarize what you learned in class today about global winds.