Unit 4 Weather Lesson 1 How Does Uneven Heating of Earth Affect Weather?

The Atmosphere -The atmosphere is a thin blanket of air that surrounds Earth. -It is very thin compared to the size of Earth. -The atmosphere is made up of many layers: troposphere, stratosphere, and ozone.

Troposphere  The troposphere is the layer that is closest to Earth’s surface.  It contains 90% of the atmosphere’s gases.  Most of the Earth’s weather happens in the troposphere.

How Do You Know Air is There?  You know the air is there because you can feel it every time the wind blows.  You can feel air blow against you because it has mass.  Everything on Earth that has mass is pulled toward Earth’s center by gravity.  This pull causes air to have weight.

Air Pressure  Air particles closer to Earth’s surface have more weight than the air higher in the atmosphere.  This means that air pressure, or the weight of air in the atmosphere in one unit area, is greatest at sea level.

Air Pressure (cont.)  The higher you go into the atmosphere, the less air there is above you.  Air pushes downward as well as in all directions. This is because gas molecules are constantly moving in all directions.  Temperature also affects air pressure. Cold air is denser than warm air. Because of this, it sinks toward Earth’s surface. This forces warmer, less dense air to rise. As warm air rises, it cools. The cooler air is now denser, so it sinks back to the surface.

Air Density  Another factor that causes air pressure to be greater at sea level is air density.  Gravity pulls most of the air in the atmosphere down to the surface.  Because of this, the air closer to Earth’s surface is much denser than the air father away from the surface.

Convection Currents  Air that is warm is less dense, so it is pushed upward by the cooler, denser air.  This upward and downward movement of air is called convection currents in the atmosphere

Sea & Land Breezes  During the day, the land heats up faster than the sea. Cooler sea air moves toward the land. This is called a sea breeze.  At night, the land loses heat faster than the sea does. Cooler air over the land moves toward the sea. This is called a land breeze.

Local Wind  Winds can be local, affecting small areas, or global, affecting larger 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.  Local winds often occur along lakeshores or seashores.

Global Winds  A prevailing wind is a global wind that almost always blows from the same direction.  Prevailing winds result from uneven heating of large parts of Earth’s surface.  An area’s latitude (distance from the equator), Earth’s rotation, and uneven heating of Earth’s surface all affect prevailing winds.

Trade Winds & Prevailing Westerlies  Winds moving north curve to the east. Winds moving south curve to the west.  Around the equator, this curving causes the prevailing winds – called trade winds – to blow from the east.  In the United States, this curving causes the prevailing winds – the prevailing westerlies – to blow from the west.

Bill Nye Videos Atmosphere Part 1 ium.org/cgi-bin/search/linfo.cgi?id=8436 Atmosphere Part 2 bin/search/linfo.cgi?id= bin/search/linfo.cgi?id=8437 Atmosphere Part 3 bin/search/linfo.cgi?id= bin/search/linfo.cgi?id=8438