Earth’s Atmosphere

Atmosphere Layer of air that surrounds Earth It is held in place by Earth’s gravity

Earth’s Early Atmosphere Was created by outgassing volcanoes. CO 2 and methane. – It was mostly comprised of CO 2 and methane. Algae and primitive plants took in the CO 2 and created O 2 through a process called photosynthesis. Algae and primitive plants took in the CO 2 and created O 2 through a process called photosynthesis.

Composition of Earth’s Atmosphere 78% Nitrogen 21% Oxygen 1% Other gases (argon, carbon dioxide, water vapor)

Structure of Earth’s Atmosphere The atmosphere is divided into 4 main layers and the divisions are based on temperature differences

Layers of the Atmosphere 1. Troposphere Layer closest to the ground Layer where weather, clouds, and smog occur Contains 75% of all atmospheric gases Temperatures decrease with altitude in this layer (warm→cold)

2. Stratosphere Ozone layer located at the top of this sphere Temperatures increase with altitude in this layer (cold→warm) It helps to protect us from ultraviolet (UV) radiation 3. Mesosphere Meteoroids burn up in this layer Known as the “middle layer” Coldest layer Temperatures decrease with altitude in this layer (warm→cold)

4. Thermosphere Known as the “heat sphere” Broken into 2 layers (ionosphere and exosphere) Ionosphere found here (layer of electrically charged particles that radio waves bounce off of) is located in this layer (Aurora Borealis occurs here) Exosphere is where the atmosphere gradually changes into space. Temperatures increase with altitude in this layer (cold→warm)

The Ozone Layer The ozone layer is located in which layer of the atmosphere? Stratosphere What is the importance of the ozone layer? It is a protective shield between Earth and harmful UV (ultraviolet) radiation from the Sun It absorbs the UV radiation (which causes sun burn and skin cancer) and does not let all of it pass through Contains the ozone (O 3 ) molecule

The Ozone Layer

More on the Ozone Layer In 1986, scientists began to find areas in the stratosphere where almost no ozone existed. They found 2 different holes: 1. Large hole over Antarctica 2. Smaller hole over the North Pole

Why was the ozone layer being depleted? The use of CFC’s (which are chlorofluorocarbons) which were breaking down the O 3 molecules How were CFC’s contributing to this problem? CFC’s react with the ozone (O 3 ) and break it apart to produce oxygen gas (O 2 ) Oxygen gas (O 2 ) can not absorb the Sun’s harmful UV rays

Laws have since been passed restricting the use of CFC’s in products such as: Laws have since been passed restricting the use of CFC’s in products such as: – Refrigerators – Air conditioners – Spray cans – Foam cups – Fast food containers

Air Pressure What is air pressure? The weight of the atmosphere pushing down on Earth 14.7 lbs./sq. inch Standard sea level pressure is 1013 millibars Air pressure is greatest at the Earth’s surface and decreases with altitude (as you move up from the surface)

Air Pressure Continued Isobars – lines of equal air pressure on a map Low pressure is called a low (cyclone). – Air rises in areas of low pressure (taking pressure off the earth) – Bad weather is associated with lows – Turn counterclockwise in the Northern Hemisphere High pressure is called a high (anticyclone). – Air sinks in areas of high pressure (putting pressure on the earth) – Good weather is associated with highs. – Turn clockwise in the Northern Hemisphere

Air Pressure decreases as you move higher up in our atmosphere

How do we measure air pressure? 1. Aneroid Barometer2. Mercury Barometer Barometer – instrument used to measure air pressure

What is the relationship between air pressure and air temperature? Cold air is more dense and has higher pressure Warm air is less dense and has lower pressure Why? Water vapor molecules weigh less than air molecules Warm air molecules move faster than cold air molecules and therefore can hold more water vapor molecules The water vapor molecules then take the place of the heavier air molecules and since they weigh less, the pressure is less

Winds Wind is the movement of air. Because the Earth is curved and not flat, areas on the Earth’s surface receive different amounts of radiation from the sun. This unequal heating is what causes wind. Air above the equator receives more direct heat from the sun than any other place on Earth; this creates a low pressure belt at the equator. Air above the poles receives less direct heat from the sun than any other place on Earth; this creates a high pressure at each of the poles.

The global wind systems that blow in between the poles and the equator are the Earth’s attempt to equalize the temperatures. Warm air rises at the equator and sinks at the poles, this is called a Hadley cell. If these winds did not blow, the equator would be too hot to live in and the poles would be too cold to venture into. Winds always blow from high to low pressure. Winds are always named in the direction they are blowing from. Winds blow in curved paths because of the Coriolis Effect.

The Global Wind System

Jet Streams Jet Streams High altitude winds that are 6-8 miles high in the upper troposphere Flow from west to east around the Earth There are two jet streams in each hemisphere One is found where the Westerlies meet the Trade Winds Another is found where the Westerlies meet the Polar Easterlies

Jet Stream Maps

Land and Sea Breezes In areas where the land meets the sea, a convection current forms because of the different heating and cooling rates of the land and water. Sea breezes are created during the day because solar radiation warms the land quicker than the sea. Land breezes are created during the night because the land cools much more rapidly than the sea

Land and Sea Breezes

Rain Shadow Effect Air if forced over to rise over mountains. – On the windward side (rising air) the air cools as it rises (adiabatic cooling) and water vapor condenses – This produces clouds, rain, and rainforests. – On the leeward side (sinking air) the air is now dry and it warms as it sinks (adiabatic warming) causing a desert to form.

Rain Shadow Diagram