22.2 Solar Energy and the Atmosphere

What happens to incoming solar radiation?

1. Scattered2. Reflected3. Absorbed

**Earth’s atmosphere is heated by the transfer of energy from the sun = radiation!2 primary sources of heat on Earth: 4. Direct: absorption of

sun’s rays5. Indirect: ocean/land

absorbs heat & gives it off

• Almost all radiation that has a wavelength shorter than visible light is absorbed by the upper atmosphere.

• X-rays, gamma rays, and UV rays are absorbed by molecules of nitrogen and oxygen in the thermosphere.

• UV rays are absorbed and act upon oxygen molecules to form ozone in the stratosphere.

• Solar rays with longer wavelengths, such as visible and infrared, reach the lower atmosphere.

Scattering

• Clouds, dust, and water vapor scatter sunlight.

• Causes rays to travel in all directions without changing wavelength.

• Makes sky appear blue!

Why is the sky red/orange at sunrise and sunset?

• Sunlight travels through a longer path in the atmosphere.

• Blue light gets scattered away first (short wavelength) and red is left (long wavelength).

Reflection• Albedo- the fraction

of solar radiation that is reflected by a surface.

• Solar radiation that is not reflected is absorbed by rocks, soil, water, and other surface materials.

Absorption

1. Short wavelength IR comes in

2. Earth absorbs short wavelength IR and readmits it as a longer wavelength IR+ UV light

3. Some escapes back to space

4. Some IR is absorbed by gasses in atmosphere (CO2, Water Vapor, NOx, CH4 )and sends it back to earth

• Absorption of thermal energy from the ground warms up the surface of the Earth.

• Warming of the surface and lower atmosphere of Earth that occurs when carbon dioxide, water vapor, and other gases in the air absorb and reradiate infrared radiation is the greenhouse effect.

• The Greenhouse Effect is a result of human activity.

• The one human activity that may have caused the average temperature of the atmosphere to increase in recent years: burning of fossil fuels.

What causes changes in temperature?

1. Time of Day• Warmest hours of day are mid to late afternoon.• Earth needs time to absorb sunlight and reradiate it as

heat.

2. Latitude 3. Season• More direct rays equal warmer temperatures• This is the primary factor that affects how

much solar energy reaches a point!• Near the equator: angle is 90*• Energy concentrated in a smaller area

• Seasonal variations occur because of the tilt of Earth’s axis.

4. Amount of Water Vapor• Mountains are warm during day but

cold at night due to thinner air with less water vapor

• Deserts are warm during day and cold at night

• Water vapor stores heat• Water heats up and cools down

faster than air does so it changes temperature less than land.

• Near large bodies of water – the water moderates the temperature and keeps if from changing too much.

5. Located near water• Have more moderate

temperatures.• Cooler during day and

warmer at night.

6. Wind Patterns• Land that gets a breeze

from the ocean will be cooler than a breeze from over land

• Transfer of energy as heat via direct contact: conduction

• Air is a poor conductor because the molecules are too far apart to effectively transfer energy.

• Conduction heats only the lowest few centimeters of the atmosphere because the air is directly contacting Earth.

• The primary cause of heating in the lower atmosphere: convection.

• Convection is why warm air rises and cold air sinks.

• Atmospheric pressure is lower beneath a mass of warm air because warm air is less dense than cool air – which means that the warm air exerts less pressure than cool air.