Radiation and Earth’s Atmosphere

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Higher temperature, shorter wavelength

Slide 7

Longwave & Shortwave Radiation

The hot sun radiates at shorter wavelengths that carry more energy, and the fraction absorbed by the cooler earth is then re-radiated at longer wavelengths.

Slide 8

Atmospheric Greenhouse Effects

T= 15°C (59°F)

T= –18°C (0°F)

Greenhouse effects make Earth’s surface warmer!

Surface Temperature With the Atmosphere

Surface Temperature Without the Atmosphere

Slide 9

Slide 10

Greenhouse Gases

Water vapor accounts for 60% of the atmospheric greenhouse effect, CO2 26%, and the remaining greenhouse gases 14%.

Water vapor (H2O)

Carbon dioxide (CO2)

Methane (CH4)

Nitrous oxide (N2O)

Ozone (O3)

Chlorofluorocarbons (CFC’s)

What are they?

CO2 contributes most (55-60%) to the anthropogenic greenhouse effect, and methane is a distant second (16%).

CFCs cause the strongest greenhouse warming on a molecule-for-molecule basis.

Slide 11

Atmospheric Absorption

Solar radiation passes rather freely through Earth's atmosphere.

Earth emits longwave energy, which either leaks through a narrow window or

is absorbed by greenhouse gases and radiated back to Earth.

Wavelength

Absorption (100%)

Nitrous Oxide

Methane

Ozone

Water Vapor

Carbon Dioxide

Total Atmo

IR

UV

Slide 12

Solar Intensity and Latitude

Solar intensity, defined as the energy per area, is different at different latitude.

A sunlight beam that strikes at an angle is spread across a greater surface area, and is a less intense heat source than a beam impinging directly.

Slide 13

Unequal Radiation on a Sphere

Insolation is stronger in the tropics (low latitudes) than in in the polar regions (high latitudes).

Slide 14

Pole-to-Equator Heating Imbalances

Slide 15

What controls the elevation of the Sun above the horizon?

Earth’s Tilt Primarily Determines Season

Slide 16

Earth's Annual Energy Balance

The balance is achieved locally at only two lines of latitude.