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Lecture 5

GEOG 1112 Lecture 5: Radiation Earth Sun (Part 2) Global Energy Balance
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Department
Geography
Course
GEOG 1112
Professor
James Shepherd
Semester
Spring

Description
LECTURE 5 | RADIATION EARTH SUN (PART 2) GLOBAL ENERGY BALANCE Atmospheric Influences on Insolation • Solar radiation at the top of the atmosphere does not pass unimpeded through the atmosphere: o Absorbed o reflected or scattered o transmitted • They affect the amount of radiation received at the surface. • Absorption o Particular gases, liquids, and solids in the atmosphere reduce the intensity by absorption. o Less energy is transferred to the surface. o Atmospheric gases are overall poor absorbers of energy. • Absorption & Emission o If an object radiates more energy than it absorbs, it cools. o If it absorbs more than it radiates, it warms. o Review - Kirchhoff’s Law. Black Body & Selective Absorbers • Black Body: A hypothetical body that is a perfect absorber and emitter of radiation (sun) • Selective Absorber: any object that absorbs some types of radiation but not others. (atmosphere, clouds, glass, snow) Selective Absorbers • The gases in the atmosphere are good at absorbing some wavelengths of radiation but not others. • This has an important impact on our energy balance. • Visible radiation is transmitted well • Some ultraviolet (UV) is absorbed by ozone in the stratosphere • Infrared is absorbed well by the “greenhouse gases”--??? • The atmospheric window is a region (8-11 μm) where the atmosphere does not absorb infrared radiation well. Greenhouse Effect • Water Vapor • Carbon Dioxide • Methane • No Greenhouse: 18oC • Greenhouse: 15oC • It is a natural phenomena o not to be confused with Global Warming! o without it, the Earth’s average temperature would be -18oC (0oF) instead of 15oC (59oF) Venus & Runaway Greenhouse Effect • Surface temperature: (480 oC or 900 oF) • 97% of atmosphere is CO2 • Compared to 0.040% on Earth. Atmospheric Influences on Insolation • Reflection o Energy is redirected by objects through reflection without being absorbed. o Albedo is the percentage of energy reflected by an object. o Specular reflection is reflection of energy as an intense beam. • Scattering o Energy reflected as disperse energy into less intense beams is diffuse reflection, or scattering. o Gases in the atmosphere scatter radiation. o Energy that reaches the surface is scattered and different in intensity from direct radiation. o Scattering agents smaller than 1/10 the wavelength of incoming radiation is known as Rayleigh Scattering. o Partial to shorter wavelength energy. o Rayleigh Scattering results in our blues skies. It’s why our skies are blue to the human eye. o Mie scattering, scattering sunlight, is pre
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