Discovering Physical Geography Third Edition by Alan Arbogast Chapter 4: The Global Energy System The Electromagnetic Spectrum and Solar Energy Solar Energy as Radiation Electromagnetic energy transmitted in waves Wavelength Wave amplitude Electromagnetic Spectrum Entire wavelength range of electromagnetic energy The Electromagnetic Spectrum and Solar Energy Shortwave Emitted by hot objects The Sun has a 6000 C surface temperature Includes gamma rays, X-rays, ultraviolet, visible light, and nearinfrared Longwave Emitted by cooler objects The Earth has a ~16 C surface temperature Includes the thermal infrared part of the spectrum 1
The Electromagnetic Spectrum and Solar Energy Two Principles in Action The hotter Sun Greater amount of radiation Mostly shortwave The cooler Earth Smaller amount of radiation Mostly longwave Most of energy released by Earth originated from the Sun Solar Energy and the Solar Constant Solar energy is produced by nuclear fusion in the Sun; it is emitted as electromagnetic radiation Sun produces energy at a nearly constant rate, so solar radiation output is also nearly constant Solar constant is the amount of solar energy received at the top of the atmosphere Result of the travel of solar energy in straight lines or rays to an area of fixed size in space, that is, the Earth Value is about 1370 (W/m 2 ) watts per square meter Composition of the Atmosphere Atmosphere is the medium through which radiation flows on its way to the surface Unique in the solar system Supports animal and plant life by providing oxygen and carbon dioxide Shields the planet from harmful wavelengths of solar radiation Consists of air 2
Composition of the Atmosphere Constant Gases More or less same proportion 99% are composed of nitrogen and oxygen Variable Gases Differ in proportion over time and space Make up only less than 1% Variable Gases: Water Vapor (H 2 0) Atmospheric water vapor (gas) is vital Absorbs and stores heat energy Moves with airflow transporting energy and moderating temperature Amount of water vapor depends on Proximity to large bodies of water Air temperature Warmer air can hold more water vapor than cooler air Variable Gases: Carbon Dioxide (CO 2 ) Atmospheric carbon dioxide is critical In the process of photosynthesis, plants absorb CO 2 and release oxygen as a by-product It contributes to the greenhouse effect and the trapping of longwave radiation Amount of carbon dioxide Currently about 0.038% of the atmosphere Levels rapidly rising due to industrial activity 3
The Greenhouse Effect Atmosphere traps longwave radiation Redirects some radiation back to the surface as counterradiation Effectively warms the surface Variable Gases: Ozone (O 3 ) Forms when gaseous chemicals react in upper atmosphere with light energy Occurs in two layers 1. Stratosphere as the UVabsorbing ozone layer 2. Ground level as a form of pollution Human Interactions: The Ozone Hole CFCs break down O 3 into O 2 and ClO Depletes the ozone layer, allowing more UV radiation to reach the surface Antarctic Ozone Hole forms every Spring in Southern Hemisphere 1987 Montreal Protocol began CFC phase-out Since then CFC amounts have been falling 4
Composition of the Atmosphere: Particulates Microscopic bodies carried in the air, existing in both liquid and solid form Liquid forms: clouds and rain Solid forms: snow, hail, pollutants, soil (dust), smoke, ash, pollen grains, and salt spray Effects on Earth Helps precipitation to form Absorbs or reflects energy, impacting temperature Negative environmental and health effects The Flow of Solar Radiation on Earth: Heat Transfer Heat transfers from hot to cold in several ways: 1. Radiation is creation and emission of electromagnetic waves 2. Conduction involves diffusion of heat through contact 3. Convection involves the upward movement of heat Flow of Solar Radiation in the Atmosphere Direct radiation is uninterrupted flow of incoming radiation that reaches Earth, amounts to 25% Remaining 75% is either absorbed or redirected Indirect radiation is radiation redirected downward toward the surface 5
Flow of Solar Radiation in the Atmosphere Absorption happens when gases and particulates interrupt the flow of radiation by absorbing specific wavelengths and gain heat Reflection is redirected radiation returning to space and depends on the albedo of a surface Albedo refers to the amount of reflection a given surface can cause Scattering is the redirection and deflection of radiation Interaction of Solar Radiation and the Earth s Surface Absorbed Radiation 96% of energy is absorbed by the surface and stored as heat Sensible heat can be sensed and measured Latent heat is hidden and cannot be measured Stored energy can be lost in several ways, through Conduction to gases in the atmosphere Removal by evaporation and stored as latent heat Radiation into atmosphere or lost to space Interaction of Solar Radiation and the Earth s Surface Reflected Radiation Energy that bounces off the surface so that it does not provide heat Depends on surface albedo High albedo surfaces reflect more Low albedo surfaces absorb more Depends on angle of incidence, or Sun s angle in the sky 6
The Global Radiation Budget Balance between incoming (shortwave) and outgoing (longwave) radiation Net radiation is the difference between incoming and outgoing radiation values The Global Radiation Budget Major variations in net radiation by latitude Surplus versus deficit Net radiation and the global transfer of heat energy Human Interactions: Solar Energy Production Efficient house design accounts for heating and cooling Efficiency across seasons can be challenging 7
Human Interactions: Solar Energy Production Potential Potential for solar energy production varies spatially What area is best suited for solar energy production? 8