Ch. 3-Solar & Terrestrial Radiation

The capacity for doing work.
Law of Energy Conservation
Energy is neither created nor destroyed but can change from one form to another; also known as the first law of thermodynamics.
Electromagnetic Radiation
Energy in the form of waves that have both electrical & magnetic properties & travel through gases, liquids, & solids, & occur even in a vacuum. All objects emit all forms of electromagnetic radiation, although each object emits its peak radiation at a certain wavelength within the electromagnetic spectrum.
Electromagnetic Spectrum
Range of electromagnetic radiation types arranged by wavelength or by wave frequency or both. Although the electromagnetic spectrum is continuous, different names are assigned to different segments. These segments extend from the longest wavelength (lowest frequency) radio waves through microwaves, infrared radiation, visible radiation, ultraviolet radiation, X-rays, to the shortest wavelength (highest frequency) gamma radiation.
The distance between successive wave crests (or equivalently, wave length).
Wave Frequency
Number of crests or troughs of a wave that pass a given point in a specified period of time, usually 1 second.
Visible Radiation
Electromagnetic radiation that is perceptible to the human eye with wavelengths ranging from about .40 (violet) to .70 (red) micrometers. Visible radiation has wavelengths lower than infrared radiation but shorter than ultraviolet radiation.
Infrared Radiation
Electromagnetic radiation at wavelengths ranging from 0.8 micrometer (near-infrared) to about 0.1 micrometers (far infrared). Infrared radiation has wavelengths shorter than microwaves & longer than visible red light; most objects in the Earth-atmosphere system have their peak emission in the infrared.
A hypothetical “body” that absorbs all electromagnetic radiation that is incident on it at every wavelength & emits all radiation at every wavelength; no radiation is reflected or transmitted. The “body” must be large compared to the wavelength of incident radiation.
Wien’s Displacement Law
A radiation law whereby the wavelength of a maximum emission by a blackbody is inversely proportional to its absolute temperature (in kelvins). For example, hot objects (such as the Sun) emit peak radiation at relatively short wavelengths, whereas cold objects (such as the Earth-atmosphere system) can emit peak radiation at longer wavelengths.
Stefan-Boltzmann Law
A radiation law that states that the total energy radiated by a blackbody at all wavelengths is directly proportional to the fourth power of the absolute temperature (in kelvins) of the body. For example, the Sun’s energy output per square meter is about 190,000 times that of the Earth-atmosphere system.
Inverse Square Law
Intensity of radiation emitted by a point source (e.g., the Sun) decreases as the inverse square of distance traveled.
Global Radiative Equilibrium
The balance between net incoming solar radiation & infrared radiation emitted to space by the Earth-atmosphere system.
The intensely bright portion of the Sun visible to the unaided eye; the several-hundred-kilometer-thick layer is what we perceive as the surface of the Sun. Features such as sunspots & faculae are observed on the photosphere.
Relatively dark, cool area that develops on the surface of the Sun’s photosphere where an intense magnetic field suppresses the flow of gases transporting heat from the Sun’s interior.
Portion of the Sun above the photosphere; consists of transparent ionized hydrogen & helium at 4,000 to 40,000 degrees Celsius (7,200 to 72,000 degrees Fahrenheit).
Solar Corona
Outermost portion of the solar atmosphere (above the chromosphere) that is a region of extremely hot (1 to 4 million degrees Celsius or 1.8 to 7.2 million degrees Fahrenheit), highly rarefied gases extending millions of kilometers into space, to the outer limits of the solar system. The solar wind originates in the solar corona.
Solar Altitude
The angle of the Sun 90 degrees or less above the horizon that influences the intensity of solar radiation striking Earth’s surface. At a maximum possible solar altitude of 90 degrees, the solar rays are most intense; the intensity declines with decreasing solar altitude (towards 0 degrees).
The time of the year when the Earth’s orbital path brings it closest (147 million kilometers or 91 million miles) to the Sun (at present, about 3rd of January).
The time of year when the Earth is farthest (152 million kilometers or 94 million miles) from the Sun (currently about 4th of July).
The first days of spring & autumn when day & night are of approximately equal length at all latitudes (except the poles) & the noon Sun is directly over the equator (solar altitude of 90 degrees).
Tropic of Cancer
A solstice pattern of the Sun with a latitude of 23 degrees 27 minutes North. On June 21st, the Sun’s noon rays are vertical (solar altitude of 90 degrees) at this latitude.
Arctic Circle
Poleward of the latitude (66 degrees 33 minutes North) there are 24 hours of sunlight at the boreal summer solstice & 24 hours of darkness at the boreal winter solstice.
Antarctic Circle
Poleward of the latitude (66 degrees 33 minutes South) there are 24 hours of sunlight on the austral summer solstice & 24 hours of darkness on the austral winter solstice.
Tropic of Capricorn
A solstice pattern of the Sun with a latitude of 23 degrees, 27 minutes South. On December 21st, the Sun’s noon rays are vertical (solar altitude of 90 degrees) at this latitude.
Solar Constant
The flux of solar radiational energy falling on a surface that is positioned at the outer edge of the atmosphere and oriented perpendicular to the solar beam when Earth is at its average distance from the Sun.
The process by which aerosols & molecules disperse radiation in all directions. Scattering is a function of the wavelength of the incident radiation & the size, surface, & composition of the scattering aerosol or molecule, where size is defined relative to the wavelength. No energy transformation results from scattering.
The process whereby a portion of the radiation that strikes the interface between two different media is redirected (backscattered). Reflection is a special case of scattering.
The fraction or percent of radiation striking a surface (or interface) that is reflected by that surface (or interface); usually applied to the reflectivity of an object to visible radiation.
The energy conversion process whereby a portion of the radiation incident on an object is converted to heat energy. Absorption is a function of the surface & composition of the absorbing material & the wavelength of the incident.
Stratospheric Ozone Shield
Ozone in the atmosphere that shields organisms at the Earth’s surface from exposure to potentially lethal intensities of solar ultraviolet radiation.
Antarctic Ozone Hole
A large area of significant stratospheric ozone depletion over the Antarctic continent that typically develops annually between late August & early October, & generally ends in mid-November. Ozone thinning is attributed to the action of chlorine (CI) liberated from a group of chemicals known as chlorofluorocarbons (CFCs).
Polar Stratospheric Clouds (PSCs)
Clouds composed of water, ice, nitric acid, & sulfuric acid which form during the Antarctic winter when extreme radiational cooling causes stratospheric temperatures to drop below -88 degrees Celsius (-126 degrees Fahrenheit).
Circumpolar Vortex
The planetary-scale circulation regime that surrounds the cold pool of air in the polar regions.
Planetary Albedo
The fraction (or percent) of incident solar radiation that is scattered & reflected back into space by the Earth-atmosphere system; measurements by satellite sensors indicate a planetary albedo of about 30%.
Greenhouse Effect
Heating of Earth’s surface & lower atmosphere as a consequence of differences in atmosphere transparency to electromagnetic radiation. The atmosphere is nearly transparent to incoming solar radiation, but much less transparent to outgoing infrared radiation. Terrestrial infrared radiation is absorbed & radiated primarily by water vapor and, to a lesser extent, by carbon dioxide & other trace gases, thereby slowing the loss of heat to space from the Earth-atmosphere system.
Greenhouse Gases
Those gases that absorb & emit appreciable infrared radiation & contribute to the greenhouse effect in the Earth-atmosphere system. The main greenhouse gas is water vapor, others are carbon dioxide, ozone, methane, & nitrous oxide.
Atmospheric Window
Wavelength bands within which atmospheric gases absorb little or no electromagnetic radiation.
Callendar Effect
The theory that global climate change can be brought about by enhancement of the greenhouse effect by increased levels of atmospheric carbon dioxide from antropogenic sources.
Global Warming Potential
An index that compares the contributions of various gases to the greenhouse effect.
Intergovernmental Panel on Climate Change (IPCC)
Entity established by WMO & UNEP to assess the technical, scientific, & socio-economic information relevant for the understanding of climate change & its potential impacts.
The standard instrument for measuring solar radiation incident on a horizontal surface; calibrates the temperature response of a special sensor in units of radiation flux, such as watts per square meter.
Infrared Radiometer
An instrument that measures the intensity of infrared radiation emitted by the surface of some object, such as clouds or the ocean.

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