- Absolute zero
- The zero point in the Kelvin temperature scale at which substance has absolutely no heat.
- Aerosol Optical Thickness (AOT)
- A number that expresses how difficult it is for light to pass through aerosols in the atmosphere. A small AOT would mean light could pass through the aerosols fairly easily. A higher AOT would mean light is being blocked or scattered by a larger amount of aerosols and is having difficulty passing through the atmosphere. This is how to find the AOT with the Sun photometer
- Aerosols
- Aerosols are minute particles suspended in the atmosphere. Learn more about Aerosols here.
- Air currents
- Air movements, usually in a certain direction, caused by uneven heating of Earth's surface.
- Air mass (M)
- The air mass is a number, which expresses a relative amount of atmosphere between the sun and the Sun photometer. The size of the air mass depends on the sun angle measured at the time that a sun photometer reading is being taken.
- There is a larger amount of atmosphere between the Sun and the instrument if the Sunlight is following the slant path than the vertical path. The ratio of these amounts of atmosphere is known as air Mass (M)
- Mathematically, the air mass is determined using a ratio
Sin(Sun angle) = Length of the vertical path
Length of the slant path- The Air Mass is the reciprocal of this expression, so that
Air Mass = Length of the slant path
Length of the vertical path= 1
sin(sun angle)- Air pressure
- The amount of force applied by air to a unit of area
- Amplifier
- Electronic equipment that increases the strength of signals.
- Atmosphere
- The area of outer space, extending to a height of 560 km above the surface of Earth, which contains clouds, aerosols, and gases.
- Atmospheric Optical Thickness (AOT)
- A number which expresses how difficult it is for light to pass through the total atmosphere (gases and aerosols).
- Attenuation
- Decrease in energy of the Sun's light occurring as the distance from the sun increases, caused by absorption or scattering.
- Atom
- The smallest particle of a chemical element that can take part in a chemical reaction without being changed. Atoms form molecules; a molecule of water (H2O) consists of 2 atoms of hydrogen and 1 atom of oxygen.
- Barometric Pressure
- The pressure of the atmosphere usually expressed in terms of the height of a column of mercury.
- Bonds
- Forces that hold compounds together; formed when atoms share or transfer electrons.
- Calibrate
- To check or adjust a measuring instrument against a known standard.
- Chemical formulas
- Symbols for chemical ingredients. H2O is the formula for water.
- Chlorine
- A chemical element important in the destruction of ozone. Its symbol is Cl.
- Chlorofluorocarbons
- Groups of chemical compounds containing the elements carbon, chlorine, and fluorine; used in refrigerants and aerosol propellants and in the manufacture of plastic foam; also called CFCs.
- Chromosphere
- The middle gaseous layer of the Sun's atmosphere.
- Climate
- The average of local temperatures, precipitation, and wind conditions, etc., over a period of years.
- Compound
- A combination of two or more chemical elements.
- Condense
- To change from a gas to a liquid or solid.
- Condensation
- The process of changing from a gas to a liquid or solid.
- Control
- The part of an experiment that remains unchanged or whose change is carefully regulated. The control is compared to the experimental subject to see if change occurs.
- Convection current
- Air movement caused by the different weights of warm and cool air. We call this movement "wind."
- Corona
- The outer layer of the Sun's atmosphere.
- Coriolis Effect
- A force created by Earth's rotation; strongly influences global wind patterns.
- Dew Point
- The air temperature at which moisture in the air begins to condense and form dew drops.
- Doldrums
- An area near the equator where the air is generally calm.
- Electron
- A negatively charged particle in an atom.
- Electron Cloud
- A "Cloud" formed by electrons revolving around a nucleus of an atom.
- Evaporate
- To change from a liquid to a vapor.
- Experiment
- A test of a scientific idea under controlled conditions.
- Experimental subject
- The subject of a scientific test.
- Extinction
- Blockage of the Sun's light caused by certain aerosols and gases in the atmosphere.
- Extraterrestrial Constant (ET)
- The ET value for the hand-held Sun photometer is the voltmeter reading of the instrument if the sun photometer could be taken up above the Earth's atmosphere. At this height above the Earth, there would be no aerosols and gases to block the Sun's light entering the instrument. The ET constant is sometimes referred to as the I0 (zero intensity) value. The ET constant varies from one Sun photometer to the next, so each instrument must be calibrated to determine its ET constant.
- The SAGE III instrument is calibrated by computer.
- The hand-held Sun photometer is calibrated by collecting data for a period of a few hours, then plotting a graph called a Langley plot.
- Fly-over
- The point in a satellite's orbit at which it is directly over a particular location.
- Fusion Reaction
- A reaction in which the nuclei of atoms combine to form more massive nuclei with a simultaneous release of huge amounts of energy.
- Gas
- The state of matter distinguished from the solid and liquid states by: relatively low density and viscosity; relatively great expansion and contraction with changes in pressure and temperature; the ability to diffuse readily; and the spontaneous tendency to become distributed uniformly throughout any container.
- Global mean temperature
- The average of all temperatures around the world.
- Ground-truth studies
- Measurements of atmospheric conditions made from Earth to verify the accuracy and precision of measurements of the same area made from space.
- Horizontal axis
- The horizontal number line of a graph.
- Hydroxyl
- A compound made of one atom each of oxygen and hydrogen.
- Hypothesis
- A scientific "guess" that is made to test the result of an action.
- Ionosphere
- The part of Earth's atmosphere containing electrically charged particles that reflect radio waves.
- Limb sounding
- A technique used from space to measure Earth's atmospheric elements by scanning the atmosphere from the horizon upwards or from the top of the atmosphere downwards.
- Magnetosphere
- A region dominated by the magnetic fields that surround Earth.
- Mesosphere
- The part of the atmosphere that begins just above the stratosphere and it extends to 85 km above Earth. It is the coldest layer of the atmosphere.
- Molecule
- The smallest particles into which a compound can be divided without changing its chemical and physical properties.
- Montreal Protocol
- An international agreement to drastically reduce CFC production, the Protocol was adopted in Montreal in 1987. It was significantly strengthened at a subsequent meeting in London in 1990 that called for a complete elimination of CFCs by the year 2000. The agreement was again amended by a Meeting of the Parties in Copenhagen in November 1992. Consumption of controlled substances--such as CFCs and halons--was greatly reduced or eliminated, and many accountability dates were moved forward, often from January 2000 to January 1, 1996.
- Nucleus
- The center of an atom consisting of protons and neutrons.
- Neutron
- A small, uncharged particle in the center of an atom.
- Occultation
- The hiding of a heavenly body from sight by the intervention of some other of the heavenly bodies; -- applied especially to eclipses of stars and planets by the moon, and to the eclipses of satellites of planets by their primaries.
- Particulates
- Small particles, especially those in the atmosphere.
- Photodiode
- A photoelectric semiconductor device for detecting and often measuring radiant energy (as light.
- Photosphere
- The Sun's lower atmosphere.
- Precipitation
- Rain, snow or ice that condenses from atmospheric water vapor and falls to Earth.
- Prominence
- A huge arc of gas emitted from the Sun's surface during a solar storm.
- Polar easterly
- Cold wind flowing away from the Earth's poles toward the west.
- Pressure Gradient Force
- Pressure variations that force air to move from place to place.
- Prevailing westerly
- Wind in the 30° - 60° latitude belts that travels from west to east.
- Radiometer
- An instrument that measures radiant energy; for example, the amount of solar energy received by the Earth.
- Rayleigh scattering
- When the Sun's light passes through a material (in this case the atmosphere), it causes electric charges in the material to vibrate. As the electric charges vibrate, they can emit light. This means that when the Sun's light passes through the atmosphere on its way to the Sun photometer, some of this light is absorbed by the atmosphere, then emitted again in a different direction. In other words, the Sun's light is scattered by atoms in the atmosphere.
- In the algorithm for calculating AOT, there is an expression which factors in the Rayleigh scattering.
- Look again at the algorithm
AOT = ET constant - ln(Vs - Vd) -(0.117M)(P/1013.25)
M- The portion of the AOT algorithm, (0.117M)(P/1013.25), is the expression which takes into account the Rayleigh scattering for Sunlight passing through the atmosphere between the Sun and the Sun photometer on Earth, as it is detected by the green light emitting diode. Notice that the amount of Rayleigh scattering depends on the amount of air mass and on the barometric pressure. When there is a larger amount of air mass and a higher pressure, there are more atmospheric molecules present between the Sun and the detector, and therefore, more Rayleigh scattering.
- Relative Humidity
- The amount of water vapor in the air at a specific temperature compared to the maximum amount it could hold at that temperature.
- Remote Sensing
- A process of obtaining information from a distance
- SAGE III instrument
- Stratospheric Aerosols and Gas Experiment
- Saturated
- Unable to hold or contain more.
- Shell
- The outside area of an electron cloud.
- Sling psychrometer
- An instrument consisting of a dry and a wet thermometer whose readings are compared to measure relative humidity.
- Solar constant
- The amount of solar energy received per unit time (e.g. second) by the upper layer of Earth's atmosphere.
- Solar flare
- A temporary outburst of solar gases from a small area of the Sun's surface.
- Solar wind
- Electrified gases ejected at high speeds from the surface of the Sun.
- Species profile
- A graph which represents how much of the Sun's light was blocked by a specific aerosol or gas.
- Spectrometer
- An instrument that measures the light emitted by the Sun and other stars.
- Spectroscope
- An instrument that separates light into specific wavelengths.
- Spectral signature
- A distinctive array of wavelengths of light emitted or reflected by a particular substance.
- Stratosphere
- A layer of Earth's atmosphere just above the tropopause, extending from about 15 km above Earth to about 50 km.
- Sun Photometer
- An instrument used to measure the intensity of the Sun's light. Look here to see the sun-detecting instruments on SAGE III.
- Sunrise and Sunset
- As the satellite orbits the Earth, the SAGE III instrument will come from behind the Earth so that the Sun is visible, much like we see the sun coming up over the horizon at sunrise on Earth's surface. As the satellite continues in its orbit and cirles behind the Earth, the Sun's rays will no longer be visible to the SAGE III instrument, much like we see a sunset on Earth's surface.
- Sunspot
- Dark spots that appear on the Sun during times of increased solar activity.
