Liquid or solid particles distributed in a finely divided state through a gas, usually air; aerosols play an important roll in the formation of precipitation providing the nucleus upon which condensation or freezing takes place.

Air Traffic

Person who supervises and guides the movement of an aircraft both in the air and on the ground.

Air Traffic

Person who is responsible for the most efficient use of time and space for aircraft both in the air and on the ground.


Called "Borealis" in the Northern Hemisphere and "Australis" in the Southern Hemisphere; a colored illumination of the night sky caused by particles from the sun, guided and accelerated by the Earth's magnetic field, that react with Earth's air molecules.


The horizontal direction measured clockwise along the horizon from a fixed direction (north) through 360o.


The portion of energy emitted by a radar that is reflected (or redirected) back toward the radar.

Bipolar (Sunspot)

A magnetic region of the sun containing at least two areas of opposing polarity.

Carbon Cycle

The progress of carbon (carbon dioxide) from air in the atmosphere as it passes through the biosphere, oceans, and sediments, then ascends back into the atmosphere in the form of carbon dioxide and methane.

Carbon Monoxide

Highly toxic, colorless, odorless, flammable gas; present in exhaust gases of internal combustion engines and furnaces; a product of incomplete combustion.

Cardinal Points

The four principal compass points: North, South, East, and West.


A temperature scale applied to pure water at standard atmospheric pressure, which is considered sea level. Zero degrees is the freezing point and 100 degrees is the boiling point of.


A group of chemicals used as propellants for aerosol sprays, in the production of some plastics, as cleaning solvents, and in air conditioning and refrigeration equipment. Chlorine atoms from CFCs are involved in the removal of ozone from the stratosphere.


The sum of all statistical weather information that helps describe atmospheric behavior at a place or region over long periods of time (from months to decades).


A towering, bulging cloud, anvil-shaped at the top, containing water droplets, ice crystals, ice pellets, and sometimes hail accompanied by thunder and lightning.

Doppler Effect

An apparent change in the frequency of light or sound waves when the observer and the source are in motion relative to each other. As the source approaches, the frequency increases; as the source moves away, the frequency decreases.

Doppler Radar

A weather radar used to detect the motion within a storm relative to the radar, based on the Doppler Effect. Air approaching the radar causes an increase in frequency; receding air causes a decrease in frequency. It can detect rotary motion within a storm, for example, a tornado.


Energy moving through space, includes all wavelengths (or frequencies): infrared, ultraviolet, visible light, radio waves, x-rays, and gamma rays.


One of three subatomic particles; orbits the atom's nucleus; has a negative electrical charge.


Environmental Protection Agency

Extent (Sunspots)

The length of a sunspot or a sunspot group measured by the easternmost to westernmost points in degrees longitude.

Flight Tag

Information on airplane flight situation maps about specific flights, for example, airline name, flight number, altitude, destination, and distance to destination.


The number of waves that pass a fixed point in a unit of time.


A freezing of living tissue that impedes blood circulation and can result in gangrene and tissue death.

Global Warming

A slow increase in global average surface or atmospheric temperature.

Greenhouse Effect

The process by which some of the heat radiated from Earth's surface is absorbed and re-radiated back to Earth by gases in the atmosphere.

Greenhouse Gases

Water vapor, carbon dioxide, methane, nitrous oxide, some chlorofluorocarbons, and other trace gases in the atmosphere trap some of the heat radiated from the Earth's surface and re-radiate it back to Earth in the Greenhouse Effect. Greenhouse gases allow solar radiation through to the Earth's surface, where it is absorbed, then re-emitted as long wave radiation.


A form of precipitation made of round or irregular lumps of ice, usually produced in cumulonimbus clouds.


Protein in blood of animals (including humans) that transports oxygen to tissues.


Subnormal inner body temperature that can result in cardiorespiratory failure and death.


A contour line of constant wind speed.

Jet Stream

A strong, narrow meandering stream of air in the westerly winds of the high troposphere.


A unit of speed equal to one nautical mile per hour. One knot equals 1.15 statute miles per hour.


The distance north or south of the equator measured in degrees.


(Light Detection and Ranging) - used to determine the amount of dust in the air. A transmitter sends a pulse of light into the air. Dust particles scatter a small part of the light back to a telescope which directs the light to a detector.


A flash of light generated by the flow of electrons between oppositely charged parts of a cumulonimbus cloud or between the cloud and the ground.


Distance east or west of the prime meridian, expressed in degrees.

Magnetic Class

Classification of the magnetic character of sunspots according to rules set by the Mount Wilson Observatory in California; most common classifications are unipolar and bipolar.

Magnetic Field

A region where magnetic forces are observable.

Mean (Arithmetic)

The average - for example, the sum of all temperatures divided by the number of observations made.


The middle number in a range of numbers.


A scientist who studies the atmosphere and atmospheric phenomena.


The study of the atmosphere, its processes, and weather.


The number in a list that occurs most often.


One of two particles that make up the nucleus of an atom; it has no electric charge.


National Oceanic and Atmospheric Administration


A two dimensional plot, usually consisting of curved lines with labels on them, that expresses a relationship between some variable and two values that it depends upon. For example, the wind chill equivalent temperature may be read from a nomogram by entering the value of temperature along one axis and the value of wind speed along the other.


An atmospheric gas containing three atoms of oxygen (O3).

Ozone Layer

A layer of the stratosphere that contains ozone; it absorbs ultraviolet radiation from the sun, thereby protecting the Earth from ultraviolet radiation.

Parts per Billion (ppb)

Units for expressing the relative amount of a trace gas to a total of a billion parts; a ratio of the volume of a dissolved substance to the sum of the volume of dissolved substance plus the volume of dissolving substance.

Parts per Million (ppm)

Units for expressing the relative amount of a trace gas to a total of a million parts; a ratio of the volume of a dissolved substance to the sum of the volume of dissolved substance plus the volume of dissolving substance.


The lighter outer portion of sunspots.


For green plants, the conversion of water, carbon dioxide, sunlight, and minerals into oxygen and carbohydrates.


One of the two particles that make up the nucleus of an atom; it has a positive electric charge.


An instrument that emits electromagnetic pulses, having a transmitter and receiver. Radars detect and compute the distance to objects by means of reflected radio energy. On certain frequency bands, radar can detect precipitation and clouds and tell if they are moving toward or away from the radar (See Doppler Radar).


Transfer of energy by electromagnetic waves that can travel through space and some materials. (See Electromagnetic Radiation)


The difference between the maximum and minimum in a list of numbers.

Radar Reflectivity

For weather radars, a measure of the energy reflected back to the radar by cloud particles, precipitation, or sometimes, in clear air, by insects or birds. The size and concentration of water or ice particles determine the level of reflectivity. Drizzle has low reflectivity, while hail has very high reflectivity.

Relative Humidity

The ratio of the amount of water vapor in the air at a given temperature compared to the maximum amount that could exist at that temperature, usually expressed in percent.

Solar Flare

A sudden eruption of energy in the solar atmosphere associated with sunspots. Solar flares cause powerful electromagnetic disturbances in the space environment surrounding Earth.

Solar Forecaster

A scientist who forecasts disturbances on the sun that can affect people and equipment on Earth and who warns users in government, industry, and the private sector of solar and geomagnetic activity.


The atmospheric layer above the troposphere showing a slight increase in temperature with increasing altitude, low moisture content, and near absence of clouds. The Earth's ozone layer is in the stratosphere.

Sulfur Dioxide

A compound of sulfur and oxygen; heavy, colorless, poisonous gas with a pungent irritating odor much like that of a just-struck match; occurs in nature in volcanic gases and in some warm springs.


A dark cool spot on the sun's surface that is formed by a magnetic field bundle that breaks through the surface of the sun.


A local storm produced by a cumulonimbus cloud and always accompanied by lightning and thunder.


A violent rotating column of air that extends downward from a cumulonimbus cloud (sometimes visible, sometimes not) and moves in a narrow path along the ground.


The lowermost layer of the atmosphere in which we live, where clouds and weather occur and where temperature generally decreases with increasing altitude.

Type (Sunspot)

A type of three letter designation for the type of a sunspot or sunspot group.


Electromagnetic radiation beyond the short wavelength (violet) end of the visible light range, emitted from the sun. It occupies that region of the electromagnetic spectrum between visible light and X-Rays.


The darkest inner portion of a sunspot with penumbra or a sunspot lacking a penumbra.

Unipolar (Sunspot)

A magnetic region of the sun having one polarity.

Upper Air Wind

Air flowing horizontally above the surface of the Earth.


Coordinated Universal Time; also known as Greenwich Mean Time.


A quantity that has magnitude and direction, commonly represented by a directed line segment whose length represents the magnitude and whose orientation in space represents the direction. A vector can represent the speed and heading of an airplane.


In meteorology, any rotating flow in the atmosphere.


The distance between a point on one wave and the identical point on the next wave; for example, the distance between two crests or two troughs.

Weather Balloon

A balloon that carries instruments and a transmitter to relay meteorological data to receiving stations on Earth; a typical balloon, which is filled with helium, rises from the surface to 60,000 feet in about one hour.

Weather Forecaster

A person who tries to predict the weather using principles of physics, computer models, and variety of statistical and empirical techniques.

Weather Front

A boundary that is a zone of weather change between two air masses of different densities. Fronts move, but sometimes remain still, or stationary.


Air that is in motion relative to the Earth's surface; named after the direction from which it blows. For example, a "north"wind or "northerly" wind is air moving from north to south.

Wind Chill

A measure of apparent temperature that uses the effects of wind and air temperature on the cooling rate of the human body. The wind chill table shows the equivalent cooling power of the atmosphere with wind on exposed flesh.

Wind Direction

The direction from which wind is blowing.

Wind Profiler

A Doppler Radar pointing successively in a mostly vertical direction. The wind profiler measures upper level wind speed and direction.

Wind Shear

Change in direction or speed of the wind; usually horizontal.


Electromagnetic waves having very short wavelengths; they can penetrate many materials.