Glossary

The glossary contains definitions for terms in the course content which may not be clear to the user. It also contains linked term (highlighted) that can be clicked on to transfer the user to the section in course that discusses the term.

absolute humidity: the mass of water vapor in a unit of volume of air; the density of the water vapor in the air (Moisture)
absolute zero: the temperature at which all motion stops; zero Kelvin (K) or -273 degrees Celsius (Temperature)
acceleration: the change in velocity over time. (Acceleration)
acid fog: fog (low lying stratus cloud) in which the cloud droplets are made up of a solution of sulfuric acid (H₂SO₄)as a result of the comibination of water and sulfur dioxide (SO₂)(Fog)
acid rain: raindrops that contain sulfuric acid (H₂SO₄) as a result of the comibination of water and sulfur dioxide (SO₂)(Pollutants)
adiabatic process: process in which a sample of gas or a parcel of air undergoes a change of state without the addition or withdrawal of heat (Temperature)
advection: the horizontal movement of heat or air. (Advection, Thermal Wind)
aerosol: synonomous with particulate matter; any liquid or solid substance suspended in air with the exception of pure liquid or frozen water. (Aerosols, More About Aerosols)
Aitken nuclei: category of aerosols that refers to the size of the aerosol, this category includes all aerosols that are less than 0.2 micrometers in diameter (Categorization of Aerosols and Their Sources)
air mass: a large volume of air with similar temperature and moisture porperties throught the horizontal direction. (Air Mass)
air pollutant: any liquid, solid, or gaseous substance that exists in the air in high enough concentrations to be considered hazardous or even a nuisance. (Aerosols, Pollutants)
albedo: the ratio of energy reflected by a surface to the energy that hits the surface. (Albedo)
aneroid barometer: meteorological instrument which measures air pressure; a dry barometer as opposed to one which contains liquid such as a mercury barometer (The Surface and Aloft)
anthropogenic: of human origin; derived from or resulting from human activities
anticyclone: any high pressure system. In NH, wind blow out of anticyclone clockwise. (Anticyclone)
buoyancy: vertical forcing in which warmer, less dense air rises. (Buoyancy)
CFCs: stands for chlorofluorocarbons, which are in the class of pollutants called volatile organic compounds (VOCs); CFCs are also considered greenhouse gases. (VOCs, greenhouse gases)
chinook wind: a warm, dry wind that blows off the eastern slope of the Rocky Mountains. (Chinook Wind)
cloud condensation nuclei: aerosols that water vapor readily condenses onto in supersaturations of 1-2% (Role of Aerosols in Cloud Formation)
cold front: boundary between a cooler, drier air mass overtaking a warmer, more humid air mass. (Cold Front)
condensation level: the pressure level to which a convective parcel of air must rise in order for condensation to occur (Lifting Condesation Level)
conduction: energy transfer from one substance to or through another due to contact between molecules. Energy shifts form a warm location to a relatively cool location. (Conduction)
convection: vertical movement of heat or air due to buoyancy. (Convection)
convergence: air that comes together. (Convergence)
Coriolis force: apparent force caused by spinning earth, deflects objects to the right in NH. (Coriolis Force)
cyclone: any low pressure system. In the NH, wind blow into cyclones counter-clockwise. (Cyclones)
density: the mass of a substance per unit of volume (Vertical Structure of the Atmosphere)
dewpoint temperature: the temperature at which a sample must be cooled to in order to be considered saturated and condensation will begin (Moisture)
diffusion: movement of molecules from areas of higher concentration to area of lower concentrations (Droplet Growth Processes)
dry adiabatic lapse rate: the change in temperature with height according to a dry adiabatic process ; approxiamately 1 degree C / 100 m (Lifting Mechanisms, Potential Temperature, The Dry Adiabatic Process)
earth-atmosphere energy balance: the concept that the total amount of energy in the earth-atmosphere system does not change over long periods of time. (Earth's Energy Balance)
eddy viscosity: viscosity due to turbulent eddies. (Microscale)
entrainment: the mixing of environmental air into a rising air parcel; has the effect of reducing instability (Entrainment)
equation of state: defines the relationship between the temperature, pressure, and density in a gas or mixture of gases (Equation of State)
equivalent potential temperature: the potential temperature of an air parcel after all of the moisture has been removed from the parcel (Equivalent Potential Temperature)
evapotranspiration: the combined processes of evaporation and transpiration. (Water Vapor in the Atmosphere)
First Law of Thermodynamics: The law of energy that states energy can be neither created nor destroyed, only converted to other forms. Also known as the Law of Conservation of Energy.
friction: force that resists motion. (Friction Force)
frontal zone: the zone in and around a front, characterized by steep temperature and wind changes. (Fronts)
gas-to-particle conversion: particles are produced when trace gases either react with other gases or particles present in the atmosphere or absorb solar radiation and, as a result, undergo photochemical reactions; sulphur dioxide can convert into various sulfates in the presence of ammonia and moisture (Categorization of Aerosols and Their Sources)
geostrophic balance: balance between pressure gradient and Coriolis forces. (Geostrophic Balance)
giant nuclei: category of aerosols that refers to the size of the aerosol, this category includes all aerosols that are greater than 2.0 micrometers in diameter (Categorization of Aerosols and Their Sources)
global scale: scale of motion that is viewed globally. (Global Scale)
gravity: the force due to the Earth's mass that is directed toward the earth's center. (Gravity)
hydrocarbons: chemical compounds which contain both hydrogen and carbon (Volatile Organic Compounds)
hydrostatic equilibrium: balance between vertical PGF and gravity (Hydrostatic Equilibrium)
hygrometer: meteorological instrument which measures moisture in the air (The Surface and Aloft)
hypsometric equation: relates atmospheric pressure to height in the atmosphere; used to compute air mas thicknesses and sea level pressures (Reduction of Pressure to Sea Level)
Ice Forming Nuclei (IFN): aerosols which water vapor and water droplets readily deposit and freeze to in sub-freezing temperatures (Ice Formation)
inversion: a layer in the atmosphere characterized by an increase in temperature with an increase in height (Troposphere, Session 6: Focus on Air Quality)
isobar: a line of constant pressure.
jet stream: a ribbon of fast moving air near the tropopause. (Jet Streams)
joule: a measurement of energy; one joule is equal to one newton meter (Nm)
katabatic wind: warm, fast winds that blow off high areas (plateaus). (Katabatic Wind)
kinetic energy.: energy of motion, associated with a molecule's rate of vibrations and its velocity. (Temperature)
land breeze: an off-shore wind that blows during night due to a thermal circulation. (Land Breeze)
large nuclei: a category of aerosols which refers to the physical size of the aerosol, this category includes all aerosols that are between 0.2 micrometers and 2.0 micrometers in diameter (Categorization of Aerosols and Their Sources)
latent heat: the energy associated with a substance's phase or state. (Latent Heat)
LIDAR: Light Detection and Ranging (Ground Based Sensing Devices)
lifting condensation level: the pressure level to which a parcel of air would have to be lifted adiabatically for condensation to occur (Lifting Condesation Level)
longitude: imaginary lines of reference that run north-south on the globe (The Surface and Aloft)
longwave radiation: radiation emitted from the Earth, with wavelengths usully greater than 5 micrometers. (Electromagnetic Spectrum)
mesoscale: scale of motion that is several meters in length and lasts for hours to days. (Mesoscale)
microscale: smallest scale of motion, motions are usually less than a meter in length and last only a few minutes. (Microscale)
Mie scattering: the scattering of all wavelengths of the visible spectrum nearly equally; Mie scattering causes clouds and fog to look white (Scattering Light)
mixing height: The mixing height is the height to which the air near the earth's surface is well mixed due to turbulence caused by the interaction between the surface and the atmosphere. The mixing height marks the top of the planetary boundary layer and is usually located at the base of a temperature inversion. (Mixing Height)
mixing ratio: the mass of the water vapor in a sample of air divided by the mass of the dry air in the sample (Moisture)
moist adiabatic lapse rate: the change in temperature with height of a saturated parcel of air as it rises or descends in the atmosphere; the moist adiabatic lapse rate is less than the dry adiabatic lapse rate due to the release of latent heat during the condensation of water vapor; approxiamately 0.65 degrees C/ 100 m (Lifting Mechanisms, The Moist Adiabatic Process, Equivalent Potential Temperature)
moist adiabatic process: synonymous with saturated adiabatic; a process in which a saturated parcel of air undergoes a change of state where the total amount of energy in the parcel is conserved but is transferred between the moisture and the rest of the parcel (Equivalent Potential Temperature, The Moist Adiabatic Process,)
mole: 6.02 x 10 ²³ molecules of a substance
molecular viscosity: viscosity to due the random motion and interaction of molecules. (Microscale)
mountain breeze: breeze that blows down a mountain during the night due to a thermal circulation. (Mountain-Valley Breezes)
NO_x: nitrogen oxides; a general expression for nitric oxide (NO) and nitrogen dioxide (NO₂). (Nitrogen Oxides)
occlusion: boundary where a cold front has overtaken a warm front and lifted the warm front; also called an occluded front. (Occluded Front)
orographic lifting: the lifting of air over topographic barriers (Lifting Mechanisms, Lifting Condensation Level)
ozone (O₃): triatomic oxygen exists in troposphere as a secondary pollutant and occurs naturally in the stratosphere where it protects us by filtering out the sun's harmful ultraviolet radiation (Ozone, greenhouse gases)
particulate matter: synonymous with aerosol; any liquid or solid substance suspended in air with the exception of pure liquid or frozen water. (Aerosols)
permanent gases: thoese gases that exist in the atmosphere at near constant concertrations in time and space.
photochemical reaction: chemical reactions which are induced by the absorption of solar radiation as in the production of smog (Smog)
photochemical smog: pollution which forms as a result of chemical reactions aided by energy from the sun; pollution which forms in the presence of sunlight. (Ozone, VOCs, Smog)
planetary boundary layer (PBL): that layer of air (up to 3 km in height) which is influenced by friction from the earth's surface and the processes that occur there such as: roughness of terrain, obstructed flow, and heat and energy transfer (What is the Planetary Boundary Layer?)
pollutant: something that pollutes or contaminates the air, soil, or water.
Poisson's equation: relates the temperature and pressure of a gas as it udergoes an adiabatic process (Potential Temperature)
potential temperature: the temperature a sample of gas would have if it were adiabatically expanded or compressed from a given state of temperature and pressure to a pressure of 1000mb (Potential Temperature)
Pressure Gradient Force (PGF): force produced by a change in pressure over a distance, pointing from high pressure toward low pressure. (Pressure Gradient Force)
primary pollutant: a pollutant which is emitted directly into the air. (Pollutants)
prime meridian: longitudinal line which represents zero degrees longitude ; The prime meridian passes through Greenwhich, England (The Surface and Aloft)
pseudoadiabatic process: when a saturated parcel of air cools and the water vapor consenses to the point that the water falls out of the parcel and is no longer a part of the air parcel (The Pseudoadiabatic Process)
RADAR: Radio Detection and Ranging (Ground Based Sensing Devices)
radiant energy: energy from the sun in the form of waves or photons. (Radiation)
radiation: energy transfer in the form of energy waves; also the type of energy that moves in waves. (Radiation)
radiosonde: a weather ballon with meteorological measuring devices and a radio transmitter attached that is used to get data for the upper atmosphere.
RASS: Radio-Acoustic Sounding System (Ground Based Sensing Devices)
Rayleigh scattering: the scattering of short wavelengths of the visible spectrum; Rayleigh scattering produces the appearance of a blue sky during the day (Scattering Light)
reflectivity: the albedo of a surface; the ratio of energy reflected to that reaching a surface. (Albedo)
relative humidity (RH): the ratio of the actual amount of water vapor in a sample of air to the maximum amount the same sample will hold at the same temperature and pressure (Moisture)
saturation mixing ratio: the maximum mixing ratio a sample of air can have; mixing ratio at eht point when the air is considered saturated (Moisture)
saturated adiabatic process: synonymous with moist adiabatic; a process in which a saturated parcel of air undergoes a change of state where the total amount of energy in the parcel is conserved but is transferred between the moisture and the rest of the parcel (Equivalent Potential Temperature)
saturated air: air that contains the maximum amount of water vapor possible at a given temperature and pressure
sea breeze: on on-shore wind due to a thermal circulation. (Sea Breeze)
secondary pollutant: a pollutant which results from a chemical reaction between a primary pollutant and some other substance in the air. (Pollutants)
shortwave radiation: radiation emitted from the sun, usually with wavelengths less than 2 micrometers. (Electromagnetic Spectrum)
sinusoidal: having a pattern that is similar to the curve of a sine function; having crests and troughs like a sine function.
SODAR: Sound Detection and Ranging (Ground Based Sensing Devices)
solar constant: the average energy from the sun that reaches the top of the atmosphere at an angle perpendicular to the solar rays; value equals 1370 Watts per square meter. (Solar Constant)
specific humidity: the mass of the water vapor in a sample of air divided by the mass of the entire sample (Moisture)
specific volume: the volume required for one unit of mass of a gas or mixture of gases at a given temperature and pressure (Equation of State)
stable: unmoving, unchanging; In meteorology, a parcel in a stable environment will not rise or sink but remains at constant height. If forced to rise or sink, the parcel will return to its initial level. (Stable, Neutral, Unstable)
stationary front: a frontal boundary that is not moving. (Stationary Front)
stratified: having many strata or layers; layered
supercooled water: water that exists in a liquid state at sub-freezing temperatures (Ice Formation)
supersaturated air: air that has a relative humidity greater than 100% with respect to a plane surface of water (Categorization of Aerosols and Their Sources)
surface layer: approximately the lower 1/10 of the planetary boundary layer where turbulent stresses are relatively constant (vary by less than 10%) (Surface Layer)
synoptic scale: scale of motion that is thousands of miles long and last for days to weeks; also called weather map scale. (Synoptic Scale)
thermal wind: change in the goestrophic wind with height; vertical geostrophic wind shear. (Thermal Wind)
thermal: parcel of relatively warm air that rises in an environment of cooler air. (Convection)
valley breeze: wind that blows up a mountain due to a thermal circulation. (Mountain-Valley Breezes)
vapor pressure (e): the pressure water vapor exerts on its surroundings due to the number of water vapor molecules present, i.e., the more molecules that are present, the greater the pressure
virtual temperature: the temperature a dry sample of air must be heated in order to have the same density as a sample of moist air at the same pressure (Virtual Temperature)
viscosity: a fluid's resistance to flow, determined mainly by the fluid's density. (Friction)
volatile organic compounds (VOCs): a class of organic compounds primarily made up of hydrocarbons; Some examples of VOCs are benzene, formaldehyde, chlorofluorocarbons (CFCs), and methane (VOCs)
warm front: boundary between a warmer air mass overtaking a cooler air mass. (Warm Front)
wet-bulb depression: the difference in the air temperature and the wet-bulb temperature (Moisture)
wet-bulb temperature: a temperature which indicates the amount of cooling that takes place due to the evaporation of water into the air to point the air is saturated with respect ot a plane surface of water; indicates the amount of water that can be evaporated into the air before the air would become saturated (Moisture)

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