Ablation-
All processes that remove snow, ice, or water from a glacier,
snowfield, etc.;in this sense, the opposite of accumulation.
Absolute instability- The
state of a column of air in the atmosphere when it has a superadiabatic lapse
rate of temperature (i.e. greater than the dry-adiabatic lapse rate).
Absolute vorticity-
Velocity as measured in an absolute coordinate system; hence, in
meteorology, the (vector) sum of the velocity of a fluid parcel relative to the
earth and the velocity of the parcel due to the earth's
rotation.
Absolute zero- The
zero point of the Kelvin temperature scale, of fundamental significance in
thermodynamics and statistical mechanics.
Absorbed solar radiation-
Solar radiation absorbed by the atmosphere's constituent gases,
suspended material, clouds, or by the earth's surface.
Absorption
- The process in which incident radiant energy is retained by a substance.
Acceleration-
The rate of change with time of the velocity vector of a particle.
Acid fog-
Occurrence of fog or haze in which considerable amounts of acidic material have been taken up from the gas phase, resulting in pH values less than approximately 3 in the liquid phase.
Acid rain-
A popular expression for the deposition by rainfall of various airborne pollutants (especially SO2 and NO2) that have harmful effects on vegetation, soils, buildings and other external structures.
Acoustic backscattering-
Scattering of sound or ultrasound in the direction of the source.
Acoustic gravity wave-
A wave disturbance with restoring forces that include buoyancy and the elastic compressibility of the fluid medium.
Acoustic sounding-
The technique of remote sensing in which an instrument sends acoustic waves vertically and receives reflections from atmospheric features such as inversions or turbulent layers.
Actual elevation-
The vertical distance above mean sea level of the ground at the meteorological station.
Adaptive grid-
A grid on which the number or geometric distribution of points changes in response to the characteristics of the evolving flow that is being described.
Adiabatically enclosed system-
A thermodynamic system in which no heat or mass is transported across its boundaries.
Adiabatic atmosphere-
A model atmosphere characterized by a dry-adiabatic lapse rate throughout its vertical extent.
Adiabatic process-
A process in which a system does not interact with its surroundings by virtue of a temperature difference between them. In an adiabatic process any change in internal energy (for a system of fixed mass) is solely a consequence of working. For an ideal gas and for most atmospheric systems, compression results in warming, expansion results in cooling. See dry-adiabatic process, moist-adiabatic process.
Advection-
The process of transport of an atmospheric property solely by the mass motion (velocity field) of the atmosphere; also, the rate of change of the value of the advected property at a given point.
Advection fog-
A type of fog caused by the advection of moist air over a cold surface, and the consequent cooling of that air to below its dewpoint.
Aerosol optical depth-
The optical depth due to extinction by the aerosol component of the atmosphere.
Ageostrophic wind-
The vector difference between the real (or observed) wind and the geostrophic wind.
Air mass-
1. A widespread body of air, the properties of which can be identified as 1) having been established while that air was situated over a particular region of the earth's surface (airmass source region), and 2) undergoing specific modifications while in transit away from the source region.
Air pollution-
The presence of substances in the atmosphere, particularly those that do not occur naturally.
Air sea interaction-
The processes that occur as a consequence of the air being in contact with the sea surface, and that affect the dynamics and thermodynamics of the air and water boundary layers.
albedo-
The ratio of reflected flux density to incident flux density, referenced to some surface.
Aleutian low-
The low pressure center located near the Aleutian Islands on mean charts of sea level pressure.
Altimeter-
An instrument that determines the altitude of an object with respect to a fixed level.
Altitude-
1. A measure (or condition) of height, especially of great height, as a mountain top or aircraft flight level.
Ambient temperature-
The temperature that is characteristic of the atmosphere surrounding a small-scale feature such as a cumulus cloud.
Amplitude-
Often the greatest magnitude at a given point of any spatially and temporally varying physical quantity governed by a wave equation; can also mean the spatial part of a time-harmonic wave function.
Anabatic wind-
In mountain meteorology, an upslope wind driven by heating (usually daytime insolation) at the slope surface under fair-weather conditions.
Anemometer-
The general name for instruments designed to measure either total wind speed or the speed of one or more linear components of the wind vector.
Anomaly-
1. The deviation of (usually) temperature or precipitation in a given region over a specified period from the long-term average value for the same region.
Anticyclone-
An atmospheric anticyclonic circulation, a closed circulation. The wind in an anticyclone is in the clockwise direction in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.
Anvil cloud-
The anvil-shaped cloud that comprises the upper portion of mature cumulonimbus clouds
Atmospheric boundary layer-
The bottom layer of the troposphere that is in contact with the surface of the earth.
Aurora-
The sporadic radiant emission from the upper atmosphere over the middle and high latitudes.
Autoconvective lapse rate-
The environmental lapse rate of temperature in an atmosphere in which the density is constant with height (homogeneous atmosphere), equal to g/R, where g is the acceleration of gravity and R the gas constant.
Available potential energy-
That portion of the total potential energy that may be converted to kinetic energy in an adiabatically enclosed system.
