Glossary

Absolute humidity

The ratio of the mass of water vapor to the volume of air.

Absolutely stable

The environmental lapse rate is less than the moist adiabatic lapse rate.

Absolutely unstable

The environmental lapse rate is greater than the dry adiabatic lapse rate.

Accretion

In cloud physics, usually the growth of an ice hydrometeor by collision with super-cooled cloud drops that freeze wholly or partially upon contact.

American Meteorological Society, cited 2020:Accretion. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Accretion.]

Adiabatic processes

A process in which a system does not interact with its surroundings by virtue of a temperature difference between them.

American Meteorological Society, cited 2019: Adiabatic processes. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Adiabatic_processes.]

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.

American Meteorological Society, cited 2020: Advection. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Advection.]

Aggregation

The process of clumping together of snow crystals following collision as they fall to form snowflakes.

American Meteorological Society, cited 2020: Aggregation. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Aggregation.]

Air mass modification

The change of characteristics of an air mass as it moves away from its region of origin.

American Meteorological Society, cited 2020: Air Mass Modification. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Airmass_modification.]

Air parcel

An imaginary volume of air to which may be assigned any or all of the basic dynamic and thermodynamic properties of atmospheric air.

American Meteorological Society, cited 2019: Air parcel. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Air_parcel.]

Albedo

The ratio of reflected flux density to incident flux density, referenced to some surface.

American Meteorological Society, cited 2019: Albedo. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Albedo.]

Anvil Cloud

The anvil-shaped cloud that comprises the upper portion of mature cumulonimbus clouds; the popular name given to a cumulonimbus capillatus cloud, particularly if it embodies the supplementary feature incus.

American Meteorological Society, cited 2020: Anvil Cloud. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Anvil_cloud.]

Atmospheric boundary layer

The bottom layer of the troposphere that is in contact with the surface of the earth.

American Meteorological Society, cited 2019: Atmospheric boundary layer. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Atmospheric_boundary_layer.]

Atmospheric windows

A range of wavelengths over which there is relatively little absorption of radiation by atmospheric gases. The major windows are the visible window, from ∼0.3 to ∼0.9 μm; the infrared window, from ∼8 to ∼13 μm; and the microwave window, at wavelengths longer than ∼1 mm.

American Meteorological Society, cited 2019: Atmospheric Window. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Atmospheric_window.]

Bergeron–Findeisen process

A theoretical explanation of the process by which precipitation particles may form within a mixed cloud (composed of both ice crystals and liquid water drops).

American Meteorological Society, cited 2020: Bergeron–Findeisen process. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Bergeron-findeisen_process.]

Blackbody

A hypothetical body that cannot be excited to radiate by an external source of electromagnetic radiation of any frequency, direction, or state of polarization except in a negligibly small set of directions around that of the source radiation.

American Meteorological Society, cited 2019: Blackbody. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Blackbody.]

Centrifugal force

The apparent force in a rotating system, deflecting masses radially outward from the axis of rotation, with magnitude per unit mass (ω^2)(R), where ω is the angular speed of rotation and R is the radius of curvature of the path.

American Meteorological Society, cited 2020: Centrifugal Force. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Centrifugal_force.]

Clausius-Clapeyron equation

The differential equation relating pressure of a substance to temperature in a system in which two phases of the substance are in equilibrium.

Climate

The slowly varying aspects of the atmosphere–hydrosphere–land surface system.

American Meteorological Society, cited 2019: Climate. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Climate.]

Cloud Condensation Nuclei

Hygroscopic aerosol particles that can serve as nuclei of atmospheric cloud droplets, that is, particles on which water condenses (activates) at supersaturations typical of atmospheric cloud formation (fraction of one to a few percent, depending on cloud type).

American Meteorological Society, cited 2019: Cloud Condensation Nuclei. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Cloud_condensation_nuclei.]

Collision–coalescence process

In cloud physics, the process produces precipitation by collision and coalescence between liquid particles (cloud droplets, drizzle drops, and raindrops).

American Meteorological Society, cited 2020: Collision-coalescence process. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Collision-coalescence_process.]

Conditionally unstable

The environmental lapse rate is between the moist and dry adiabatic lapse rates.

Conduction

Transport of energy (charge) solely as a consequence of random motions of individual molecules (ions, electrons) not moving together in coherent groups.

American Meteorological Society, cited 2019: Conduction. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Conduction.]

Contact freezing

When many freezing nuclei cause super-cooled liquid droplets.

Contour

Generally, an outline or configuration of a body or surface. Often, the term is used for one of a set of lines (contour lines) drawn to represent the configuration of a surface.

American Meteorological Society, cited 2020: Contour. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Contours.]

Convection

The movement within a fluid due to the tendency of lower density fluid to rise over higher density fluid, which sinks due to the force of gravity resulting in heat transfer within the fluid.

Convective Available Potential Energy

Also known as CAPE, is the maximum buoyancy of an undiluted air parcel, related to the potential updraft strength of thunderstorms.

American Meteorological Society, cited 2019: Convective Available Potential Energy. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Convective_available_potential_energy.]

Convective inhibition

Also known as CIN, is the energy needed to lift an air parcel upward adiabatically to the lifting condensation level (LCL) and then as a pseudo-adiabatic process from the LCL to its level of free convection (LFC).

American Meteorological Society, cited 2019: Convective Inhibition. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Convective_inhibition.]

Coriolis force

An apparent force on moving particles in a non-inertial coordinate system, that is, the Coriolis acceleration as seen in this (relative) system.

American Meteorological Society, cited 2020: Coriolis Force. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Coriolis_force.]

Cumuliform

Like cumulus; generally descriptive of all clouds, the principal characteristic of which is vertical development in the form of rising mounds, domes, or towers.

American Meteorological Society, cited 2019: Cumuliform. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Cumuliform.]

Cyclogenesis

Any development or strengthening of cyclonic circulation in the atmosphere; the opposite of cyclolysis.

American Meteorological Society, cited 2020: Cyclogenesis. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Cyclogenesis.]

Cyclostrophic wind

That horizontal wind velocity for which the centripetal acceleration exactly balances the horizontal pressure force. The cyclostrophic wind can be an approximation to the real wind in the atmosphere only near the equator, where the Coriolis acceleration is small; or in cases of very great wind speed and curvature of the path (such as a tornado or hurricane), so that the centripetal acceleration is the dominant one.

American Meteorological Society, cited 2020: Cyclostrophic wind. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Cyclostrophic_wind.]

Dew point temperature

The temperature to which the air must be cooled to reach saturation, without changing the moisture or air pressure.

Diabatic process

A thermodynamic change of state of a system in which the system exchanges energy with its surroundings by virtue of a temperature difference between them.

American Meteorological Society, cited 2019: Diabatic process. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Diabatic_process.]

Doldrums

A nautical term for the equatorial trough, with special reference to the light and variable nature of the winds.

American Meteorological Society, cited 2020: Doldrums. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Doldrums.]

Downburst

An area of strong, often damaging, winds produced by one or more convective downdrafts. Downbursts over horizontal spatial scales ≤ 4 km are referred to as micro-bursts, whereas larger events with horizontal spatial scales > 4 km are termed macro-bursts.

American Meteorological Society, cited 2020: Downburst. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Downburst.]

Downdraft

Sinking air.

Dropsondes

When the radiosonde packages are dropped from an aircraft.

Dry adiabatic lapse rate

A process lapse rate of temperature, the rate of decrease of temperature with height of a parcel of dry air lifted by a reversible adiabatic process through an atmosphere in hydrostatic equilibrium. The adiabatic lapse rate of unsaturated air containing water vapor.

American Meteorological Society, cited 2019: Dry-adiabatic lapse rate. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Dry-adiabatic_lapse_rate.]

Eccentricity

The circularity of a planetary orbit.

Electromagnetic radiation

Energy propagated in the form of an advancing electric and magnetic field disturbance.

American Meteorological Society, cited 2019: Electromagnetic radiation. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Electromagnetic_radiation.]

Energy

A measurable physical quantity, with dimensions of mass times velocity squared, that is conserved for an isolated system. Energy of motion is kinetic energy; energy of position is potential energy.

American Meteorological Society, cited 2019: Energy. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Energy.]

Enhanced-Fujita scale

A scale used to classify tornado strength based on the amount of damage that was caused.

Equation of State

Also known as the ideal gas law or the Charles–Gay–Lussac law. An equation relating temperature, pressure, and volume of a system in thermodynamic equilibrium.

American Meteorological Society, cited 2019: Equation of state. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Equation_of_state.]

Equilibrium level

The level at which an air parcel, rising or descending adiabatically, attains the same density as its environment.

American Meteorological Society, cited 2019: Level of neutral buoyancy. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Level_of_neutral_buoyancy.]

Eulerian framework

A fixed framework, relative to a single point on the Earth’s surface.

Ferrel cell

A zonally symmetric circulation that appears to be thermally indirect (when viewed using height or pressure as the vertical coordinate) first proposed by William Ferrel in 1856 as the middle of three meridional cells in each hemisphere.

American Meteorological Society, cited 2020: Ferrel cell. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Ferrel_cell.]

First law of thermodynamics

The total internal energy U of an isolated system is constant. Energy cannot be created or destroyed.

American Meteorological Society, cited 2019: First law of thermodynamics. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/First_law_of_thermodynamics.]

Flanking line

An organized lifting zone of cumulus and towering cumulus clouds, connected to and extending outward from the mature updraft tower of a supercell or strong multicell convective storm.

American Meteorological Society, cited 2020: Flanking Line. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Flanking_line.]

Freezing nuclei

Ice nuclei that are effective at causing the freezing of super-cooled liquid droplets.

Front

In meteorology, generally, the interface or transition zone between two air masses of different density.

American Meteorological Society, cited 2020: Front. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Front.]

Frontal wave

A horizontal wave-like deformation of a front in the lower levels, commonly associated with a maximum of cyclonic circulation in the adjacent flow.

American Meteorological Society, cited 2020: Frontal Wave. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Frontal_wave.]

Geometric optics

The application of ray tracing to explain scattering and refractive effects by particles that are very large compared with the wavelength of the radiation.

American Meteorological Society, cited 2020: Geometric Optics. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Geometric_optics.]

Geostrophic adjustment

The process by which an unbalanced atmospheric flow field is modified to geostrophic equilibrium, generally by a mutual adjustment of the atmospheric wind and pressure fields depending on the initial horizontal scale of the disturbance.

American Meteorological Society, cited 2020: Geostrophic Adjustment. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Geostrophic_adjustment.]

Geostrophic balance

Describes a balance between Coriolis and horizontal pressure-gradient forces.

American Meteorological Society, cited 2020: Geostrophic Balance. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Geostrophic_balance.]

Gradient winds

Winds flowing along curved isobars.

Graupel

Heavily rimed snow particles, often called snow pellets; often indistinguishable from very small soft hail except for the size convention that hail must have a diameter greater than 5 mm.

American Meteorological Society, cited 2020: Graupel. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Graupel.]

Greenhouse gases

Those gases, such as water vapor, carbon dioxide, ozone, methane, nitrous oxide, and chlorofluorocarbons, that are fairly transparent to the short wavelengths of solar radiation but efficient at absorbing the longer wavelengths of the infrared radiation emitted by the earth and atmosphere. The trapping of heat by these gases controls the earth's surface temperature despite their presence in only trace concentrations in the atmosphere.

American Meteorological Society, cited 2019: Greenhouse gases. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Greenhouse_gases.]

Gust front

The leading edge of a meso-scale pressure dome separating the outflow air in a convective storm from the environmental air.

American Meteorological Society, cited 2020: Gust Front. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Gust_front.]

Hadley cell

A direct thermally driven and zonally symmetric circulation under the strong influence of the earth's rotation, first proposed by George Hadley in 1735 as an explanation for the trade winds.

American Meteorological Society, cited 2020: Hadley Cell. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Hadley_cell.]

Hailstones

A single unit of hail, ranging in size from that of a pea to, on rare occasions, exceeding that of a grapefruit (i.e., from 5 mm to more than 15 cm in diameter).

American Meteorological Society, cited 2020: Hailstones. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Hailstones.]

Heat

The transfer of thermal energy due to the temperature difference between two objects.

Heat capacity

The ratio of the energy or enthalpy absorbed (or released) by a system to the corresponding temperature rise (or fall).

American Meteorological Society, cited 2019: Heat capacity. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Heat_capacity.]

Hook echo

A pendant, curve-shaped region of reflectivity caused when precipitation is drawn into the cyclonic spiral of a meso-cyclone.

American Meteorological Society, cited 2020: Hook Echo. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Hook_echo.]

Hydrostatic balance

Describes a balance between vertical pressure gradient and buoyancy forces.

American Meteorological Society, cited 2019: Hydrostatic balance. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Hydrostatic_balance.]

Hypsometric equation

An equation relating the thickness, h, between two isobaric surfaces to the mean virtual temperature of the layer. The hypsometric equation is derived from the hydrostatic equation and the ideal gas law.

American Meteorological Society, cited 2019: Hypsometric equation. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Hypsometric_equation.]

Ice nuclei

Any particle that serves as a nucleus leading to the formation of ice crystals without regard to the particular physical processes involved in the nucleation.

American Meteorological Society, cited 2020: Ice nucleus. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Ice_nucleus.]

Instability

A property of the steady state of a system such that certain disturbances or perturbations introduced into the steady state will increase in magnitude, the maximum perturbation amplitude always remaining larger than the initial amplitude.

American Meteorological Society, cited 2020: Instability. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Instability.]

Intertropical Convergence Zone (ITCZ)

The axis, or a portion thereof, of the broad trade-wind current of the Tropics. This axis is the dividing line between the southeast trades and the northeast trades (of the Southern and Northern Hemispheres, respectively).

American Meteorological Society, cited 2020: Intertropical Convergence Zone. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Intertropical_convergence_zone.]

Isobars

A line of equal or constant pressure; an isopleth of pressure.

American Meteorological Society, cited 2020: Isobars. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Isobars.]

Isopleths

In common meteorological usage, a line of equal or constant value of a given quantity, with respect to either space or time.

American Meteorological Society, cited 2020: Isopleths. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Isopleths.]

Isotherms

A line of equal or constant temperature.

American Meteorological Society, cited 2020: Isotherms. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Isotherms.]

Jet stream

Relatively strong winds concentrated within a narrow stream in the atmosphere.

American Meteorological Society, cited 2020: Jet Steam. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Jet_stream.]

Kinetic energy

The energy that a body possesses as a consequence of its motion, defined as one- half the product of its mass and the square of its speed.

American Meteorological Society, cited 2019: Kinetic energy. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Kinetic_energy.]

Lagrangian framework

A framework that is constantly moving and travels with the air.

Lapse rate

The decrease of an atmospheric variable with height, the variable being temperature, unless otherwise specified.

American Meteorological Society, cited 2019: Lapse rate. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Lapse_rate.]

Latent heat

The specific enthalpy difference between two phases of a substance at the same temperature.

American Meteorological Society, cited 2019: Latent heat. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Latent_heat.]

Lee Cyclogenesis

The synoptic-scale development of an atmospheric cyclonic circulation on the downwind side of a mountain range.

American Meteorological Society, cited 2020: Lee Cyclogenesis. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Lee_cyclogenesis.]

Level of free convection

The level at which a parcel of air lifted dry-adiabatically until saturated and saturation-adiabatically thereafter would first become warmer than its surroundings in a conditionally unstable atmosphere.

American Meteorological Society, cited 2019: Level of Free Convection. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Level_of_free_convection.]

Lifting Condensation Level

The level at which a parcel of moist air lifted dry-adiabatically would become saturated. This is where clouds form.

American Meteorological Society, cited 2019: Lifting Condensation Level. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Lifting_condensation_level.]

Lightning

Lightning is a transient, high-current electric discharge with path lengths measured in kilometers.

American Meteorological Society, cited 2020: Lightning. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Lightning.]

Mesoscale convective complex

A subset of mesoscale convective systems (MCS) that exhibit a large, circular (as observed by satellite), long-lived, cold cloud shield.

American Meteorological Society, cited 2020: Mesoscale Convective Complex. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Mesoscale_convective_complex.]

Microburst

A convective downdraft (downburst) that covers an area less than 4 km along a side with peak winds that last 2–5 minutes.

American Meteorological Society, cited 2020: Microburst. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Microburst.]

Mie scattering

Scattering of electromagnetic waves by homogeneous spheres of arbitrary size, named after Gustav Mie (1868–1957), whose theory of 1908 explains the process.

American Meteorological Society, cited 2020: Mie Scattering. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Mie_scattering.]

Mixing ratio

The ratio of the mass of water vapor to the mass of dry air.

Moist adiabatic lapse rate

The rate of decrease of temperature with height along a moist adiabat.

American Meteorological Society, cited 2019: Moist adiabatic lapse rate. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Moist-adiabatic_lapse_rate.]

Neutral stability

A condition of a system for which a small perturbation of a parcel of the system causes it to neither depart from its new position nor return to its previous one.

American Meteorological Society, cited 2019: Neutral stability. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Neutral_stability.]

Obliquity

The degree of tilt in the axis of rotation.

Occluded front

A front that forms as a cyclone moves deeper into colder air.

American Meteorological Society, cited 2020: Occluded Front. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Occluded_fronts.]

Outflow boundary

A surface boundary formed by the horizontal spreading of thunderstorm-cooled air.

American Meteorological Society, cited 2020: Outflow Boundary. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Outflow_boundary.]

Overshooting top

A domelike protrusion above a cumulonimbus anvil, representing the intrusion of an updraft through its equilibrium level (level of neutral buoyancy).

American Meteorological Society, cited 2020: Overshooting Top. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Overshooting_top.]

Planck's radiation law

The distribution law of photon energies for radiation in equilibrium with matter at absolute temperature T.

American Meteorological Society, cited 2019: Planck’s radiation law. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Planck%27s_radiation_law.]

Polar cell

A weak meridional circulation in the high-latitude troposphere characterized by ascending motion in the sub-polar latitudes (50°–70°), descending motion over the pole, poleward motion aloft, and equatorward motion near the surface.

American Meteorological Society, cited 2020: Polar Cell. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Polar_cell.]

Polar Easterlies

Air typically flowing from the northeast while in the Antarctic, air flowing from the southeast.

Polar front

According to the polar-front theory, the semi-permanent, semi-continuous front separating air masses of tropical and polar origin.

American Meteorological Society, cited 2020: Polar Front. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Polar_front.]

Polar Front theory

A theory originated by the Scandinavian school of meteorologists whereby a polar front, separating air masses of polar and tropical origin, gives rise to cyclonic disturbances that intensify and travel along the front, passing through various phases of a characteristic life history.

American Meteorological Society, cited 2020: Polar Front Theory. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Polar-front_theory.]

Polar jet stream

Relatively strong winds concentrated within a narrow stream in the atmosphere. The polar-front jet stream is associated with the polar front of middle and upper-middle latitudes.

American Meteorological Society, cited 2020: Polar Jet Stream. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Polar-front_jet_stream.]

Potential energy

The energy a system has by virtue of its position; the negative of the work done in taking a system from a reference configuration, where the potential energy is assigned the value zero, to a given configuration, with no change in kinetic energy of the system.

American Meteorological Society, cited 2019: Potential energy. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Potential_energy.]

Potential temperature

The temperature that an unsaturated parcel of dry air would have if brought adiabatically and reversibly from its initial state to a standard pressure, p₀, typically 100 kPa.

American Meteorological Society, cited 2019: Potential temperature. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Potential_temperature.]

Precession

The wobble in the rotational axis of a planet that slowly traces out a cone.

Precipitation

All liquid or solid phase aqueous particles that originate in the atmosphere and fall to the earth's surface.

American Meteorological Society, cited 2020: Precipitation. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Precipitation.]

Pressure Gradient force

The force due to differences of pressure within a fluid mass.

American Meteorological Society, cited 2020: Pressure Gradient Force. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Pressure-gradient_force.]

Radiation

The process by which electromagnetic radiation is propagated through free space.

American Meteorological Society, cited 2019: Radiation. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Radiation.]

Radiosonde

An expendable meteorological instrument package, often borne aloft by a free-flight balloon, that measures, from the surface to the stratosphere, the vertical profiles of atmospheric variables and transmits the data via radio to a ground receiving system. Radiosondes typically measure temperature, humidity, and, in many cases, pressure.

American Meteorological Society, cited 2020: Radiosonde. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Radiosonde.]

Rawinsondes

Radiosondes that also infer wind data at different heights.

Rayleigh scattering

Approximate theory for electromagnetic scattering by small particles named for Lord Rayleigh (John William Strutt, 1842–1919), who in 1871 showed that the blue color of the clear sky is explained by the scattering of light by molecules in the atmosphere.

American Meteorological Society, cited 2020: Rayleigh Scattering. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Rayleigh_scattering]

Relative humidity

The ratio of the amount of water vapor present in the air to the maximum amount of water vapor needed for saturation at a certain pressure and temperature.

Saturation

The condition in which vapor pressure is equal to the equilibrium vapor pressure over a plane surface of pure liquid water, or sometimes ice.

American Meteorological Society, cited 2019: Saturation. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Saturation.]

Shelf cloud

A low-level, horizontal, wedge-shaped arcus cloud associated with a convective storm's gust front (or occasionally a cold front).

American Meteorological Society, cited 2020: Shelf Cloud. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Shelf_cloud.]

Snowflake

Colloquially an ice crystal, or more commonly an aggregation of many crystals that falls from a cloud.

American Meteorological Society, cited 2020: Snowflake. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Snowflakes.]

Sounding

A vertical profile of the environmental lapse rate by releasing a radiosonde attached to a weather balloon.

Specific heat

The heat capacity of a system divided by its mass.

American Meteorological Society, cited 2019: Specific heat. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Specific_heat.]

Specific humidity

The ratio of the mass of water vapor to the total mass of air (dry air and water vapor combined).

Spontaneous freezing

When liquid water droplets freeze without any sort of nucleus.

Squall line

A line of active deep moist convection frequently associated with thunder, either continuous or with breaks, including contiguous precipitation areas.

American Meteorological Society, cited 2020: Squall Line. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Squall_line.]

Stability

The characteristic of a system if sufficiently small disturbances have only small effects, either decreasing in amplitude or oscillating periodically; it is asymptotically stable if the effect of small disturbances vanishes for long time periods.

American Meteorological Society, cited 2019: Stability. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Stability.]

Stationary front

A type of frontal system that are almost stationary with the winds flowing nearly parallel and from the opposite paths in each side separated by the front.

Steady-state

A fluid motion in which the velocities at every point of the field are independent of time; streamlines and trajectories are identical.

American Meteorological Society, cited 2019: Steady state. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Steady_state.]

Stefan-Boltzmann Law

One of the radiation laws, which states that the amount of energy radiated per unit time from a unit surface area of an ideal blackbody is proportional to the fourth power of the absolute temperature of the blackbody.

American Meteorological Society, cited 2019: Stefan-Boltzmann Law. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Stefan-boltzmann_law.]

Stoke’s Drag Law

Equation to find the terminal velocity of a falling cloud droplet.

Stratiform

Descriptive of clouds of extensive horizontal development, as contrasted to the vertically developed cumuliform types.

American Meteorological Society, cited 2019: Stratiform. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Stratiform.]

Subpolar Low

A band of low pressure located, in the mean, between 50° and 70° latitude.

American Meteorological Society, cited 2020: Subpolar Low. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Subpolar_low_pressure_belt]

Subtropical Highs

These highs appear as centers of action on mean charts of sea level pressure, generally between 20° and 40° latitude. They lie over the oceans and are best developed in the summer season.

American Meteorological Society, cited 2020: Subtropical Highs. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Subtropical_high.]

Super-cooled water

Liquid water that exists below the freezing point of water (below 0°C).

Supercell

An often dangerous convective storm that consists primarily of a single, quasi-steady rotating updraft, which persists for a period of time much longer than it takes an air parcel to rise from the base of the updraft to its summit (often much longer than 10–20 min).

American Meteorological Society, cited 2020: Supercell. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Supercell.]

Synoptic

In meteorology, this term has become somewhat specialized in referring to the use of meteorological data obtained simultaneously over a wide area for the purpose of presenting a comprehensive and nearly instantaneous picture of the state of the atmosphere.

American Meteorological Society, cited 2020: Synoptic. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Synoptic.]

Terminal velocity

The particular falling speed, for any given object moving through a fluid medium of specified physical properties, at which the drag forces and buoyant forces exerted by the fluid on the object just equal the gravitational force acting on the object.

American Meteorological Society, cited 2020: Terminal Fall Velocity. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Terminal_fall_velocity.]

Thermal energy

A form of energy transferred between systems, existing only in the process of transfer. Also the same as enthalpy.

American Meteorological Society, cited 2019: Heat. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Heat.]

Thunder

The sound emitted by rapidly expanding gases along the channel of a lightning discharge.

American Meteorological Society, cited 2020: Thunder. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Thunder.]

Thunderstorm

In general, a local storm, invariably produced by a cumulonimbus cloud and always accompanied by lightning and thunder, usually with strong gusts of wind, heavy rain, and sometimes with hail.

American Meteorological Society, cited 2020: Thunderstorm. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Thunderstorm.]

Trade winds

The wind system, occupying most of the Tropics, that blows from the subtropical highs toward the equatorial trough; a major component of the general circulation of the atmosphere.

American Meteorological Society, cited 2020: Trade Winds. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Trade_winds.]

Turbulent drag

The relationship between wind speed and force caused by the wind against objects or along surfaces.

American Meteorological Society, cited 2020: Turbulent Drag. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Drag_law.]

Updraft

Rising air.

Vapor pressure

The pressure exerted by the molecules of a given vapor.

American Meteorological Society, cited 2019: Vapor pressure. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Vapor_pressure.]

Virtual temperature

Also called Density temperature. The temperature that dry dry air would have if its pressure and density were equal to those of a given sample of moist air.

American Meteorological Society, cited 2019: Virtual temperature. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Virtual_temperature.]

Wall cloud

A local, often abrupt lowering from a cumulonimbus cloud base into a low-hanging accessory cloud, normally a kilometer or more in diameter.

American Meteorological Society, cited 2020: Wall Cloud. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Wall_cloud.]

Warm front

Any non-occluded front, or portion thereof, that moves in such a way that warmer air replaces cold air.

American Meteorological Society, cited 2020: Warm Front. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Warm_front.]

Warm sector

The region of warmer air between the cold and warm fronts.

Weather

The state of the atmosphere, mainly with respect to its effects upon life and human activities. As distinguished from climate, weather consists of the short-term (minutes to days) variations in the atmosphere. Popularly, weather is thought of in terms of temperature, humidity, precipitation, cloudiness, visibility, and wind.

American Meteorological Society, cited 2019: Weather. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Weather.]

Westerlies

Specifically, the dominant west-to-east motion of the atmosphere, centered over the middle latitudes of both hemispheres.

American Meteorological Society, cited 2020: Westerlies. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Westerlies.]

Wet-Bulb temperature

The lowest temperature that can be achieved if water evaporates within the air.

Wien’s Law

A radiation law that is used to relate the wavelength of maximum emission from a blackbody inversely to its absolute temperature.

American Meteorological Society, cited 2019: Wien’s law. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Wien%27s_law.]

Wind shear

The local variation of the wind vector or any of its components in a given direction.

American Meteorological Society, cited 2020: Wind Shear. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Wind_shear.]

Work

A form of energy arising from the motion of a system against a force, existing only in the process of energy conversion.

American Meteorological Society, cited 2019: Work. Glossary of Meteorology. [Available online at http://glossary.ametsoc.org/wiki/Work.]

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Atmospheric Processes and Phenomenon Copyright © by Alison Nugent, David DeCou, Shintaro Russell, and Christina Karamperidou. All Rights Reserved.

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