Meteorology Today 9th ed. Chapter 6
Terms in this set (33)
Absolutely stable atmosphere
An atmospheric condition that exists when the environmental lapse rate is less than the moist adiabatic rate. This results in a lifted parcel of air being colder than the air around it.
Absolutely unstable atmosphere
An atmospheric condition that exists when the environmental lapse rate is greater than the dry adiabatic rate. This results in a lifted parcel of air being warmer than the air around it.
A process that takes place without a transfer of heat between the system (such as an air parcel) and its surroundings. In an adiabatic process, compression always results in warming, and expansion results in cooling.
See Parcel of air.
An altocumulus cloud showing vertical development. Individual cloud elements have towerlike tops, often in the shape of tiny castles.
Broad, nearly parallel lines of wavelike clouds oriented at right angles to the wind. Also called Kelvin-Helmholtz wave clouds.
Buoyant force (buoyancy)
The upward force exerted upon an air parcel (or any object) by virtue of the density (mainly temperature) difference between the parcel and that of the surrounding air.
Lines or rows of cumuliform clouds.
The level above the surface marking the base of a cumuliform cloud.
Conditionally unstable atmosphere
An atmospheric condition that exists when the environmental lapse rate is less than the dry adiabatic rate but greater than the moist adiabatic rate. Also called conditional instability.
Instability arising in the atmosphere when a column of air exhibits warm, moist, nearly saturated air near the surface and cold, dry air aloft. When the lower part of the layer is lifted and saturation occurs, it becomes unstable.
Dry adiabatic rate
The rate of change of temperature in a rising or descending unsaturated air parcel. The rate of adiabatic cooling or warming is about 10°C per 1000 m (5.5°F per 1000 ft).
Lines on an adiabatic chart that show the dry adiabatic rate for rising or descending air. They represent lines of constant potential temperature.
The mixing of environmental air into a pre-existing air current or cloud so that the environmental air becomes part of the current or cloud.
Environmental lapse rate
The rate of decrease of air temperature with elevation. It is most often measured with a radiosonde.
Level of free convection
The level in the atmosphere at which a lifted air parcel becomes warmer than its surroundings in a conditionally unstable atmosphere.
Lifting condensation level (LCL)
The level at which a parcel of air, when lifted dry adiabatically, would become saturated.
A cloud containing both water drops and ice crystals.
Moist adiabatic rate
The rate of change of temperature in a rising or descending saturated air parcel. The rate of cooling or warming varies but a common value of 6°C per 1000 m (3.3°F per 1000 ft) is used.
Lines on an adiabatic chart that show the moist adiabatic rate for rising and descending air.
Neutral stability (neutrally stable atmosphere)
An atmospheric condition that exists in dry air when the environmental lapse rate equals the dry adiabatic rate. In saturated air the environmental lapse rate equals the moist adiabatic rate.
Clouds produced by lifting along rising terrain, usually mountains.
The lifting of air over a topographic barrier. Clouds that form in this lifting process are called orographic clouds.
Parcel of air
An imaginary small body of air a few meters wide that is used to explain the behavior of air.
The temperature that a parcel of dry air would have if it were brought dry adiabatically from its original position to a pressure of 1000 mb.
The region on the leeside of a mountain where the precipitation is noticeably less than on the windward side.
A turbulent cumuliform type of cloud that forms on the leeward side of large mountain ranges. The air in the cloud rotates about an axis parallel to the range.
An upper-air observation, such as a radiosonde observation. A vertical profile of an atmospheric variable such as temperature or winds.
See Absolutely stable atmosphere.
The slow sinking of air, usually associated with high-pressure areas.
A temperature inversion produced by compressional warming—the adiabatic warming of a layer of sinking air.
See Absolutely unstable atmosphere.
The side of an object facing into the wind.