Meteorology: Chapter 1

Carbon dioxide (CO2)

A colorless, odorless gas whose concentration is about 0.038 percent (385 ppm) in a volume of air near sea level. It is a selective absorber of infrared radiation and, consequently, it is important in the earth's atmospheric greenhouse effect. Solid CO2 is called dry ice.

Thunderstorm

A convective storm (cumulonimbus cloud) with lightning and thunder. Thunderstorms can be composed of an ordinary cell, multicells, or a rapidly rotating supercell.

Middle-latitude cyclone

A cyclonic storm that most often forms along a front in middle and high latitudes. Also called a middle-latitude cyclonic storm, a depression, and a low. It is not a tropical storm or hurricane. See Extratropical cyclone.

Ozone hole

A sharp drop in stratospheric ozone concentration observed over the Antarctic during the spring.

Hurricane

A tropical cyclone having winds in excess of 64 knots (74 mi/hr).

Wind

Air in motion relative to the earth's surface.

Ozone (O3)

An almost colorless gaseous form of oxygen with an odor similar to weak chlorine. The highest natural concentration is found in the stratosphere where it is known as stratospheric ozone. It also forms in polluted air near the surface where it is the main ingredient of photochemical smog. Here, it is called tropospheric ozone.

Ionosphere

An electrified region of the upper atmosphere where fairly large concentrations of ions and free electrons exist.

Temperature inversion

An increase in air temperature with height, often simply called an inversion.

Tornado

An intense, rotating column of air that often protrudes from a cumuliform cloud in the shape of a funnel or a rope whose circulation is present on the ground. (See Funnel cloud.)

Pollutants

Any gaseous, chemical, or organic matter that contaminates the atmosphere, soil, or water.

Climate

The accumulation of daily and seasonal weather events over a long period of time.

Thermosphere

The atmospheric layer above the mesosphere (above about 85 km) where the temperature increases rapidly with height.

Mesosphere

The atmospheric layer between the stratosphere and the thermosphere. Located at an average elevation between 50 and 80 km above the earth's surface.

Tropopause

The boundary between the troposphere and the stratosphere.

Weather

The condition of the atmosphere at any particular time and place.

Wind direction

The direction from which the wind is blowing.

Atmosphere

The envelope of gases that surround a planet and are held to it by the planet's gravitational attraction. The earth's atmosphere is mainly nitrogen and oxygen.

Pressure

The force per unit area. See also Air pressure.

Stratosphere

The layer of the atmosphere above the troposphere and below the mesosphere (between 10 km and 50 km), generally characterized by an increase in temperature with height.

Troposphere

The layer of the atmosphere extending from the earth's surface up to the tropopause (about 10 km above the ground).

Exosphere

The outermost portion of the atmosphere.

Air pressure (atmospheric pressure)

The pressure exerted by the mass of air above a given point, usually expressed in millibars (mb), inches of mercury (Hg) or in hectopascals (hPa).

Lapse rate

The rate at which an atmospheric variable (usually temperature) decreases with height. (See Environmental lapse rate.)

Wind speed

The rate at which the air moves by a stationary object, usually measured in statute miles per hour (mi/hr), nautical miles per hour (knots), kilometers per hour (km/hr), or meters per second (m/sec).

Density

The ratio of the mass of a substance to the volume occupied by it. Air density is usually expressed as g/cm3 or kg/m3.

Heterosphere

The region of the atmosphere above about 85 km where the composition of the air varies with height.

Homosphere

The region of the atmosphere below about 85 km where the composition of the air remains fairly constant.

Middle latitudes

The region of the world typically described as being between 30° and 50° latitude.

Outgassing

The release of gases dissolved in hot, molten rock.

Meteorology

The study of the atmosphere and atmospheric phenomena as well as the atmosphere's interaction with the earth's surface, oceans, and life in general.

Front

The transition zone between two distinct air masses.

Aerosols

Tiny suspended solid particles (dust, smoke, etc.) or liquid droplets that enter the atmosphere from either natural or human (anthropogenic) sources, such as the burning of fossil fuels. Sulfur-containing fossil fuels, such as coal, produce sulfate aerosols.

Water vapor

Water in a vapor (gaseous) form. Also called moisture.

Radiosonde

A balloon-borne instrument that measures and transmits pressure, temperature, and humidity to a ground-based receiving station.

Oxygen (O2)

A colorless and odorless gas that occupies about 21 percent of dry air in the lower atmosphere.

Nitrogen (N2)

A colorless and odorless gas that occupies about 78 percent of dry air in the lower atmosphere.