Meteorological Dictionary


Advection-Horizontal transport of air or atmospheric properties, such as wind.

Cold Front-The discontinuity at the forward edge of and advancing cold air mass that is displacing a warmer and often higher in moisture air mass.

Conditionally Unstable-Atmosphere that is stable with respect to an unsaturated parcel of air, but unstable with respect to a saturated parcel of air.

Coriolis Effect-The deflective effect of the earth's rotation on all free-moving objects, including the atmosphere and oceans. To the right in the northern hemisphere and left in the southern hemisphere.

Cyclone-An area of low atmospheric pressure characterized by rotating and converging winds and ascending air.

Dew Point Temperature-The temperature to which the air must be cooled for water vapor to reach saturation, i.e. cloud formation.

Divergence-The condition that exists when the distribution of winds within a given area results in a net horizontal outflow of air from the region. In divergence at upper levels, the resulting deficit is compensated by an upward movement of air from below, favoring cloud formation and precipitation.

Dryline-A region where there is a strong gradient in dew point temperatures. It is often found in a region where strong thunderstorms develop.

Frequency- Number of cycles or sound waves per second

Geopotential Height- approximates the actual height of a pressure surface above mean sea-level in meters. For example a geopotential height of 1500 is the number of meters above sea-level one would have to be to reach a pressure of 850mb.

Isobar-Connecting points of equal barometric pressure on a map.

Jet Streak-Region of fastest flow within the jet stream.

Jet Stream-A river of fast flowing air at high altitudes above the earth that generally flows from west to east over the mid-latitudes. The jet stream separates cold polar air from warmer air to the south and generally "steers" surface features such as fronts and low pressure systems.

Kinetic Energy-The energy which a body possesses as a consequence of it's motion.

Lapse Rate-The decrease of an atmospheric variable with height, usually temperature.

Millibars-Unit of atmospheric pressure. Other possible units of pressure used by scientists are inches of Mercury, and torr.

Planetary Boundary Layer-The atmospheric boundary layer from the surface to the level where the frictional influence is absent.

Pressure-The force exerted by the interaction of the atmosphere and gravity.

Potential Energy-The energy which a body possesses as a consequence of it's position in the field of gravity, the work required to bring the body up against gravity from a standard level.

Pressure Gradient-The amount of pressure change occurring over a given distance.

Radiosonde-A lightweight package of weather instruments fitted with a radio transmitter and carried up into the atmosphere by a balloon.

Relative Humidity-The ratio of the air's water vapor content to its water water vapor capacity.

Severe Thunderstorm-Any one of the three conditions must be met. 1) Tornadoes 2) Hailstones larger than 3/4" 3) Wind gusts greater than 58 miles per hours.

Stratosphere-The layer above the troposphere where temperatures gradually increase with height. This layer begins at approximately 10km and ends around 50km. The earth's ozone is concentrated here.

Supercooled-The presense of water droplets that remain in a liquid state at temperatures well below 0C.

Temperature-The measure of the average kinetic energy of the molecules of a substance. The greater the kinetic energy the higher the temperature. A measure of how fast the air molecules are moving.

Troposphere-The lowest layer of the atmosphere marked by considerable turbulence and a decrease in temperature with height. This layer stretches from the surface to approximately 10km. Weather on earth is created here.

Wind-A result due to the differences in air mass pressures (temperature). The wind blows as a result of nature trying to balance the differences. The larger the differences between air masses, the stronger the wind.