Science / Weather Glossary

Ionosphere: A complex atmospheric zone of ionized gases that extends between 50 and 400 miles (80 to 640 kilometers) above the earth's surface. It is located between the mesosphere and the exosphere and . . . View Full Definition

Isallobar: The line of equal change in atmospheric pressure during a certain time period. It marks the change in pressure tendency.

Isobar: The line drawn on a weather map connecting points of equal barometric pressure.

Isodrosotherm: The line drawn on a weather map connecting points of equal dew point.

Isohel: A line drawn through geographic points having equal duration of sunshine or another form of solar radiation during a specified time period.

Isohyet: The line drawn through geographic points recording equal amounts of rainfall during a given time or for a given of storm.

Isopleth: A line connecting equal points of value. Also called an isoline.

Isotach: A line connecting equal wind speeds.

Isotherm: The line of equal or constant air temperature. If something is isothermal, it is of equal or constant temperature with respect to either time or space.

Jet Streak: A region of accelerated wind speed along the axis of a jet stream.

Jet Stream: An area of strong winds that are concentrated in a relatively narrow band in the upper troposphere of the middle latitudes and subtropical regions of the Northern and Southern Hemispheres. F . . . View Full Definition

K Index: The measure of thunderstorm potential based on the vertical temperature lapse rate, the moisture content of the lower atmosphere and the vertical extent of the moist layer.

Katabatic Wind: A wind that is created by air flowing downhill. When this air is warm, it may be called a foehn wind, and regionally it may be known as a Chinook or Santa Ana. When this air is cold or cool, . . . View Full Definition

Katafront: A front where the warm air descends the frontal surface, except in the low layers of the atmosphere.

Kelvin Temperature Scale: A temperature scale with the freezing point of +273°K (Kelvin) and the boiling point of +373° K. It is used primarily for scientific purposes. Also known as the Absolute Temperature Scale. P . . . View Full Definition

Knot: A nautical unit of speed equal to the velocity at which one nautical mile is traveled in one hour. Used primarily by marine interests and in weather observations. A knot is equivalent to 1.1 . . . View Full Definition

Lake Effect Snow: Snow showers that are created when cold dry air passes over a large warmer lake, such as one of the Great Lakes, and picks up moisture and heat.

Land Breeze: A diurnal coastal breeze that blows offshore, from the land to the sea. It is caused by the temperature difference when the sea surface is warmer than the adjacent land. Predominate during t . . . View Full Definition

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