Katabatic wind - A downslope wind that flows from high elevations down to the valleys or plains below. Katabatic winds are driven by the fact that cold air is heavier and more dense than relatively warmer air. When cold air pools in higher elevations and becomes significantly colder than the air below, the heavier air accelerates down into the lower elevations. Katabatic winds are most common near the elevated ice sheets of Antarctica and Greenland and can exceed hurricane force at times.

Millibar - A millibar is a measure of atmospheric pressure taken by a barometer. The standard pressure measured at the surface is 1,013 millibars. Other units that are used for pressure measurements are inches of mercury and pascals. The lowest pressure readings that have occurred at the surface have been measured underneath intense hurricanes.

Meteorology - The study of the physics, chemistry, and dynamics of the atmosphere and the direct effects of the atmosphere upon the Earth's surface, the oceans, and life in general. An understanding of these atmospheric processes is applied when predicting the weather.

Rain Gauge - An instrument used to measure the amount of rainfall that occurs over a specific site. A standard rain gauge can measure up to 8 inches. The first known device that was used for measuring rainfall was invented in Korea in 1441.

Sferics - Radio waves that are produced in the atmosphere by lightning strikes. When lightning strikes, a disturbance in the electric field occurs, which results in a radio wave being emitted. This concept is used in ground-based lightning detection systems.

Trowal - An acronym for "trough of warm air aloft." It is usually a similar type of frontal structure as is found in the vicinity of an occluded frontal boundary. Organized areas of precipitation can be expected in this region.

Exosphere - The Exosphere is the outermost layer of the atmosphere. It extends from the top of the thermosphere and is 6,200 miles thick. In this layer, atoms and molecules escape into space and satellites orbit the earth. Some scientists place the outer reaches of the exosphere about 120,000 miles from the earths surface, making it near the half way point to the moon.