Glossary

Air Density: The ratio of the mass of a substance to the volume it occupies. In oceanography, it is equivalent to specific gravity and represents the ratio of the weight of a given volume of sea water to that of an equal volume of distilled water at 4.0 degrees Celsius or 39.2 degrees Fahrenheit.

Atmospheric Pressure: Atmospheric pressure is the pressure above any area in the Earth's atmosphere caused by the weight of air. Its measurement can be expressed in several ways. One is in millibars. Another is in inches or millimeters of mercury (Hg).

Barometer: An instrument used to measure atmospheric pressure.

Barometric Pressure: See Atomspheric Pressure

Beaufort Wind Scale: A system of estimating and reporting wind speeds. It is based on the Beaufort Force or Number, which is composed of the wind speed, a descriptive term, and the visible effects upon land objects and/or sea surfaces. The scale was devised by Sir Francis Beaufort (1777-1857), hydrographer to the British Royal Navy.

Precipitation: Any and all forms of water, liquid or solid, that falls from clouds and reaches the ground. This includes drizzle, freezing drizzle, freezing rain, hail, ice crystals, ice pellets, rain, snow, snow pellets, and snow grains. The amount of fall is usually expressed in inches of liquid water depth of the substance that has fallen at a given point over a specified time period.