ARB's Meteorology Program - Glossary

This page last reviewed June 18, 2008

Glossary

The following is a list of terms and definitions associated with the Meteorological Database.


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Atmospheric Pressure
The pressure exerted by the atmosphere at a given point.

Dew Point (deg C)
The temperature, expressed in degrees Celsius, to which air must be cooled at a constant pressure to become saturated.

Dew Point (deg F)
The temperature, expressed in degrees Fahrenheit, to which air must be cooled at a constant pressure to become saturated.

Evapotranspiration
The total amount of water that is transferred from the earth's surface to the atmosphere. It is made up of the evaporation of liquid or solid water plus the transpiration from plants.

Fuel Temperature (deg C)
The internal temperature, in degrees Celsius, of a pine dowel (0.5 in. x 4.5 in.) exposed to ambient air at some U.S. Forest Service and other land management weather stations. This measurement is used to monitor fire danger.

Fuel Temperature (deg F)
The internal temperature, in degrees Fahrenheit, of a pine dowel (0.5 in. x 4.5 in.) exposed to ambient air at some U.S. Forest Service and other land management weather stations. This measurement is used to monitor fire danger.

Net Radiation
The net radiant energy available at the surface of the earth for evaporating water, heating the surface, and heating the air. It is calculated as a balance between the incoming and outgoing radiant energies.

Peak Wind (knots)
The highest instantaneous wind speed observed or recorded, expressed in knots.

Peak Wind (mph)
The highest instantaneous wind speed observed or recorded, expressed in miles per hour.

Peak Wind (mps)
The highest instantaneous wind speed observed or recorded, expressed in meters per second.

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.

Relative Humidity
The ratio of the amount of water vapor in the air to the amount of water vapor the air could hold if it was saturated. It is generally expressed as a percentage,

Resultant Wind (knots)
The vectorial average of all wind directions and speeds (in knots) for a given time period.

Resultant Wind (mph)
The vectorial average of all wind directions and speeds (in miles per hour) for a given time period.

Resultant Wind (mps)
The vectorial average of all wind directions and speeds (in meters per second) for a given time period.

Scalar Wind (knots)
The average of all wind speeds (in knots) for a given time period, irrespective of wind direction.

Scalar Wind (mph)
The average of all wind speeds (in miles per hour) for a given time period, irrespective of wind direction.

Scalar Wind (mps)
The average of all wind speeds (in meters per second) for a given time period, irrespective of wind direction.

Sea Level Pressure
The atmospheric pressure at mean sea level, usually determined from the observed station pressure. For stations above sea level, it is the atmospheric pressure that would exist at a point at sea level directly below if the air at the surface extended all the way down to sea level.

Sea Surface Temperature (deg C)
The water temperature close to the oceans surface, expressed in degrees Celsius. The exact meaning of surface varies according to the measurement method used, but it is between 1 millimetre (0.04 in) and 20 metres (70 ft) below the sea surface.

Sea Surface Temperature (deg F)
The water temperature close to the oceans surface, expressed in degrees Fahrenheit. The exact meaning of surface varies according to the measurement method used, but it is between 1 millimetre (0.04 in) and 20 metres (70 ft) below the sea surface.

Sigma Theta (wind direction)
The standard deviation of wind direction. Provides an indication of the variability of the wind direction. Used in calculations of atmospheric stability.

Solar Radiation
A measurement of the total solar energy (sunlight) reaching the ground.

Station Pressure
The atmospheric pressure with respect to the station elevation.

Temperature (deg C)
The air temperature outside the station, expressed in degrees Celsius.

Temperature (deg F)
The air temperature outside the station, expressed in degrees Fahrenheit.

Vapor Pressure
In meteorology, the part of total atmospheric pressure due to the water vapor content.

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