HOPKINS GLOSSARY OF WEATHER TERMS H
- A type of an instrument (hygrometer) that measures
atmospheric relative humidity by means of the variation
in length of a bundle of human hairs as they adsorb atmospheric
- The maximum distance in the horizontal direction that one
can see; usually this observation is made from a near surface
position. Compare with slant range.
- A type of instrument used for measuring wind speed by measuring
the wind induced changes in the temperature of a metal wire that
is heated by an electric current and cooled by convective heat
loss. As the wind speed increases, more heat is lost from the
wire. Some hot-wire anemometers utilize the changes in the electric
resistance of the wire.
- A generic term describing the amount of water vapor contained
in the air, but not considering any liquid or ice content.
Humidity may be expressed by some measure such as mixing ratio
, vapor pressure, relative humidity, dewpoint
or wet bulb temperature.
- An electrical instrument designed to measure the water vapor
in the atmosphere by using a material (e.g., lithium chloride)
whose electrical resistance varies with atmospheric humidity
; often used onboard radiosondes.
- Any instrument used to measure the water vapor content of
an air parcel (atmospheric humidity). A hair hygrometer
measures the relative humidity; a dewpoint hygrometer
measures the dewpoint temperature. See also psychrometer.
- A recording-type hygrometer.that produces a
- Any substance that has an affinity for water, thereby enhancing
condensation of water vapor. Cloud condensation nuclei
are typically hygroscopic, consisting of salts that produce
aqueous solutions that have equilbrium vapor pressures less than
those for pure water at the same temperature.
- A recording instrument that consists of a recording hygrometer
(or hygrograph) and a recording thermometer (or thermograph
), which together provide a combined permanent trace of the
variatrion of air temperature and relative humidity as a function
of time upon a single chart. Typically, the hygrograph is a recording
hair hygrometer, while the thermograph is a recording
Last update 6 June 1996
Edward J. Hopkins, Ph.D.
Department of Atmospheric and Oceanic Sciences
University of Wisconsin-Madison