HOPKINS GLOSSARY OF WEATHER TERMS H

hair hygrometer

• 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 water vapor.

horizontal range

• 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.

hot-wire anemometer

• 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.

humidity

• 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.

hygristor

• 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.

hygrometer

• 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.

hygrograph

• A recording-type hygrometer.that produces a permanent hygrogram.

hygroscopic

• 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.

hygrothermograph

• 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 deflection-type thermometer.