Heat index

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== heat index ==
 
== heat index ==
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<div class="definition"><div class="short_definition">As used by C. W. Thornthwaite in his 1948 [[climatic classification]], a function of [[temperature]] designed to have low magnitude under cold conditions, increasing exponentially with  increasing temperature. For a given [[station]], it is numerically equal to the sum of the 12 monthly  values of the expression  <div class="display-formula"><blockquote>[[File:ams2001glos-He8.gif|link=|center|ams2001glos-He8]]</blockquote></div> where ''t'' is the [[normal]] monthly temperature in &#x000b0;C.</div><br/> <div class="paragraph">The heat index is used in the computation of [[potential evapotranspiration]], which, in turn, is one of the basic parameters of the 1948 classification.</div><br/> </div><div class="reference">Thornthwaite, C. W. 1948. An approach toward a rational classification of climate. Geogr. Rev.. 38. 55&ndash;94. </div><br/>
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<div class="definition"><div class="short_definition">The heat index (HI) or “apparent temperature” is an approximation of how hot it “feels” for a given combination of air temperature and relative humidity (RH). Generally, higher RH values at the same temperature feel warmer or more stressful because of less evaporative cooling when people perspire. The HI is the result of extensive biometeorological studies over a period of decades by various researchers, most notably Robert G. Steadman.
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The U.S. National Weather Service (NWS) performed regression analysis to adapt Steadman’s data into an NWS HI equation that can use readily available variables as input. This equation requires only air temperature and RH. The NWS HI table is formulated from that equation.
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[[File:Heatindex.png|center|640px]]
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Reference:
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Steadman, R. G., 1979: The assessment of sultriness. Part I: A temperature–humidity index based on human physiology and clothing science. J. Appl. Meteor., 18, 861–873.
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(Image from NOAA/NWS)
 
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Latest revision as of 12:19, 25 September 2013


[edit] heat index

The heat index (HI) or “apparent temperature” is an approximation of how hot it “feels” for a given combination of air temperature and relative humidity (RH). Generally, higher RH values at the same temperature feel warmer or more stressful because of less evaporative cooling when people perspire. The HI is the result of extensive biometeorological studies over a period of decades by various researchers, most notably Robert G. Steadman.

The U.S. National Weather Service (NWS) performed regression analysis to adapt Steadman’s data into an NWS HI equation that can use readily available variables as input. This equation requires only air temperature and RH. The NWS HI table is formulated from that equation.

Heatindex.png

Reference:

Steadman, R. G., 1979: The assessment of sultriness. Part I: A temperature–humidity index based on human physiology and clothing science. J. Appl. Meteor., 18, 861–873.

(Image from NOAA/NWS)

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