- Thermal equator
The thermal equator (also known as "the heat equator") is a belt encircling the
Earth , defined by the set of locations having the highestmean annualtemperature at eachlongitude around the globe. Because local temperatures are sensitive to thegeography of a region, and mountain ranges and ocean currents ensure that smooth temperature gradients (such as might be found if the Earth were uniform in composition and devoid of surface irregularities) are impossible, the location of the thermal equator is not identical to that of the geographicequator .The term is less frequently used to describe the belt of maximum temperatures encircling the globe which migrates roughly between the
Tropic of Cancer and theTropic of Capricorn , the region known as theIntertropical convergence zone , as the Earthorbit s the sun.Still another definition states that the thermal equator is the latitude at which
insolation is identical throughout the year; this is not the same as the astronomicalequator because the Earth reachesperihelion (the minimum distance from theSun in its orbit) in early January and is ataphelion (maximum distance) in early July; therefore,insolation is somewhat higher at 0° latitude in January than in July even though the height of the sun (at noon) and the length of day (from sunrise to sunset) is essentially the same. At a few degrees north of the equator the perihelion/aphelion factor is balanced by the fact that the angle of the Sun is slightly more direct, and the days are slightly longer, at the time of the summersolstice for the Northern Hemisphere (most commonly onJune 21 ), making the level ofinsolation virtually the same in both "summer" and "winter."External links
* [http://www.ssec.wisc.edu/data/comp/latest_cmoll.gifCurrent temperature map]
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