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In
meteorology Meteorology is a branch of the atmospheric sciences which includes atmospheric chemistry and atmospheric physics, with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorolo ...
, diurnal temperature variation is the variation between a high temperature and a low temperature that occurs during the same
day A day is approximately the period during which the Earth completes one rotation around its axis, which takes around 24 hours. A solar day is the length of time which elapses between the Sun reaching its highest point in the sky two consecutive t ...
.


Temperature lag

Temperature lag is an important factor in diurnal temperature variation: peak daily temperature generally occurs ''after'' noon, as air keeps net absorbing heat even after noon, and similarly minimum daily temperature generally occurs substantially after midnight, indeed occurring during early morning in the hour around dawn, since heat is lost all night long. The analogous annual phenomenon is seasonal lag. As solar energy strikes the Earth's surface each morning, a shallow layer of air directly above the ground is heated by conduction. Heat exchange between this shallow layer of warm air and the cooler air above is very inefficient. On a warm summer's day, for example, air temperatures may vary by from just above the ground to waist height. Incoming solar radiation exceeds outgoing heat energy for many hours after noon and equilibrium is usually reached from 3–5 p.m. but this may be affected by a variety of different things such as large bodies of water, soil type and cover, wind, cloud cover/water vapor, and moisture on the ground.M. Hackworth "Weather & Climate" course notes, with prior permission


Differences in variation

Diurnal temperature variations are greatest very near Earth's surface. High desert regions typically have the greatest diurnal-temperature variations, while low-lying humid areas typically have the least. This explains why an area like the
Snake River Plain
Snake River Plain
can have high temperatures of during a summer day, and then have lows of . At the same time, Washington D.C., which is much more humid, has temperature variations of only ; urban
Hong Kong Hong Kong (, ), officially the Hong Kong Special Administrative Region of the People's Republic of China (HKSAR) (), is a metropolitan area and Special administrative regions of China, special administrative region of the China, People's Repu ...
has a diurnal temperature range of little more than . While the
National Park Service The National Park Service (NPS) is an List of federal agencies in the United States, agency of the federal government of the United States that manages all List of areas in the United States National Park System, national parks, many National mon ...
claimed that the world single-day record is a variation of (from to ) in Browning, Montana in 1916, the Montana Department of Environmental Quality claimed that Loma, Montana also had a variation of (from to ) in 1972.Montana Department of Environmental Quality (DEQ) - FAQ
Both these extreme daily temperature changes were the result of sharp air-mass changes within a single day. The 1916 event was an extreme temperature drop, resulting from frigid Arctic air from Canada invading northern Montana, displacing a much warmer air mass. The 1972 event was a
chinook
chinook
event, where air from the Pacific Ocean overtopped mountain ranges to the west, and dramatically warmed in its descent into Montana, displacing frigid Arctic air and causing a drastic temperature rise. In the absence of such extreme air-mass changes, diurnal temperature variations typically range from 10 or fewer degrees in humid, tropical areas, to 40-50 degrees in higher-elevation, arid to semi-arid areas, such as parts of the U.S. Western states' Intermountain Plateau areas, for example Elko, Nevada, Ashton, Idaho and Burns, Oregon. The higher the
humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation (meteorology), precipitation, dew, or fog to be ...

humidity
is, the lower the diurnal temperature variation is.


Viticulture

Diurnal temperature variation is of particular importance in viticulture. Wine regions situated in areas of high altitude experience the most dramatic swing in temperature variation during the course of a day. In
grape
grape
s, this variation has the effect of producing high
acid An acid is a molecule or ion capable of donating a proton (hydrogen ion H+) (a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid), or, alternatively, capable of forming a covalent bond with an electron pair (a Lewis acid). The fir ...
and high sugar content as the grapes' exposure to sunlight increases the ripening qualities while the sudden drop in temperature at night preserves the balance of natural acids in the grape.J. Robinson ''"The Oxford Companion to Wine"'' Third Edition pg 691 Oxford University Press 2006


See also

*Diurnal cycle


References

{{Climate oscillations Meteorological phenomena Viticulture fr:Amplitude thermique#Types