Diurnal Air Temperature Variation
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In
meteorology Meteorology is the scientific study of the Earth's atmosphere and short-term atmospheric phenomena (i.e. weather), with a focus on weather forecasting. It has applications in the military, aviation, energy production, transport, agricultur ...
, diurnal temperature variation is the variation between a high
air temperature Atmospheric temperature is a measure of temperature at different levels of the Earth's atmosphere. It is governed by many factors, including incoming solar radiation, humidity, and altitude. The abbreviation MAAT is often used for Mean Annual Air ...
and a low temperature that occurs during the same
day A day is the time rotation period, period of a full Earth's rotation, rotation of the Earth with respect to the Sun. On average, this is 24 hours (86,400 seconds). As a day passes at a given location it experiences morning, afternoon, evening, ...
.


Temperature lag

Temperature lag, also known as
thermal inertia Thermal inertia is a term commonly used to describe the observed delays in a body's temperature response during heat transfers. The phenomenon exists because of a body's ability to both store and transport heat relative to its environment. Sinc ...
, is an important factor in diurnal temperature variation. Peak daily temperature generally occurs ''after'' noon, as air keeps absorbing net heat for a period of time from morning through noon and some time thereafter. 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 Seasonal lag is the phenomenon whereby the date of maximum average air temperature at a geographical location on a planet is delayed until some time after the date of maximum daylight (i.e. the summer solstice). This also applies to the minimum ...
. 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 chest 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 factors 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. The Tibetan and Andean Plateaus present one of the largest differences in daily temperature on the planet, as does the
Western US The Western United States (also called the American West, the Western States, the Far West, the Western territories, and the West) is census regions United States Census Bureau As American settlement in the U.S. expanded westward, the mea ...
and the western portion of
southern Africa Southern Africa is the southernmost region of Africa. No definition is agreed upon, but some groupings include the United Nations geoscheme for Africa, United Nations geoscheme, the intergovernmental Southern African Development Community, and ...
. High desert regions typically have the greatest diurnal-temperature variations, while low-lying humid areas near the shores (tropical, oceanic, and arctic) typically have the least. Large cities (urban heat islands) also tend to have a lower diurnal temperature variation than surrounding areas. This explains why an area like the Pinnacles National Park can have high temperatures of during a summer day, and then have lows of . At the same time,
Washington D.C. Washington, D.C., formally the District of Columbia and commonly known as Washington or D.C., is the capital city and federal district of the United States. The city is on the Potomac River, across from Virginia, and shares land borders with ...
, which is much more humid, has temperature variations of only ; urban
Hong Kong Hong Kong)., Legally Hong Kong, China in international treaties and organizations. is a special administrative region of China. With 7.5 million residents in a territory, Hong Kong is the fourth most densely populated region in the wor ...
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, United States federal government, within the US Department of the Interior. The service manages all List ...
claimed that the world single-day record is a variation of (from to ) in
Browning, Montana Browning is a former town and current Census-designated place in Glacier County, Montana, Glacier County, Montana, United States. It is the headquarters for the Blackfeet Indian Reservation and was the only incorporated town on the Reservation. T ...
in 1916, the Montana Department of Environmental Quality claimed that
Loma, Montana Loma is a census-designated place (CDP) in Chouteau County, Montana, United States. The population was 85 at the 2010 census. History James Kipp, of the American Fur Company founded the first community here in 1831. The Blackfeet laid siege to ...
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 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 or smaller in humid, tropical areas, up to in higher-elevation, arid to semi-arid areas, such as parts of the U.S. Western states' Intermountain Plateau areas, for example
Elko, Nevada Elko is a city in and the county seat of Elko County, Nevada, United States. As of the official 2020 U.S. Census, the city has a population of 20,564. Elko serves as the center of the Ruby Valley, a region with a population of over 55,000. Elko ...
,
Ashton, Idaho Ashton is a city in Fremont County, Idaho, United States. The population was 1,127 at the 2010 United States Census, 2010 census, and it is part of the Rexburg micropolitan area, Rexburg Micropolitan Statistical Area. The district is noted for s ...
and
Burns, Oregon Burns is a city in and the county seat of Harney County, Oregon, Harney County, in the U.S. state of Oregon. According to the 2020 United States census, 2020 census, the population was 2,730. Burns and the nearby city of Hines, Oregon, Hines are ...
. 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 t ...
is, the lower the diurnal temperature variation is. In
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
, due to its more northern latitude and close proximity to large warm water bodies (such as the
Mediterranean The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern ...
), differences in daily temperature are not as pronounced as in other continents. However, places in
Southern Europe Southern Europe is also known as Mediterranean Europe, as its geography is marked by the Mediterranean Sea. Definitions of southern Europe include some or all of these countries and regions: Albania, Andorra, Bosnia and Herzegovina, Bulgaria, C ...
significantly far from the Mediterranean tend to have high differences in daily temperatures, some around . These include Southwestern
Iberia The Iberian Peninsula ( ), also known as Iberia, is a peninsula in south-western Europe. Mostly separated from the rest of the European landmass by the Pyrenees, it includes the territories of peninsular Spain and Continental Portugal, compri ...
(e.g.
Alvega Alvega is a former ''freguesia'' ("civil parish"), located in the municipality of Abrantes, in Santarém District, Portugal. In 2013, the parish merged into the new parish Alvega e Concavada. The population in 2011 was 1,499, in an area of 55.33& ...
or
Badajoz Badajoz is the capital of the Province of Badajoz in the autonomous communities of Spain, autonomous community of Extremadura, Spain. It is situated close to the Portugal, Portuguese Portugal–Spain border, border, on the left bank of the river ...
) or the high-altitude plateaus of Turkey (if considered part of Europe) (e.g.
Kayseri Kayseri () is a large List of cities in Turkey, city in Central Anatolia, Turkey, and the capital of Kayseri Province, Kayseri province. Historically known as Caesarea (Mazaca), Caesarea, it has been the historical capital of Cappadocia since anc ...
). In
Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
, significant diurnal temperature variations generally occur in the
Red Centre Central Australia, also sometimes referred to as the Red Centre, is an inexactly defined region associated with the geographic centre of Australia. In its narrowest sense it describes a region that is limited to the town of Alice Springs and ...
around
Alice Springs Alice Springs () is a town in the Northern Territory, Australia; it is the third-largest settlement after Darwin, Northern Territory, Darwin and Palmerston, Northern Territory, Palmerston. The name Alice Springs was given by surveyor William ...
and
Uluru Uluru (; ), also known as Ayers Rock ( ) and officially gazetted as UluruAyers Rock, is a large sandstone monolith. It outcrop, crops out near the centre of Australia in the southern part of the Northern Territory, south-west of Alice Spri ...
.


Viticulture

Diurnal temperature variation is of particular importance in
viticulture Viticulture (, "vine-growing"), viniculture (, "wine-growing"), or winegrowing is the cultivation and harvesting of grapes. It is a branch of the science of horticulture. While the native territory of ''Vitis vinifera'', the common grape vine ...
.
Wine regions Wines are produced in significant growing regions where vineyards are planted. Wine grapes berries mostly grow between the 30th and the 50th degrees of latitude, in both the Northern and Southern Hemispheres, typically in regions of Mediterranean ...
situated in areas of high
altitude Altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum (geodesy), datum and a point or object. The exact definition and reference datum varies according to the context (e.g., aviation, geometr ...
experience the most dramatic swing in temperature variation during the course of a day. In
grape A grape is a fruit, botanically a berry, of the deciduous woody vines of the flowering plant genus ''Vitis''. Grapes are a non- climacteric type of fruit, generally occurring in clusters. The cultivation of grapes began approximately 8,0 ...
s, this variation has the effect of producing high
acid An acid is a molecule or ion capable of either donating a proton (i.e. Hydron, hydrogen cation, H+), known as a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis ...
and high
sugar Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecul ...
content as the grapes' exposure to
sunlight Sunlight is the portion of the electromagnetic radiation which is emitted by the Sun (i.e. solar radiation) and received by the Earth, in particular the visible spectrum, visible light perceptible to the human eye as well as invisible infrare ...
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 A diurnal cycle (or diel cycle) is any pattern that recurs every 24 hours as a result of one full Earth's rotation, rotation of the planet Earth around its axis. Earth's rotation causes surface diurnal temperature variation, temperature fluctuati ...


References

{{Climate oscillations Meteorological phenomena Daily events Atmospheric temperature fr:Amplitude thermique#Types