Diurnal temperature variation
Diurnal temperature variation is a meteorological term that relates to the variation in temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...

 that occurs from the highs of the day
A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun...

 to the cool of night
Night or nighttime is the period of time when the sun is below the horizon. This occurs after dusk. The opposite of night is day...


Temperature lag

Temperature lag is an important factor in diurnal temperature variation. As solar energy strikes the earth’s surface each morning, a shallow (1–3 cm) 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 30°F from just above the
ground to waist level. Incoming solar radiation exceeds outgoing heat energy for
many hours after noon. 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.

Differences in variation

Diurnal temperature variations are greatest very near the earth’s surface.
High desert areas typically have the greatest diurnal temperature variations. Low lying, humid areas typically have the least. This explains why an area like the Snake River Plain
Snake River Plain
The Snake River Plain is a geologic feature located primarily within the state of Idaho in the United States of America. It stretches about westward from northwest of the state of Wyoming to the Idaho-Oregon border. The plain is a wide flat bow-shaped depression, and covers about a quarter of Idaho...

 can have high temperatures of 38°C (100°F) during a summer day, and then have lows of 5-10°C (40-50°F). At the same time, Washington D.C., which is much more humid, has temperature variations of only 8°C (15°F).


Diurnal temperature variation is of particular importance in viticulture
Viticulture is the science, production and study of grapes which deals with the series of events that occur in the vineyard. When the grapes are used for winemaking, it is also known as viniculture...

. Wine regions situated in areas of high altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...

 experience the most dramatic swing in temperature variation during the course of a day. In grape
A grape is a non-climacteric fruit, specifically a berry, that grows on the perennial and deciduous woody vines of the genus Vitis. Grapes can be eaten raw or they can be used for making jam, juice, jelly, vinegar, wine, grape seed extracts, raisins, molasses and grape seed oil. Grapes are also...

s, this variation has the effect of producing high acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...

 and high sugar
Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...

 content as the grapes' exposure to sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...

increases the ripening qualities while the sudden drop in temperature at night preserves the balance of natural acids in the grape.
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