Diurnal cycle

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Earth's rotation relative to the Sun causes the 24-hour day/night cycle.

A diurnal cycle (or diel cycle) is any pattern that recurs every 24 hours as a result of one full rotation of the planet Earth around its axis.[1] Earth's rotation causes surface temperature fluctuations throughout the day and night, as well as weather changes throughout the year. The diurnal cycle depends mainly on incoming solar radiation.[2]

Climate and atmosphere[edit]

Diurnal variation of air temperature (blue) lag by 3 to 4 hours behind insolation at solar noon (red).

In climatology, the diurnal cycle is one of the most basic forms of climate patterns, including variations in diurnal temperature and rainfall.[1] Diurnal cycles may be approximately sinusoidal or include components of a truncated sinusoid (due to the Sun's rising and setting) and thermal relaxation (Newton cooling) at night.[1] The diurnal cycle also has a great impact on carbon dioxide levels in the atmosphere, due to processes such as photosynthesis and cellular respiration.[3]

Biological effects[edit]

Diurnal cycles of light and temperature can result in similar cycles in biological processes, such as photosynthesis in plants[3] and clinical depression in humans.[4] Plant responses to environmental cycles may even induce indirect cycles in rhizosphere microbial activities, including nitrogen fixation.[5]

Semi-diurnal cycle[edit]

A semi-diurnal cycle refers to a pattern that occurs about every twelve hours or about twice a day. Often these can be related to lunar tides, in which case the interval is closer to 12 hours and 25 minutes.

See also[edit]


  1. ^ a b c Betts, A (2015). "BOUNDARY LAYER (ATMOSPHERIC) AND AIR POLLUTION | Diurnal Cycle". Diurnal Cycle (2nd ed.). pp. 319–23. doi:10.1016/B978-0-12-382225-3.00135-3. ISBN 9780123822253. {{cite encyclopedia}}: |journal= ignored (help)
  2. ^ Hartmann, Dennis L. (1994). "The Energy Balance of the Surface". International Geophysics. 56: 81–114. doi:10.1016/S0074-6142(08)60561-6. ISSN 0074-6142.
  3. ^ a b Matthews, Jack S.A.; Vialet-Chabrand, Silvere R.M.; Lawson, Tracy (2017). "Diurnal Variation in Gas Exchange: The Balance between Carbon Fixation and Water Loss". Plant Physiology. 174 (2): 614–623. doi:10.1104/pp.17.00152. ISSN 0032-0889. PMC 5462061. PMID 28416704.
  4. ^ Wirz-Justice, Anna (2008). "Diurnal variation of depressive symptoms". Dialogues in Clinical Neuroscience. 10 (3): 337–343. doi:10.31887/DCNS.2008.10.3/awjustice. ISSN 1294-8322. PMC 3181887. PMID 18979947.
  5. ^ G.K., Sims; Dunigan, E.P. (1984). "Diurnal and seasonal variations in nitrogenase activity (C2H2 reduction) of rice roots". Soil Biology and Biochemistry. 16 (1): 15–18. doi:10.1016/0038-0717(84)90118-4. ISSN 0038-0717.