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Climate Science: Investigating Climatic and Environmental Processes
The Diurnal Cycle (~10-.027 year)
Forcing Factors
Earth's Daily Pulse
Diurnal Cycle & Carbon Cycle

Example of diurnal variation of radiation and surface temperatureAs the Earth rotates on its axis, creating the cycle of night and day that scientists refer to as the diurnal cycle, there is a delay between the time when the earth-atmosphere system is irradiated and when the temperature begins to increase on the surface of the planet. This delay is known as the thermal response, and depending on the time of the year and the latitude, the lag can be as long as three or four hours. An example would be that the hottest time of day during a typical summer afternoon would be in the mid afternoon, not at solar noon.

The figures to the right, from the NOAA Climate Prediction Center show global and ultraviolet (UV) radiation (top graph) on a mostly clear day, and the variation of surface temperature (below graph) for the same time period. By the time the surface temperature reaches its maximum, the amount of UV radiation reaching the surface has decreased almost by half of that at solar noon. Also see Solar Heating Sensitivity- Land vs. Ocean.

The "dark side" of the diurnal cycle is particularly important in regions where temperatures drop below the freezing point of water, normally 0 degrees Celsius, when water turns to ice and expands. This force, which can crack boulders and burst pipes, is a major mechanism for geologic weathering, especially through repeated cycles of freeze and thaw.

Earth's Daily Pulse

Over the course of a day, the rhythm of night and day influences other natural pulses, such as the tides.
The gravitational effects of the sun and moon, which will vary over the course of the year and lunar phase, have an impact on daily tide cycles.
Image of tide movement across the globe

Image above from NASA shows a synthetic view of how the tides move around the world's oceans over a sixteen day period. Blue indicates places where the ocean level is lower than average reference height, and red areas depict where it's higher.

See NOAA's Tides Online for access to current tidal data from the National Ocean Service.

Image of rainforest from NPSPlants have a role in weather and climate patterns, and one of the ways they influence the climate system is through the process of photosynthesis. Driven by the sunlight during the day, plants take in carbon dioxide, splitting off the carbon which it then combines with hydrogen from water to form carbohydrates which can be stored as fuel for later. The remaining oxygen is released as free oxygen and water vapor is transpired in active photosynthesis.

Image of globe

The tilt of the Earth's axis creates seasonal variability, but there are other factors that may impact climate systems at the annual scale, such as volcanic aerosols which can cool climate and shorten growing seasons.

How Measured
Instruments used to track annual variability and climate patterns include thermometers, rain gauges, and stream gauges. Paleo proxies such as tree rings and cores from corals and ice caps and glaciers also provide information on an annual resolution in terms of precipitation and in some cases extreme events such as fires or volcanic activity.

Diurnal Cycle & Carbon Cycle
Image of modelled effect of the diurnal cycle of carbon metabolism
The image above shows the modeled effect of the diurnal cycle of carbon metabolism on the annual mean atmospheric CO2 concentration and is from a study by "Terrestrial Carbon Metabolism and Atmospheric CO2 " by Dr. David Randall, Colorado State University, Department of Atmospheric Science.

Images from NWS, NOAA and NASA.

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Last Updated Wednesday, 20-Aug-2008 11:22:39 EDT by
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