Surface radiation balance

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At the Earth's surface, the concept of net radiation is a useful paradigm. In its simplest form, net radiation is expressed as

where Rn is net all-wave radiation, K# is incoming shortwave solar radiation, K" is the outgoing shortwave radiation or the albedo of the surface, L# is the longwave emission from the atmosphere directed downward to the Earth, and L" is the longwave emission from the Earth's surface. On an annual basis, Figure 2.3 shows that the Earth's surface is a net absorber of radiant energy and net radiation for the Earth's surface is 102Wm—2. This condition is commonly referred to as an energy surplus and is contrasted with an energy deficit in which net radiation is a negative value. Specific locations commonly experience a period of net radiation surplus during the day and a period of net radiation deficit at night. Hourly net radiation data for Davis, California, (39° N) for two days (Fig. 2.7) show seasonal changes in the magnitude of the net radiation surplus and in the period of the net radiation deficit. Locations at high latitudes have greater contrasting seasonal summations of energy surplus and energy deficit, and these seasonal contrasts diminish at lower latitudes.

Hour

Fig. 2.7. Net radiation at Davis, California (39° N). Dotted line is 15 January 2006, and solid line is 15 July 2006. (Data courtesy of the California Department of Water Resources from their website at http://wwwcimis.water.ca.gov/.)

Hour

Fig. 2.7. Net radiation at Davis, California (39° N). Dotted line is 15 January 2006, and solid line is 15 July 2006. (Data courtesy of the California Department of Water Resources from their website at http://wwwcimis.water.ca.gov/.)

Conduction does not appear in Figure 2.3 because the average annual flux into and out of the soil is zero. Also, photosynthesis is not included because it is a relatively small quantity of about 1% globally of solar radiation, and this is significantly smaller than the radiation or other non-radiative fluxes. The heat flow associated with Earth's radioactive heating is disregarded due to its small magnitude of 0.0002% of the radiant energy received from the Sun. The fact that the total radiation at the surface and at the top of the atmosphere must balance is a considerable constraint that lends confidence to the assigned values (Kiehl and Trenberth, 1997).

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Responses

  • geremia
    Which latitude experiences a radiation surplus on an annual basis?
    9 years ago
  • maeve
    Which of the following latitudes experiences a radiation surplus on an annual basis?
    1 month ago

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