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Solar irradiance spectrum at top of atmosphere, on a linear scale and plotted against wavenumber. The solar constant (G SC) measures the amount of energy received by a given area one astronomical unit away from the Sun. More specifically, it is a flux density measuring mean solar electromagnetic radiation (total solar irradiance) per unit
This integrated solar irradiance is called solar irradiation, solar exposure, solar insolation, or insolation. Irradiance may be measured in space or at the Earth's surface after atmospheric absorption and scattering. Irradiance in space is a function of distance from the Sun, the solar cycle, and cross-cycle changes. [2]
Solar radiation pressure on objects near the Earth may be calculated using the Sun's irradiance at 1 AU, known as the solar constant, or G SC, whose value is set at 1361 W/m 2 as of 2011. [17] All stars have a spectral energy distribution that depends on their surface temperature. The distribution is approximately that of black-body radiation.
The updated figure (right) shows the variations and contrasts solar cycles 14 and 24, a century apart, that are quite similar in all solar activity measures (in fact cycle 24 is slightly less active than cycle 14 on average), yet the global mean air surface temperature is more than 1 degree Celsius higher for cycle 24 than cycle 14, showing the ...
W⋅m −2 ⋅Hz −1: M⋅T −2: Irradiance of a surface per unit frequency or wavelength. This is sometimes also confusingly called "spectral intensity". Non-SI units of spectral flux density include jansky (1 Jy = 10 −26 W⋅m −2 ⋅Hz −1) and solar flux unit (1 sfu = 10 −22 W⋅m −2 ⋅Hz −1 = 10 4 Jy). E e,λ [nb 4] watt per ...
In geophysics, shortwave flux is a result of specular and diffuse reflection of incident shortwave radiation by the underlying surface. [3] This shortwave radiation, as solar radiation, can have a profound impact on certain biophysical processes of vegetation, such as canopy photosynthesis and land surface energy budgets, by being absorbed into the soil and canopies. [4]
The relative spectral flux density is also useful if we wish to compare a source's flux density at one wavelength with the same source's flux density at another wavelength; for example, if we wish to demonstrate how the Sun's spectrum peaks in the visible part of the EM spectrum, a graph of the Sun's relative spectral flux density will suffice.
In active regions the energy flux is about 10 7 erg cm −2 sec −1, in the quiet Sun it is roughly 8 10 5 – 10 6 erg cm −2 sec −1, and in coronal holes 5 10 5 - 8 10 5 erg cm −2 sec −1, including the losses due to the solar wind. [1] The required power is a small fraction of the total flux irradiated from the Sun, but this energy is ...