Average transmission characteristics of the atmosphere

A valuable summary of the effects of the atmosphere as a whole on the transmission of solar radiation from space to the Earth's surface has been provided by Gates (1962) in terms of the average fate of the radiant flux incident on the northern hemisphere. Over a year, 34% of the incoming solar radiation is reflected to space by the atmosphere; this is made up of 25% reflected by clouds and 9% scattered out to space by other constituents of the atmosphere. Another 19% of the incoming radiation is absorbed by the atmosphere: 10% within clouds, 9% by other components. This leaves 47% of the solar flux, which, on average, reaches the Earth's surface. Of this 47%, 24% consists of the direct solar beam and 23% of diffuse light scattered from clouds (17%) and from the air (6%).

In the cloudy, dirty, moist atmosphere of London, about a third of the incident solar radiation per year is scattered back to space, about a third is absorbed within the atmosphere and the remainder penetrates to the Earth's surface.928 Of the 30% or so that is absorbed, 13% is by water vapour, 9% within clouds and 8% by dust and smoke.

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