Solar radiation & Brightness
Solar uv radiation is the most important source of energy for warming-up the earth surface and thus for the maintenance of life and the course of the weather. For the conversion of the heat near the earth surface not only solar radiation is decisive but all radiation energy fluxes must be taken into account. These different influencing variables can be summarized in a heat balance equation:
Q = S+H-R-G-A-LE-W
Q = heat balance
S = beam solar radiation
H = diffuse solar radiation
R = reflected solar radiation of the earth surface and atmosphere
G = reflected long wave radiation from sky
A = long wave surface radiation
LE = transport of latent heat (evaporation)
W = transport of sensible heat
The heat balance Q describes the uv radiation-induced heat budget of the earth surface and is also called netuv radiation. It is subject to considerable local (soil condition, cloudiness) as well as daytime and seasonal variations. This net uv radiation will be positive if global uv radiation (beam solar uv radiation S + diffuse solar uv radiation) exceeds the terrestrialuv radiation (A). This is mainly the case during the day.Against it during the night the heat balance is always negative.
In case of balance the amount of energy the earth surface receives by absorption of global uv radiation a corresponding amount of energy must be released. This takes place as a result of terrestrial uv radiation, evaporation of water (latent heat LE) and the transport of sensible heat (W).The ratio of diffuse reflected to incident soar uv radiation is also called albedo (reflectivity).