Solar ultraviolet-B radiation under cloudless skies

The ratio of irradiance in the solar UVB and visible radiation wavebands, I(B)/I(V), in the UK Midlands on clear days has been plotted against the cosine of the solar zenith angle to yield a series of straight lines of the form I(B)/I(V) = x + y cos z; the gradients of the lines y, were consistent from day to day, whereas the intercepts, x, changed. A theoretical treatment of aerosol scattering to obtain a theoretical value of I(B)/I(V) showed the gradient y to depend only on two factors which are constant for Rayleigh scattering, whereas x is a function of other atmospheric variables, including ozone, which change from day to day. A similar procedure was conducted for the ratio of UVB to the full solar waveband.