Pmde. Forster et Kp. Shine, A COMPARISON OF 2 RADIATION SCHEMES FOR CALCULATING ULTRAVIOLET-RADIATION, Quarterly Journal of the Royal Meteorological Society, 121(525), 1995, pp. 1113-1131
Increases in ultraviolet radiation (UV) caused by ozone depletion in t
he stratosphere are expected to have physiological effects on plants a
nd animals. Biologists require that the UV data have high wavelength r
esolution to assess these effects adequately. Numerical simulations of
scattering and absorption in the atmosphere provide a useful way of p
redicting the UV irradiance reaching the ground and the results from s
uch radiative transfer calculations are presented. Two different metho
ds were used to calculate the diffuse irradiances: the Discrete Ordina
te (D-O) method and the Delta-Eddington (D-E) approximation. Surface U
V irradiances for a wide variety of atmospheric conditions, obtained w
ith the D-O method were compared with those obtained using the D-E app
roximation to assess how changes in tropospheric aerosol and cloud aff
ect the accuracy of the D-E approximation. Stratospheric aerosol has b
een shown to be capable of increasing the UV irradiances at the ground
, the magnitude of these increases depending heavily on the absorption
by ozone of multiply-scattered photons. The prediction of these incre
ases by means of numerical models provides a good test of the accuracy
of the radiative transfer approximations used. It is shown that the D
-E approximation appears to be deficient for the prediction of surface
irradiance at high spectral resolution, under certain circumstances.