Search Results

You are looking at 1 - 2 of 2 items for

  • Author or Editor: Piers M. De F. Forster x
  • Refine by Access: All Content x
Clear All Modify Search
Piers M. De F. Forster

Abstract

A discrete-ordinate radiative transfer model is employed for the prediction of surface UV irradiances. A wide-ranging sensitivity study is undertaken to show how changes to the model input parameters aged UV irradiances at the surface. The effects of surface albedo, surface pressure, aerosol, cloud, and ozone on the UV irradiances are examined as well as the effects of model resolution. The ozone vertical profile and the temperature of the ozone layer are found to strongly influence UVB (280–320 nm) surface irradiances; the irradiance at 305 nm can be changed by as much as 17% for a fixed amount of total column ozone. The surface albedo is found to have a maximum influence on wavelengths near 320 nm; an uncertainty in the surface albedo of 0.2 leads to an 8% error in the UVB prediction. Clouds and tropospheric aerosol decrease the UV, their influence depending little on wavelength. Stratospheric aerosol is shown to be able to enhance the midwinter UVB surface irradiances while decreasing the UVA (320–400 nm) surface irradiances.

Full access
Piers M. De F. Forster, Keith P. Shine, and Ann R. Webb

Abstract

High-resolution measurements in the spectral region of 280–400 nm using a double monochromator are compared with detailed radiative transfer calculations at Reading, United Kingdom (52°N, 0°), for clear and totally overcast days, using aerosol and cloud information deduced from empirical methods. For clear skies, instrument and model agree well in the UVA (320–400 nm), but agreement is worse in the UVB (280–320 nm). A number of possible reasons for the discrepancies are explored. Volcanic aerosols in the stratosphere of the model are found to improve agreement between the model and the instrument for high solar zenith angles by increasing the model UVB irradiances by as much as 6%. Convolving the model surface irradiances with the bandpass of the instrument leads to smaller differences between instrument and model at short wavelengths and also reduces the noisiness of the difference. When the model included stratospheric aerosol and the instrument's bandpass function, UVB irradiances within 10% of the measured irradiances could be produced by the model for clear skies. For cloudy conditions, differences between instrument and model are larger, reaching 20%, integrated over the UVB.

Full access