Erythemal UV at 45ºS: Longitudinal and secular variability
A single layer model for calculating clear-sky global ultraviolet (UV) irradiance is used to investigate the zonal variation in erythemal UV along the 45ºS parallel. Daily total column ozone data from the Total Ozone Mapping Spectrometer (TOMS) experiment together with geographic location and day number provide the required inputs to the UV model. Monthly averages of total ozone during the years of 1979 (the first complete year of TOMS data) to 1992 (the last complete year of TOMS data) are used to model surface UV irradiance providing an indication of the variations that can be expected over a 13 year period. Although an increase in surface UV is evident in the results, spatial variations may exceed temporal variations a t 45ºS. I n addition, coefficients from a statistical model of global ozone variation have been used to provide an estimate of weekly average total column ozone along 45ºS for the years 1979, 1992 and 2000. These data, when used as input to the UV model, indicate a sustained increase in surface UV at these latitudes. Results based on such future projections should be treated with caution due to unforeseen future perturbations to the total column ozone trends.