Surface UV radiation over Australia, 1979-1992: Effects of ozone and cloudcover changes on variations of UV radiation

Time series of daily erythemal ultraviolet radiation (UVR) exposure, ozone, and cloud cover were analyzed over the Australian continent using data set s from the NASA Total Ozone Mapping Spectrometer (TOMS) from 1979-1992, The TOMS UVR exposures showed good agreement with data from surface observatio ns. Using a relationship derived from comparisons of the TOMS partial cloud reflectivities with surface cloud cover observations, the TOMS reflectivit ies were converted into estimates of cloud cover for several Australian reg ions. It was shown that the deseasonalized time series of UVR exposures can be statistically described as a linear function of ozone and cloud cover a nomalies. Results of a trend analysis indicated statistically significant i ncreases in UVR exposures of 10% decade(-1) in the summer months in the tro pics. These were associated with a simultaneous depletion of ozone and a de crease in cloud cover, Midlatitudinal regions showed no significant trends of UVR, It was found that variations of ozone and UVR over Australia were s ignificantly influenced by the quasi-biennial oscillation (QBO). An increas e in zonal wind strength of 20 m s(-1) was correlative with reductions of o zone of 1.7% and enhancements of UVR exposures of 2.2%. An increase in sola r radio flux of 100x10(-22) W m(-2) (Hz)(-1) was associated with significan t reductions of UVR of 5-10% in the tropical and subtropical regions in sum mer, The results suggested that enhancements in summer UVR exposures of abo ut 10-20% above the climatological average might be expected in years in wh ich the QBO is in its westerly phase and the solar cycle is at its minimum.