Interannual variability of ozone and UV-B ultraviolet exposure

Zonal averages of annual and seasonal averages of ozone amounts from Nimbus 7/TOMS (1979-1992) have been examined to estimate the systematic interannu al variability of UV-B (390-320 nm) exposure to solar radiation between +/- 60 degrees latitude. As shown from statistical modeling, clear-sky interann ual UV-B changes can be ascribed mainly to the quasi-biennial oscillation ( QBO) driven by stratospheric winds. The QBO oscillations can cause interann ual changes in UV-B exposure of +/-15% at 300 nm and +/-5% at 310 nm at the equator and at middle latitudes. In addition to QBO effects, there are lar ger interannual changes in ozone and UV-B associated with dynamical effects at higher latitudes. When UV-B attenuation from clouds is included, the ge neral latitudinal structure of the interannual variability is maintained. A t the equator the interannual variability of ozone amounts and UV exposure caused by the combination of the 2.3 year QBO and annual cycles implies tha t there is about a 5 year periodicity in UV-B variability caused by dynamic al effects. At higher latitudes the appearance of the interannual UV-B maxi mum is predicted by the QBO but without the regular periodicity. The QBO ef fects on UV-B irradiance are larger than the long-term changes caused by th e decrease in ozone amounts.