A note on the interannual variations of UV-B erythemal doses and solar irradiance from ground-based and satellite observations

This study examines three UV-B data sets: groundbased long-term spectral re cords at Thessaloniki, Greece (40.5 degrees N, 22.9 degrees E) and San Dieg o, California, USA (33.7 degrees N, 117.2 degrees W) as well as a global da ta set of daily erythemal dose obtained from the Total Ozone Mapping Spectr ometer (TOMS) onboard the Nimbus-7 satellite. Both ground-based stations ha ve long enough records of spectral UV-B measurements to allow independent t ime series analyses. For 63 degrees solar zenith angle (SZA) and clear sky conditions the quasi biennial oscillation (QBO) effect in solar irradiance at 305nm E-305 is about 32% of the annual cycle for both San Diego and Thes saloniki. The effect slightly increases with cloud cover of up to 4/8, and decreases thereafter for cloud cover greater than 4/8. The data reveal that cloudiness cannot offset interannual signals in UV-B records. The observat ions at San Diego provide an independent confirmation of the widespread nat ure of the QBO in UV-B, which about coincides in amplitude at the two stati on studies, both located in the latitude zone 30 degrees -40 degrees N. The peak-to-peak amplitude of the QBO in erythemal dose derived from TOMS/Nimb us7 data is 6.5% at Thessaloniki. This is similar to the values calculated from ground-based measurements from this station. Based on satellite data, we find that the amplitude of the QBO in the erythemal dose is almost 40% o f the amplitude of the annual cycle only in the tropics. The ratio of the a mplitudes of the QBO over the annual cycle in erythemal dose decreases towa rds the extratropics, becoming less than 5% over middle latitudes.