Observed long-term ozone and UV changes

Laboratory of Atmospheric Physics Physics Dept., Campus Box 149 Aristotle University of Thessaloniki GR-54006 Thessaloniki, Greece 

In addition clouds and haze level (Bais et al., 1993, Estupinan, et al., 1996, Seckmeyer et al. 1996), as well as other tropospheric minor constituents such as S02 (Zerefos et al. 1995a) and surface albedo (WMO, 1994) are also very important in determining UV-B levels at ground, and are among the controlling factors of UV-B transfer through the atmosphere (Zerefos, 1997). 

In this study the inverse UV-B / ozone relationship on longer time scales is investigated. This includes the long-term UV-B modulation caused by the ozone depletion and/or by the Quasi-Biennial Oscillation (QBO) in total ozone (Zerefos et al., 1998). This oscillation in UV-B is also of great importance because it provides a quasi-regular rhythm to many biological UV-B related processes, a QBO-biorhythm, with additional implications in atmospheric chemistry particularly in the tropics. 

The TUV model predicts a Radiation Amplification Factor (RAF) at 305nm of 2.8 which when multiplied by the 0.45% change of ozone per decade gives 1.26% change per year for the irradiance, which is only. 32% per year different from the observational result. This difference is within the uncertainty of the observations. The RAF estimations of the TUV model have been verified from the Brewer measurements and are in accordance with the RAF calculated with the use of equation 2 (WMO, 1998). 

The long-term inverse relationship between total ozone and UV-B is also modulated by the QBO. The QBO in total ozone is nearly in-phase with the 30hPa QBO in stratospheric zonal winds at the equator and lags in phase with increasing latitudes (Zerefos et al., 1994). The total ozone QBO at middle latitudes lags the equatorial stratospheric QBO by a few months. The amplitude of the zonal anomalies of QBO in total ozone are about 3-4% of the mean at middle latitudes but at individual stations, like Thessaloniki, the amplitude is closer to 8%. 

---