ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-2469-2012 Evidence of a possible turning point in solar UV-B over Canada, Europe and Japan Zerefos C. S. 1 2 4 Tourpali K. 3 Eleftheratos K. 1 4 Kazadzis S. 5 Meleti C. 3 Feister U. 6 Koskela T. 7 Heikkilä A. 7 Biomedical Research Foundation of the Academy of Athens, Athens, Greece Navarino Environmental Observatory (N.E.O.), Greece Department of Physics, University of Thessaloniki, Greece Faculty of Geology and Geoenvironment, University of Athens, Greece Institute for Environmental Research and Sustainable Development, National Observatory of Athens, Greece Meteorological Observatory Lindenberg, German Meteorological Service, Germany Climate Change Unit, Finnish Meteorological Institute, Helsinki, Finland 05 03 2012 12 5 2469 2477 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/2469/2012/acp-12-2469-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/2469/2012/acp-12-2469-2012.pdf

This study examines the long-term variability of UV solar irradiances at 305 nm and 325 nm over selected sites in Canada, Europe and Japan. Site selection was restricted to the availability of the most complete UV spectroradiometric datasets during the period 1990–2011. The analysis includes the long-term variability of total ozone, aerosol optical depth and cloud fraction at the sites studied. The results, based on observations and modeling, suggest that over Canada, Europe and Japan the period under study can be divided into three sub-periods of scientific merit: the first period (1991–1994) is the period perturbed by the Pinatubo volcanic eruption, during which excess volcanic aerosol has enhanced the "conventional" amplification factor of UV-B at ground level by an additional factor that depends on solar elevation. The increase of the UV-B amplification factor is the result of enhanced scattering processes caused by the injection of huge amounts of volcanic aerosols during the perturbed period. The second period (1995–2006) is characterized by a 0.14% yr<sup>−1</sup> increase in total ozone and an increasing trend in spectral irradiance by 0.94% yr<sup>−1</sup> at 305 nm and 0.88% yr<sup>−1</sup> at 325 nm. That paradox was caused by the significant decline of the aerosol optical depth by more than 1% yr<sup>−1</sup> (the "brightening" effect) and the absence of any statistically significant trend in the cloud fraction. The third period (2007–2011) shows statistically significant evidence of a slowdown or even a turning point in the previously reported upward UV-B trends over Canada, Europe and Japan.

 References Bais, A. F., Zerefos, C. S., Meleti, C., Ziomas, I. C., and Tourpali, K.: Spectral measurements of solar UVB radiation and its relations to total ozone, SO<sub>2</sub>, and clouds, J. Geophys. Res., 98, 5199–5204, 1993. Cermak, J., Wild, M., Knutti, R., Mishchenko, M. I., and Heidinger, A. K.: Consistency of global satellite-derived aerosol and cloud data sets with recent brightening observations, Geophys. Res. Lett., 37, L21704, http://dx.doi.org/10.1029/2010GL044632doi:10.1029/2010GL044632, 2010. Chipperfield, M. P., Fioletov, V. E., Bregman, B., Burrows, J., Connor, B. J., Haigh, J. D., Harris, N. R. P., Hauchecorne, A., Hood, L. L., Kawa, S. R., Krzyscin, J. W., Logan, J. A., Muthama, N. J., Polvani, L., Randel, W. J., Sasaki, T., Staehelin, J., Stolarski, R. S., Thomason, L. W., and Zawodny, J. M.: Global ozone: past and present. Chapter 3 in Scientific Assessment of Ozone Depletion: 2006, Global Ozone Research and Monitoring Project-Report No. 50, 572~pp., World Meteorological Organization, Geneva, Switzerland, 2007. den Outer, P. N., Slaper, H., Kaurola, J., Lindfors, A., Kazantzidis, A., Bais, A. F., Feister, U., Junk, J., Janouch, M., and Josefsson, W.: Reconstructing of erythemal ultraviolet radiation levels in Europe for the past~4 decades, J. Geophys. Res., 115, D10102, http://dx.doi.org/10.1029/2009JD012827doi:10.1029/2009JD012827, 2010. Fioletov, V. E., McArthur, L. J. B., Kerr, J. B., and Wardle, D. I.: Long-term variations of UV-B irradiance over Canada estimated from Brewer observations and derived from ozone and pyranometer measurements, J. Geophys. Res., 106, 23009–23027, http://dx.doi.org/10.1029/2001JD000367doi:10.1029/2001JD000367, 2001. Fioletov, V. E., Kimlin, M. G., Krotkov, N., McArthur, L. J. B., Kerr, J. B., Wardle, D. I., Herman, J. R., Meltzer, R., Mathews, T. W., and Kaurola, J.: UV index climatology over the United States and Canada from ground-based and satellite estimates, J. Geophys. Res., 109, D22308, http://dx.doi.org/10.1029/2004JD004820doi:10.1029/2004JD004820, 2004. Harris, N. R. P., Kyrö, E., Staehelin, J., Brunner, D., Andersen, S.-B., Godin-Beekmann, S., Dhomse, S., Hadjinicolaou, P., Hansen, G., Isaksen, I., Jrrar, A., Karpetchko, A., Kivi, R., Knudsen, B., Krizan, P., Lastovicka, J., Maeder, J., Orsolini, Y., Pyle, J. A., Rex, M., Vanicek, K., Weber, M., Wohltmann, I., Zanis, P., and Zerefos, C.: Ozone trends at northern mid- and high latitudes – a European perspective, Ann. Geophys., 26, 1207–1220, http://dx.doi.org/10.5194/angeo-26-1207-2008doi:10.5194/angeo-26-1207-2008, 2008. Granier, C. and Brasseur, G.: Impact of Heterogeneous Chemistry on Model Predictions of Ozone Changes, J. Geophys. Res., 97, 18015–18033, 1992. Levy, R. C., Remer, L. A., Mattoo, S., Vermote, E. F., and Kaufman, Y. J.: Second-generation operational algorithm: Retrieval of aerosol properties over land from inversion of Moderate Resolution Imaging Spectroradiometer spectral reflectance, J. Geophys. Res., 112, D13211, http://dx.doi.org/10.1029/2006JD007811doi:10.1029/2006JD007811, 2007. Mayer, B. and Kylling, A.: Technical note: The libRadtran software package for radiative transfer calculations – description and examples of use, Atmos. Chem. Phys., 5, 1855–1877, http://dx.doi.org/10.5194/acp-5-1855-2005doi:10.5194/acp-5-1855-2005, 2005. Mishchenko, M. I., Geogdzhayev, I. V., Rossow, W. B., Cairns, B., Carlson, B. E., Lacis, A. A., Liu, L., and Travis, L. D.: Long-term satellite record reveals likely recent aerosol trend, Science, 315, 1543, http://dx.doi.org/10.1126/science.1136709doi:10.1126/science.1136709, 2007a. Mishchenko, M. I., Geogdzhayev, I. V., Cairns, B., Carlson, B. E., Chowdhary, J., Lacis, A. A., Liu, L., Rossow, W. B., Travis, L. D., Past, present, and future of global aerosol climatologies derived from satellite observations: A perspective, J. Quant. Spectrosc. Ra., 106, 325–347, http://dx.doi.org/10.1016/j.jqsrt.2007.01.007doi:10.1016/j.jqsrt.2007.01.007, 2007b. Newchurch, M. J., Yang, E.-S., Cunnold, D. M., Reinsel, G. C., Zawodny, J. M., and Russell III, J. M.: Evidence for slowdown in stratospheric ozone loss: First stage of ozone recovery, J. Geophys. Res., 108, 4507, http://dx.doi.org/10.1029/2003JD003471doi:10.1029/2003JD003471, 2003. Newman, P. A., Oman, L. D., Douglass, A. R., Fleming, E. L., Frith, S. M., Hurwitz, M. M., Kawa, S. R., Jackman, C. H., Krotkov, N. A., Nash, E. R., Nielsen, J. E., Pawson, S., Stolarski, R. S., and Velders, G. J. M.: What would have happened to the ozone layer if chlorofluorocarbons (CFCs) had not been regulated?, Atmos. Chem. Phys., 9, 2113–2128, http://dx.doi.org/10.5194/acp-9-2113-2009doi:10.5194/acp-9-2113-2009, 2009. Reinsel, G. C.: Trend analysis of upper stratospheric Umkehr ozone data for evidence of turnaround, Geophys. Res. Lett., 29, 1451, http://dx.doi.org/10.1029/2002GL014716doi:10.1029/2002GL014716, 2002. Rossow, W. B. and Schiffer, R. A.: Advances in understanding clouds from ISCCP, B. Am. Meteorol. Soc., 80, 2261–2287, 1999. WMO: Scientific Assessment of Ozone Depletion: 2010, Global Ozone Research and Monitoring Project – Report No. 52, 516~pp., Geneva, Switzerland, 2011. Wild, M.: Global dimming and brightening: A review, J. Geophys. Res., 114, D00D16, http://dx.doi.org/10.1029/2008JD011470doi:10.1029/2008JD011470, 2009. Wild, M., Trüssel, B., Ohmura, A., Long, C. N., König-Langlo, G., Dutton, E. G., and Tsvetkov, A.: Global dimming and brightening: An update beyond 2000, J. Geophys. Res., 114, D00D13, http://dx.doi.org/10.1029/2008JD011382doi:10.1029/2008JD011382, 2009. Zanis, P., Maillard, E., Staehelin, J., Zerefos, C., Kosmidis, E., Tourpali, K., and Wohltmann, I.: On the turnaround of stratospheric ozone trends deduced from the reevaluated Umkehr record of Arosa, Switzerland, J. Geophys. Res., 111, D22307, http://dx.doi.org/10.1029/2005JD006886doi:10.1029/2005JD006886, 2006. Zerefos, C. S.: Long-term ozone and UV variation at Thessaloniki, Greece, Phys. Chem. Earth, 27, 455–460, 2002. Zerefos, C. S., Tourpali, K., and Bais, A. F.: Further studies on possible volcanic signal to the ozone layer, J. Geophys. Res., 99, 25741–25746, 1994. Zerefos, C. S., Contopoulos, G., and Skalkeas, G.: Twenty years of Ozone Decline. Proceedings of the Symposium for the 20th Anniversary of the Montreal Protocol, 470~pp., Springer Science + Business Media B. V., 2009a. Zerefos, C. S., Eleftheratos, K., Meleti, C., Kazadzis, S., Romanou, A., Ichoku, C., Tselioudis, G., and Bais, A.: Solar dimming and brightening over Thessaloniki, Greece, and Beijing, China, Tellus, 61B, 657–665, http://dx.doi.org/10.1111/j.1600-0889.2009.00425.xdoi:10.1111/j.1600-0889.2009.00425.x, 2009b.