eesti teaduste
akadeemia kirjastus
Estonian Journal of Engineering

Relationship between daily relative sunshine duration and relative sum of direct irradiance at Tartu-Tõravere meteorological station in 1967–2008; pp. 12–25

Full article in PDF format | doi: 10.3176/eng.2012.1.02

Kalju Eerme, Ilmar Ansko, Uno Veismann


Solar radiation effects at any site depend strongly on the presence of direct sunshine and on solar elevation. The daily sum of direct irradiance S' on horizontal surface is a more appropriate measure of sunshine energy than the daily sunshine duration Sundur. The latter, however, is more frequently recorded. A long-term data set of both quantities at a typical Estonian rural site, at the Tartu-Tõravere Meteorological Station (58°16'N, 26°28'E, 70 m a.s.l.) is examined on the monthly level. The used daily values are expressed as the ratios relative to normal cloudless conditions S '/S 'clear and Sundur/Sundurclear as well as their ratio R = (S '/S 'clear)/(Sundur/Sundurclear). The study was performed on the level of monthly totals and also of daily values meeting the condition Sundur/Sundurclear > 0.1 integrated within each month. The minimum values of R, 0.80 for monthly totals and 0.75 for the amount of selected days, were found in July and August due to frequent convective clouds around noon. In March to September the estimated monthly relative direct irradiances using Sundur/Sundurclear and R agreed with the measured ones within ± 10% in more than 70% of cases and within ± 15% in about 90% of cases.


  1. McKenzie, R. L., Liley, J. B. and Björn, L. O. UV radiation: balacing risks and benefits. Photochem. Photobiol., 2009, 85, 88–98.

  2. Norval, M., Lucas, R. M., Cullen, A. P., de Gruijl, F. R., Longstreth, J., Takizavwa, Y. and van der Leun, J. C. The human health effects of ozone depletion and interaction with climate change. Photochem. Photobiol. Sci., 2011, 10, 199.

  3. Springbett, P., Buglass, S. and Young, A. R. Photoprotection and vitamin D status. J. Photochem. Photobiol. B., 2010, 101, 160–168.

  4. Grant, W. B. Relation between prediagnostic serum 25-hydroxyvitamin D level and incidence of breast, colorectal, and other cancers. J. Photochem. Photobiol. B, 2010, 101, 130–136.

  5. Kimlin, M. G. and Tentake, T. D. Occupational exposure to ultraviolet radiation: the duality dilemma. Rev. Environ. Health., 2007, 22, 1–37.

  6. Siani, A. M., Casale, G. R., Diemoz, H., Agnesod, G., Kimlin, M. G., Lang, C. A. and Colosimo, A. Personal UV exposure in high albedo alpine sites. Atmos. Chem. Phys., 2008, 8, 3749–3760.

  7. Siani, A. M., Casale, G. R., Sisto, R., Colosimo, A., Lang, C. A. and Kimlin, M. G. Occupa­tional exposures to solar ultraviolet radiation of vineyard workers in Tuscany (Italy). Photochem. Photobiol., 2011, 87, 925–934.

  8. Schmalwieser, A. W., Cabaj, A., Schauberger, G., Rohn, H., Maier, B. and Maier, H. Facial solar UV exposure of Austrian farmers during occupation. Photochem. Photobiol., 2010, 86, 1404–1413.

  9. Neale, P. J., Helbing, E. W. and Day, T. A. UV effects in aquatic and terrestrial environments. Introduction. Photochem. Photobiol., 2007, 83, 775–776.

10. Belzile, C., Demers, S., Ferreyra, G. A., Schloss, I., Nozais, C., Lacoste, K., Mostajir, B., Roy, S., Gosselin, M., Pelletier, E. et al. UV effects on marine planktonic food webs: A synthesis of results from mesocosm studies. Photochem. Photobiol., 2006, 82, 850–856.

11. Brönnimann, S., Eugster, W. and Wanner, H. Photo-oxidant chemistry in the polluted boundary layer under changing UV-B radiation. Atmos. Environ., 2001, 35, 3789–3797.

12. Lindfors, A., Arola, A., Kaurola, J., Taalas, P. and Svenoe, T. Long-term erythemal UV doses at Sodankylä estimated using total ozone, sunshine duration, and snow depth. J. Geophys. Res., 2003, 108, 4518.

13. Lindfors, A. and Vuilleumier, J. Erythemal UV at Davos (Switzerland), 1926–2003, estimated using total ozone, sunshine duration, and snow depth. J. Geophys. Res., 2005, 110, D02104.

14. Eerme, K., Veismann, U. and Koppel, R. Variations of erythemal ultraviolet irradiance and dose at Tartu/Tõravere, Estonia. Climate Res., 2002, 22, 245–253.

15. Eerme, K., Veismann, U. and Lätt, S. Proxy-based reconstruction of erythemal UV doses over Estonia for 1955–2004. Ann. Geophys., 2006, 24, 1767–1782.

16. Koepke, P., De Backer, H., Bais, A., Curylo, A., Eerme, K., Feister, U., Johnsen, B., Junk, J., Kazantzidis, A., Krzyscin, J. et al. Modelling Solar UV Radiation in the Past: Comparison of the Algorithms and Input Data. Cost Action 726. Earth System Science and Environ­mental Management. Final Report. COST Office, Luxembourg, 2008.

17. Stjern, C. W., Kristjánsson, J. E. and Hansen, A. W. Global dimming and global brightening – an analysis of surface radiation and cloud cover data in northern Europe. Int. J. Climatol., 2009, 29, 643–653.

18. Sanchez-Lorenzo, A., Calbó, A. and Martin-Vide, J. Spatial and temporal trends in sunshine duration over Western Europe (1938–2004). J. Climate, 2008, 21, 6089–6098.

19. Ångström, A. Solar and terrestrial radiation. Q. J. Roy. Meteor. Soc., 1924, 50, 121–126.

20. Prescott, J. A. Evaporation from water surface in relation to solar radiation. Trans. Roy. Soc. Austr., 1940, 40, 114–116.

21. Sen, Z. Fuzzy algorithm for estimation of solar irradiation from sunshine duration. Solar Energy, 1998, 63, 39–49.

22. Sen, Z. Angström equation parameter estimation by unrestricted method. Solar Energy, 2001, 71, 95–107.

23. Cancillo, M. L., Serrano, A., Ruiz, A., Garcia, J. A., Anton, M. and Vaquero, J. M. Solar global radiation and sunshine duration in Extremadura (Spain). Physica Scripta, 2005, T118, 24–28.

24. Mubiru, J. and Banda, E. J. K. B. Estimation of monthly average daily global solar irradiation using artificial neural networks. Solar Energy, 2008, 82, 181–187.

25. Power, H. C. Estimating clear-sky beam irradiation from sunshine duration. Solar Energy, 2001, 71, 217–224.

26. WMO. Manual on the Global Observing System, WMO-No. 544, Geneva, 2003.

27. Eerme, K. Variations of total solar radiation and estimated erythemal UV doses in Estonia during 1953–2004. Ann. der Meteorologie, 2005, No. 41, Bd. 2, 663–666.

28. Russak, V. and Kallis, A. (compilers), Tooming, H. (ed.). Handbook of Estonian Solar Radia­tion Climate. EMHI, Tallinn, 2003.

29. Teral, H., Ohvril, H., Okulov, O., Russak, V., Reinart, A. and Laulainen, N. Spectral aerosol optical thickness from solar broadband direct irradiance – summer 2002, Tõravere, Estonia. J. Aerosol Science, 2004, 35, 547–548.

30. Eerme, K., Kallis, A., Veismann, U. and Ansko, I. Long-term variations of available solar radia­tion on seasonal timescales in 1955–2006 at Tartu-Tõravere Meteorological Station, Estonia. Theor. Appl. Climatol., 2010, 101, 371–379.

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