A simple engineering method for calculating the aerosol optical thickness at 500 nm (AOT500) is proposed for Estonian summer conditions. The method is expressed by a single formula and represents a simplified version of a more complicated model developed at Moscow University, which assumes fulfilment of the Ångström formula. For the input our method uses three parameters: (1) the Ångström wavelength exponent (a), which can be given as its seasonal climatological mean; (2) broadband Bouguer coefficient (p2) of atmospheric transparency for optical mass m = 2 (solar elevation » 30°); and (3) the amount of columnar precipitable water vapour (W). The method was evaluated using the AERONET Tõravere data on aerosol optical thickness for three summer months (JJA) during 2002–2004. Because of the absence of high quality data on precipitable water, it was estimated approximately using surface water vapour pressure. Evaluation of the method demonstrated a good overall agreement with the observed AERONET 418 summer values of the AOT500 from 2002–2004. The evaluation also raised doubt that precipitable water is underestimated in our model compared to the AERONET Level 2 Version 1 observations. Due to its simplicity the method can be used for express estimations of the AOT500 under summer conditions in regions with similar climates to the Estonian one. Transition to other wavelengths is available using the Ångström formula.
Ångström, A. 1929. On the atmospheric transmission of sun radiation and on dust in the air. Geogr. ann., 11, 156–166.
Ångström, A. 1930. On the atmospheric transmission of sun radiation. II. Geogr. ann., 12, 130–159.
Carlund, T., Hakansson, B. & Land, P. 2005. Aerosol optical depth over the Baltic Sea derived from AERONET and Sea WiFS measurements. Int. J. Remote Sens., 26(2), 233–245.
Gorbarenko, E. V. 1997. Spatial and temporal variability of the atmospheric aerosol thickness on the territory of former USSR. In IRS ’96: Current Problems in Atmospheric Radiation (Smith, W. L. & Stamnes, K., eds), pp. 774–777. A. Deepak Publishing, Hampton, Virginia, USA.
Gueymard, C. 1998. Turbidity determination from broadband irradiance measurements: a detailed multicoefficient approach. J. Appl. Meteorol., 37,414–435.
Kallis, A., Russak, V. & Ohvril, H. 2005. 100 years of solar radiation measurements in Estonia. World Climate Research Programme, Report of the Eighth Session of the Baseline Surface Radiation Network (BSRN), Workshop and Scientific Review (Exeter, UK, 26–30 July 2004), WCRP Informal Report No. 4, C1–C4.
Ohvril, H., Okulov, O., Teral, H. & Teral, K. 1999. The atmospheric integral transparency coefficient and the Forbes effect. Sol. Energy, 66(4), 305–317.
Okulov, O., Ohvril, H., Teral, H., Tee, M., Russak, V. & Abakumova, G. 2001. Multiannual variability of atmospheric transparency in Estonia and Moscow. In IRS 2000: Current Problems in Atmospheric Radiation (Smith, W. L. & Timofeyev, Yu. M., eds), pp. 725–728. A. Deepak Publishing, Hampton, Virginia, USA.
Okulov, O., Ohvril, H. & Kivi, R. 2002. Atmospheric precipitable water in Estonia, 1990–2001. Boreal Env. Res., 7, 291–300.
Shifrin, K. S. 1995. Simple relationships for the Ångström parameter of disperse systems. Appl. Opt., 34(21), 4480–4485.
Tarasova, T. A. & Yarkho, E. V. 1991a. Determination of atmospheric aerosol optical thickness from land-based measurements of integral direct solar radiation. Meteorol. Gidrol., 12, 66–71 (in Russian).
Tarasova, T. A. & Yarkho, E. V. 1991b. Determination of atmospheric aerosol optical thickness from land-based measurements of integral direct solar radiation. Soviet Meteorol. Hydrol., 12, 53–58 (translation from Russian).
Teral, H., Ohvril, H. & Laulainen, N. 2004. Variability of Ångström coefficients during summer in Estonia. In Fourth Study Conference on BALTEX (24–28 May 2004, Gudhjem, Bornholm, Denmark), Conference Proceedings (Isemer, H.-J., ed.), pp. 82–83. International BALTEX Secretariat, 29.
