Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 7 4 2007 10.5194/acpd-7-12781-2007 http://www.atmos-chem-phys-discuss.net/7/12781/2007/ http://www.atmos-chem-phys-discuss.net/7/12781/2007/acpd-7-12781-2007.html http://www.atmos-chem-phys-discuss.net/7/12781/2007/acpd-7-12781-2007.pdf 12781 12805 2007-08-30 Some considerations about Ångström exponent distributions F. Wagner frankwagner@uevora.pt A. M. Silva Centro de Geofísica, Évora, Portugal Universidade de Évora, Departamento de Física, Évora, Portugal A simulation study has been performed in order to show the influence of the aerosol optical thickness (AOT) distribution together with the corresponding error distribution on the resulting Ångström exponent (AE) distribution. It will be shown that the Ångström exponent frequency of occurrence distribution is only normal distributed when the relative error at the two wavelengths used for estimation of the Ångström exponent is the same. In all other cases a shift of the maximum of the AE-distribution will occur. It will be demonstrated that the Ångström exponent (or the maximum of an AE distribution) will be systematically over- or underestimated depending on whether the relative error of the shorter wavelength is larger or smaller compared with the relative error of the longer wavelength. In such cases the AE distribution are also skewed. Ångström, A.: On the atmospheric transmission of sun radiation and on dust in the air, Geogr. Ann., 11, 156–166, 1929. Ångström, A.: On the atmospheric transmission of sun radiation II, Geogr. Ann., 12, 130–159, 1930. Ångström, A.: Techniques of Determining the Turbidity of the Atmosphere, Tellus, 13, 214–223, 1961. Ångström, A.: The parameters of atmospheric turbidity, Tellus, 16, 64–75, 1964. Cachorro, V. E., Romero, P. M., Toledano, C., Cuevas, E., and de Frutos, A. M.: The fictitious diurnal cycle of aerosol optical depth: A new approach for "in situ" calibration and correction of AOD data series, Geophys. Res. Lett., 31, L12106, doi:10.1029/2004GL019651, 2004. Campanelli, M., Estellés, V., Tomasi, C., Nakajima, T., Malvestuto, V., and Martínez-Lozano, J. A.: Application of the SKYRAD Improved Langley plot method for the in situ calibration of CIMEL Sun–sky photometers, Appl. Optics, 46(14), 2688–2702, 2007. Eck, T. F., Holben, B. N., Reid, J. S., Dubovik, O., Smirnov, A., O'Neill, N. T., Slutsker, I., and Kinne, S.: Wavelength Dependence of the Optical Depth of Biomass Burning, Urban, and Desert Dust Aerosols, J. Geophys. Res., 104(D24), 31 333–31 349, 1999. Gobbi, G. P., Kaufman, Y. J., Koren, I., and Eck, T. F.: Classification of aerosol properties derived from AERONET direct sun data, Atmos. Chem. Phys., 7, 453–458, 2007. Gong, S. L.: A parameterization of sea-salt aerosol source function for sub- and super-micron particles, Global Biogeochem. Cy., 17(4), 1097, doi:10.1029/2003GB002079, 2003. Hamonou, E., Chazette, P., Balis, D., Dulac, F., Schneider, X., Galani, E., Ancellet, G., and Papayannis, A.: Characterization of the vertical structure of Saharan dust export to the Mediterranean basin, J. Geophys. Res., 22 257–22 270, 1999. Holben, B. N., Eck, T. F., Slutsker, I., Tanre, D., Buis, J. P., Setzer, A., Vermote, E., Reagan, J. A., Kaufman, Y. J., Nakajima, T., Lavenu, F., Jankowiac, I., and Smirnov, A.: AERONET – A Federated Instrument Network and Data Archive for Aerosol Characterization, Remote Sens. Environ., 66, 1–16, 1998. Ignatov, A., Stowe, L., and Singh, R.: Sensitivity study of the Angstrom exponent derived from AVHRR over the Oceans, Adv. Space Res., 21(3), 439–442, 1998. Knobelspiesse, K. D., Pietras, C., Fargion, G. S., Wang, M., Frouin, R., Miller, M. A., Subramaniam, A., and Balch, W. M.: Maritime aerosol optical thickness measured by handheld sun photometers, Remote Sens. Environ., 93, 87–106, 2004. O'Neill, N. and Royer, A.: Extraction of bimodal aerosol-size distribution radii from spectral and angular slope (Angstrom) coefficients, Appl. Optics, 32(9), 1642–1645, 1993. O'Neill, N. T., Ignatov, A., Holben, B. N., and Eck, T. F.: The lognormal distribution as a reference for reporting aerosol optical depth statistics; Empirical tests using multi-year, multi-site AERONET sun photometer data, Geophys. Res. Lett., 27(20), 3333–3336, 2000. Remer, L. A., Kaufman, Y. J., Tanre, D., Mattoo, S., Chu, D. A., Martins, J. V., Li, R.-R., Ichoku, C., Levy, R. C., Kleidman, R. G., Eck, T. F., Vermote, E., and Holben, B. N.: The MODIS Aerosol Algorithm, Products and Validation, J. Atmos. Sci., 62(4), 947–973, 2005. Smirnov, A., Holben, B. N., Savoie, D., Prospero, J. M., Kaufman, Y. J., Tanre, D., Eck, T. F., and Slutsker, I.: Relationship between column aerosol optical thickness and in situ ground based dust concentrations over Barbados, Geophys. Res. Lett., 27(11), 1643–1646, 2000. Smirnov, A., Holben, B. N., Eck, T. F., Dubovik, O., and Slutsker, I.: Effect of wind speed on columnar aerosol optical properties at Midway Island, J. Geophys. Res., 108(D24), 4802, doi:10.1029/2003JD003879, 2003. Wai, K.-M. and Tanner, P. A.: Wind-dependent sea salt aerosol in a Western Pacific coastal area, Atmos. Environ., 38, 1167–1171, 2004. Tahnk, W. R. and Coakley Jr., J. A.: Aerosol optical depth and direct radiative forcing for \mboxINDOEX derived from AVHRR: Observations, January–March 1996–2000, J. Geophys. Res., 107(D19), 8010, doi:10.1029/2000JD000183, 2002. Verein Deutscher Ingenieure VDI: Environmental Meteorology: Measurements of the Atmospheric Turbidity Due to Aerosol Particles with Sunphotometers, VDI 3786, 32pp., 1994. Voss, K. J., Welton, J. E. J., Quinn, P. K., Frouin, R., Miller, M., and Reynolds, R. M.: Aerosol optical depth measurements during the Aerosols99 experiment, J. Geophys. Res., 106(D18), 20 811–20 819, 2001. Zhang, K. M., Knipping, E. M., Wexler, A. S., Bhave, P. V., and Tonnesen, G. S.: Size distribution of sea-salt emissions as a function of relative humidity, Atmos. Environ., 39, 3373–3379, 2005.