Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 7 1 2007 10.5194/acpd-7-499-2007 http://www.atmos-chem-phys-discuss.net/7/499/2007/ http://www.atmos-chem-phys-discuss.net/7/499/2007/acpd-7-499-2007.html http://www.atmos-chem-phys-discuss.net/7/499/2007/acpd-7-499-2007.pdf 499 535 2007-01-15 Simulation of solar radiation during a total solar eclipse: a challenge for radiative transfer C. Emde claudia.emde@dlr.de B. Mayer Institut für Physik der Atmosphäre, Deutsches Zentrum für Luft- und Raumfahrt (DLR), Oberpfaffenhofen, 82234 Wessling, Germany A solar eclipse is a rare but spectacular natural phenomenon and furthermore it is a challenge for radiative transfer modeling. Whereas a simple one-dimensional radiative transfer model with reduced solar irradiance at the top of the atmosphere can be used to calculate the brightness during partial eclipses a much more sophisticated model is required to calculate the brightness (i.e. the diffuse radiation) during the total eclipse. The reason is that radiation reaching a detector in the shadow gets there exclusively by horizontal (three-dimensional) transport of photons in a spherical shell atmosphere. In this study the first accurate simulations are presented examplified by the solar eclipse at 29 March 2006. Using a backward Monte Carlo model we calculated the diffuse radiation in the umbra and simulated the changing colors of the sky. Radiance and irradiance are decreased by 3 to 4 orders of magnitude, depending on wavelength. We found that aerosol has a comparatively small impact on the radiation in the umbra. We also estimated the contribution of the solar corona to the radiation under the umbra and found that it is negligible compared to the diffuse solar radiation in most parts of the spectrum. Spectrally resolved measurements in the umbra are not yet available. They are challenging due to the low intensity and therefore need careful planning. The new model may be used to support measurements during future solar eclipses. Anderson, G., Clough, S., Kneizys, F., Chetwynd, J., and Shettle, E.: AFGL Atmospheric Constituent Profiles (0-120 km), Tech. Rep. AFGL-TR-86-0110, AFGL (OPI), Hanscom AFB, MA 01736, 1986. Aplin, K L. and Harrison, R G.: Meteorological effects of the eclipse of 11 August 1999 in cloudy and clear conditions, Proc. R. Soc. Lond. A, 459, 353–371, 2003. Blumthaler, M., Bais, A., Webb, A., Kazadzis, S., Kift, R., Kouremeti, N., Schallhart, B., and Kazantzidis, A.: Variations of solar radiation at the Earth's surface during the total solar eclipse of 29 March 2006, in: SPIE Proceedings, Stockholm, 2006. Cahalan, R., Oreopoulos, L., Marshak, A., Evans, K., Davis, A., Pincus, R., Yetzer, K., Mayer, B., Davies, R., Ackerman, T., H.W., B., Clothiaux, E., Ellingson, R., Garay, M., Kassianov, E., Kinne, S., Macke, A., O'Hirok, W., Partain, P., Prigarin, S., Rublev, A., Stephens, G., Szczap, F., Takara, E., Varnai, T., Wen, G., and Zhuraleva, T.: The International Intercomparison of 3D Radiation Codes (I3RC): Bringing together the most advanced radiative transfer tools for cloudy atmospheres, Bull. Am. Meteorol. Soc., 86, 1275–1293, 2005. Dahlback, A. and Stamnes, K.: A new spherical model for computing the radiation field available for photolysis and heating at twilight, Planet. Space Sci., 39, 671–683, 1991. Espenak, F. and Anderson, J.: Total solar eclipse of 2006 March 29, Tech. rep., Goddard Space Flight Centre, 2004. Fabian, P., Winterhalter, M., Rappenglück, B., Reitmayer, H., Stohl, A., Koepke, P., Schlager, H., Berresheim, H., Foken, T., Wichura, B., Häberle, K.-H., Matyssek, R., and Kartschall, T.: The BAYSOFI Campain- Measurements carried out during the total solar eclipse of August 11, 1999, Meteorologische Zeitschrift, 10, 165–170, 2001. Koepke, P., Reuder, J., and Schween, J.: Spectral variation of the solar radiation during an eclipse, Meteorologische Zeitschrift, 10, 179–186, 2001. Koutchmy, S.: Coronal physics from eclipse observations, Adv. Space Res., 14, 29–39, 1994. Marshak, A. and Davis, A. (Eds.): 3D radiative transfer in cloudy atmospheres, Springer, Berlin, Heidelberg, New York, 2005. Mayer, B.: I3RC phase 1 results from the MYSTIC Monte Carlo model, in: Intercomparison of three-dimensional radiation codes: Abstracts of the first and second international workshops, pp. 49–54, University of Arizona Press, iSBN 0-9709609-0-5, 1999. Mayer, B.: I3RC phase 2 results from the MYSTIC Monte Carlo model, in: Intercomparison of three-dimensional radiation codes: Abstracts of the first and second international workshops, pp. 107–108, University of Arizona Press, iSBN 0-9709609-0-5, 2000. 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, 2005. Mayer, B., Kylling, A., Madronich, S., and Seckmeyer, G.: Enhanced absorption of UV radiation due to multiple scattering in clouds: experimental evidence and theoretical explanation, J. Geophys. Res., 103, 31 241–31 254, 1998. November, L J. and Koutchmy, S.: White-light coronal dark threads and density fine structure, Astrophys. J., 466, 512–528, 1996. Sharp, W E., Silverman, S M., and Lloyd, J W F.: Summary of sky brightness measurements during eclipses of the sun, Appl. Opt., 10, 1207–1210, 1971. Shaw, G E.: Sky brightness and polarization during the 1973 African eclipse, Appl. Opt., 14, 388–394, 1975. Shaw, G E.: Sky radiance during a total solar eclipse: a theoretical model, Appl. Opt., 17, 272–278, 1978. Shettle, E.: Models of aerosols, clouds and precipitation for atmospheric propagation studies, in: Atmospheric propagation in the uv, visible, ir and mm-region and related system aspects, no. 454 in AGARD Conference Proceedings, 1989. Silverman, S M. and Mullen, E G.: Sky brightness during eclipses: a review, Appl. Opt., 14, 2838–2843, 1975. Walker, J.: Colour Rendering of Spectra, http://www.fourmilab.ch/documents/specrend, 2003.