Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 7 3 2007 10.5194/acp-7-575-2007 http://www.atmos-chem-phys.net/7/575/2007/ http://www.atmos-chem-phys.net/7/575/2007/acp-7-575-2007.html http://www.atmos-chem-phys.net/7/575/2007/acp-7-575-2007.pdf 575 586 2007-01-31 On the variability of the Ring effect in the near ultraviolet: understanding the role of aerosols and multiple scattering A. O. Langford andrew.o.langford@noaa.gov R. Schofield J. S. Daniel R. W. Portmann M. L. Melamed H. L. Miller E. G. Dutton S. Solomon NOAA Earth System Research Laboratory/Chemical Sciences Division, Boulder, Colorado NOAA Earth System Research Laboratory/Global Monitoring Division, Boulder, Colorado CIRES, University of Colorado, Boulder, Colorado now at: Alfred-Wegener-Institute for Polar and Marine Research, Research Department Potsdam, Potsdam, Germany The "filling-in" (FI) of Fraunhofer lines, often referred to as the Ring effect, was examined using measurements of near ultraviolet sunlight scattered from the zenith sky above Boulder, Colorado during July and August 2005. The FI of the 344.1 nm Fe I line was directly determined by comparing direct sun and cloud-free zenith sky spectra recorded on the same day. The results, obtained over solar zenith angles (SZA) from 20° to 70°, are compared to the predictions of a simple rotational Raman Scattering (RRS) spectral model. The measured FI was found to be up to 70% greater than that predicted by first-order molecular scattering with a much stronger SZA dependence. Simultaneously measured aerosol optical depths and Monte Carlo calculations show that the combination of aerosol scattering and second-order molecular scattering can account for these differences, and potentially explain the contradictory SZA dependences in previously published measurements of FI. These two scattering processes also introduce a wavelength dependence to FI that complicates the fitting of diffuse sunlight observations in differential optical absorption spectroscopy (DOAS). A simple correction to improve DOAS retrievals by removing this wavelength dependence is described. Aben, I., Stam, D. M., and Helderman, F.: The Ring effect in skylight polarization, Geophys. Res. Lett., $28$, 519–522, 2001. Andrews, E., Sheridan, P. J., M. Fiebig, M., McComiskey, A., Ogren, J. A., Arnott, P., Covert, D., Elleman, R., Gasparini, R., Collins, D., Jonsson, H., Schmid, B., and Wang, J.: Comparison of methods for deriving aerosol asymmetry parameter, J. Geophys. Res., $111$, D05S04, doi:10.1029/2004JD005734, 2006. Barmore, F. E.: The filling-in of Fraunhofer line in the day sky, J. Atmos. Sci., $32$, 1489–1493, 1975. Bobrowski, N., Honninger, G., Galle, B., and Platt, U.: Detection of bromine monoxide in a volcanic plume, Nature, $423$, 273–276, 2003. Brinkmann, R. T.: Rotational Raman scattering in planetary atmospheres, Astrophys. J., $154$, 1087–1093, 1968. Burrows, J., Vountas, M., Haug, H., Chance, K., Marquard, L., Muirhead, K., Platt, U., Richter, A., and Rozanov, V. V.: Study of the Ring Effect, ESA Contract 10996/94/NL/CN (European Space Agency, Noordivijk, The Netherlands), 1996. Burrows, J. P., Richter, A., Dehn, A., Deters, B., Himmelmann, S., Voight, S., and Orphal, J.: Atmospheric remote-sensing reference data from GOME: Part 2. Temperature-dependent absorption cross sections of O₃ in the 231–794 nm range, J. Quant. Spectros. Radiat. Transfer, 509–517, 1999. Chance, K. V. and Spurr, R. J. D.: Ring effect studies: Rayleigh scattering, including molecular parameters for rotational Raman scattering, and the Fraunhofer spectrum, Appl. Opt., $36$, 5224–5230, 1997. Chanin, M.-L.: Filling in of the Fraunhofer lines by scattering on the ground, J. Geophys. Res., $80$, 2859–2862, 1975. Conde, M., Greet, P., and Jacka, F.: The Ring effect in the sodium D2 Fraunhofer line of day skylight over Mawson, Antarctica, J. Geophys. Res., $97$, 11 561–11 565, 1992. de Beek, R., Vountas, M., Rozanov, V. V., Richter, A., and Burrows, J. P.: The Ring Effect in the cloudy atmosphere, Geophys. Res. Lett., $28$, 721–724, 2001. Dvorjashin, S. V.: Fraunhofer lines "filling in" in clouds, Atmos. Ocean. Phys., $30$, 456–460, 1995. Fish, D. J. and Jones, R. L.: Rotational Raman scattering and the Ring effect in zenith-sky spectra, Geophys. Res. Lett., $22$, 811–814, 1995. Grainger, J. F. and Ring, J.: Anomalous Fraunhofer line profiles, Nature, $193$, 762, 1962. Gray, D. F., Tychner, C., and Brown, K.: Spectral-line profiles in daytime sunlight, Publ. Astron. Soc. Pac., $112$, 328–334, 2000. Greenblatt, G. D., Orlando, J. J., Burkholder, J. B., and Ravishankara, A. R.: Absorption measurements of oxygen between 330 and 1140 nm, J. Geophys. Res., $95$, 18 577–18 582, 1990. Harrison, A. W.: Diurnal variation of the Ring effect, Can. J. Phys., $54$, 1000–1005, 1976. Harrison, L., Michalsky, J., and Berndt, J.: Automated Multifilter Rotating Shadow-Band Radiometer: An Instrument for Optical Depth and Radiation Measurements, Appl. Opt., $33$, 5118–5125, 1994. Henyey, L. G. and Greenstein, J. L.: Diffuse radiation in the Galaxy, Astrophys. J., $93$, 1941. Herman, J. R., Celarier, E., and Larko, D.: UV 380 nm reflectivity of the Earth's surface, clouds, and aerosols, J. Geophys. Res., $106$, 5335–5351, 2001. Hunten, D. M.: Surface albedo and the filling-in of Fraunhofer lines in the day sky, Astrophys. J., $159$, 1107–1110, 1970. Johnston, P. V. and McKenzie, R. L.: NO₂ observations at 45\r S during the decreasing phase of solar cycle 21, from 1980 to 1987, J. Geophys. Res., $94$, 3473–3486, 1989. Joiner, J. and Bhartia, P. K.: The determination of cloud pressures from rotational Raman scattering in satellite backscatter ultraviolet measurements, J. Geophys. Res., $100$, 23 019–23 026, 1995. Joiner, J., Bhartia, P. K., Cebula, R. P., Hilsenrath, E., McPeters, R. D., and Park, H.: Rotational Raman scattering (Ring effect) in satellite backscatter ultraviolet measurements, Appl. Opt., $34$, 4513–4525, 1995. Kattawar, G. W., Young, A. T., and Humphreys, T. J.: Inelastic scattering in planetary atmospheres. I. The Ring effect, without aerosols, Astrophys. J., $243$, 1049–1057, 1981. Kurucz, R. L., Furenlid, I., Brault, J., and Testerman, L.: Solar Flux Atlas from 296 to 1300 nm, National Solar Observatory, Atlas No. 1, 19984. Li, Z., Shaw, P.-S., Arp, U., Yoon, H., Saunders, R. D., and Lykke, K. R.: Characterization of integrating spheres for ultraviolet radiometry, paper presented at Sixth Workshop on Ultraviolet Radiation Measurements, Davos, Switzerland, 28 October 2005, 2006. Liu, X., Chance, K., Sioris, C. E., Spurr, R. J. D., Kurosu, T. P., Martin, R. V., and Newchurch, M. J.: Ozone profiling and tropspheric ozone retrievals from the Global Ozone Monitoring Experiment: Algorithm description and validation, J. Geophys. Res., $110$, D20307, doi:20310.21029/22005JD006240, 2005. Michalsky, J., Schlemmer, J., Berkheiser III, W., Berndt, J., Harrison, L., Laulainen, N., Larson, N., and Barnard , J.: Multi-Year Measurements of Aerosol Optical Depth in the Atmospheric Radiation Measurement and Quantitative Links Programs, J. Geophys. Res., $106$, 12 099–12 107, 2001. Mills, M. J., Langford, A. O., O'Leary, T. J., Arpag, K., Miller, H. L., Proffitt, M. H., Sanders, R. W., and Solomon, S.: On the relationship between stratospheric aerosols and nitrogen dioxide, Geophysical Research Letters, $20$, 1187–1190, 1993. Noxon, J. and Goody, R.: Noncoherent scattering of skylight, Atmos. Ocean. Phys., $1$, 163–166, 1965. Noxon, J. F., Whipple, E. C., and Hyde, R. S.: Stratospheric NO₂ 1. Observational method and behavior at mid-latitude, J. Geophys. Res., $84$, 5047–5065, 1979. Pallamraju, D., Baumgardner, J., and Chakrabarti, S.: A multiwavelength investigation into the Ring effect in the day sky spectrum, Geophys. Res. Lett., $27$, 1875–1878, 2000. Schofield, R., Connor, B. J., Kreher, K., Johnston, P. V., and Rodgers, C. D.: The retrieval of profile and chemical information from ground-based UV-Visible spectroscopic measurements, J. Quant. Spectros. Radiat. Transfer, $86$, 115-131, 2004. Shefov, N. N.: Spectroscopic, photoelectric, and radar investigations of the aurora and the nightglow, Izd. Akad. Nauk., $1$, 1959. Sioris, C. E., Courreges-Lacoste, G. B., and Stoll, M.-P.: Filling in of Fraunhofer lines by plant fluorescence: Simulations for a nadir-viewing satellite-borne instrument, J. Geophys. Res., $108$, 4133, doi:10.129/2001JD001321, 2003. Sioris, C. E. and Evans, W. F. J.: Filling in of Fraunhofer and gas-absorption lines in sky spectra as caused by rotational Raman scattering, Appl. Opt., $38$, 2706–2713, 1999. Sioris, C. E. and Evans, W. F. J.: Impact of rotational Raman scattering in the O₂ A band, Geophys. Res. Lett., $27$, 4085–4088, 2000. Sioris, C. E. and Evans, W. F. J.: Modeling higher order radiation fields using iterated integrals of phase functions, J. Quant. Spec. Rad. Trans., $72$, 227–236, 2002. Sioris, C. E., Evans, W. F. J., Gattinger, R. L., McDade, I. C., Degenstein, D. A., and Llewellyn, E. J.: Ground-based Ring-effect measurements with the OSIRIS development model, Can. J. Phys., $80$, 483–491, 2002. Solomon, S., Schmeltekopf, A. L., and Sanders, R. W.: On the interpretation of zenith sky absorption measurements, J. Geophys. Res., $92$, 8311–8319, 1987. Stam, D. M., Aben, I., and Helderman, F.: Skylight polarization spectra: Numerical simulation of the Ring effect, J. Geophys. Res., $107$, 4419, doi:10:1029/2001JD000951, 2002. Stamnes, K., Tsay, S. C., Wiscombe, W., and Jayaweera, K.: A numerically stable algorithm for discrete-ordinate-method radiative transfer in scattering and emitting layered media, Appl. Opt., $27$, 2502–2509, 1988. Vountas, M., Rozanov, V. V., and Burrows, J. P.: Ring effect: Impact of rotational Raman scattering on radiative transfer in Earth's atmosphere, J. Quant. Spectros. Radiat. Transfer, $60$, 943–961, 1998. Wagner, T., Dix, B., v. Friedburg, C., Frieß, U., Sanghavi, S., Sinreich, R., and Platt, U.: MAX-DOAS O₄ measurements: A new technique to derive information on atmospheric aerosols-Principles and information content, J. Geophys. Res., $109$, D22205, doi:10.1029/2004JD004904, 2004. Wagner, T. F., Chance, K., Freiß, U., Gil, M., Goutail, F., Hönninger, G., Johnston, P. V., Karlsen-Tørnkvist, K., Kostadinov, I., Leser, H., Petritoli, A., Richter, A., Van Roozendael, M., and Platt, U.: Correction of the Ring effect and I$_0$-effect for DOAS observations of scattered sunlight, paper presented at 1st DOAS Workshop, Heidelberg, Germany, 13-14 September, 2001. Wagner, T. F., von Freideburg, C., Wenig, M., Otten, C., and Platt, U.: UV-visible observations of atmospheric O₄ absorptions using direct moonlight and zenith-scattered sunlight for clear-sky and cloudy sky conditions, J. Geophys. Res., $107$, 4424, doi:10.1029/2001JD001026, 2002.