Abstract

Zenith skylight is often distinctly blue during clear civil twilights, and much of this color is due to preferential absorption at longer wavelengths by ozone’s Chappuis bands. Because stratospheric ozone is greatly depleted in the austral spring, such decreases could plausibly make Antarctic twilight colors less blue then, including at the zenith. So for several months in 2005, we took digital images of twilight zenith and antisolar skies at Antarctica’s Georg von Neumayer Station. Our colorimetric analysis of these images shows only weak correlations between ozone concentration and twilight colors. We also used a spectroradiometer at a midlatitude site to measure zenith twilight spectra and colors. At both locations, spectral extinction by aerosols seems as important as ozone absorption in explaining colors seen throughout the twilight sky.

© 2011 Optical Society of America

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References

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  1. E. O. Hulburt, “Explanation of the brightness and color of the sky, particularly the twilight sky,” J. Opt. Soc. Am. 43, 113–118 (1953).
    [CrossRef]
  2. J. Dubois, “Contribution a l’étude de l’ombre de la terre,” Ann. Géophys. 7, 103–107, 145–163 (1951).
  3. M. Gadsden, “The colour of the zenith twilight sky: absorption due to ozone,” J. Atmos. Terr. Phys. 10, 176–180 (1957).
    [CrossRef]
  4. N. B. Divari, “Variations in the color of the twilight sky,” Dokl. Akad. Nauk SSSR 122, 795–798 (1958).
  5. F. E. Volz and R. M. Goody, “The intensity of the twilight and upper atmospheric dust,” J. Atmos. Sci. 19, 385–406 (1962).
    [CrossRef]
  6. M. Gadsden, “The colour of the zenith twilight sky: absorption due to ozone,” J. Atmos. Terr. Phys. 10, 176–180 (1957).
    [CrossRef]
  7. G. V. Rozenberg, Twilight: A Study in Atmospheric Optics(Plenum, 1966), pp. 216, 236–249.
  8. F. E. Volz, “Twilights and stratospheric dust before and after the Agung eruption,” Appl. Opt. 8, 2505–2517 (1969).
    [CrossRef] [PubMed]
  9. J. V. Dave and C. L. Mateer, “The effect of stratospheric dust on the color of the twilight sky,” J. Geophys. Res. 73, 6897–6913 (1968).
    [CrossRef]
  10. R. L. Lee, Jr. and J. Hernández-Andrés, “Measuring and modeling twilight’s purple light,” Appl. Opt. 42, 445–457 (2003).
    [CrossRef] [PubMed]
  11. W. G. Blättner, H. G. Horak, D. G. Collins, and M. B. Wells, “Monte Carlo studies of the sky radiation at twilight,” Appl. Opt. 13, 534–547 (1974).
    [CrossRef] [PubMed]
  12. C. N. Adams, G. N. Plass, and G. W. Kattawar, “The influence of ozone and aerosols on the brightness and color of the twilight sky,” J. Atmos. Sci. 31, 1662–1674 (1974).
    [CrossRef]
  13. K. L. Coulson, “Characteristics of skylight at the zenith during twilight as indicators of atmospheric turbidity. 2: Intensity and color ratio,” Appl. Opt. 20, 1516–1524 (1981).
    [CrossRef] [PubMed]
  14. C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation (Wiley-VCH, 2006), pp. 409–415.
  15. C. F. Bohren and A. B. Fraser, “Colors of the sky,” Phys. Teach. 23, 267–272 (1985).
    [CrossRef]
  16. S. D. Gedzelman, “Simulating colors of clear and partly cloudy skies,” Appl. Opt. 44, 5723–5736 (2005).
    [CrossRef] [PubMed]
  17. D. K. Lynch and W. Livingston, Color and Light in Nature (Cambridge, 1995), p. 38.
  18. J. C. Naylor, Out of the Blue: A 24-hour Skywatcher’s Guide (Cambridge, 2002), p. 71.
  19. P. Pesic, Sky in a Bottle (MIT Press, 2005), pp. 173–175.
  20. G. Hoeppe, Why the Sky is Blue: Discovering the Color of Life (Princeton, 2007), pp. 259–260, 308 n. 16.
  21. J. C. Farman, B. G. Gardiner, and J. D. Shanklin, “Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction,” Nature 315, 207–210 (1985). For our purposes, the atmospheric chemistry and dynamics that drive Antarctica’s ozone fluctuations are just means to an optical end, so we do not consider its ozone meteorology in detail.
    [CrossRef]
  22. E. O. Hulburt, “Explanation of the brightness and color of the sky, particularly the twilight sky,” J. Opt. Soc. Am. 43, 113–118 (1953).
    [CrossRef]
  23. C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation (Wiley-VCH, 2006), pp. 409–415.
  24. The LOWTRAN7 radiative transfer model is described in R. W. Fenn, S. A. Clough, W. O. Gallery, R. E. Good, F. X. Kneizys, J. D. Mill, L. S. Rothman, E. P. Shettle, and F. E. Volz, “Optical and infrared properties of the atmosphere,” Handbook of Geophysics and the Space Environment, A.S.Jursa, ed. (Air Force Geophysics Laboratory, Hanscom Air Force Base, 1985), pp. 18:44–51.
  25. A Dobson unit or DU is 2.69×1020 O3 molecules/m2, equivalent to 100 times the thickness in millimeters of total column ozone reduced to a uniform layer at surface pressure and 0 °C.
  26. LOWTRAN7 model parameters used throughout this paper include a default subarctic winter atmospheric profile of temperature, pressure, humidity, and gas mixing ratios; a surface temperature of −10 °C; tropospheric aerosols typical of rural sites; background stratospheric dust and other aerosols (i.e., ordinary rather than volcanic twilights); no clouds or rain; multiple scattering; a surface diffuse albedo of 0.85 that simulates snowcover; and Mie aerosol phase functions. To decrease ozone concentration from its maximum in the subarctic winter model, we use different vertical distributions of ozone from other LOWTRAN7 default models.
  27. C. F. Bohren and A. B. Fraser, “Colors of the sky,” Phys. Teach. 23, 267–272 (1985).
    [CrossRef]
  28. R. L. Lee, Jr., “Measuring overcast colors with all-sky imaging,” Appl. Opt. 47, H106–H115 (2008).
    [CrossRef] [PubMed]
  29. Neumayer Station meteorological data is archived at http://www.awi.de/en/infrastructure/stations/neumayer_station/observatories/meteorological_observatory/data_access/.
  30. Images that include the topographic horizon are centered a few degrees above it.
  31. See R. L. Lee, Jr., “What are ‘all the colors of the rainbow’?,” Appl. Opt. 30, 3401–3407, 3545 (1991) for a quantitative definition of chromaticity gamut.
    [CrossRef] [PubMed]
  32. MacAdam JNDs are described in G. Wyszecki and W. S. Stiles, Color Science: Concepts and Methods, Quantitative Data and Formulae (Wiley, 1982, 2nd ed.), pp. 306–310.
  33. Smaller p-values mean that the observed correlation is less likely to have arisen by chance. Thus for a given r, a smaller p-value indicates higher confidence in r’s reliability.
  34. C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation (Wiley-VCH, 2006), Fig. 8.15.
    [CrossRef]
  35. C. N. Adams, G. N. Plass, and G. W. Kattawar, “The influence of ozone and aerosols on the brightness and color of the twilight sky,” J. Atmos. Sci. 31, 1662–1674 (1974).
    [CrossRef]
  36. R. Weller and A. Lampert, “Optical properties and sulfate scattering efficiency of boundary layer aerosol at coastal Neumayer Station, Antarctica,” J. Geophys. Res. 113, D16208(2008).
    [CrossRef]
  37. C. Rathke, J. Notholt, J. Fischer, and A. Herber, “Properties of coastal Antarctic aerosol from combined FTIR spectrometer and sun photometer measurements,” Geophys. Res. Lett. 29, 2131 (2002).
    [CrossRef]
  38. Neumayer Station aerosol data is archived at http://www.awi.de/en/infrastructure/stations/neumayer_station/observatories/air_chemistry_observatory/data_download/.
  39. All date stamps in Fig.  (Media 1) are for the ozone soundings closest in time to its photographs. These coincide with the photography and Σ(βaer) dates except for 11 September 2005, for which photographs were taken one day earlier.
  40. PR-650 spectroradiometer from Photo Research, Inc., 9731 Topanga Canyon Place, Chatsworth, Calif. 91311. According to Photo Research, at specified radiance levels, a properly calibrated PR-650 measures luminance and radiance accurate to within ±4%, has a spectral accuracy of ±2 nm, and its CIE 1931 colorimetric errors are x<0.001, y<0.001 for a 2856 K blackbody (CIE standard illuminant A).
  41. Sun photometer data on τaer,λ is acquired and archived by AERONET at http://aeronet.gsfc.nasa.gov. Figure ’s τaer data is from the stations closest to Owings: Goddard Space Flight Center in Greenbelt, Maryland and the Smithsonian Environmental Research Center in Edgewater, Maryland.
  42. Surface-based Dobson spectrophotometer data is archived by the Meteorological Service of Canada at http://www.woudc.org/data_e.html. Figure ’s ozone data is from the stations closest to Owings: Wallops Island, Virginia and Goddard Space Flight Center in Greenbelt, Maryland.
  43. Some aerosol concentrations and composition in this region are analyzed in B. I. Magi, P. V. Hobbs, T. W. Kirchstetter, T. Novakov, D. A. Hegg, S. Gao, J. Redemann, and B. Schmid, “Aerosol properties and chemical apportionment of aerosol optical depth at locations off the U. S. east coast in July and August 2001,” J. Atmos. Sci. 62, 919–933 (2005).
    [CrossRef]
  44. C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation (Wiley-VCH, 2006), Fig. 8.13.
    [CrossRef]
  45. R. L. Lee, Jr. and J. Hernández-Andrés, “Measuring and modeling twilight’s purple light,” Appl. Opt. 42, 445–457(2003).
    [CrossRef] [PubMed]
  46. E. O. Hulburt, “Explanation of the brightness and color of the sky, particularly the twilight sky,” J. Opt. Soc. Am. 43, 113–118 (1953).
    [CrossRef]
  47. C. F. Bohren, Clouds in a Glass of Beer: Simple Experiments in Atmospheric Physics (Wiley, 1987), pp. 91–97.
  48. P. Pesic, “A simple explanation of blue suns and moons,” Eur. J. Phys. 29, N31–N36 (2008).
    [CrossRef]
  49. G. Hoeppe, Why the Sky is Blue: Discovering the Color of Life (Princeton, 2007), pp. 235–237.
  50. G. Wyszecki and W. S. Stiles, Color Science: Concepts and Methods, Quantitative Data and Formulae (Wiley, 1982, 2nd ed.), p. 406.

2008 (3)

R. L. Lee, Jr., “Measuring overcast colors with all-sky imaging,” Appl. Opt. 47, H106–H115 (2008).
[CrossRef] [PubMed]

R. Weller and A. Lampert, “Optical properties and sulfate scattering efficiency of boundary layer aerosol at coastal Neumayer Station, Antarctica,” J. Geophys. Res. 113, D16208(2008).
[CrossRef]

P. Pesic, “A simple explanation of blue suns and moons,” Eur. J. Phys. 29, N31–N36 (2008).
[CrossRef]

2005 (2)

Some aerosol concentrations and composition in this region are analyzed in B. I. Magi, P. V. Hobbs, T. W. Kirchstetter, T. Novakov, D. A. Hegg, S. Gao, J. Redemann, and B. Schmid, “Aerosol properties and chemical apportionment of aerosol optical depth at locations off the U. S. east coast in July and August 2001,” J. Atmos. Sci. 62, 919–933 (2005).
[CrossRef]

S. D. Gedzelman, “Simulating colors of clear and partly cloudy skies,” Appl. Opt. 44, 5723–5736 (2005).
[CrossRef] [PubMed]

2003 (2)

2002 (1)

C. Rathke, J. Notholt, J. Fischer, and A. Herber, “Properties of coastal Antarctic aerosol from combined FTIR spectrometer and sun photometer measurements,” Geophys. Res. Lett. 29, 2131 (2002).
[CrossRef]

1991 (1)

1985 (3)

J. C. Farman, B. G. Gardiner, and J. D. Shanklin, “Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction,” Nature 315, 207–210 (1985). For our purposes, the atmospheric chemistry and dynamics that drive Antarctica’s ozone fluctuations are just means to an optical end, so we do not consider its ozone meteorology in detail.
[CrossRef]

C. F. Bohren and A. B. Fraser, “Colors of the sky,” Phys. Teach. 23, 267–272 (1985).
[CrossRef]

C. F. Bohren and A. B. Fraser, “Colors of the sky,” Phys. Teach. 23, 267–272 (1985).
[CrossRef]

1981 (1)

1974 (3)

W. G. Blättner, H. G. Horak, D. G. Collins, and M. B. Wells, “Monte Carlo studies of the sky radiation at twilight,” Appl. Opt. 13, 534–547 (1974).
[CrossRef] [PubMed]

C. N. Adams, G. N. Plass, and G. W. Kattawar, “The influence of ozone and aerosols on the brightness and color of the twilight sky,” J. Atmos. Sci. 31, 1662–1674 (1974).
[CrossRef]

C. N. Adams, G. N. Plass, and G. W. Kattawar, “The influence of ozone and aerosols on the brightness and color of the twilight sky,” J. Atmos. Sci. 31, 1662–1674 (1974).
[CrossRef]

1969 (1)

1968 (1)

J. V. Dave and C. L. Mateer, “The effect of stratospheric dust on the color of the twilight sky,” J. Geophys. Res. 73, 6897–6913 (1968).
[CrossRef]

1962 (1)

F. E. Volz and R. M. Goody, “The intensity of the twilight and upper atmospheric dust,” J. Atmos. Sci. 19, 385–406 (1962).
[CrossRef]

1958 (1)

N. B. Divari, “Variations in the color of the twilight sky,” Dokl. Akad. Nauk SSSR 122, 795–798 (1958).

1957 (2)

M. Gadsden, “The colour of the zenith twilight sky: absorption due to ozone,” J. Atmos. Terr. Phys. 10, 176–180 (1957).
[CrossRef]

M. Gadsden, “The colour of the zenith twilight sky: absorption due to ozone,” J. Atmos. Terr. Phys. 10, 176–180 (1957).
[CrossRef]

1953 (3)

1951 (1)

J. Dubois, “Contribution a l’étude de l’ombre de la terre,” Ann. Géophys. 7, 103–107, 145–163 (1951).

Adams, C. N.

C. N. Adams, G. N. Plass, and G. W. Kattawar, “The influence of ozone and aerosols on the brightness and color of the twilight sky,” J. Atmos. Sci. 31, 1662–1674 (1974).
[CrossRef]

C. N. Adams, G. N. Plass, and G. W. Kattawar, “The influence of ozone and aerosols on the brightness and color of the twilight sky,” J. Atmos. Sci. 31, 1662–1674 (1974).
[CrossRef]

Blättner, W. G.

Bohren, C. F.

C. F. Bohren and A. B. Fraser, “Colors of the sky,” Phys. Teach. 23, 267–272 (1985).
[CrossRef]

C. F. Bohren and A. B. Fraser, “Colors of the sky,” Phys. Teach. 23, 267–272 (1985).
[CrossRef]

C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation (Wiley-VCH, 2006), pp. 409–415.

C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation (Wiley-VCH, 2006), Fig. 8.15.
[CrossRef]

C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation (Wiley-VCH, 2006), Fig. 8.13.
[CrossRef]

C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation (Wiley-VCH, 2006), pp. 409–415.

C. F. Bohren, Clouds in a Glass of Beer: Simple Experiments in Atmospheric Physics (Wiley, 1987), pp. 91–97.

Clothiaux, E. E.

C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation (Wiley-VCH, 2006), pp. 409–415.

C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation (Wiley-VCH, 2006), Fig. 8.13.
[CrossRef]

C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation (Wiley-VCH, 2006), Fig. 8.15.
[CrossRef]

C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation (Wiley-VCH, 2006), pp. 409–415.

Clough, S. A.

The LOWTRAN7 radiative transfer model is described in R. W. Fenn, S. A. Clough, W. O. Gallery, R. E. Good, F. X. Kneizys, J. D. Mill, L. S. Rothman, E. P. Shettle, and F. E. Volz, “Optical and infrared properties of the atmosphere,” Handbook of Geophysics and the Space Environment, A.S.Jursa, ed. (Air Force Geophysics Laboratory, Hanscom Air Force Base, 1985), pp. 18:44–51.

Collins, D. G.

Coulson, K. L.

Dave, J. V.

J. V. Dave and C. L. Mateer, “The effect of stratospheric dust on the color of the twilight sky,” J. Geophys. Res. 73, 6897–6913 (1968).
[CrossRef]

Divari, N. B.

N. B. Divari, “Variations in the color of the twilight sky,” Dokl. Akad. Nauk SSSR 122, 795–798 (1958).

Dubois, J.

J. Dubois, “Contribution a l’étude de l’ombre de la terre,” Ann. Géophys. 7, 103–107, 145–163 (1951).

Farman, J. C.

J. C. Farman, B. G. Gardiner, and J. D. Shanklin, “Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction,” Nature 315, 207–210 (1985). For our purposes, the atmospheric chemistry and dynamics that drive Antarctica’s ozone fluctuations are just means to an optical end, so we do not consider its ozone meteorology in detail.
[CrossRef]

Fenn, R. W.

The LOWTRAN7 radiative transfer model is described in R. W. Fenn, S. A. Clough, W. O. Gallery, R. E. Good, F. X. Kneizys, J. D. Mill, L. S. Rothman, E. P. Shettle, and F. E. Volz, “Optical and infrared properties of the atmosphere,” Handbook of Geophysics and the Space Environment, A.S.Jursa, ed. (Air Force Geophysics Laboratory, Hanscom Air Force Base, 1985), pp. 18:44–51.

Fischer, J.

C. Rathke, J. Notholt, J. Fischer, and A. Herber, “Properties of coastal Antarctic aerosol from combined FTIR spectrometer and sun photometer measurements,” Geophys. Res. Lett. 29, 2131 (2002).
[CrossRef]

Fraser, A. B.

C. F. Bohren and A. B. Fraser, “Colors of the sky,” Phys. Teach. 23, 267–272 (1985).
[CrossRef]

C. F. Bohren and A. B. Fraser, “Colors of the sky,” Phys. Teach. 23, 267–272 (1985).
[CrossRef]

Gadsden, M.

M. Gadsden, “The colour of the zenith twilight sky: absorption due to ozone,” J. Atmos. Terr. Phys. 10, 176–180 (1957).
[CrossRef]

M. Gadsden, “The colour of the zenith twilight sky: absorption due to ozone,” J. Atmos. Terr. Phys. 10, 176–180 (1957).
[CrossRef]

Gallery, W. O.

The LOWTRAN7 radiative transfer model is described in R. W. Fenn, S. A. Clough, W. O. Gallery, R. E. Good, F. X. Kneizys, J. D. Mill, L. S. Rothman, E. P. Shettle, and F. E. Volz, “Optical and infrared properties of the atmosphere,” Handbook of Geophysics and the Space Environment, A.S.Jursa, ed. (Air Force Geophysics Laboratory, Hanscom Air Force Base, 1985), pp. 18:44–51.

Gao, S.

Some aerosol concentrations and composition in this region are analyzed in B. I. Magi, P. V. Hobbs, T. W. Kirchstetter, T. Novakov, D. A. Hegg, S. Gao, J. Redemann, and B. Schmid, “Aerosol properties and chemical apportionment of aerosol optical depth at locations off the U. S. east coast in July and August 2001,” J. Atmos. Sci. 62, 919–933 (2005).
[CrossRef]

Gardiner, B. G.

J. C. Farman, B. G. Gardiner, and J. D. Shanklin, “Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction,” Nature 315, 207–210 (1985). For our purposes, the atmospheric chemistry and dynamics that drive Antarctica’s ozone fluctuations are just means to an optical end, so we do not consider its ozone meteorology in detail.
[CrossRef]

Gedzelman, S. D.

Good, R. E.

The LOWTRAN7 radiative transfer model is described in R. W. Fenn, S. A. Clough, W. O. Gallery, R. E. Good, F. X. Kneizys, J. D. Mill, L. S. Rothman, E. P. Shettle, and F. E. Volz, “Optical and infrared properties of the atmosphere,” Handbook of Geophysics and the Space Environment, A.S.Jursa, ed. (Air Force Geophysics Laboratory, Hanscom Air Force Base, 1985), pp. 18:44–51.

Goody, R. M.

F. E. Volz and R. M. Goody, “The intensity of the twilight and upper atmospheric dust,” J. Atmos. Sci. 19, 385–406 (1962).
[CrossRef]

Hegg, D. A.

Some aerosol concentrations and composition in this region are analyzed in B. I. Magi, P. V. Hobbs, T. W. Kirchstetter, T. Novakov, D. A. Hegg, S. Gao, J. Redemann, and B. Schmid, “Aerosol properties and chemical apportionment of aerosol optical depth at locations off the U. S. east coast in July and August 2001,” J. Atmos. Sci. 62, 919–933 (2005).
[CrossRef]

Herber, A.

C. Rathke, J. Notholt, J. Fischer, and A. Herber, “Properties of coastal Antarctic aerosol from combined FTIR spectrometer and sun photometer measurements,” Geophys. Res. Lett. 29, 2131 (2002).
[CrossRef]

Hernández-Andrés, J.

Hobbs, P. V.

Some aerosol concentrations and composition in this region are analyzed in B. I. Magi, P. V. Hobbs, T. W. Kirchstetter, T. Novakov, D. A. Hegg, S. Gao, J. Redemann, and B. Schmid, “Aerosol properties and chemical apportionment of aerosol optical depth at locations off the U. S. east coast in July and August 2001,” J. Atmos. Sci. 62, 919–933 (2005).
[CrossRef]

Hoeppe, G.

G. Hoeppe, Why the Sky is Blue: Discovering the Color of Life (Princeton, 2007), pp. 259–260, 308 n. 16.

G. Hoeppe, Why the Sky is Blue: Discovering the Color of Life (Princeton, 2007), pp. 235–237.

Horak, H. G.

Hulburt, E. O.

Kattawar, G. W.

C. N. Adams, G. N. Plass, and G. W. Kattawar, “The influence of ozone and aerosols on the brightness and color of the twilight sky,” J. Atmos. Sci. 31, 1662–1674 (1974).
[CrossRef]

C. N. Adams, G. N. Plass, and G. W. Kattawar, “The influence of ozone and aerosols on the brightness and color of the twilight sky,” J. Atmos. Sci. 31, 1662–1674 (1974).
[CrossRef]

Kirchstetter, T. W.

Some aerosol concentrations and composition in this region are analyzed in B. I. Magi, P. V. Hobbs, T. W. Kirchstetter, T. Novakov, D. A. Hegg, S. Gao, J. Redemann, and B. Schmid, “Aerosol properties and chemical apportionment of aerosol optical depth at locations off the U. S. east coast in July and August 2001,” J. Atmos. Sci. 62, 919–933 (2005).
[CrossRef]

Kneizys, F. X.

The LOWTRAN7 radiative transfer model is described in R. W. Fenn, S. A. Clough, W. O. Gallery, R. E. Good, F. X. Kneizys, J. D. Mill, L. S. Rothman, E. P. Shettle, and F. E. Volz, “Optical and infrared properties of the atmosphere,” Handbook of Geophysics and the Space Environment, A.S.Jursa, ed. (Air Force Geophysics Laboratory, Hanscom Air Force Base, 1985), pp. 18:44–51.

Lampert, A.

R. Weller and A. Lampert, “Optical properties and sulfate scattering efficiency of boundary layer aerosol at coastal Neumayer Station, Antarctica,” J. Geophys. Res. 113, D16208(2008).
[CrossRef]

Lee, R. L.

Livingston, W.

D. K. Lynch and W. Livingston, Color and Light in Nature (Cambridge, 1995), p. 38.

Lynch, D. K.

D. K. Lynch and W. Livingston, Color and Light in Nature (Cambridge, 1995), p. 38.

Magi, B. I.

Some aerosol concentrations and composition in this region are analyzed in B. I. Magi, P. V. Hobbs, T. W. Kirchstetter, T. Novakov, D. A. Hegg, S. Gao, J. Redemann, and B. Schmid, “Aerosol properties and chemical apportionment of aerosol optical depth at locations off the U. S. east coast in July and August 2001,” J. Atmos. Sci. 62, 919–933 (2005).
[CrossRef]

Mateer, C. L.

J. V. Dave and C. L. Mateer, “The effect of stratospheric dust on the color of the twilight sky,” J. Geophys. Res. 73, 6897–6913 (1968).
[CrossRef]

Mill, J. D.

The LOWTRAN7 radiative transfer model is described in R. W. Fenn, S. A. Clough, W. O. Gallery, R. E. Good, F. X. Kneizys, J. D. Mill, L. S. Rothman, E. P. Shettle, and F. E. Volz, “Optical and infrared properties of the atmosphere,” Handbook of Geophysics and the Space Environment, A.S.Jursa, ed. (Air Force Geophysics Laboratory, Hanscom Air Force Base, 1985), pp. 18:44–51.

Naylor, J. C.

J. C. Naylor, Out of the Blue: A 24-hour Skywatcher’s Guide (Cambridge, 2002), p. 71.

Notholt, J.

C. Rathke, J. Notholt, J. Fischer, and A. Herber, “Properties of coastal Antarctic aerosol from combined FTIR spectrometer and sun photometer measurements,” Geophys. Res. Lett. 29, 2131 (2002).
[CrossRef]

Novakov, T.

Some aerosol concentrations and composition in this region are analyzed in B. I. Magi, P. V. Hobbs, T. W. Kirchstetter, T. Novakov, D. A. Hegg, S. Gao, J. Redemann, and B. Schmid, “Aerosol properties and chemical apportionment of aerosol optical depth at locations off the U. S. east coast in July and August 2001,” J. Atmos. Sci. 62, 919–933 (2005).
[CrossRef]

Pesic, P.

P. Pesic, “A simple explanation of blue suns and moons,” Eur. J. Phys. 29, N31–N36 (2008).
[CrossRef]

P. Pesic, Sky in a Bottle (MIT Press, 2005), pp. 173–175.

Plass, G. N.

C. N. Adams, G. N. Plass, and G. W. Kattawar, “The influence of ozone and aerosols on the brightness and color of the twilight sky,” J. Atmos. Sci. 31, 1662–1674 (1974).
[CrossRef]

C. N. Adams, G. N. Plass, and G. W. Kattawar, “The influence of ozone and aerosols on the brightness and color of the twilight sky,” J. Atmos. Sci. 31, 1662–1674 (1974).
[CrossRef]

Rathke, C.

C. Rathke, J. Notholt, J. Fischer, and A. Herber, “Properties of coastal Antarctic aerosol from combined FTIR spectrometer and sun photometer measurements,” Geophys. Res. Lett. 29, 2131 (2002).
[CrossRef]

Redemann, J.

Some aerosol concentrations and composition in this region are analyzed in B. I. Magi, P. V. Hobbs, T. W. Kirchstetter, T. Novakov, D. A. Hegg, S. Gao, J. Redemann, and B. Schmid, “Aerosol properties and chemical apportionment of aerosol optical depth at locations off the U. S. east coast in July and August 2001,” J. Atmos. Sci. 62, 919–933 (2005).
[CrossRef]

Rothman, L. S.

The LOWTRAN7 radiative transfer model is described in R. W. Fenn, S. A. Clough, W. O. Gallery, R. E. Good, F. X. Kneizys, J. D. Mill, L. S. Rothman, E. P. Shettle, and F. E. Volz, “Optical and infrared properties of the atmosphere,” Handbook of Geophysics and the Space Environment, A.S.Jursa, ed. (Air Force Geophysics Laboratory, Hanscom Air Force Base, 1985), pp. 18:44–51.

Rozenberg, G. V.

G. V. Rozenberg, Twilight: A Study in Atmospheric Optics(Plenum, 1966), pp. 216, 236–249.

Schmid, B.

Some aerosol concentrations and composition in this region are analyzed in B. I. Magi, P. V. Hobbs, T. W. Kirchstetter, T. Novakov, D. A. Hegg, S. Gao, J. Redemann, and B. Schmid, “Aerosol properties and chemical apportionment of aerosol optical depth at locations off the U. S. east coast in July and August 2001,” J. Atmos. Sci. 62, 919–933 (2005).
[CrossRef]

Shanklin, J. D.

J. C. Farman, B. G. Gardiner, and J. D. Shanklin, “Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction,” Nature 315, 207–210 (1985). For our purposes, the atmospheric chemistry and dynamics that drive Antarctica’s ozone fluctuations are just means to an optical end, so we do not consider its ozone meteorology in detail.
[CrossRef]

Shettle, E. P.

The LOWTRAN7 radiative transfer model is described in R. W. Fenn, S. A. Clough, W. O. Gallery, R. E. Good, F. X. Kneizys, J. D. Mill, L. S. Rothman, E. P. Shettle, and F. E. Volz, “Optical and infrared properties of the atmosphere,” Handbook of Geophysics and the Space Environment, A.S.Jursa, ed. (Air Force Geophysics Laboratory, Hanscom Air Force Base, 1985), pp. 18:44–51.

Stiles, W. S.

MacAdam JNDs are described in G. Wyszecki and W. S. Stiles, Color Science: Concepts and Methods, Quantitative Data and Formulae (Wiley, 1982, 2nd ed.), pp. 306–310.

G. Wyszecki and W. S. Stiles, Color Science: Concepts and Methods, Quantitative Data and Formulae (Wiley, 1982, 2nd ed.), p. 406.

Volz, F. E.

F. E. Volz, “Twilights and stratospheric dust before and after the Agung eruption,” Appl. Opt. 8, 2505–2517 (1969).
[CrossRef] [PubMed]

F. E. Volz and R. M. Goody, “The intensity of the twilight and upper atmospheric dust,” J. Atmos. Sci. 19, 385–406 (1962).
[CrossRef]

The LOWTRAN7 radiative transfer model is described in R. W. Fenn, S. A. Clough, W. O. Gallery, R. E. Good, F. X. Kneizys, J. D. Mill, L. S. Rothman, E. P. Shettle, and F. E. Volz, “Optical and infrared properties of the atmosphere,” Handbook of Geophysics and the Space Environment, A.S.Jursa, ed. (Air Force Geophysics Laboratory, Hanscom Air Force Base, 1985), pp. 18:44–51.

Weller, R.

R. Weller and A. Lampert, “Optical properties and sulfate scattering efficiency of boundary layer aerosol at coastal Neumayer Station, Antarctica,” J. Geophys. Res. 113, D16208(2008).
[CrossRef]

Wells, M. B.

Wyszecki, G.

MacAdam JNDs are described in G. Wyszecki and W. S. Stiles, Color Science: Concepts and Methods, Quantitative Data and Formulae (Wiley, 1982, 2nd ed.), pp. 306–310.

G. Wyszecki and W. S. Stiles, Color Science: Concepts and Methods, Quantitative Data and Formulae (Wiley, 1982, 2nd ed.), p. 406.

Ann. Géophys. (1)

J. Dubois, “Contribution a l’étude de l’ombre de la terre,” Ann. Géophys. 7, 103–107, 145–163 (1951).

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Dokl. Akad. Nauk SSSR (1)

N. B. Divari, “Variations in the color of the twilight sky,” Dokl. Akad. Nauk SSSR 122, 795–798 (1958).

Eur. J. Phys. (1)

P. Pesic, “A simple explanation of blue suns and moons,” Eur. J. Phys. 29, N31–N36 (2008).
[CrossRef]

Geophys. Res. Lett. (1)

C. Rathke, J. Notholt, J. Fischer, and A. Herber, “Properties of coastal Antarctic aerosol from combined FTIR spectrometer and sun photometer measurements,” Geophys. Res. Lett. 29, 2131 (2002).
[CrossRef]

J. Atmos. Sci. (4)

Some aerosol concentrations and composition in this region are analyzed in B. I. Magi, P. V. Hobbs, T. W. Kirchstetter, T. Novakov, D. A. Hegg, S. Gao, J. Redemann, and B. Schmid, “Aerosol properties and chemical apportionment of aerosol optical depth at locations off the U. S. east coast in July and August 2001,” J. Atmos. Sci. 62, 919–933 (2005).
[CrossRef]

F. E. Volz and R. M. Goody, “The intensity of the twilight and upper atmospheric dust,” J. Atmos. Sci. 19, 385–406 (1962).
[CrossRef]

C. N. Adams, G. N. Plass, and G. W. Kattawar, “The influence of ozone and aerosols on the brightness and color of the twilight sky,” J. Atmos. Sci. 31, 1662–1674 (1974).
[CrossRef]

C. N. Adams, G. N. Plass, and G. W. Kattawar, “The influence of ozone and aerosols on the brightness and color of the twilight sky,” J. Atmos. Sci. 31, 1662–1674 (1974).
[CrossRef]

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[CrossRef]

M. Gadsden, “The colour of the zenith twilight sky: absorption due to ozone,” J. Atmos. Terr. Phys. 10, 176–180 (1957).
[CrossRef]

J. Geophys. Res. (2)

J. V. Dave and C. L. Mateer, “The effect of stratospheric dust on the color of the twilight sky,” J. Geophys. Res. 73, 6897–6913 (1968).
[CrossRef]

R. Weller and A. Lampert, “Optical properties and sulfate scattering efficiency of boundary layer aerosol at coastal Neumayer Station, Antarctica,” J. Geophys. Res. 113, D16208(2008).
[CrossRef]

J. Opt. Soc. Am. (3)

Nature (1)

J. C. Farman, B. G. Gardiner, and J. D. Shanklin, “Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction,” Nature 315, 207–210 (1985). For our purposes, the atmospheric chemistry and dynamics that drive Antarctica’s ozone fluctuations are just means to an optical end, so we do not consider its ozone meteorology in detail.
[CrossRef]

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[CrossRef]

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[CrossRef]

Other (24)

C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation (Wiley-VCH, 2006), pp. 409–415.

The LOWTRAN7 radiative transfer model is described in R. W. Fenn, S. A. Clough, W. O. Gallery, R. E. Good, F. X. Kneizys, J. D. Mill, L. S. Rothman, E. P. Shettle, and F. E. Volz, “Optical and infrared properties of the atmosphere,” Handbook of Geophysics and the Space Environment, A.S.Jursa, ed. (Air Force Geophysics Laboratory, Hanscom Air Force Base, 1985), pp. 18:44–51.

A Dobson unit or DU is 2.69×1020 O3 molecules/m2, equivalent to 100 times the thickness in millimeters of total column ozone reduced to a uniform layer at surface pressure and 0 °C.

LOWTRAN7 model parameters used throughout this paper include a default subarctic winter atmospheric profile of temperature, pressure, humidity, and gas mixing ratios; a surface temperature of −10 °C; tropospheric aerosols typical of rural sites; background stratospheric dust and other aerosols (i.e., ordinary rather than volcanic twilights); no clouds or rain; multiple scattering; a surface diffuse albedo of 0.85 that simulates snowcover; and Mie aerosol phase functions. To decrease ozone concentration from its maximum in the subarctic winter model, we use different vertical distributions of ozone from other LOWTRAN7 default models.

Neumayer Station meteorological data is archived at http://www.awi.de/en/infrastructure/stations/neumayer_station/observatories/meteorological_observatory/data_access/.

Images that include the topographic horizon are centered a few degrees above it.

MacAdam JNDs are described in G. Wyszecki and W. S. Stiles, Color Science: Concepts and Methods, Quantitative Data and Formulae (Wiley, 1982, 2nd ed.), pp. 306–310.

Smaller p-values mean that the observed correlation is less likely to have arisen by chance. Thus for a given r, a smaller p-value indicates higher confidence in r’s reliability.

C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation (Wiley-VCH, 2006), Fig. 8.15.
[CrossRef]

G. V. Rozenberg, Twilight: A Study in Atmospheric Optics(Plenum, 1966), pp. 216, 236–249.

C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation (Wiley-VCH, 2006), pp. 409–415.

D. K. Lynch and W. Livingston, Color and Light in Nature (Cambridge, 1995), p. 38.

J. C. Naylor, Out of the Blue: A 24-hour Skywatcher’s Guide (Cambridge, 2002), p. 71.

P. Pesic, Sky in a Bottle (MIT Press, 2005), pp. 173–175.

G. Hoeppe, Why the Sky is Blue: Discovering the Color of Life (Princeton, 2007), pp. 259–260, 308 n. 16.

C. F. Bohren, Clouds in a Glass of Beer: Simple Experiments in Atmospheric Physics (Wiley, 1987), pp. 91–97.

C. F. Bohren and E. E. Clothiaux, Fundamentals of Atmospheric Radiation (Wiley-VCH, 2006), Fig. 8.13.
[CrossRef]

Neumayer Station aerosol data is archived at http://www.awi.de/en/infrastructure/stations/neumayer_station/observatories/air_chemistry_observatory/data_download/.

All date stamps in Fig.  (Media 1) are for the ozone soundings closest in time to its photographs. These coincide with the photography and Σ(βaer) dates except for 11 September 2005, for which photographs were taken one day earlier.

PR-650 spectroradiometer from Photo Research, Inc., 9731 Topanga Canyon Place, Chatsworth, Calif. 91311. According to Photo Research, at specified radiance levels, a properly calibrated PR-650 measures luminance and radiance accurate to within ±4%, has a spectral accuracy of ±2 nm, and its CIE 1931 colorimetric errors are x<0.001, y<0.001 for a 2856 K blackbody (CIE standard illuminant A).

Sun photometer data on τaer,λ is acquired and archived by AERONET at http://aeronet.gsfc.nasa.gov. Figure ’s τaer data is from the stations closest to Owings: Goddard Space Flight Center in Greenbelt, Maryland and the Smithsonian Environmental Research Center in Edgewater, Maryland.

Surface-based Dobson spectrophotometer data is archived by the Meteorological Service of Canada at http://www.woudc.org/data_e.html. Figure ’s ozone data is from the stations closest to Owings: Wallops Island, Virginia and Goddard Space Flight Center in Greenbelt, Maryland.

G. Hoeppe, Why the Sky is Blue: Discovering the Color of Life (Princeton, 2007), pp. 235–237.

G. Wyszecki and W. S. Stiles, Color Science: Concepts and Methods, Quantitative Data and Formulae (Wiley, 1982, 2nd ed.), p. 406.

Supplementary Material (2)

» Media 1: MOV (870 KB)     
» Media 2: MOV (1026 KB)     

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Figures (10)

Fig. 1
Fig. 1

Portion of the CIE 1976 UCS diagram, showing simulated zenith chromaticity coordinates u , v for different unrefracted sun elevations h 0 during twilight and for different amounts of ozone ( O 3 ). The Bohren and Clothiaux model uses molecular single scattering either without ozone or with absorption by 358 column total Dobson units (DU) of ozone. The chromaticity curve generated by LOWTRAN7’s subarctic winter model is drawn in order of increasing ozone concentration.

Fig. 2
Fig. 2

Mean twilight chromaticities measured from Nikon E5700 digital images of the zenith sky (marked with circles) and antisolar sky (marked with ×s) at Neumayer Station, Antarctica from May–October 2005. Sun elevation h 0 is lower for the zenith images because these were taken 15 20 min after the antisolar images during evening twilights. An asymmetric cross labeled “ u , v JNDs” indicates u and v MacAdam just-noticeable differences (JNDs) typical of this range of skylight chromaticities.

Fig. 3
Fig. 3

Scatterplots of Fig. 2’s antisolar and zenith skylight CCTs versus column total ozone as measured by radiosonde at Neumayer Station. For each sky direction, linear regression fits between ozone and CCT are statistically insignificant. Image sequences that are sorted in order of decreasing ozone concentration display these weak correlations for the (a) antisolar (Media 1) and (b) zenith skies (Media 2).

Fig. 4
Fig. 4

Similar radiosonde profiles of ozone partial pressures at Neumayer Station during twilights that were either visibly bluish (12 October 2005, O 3 = 106.9 DU, mean CCT 10030 K ) or reddish (16 October 2005, O 3 = 112.3 DU, mean CCT 9270 K ) at the zenith when h 0 5.2 ° . See Figs. 3a (Media 1) and 3b (Media 2) to compare photographs of these two twilights.

Fig. 5
Fig. 5

Scatterplots of Fig. 2’s antisolar and zenith skylight CCTs versus combined surface aerosol extinction coefficients Σ ( β aer ) as measured by nephelometer at Neumayer Station. Linear regression fits between Σ ( β aer ) and CCT are statistically insignificant: null-hypothesis two-sided p-values are 0.1947 and 0.4760 for the antisolar and zenith data, respectively.

Fig. 6
Fig. 6

LOWTRAN7 zenith chromaticities as functions of meteorological range V for two different ozone concentrations (subarctic winter model, h 0 = 5.2 ° , V = 0.5 70 km ). In this comparison, a very clear atmosphere with less ozone (case C) can have a bluer zenith than a more turbid atmosphere with more ozone (case D).

Fig. 7
Fig. 7

Zenith chromaticities measured during 20 clear twilights at Owings, Maryland with a Photo Research PR-650 spectroradiometer ( 1 ° field of view). The underlying skylight radiance spectra were measured during January–February 2000, January 2001, and April–May 2010 for 5.22 ° h 0 5.13 ° . Chromaticities E and F are this figure’s colorimetric and spectral extremes.

Fig. 8
Fig. 8

Scatterplots of zenith skylight λ d at Owings, Maryland versus (1) column total ozone and (2) ratio of normal aerosol extinction at 440 and 675 nm , τ aer , 440 / τ aer , 675 . The linear correlation r = 0.5218 between λ d and ozone is statistically significant at the 2% level (two-sided p- value = 0.0183 ), whereas the aerosol r = + 0.4013 is significant at the 10% level ( p = 0.0795 ). Because λ d increases as CCT decreases, r’s signs here are reversed compared with zenith r values in Figs. 3, 5.

Fig. 9
Fig. 9

Relative spectral radiances L rel , λ measured at h 0 5.2 ° on two days with visibly different zenith colors at Owings, Maryland. The ratio L rel , λ = L λ ( h 0 = 5.2 ° ) / L λ ( h 0 = + 4.5 ° ) shows the spectral shifts that skylight undergoes between late afternoon and late civil twilight on these dates.

Fig. 10
Fig. 10

LOWTRAN7 zenith chromaticities as a function of observer altitude z above the surface (subarctic winter model, h 0 = 5.2 ° , z = 0 5 km , V = 1.0 km ). Below z = 0.6 km , increasing z makes zenith skylight redder as the observer rises through the densest part of the surface aerosol layer and so receives less multiply scattered skylight. At higher z, rapidly diminishing aerosol extinction above the observer makes skylight bluer.

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