Abstract

Near-forward scattering by cloud droplets is known to give rise to colored rings, centered on the Sun or the Moon, which are called the corona. Because of the spherical shape of the droplets, the corona can be circular. A Finnish amateur astronomers' network has found a corona, in a seemingly cloudless sky, with a regular vertically elliptical shape. The aspect ratio of these ellipses changes with the altitude of the Sun or the Moon. Some brightening in the coronas has also been reported. Because of observations of high pollen concentrations at the time of occurrence of these coronas, we propose that some coronas can be explained as a result of scattering by birch pollen grains, which are more or less spheroidal. To explain other observed coronas, pollen grains with more complicated shapes, such as pine and spruce pollen grains, must be invoked. Our analysis is limited to spheroidal grains, for which the Fraunhofer theory gives analytical expressions of simple form. The more complicated shapes require numerical simulations or laboratory experiments, which we have not done.

© 1994 Optical Society of America

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  1. W. J. Humphreys, Physics of the Air (McGraw-Hill, New York, 1940), Chap. VI, pp. 547–556.
  2. V Mäkelä, “Värit ja valot,” Ursa Minor No. 4, 16–21 (1993); (news bulletin of Finnish amateur astronomers, Ursa Astronomical Association, Helsinki).
  3. R. A. R. Tricker, Introduction to Meteorological Optics (Elsevier, New York, 1970), Chap. V, pp. 146–168
  4. R. G. Greenler, Rainbows, Halos and Glories (Cambridge U. Press, Cambridge, 1980), Chap. 6.
  5. C. F. Bohren, D. R. Huffman, Absorption and Scattering of Light by Small Particles (Wiley-Interscience, New York, 1981).
  6. H. C. van de Hulst, Light Scattering by Small Particles (Wiley, New York, 1957;reprinted by Dover, New York, 1981), Chap. 13, pp. 228–266; Chap. 20, pp. 414–439.
  7. J. M. Pernter, F. M. Exner, Meteorologische Optik, 2nd ed. (Braumüller, Vienna, 1922), Chap. 2, pp. 445–519.
  8. M. G. J. Minnaert, The Nature of Light and Color in the Outdoors (Springer-Verlag, New York, 1993), articles 183,184, and 189.
  9. W. R. Corliss, Rare Halos, Mirages, Anomalous Rainbows and Related Electromagnetic Phenomena, 1st ed. (Sourcebook Project, Glen Arm, Md., 1984), Chap. GEH, p. 55.
  10. G. Dietze, Einf¨hrung in die Optik der Atmosphäre (Akademische Verlagsgesellschaft Geest&Portig K.-G., Leipzig, 1957), Chap. 6, pp. 101–112.
  11. A.-M. Pessi, A. Rantio-Lehtimäki, eds., The Finnish Pollen Bulletin, supplements to Vols. 14 (1989) (Finnish Aerobiology Group, Department of Biology, University of Turku, Turku, Finland),The Finnish Pollen Bulletin, 15 (1990) (Finnish Aerobiology Group, Department of Biology, University of Turku, Turku, Finland),The Finnish Pollen Bulletin, 16 (1991) (Finnish Aerobiology Group, Department of Biology, University of Turku, Turku, Finland),The Finnish Pollen Bulletin, 17 (1992) (Finnish Aerobiology Group, Department of Biology, University of Turku, Turku, Finland), andThe Finnish Pollen Bulletin, 18 (to appear in 1994) (Finnish Aerobiology Group, Department of Biology, University of Turku, Turku, Finland).
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    [CrossRef] [PubMed]
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  14. G. Erdtman, Introduktion till Palynologin (Bokförlaget Natur och Kultur, Stockholm, 1963), Chap. 7, p. 108.
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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  19. Y. Takano, S. Asano, “Fraunhofer diffraction by ice crystals suspended in the atmosphere,” J. Meteorol. Soc. Jpn. 61, 289–300 (1983).
  20. A. Ashkin, J. M. Dziedzic, “Observation of light scattering from nonspherical particles using optical levitation,” Appl. Opt. 19, 660–668 (1980).
    [CrossRef] [PubMed]

1994 (1)

1991 (2)

1985 (1)

1983 (1)

Y. Takano, S. Asano, “Fraunhofer diffraction by ice crystals suspended in the atmosphere,” J. Meteorol. Soc. Jpn. 61, 289–300 (1983).

1980 (1)

Asano, S.

Y. Takano, S. Asano, “Fraunhofer diffraction by ice crystals suspended in the atmosphere,” J. Meteorol. Soc. Jpn. 61, 289–300 (1983).

Ashkin, A.

Bohren, C. F.

C. F. Bohren, G. Koh, “Forward-scattering corrected extinction by non-spherical particles,” Appl. Opt. 24, 1023–1029 (1985).
[CrossRef] [PubMed]

C. F. Bohren, D. R. Huffman, Absorption and Scattering of Light by Small Particles (Wiley-Interscience, New York, 1981).

Bom, M.

M. Bom, E. Wolf, Principles of Optics, 3rd ed. (Pergamon Press, Oxford, 1965).

Corliss, W. R.

W. R. Corliss, Rare Halos, Mirages, Anomalous Rainbows and Related Electromagnetic Phenomena, 1st ed. (Sourcebook Project, Glen Arm, Md., 1984), Chap. GEH, p. 55.

Dietze, G.

G. Dietze, Einf¨hrung in die Optik der Atmosphäre (Akademische Verlagsgesellschaft Geest&Portig K.-G., Leipzig, 1957), Chap. 6, pp. 101–112.

Dziedzic, J. M.

Erdtman, G.

G. Erdtman, Introduktion till Palynologin (Bokförlaget Natur och Kultur, Stockholm, 1963), Chap. 7, p. 108.

Exner, F. M.

J. M. Pernter, F. M. Exner, Meteorologische Optik, 2nd ed. (Braumüller, Vienna, 1922), Chap. 2, pp. 445–519.

Greenler, R. G.

R. G. Greenler, Rainbows, Halos and Glories (Cambridge U. Press, Cambridge, 1980), Chap. 6.

Huffman, D. R.

C. F. Bohren, D. R. Huffman, Absorption and Scattering of Light by Small Particles (Wiley-Interscience, New York, 1981).

Humphreys, W. J.

W. J. Humphreys, Physics of the Air (McGraw-Hill, New York, 1940), Chap. VI, pp. 547–556.

Koh, G.

Lock, J. E.

Mäkelä, V

V Mäkelä, “Värit ja valot,” Ursa Minor No. 4, 16–21 (1993); (news bulletin of Finnish amateur astronomers, Ursa Astronomical Association, Helsinki).

Mielke, B.

Minnaert, M. G. J.

M. G. J. Minnaert, The Nature of Light and Color in the Outdoors (Springer-Verlag, New York, 1993), articles 183,184, and 189.

Nilsson, L.

S. Nilsson, J. Praglowski, L. Nilsson, Atlas of Airborne Pollen Grains and Spores in Northern Europe (Bokförlaget Natur och Kultur, Örebro, Sweden, 1977), pp. 135 and 146.

Nilsson, S.

S. Nilsson, J. Praglowski, L. Nilsson, Atlas of Airborne Pollen Grains and Spores in Northern Europe (Bokförlaget Natur och Kultur, Örebro, Sweden, 1977), pp. 135 and 146.

Pernter, J. M.

J. M. Pernter, F. M. Exner, Meteorologische Optik, 2nd ed. (Braumüller, Vienna, 1922), Chap. 2, pp. 445–519.

Praglowski, J.

S. Nilsson, J. Praglowski, L. Nilsson, Atlas of Airborne Pollen Grains and Spores in Northern Europe (Bokförlaget Natur och Kultur, Örebro, Sweden, 1977), pp. 135 and 146.

Sassen, K.

Takano, Y.

Y. Takano, S. Asano, “Fraunhofer diffraction by ice crystals suspended in the atmosphere,” J. Meteorol. Soc. Jpn. 61, 289–300 (1983).

Tränkle, E.

Tricker, R. A. R.

R. A. R. Tricker, Introduction to Meteorological Optics (Elsevier, New York, 1970), Chap. V, pp. 146–168

van de Hulst, H. C.

H. C. van de Hulst, Light Scattering by Small Particles (Wiley, New York, 1957;reprinted by Dover, New York, 1981), Chap. 13, pp. 228–266; Chap. 20, pp. 414–439.

Wolf, E.

M. Bom, E. Wolf, Principles of Optics, 3rd ed. (Pergamon Press, Oxford, 1965).

Yang, L.

Appl. Opt. (5)

J. Meteorol. Soc. Jpn. (1)

Y. Takano, S. Asano, “Fraunhofer diffraction by ice crystals suspended in the atmosphere,” J. Meteorol. Soc. Jpn. 61, 289–300 (1983).

Other (14)

W. J. Humphreys, Physics of the Air (McGraw-Hill, New York, 1940), Chap. VI, pp. 547–556.

V Mäkelä, “Värit ja valot,” Ursa Minor No. 4, 16–21 (1993); (news bulletin of Finnish amateur astronomers, Ursa Astronomical Association, Helsinki).

R. A. R. Tricker, Introduction to Meteorological Optics (Elsevier, New York, 1970), Chap. V, pp. 146–168

R. G. Greenler, Rainbows, Halos and Glories (Cambridge U. Press, Cambridge, 1980), Chap. 6.

C. F. Bohren, D. R. Huffman, Absorption and Scattering of Light by Small Particles (Wiley-Interscience, New York, 1981).

H. C. van de Hulst, Light Scattering by Small Particles (Wiley, New York, 1957;reprinted by Dover, New York, 1981), Chap. 13, pp. 228–266; Chap. 20, pp. 414–439.

J. M. Pernter, F. M. Exner, Meteorologische Optik, 2nd ed. (Braumüller, Vienna, 1922), Chap. 2, pp. 445–519.

M. G. J. Minnaert, The Nature of Light and Color in the Outdoors (Springer-Verlag, New York, 1993), articles 183,184, and 189.

W. R. Corliss, Rare Halos, Mirages, Anomalous Rainbows and Related Electromagnetic Phenomena, 1st ed. (Sourcebook Project, Glen Arm, Md., 1984), Chap. GEH, p. 55.

G. Dietze, Einf¨hrung in die Optik der Atmosphäre (Akademische Verlagsgesellschaft Geest&Portig K.-G., Leipzig, 1957), Chap. 6, pp. 101–112.

A.-M. Pessi, A. Rantio-Lehtimäki, eds., The Finnish Pollen Bulletin, supplements to Vols. 14 (1989) (Finnish Aerobiology Group, Department of Biology, University of Turku, Turku, Finland),The Finnish Pollen Bulletin, 15 (1990) (Finnish Aerobiology Group, Department of Biology, University of Turku, Turku, Finland),The Finnish Pollen Bulletin, 16 (1991) (Finnish Aerobiology Group, Department of Biology, University of Turku, Turku, Finland),The Finnish Pollen Bulletin, 17 (1992) (Finnish Aerobiology Group, Department of Biology, University of Turku, Turku, Finland), andThe Finnish Pollen Bulletin, 18 (to appear in 1994) (Finnish Aerobiology Group, Department of Biology, University of Turku, Turku, Finland).

S. Nilsson, J. Praglowski, L. Nilsson, Atlas of Airborne Pollen Grains and Spores in Northern Europe (Bokförlaget Natur och Kultur, Örebro, Sweden, 1977), pp. 135 and 146.

G. Erdtman, Introduktion till Palynologin (Bokförlaget Natur och Kultur, Stockholm, 1963), Chap. 7, p. 108.

M. Bom, E. Wolf, Principles of Optics, 3rd ed. (Pergamon Press, Oxford, 1965).

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