Abstract

Coronas are colorful, concentric rings centered on a bright light such as the Sun, the Moon, or even a streetlamp. Coronas are most commonly caused by water droplets or ice particles of relatively uniform size. Observers in Finland have reported spectacular clear-sky coronas caused by pollen grains. A clear-sky corona in central Texas occurred during the peak of the juniper pollinating season. The aerosol optical thickness at each of three wavelengths was highest when the corona was most prominent. Photographic measurements of the corona infer a particle diameter of ∼32.4 μm. Because juniper pollen grains have a diameter of from 22 to 30 μm, they are the aerosol most likely to have caused the corona.

© 1998 Optical Society of America

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References

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  1. K. Sassen, “Corona-producing cirrus cloud properties derived from polarization lidar and photographic analysis,” Appl. Opt. 30, 3421–3428 (1991).
    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
  5. J. R. Meyer-Arendt, Introduction to Classical and Modern Optics (Prentice-Hall, Englewood Cliffs, N.J., 1972), pp. 354–355.
  6. E. Levetin, University of Tulsa, Tulsa, Oklahoma, Biol_el@centum.utulsa.edu (personal communication, 1997).
  7. M. Muilenberg, Harvard School of Public Health, mmuil@hohp.harvard.edu (personal communication, 1997).
  8. K. L. Coulson, Polarization and Intensity of Light in the Atmosphere (Deepak, Hampton, Va., 1988), p. 397.

1994 (3)

1991 (1)

Bohren, C. F.

Coulson, K. L.

K. L. Coulson, Polarization and Intensity of Light in the Atmosphere (Deepak, Hampton, Va., 1988), p. 397.

Levetin, E.

E. Levetin, University of Tulsa, Tulsa, Oklahoma, Biol_el@centum.utulsa.edu (personal communication, 1997).

Mäkelä, V.

Meyer-Arendt, J. R.

J. R. Meyer-Arendt, Introduction to Classical and Modern Optics (Prentice-Hall, Englewood Cliffs, N.J., 1972), pp. 354–355.

Mielke, B.

Muilenberg, M.

M. Muilenberg, Harvard School of Public Health, mmuil@hohp.harvard.edu (personal communication, 1997).

Parviainen, P.

Riikonen, M.

Ruoskanen, J.

Sassen, K.

Tränkle, E.

Appl. Opt. (4)

Other (4)

J. R. Meyer-Arendt, Introduction to Classical and Modern Optics (Prentice-Hall, Englewood Cliffs, N.J., 1972), pp. 354–355.

E. Levetin, University of Tulsa, Tulsa, Oklahoma, Biol_el@centum.utulsa.edu (personal communication, 1997).

M. Muilenberg, Harvard School of Public Health, mmuil@hohp.harvard.edu (personal communication, 1997).

K. L. Coulson, Polarization and Intensity of Light in the Atmosphere (Deepak, Hampton, Va., 1988), p. 397.

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Figures (2)

Fig. 1
Fig. 1

Photograph of a solar corona apparently caused by juniper pollen over central Texas on 29 December 1996. The solar disk is blocked by a coin (penny) on a rod. The photograph was taken with a camera equipped with a 45-mm focal-length lens and Kodacolor 100 film.

Fig. 2
Fig. 2

AOT at three wavelengths when the pollen corona was prominent (forenoon) and declining (afternoon). The points are connected for visual clarity. The simultaneous reductions of the AOT and the decline in the prominence of the corona imply a reduction in the density of the pollen grains that apparently caused the corona.

Tables (1)

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Table 1 AOT During a Pollen Corona Observed from Central Texasa

Equations (1)

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d = a λ f / r ,

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