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POLLEN CORONAS IN FOCUS 1/3
In Finland there is springtime just coming. The interest of
atmospheric amateurs is rising due the halos and especially
pollen coronas. Since 1989 atmospheric optical phenomena
section have recorded coronas caused by pollen grains.
This phenomenon is very interesting due to several points:
(1) There is very few old information of these, (2) the
shape and the size of coronas varies by plants and by solar
altitude, (3) the existence of coronae varies year by year
and (4) the period of appearance of rather short.
(1) Before Finnish observations there are not very much
references in atmospheric literature about pollen coronas. And
about pollen hypothesis there is any notification in old sources.
Minnaert writes about "clear sky coronas" (M.Minnaert: Light
and Color in the Outdoors, p. 243, Springer version 1994).
Minnaert's theorie is diffraction due to dust particles, but
pollen is, in my opionion, possible explanation. Also some
Dutch observation look like pollen coronae observations. In
Corliss' Sourcebook project (W.R.Corliss: Rare Halos, Mirages,
Anomalous Rainbows and Related Electromagnetic Phenomena, 1984)
there is described a diamond-shaped halo, which looks much
like a pine and spruce pollen coronas observed in Finland.
If anyone knows more older references, please inform us here
in mailing list.
About Finnish observations there is a paper in Applied Optics,
Light and color in the open air special issue (Parviainen,
Bohren, Makela: Vertical elliptical coronas caused by pollen,
Appl.Opt. Vol 33 No. 21, 20 July 1994, pp. 4548-4551). Also
much material is available directly from Ursa Astronomical
Association, Atmospheric optical phenomena section for those
who are really interested in this phenomenon.
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