Category Archives: pollen and algae phenomena
Excavating the literature finally gave confirmation that it is the alga Chromulina rosanoffii that causes Quetelet rings and glory on water surface. This unique sort of alga separates itself from the water surface by forming a stalk on top of which it rests. This is seen in the right hand microphoto which is taken parallel to the water surface. Light blue is air and black is water. On the left is a photo taken at right angle to the water surface, thus giving a look at the C. rosanoffii forest from above (transmitted light). If the alga is for some reason submerged in the water, it sheds its stalk and starts immediately swimming. The b&w photos here show C. rosanoffii submerged in water.
Also two photos of the optical phenomena caused by this alga are displayed in the composite. On the left is a fisheye view with Quetelet rings. The glow around the camera shadow is fogbow. Notice the brightening towards nadir in fogbow, indicating possibly non-spherical particles. The photo on right is taken further away from the cultivation tub, showing spectral colored glory rings. Attached to the outmost glory ring is faint, white fogbow.
All said here about the biology of C. rosanoffii was known long time ago. The alga was described in 1880 by Russian botanist Woronin, who encountered it while visiting Finland. One aspect of the studies carried since has been the golden glow that well developed C. rosanoffii surface film displays, as shown beside and here. But I have not yet met in the literature any mention of the spectral colors, which strikes me as a small wonder. However, there is still plenty of reading to be done, so something may come up.
[Posted by Marko Riikonen]
Some time ago Jari Piikki posted me a couple of drops of the surface film that produced his colourful corona. I mixed it in a bucket full of tap water with also some forest litter added. After a week or so there appeared a bluish film on water surface. Closer inspection with point-like light revealed more colors. It was actually a large corona, with blue inside, and green and red on the outer edge.
Only a segment of the corona could be seen in the small bucket. This is shown in the upper left image. Unlike the peculiar corona described by Piikki, this one has true blue aureole starting right from the reflection image of the lamp. Outside the blue some green and perhaps red maybe distinguished – visually these colors were clear. Upper right image is microphotograph of the film. It consisted of bacteria.
Day after taking the upper photographs the phenomenon in the bucket changed. Now there was similar corona as what Piikki photographed, only less bright. This is shown in lower left. There was no aureole, but instead a dark area surrounded the light source. This also was consistent with Piikki’s observation. Microphotograph of the film on this stage is shown on the lower right.
The most conspicuous difference in the bacterial level between the two stages is the crowding – there are more bacteria in the latter stage. Is this somehow related to the changes in the phenomena? Perhaps Minnaert can give an answer. In the chapter about coronas seen in windows, he describes how these coronas have an aureole replaced by dark area. He speculates the dark area forms because in the two dimensional plane of the window surface the droplets can be evenly spaced – a situation which can not happen when particles are freely floating in the air.
Now, if one looks at the lower right microphotograph, one can imagine that these bacteria indeed are spaced more evenly as compared to the upper photo. In the Piikki’s microphotograph, which looks like a maze, the bacterial film might consist solely on the long strands that are seen in small numbers also in my lower right photo. When packed next to each other, these kind of strands would possibly be very evenly spaced, thus perhaps contributing to the stronger corona. Piikki’s photograph is, however, too much out of focus to be sure of this interpretation.
The bacteria species could be Nevskia ramosa, which is well known neustonic (water surface inhabiting) bacteria. Genomic fingerprinting would be needed for confirmation. For the last note it should be said that the inverted colors between the two microphotographs are due to differences in focus. The upper image is a bit out of focus and thus the bacteria shows as dark spots.
[Posted by Marko Riikonen]
Jari Piikki have also found some ponds with algal films that show optical phenomena. The ponds were sampled and the alga allowed to breed for some weeks. Extracts were photographed through a microscope. In one pond, Botryococcus alga was abundant nine years ago but then disappeared. Now it is back and quite large Quetelet rings and a corona were visible. Another pond on one island possibly contained Chromulina rosanoffi and microscope images showed it floating on the water surface.
Jari Piikki also found a new optical phenomenon. He took (like Marko) some samples from ponds and cultivated them. In one of them Chromulina disappeared and some other alga appeared. There could be seen a very colourful ring with two zones of spectral colours around the reflection from the surface of the Sun or an artificial light. The ring was oval and became smaller, when the light was brought closer to the water surface. Its diameter in sunlight was about 30 degrees and the inside was dark, so it was not an aureole. also visible when the light shone through the alga from below. Many photographs of the surface were taken with a microscope to show its structure. You can see it in some photos. The alga constantly changes constantly and now shows small colourful blotches.
[Text: Jari Piikki]
Here are some results from the work I have done this summer on the phenomena caused by algal film on water surface.
The upper pair of photographs shows elliptical corona and the alga that caused it. Pine pollen gives the scale. This corona-type display has no other phenomena.
The lower photo shows another type of display, which exhibits Quetelet rings, brightenings around sun””s reflection image, glory and fogbow. In this case there is also unidentified diffuse feature marked with arrows. In addition, fogbow and glory have spot-like brightening towards nadir. Two B&W photos of the algae causing this type of display are shown. In the lower photo the algae are possibly turned 90° in comparison to upper, showing elliptical shape. This species might be Chromulina rosanoffii. It””s about 5-10 µm in size (not to scale with upper color photo) and well transparent to make glory.
These phenomena turned out to be common, at least this summer. They were most abundant on rocky Finnish archipelago islands, which harbour endless number of small rock pools.
[Posted by Marko Riikonen]
Continuing on the favorite topic of pollen coronas, here are two rather painstakenly constructed images of pine pollen corona.
The white dots are wind dispersing seeds, probably of some willow species. They are more abundant in the lower image, which was taken in town. The upper image was shot in the midst of pine heath, with correspondingly less white fluffs in the air.
[Posted by Marko Riikonen]
A pollen corona was seen by several observers at the Southern coast of Turkey during the total solar eclipse of 29th March 2006. This nice picture taken by Emma Herranen shows the atmospheric pollen corona with three colour segments only a few seconds before the second contact, as illuminated by the diamond ring phenomenon. The inner parts of the solar corona are seen as a white circle around the Moon.
I saw this extremely splendid cedar pollen corona on May 19, 2005 at Hachioji, Tokyo. Last year, the amount of cedar pollen was so large that we could observe some beautiful coronae (but it was a nightmare for people caught by hay fever).
Cypress pollen is another source of pollen coronae in Japan. However, the season of Japanese cypress pollen is almost same as that of our cedar pollen so that it is hard to distinguish its contribution from the cedar pollen”s contribution. (The amount of cypress pollen is less than cedar pollen.)
Posted by Yuji Ayatsuka
In Japan, pollen coronae are normally caused by ceder pollen (and possibly Japanese cypress pollen). However, a pollen corona by a false acacia is observed by Mr. Yasuike on May 25th 2006, in Matsumoto. He said that an amount of false acacia pollen is quite large in this season around Matsumoto (it is not typical for the other areas in Japan).
It might be the first report of a pollen corona in Japan, other than by ceder (or cypress) pollen.
[Posted by Yuji Ayatsuka]
The 27th of March was in a manner of speaking one of our first warm days this year. Owing to the long and cold winter together with the abrupt change the plants exploded into life and produced a very strong pollen concentration in the air. The humidity was very low and so the resulting pollen coronae stood out against the dry sky. The coronae originated from from alders which are very common in the area (Barsinghausen, near Hannover). Hazel were also flowering at that time but would have made a different form of corona.
That day Reinhard Nitze took very unusual pictures of the alder coronae. On the one hand the coronae were intense but appeared together with another phenomena, e.g. with iridescence clouds or cloud rays. Sometimes, however, Reinhard saw them “undecorated”.
Middle Europe we see pollen coronae produced primarily by birch, spruce, pine, hazel and alder. However, by deliberately shaking the bushes to discharge clouds of pollen it is possible to generate other types of coronae. In this example Karl Kaiser photographed a coronae from male hop blooms. Other pollen coronae by Karl are here.