Monday, December 25, 2006

Mother-of-pearl clouds in Finland

A period of westerly tropospheric flows in Scandinavia is continuing to provide occasions of Mother-of-pearl (MoP) clouds to Finnish observers. Several MoP displays have been observed just before the Christmas at different locations, in particular in Central and Northern parts of Finland, but also at the Southern coast. The photograph taken by Mauri Laitinen in Kuopio, Eastern Finland, shows the beautifully coloured details of the afternoon display of 23rd December.

MoP clouds are seen a number of times each winter in Finland, but displays as bright as this one are fairly rare.
Usually the MoP clouds are related to stratospheric temperature colder than -80°C.

Tuesday, November 14, 2006

Alien hunt on the lake Königssee in Bavaria/Germany

October 13th 2006 was a sunny and very warm autumn day, which we wanted to spend on a hike at the Königssee. However, we did not get very far because the scene over the very cold, deeply shielded mountain lake was entrancing. Ships flew over the water, islands floated in the air and aliens over the lake were hunted. It was really fascinating to pursue the fast changing mirages.

More Pictures: 1 2 3 4 5 6 7

Friday, November 10, 2006

Wendelstein Shadow and Rainbow

After the passage of a front on August 12, 2006, the sky over Bavaria (Germany) began to clear up and turned into a sunny mood about 30 minutes before sunset. This image by Christoph Ries was taken looking toward the antisolar point as Mt. Wendelstein's (1,838 m or 6,030 ft) triangular shadow emerged over the Wildalpjoch Mountains (background). Both ends of this amazing rainbow were visible. By clicking on the image, you may be able to detect the faint left portion of the bow. Note that because the image was taken at altitude, the bow's nearly circular composition is observed. From flat terrain, we see rainbows as semi-circles, but when not confined by a horizon, it's easy to see that they're actually rain-circles. The image was stitched from three individual images using "autostitch" and "The Gimp."

Tuesday, October 31, 2006

Mother-of-pearl clouds over Colorado?

Caleb Jones took this photo in Estes Park, Colorado (USA) on 28 October, around 3:10pm local time. The weather had been mostly clear on this day. These clouds were relatively far from the sun, and the vivid iridescent colors seem to be caused by very small droplets that polar stratospheric clouds have. But the edges of the wave cloud look more like regular mid-level waveclouds.

The 00 UTC 29 October sounding of Denver doesn't show unusually strong winds at high altitude, at 40 to 50 kts from the NW. In fact the entire troposphere seems rather dry on that particular sounding for lenticular clouds to occur.

I do not think this was caused by a missile launch either, considering the lenticular shape of the clouds.

I am wondering if these could be stratospheric clouds, or just some quite unusual appearance of lenticular mountain wave clouds. I received another report from someone else in Colorado who also took images, and am waiting for her approval to post them here as well.

Thursday, October 26, 2006

Brigitte Rauch and her husband spend every free minute on their motor-boat on the waters around their home island Helgoland, whichis only about one square km large and situated in the open North Sea. If possible, they do not miss any sunset and always have their camera ready to hand. This photograph of reflections on the water surface was taken on July 17, 2006, just after sunset. The colour of the sky and the clouds are reflected from the water surface, which was relatively smooth that evening. The patterns are caused by small waves. This richly coloured interplay of sky, clouds and waves can be seen only on a few days of the year.

More pictures: 1 2 3 4

Tuesday, October 17, 2006

Tunnel Glory in Italy

Gerald Berthold spent the beginning of October in the South Tyrol, Italy. On 5th October 2006 he climbed the 2778m high Piccolo Lagazuio. The descent leads partly through tunnels dating to the First World War. Where they breakthrough the mountainside they give fantastic views of the Dolomites. On one of these galleries the sun shone along the tunnel through fog which developed because the humidity and lower temperature inside. In this formed a spectre of the Brocken with a spectacular multiple ringed glory (the camera is pointing away from the sunlight direction). The glory seemed almost graspable and was sensationally bright.

Sunday, October 15, 2006

Small coronas from bacterial film on water surface

Most of the cultivation pools in my room are now showing much smaller coronas than earlier. In each pool the corona is of constant size over the whole bacterial film surface, but from pool to pool their size vary.

Even though these coronas are smaller than before, they still are large as compared to pollen coronas. Unfortunately I have no photos for comparison.

In the composite image are two coronas photographed with same lens (not to scale with upper single image, which has been taken with zoom lens). The microphotograph of the bacterial film is from the smaller corona on the left.

The light source was a 50 W halogen spotlight that I made even more concentrated by placing the lamp in a cardboard box, into which a small hole was made for light to come through. When taking photos, the room was otherwise darkened.

Saturday, October 14, 2006

Artificial Spectre in Brocken Mountains

This artificial Spectre of Brocken with fogbow was taken April 14, 2003 in the Brocken Mountains in central Germany. A helium lamp, positioned behind the photographer, was used to illuminate this very thick fog layer - the visibilty was less than about 5 m. The great size of the Brocken Spectre results from the shadow not lying in one plane but rather extending over a depth of several metres.

A camera team made a film [40MB, for WINDVD, in German!] about search of the Spectre and the edge Ghost but unfortunately the quality of digital version is not very good.

Spooky greetings from the ghost heaven!!!

Friday, October 13, 2006

Divergent Light Rainbow


On the evening of October 7 the weather was windy and rainy. I went out to take photos of rainbow using very powerfull light source. The shaft of light is narrow, but it illuminates buildings that are more than one kilometer away. The distance from the photographing spot to light source was about 150 meters. On October 10 I took photos of fogbow. It was amazingly bright and seemed to show up better closer to the light source.

Friday, October 06, 2006

Reflectet Light Rainbow

Uwe Mueller from Bremerhaven photographed this reflected light rainbow at the 06/10/04. The reflector surface is with large probability the transatlantic harbor at the external Weser, which was at the time of the admission behind the observer. This rainbow was visibly of 15.45 UT- 15,54 UT. At the beginning of the sifting the reflected light rainbow was good visible. It became then fast weaker.

Primary, Secondary and Interference Rainbow

Mike Nicholson took this shot just after sunup on Sept 7 2006 last. He has to enhance it in PhotoShop Elements 4.0 so the colour is a bit overdone. It was shot on a Pentax *ist DS, 18-55mm lens set to 20mm. ISO was on auto (probably 200), 1/250 sec f/8. A circular polarizer was used.
Location: Papatoetoe, Auckland, New Zealand.

Wednesday, October 04, 2006

Interference arc outside of secondary 9-28-06

I was outside watching small rainshowers come and go and later on as the sun came out I got small rainbow fragments here and there. Later on while helping my mother take care of the farm animals another strong rainbow formed and this one was unusual because I counted 4 supernummery arcs inside the main bow and I could also see a very well-defined supernummery outside the secondary bow. I enhance both macro images made of the two bows. The USM of the primary shows 5 supernummeries.

Saturday, September 30, 2006

Chromulina rosanoffii as a cause of optical phenomena on water surface

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.

Wednesday, September 27, 2006

New results on the large coronas on water surface

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.

Tuesday, September 26, 2006

Polarized fogbow in car headlights

I spent the past summer at Langmuir Laboratory on the Magdalena Mountains, in southwest-central New Mexico (USA) at an elevation of 3.2 km. The purpose of this was thunderstorm research. The monsoon here was unusually wet and on several days and nights the mountain laboratory was actually foggy. This is relatively rare considering the New Mexico climate. I took this opportunity to view polarized fogbows in my car's headlights, and on September 2nd, I was particularly successful.

When I programmed a Mie simulation algorithm late last year and plotted a polarized fogbow on my screen, I was surprised that the polarized bow looked as it did, with the typical Brewster's angle 'gap' in the main bow for parallel polarization. How excited I was to see that the actual fogbow indeed looked like the simulation! I had never seen it before in nature.

I am sure this has been done before by someone else, but I thought I would post the images anyway.

I covered up one of the car's headlamps as to not have a double bow. I positioned myself about 50 meters in front of the truck, which I had parked on a slight inclination so the bow would be better visible against a featureless sky and be more complete. The fisheye lens was equipped with a polarizer at the place in the lens where the rays go parallel.

The simulation I made earlier, for a 10 micrometer radius droplet. It looks sharper because I assumed a point light source, assumed a monodisperse droplet distribution, and it was not divergent light. It is not a perfect match either considering the placement of the supernumeraries: probably the droplets in the actual display were a bit smaller. Because of the divergent light source, and because I don't know the distance to the truck accurately, I doubt I will ever be able to accurately tell the actual droplet radii in the display.

The polarized glory was also obvious, but my shadow was blocking most of the part that was most polarized. I am including the unpolarized glory here.

The close-ups of the polarized and unpolarized fogbow were made with a 24mm/2.8 lens. The camera was a Canon 300d (modified version - i.e. with IR filter removed). I did not need to adjust the brightness and contrast much to get the results as displayed here. The fogbow had good contrast by itself.

About 10 days later I documented a natural fogbow in sunlight from the laboratory, through a polarizer. I photographed that with film; I have not processed those photos yet.

Tuesday, September 19, 2006

Crepuscular ray 1 hour after sunset

On September 12th Claudia Hinz observed the sunset from the 1835m high Wendelstein Observatory.

At 19.18 CET (Daylight saving) the sun disappeared behind a 250 km distant thunder cloud over the Black Forest, Schwarzwald, in South Eastern Germany. Then the sun would have been ~2° above the astronomical horizon. The sea level horizon was 197 km distant and dipped 1.4°.

At around 20.00 sheet lightning was noticed on the horizon.

At 20.15 a 30° long crepuscular ray was formed by the thundercloud. At that time, nearly an hour after sunset, the sun was 8° below the astronomical horizon. The ray was faint but clearly seen over the remaining twilight colours. The image was made with a 150mm lens and a 4s exposure.

Claudia Hinz

Wednesday, September 13, 2006

Divergent double rainbow

On the night of Dec 12 2004 the weather was was quite murky and the rain was unusual because it was a misy where the drops were quite small but large enough to be felt. That night I turned on my car's headlights and got this stunning set of divergent light rainbows. In the first photo you can see a single set of bows and the second shows three possibly 4 bows due to the camera being positioned between the two headlights.

Monday, September 11, 2006

Water colours at Juva & a new optical phenomenon

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]

Saturday, September 09, 2006

Optical phenomena from algal film on water surface

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.

Friday, September 08, 2006

divergent light rainbows

Fogbows have a similar origin to rainbows. For this reason, Christian Fenn, who had previously photographed fogbows made by divergent light, decided to attempt to image a divergent light rainbow. On 19th April in Hammelburg, Bavaria he managed, in pouring rain, to image a rainbow formed by light from car headlamps.

A divergent light source can actually produce a multiplicity of rainbows, not only of angle 42° but at larger angles also. The net result is that the bows overlap and a discrete coloured arc is no longer visible. Another negative factor is that the rainbow cannot develop a high intensity like those sourced by the sun because only a narrow range of rays fall on the "rainbow cone" having its tip at the observer's eye. To see a divergent light bow it is necessary to be far away from the light source so that its rays are as parallel as possible and develop a bow of sufficient contrast.

In the photograph the divergent light bow is wider horizontally than vertically. This is because the two car headlamps each form bows and so produce an apparent broadening.

Sunday, August 13, 2006

Brocken Spectre in sea fog

On March 24th 2005, Thorsten Gaulke was sailing homeward bound from Oslo to Kiel on a scarcely four month old ship called "Color Fantasy". The ship entered an area of sea fog no higher than the ship formed by the cooling effect of the cold Baltic waters. With the sun to his back he was able to observe his Brocken Spectre surrounded by a bright glory. There is a trace of a much large glory-like phenomenon that might have resulted from much smaller droplets. Alternatively it could be a fragment of an inner supernumerary of the surrounding fogbow.

Saturday, July 08, 2006

Icebow?

Claudia Hinz observed a strange ‘rainbow’ on 5 May 2005 from Mt. Wendelstein (alt. 1835m). During a strong ice pellet shower from collapsing cumulonimbus there appeared an almost 20° long faint, but coloured piece of bow. It was rather diffuse, ragged and very broad. The sketch shows the bow. The sun was 50° high and the bow was approx 8° below the horizon.

From meteorological experience, a dying cumulonimbus can only produce ice when it collapses from the top and in the lower levels the temperature is low enough that the ice does not melt. That was the case here, the cloud collapsed and decayed fully into graupel. There was definitely no rain, which I had also not experienced previously with a ice pellet showers.

I do not want to commit myself whether there can be an ice pellet bow. However, the ice grains may occasionally be covered with a water layer, giving a smooth outer surface. Of course, the refraction in the ice-water interface must also be considered. If that interface was uneven it could explain some of the bow width.

On 11th of January 2006 Christian Fenn reported crystal-clear ice balls (photo 1, 2), in sleet falling at an air temperature of -4°C. He searched for an ice bow formed from the headlights of his car. In this picture the possible ice bow is compared to a (terrestrial) rainbow. There are also images by Christan Fenn of the ice balls.

Friday, June 23, 2006

Pine pollen corona in Finland

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.

On 13. June 2006 in Eastern Finland. Larger sized versions are here.

Thursday, June 22, 2006

Miraged Ships

On June 11, 2006, Thorsten Falke and his girlfriend Bärbel Wichmann decided to have a picnic at the south-beach of Düne, a one square kilometer little island in the North Sea and in the neighbourhood of Heligoland.

Even though the picnic basket contained several tasty titbits the sky was even more tempting with its unusual mirages. Ships passing Heligoland and Düne at a distance of 10 km or more appeared somehow "stretched". They looked longer than they really were.

Thorsten and Bärbel are still wondering how this effect come about. The sun was shining the whole day and because there was almost no wind, a warm air layer probably lay above the water surface. They suggest that when a ship is on a course of 45° (for example) towards or away from the observer, the bow of the ship is closer/further to the observer than the stern. This, combined with the warm air layer, may cause the unusual extension/or sometimes shortening of the ship.

The two images are 15s apart. More mirage images here.

[Text: Thorsten Falke & Bärbel Wichmann]

Tuesday, June 20, 2006

Pollen corona during solar eclipse

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.

Thursday, June 15, 2006

Colourful refraction by the surface waves

On June 13th Thorsten Falke from the German North Sea isle "Düne" (near of isle "Helgoland") was walking along the seashore, when he saw criss-cross light structures on the seabed obviously caused by refraction by the surface waves. He had seen the phenomena often before but this time it seemed to be coloured. He decided to paddle out into the water to take pictures. It was difficult to see the colours visually because of the rapid movement of the little waves (only 2 cm "high") but in many of the pictures the colours were evident. The appended picture was taken with a macro lens and shows a shell in 10 cm deep water with a colourful refraction band across it. Because of the macro lens the picture is nearly 2 times life size. Another refraction is located at the upper edge of the picture. If he remembers rightly, the light was coming from the left side and was parallel to the wave crests. The main interest of Thorsten is to observe whether the colourful refraction is seen only when the wave crests are parallel to the light direction or if it is also visible when the crests are at right angles to the sunlight.

Tuesday, June 13, 2006

Cedar Pollen Corona


















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.)

Saturday, June 03, 2006

Subhorizon rainbow

This deep-subhorizon part of a rainbow was photographed by Günther Können on 2 Oct 2005 on a flight from Amsterdam to Madrid. Although cloudbows are frequently seen from an airliner, rainbow sightings are relatively rare. To my (Günther's) experience, the best chances are when the altitude of the plane is not too high. It was the second time that I saw such a distinct one, the first time being 23 yr ago.

Pollen Corona by a False Acacia

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.

Tuesday, May 30, 2006

Spider web reflections

In Germany October 2005 was very dry, calm and warm with no frosts. The weather gave rise to a large number of spiders and of course their webs. Towards the end of the month, Reinhard Nitze’s attention was drawn to an unusual light phenomenon on a ploughed field. The sun produced a silvery reflection like the glitter path seen on waves when the sun is low. He had seen the effect earlier on scythed grain and grass fields but never so conspicuous. The effects were produced by sunlight reflecting off threads of spider silk that happened to be perpendicular to the sun – eye line in the numerous webs in the fields (more images 1,2,3).

The effect is seen also in the lower left image where the web reflections in trees make concentric rings.

Bare and wet twigs produce similar effects as do support wires in vineyards. Perhaps observers have seen other reflection effects like these?

[Report: Reinhard Nitze]

Wednesday, May 24, 2006

Unusual Coronae & Sunsets - Finland

Very large coronae were observed in Southern Finland at the beginning of May 2006. Their radius was about 45° and they had a bluish disk and a brown ring. The sky was very clear and quite dark outside the corona. Also, very beautiful red sunsets were seen on those days.

The phenomena were visible on many days between May 2-11 and were possibly produced by smoke carried from Eastern Europe.

In the above corona image taken on 11th May a small segment of another photo has been added to show the size of 22° halo for comparison.

The sunset was photographed on 4th May.

Large coronae can be seen during very warm weather periods when the sky is usually hazy. This was the first large corona seen in Finland since the Bishop’s rings of 1991-1992. Smaller coronae (radius of about 5°) with a blue disk and brown ring have sometimes been observed.


[Text & Report: Jari Piikki, Juva Finland]

Monday, May 22, 2006

Fogbow with supernumeraries and Glory

This fogbow and glory was photographed by Ken Tape on May 12, 2006 while descending to a place called "Isachsen" located at 79 degrees North in the Canadian archipelago. The display and descent lasted for about 10 minutes, and the strength of the bows was fairly constant throughout. The intensity of the fogbow supernumeraries was strengthened by the use of a polarization filter. Note that the color sequence in the supernumeraries – blue outside – is reversed compared to that in the main maximum. The shadow in the glory is of a Twin Otter on skis. Nikon D70 with old 20mm lens (effective 30mm).
[Text: Ken Tape, edited by Günther Können]

Saturday, May 20, 2006

Reflected rainbow at a fountain

Alexander Haussmann searched specifically for a reflected rainbow at the fountain of the palace pond at Dresden. And with his precise look he found it – but it was faint. With a polarising filter he could increase its contrast. The reflected bow changed in brightness, occasionally it was obvious but then it became faint again. The visibility was most probably influenced by the wind and the smoothness of the water surface that was to some extent disturbed by the falling drops. This example shows that it is not difficult to find a (artificial) reflected rainbow with help of a fountain.

Friday, May 19, 2006

Alder corona with iridescence and cloud rays

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".

Pollen Corona produced by hop blooms

Here in Germany 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.

Sunday, May 14, 2006

Very large corona in Chile

This corona was photographed in December 2000 while camping at the El Tatio geyser field at 4300 meters elevation in the Chilean Andes. The corona radius is approximatly 50°. Blue inner disk extends to about 35° from the sun. In between the blue and red, a green band was seen visually, but it was not reproduced on film. Altocumulus clouds were developing from the stuff that made the corona. The corona may be related to the dust that is released in large amounts in the air from some mines in the area.

Cyan saturation was increased in the photo to make the inner blue disk better visible. Otherwise the photo is as scanned from the slide. See here for some more material. The degree grid is made with HaloSim by Les Cowley and Michael Schroeder.

Small and large coronas

How small is a pollen corona! On 14 May, a fine circular pollen corona re-appeared in clear sky blue over Deventer. It was magnified by zooming the camera lens, but actually real proportions of this small phenomenon are disguised by doing so. Here we see a fraction of a common water droplet corona in Fractocumulus too, left in the image. It is nice to see the differences in corona proportions, by considering pollencoronas, via common cloud coronas, to Bishops' ring....