2010. december 26., vasárnap
Now anyone can photograph bright halos, but what about the faint halos? The pillar in light clear sky snowfall is prominent here, but the parhelia in the other photo is less so. Not faintest possible, sure, I gave it even some contrast with slight usming. Also shown is factory exhaust plume. This is still rather minor, it was not that cold. The photos are from 22 December 2010.
2010. december 25., szombat
I spent whole day out on Pyhäjärvi ice to look for this display. In the beginning had to do some running to get inside the diamond dust which was at the far end of the lake. Reflected Lowitz arcs are seen in stacked images. A reminder of Moilanen arc and helic arc are also present. Yet another helic arc without Parry arc. Sometime after midday the the diamond dust vanished and I started to pack up to walk back about 4 km to car. But this was a very short lived moment and the diamond dust enshrouded the place again and I stayed untill sunset. At the end there was only sun pillar. Tempereture was below -20 C.
2010. december 24., péntek
2010. december 21., kedd
Some elementary stuff. Although there is high cloud, light snowfall made the sun pillar. In the evening there was moon corona. Took a hdr set and worked it with FDR-tools, which is good for coronas.
This one was seen from automatic gas station lights. The helic arc is rises diagonally from the lamp. I was desperately looking for a place for the spotlight, but the surroundings were totally light polluted. Just 300-400 meters away it was totally dark wilderness, though, but the diamond dust never reached there. So I just photographed the halos in this light. I walked closer to see if I could see 3D structure in helic arc, but as expected, it disappeared. The tangent arc had no seagull shape at the appropriate lamp elevation, indicating presence of Parry arc, which certainly was there. The helic arc is doubled because there are two lights.
2010. december 20., hétfő
This one came as an almost complete surprise. I had seen moment before parhelia from streetlight when driving, but they were weak. The pillars were almost non existent, so when I parked at the hospital area and turned on the long lights, I was surprised to see the crystals glitter in the beam in a very much all sky display manner. This was confirmed as I walked the beam.
Taking on the spotlight took some time and I did not get much photos. There was also serious light pollution. Just a bit further away towards the lake it would have been darker, but you have to take the first photos where ever the display is, or you risk not getting photos at all (this wisdom Luomanen told me recently).
Simulations of the display are made with Jukka Ruoskanen's HaloPoint 2.0. The most interesting point to me is the 5 degree rotational Parry population that had to be used to get the intensity of the diffuse B arc right. Nothing new here, of course, this kind of effect is pretty common in the spotlight displays. Lessen the rotation and they turn into subanthelic arcs. The Parry population makes also right kind of brightenings at Tape arc locations. Should they be called Tape arcs or 46° supralateral arc, is probably a matter of taste.
In simulation the subhelic /helic arc (they overlap at 0° light elevation) is too intense as always. Perhaps the Lefadeux hollowed crystal simulations could fix it. I have included also simulations showing the diffuse anthelic arc A and B components (well, actually they are independent halos), which are clearly discerned in the photo. In sun displays these are less easy to distinguish, which is why we normally talk only about the diffuse arcs.
Temperature was around -22° C. It is rather unusual to get column (or Parry) stuff at these temps.
2010. december 19., vasárnap
Some stuff from the night of 11/12. December 2010 with Luomanen. We took replicas of the Moilanen arc display, but they failed. Could have been an enlightening case. On the windshieldd there was also parhelic circle, cza, cha - the usual stuff. Luomanen is holding the lamp.
2010. december 18., szombat
Mustavuori snowguns made this display. Some driving around and quick stops were involved as the diamond dust changed its location. Moilanen arc occurred on two stages, better second time. The photos of it above are 101 and 120 seconds stacks with 43 and 52 frames respectively. Crystal sample was taken, but too late, the display started soon vanish as I got the dish out. There were not much crystals in the sample and nothing special shows up in the two photos.
There is faint helic arc but no Parry arc (not even with heavy usm). Helic arc occurs pretty much in any diamond dust halo display. It has been seen even with sun pillar only. The question is what kind of helic arcs these non-Parry occurrences are? Do they arise from the same angle as Parry helic arc? If not, how many different helic arcs there are? Should probably compare this one with simulations, it comes out pretty strong with heavy usm (checked that, it has the same angle as normal helic arc).
The photos with sun in it has a pretty strong overexposed area. I have had Nikon D70 for about 5 years and this has always been the problem. Only now I realized that blocking the sun is the cure for it. So, in the future photos there will always be blocker. Actually, it is good to stack even the smooth diamond dust displays. Earlier I did not think it would help much, but it does.
2010. december 16., csütörtök
I went to check the diamond dust even though it was cloudy. There was nothing, as expected. I was reporting in the phone to Luomanen the situation when hole punch cloud caught my attention. The Ac was probably the slowest moving I have ever seen and there was plenty of time to photograph this. Much different from the other hole puch a few days earlier in Hervanta, which moved and changed really fast. I have never seen hole punch clouds before and now two cases in the row!
2010. december 9., csütörtök
[gallery link="file" columns="5"]
Halos from column orientation were the main feature of this night in Tampere. In the beginning I was looking at the display with Luomanen but we did not have cameras. The display sort of took us off guard, it was thickly overcast and temperature at -5 C. Anyway, Y-pillars were visible in Hervanta and we got crystal replicas at least. Closer to the streelights beautiful circumscribed halos appreared, but it looked like there was some tilt involved. Columns with hollow ends in the replicas.
Later I continued on my own and took photos under streelight near Mustavuori. Took also crystal photos - the crystals have become more equidimensional (the temp also had dropped to -7 C). Plenty of triangles (the photos above are all from this live sample) which probably have been falling in Parry orientation but Parry was impossible to distinquish under the lamp. Certainly triangular thick plates do not take plate orientations because there was no sign of plate halos in this display. Kern from triangular plates is only theoretical consideration.
For the last I went back to Hervanta where I photographed the Y-halo from the police training area floodlight. Also helic arc is visible. At some place there was also parhelia. The display lasted several hours and who knows how long it had been going on before we entered the scene.
2010. december 4., szombat
It was cold morning, at lowest the car showed -31 C. I drove to Mustavaara but guns were not on. But at the distance about 10 km away I saw there was swarm at Kontiolahti biathlon stadium so I drove there and got this little display from lake Höytiäinen ice. The ice fog was a bit too thick and Ac was taking over the sky. Temperature at the location was around -25 C.
There are two rules for success in seeing diamond dust halos. First you have to go where the diamond dust is. Second, when you think it is time to go home, you don't. On many nights I am actually going back to home two three times, but turn back and get results. There should be a rule for example for the cases when the sky turns overcast: don't go home until after you have waited minimum 1½ hours. Often ehough I have noticed how the sky has gotten soon clear again on the way home. And you never go home when the diamond dust is on the treshold. Treshold conditions may last hours but eventually the diamond dust develops. It may not be untill the early morning hours, but it develops. And even if the diamond dust is not that good, you don't go home. Change in wind direction can make dramatic changes in halos.
This night I did not have to wait for the condition to develop. The swarm was on as I arrived to the scene soon after darkfall, temperatures around -25 C. But it was not that good, only weak pillars were seen. But I waited and eventually in the morning hours got some photos in Heinävaara, where the swarm headed from Mustavaara. Nothing spectacular but the half moon submoon was really worth the wait. It was an eerie apparition, following by your side like a messenger from beyond.
2010. december 3., péntek
I screwed up this one. The condidionts were on and I was waiting in Mustavaara for three hours for them to start the snowguns while there was actually diamond dust from Kontiolahti biathlon stadium snow gunning not far from Mustavaara. Eventuallly I saw the Kontiolahti swarm in the distance as I walked up the Mustavaara flank. After three km of driving I entered the diamond dust and got a couple of photos from parhelia against pine forest. The ice fog extended at least 12 km from the source, but I was still deep within. Who knows how far it reached.
The moon halos disappeared as the cloud got thicker and I headed back to Joensuu. The wind was even stronger now, with snowdrift and snowdevils on the road and snow dropping off the trees. On the way at the quarry, however, there was a swarm and I took there some photos with positive and negative lamp elevation. Nothing special, but the photos show nicely the effect of varying crystal tilts on halos. Eventually the swarm died off and moon was shining again surrounded by 22° halo in high clouds.
When it is windy you don't get diamond dust halos in Finland. For some reason (could it be that in still weather radiative cooling is stronger and thus relative humidity can rise to reach ice saturation?) there is not enought moisture in the air for ice crystal growth in windy weather. This night is was windy but I nevertheless drove 25 km to Mustavaara to check the situation. As expected there was no diamond dust and I was thinking of going back to Joensuu. Still it looked like it was on the treshold so I decided to wait. This paid off as eventually the ice fog from the snow guns starting spreading and 22° halo was seen in it. Further away the display was a bit better, with also parhelia visible (there was also high cloud in the background, which may have partly contributed to the display, in the second photo the 22° halo on the left is in high clouds). I tracked the cloud extent to 10 km from the source but at that time it was already receding, so probably it was wider at its best.
So this display broke the "no wind" curse for me in Finland. At polar areas where it is hardly ever calm, diamond dust halo displays seem to occur at any wind speeds.
2010. december 2., csütörtök
The moon halo display vanished as it got eventually overcast. It was still low stratus with occasional fog on the ground, but apparently the moisture just became too much for the snow guns' ice dust to nucleate a hole. Diamond dust nevertheless continued under cloudy skies and I turned on the spotlight. It was rather good, plate crystals still in charge and with negative elevation lamp (about 11° below horizon) there appeared several "super"-halos (equal to "sub"-halos when light is above the horizon). All were visible to the naked eye, the superparhelic circle at the superanthelic region was bright. At its best the superparhelic circle extended all the way to the superparhelia but I did not get that stage photographed. At the same time was also normal parhelic circle visible. I though of seeing a ghost of super-120° parhelion, but decided it was just white snow on the far hill. In the photos, however, super-120° parhelia are visible in a similar ghostly manner, so probably that was what I saw.
Getting these photos was mostly waiting. Mainly it was water fog, but then, for maximum few minutes at a time good crystal swarms swept by. In one exposure both water fog and diamond dust stage was captured so that there is also fogbow visible. In reality halos and fogbow were not much visible at the same time. Water fog and diamond dust don't just occur simultaneously. Eventually it got worse and I headed back to Joensuu. But on the way there was diamond dust at the quarry, 7 km as the crow flies from Mustavaara. So I took some photos there as well, climbing up a gravel mountain, leaving the lamp at the bottom and thus obtaining about 35° negative light source elevation.
This display was a result of low Stratus turning into ice crystals. It was right on when I arrived with car to the scene, which made me regret my idling in the comfort of indoors. The nucleating agent was the ice dust from Mustavaara snowguns. Essentially this created a punch hole in the cloud layer. All around this few kilometers wide opening it was overcast. Moon was three days short of full and an all sky plate crystal display was seen. The best of the crystal swarm moved back and forth and I tried to follow it with car.
2010. november 10., szerda
I soon was seeing "sun dogs" on the parhelic circle. I then was clearly seeing the Wegener arc inside the parhelic circle. It was very vivid as with my eyes I could clearly see the rainbow colors. To be honest I never did see the Heliac arc before. I was flipping through pictures inside later and it simply jumped out. I was like, what is that arc..then looked it up.
The top of the 22 degree halo visually looked crazy most of the time. Very clear and colorful and odd arcing. I thought it was just an intense circumscribed arc in there but it didn't look placed right and like more was happening. ( 1 - 2 - 3 - 4 - 5 )
The show only lasted 30-40 minutes I'd guess. Then it was pretty hard to get any optics at all. What was strange was visually nothing much was changed about the sky. I was watching for hours so there were different periods of less contrail garbage blocking out the sun. I had friends in Omaha, 20 miles south, and Lincoln another 45 miles south of that, looking too. They never saw anything good. They watched till sunset too, but they also didn't get out as soon as I was and that was the best part. I wonder what I missed before I got out.
The satellite loop for that day may give the key ( 6 ). I'm located in eastern NE which is at the top center. It was much like the crystals you get right behind a blizzard in air just where it is clearing behind the storm. You can see a more puffy nature to the clouds, they pass and the ice crystals are left in the air. That stuff on satellite is below typical cirrus level/flight level...but still up there. It for sure was different than normal cirrus. A lot of that "cirrus" in the shot is left over form all the contrails. Once the sun got lower you could see the moisture/clouds clearly below the contrails. So anyway, probably worth noting the clouds coming across at the time were more along the lines of mid-level clouds/moisture.
2010. október 30., szombat
On 18 October 2010 a superb diamonddust halodisplay was observed at the meteorological station Sonnblickobservatorium ( 1 ) in the Austrian Alps (3106 m, 12°57’ E, 47°03’ N). Hermann Scheer, member of the meteorological team at the observatorium, took images of 13 different haloforms between 08:30 and 09:00 CEST (06:30 and 07:00 UT): parhelia, 22°-halo, 46°-halo, lower tangent arc, subsun, subparhelia, infralateral arc with Parry-infralateral arc, supralateral arc, parhelic circle, subparhelic circle, subhorizon Wegener arc and helic arc. ( 2 - 3 - 4 - 5 - 6 ) The images were taken at a sun elevation of 8,9° to 10,3° between 08:31 and 08:40 CEST, the file names indicate the exact time.
The brightness of the Wegener arc was incredible. Very interesting is the combination of Parry-infralateral arc with infralateral and faint supralateral arc. This part of the phenomenon is similar to an observation in the Czech Republic (26th of December, at Lysa hora in Krkonose (Giant Mountains)), described at Optické Úkazy v Atmosférè ( 7 - 8 ) Thanks to Tomas Trzicky for the links. And also in Ice Crystal Halos ( 9 ). In this very small area of the display we can see a 46°-halo, Wegener arc, helic arc and the subparhelic circle too.
The display was observed at the upper boundary of the stratiform layer; weather conditions: 06:00 UT - air temperature -6,8°C, air relative humidity 96%.
Credit to Hermann Scheer for giving the permission to show his images at Crystal Halos Blog under this licence: ( 10 ). Homepages of Hermann Scheer: ( 11 - 12 - 13 ). This diamond dust display is described on the page "Atmospheric phaenomenons observed in Austria" too: ( 14 )
2010. szeptember 22., szerda
2010. augusztus 4., szerda
2010. július 24., szombat
I certainly do not live anywhere near to a ski slope or factory chimney that would produce lots of ice crystals. There is no evidence on the photo of local ice crystals as we see often in diamond-dust displays. The climate here is very dry and we often find low-lying layers of diamond dust particularly over our river.
Thus, I hesitate to claim that this is a "natural" Moilanen arc but it was not taken near to ski slopes. Maybe our furnaces produce the requisite crystals sometimes, in which case I will be on the lookout next winter for a repeat of this display.
2010. július 2., péntek
Alan has sent another pair of odd radius halo images. These were taken from Calgary, Alberta, Canada in May, 2009. ( 2 - 3 )
2010. június 29., kedd
As Elmar Schmidt tells: "All in all the phenomenon looked spectacular and eery with the broad belt starting at the 18-deg-radius. Of note is also its quite southerly location and the longevity, which might be interesting to compare with simulations, especially at the sun's elevation of 57 degrees." ( 1 )
Further images of the display between solar altitude 54 and 29 degrees are also available ( 2- 3- 4- 5 )
2010. június 20., vasárnap
2010. június 12., szombat
2010. június 4., péntek
The elliptical halo display observed yesterday by Marko Riikonen and Jari Luomanen was formed - as usual - in Ac virga. Marko had been paying much attention to Ac virgas for some time, and could therefore observe the whole display from beginning to end. From his perspective the display lasted six minutes between 10:18 - 10:24 and was uniformly good during the whole period. From Jari's place of observation, the best phase lasted a couple of seconds only.
More photos of the observation can be seen in their galleries ( 1 - 2 ).
2010. május 17., hétfő
2010. május 14., péntek
There is also, before the odd radius started, photo of parhelia with sun elevation of 33 degrees ( 2 ). Do you think there is something strange? To me they seemed not be on a same level. Although in the photo it may look like the right one is abnormallly high, it was actually the left one that was abnormally low. Or at least that's how it looked. I knew this is hard to photograph because of the lens distortion. Maybe it was illusion. I have seen these things also before, at least in 30.9.1987 display. Also that time it got me rushing to photograph it. But that photo is not conclusive either.
2010. május 10., hétfő
Here are some simulations to follow up with the possible new arc from Moilanen crystals ( 1 ). As suggested by Marko, I did some “photo quality” simulations with the two Moilanen arcs using Jukka Ruoskanen software. The Moilanen crystals are simulated using 34deg prisms pointing up.
First I simulated Jari Luomanen’s picture ( 2 ) which shows best the two arcs. I found that two Moilanen population tumbling with 1° and 14° deviation matched well the display.
Then I tried to compare two low source elevation displays from Marko Riikonen ( 3 - 4 ),and Milan Osecky ( 5 - 6 ). I simulated them with the same populations as the one I found from Jari Luomanen picture (1deg and 14deg standard deviation tumbling angle). The differences between the two populations are pretty subtle at this low source elevation. They are mostly in the shape of the outer edge of the Moilanen arc and in aspect which can be either hollow or solid. New arc has a more solid and curved edge. Although it is difficult to know for sure, I think the two pictures show the two different arcs.
Finally, I did some simulations that shows how one arc becomes another when the tumbling angles are increased, and for different source elevations ( 7 - 8 - 9 - 10 ). The limit between the two arcs would be somewhere between 8 and 16deg tumbling angles. The amount of crystals is kept constant in the simulations so brigthness can be compared. The two arcs vanish quickly when source elevation is increased. With the tumbling angles used (up to 64deg standard deviation), no lower component appears for the new arc.
2010. május 3., hétfő
Frank Le Blancq
2010. április 22., csütörtök
I found my record, sketch ( <a href=" http://www.ursa.fi/blogit/media/blogs/halos/Lefaudeux/18-09-98-17h15-17h55HL_post.jpg">1 ) and pictures ( 2 - 3 - 4 ), and realized there were very prominent Lowitz arcs too!
From my notes, the display happened on September 18th, 1998, between 17h15 and 17h55 local time. The sun was at 24 degrees altitude at the middle of the display. At that time, I had little knowledge of the halos. I just knew from astronomy books about parhelia, 22° and 46° halos. I had observed before upper tangent arc (which I called upper 22° parhelion) and circumzenithal arc (which I called upper 46° parhelion), but never Parry arc.
During the display, I was mesmerized by the colourful upper suncave parry arc and by the parhelion brightness. My notes are focused on these arcs, especially the Parry one, with detailed description of its length, width, brightness and colors. Nothing on the Lowitz arcs except the sketch which shows radiating arcs from parhelia.
The stitched picture shows almost complete upper Lowitz arc, very long Parry arc and faint 22° halo. There are also some weird bands on the bright parhelion. I think I have some memories of shadow bands running across the parhelion, a bit like in the video by Anna Herbst ( <a href=" http://spaceweather.com/swpod2010/11feb10/anna-herbst1.mov?PHPSESSID=liolll4f05nuq4m9ascc45gpg5">5 ), but cannot be sure as there is no mention of these in my notes.
I really wish I could observe again such an exceptional display now that I am able to appreciate it to its true worth
2010. április 12., hétfő
I suggest the following explanation: The ice crystal halo display is not made simply from idealized halo surfaces (or, more general, from an intensity field in space which takes into account all the subtle intensity variations along parhelia, tangent arcs, and so on) rather than from individual crystals that fall down or drift around in space and sample the intensity field pointwise along their trajectories. These crystals are real physical objects and should be perceived stereoscopically at their actual position, if being illuminated externally at equal brightness for each eye. But in case of a streetlight halo they deflect light by themselves to the observer according to the intensity field which lies stereoscopically flat around the lamp. Thus, especially crystals near to the observer should not appear at equal intensity for both eyes. But as long as both eyes receive light without any large difference in intensity the crystal should be perceived at its actual position and not pinned to some plane in the lamp’s distance, and so we get the stereoscopic depth impression of the halo display. This also implies that on a long-exposed stereo photo all contributions form individual crystal trajectories should be averaged, which would lead to a smooth and stereoscopically flat image of the intensity field.
At this point, I had the idea of an animated simulation. Spatial perception is still not fully understood physiologically, and there might also be an influence of dynamic effects from the moving crystals as well. So some kind of stereo animation should be the suitable representation of the problem, and then we can leave the interpretation work to the brain just like in a real display. I started the computation with typically 200000 random crystal positions in a cube between observer and light source that were tracked for 100 time steps. From one step to the next the crystals move a small distance downwards (when reaching the ground, a new position is generated to prevent from loosing the crystals). From geometry, it is quite easy to calculate the intensity for different halo species if the intensity field is provided as some look-up table or analytical fit. This is done separately for each eye. The images linked below show the results for cross-eyed viewing (left image on the right side) and as anaglyph (left image red).
( 2 - 3 - 4 - 5 )
The included halo species are super/sublamps, 22° super/subparhelia, 22° parhelia, and 22° tangent arcs. The distance observer-lamp (in horizontal projection) is 10 m, the lamp elevation is +5° for the first and –5° for the second series. For the first simulation, the field of view corresponds to a 28 mm lens on 35 mm film (cropped to a square area), for the second it corresponds to 20 mm. The histogram had to be cropped at the white edge and the gamma value was increased as well since the original images that were normalized with respect to the brightest pixel would appear much to dark.
There are some simplifications in the model that I don’t want to conceal: No colour dispersion for refraction halos was taken into account, all calculations were done with a fixed index of refraction. Diffraction and defocus blurring were also neglected, each crystal is assigned to a single pixel (but more than one crystal can contribute to the brightness information of one pixel). The intensity ratios between the halo species were set arbitrarily and are not determined by a predefined set of crystals with certain orientations, aspect ratios, and so on. A subtle matter is that remaining degrees of freedom (such as the rotation angle around the vertical axis for parhelia oriented crystals) are already averaged by taking the intensity from a look-up table and not assigning these degrees of freedom to the simulated crystal the same way as it was done with the spatial coordinates. Otherwise the computation time would have increased dramatically. So I did not simulate individual crystals in this sense, or otherwise I have to assume that they are spinning around their allowed axes at quite a high speed in order to do the averaging.
Nonetheless, it can be seen quite nicely from the animations that eye-connected halos (parhelia, upper tangent arc for positive lamp elevation, “super”parhelia at negative lamp elevation…) near their classical positions – when crystals close to the observer are involved – seem to pop out of the screen and show a distinct stereoscopic depth impression.
2010. április 11., vasárnap
The three displays shown above were seen on successive days in Tampere on the period of 31 March to 2 April this year ( 1 ). Abundant start of odd radius halos may indicate a good year of high cloud halos coming. 1987 and 1996 were the best high cloud halo years in Finland.
Other displays from this spring:
2010. április 10., szombat
2010. április 9., péntek
At lower source elevation, the new arc would mix with the usual Moilanen arc so it is difficult to make the distinction between the two arcs. The main difference is that usual Moilanen appears as a hollow “V” while new arc would be more like a solid wedge. This new arc could be responsible of some appearance of the Moilanen arc when it appears as diffuse ( 3 ) compared to more usual sharp arc ( 4 ).
To draw a parallel, the usual sharp Moilanen is a bit like the upper sunvex Parry arc while the new arc is more like the upper tangent arc. To the extremes, if the crystals take all the rotational angles, there would be a lower component like the lower tangent arc, or if the source is very high, there would be a complete circle like the circumscribed halo.
More observations are needed to confirm the existence of this arc especially at high source elevation when it is clearly separated from usual Moilanen arc, so monitoring about this possibility is encouraged!
2010. április 7., szerda
Changing crystal shape causes surprising behavior with Liljequist parhelion, casting doubts on its identity as a halo form. Look at the simulations above, larger image opens by clicking.
I have simulated (software: HaloPoint2.0) the anthelic side of the plate parhelic circle with three crystal shapes. On the left are all rays, on the right only the 3-5-6-7-3 rays that I have often referred as the main contributor to the Liljequist parhelion. But the shape of light stripe created by the 3-5-6-7-3 rays depends on the crystal shape. This means that the definition of the Liljequist parhelion becomes so murky that we might as well forget about it; 3-5-6-7-3 rays are just rays that light the parhelic circle, nothing more.
The other ray that I have mentioned of being responsible for the Liljequist parhelion is the 3-5-6-7 ray. Its product does not change with crystal shape, but it is probably too weak alone to produce any visible brightening on parhelic circle. I think it was me who originally brought up the Liljequist parhelion. I apologize for the mess. I guess we should let go of Liljequist, but it has been around for a while, so that may be easier said than done.
2010. április 6., kedd
Three earlier observations of the reflection subsun are known, two of which have been shown in this blog ( 2 - 3 ).
2010. április 1., csütörtök
For a change a display from Africa. This was see in Accra, Ghana, on 10 March this year. The photo was taken by Kwaku Chintoh.
Sun is at 75.5 degrees elevation. The two sun concentric halos are rather 9° column arc and circumscribed halo than 9° and 22° halos. That is because of their sharpness - circular halos from randomly or very poorly oriented crystals are expected to be more diffuse. There is also parhelic circle.
In the simulation column oriented prismatic and pyramidal crystals were used. Pyramid crystal tilts are 7 degrees. Simulation was made with HaloPoint2.0 -software. Parameter-file is available ( 1 )
2010. március 29., hétfő
The original observation was made by C. F. Bottlinger during an air balloon flight on 13 March 1909 over Göttingen, Germany ( 2 ). The phenomenon lasted long, from 1 to 1½ hours. Bottlinger suggested that the ring could form from a reflection in crystals falling in pendulum motion. Computer simulations by Lynch et. al. in 1994 ( 3 ) showed, however, that this motion would produce uniform elliptical glow instead of defined ring. As an alternative they suggested plate crystals in gyration motion for the explanation.
Intuitively it would seem unlikely that all ice crystals in the cloud would fall exactly in the same inclination angle to produce Bottlinger's rings. Bottlinger's rings form in the same Altocumulus virga as elliptical halos around the sun, for which pyramidal crystals with very low apex angles has been suggested as an explanation by dutch S. W. Visser in 1960. These crystals would produce also Bottlinger's rings. The gyrating crystals could make elliptical halos by assuming that they are reflections of the Bottlinger's rings from horizontal plate crystals. This was suggested by Lynch et. al. Simulations by Sillanpää et. al. in 1999, however, showed that this can not model the observed elliptical halos, while pyramidal crystals yield much more satisfying results.
A photograph taken by Claudia Hinz ( 4 ) also clearly proves that elliptical halos are not reflections of Bottlinger's rings. These two halos have not been observed simultaneously, but an almost simultaneous observation was made by Leena Virta and I in 1999 in Resolute Bay, Canada. We observed Bottlinger's rings from an airplane that was flying under the Ac cloud layer and when the plane landed, the same cloud showed elliptical halos around the sun.
Tim Stone's photos show also fainter ring outside the main ring. Assuming the gyration explanation this would require two ice crystal populations with constant inclination angles. It will be interesting to try to simulate this with pyramidal crystal model. Les has already a simulation on his site, but he says the parameters could be fine tuned. The rings' dimensions and sun elevation are provided, so anybody can give it a try!
2010. március 19., péntek
2010. március 16., kedd
I continued supervision. Where I went on ice of the frozen gulf, halo followed ahead of me - is visible the big area has been covered by crystals. Soon in the sky has started to inflame 22° halo which has then reached enough big brightness. This all looked very unusual - small halo in the sky, and big on the earth.
Nikita Kulanov - Saint-Petersburg, Russia
2010. március 13., szombat
In numerous entries of this blog there are halo simulations made with "a simulation software by Jukka Ruoskanen". The software has been under development for the past couple of years and has now reached the point where it is ready enough to be published. The software, HaloPoint 2.0, has its own webpage from which the software as well as it's user manual can be downloaded.
The software package is a zip-file. Simply extract it into a suitable directory and keep the two components of the software, HaloPoint.exe and Simulation.dll, always in same directory. The software runs in computers having Windows operating system (tested in XP and Vista). Also a .NET Framework 1.1 is required, which is already installed in most computers, but in case it is missing it can be downloaded for free from Microsoft pages.
In software homepage there are simulation examples together with parameter files so that getting started with the software is easy. In addition to the examples it is advisable to take a glance at the user manual so that the various features of HaloPoint 2.0 can be utilized.
Hope you'll have fun with it.
2010. február 28., vasárnap
On my way home from work I observed 14 different haloforms within 1 and a half hour (14:15 - 15:45 CET). It started with a bright circumzenith arc, sundogs and a clearely vertically elongated left hand side 120° parhelion on a short parhelic circle. Later the 120° parhelion on the right hand side appeared. The highlight (about 15:15 CET) was the observation of the CZA, supralateral arc, 46° halo, suncave and sunvex Parry arcs, upper tangent arc, 22° halo with sundogs, Tape arc, helic arc, subhelic arc and a little bit later a small part of the left infralateral arc.
I run a simulation with Halosim from L. Cowley and M. Schroeder that shows the halos I have observed near the sun quite good. A report and many images can be seen by clicking the image above. I invite you to take a look at the site.
2010. február 25., csütörtök
The morning of 24th February at Riihimäki started with a solitary patch of supralateral arc ( 1 ) which was seen in a passing cloud and lasted for only a few minutes. Later on during the day a clearly elliptical glow could be seen in the vicinity of the Sun, and suddenly the glow started to have a defined shape: an elliptical halo. During the 2-3 minutes it took to gather photo gear and go back out was enough to lose the ring; the glow is all that can be seen in the 30 frame stack ( 2 ).
While the ellipse-stack was ongoing my attention was caught by two odd visitors: 23° upper plate arc and circumzenith arc. Immediately after change of lens the camera was grabbing images of that strange sight, see a 30 frame stack ( 3 ) and a 120 frame stack (taken with 3 second intervals, so total duration was about 6 minutes) ( 4 ).
The elliptical glow remained and sometimes seemed to have a true halo at its outer edge. The last two shots ( 5 - 6 ) show perhaps some kind of an ellipse, but it is hard to be confident since due to severe rush the images are not perfectly exposed and the 12bit sensor data is clearly in trouble because of the strong intensity gradient. Furthermore, the horrible dust of the lens spoils the images completely. Digital image processing methods, such as levels- and curves -adjustment and unsharp mask filter, are merciless regarding the cleanliness of the optical surfaces. Apologies for that.
During the ellipse - 23° plate arc - CZA -phase the sky was blue and snowflakes were floating down. The wind was not hard, but clearly noticeable and temperature in the ground was about -13°C. The halos seemed to be formed in an AC virga -type of "cloud", but the origin of the virga remained a mystery - there were no clouds seeding it. It is impossible to say whether the ellipse and the other halos were formed by the same cloud material or not. Some of the snowflakes were studied under microscope, but nothing peculiar was seen, just plain snowflakes.
On the 22nd of February Eetu Saarti managed to shoot a lunar elliptical halo in Tampere, whose duration was less than 30 seconds(!) ( 7 ).
2010. február 11., csütörtök
2010. január 30., szombat
Photos and videos of the windshield halos seen on the night of 26/27 January in Tampere are now available in two galleries ( 1 - 2 ). The display was dominated by plate and Parry oriented halos. Circumzenith and circumhorizon arcs were strong as were the upper and lower suncave Parry arcs. Parhelic circle and 120° parhelia were also well developed. Less conspicuous were the subhelic arc ( 3 ), upper sunvex Parry, 46° Parry and the blue spot. Additionally, two unidentified features were seen.
We did not photograph the crystals, but we think the display was formed in frost crystals that have their basal or prism faces parallel to the windscreen. Both populations could be separate crystals, but also 90 degree crossed crystals could be a consideration. Visually the frost seemed rather grainy, which suggests compound crystals.
The halos were observed with a LED lamp pointed through the windshield as well as with reflected light (the lamp on the same side of the windshield as the observer). By moving the lamp we were able to observe in real time the transformations in halos that occur as the light source elevation changes (4). Videos show the shift between circumzenith and circumhorizon arc. There are also peculiarities. One is that the parhelia does not seem to move much further from 22 halo as the lamp elevation rises.
Both two unidentified features were documented. The other one was found from the video: in the video, far below parhelic circle at around 120 azimuth, appears a vertical pillar (5). The other effect was a diffuse arc that was seen when we lit up the windscreen from the front of the car and watched it from behind the lamp. This elusive effect was documented in a video (6).
After hours of documenting we ended the night by taking a ride and videoed the halos as they swept the windshield. As we neared a streetlamp, first one to sweep the screen upwards was the lower suncave Parry followed by circumhorizon arc. Then, as the lamp was overhead and behind, parhelic circle swept the screen downwards. If the lamps were a bit further on the side relative to our driving line, then also 120 parhelion was seen on parhelic circle.
It was a great night. In those six hours that we spent worshipping this complex display, we learned all the time more on what we were seeing and created new tricks to take photos. Certainly this winter’s top halo experience for both of us.
Marko Riikonen, Jari Luomanen
2010. január 29., péntek
The responsible crystal would be a crystal made of a two hexagonal usual hexagonal crystals stuck together. The simplest configuration would be the one of a plate crystal (called the main plate) with another plate or a column stuck on one of its base (called the stuck crystal).
Condition of creation of Moilanen arc
The conditions for the creation of a Moilanen arc from this configuration are the following:
1: The main plate must be horizontal
2: The stuck crystal is on the inferior base of the plate
3: The bases of the stuck crystal must be perpendicular to two side faces of the main plate
1 and 2: this configuration is aerodynamically stable when stuck crystal is centered on the inferior base plate. To figure this, one can think of a paratrooper, the parachute being the plate crystal and stuck plate or column being the charge. So naturally the main plate will rotate so the stuck crystal is on the inferior base. Now why would the stuck crystal be centered on the main plate? I think that for this stuck crystal configuration to happen, the crystal density must be very high. So in the case of crystal swarms created by snow machine, the crystals would be stuck when they are small, just after their creation. So the growth of the crystal, will happen after. The growth being isotropic, the stuck crystal will naturally be centered on the main crystal. And the aerodynamically stable condition is the main plate being horizontal with stuck crystal on the inferior base.
3: I have to admit that the perpendicularity of the bases of the stuck crystal and two sides of the main plate is the most challenging point. My best explanation on this is that as the two components are crystals, there are definitely orientations of stucking that will be more stable. I hope that crystal experts will be able to help on this point to validate that this orientation is more likely to happen than any other. Crystal samples obtained during the display of 14th of December 2009 by Mika Aho, Ágnes Kiricsi and Marko Riikonen show some crystal looking very much alike the one described in the proposed explanation
Figure 2 and 3.
Ray path responsible of Moilanen arc
The ray path responsible of the Moilanen arc is the rays entering a vertical side face of the main plate and exiting the upper lateral side face of the stuck crystal. The prism angle in this configuration is 30° but with the entrance face vertical.
Usually associated halos
This configuration of crystal is so still capable of producing all the plate arcs (parhelia, parhelic circle, circumzenithal arc, pillars, etc…) and also the Parry arcs (sunvex through the stuck crystal and suncave through the upper base of the plate and the stuck crystal. So this configuration seems to be well compatible with the halos usually observed with the Moilanen arc.
I have been able to check it thoroughly but there does not seem to be any spurious arcs from this configuration. Spurious arcs would be created by rays entering side faces of the main plate and side faces of the stuck crystal. I will try to check it, but for the most simple other rays, it does not seem to exist direct ray path, at least if the stuck crystal is a regular hexagonal crystal.
Other rays would just create already known halos. Rays entering by the base of main plate and exiting by the sides of stuck crystal would create parry arcs, and by the base of main plate and exiting by the base of stuck crystal would create circumzenithal and supralateral arcs.
Distance from the sun
The distance between the apex of the Moilanen arc and the sun can be easily calculated using the 30° prism with vertical entrance face description. At low sun elevation, the distance is about 11°. It increases slowly to 13° at 10° solar elevation, 15° at 15° solar elevation, 18° at 20° solar elevation. As the sun elevation increases, the rays path becomes less likely because of the stucking area and also of the increased incidence on the exit face. The total internal reflection condition is met when the solar elevation is higher than 26°. This is in agreement with the fact that Moilanen arc are usually observed at low sun elevations.
I have made a simple ray tracing program to simulate the Moilanen arc shape. This simulation tool does not take into account the real crystal shape, only the relative orientation of the faces. The shape are represented for 0°, 3°, 6°, 9°, 12°, 15° and 18° solar elevation. The simulated shape matches very well the photographs of the arc, with a reduced curvature at higher solar elevation. The simulation shows the arc being more extended on the sides as I don’t take into account the real 3D shape of the crystal, but just the relative face orientation.
Figures 6, 7, 8.
The proposed explanation is based on a 30° prism which entrance face is vertical. In this explanation, the responsible is a horizontal plate on which is stuck a plate or column crystal. I think this type of crystal explains very well most (if not all) of the observed properties of Moilanen arc. More simulations to check that no spurious arcs arc created would help confirm this, as well as some insights of crystals experts on the probability of getting such configuration.
Nicolas Lefaudeux, January 29th 2010
2010. január 28., csütörtök
2010. január 27., szerda
2010. január 26., kedd
2010. január 25., hétfő
January 2010 in Tampere, Finland has seen an incredible onslaught of pillars. Starting from New Year’s Eve cold weather (which recently has been fed by Siberian high) has settled over Finland. The temperatures have been around -20 °C. Pillar forests have reigned night after night, as the conditions have been mostly favourable to crystals that only produce pillars.
Snow making in the ski centres of Tampere area has stopped about two weeks ago. Despite this, diamond dust has been a nightly occurrence. Sufficient humidity and probably urban emissions have contributed to crystal precipitation.
We have hunted halos practically every night, driving around Tampere to find the crystal swarms. To our surprise these swarms - usually a few kilometers across - remained in one place throughout the night. Our impression is that local topography affects this behaviour.
More images and some further observations are available in separate galleries (1 - 2)
Marko Riikonen and Jari Luomanen
2010. január 19., kedd
In the image above, there is a comparison of a single photo and a lighten stack of 99 photos. The camera was on tripod and the photos were shot fast with series mode. During shooting a car was moving in the parking lot (a ghostly image of it is seen on the right in the stacked image). These frames were omitted from the series because sun's reflections from the car might have been disturbingly imprinted in the stack as the lighten mode takes always the brightest pixel of the stacked images.
2010. január 18., hétfő
2010. január 17., vasárnap
2010. január 16., szombat
A video and two new images of the 09-10 January 2010 Display in Kangasala, Finland are now available for viewing (1 - 2 - 3). As you follow the first link please note that the video is displayed below the still image.
The video consists of 79 consecutive still images, each shot with a 6s exposure time. The camera shot a new frame automatically as the last one finished so the exposures lasted for 479 seconds (just under 8 minutes). Based on the EXIF data recorded by the camera the 79 frame sequence lasted for 585 seconds (so 106 seconds of the time were used by the camera's internal electronics and the operation of the shutter mechanism between frames). This time frame of 585 seconds is compressed into 20 seconds on the video.
The width of the halo changes abruptly between frames in the video. At one point (about three seconds into the video) the shift is particularly dramatic. Either the change is due to sudden changes in crystal orientations or the apex angle of the halo forming wedge in the crystals was changing (probably in steps, not in smooth continuity).
Part I of this post can be found here: (4)
Edit: new animated images are available (5 - 6). See comments for more information.
2010. január 13., szerda
Stacking revealed the odd radius halos better. The one above - a stack of 138 photos - is made with lighten mode in Photoshop, and shows 9, 20, 24 and 35° odd radius halos. The 24° one is not well separated from the 22° halo and it shows better in 293 frame stack by average mode using Registax ( 1 ).
The lighten method (introduced by Jari Piikki for snow surface halos), which chooses the brightest pixel of the stacked photos, provides more realistic looks with the crystal glitter and here the realism is somewhat enhanced due to high number stack. It has the downside is losing colors: colored pixel is replaced if it overlaps with a white one. But you can still see plenty colored crystal glitter in the 46° halo in the larger image that opens by clicking the photo.
For the lighten method stack photos are taken low down where most of the halo is formed of separate crystals. From standing height the halo becomes more solid, especially near the horizon and then average stacking mode works better.
Having seen a couple of snow surface odd radius displays now it seems they can be expected when the snow surface has been fed with water fog. The odd radius halos rarely show up clearly visually, but a broad 22° halo, that is not well defined from its inner edge, seems to be a sure sign.
The display was photographed by Harri Mänty on January 9 in Vantaa, Finland. The temperature was about -15 to -16° C. Click the image to see the rest of Mänty's photos.
2010. január 12., kedd
2010. január 10., vasárnap
The display was visible for almost four hours in a very localized pocket of the Kangasala industrial area of 500 meters across at most. Atmospheric humidity was high, the area was surrounded by water fog. Probably emissions in the industrial area initiated nucleation of this fog to ice crystals. The temperature was -16 degrees Celsius.
This halo probably arises from a simple reflection from nearly horizontal crystal faces. The crystals we used in the simulation (see above image; software used: HaloPoint 2.0 beta by Jukka Ruoskanen) are similar to those used in simulating elliptical halos and Bottlinger's rings. The raypath for the halo is same as for Bottlinger's rings, except that it occurs on the lower pyramidal face. The atmospheric conditions (temperature, high humidity) support the idea of such a crystals since Bottlinger's rings and elliptical halos are mostly observed in altocumulus virga, which form in similar conditions.
Due to the halo forming raypath, this halo could be called as the super-Bottlinger if we were to adapt the naming system suggested by Walter Tape or the supra-Bottlinger in case Gunther Können’s naming system was used.
The series of images captured in the spotlight beam show variation in the angle of these new arcs. Presumably this happened because the angles of the reflecting faces changed. It had been long suspected that elliptical halo sizes can change during the display - our observation provides now supporting evidence. However, we did not observe any elliptical halos. At times an elliptical glow was suspected around streetlights but these were never confirmed by photographs.
Crystals were sampled and photographed at the same time as the display was photographed in the spotlight beam. The crystals have dendritic growth and it is difficult to see the structure responsible for the new halo. Possibly the tips of the branches are sloping. Such feature has been earlier pointed out by Walt Tape in a snow crystal photo. From the brightness variation between the pillar and the new halo in different stages of the display, we may assume that the extent of the sloping area in the crystal varies.
Additionally, the display contained diffuse helic arc like extensions from the lamp, as seen in the middle photograph. These were also observed when only pillar was visible. Possibly the abundant crossed plates were behind their formation.
See more photos from this night of halo hunting ( 1 - 2 ).
Jari Luomanen, Marko Riikonen
2010. január 4., hétfő