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Some Bishop's rings for a change. Bishop's rings are very large coronas that form from very small particles. These are the four Bishops that I have photographed. The first photo shows a "genuine" Bishop: it formed from volcanic eruption particles in stratosphere, ejected there by the cataclysmic eruption of Mt. Pinatubo in June 1991. As there is no cleaning rain in stratosphere, the particles drift around a long time and this Bishop was photographed a year later on 1 May 1992 in Vuontisjärvi, Lappland. The corona was visible for about two years after the Pinatubo eruption. It was seen in the sky pretty much all the time, but its intensity varied from day to day. Stratospheric Bishops are rare because only the largest volcanic eruptions can penetrate the tropopause.
Some photos are also shown from the four days trip to Pinatubo that I made with Holger and Hans in May 1994, three years after the main eruption. Pinatubo was still active, but these were tiny secondary eruptions on the flanks initiated by rainwater seeping to the ground and interacting with the hot pyroclastic material deposited during the main eruption. It was not a safe trip.
Three other Bishop's rings are tropospheric Bishops. First are three images of a Bishop's ring at El Tatio geysir field in Chile at 4300 meters elevation in December 2000. I was watching this with Leena Virta. It was a huge "super-Bishop", with the outer red edge at about 55 degrees from the sun. In one image comparison is also given with 22° halo. Visually this was of course more impressive and between the inner blue disk and broad red outer rim there was also narrower green segment, but that did not catch on film (Ektachrome 100 WS or SV was the film). The corona was seen in some stuff that formed Altocumulus, the developing clouds are seen in the photo.
Then there are two cases of stratospheric Bishops from last summer in Tampere. These ones also formed in "pre-Altocumulus". For the first case size comparison is given with 22° halo. I have been wondering whether the Islandic volcanic eruption may have had something to do with these, at least in Lappland red volcanic sunsets were observed. But I have a recollection that the second one could not have been caused by that eruption anymore.
Photographing Bishop's rings is always disappointment, the colors do not reproduce well. Faint Bishops during hot weather (caused by the forest fires in the Russia, for example) are not uncommon in the summer in Finland, but I think it would be hopeless to try to photograph them.
2011. február 8., kedd
2011. február 6., vasárnap
Halo observations by J. R. Blake in the Antarctic (part II)
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Completing the first post of Roger Blake's halo observations in the Antarctic, here are the rest of his halo drawings together with the written descriptions. The display at midnight between 2 and 3 December 1958 comes as two dravings in Blake's book. It was remarkalbly accurate observation of a complex diplay with all four kaleidoscopic arcs, especially when one takes in to account that it was observed from a moving dog sledge. The display had also its contribution to halo science: both Tricker and Greenler used the observation to support the theoretical considerations of the kaleidoscopic arcs. In the drawing these arcs are 1) helic arc; 2) subhelic arc; 3) subanthelic arc and 4) Tricker arc. The observational account in the above image is not given full, but only from the part concerning these arcs.
Completing the first post of Roger Blake's halo observations in the Antarctic, here are the rest of his halo drawings together with the written descriptions. The display at midnight between 2 and 3 December 1958 comes as two dravings in Blake's book. It was remarkalbly accurate observation of a complex diplay with all four kaleidoscopic arcs, especially when one takes in to account that it was observed from a moving dog sledge. The display had also its contribution to halo science: both Tricker and Greenler used the observation to support the theoretical considerations of the kaleidoscopic arcs. In the drawing these arcs are 1) helic arc; 2) subhelic arc; 3) subanthelic arc and 4) Tricker arc. The observational account in the above image is not given full, but only from the part concerning these arcs.
2011. február 4., péntek
Diamond dust halos at -2° C from Italy
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Diamond dusts close to freezing point are not common. This display, photographed by Francesco Cadini on 3 February 2011 a few kilometers outside Milano, occurred when Francesco's car thermometer showed values between -1.5 and -2° C. Taking into account a possible inaccuracy, he says that it could not have been colder than -3° C.
The display formed from thick water fog. Cadini tells that in the area where the display was seen there is a phenomenon called the "chemical snow", which occurs in high pressure situation with fog and clear sky above the fog. The abundant pollutans in the air are supposed to initiate this chemical snowing and in one case 2 cm of snow accumulation has been recorded. There is an Italian language description of the phenomenon.
Most likely the pollutants were also responsible for the transformation of the water fog to observed diamond dust. A quick look at some papers reveals that if certain substance acts as an immersion freezing nuclei and contact freezing nuclei, the latter works at much higher temperatures. So probably the formation of this diamond dust was initiated by pollutant particles colliding with water droplets. Once the process starts, sudden freezing of droplets may produce splinters that further freeze other droplets and chain reaction is created. The water droplets also evaporate and the released water vapor deposits on ice particles, and through this growth we get the crystals with proper faces for halo making.
Supercooled water fog in general has a tendecy to turn into diamond dust locally. If you drive around the city when it is below freezing you are likely to encounter spots of diamond dusts. Usually only the lower layer of the fog turns into diamond dust and thus you can see halos only at night in the light of streelamps. Sometimes, though, as in Cadini's case, a whole fog column turns into ice crystals and sun or moon halos can be observed. The process punches a hole in the fog and in the photos above the edge of the foggy wall is seen clearly.
Cadini's display has also weak Moilanen arc, which shows best in heavily usmed image. He suspects that this might be the first Moilanen arc photographed in Italy.
Diamond dusts close to freezing point are not common. This display, photographed by Francesco Cadini on 3 February 2011 a few kilometers outside Milano, occurred when Francesco's car thermometer showed values between -1.5 and -2° C. Taking into account a possible inaccuracy, he says that it could not have been colder than -3° C.
The display formed from thick water fog. Cadini tells that in the area where the display was seen there is a phenomenon called the "chemical snow", which occurs in high pressure situation with fog and clear sky above the fog. The abundant pollutans in the air are supposed to initiate this chemical snowing and in one case 2 cm of snow accumulation has been recorded. There is an Italian language description of the phenomenon.
Most likely the pollutants were also responsible for the transformation of the water fog to observed diamond dust. A quick look at some papers reveals that if certain substance acts as an immersion freezing nuclei and contact freezing nuclei, the latter works at much higher temperatures. So probably the formation of this diamond dust was initiated by pollutant particles colliding with water droplets. Once the process starts, sudden freezing of droplets may produce splinters that further freeze other droplets and chain reaction is created. The water droplets also evaporate and the released water vapor deposits on ice particles, and through this growth we get the crystals with proper faces for halo making.
Supercooled water fog in general has a tendecy to turn into diamond dust locally. If you drive around the city when it is below freezing you are likely to encounter spots of diamond dusts. Usually only the lower layer of the fog turns into diamond dust and thus you can see halos only at night in the light of streelamps. Sometimes, though, as in Cadini's case, a whole fog column turns into ice crystals and sun or moon halos can be observed. The process punches a hole in the fog and in the photos above the edge of the foggy wall is seen clearly.
Cadini's display has also weak Moilanen arc, which shows best in heavily usmed image. He suspects that this might be the first Moilanen arc photographed in Italy.
2011. február 2., szerda
Old photos of halos from anthelic and subanthelic region
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Alan Clark sent these scans of his old slides. The anthelic arcs in the first two photos were photographed in 1980 in Canada, while the two latter images with subparhelic circle, subanthelion and possible faint arcs upwards from the subanthelion were photographed in 1978 on a flight across the US, en route to NASA Ames. Halos suffer markedly when scanned from slides but it is always nice to see any documents of these rare halos.
Alan Clark sent these scans of his old slides. The anthelic arcs in the first two photos were photographed in 1980 in Canada, while the two latter images with subparhelic circle, subanthelion and possible faint arcs upwards from the subanthelion were photographed in 1978 on a flight across the US, en route to NASA Ames. Halos suffer markedly when scanned from slides but it is always nice to see any documents of these rare halos.
2011. február 1., kedd
Halo observations by J. R. Blake in the Antarctic
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There are two books devoted to halo observations in the Antarctic in 1950's. One is by the Swedish meteorologist Göstä Liljequist and another by the Australian glasiologist Roger Blake. The images above are from Blake's book "Solar Halos in Antarctica", which I found for sale in an Australian antikvariat a few years ago. Blake was in a project called the "Souther Seismic Traverse", using the Australian research station Mawson as a base for the trips further south. The time he spent in the Antarctic spanned from 30 September 1958 to 17 January 1959 and halos were a sideline research for him, clearly inspired by the Liljequists's work in the early 50's. Above are shown three displays from Blake's book.
The first display, observed from a field trip at the location 70.1° S and 62.1° E on 21 November 1958, contains 9° halo. Blake wrote the following notes on it: "The parhelic circle extended only about 10° either side of the sun, being rather faint. It formed a closed semicircle with a very faint Hall's halo, the radius of that halo being approximately half that of the 22° halo, but observations being greatly impeded by the sun's brightness."
The second display was seen near the first display's location, on 28 November 1958. It has sunvex Parry arc and halos at the anthelic region: "Through the anthelic point was a bright, white vertical pillar, reaching the ground. Also visible was part of the parhelic circle, the intersection of the two arcs being a 'spot' of greater intensity. The parhelic circle did not exists elsewhere."
The third observation on 29 November 1958 was made in the same area as two previous ones. It has several interesting features: "The 22° and 46° halos were both very brightly coloured, and both 22° and 46° parhelia were present, both pair being very bright. The vertical pillar extended from the horizon to the top of the 22° halo, which was brilliant. From this point extended the upper contact arc which merged smoothly with Parry's Arc; both these arcs were coloured and very bright. [... ] The circumzenithal arc was also present, being very brightly coloured. A fairly bright, coloured arc, passing through or close to the zenith and concave to the sun was visible, the colours being very pure and distinct. Because of its position, it was difficult to obtain any estimates; however, it appeared to have approximately the same curvature as the 22° halo. The full 180° of the parhelic circle was visible on either side of the sun, being intersected approximately 90° from the sun by a pair of white pillars extending from the horizon slightly above the parhelic ring. The points of intersection resembled mock-suns, though white. Also at 180° there existed a somewhat fainter, white pillar extending to just above the horizon, the point of intersection with the parhelic circle again being brighter. The display disappeared as the cloud cover increased."
Now I could go on discussing what Blake really saw in 29th November display, but that would not lead anywhere. Suffice to say: a photograph would have been nice.
There are two books devoted to halo observations in the Antarctic in 1950's. One is by the Swedish meteorologist Göstä Liljequist and another by the Australian glasiologist Roger Blake. The images above are from Blake's book "Solar Halos in Antarctica", which I found for sale in an Australian antikvariat a few years ago. Blake was in a project called the "Souther Seismic Traverse", using the Australian research station Mawson as a base for the trips further south. The time he spent in the Antarctic spanned from 30 September 1958 to 17 January 1959 and halos were a sideline research for him, clearly inspired by the Liljequists's work in the early 50's. Above are shown three displays from Blake's book.
The first display, observed from a field trip at the location 70.1° S and 62.1° E on 21 November 1958, contains 9° halo. Blake wrote the following notes on it: "The parhelic circle extended only about 10° either side of the sun, being rather faint. It formed a closed semicircle with a very faint Hall's halo, the radius of that halo being approximately half that of the 22° halo, but observations being greatly impeded by the sun's brightness."
The second display was seen near the first display's location, on 28 November 1958. It has sunvex Parry arc and halos at the anthelic region: "Through the anthelic point was a bright, white vertical pillar, reaching the ground. Also visible was part of the parhelic circle, the intersection of the two arcs being a 'spot' of greater intensity. The parhelic circle did not exists elsewhere."
The third observation on 29 November 1958 was made in the same area as two previous ones. It has several interesting features: "The 22° and 46° halos were both very brightly coloured, and both 22° and 46° parhelia were present, both pair being very bright. The vertical pillar extended from the horizon to the top of the 22° halo, which was brilliant. From this point extended the upper contact arc which merged smoothly with Parry's Arc; both these arcs were coloured and very bright. [... ] The circumzenithal arc was also present, being very brightly coloured. A fairly bright, coloured arc, passing through or close to the zenith and concave to the sun was visible, the colours being very pure and distinct. Because of its position, it was difficult to obtain any estimates; however, it appeared to have approximately the same curvature as the 22° halo. The full 180° of the parhelic circle was visible on either side of the sun, being intersected approximately 90° from the sun by a pair of white pillars extending from the horizon slightly above the parhelic ring. The points of intersection resembled mock-suns, though white. Also at 180° there existed a somewhat fainter, white pillar extending to just above the horizon, the point of intersection with the parhelic circle again being brighter. The display disappeared as the cloud cover increased."
Now I could go on discussing what Blake really saw in 29th November display, but that would not lead anywhere. Suffice to say: a photograph would have been nice.
2011. január 30., vasárnap
Halo Stamps
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I have never considered myself a stamp collector until Jarmo donated two halo stamps recently. They are beautiful. See Jarmo's site for more.
I have never considered myself a stamp collector until Jarmo donated two halo stamps recently. They are beautiful. See Jarmo's site for more.
2011. január 28., péntek
Double-V above lamps
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Mike Hollingshead photographed these pillars on 26 January 2011 in Blair, Nebraska. The curious thing is that there are two V's above the lamp. Normally only one is seen, the upper tangent arc. While the lower V in Hollingshead's photos is the tangent arc, the upper must be the sunvex Parry arc. Or is it? Lets see if simulations are of any help. Above are two simulations made with Lars Gislen's Streetlight Halo software, which assumes omnidirectional light source. On the right is simulation with column oriented crystals, on the left with Parry oriented crystals. Light source elevation is 2 degrees. The Parry is nothing like the upper arc in Hollingshead's photos, and actually the simulations rather depict what the lower arc should look like. In the lower position Parry and tangent arcs overlap and would be indistinquishable from each other. So, not much help from simulations in identifying the upper arc. But the situation between photos and omnidirectional light simulations is not entirely comparable because even floodlighs give to some extent directed light and this why the upper arc can be seen.
Whathever the upper arc is, it is its classical form, i.e. the form that is similar to what is seen in sun light and which in divergent light situation is formed in crystals near observer. The stronger V below is the divergent light form that shows in Gislen's simulations, made by crystals further away from the observer. The upper arc could be either tangent arc or Parry arc or both, same with the lower arc. The helic arc in two of Hollingshead's images seems to indicate there is Parry population present, so perhaps Parry arc is involved in some way or another. But then again if the lamp is near 0 degrees elevation (the two degrees in the simulation may be overestimate) helic and subhelic arcs overlap, and then the halo would not be sure indication of Parry orientation, because subhelic arc forms also from column oriented crystals. Anyway, usually these displays do have Parry orientation halos and sometimes they even dominate over the column orientation halos.
Mike's photos appeared in Spaceweather.
Mike Hollingshead photographed these pillars on 26 January 2011 in Blair, Nebraska. The curious thing is that there are two V's above the lamp. Normally only one is seen, the upper tangent arc. While the lower V in Hollingshead's photos is the tangent arc, the upper must be the sunvex Parry arc. Or is it? Lets see if simulations are of any help. Above are two simulations made with Lars Gislen's Streetlight Halo software, which assumes omnidirectional light source. On the right is simulation with column oriented crystals, on the left with Parry oriented crystals. Light source elevation is 2 degrees. The Parry is nothing like the upper arc in Hollingshead's photos, and actually the simulations rather depict what the lower arc should look like. In the lower position Parry and tangent arcs overlap and would be indistinquishable from each other. So, not much help from simulations in identifying the upper arc. But the situation between photos and omnidirectional light simulations is not entirely comparable because even floodlighs give to some extent directed light and this why the upper arc can be seen.
Whathever the upper arc is, it is its classical form, i.e. the form that is similar to what is seen in sun light and which in divergent light situation is formed in crystals near observer. The stronger V below is the divergent light form that shows in Gislen's simulations, made by crystals further away from the observer. The upper arc could be either tangent arc or Parry arc or both, same with the lower arc. The helic arc in two of Hollingshead's images seems to indicate there is Parry population present, so perhaps Parry arc is involved in some way or another. But then again if the lamp is near 0 degrees elevation (the two degrees in the simulation may be overestimate) helic and subhelic arcs overlap, and then the halo would not be sure indication of Parry orientation, because subhelic arc forms also from column oriented crystals. Anyway, usually these displays do have Parry orientation halos and sometimes they even dominate over the column orientation halos.
Mike's photos appeared in Spaceweather.
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