2011. február 8., kedd

Bishop's rings

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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.

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