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Some pickups on the topics of METEOPTIC mailing list
I'll write a short overview of some topics included in this list and
also some pickups what we have done in Ursa Astronomical Association.
Halos
In the last ten years the modern research methods have open whole new
possibities to halo science. Computer simulations have made easier to
trace light paths in ice crystals and look what should be visible in the
sky. Ice crystal populations in low level ice clouds can be studied by
taking samples of ice crystals. Photographs have proved many
questionary halo phenomena. Even these new methods have made halo
research more reliable, there is also need to know history of halo
research.
In Finland we have active halo network with about 30-50 observers.
Ursa halo section have recorded halo phenomena since late 1970's.
Finnish group have got first photographs of some rare halo phenomena.
One of the most interesting case are the vertical elliptical halos. The
reliable theorie of this phenomenon is still missing. One the latest
debate have been around Lowitz arcs. On 31th August 1994 there were
photographed one of most reliable Lowitz arcs with extraordinary third
component of this halo form.
Some other halo activities in Finnish group: Mr. Marko Pekkola have
made a large literature survey of halo research. Exactly at the moment
Marko is in some meteorological library somewhere in Europe to
collecting new sources. Mr. Marko Riikonen, Jukka Ruoskanen and Timo
Kinnunen have made two decade survey of lunar halos from aurora films
recorded be Finnish Meteorological Institute.
Rainbows
You maybe think this ordinary phenomenon is already known as well we
can, but there are still many questions. Rainbows, cloudbows and fogbows
are also in interest of amateur sky watchers.
In last two summers some of Finnish observers have studied fog
phenomena, fogbows and glories. Using car head lights and taking long
exposure photos you can record quite faint effects, such as interference
bows outside the secondary fogbow. Some of these photographs we
published in Sky and Telescope magazine.
Coronae
Coronae are very common phenomena is clouds. Time by time these are
still very colourful and magnificient. Finnish observers have recorded
coronae caused by pollen grains. There are huge number of plants with
different shapes of pollen grains, but only some (mainly trees) can give
so big concentration of pollen particles, that coronae are visible.
Asymmetric grains caused also some asymmetricies (elliptical shape,
brightnenings) for coronae.
These natural phenomena are so common, that it sounds impossible, they
haven't noticed earlier. It would be interested to study if there are
different kind of pollen coronae in different parts of the world.
Refraction: Mirages and green flash
In Finland we have studied refraction phenomena by photographing. One
of the largest project is made by Mr. Pekka Parviainen, who have
phtographed almost every sunsets during last few years to record green
flashes and other low-sun phenomena. Pekka have also large collection
of mirage photos. A Japanese film group visit Pekka's summer place last
summer. They were making a film about mirages.
Volcano phenomena
After Mt Pinatubo eruption 1991 we have had possibilities to follow
which kind optical phenomena volcano ash and aerosols can caused in the
atmosphere. Of course there have been several minor cases of these
volcano phenomena during last decades, but Pinatubo was the most global.
We have recorded strong twilights, afterglows, nacreous-type clouds,
ash streaks and Bishop's ring. Finnish group have rather regular visual
followup of Pinatubo phenomena during 1991-1994.
Nacreous clouds
Nacreous or mother-of-pearl clouds are typical only in the specified
areas in the world. Strong wind over mountains caused a lee wave, which
is one important part of the formation of this phenomenon. Scandinavia,
Scotland and mountain around of Artartica are very well known
mother-of-pearl cloud areas.
In Finland we have noticed sometimes very strong twilights related in
the nacreos cloud displays.
Noctilucent clouds
NLCs are high mesospheric clouds visible in summer times. NLCs are now
studied about 100 years and there are still many mysteries in formation
of this phenomenon.
Finnish observers have followed NLC from 1970s and we have planned
systematic observing methods to recording. There have been many
professional projects to study NLC and amateur observers have
participate these eg. by photographing. Mr. Pekka Parviainen have made
some experiments to take stereographic photos of NLCs.
Man-made phenomena
Finland is located near active rocket lauch areas (Esrange, Kiruna in
Sweden and Plesestk in Russia). So we have several recordings of
rocket launches and atmospheric experiments, such as Barium releases.
In summer 1988 a missile test launch caused colorful artifical NLCs in
the Finnish night sky.
These are just examples of large category atmospherci phenomena. I'll
try to tell later more what is in at the moment in our group.
regards,
Veikko Makela
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