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Alue Inet, Viesti nro 34, 01.07.96 23.28.08
L{h: Marko Riikonen
Vast: Uucp
Aihe: Pearlescent clouds
TO: meteopric_at_listserv.funet.fi
Hi Jun,
The first observation you describe on the pearlescent clouds is
interesting.
In April 1994 when I was in Zambales on my way to Mt.Pinatubo summit I saw
clouds that could be the same you have seen. It was early morning, sun had
just risen above the horizon (that's what I estimated, can't be sure) and
there were at the sun side of the sky strange pearlescent clouds that
showed
nice spectral colors. There was - like in your observation - one cloud
patch,
that was in a shape of oval and was the most best colored of all the
clouds.
The other clouds around were not so colorful and somewhat more irregular
in
shape than the oval. This also fits well your description of the display.
I have seen similar looking Mother of Pearl clouds in Finland. They are
somewhat rare clouds located in the atmosphere about 30 km from ground and
often show vivid spectral coloring. They are only seen during the
wintertime
and are caused by mountains that make humid air to rise as high as 30 km.
But there shouldn't be Mother of Pearl clouds in Philippines since they
are,
as far a I know, limited only to polar areas (they are seen also in
Antractic).
Veikko Makela suggested that the clouds you have seen could be just
ordinary
iridescent clouds that are often seen when altocumulus clouds (altocumulus
clouds are located about 3 km from the ground). I have seen so many normal
iridescent clouds in Finland, that I think that I can regognice such
display
even if I would see it in Philippines. The clouds that I saw in Zambales
surely did not look like normal iridescent clouds, but looked more like
Mother of Pearl clouds.
It might be that you and I have seen something "new", something that
doesn't
yet exist in a atmospheric optics literature. My observation is backed up
with photographs and it would would be good, Jun, that you would use your
camera too if these clouds make more appearances there. It is hard to go
any
further with this thing at the moment. More observations are needed. When
you
see these clouds again watch how long they last: at what sun elevation
they
disappear and appear. Watch also if you see any movement in them.
Altocumulus
that shows beautiful iridescent is usually young, just formed cloud and is
always chancing it's form very fast.
The other display that you saw after early morning rainshower, sounds like
more "normal" display of iridescent clouds. I think the iridescent cloud
you saw that morning was Cumulonimbus pileus, i.e kind of "veil" that
develops on the top of cumulonimbus clouds. Iridescence is seen in pileus
when sun is just behind the top edge of Cumulonimbus cloud. In Finland
these are very rare, but I have seen them in several occasions in
Phillippinens and Malaysia.
Marko Riikonen
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