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The biggest surprise on march 29. was the independent observation of 90
deg
parhelia by three observers within an area of 40 kilometers.
That should have been the final proof for the existance of this halo
type,
because three observers cannot have been fooled independently at the
same
time. It's true that there is still no photographic proof of the 90 deg
halo, but photographs (like the one from August 17, 1998) could be
hardly
used for measurements, anyway, due to the large image distortion
introduced by the wide angle objective lens. A standard lens does not
help
as it will show no other halo types for reference. The only chance one
has is to use an all-sky mirror, but who has by chance one of these at
hand if there is just one 90 deg parhelion every five years? So the
photographic proof is still open.
The statistics of German Halo Network (about 75000 German and Austrian
halo observations) contain an overall of 23 visual observations of 90
deg
parhelia until 2001. There is another series of independent observations
like the one described above: On September 29, 1997, a left 90 deg
parhelion was observed at 12:05 in Rostock. At 14:50 it was spotted in
Dresden, and yet 25 minutes later in Chemnitz (see MM 12/97).
We assume that it must be a reflection halo, as in almost all cases the
90 deg parhelion was white and circular. Only in two cases a reddish
appearance was reported, but that could have been caused by diffraction
as
the parhelia were very bright in these cases. Similar effects have been
observed in connection with parhelic circle fragments and with 120 deg
parhelia. Furthermore it is remarkable that 90 deg parhelia occured in
several cases together with the Liljequist parhelia and the rare oblique
arcs of the 120 deg parhelia. Maybe this is an important clue for halo
theorists to find an explanation for the origin of this controversial
halo
type.
Best regards
Claudia Hinz
German Halo Network
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________________________________________________________________________
Claudia & Wolfgang Hinz
Private Homepage: http://www.glorie.de
Homepage Atmosphaerische Erscheinungen: http://www.meteoros.de
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