||Image ©Gary Saunders, reproduced
Middle Lowitz arc over the Atlantic Ocean.
Imaged by Gary Saunders 12th September 2005 from the flight deck
of an aircraft at 33,000ft.
A rare combination of
Lowitz, sunvex Parry, upper tangent arc and 22° halo.
Mouse over the image for an enhanced
view and halo key.
The relative positions and shapes of the Parry and upper tangent
arcs fix the solar elevation at ~4°. At this sun height the
middle Lowitz arc curves upwards and over the sun but it remains
tangential to a sunvex Parry arc.
In the HaloSim4 simulation, the rectangle shows the area covered
by the image. Arcs formed by classically oriented Lowitz
plates appear in red.
used 38% Lowitz oriented plates, 1% ordinarily oriented plates
to produce the parhelia, 5% Parry oriented columns, 15% singly
oriented columns and 41% randomly oriented columns.
The figures illustrate the relatively
large concentrations of Lowitz oriented plates that are necessary
to produce a display and perhaps partly accounts for the paucity
Upper and lower Lowitz components are clustered
around the sundogs but they do not appear in several of Gary
Saunder's images of the left hand parhelion. This could be taken
as evidence for semi-regular hexagonal Lowitz crystals that enhance
the intensity of the middle arc as suggested by Riikonen
et.al. However, other factors such as the known transience of the Lowitz
appearance in this display and variations in crystal concentrations
across the sky could be responsible.