Tangent arc index
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Lower tangent arc and other halos. When the sun is low the
horizon hides the lower tangent arc but it can be seen from from hills
or mountains when there are clouds or cold air below containing the
necessary ice crystals. Ryan Skorecki (site)
caught these arcs at Girdwood Alaska. ©Ryan Skorecki,
reproduced with permission.
 The HaloSim
simulation for a solar altitude of 6º. The bright subsun
and part of the lower sun pillar
in the image were partly produced by reflection from the water or
ice of Turnagain Arm deep in the valley.
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