Thursday, January 16, 2014

From the field: icy sunset rainbows

Posted by Kirk
Atmospheric conditions were just right this evening for a spectacular sight. As the sun set in Minnesota, Ice rainbows appeared on each side. This is the same atmospheric lens effect that causes sun dogs during the middle of the day in the winter. These atmospheric effects are usually about 22° to either side of the sun. Tonight there was a rainbow on both sides of the sun as it set. Unlike rainbows in the summer that are caused by tiny water droplets in the atmosphere refracting the sunlight, these are caused by ice crystals in the atmosphere. The end result is similar but you only get a bright spot instead of the full arc. It didn't snow today, so that means these ice crystals may have been whipped up from the ground and into the atmosphere by the blizzard force winds.