HILLSIDE GREEN FLASH:Green flashes are rare and lovely. They are most often seen by people on beaches at the end of the day. As the sun sinks into the waves, temperature gradients in the air above the sea surface magnify tiny differences in atmospheric refraction of red and green light. Voila!--an emerald-green mirage.
Not every green flash, however, requires an ocean. This one, photographed by Daisuke Tomiyasu of Higashinada-ku, Japan, appeared over a hill:
"I saw this green flash at sunrise on Dec. 8th," says Tomiyasu. "Once I knew this hill produced green flashes, I returned the next morning, Dec. 9th, and there it was again!"
Atmospheric optics expert Les Cowley explains what happened: "Green flashescome in several varieties. These could be hillside flashes. When wind blows over a hilly ridge the air streamlines are pushed closer together and any small vertical temperature gradients are strengthened. The bending of sunrays across the gradients gets stronger too and maybe enough to create the mirage conditions that all green flashes need."
Bron:http://www.spaceweather.com/ | Gewijzigd: 12 december 2015, 10:12 uur, door Joyce.s