|Sarychev Skies - Imaged from Kansas by Doug Zubenel on July 21 and (lowest two images) July 12.
©Doug Zubenel, shown with permission.
While the upper atmosphere at 50 miles altitude has this month seen spectacular noctilucent cloud displays(1,2), the still rarefied air lower down - the stratosphere - has not been entirely uneventful.
On June 12, '09 the Sarychev Peak volcano injected fine ash and gaseous sulfur dioxide into the stratosphere. The resultant sulfate aerosol now encircles the Northern Hemisphere in at least three discrete layers between 15 - 23km (9 - 15 miles) altitude.
Volcanic aerosol scatters sunlight to produces spectacular sunset and twilight effects. 'Ordinary' twilights can be spectacular too and many are labeled volcanic. The following taken together are especially characteristic of volcanic effects:
1. A bright yellow twilight arch shortly after sunset
2. An intense purple glow higher in the sky - the 'purple light'
3. Diffuse (not sharp) crepuscular
rays and shadows
4. Fine structure in the yellow clouds
visible through binoculars or long
Last year the eruption of Kasotochi also provided us with these spectacles (1,2,3,4,5,6,7,8,9).