Depending on your location, you may have observed some stunning purple sunsets late summer, caused by two volcanic eruptions. The first, on July 22 when the Raikoke volcano in the Kuril Islands in Russia’s Sakhalin Oblast region erupted after being dormant for more than a century. The latest eruption sent a mass of volcanic debris and ash ten miles into the sky, reaching the stratosphere, a layer of the atmosphere.
Just short of two weeks later, the Ulawun volcano in New Guinea erupted, blasting ash nine miles into the sky and causing the evacuation of 15,000 people in the area.
The sulfuric gas from these eruptions reached the stratosphere, turning the skies in some parts of the world purple at sunset. The fine volcanic aerosols in the stratosphere caused blue light particles to scatter and when combined with a normal red sunset, creates a purple glow.
Website Space Weather added: “The purple colour is often preceded by a yellow arch hugging the horizon. Violet beams emerge from the yellow, overlapping to fill the western sky with a soft purple glow. High-quality pictures of the phenomenon often show horizontal bands cross-crossing the yellow arch. These bands are the volcanic gas.”
The purple skies were prominent across North America, with Greg Ainsworth, a photographer from Montana, US, told Space Weather: “On Aug 26th I believe I captured the purplish sunset colours, as well as horizontal banding in the yellow/orange area associated with the volcanic aerosols in the stratosphere.”
Gabriel Cyr, an amateur photographer in Quebec, Canada, got a glimpse and said: “This has got to be one of those sunsets caused by volcanic gas. The skies were perfectly clear with no tropospheric clouds visible to the naked eye, making the phenomenon easier to distinguish from a ‘regular’ sunset.”
Another activity on the ground this month affected what is happening in the clouds over North America. Investigating the effects of the Williams Flats wildfires in Washington, scientists at NASA and the National Oceanic and Atmospheric Administration (NOAA) observed ‘fire clouds’.
The wildfires have now spread across 44,000 acres across Washington State and offered NASA a unique perspective because fire clouds began forming over North America.
Fire clouds, scientifically called pyrocumulonimbus (pyroCb), form when the heat from the fires lift into the atmosphere, the heat take the form of smoke-filled thunderclouds sitting on top of the fire’s plumes on the ground.
The clouds look beautiful, showing an orange haze on top of normal clouds created when the smoke reflects the Sun’s light and they can be harmful.
More wildfires can be created by thunderstorms and NASA explained that fire clouds can act as a chimney by funnelling smoke into the lower atmosphere.
With a bird’s eye view from the cockpit of NASA’s DC-8 when it flew through the clouds, David Peterson, lead forecaster for FIREX-AQ, said: “PyroCb are like large chimneys, transporting a large quantity of smoke into the lower stratosphere.”