A graphical representation of the location of the thinning of the ozone layer over Antarctica.
Jason Ahrns, a graduate student at the University of Alaska-Fairbanks, goes sprite-chasing at night during electrical storms. Here he captures column-shaped red sprites over Red Willow County, Nebraska, on Aug. 12, 2013.
A “jellyfish” sprite photographed over Republic County, Kansas, on August 3, 2013. "I have very good low light eyesight, and I've watched tons of sprites in real time on the context cameras so I know exactly what and where to look. I was watching intently out the window while I snapped these shots, and the camera caught a sprite that I didn't see," writes Ahrns in his blog: http://musubk.blogspot.fr/2013/08/sprites-2013-update-4.html
Like flames from a butane lighter, three blue jets (slightly blurred due to the motion of the aircraft) appear above the lightning-lit clouds in this photo taken over Republic County, Kansas, on August 3, 2013. Ahrns describes this picture as the "the cream of the crop," due to the difficult nature of capturing blue jets. "Since jets tend to hug the top of the clouds it's understandable that they're more difficult for a ground observer to see/photograph, so it makes sense that being up in a sprite-chasing aircraft would give me a serious advantage," he writes.
"Unlike sprites, blue jets aren’t directly triggered by lightning, but seem to be somehow related to the presence of hail storms," reports the Smithsonian: http://blogs.smithsonianmag.com/artscience/2013/08/scientists-capture-rare-photographs-of-red-lightning/.
Red sprite over Canadian County, Oklahoma, on August 6, 2013. "I was also able to see quite a few jets with my naked eyes! That's a first for me, and I'm always excited to see a new sky phenomenon for myself. I still haven't been able to see a sprite naked-eye, and it impresses me just how difficult that actually is," Ahrns writes.
Ahrns' Nikon D7000 on a flexible tripod points out the window of the sprite-chasing aircraft, a Gulfstream V with the National Center for Atmospheric Research. "I butted the camera up against the window glass and put my weight on it to get rid of most of the wobbles and light leaks, but the motion of the aircraft itself still showed up, especially when we hit a patch of turbulence (we are, you know, flying right next to a thunderstorm)," he writes.
Worried scientists said Sunday they had found four new ozone-destroying gases in the atmosphere, most likely put there by humans in the last 50-odd years despite a ban on these dangerous compounds.
It is the first time since the 1990s that new substances damaging to Earth's stratospheric shield have been found, and others may be out there, they said.
"Our research has shown four gases that were not around in the atmosphere at all until the 1960s, which suggests they are man-made," the team from Europe and Australia wrote in the journal Nature Geoscience.
They analyzed unpolluted air samples collected in Tasmania between 1978 and 2012, and from deep, compacted snow in Greenland.
"The identification of these four new gases is very worrying as they will contribute to the destruction of the ozone layer," added a statement from the team.
"We don't know where the new gases are being emitted from, and this should be investigated."
Three of the gases are chlorofluorocarbons (CFCs) -- a group which includes chemicals traditionally found in air-conditioning, refrigerators and aerosol spray cans but banned under the Montreal Protocol.
The fourth is a hydrochlorofluorocarbon (HCFC), part of a closely-related group of compounds which replaced CFCs but are being phased out.
More than 74,000 tonnes of the four newly-identified gases had accumulated in the atmosphere by 2012, said the team.
This is very small compared with peak emissions of CFCs in the 1980s of more than a million tonnes per year.
"However, the reported emissions are clearly contrary to the intentions behind the Montreal Protocol, and raise questions about the sources of these gases," the team wrote.
Two of the gases, one CFC and the HCFC, are still accumulating.
Previously, seven types of CFC and six of HCFC were known to contribute to ozone destruction.
CFCs, the main cause of the hole in the ozone layer over Antarctica, are man-made organic compounds made of carbon, chlorine and fluorine.
They were phased out from 1989, followed by a total ban in 2010.
HCFCs, CFC-like compounds which also include one or more hydrogen atoms, are less ozone-damaging but contribute to climate change by trapping more of the sun's heat in the atmosphere.
The ozone layer comprises triple-atom oxygen molecules that are spread thinly in the stratosphere.
It plays a vital role in protecting life by filtering out ultraviolet rays that can damage vegetation and cause skin cancer.
In high latitudes in the Southern Hemisphere, where the ozone layer is damaged or subject to seasonal fluctuations, people are advised to cover exposed skin and wear sunglasses.
Possible sources for the new gases include chemicals used for insecticide production and solvents for cleaning electronic components, said the researchers.
Concentration differences between the samples suggested the dominant source was in the industrialized Northern Hemisphere, they added.
Study co-author Johannes Laube from the University of East Anglia's School of Environmental Sciences said the ozone layer stopped thinning from the late 1990s and there were signs of it starting to recover.
"As many ODSs [ozone-depleting substances], and especially CFCs, take a long time to break down once released into the atmosphere, it will be many decades until it will fully recover," he told AFP.
"Provided we do not have further unpleasant surprises."
Martyn Chipperfield, a professor of atmospheric chemistry at the University of Leeds in northern England, said the low concentrations of the four gases "do not present concern at the moment."
But, he added, "the fact that these gases are in the atmosphere and some are increasing needs investigation."