An international team of researchers has just discovered that aerosols even from comparatively small volcanic eruptions can make it into the high atmosphere when assisted by weather systems such as monsoons. Once in the high atmosphere, aerosols are capable of affecting global temperatures for a short time. If they don’t make into into the high atmosphere, like the aerosols from most small eruptions don’t, then they can’t affect the global climate.
Until this discovery it had been thought that only a massively energetic eruption was capable of injecting aerosols “past the troposphere, the turbulent atmospheric layer closest to Earth, into the stable layers of the stratosphere higher up.”
“If an aerosol is in the lower atmosphere, it’s affected by the weather and it precipitates back down right away,” said Adam Bourassa, the lead researcher from the University of Saskatchewan’s Institute of Space and Atmospheric Studies. “Once it reaches the stratosphere, it can persist for years, and with that kind of a sustained lifetime, it can really have a lasting effect.” The effect that he is referring to is the potential cooling of the Earth’s surface caused by the incoming sunlight being scattered.
The researchers analyzed the June 2011 eruption of the Nabro volcano in Eritrea in northeast Africa. “Wind carried the volcanic gas and aerosol — minute droplets of sulfuric acid — into the path of the annual Asian summer monsoon.”
“The stratosphere’s calm layers are high — from 10 km up at the poles to 17 km altitude at the equator — and it was thought storms could not pierce it. For example, the distinctive flattened ‘anvil’ shape at the top of large thunderstorms is created as the storm pushes against the stratosphere.”
“Dust from the Nabro volcano, being slightly heavier, settled out, but the monsoon lofted volcanic gas and the lighter liquid droplets into the stratosphere where they were detected by the Canadian Space Agency’s OSIRIS instrument aboard the Swedish satellite Odin. The Nabro volcano caused the largest stratospheric aerosol load ever recorded by OSIRIS in its more than 10 years of flight.”
OSIRIS was developed to study the upper atmosphere, especially the ozone layer and atmospheric aerosols. Though it was originally intended as a two-year mission, the instrument has been functioning perfectly since its launch back in 2001. It circles around the Earth from North Pole to South Pole once every hour and a half, continually giving new data to the analysis centre at the U of S campus.
“There are only a few instruments that can measure stratospheric aerosols, and OSIRIS is one of them,” Bourassa says. “It’s become extremely important for climate studies, because we’ve captured more than a full decade of data. The longer it’s up, the more valuable it becomes.”
The researchers hope that these findings will help in the refinement of climate models, allowing for the development of models even more accurate than the ones used now.
The research team included scientists from the U of S, Rutgers University in New Jersey, the National Centre for Atmospheric Research in Colorado, and the University of Wyoming. The funding was provided by NSERC, the Canadian Space Agency, and the U.S. National Science Foundation, with support from the NASA Aura Science Team.
The research appears in the July 6 issue of the journal Science.
Source: University of Saskatchewan
Image Credits: NASA Earth Observatory image by Robert Simmon, using EO-1 ALI data; NASA Earth Observatory; NOAA