LARAMIE, Wyo. — Laramie is known for its unpredictable weather. Apparently, the local atmosphere may also be affected by volcanic activity originating continents away.
Terry Deshler is a University of Wyoming professor of atmospheric science. He recently measured a volcanic aerosol cloud with a research balloon, which flew to 100,000 feet above Laramie. These measurements contributed to a research article focusing on the effects of a June 13, 2011, eruption of Nabro Volcano in Eritrea — a country in northeastern Africa — and demonstrated that volcanic eruptions could affect climate without being powerful enough to inject sulfur dioxide directly into the stratosphere.
Deshler is one of eight authors of the research, which was published in an article in this month’s issue of Science Magazine, which hit newsstands Friday.
“If volcanic eruptions occur in the vicinity of large monsoons, the monsoonal thunderstorms create an additional pathway to carry aerosol particles into the stratosphere, where they have a longer life than in the lower atmosphere, where there are clouds,” Deshler said. “The impact of large volcanoes on stratospheric aerosol is to cause a slight cooling, which may last for several years. A small eruption like this one impacts (climate) on the order of a year.”
The theory that severe thunderstorms could enhance the impact of small volcanoes may have been suggested before, but this is the first time such a process has been observed and subsequently published, Deshler said.
Deshler’s contribution to the research article was recording balloon-borne measurements, taken from Laramie, of the size distribution of the Nabro aerosol cloud — essentially a suspension of volcanic ash particles in the air. The cloud was distributed via the Asian summer monsoon, and then the global stratospheric winds in the Northern Hemisphere. Deshler made his observations in late July and early November 2011.
“If the Asian monsoon had not been involved, we may have never seen it,” Deshler said of the processes that carried the volcanic aerosol over Laramie.
The Nabro strato eruption produced the largest stratospheric cloud in 20 years, injecting approximately 1.3 teragrams (more than 1,300 million metric tons) of sulfur dioxide to altitudes of nine to 14 kilometers in the upper troposphere, or the lowest portion of the Earth’s atmosphere, according to the Science article. From there, the Asian monsoon lifted the sulfur dioxide and ash into the stratosphere, which resulted in a large aerosol enhancement in the stratosphere, located just above the troposphere.
According to the Science article, this was the largest increase in the stratospheric aerosol load since Mount Pinatubo erupted in 1991. The article says the impact of the Nabro eruption appears to have been enhanced by its timing and location, which allowed the Asian monsoon to enhance the vertical transport while confining the majority of the aerosol over Asia and the Middle East until late July 2011.
That’s when the enhanced aerosol dispersed and circulated throughout the Northern Hemisphere, likely a result of the weakened anticyclone associated with the end of the monsoon season, the article says. The article mentions that measurements of stratospheric aerosol above Laramie “confirm the transport of volcanic aerosol over North America, and provide estimates of particle size and concentration at 46 and 140 days after the eruption.”
Deshler said his opportunity for involvement in this paper relied on “a little bit of serendipity.”
In November, Deshler was invited to a research conference in Pasadena, Calif. At the conference, Deshler was asked by Adam Bourassa, a professor of physics at the University of Saskatchewan, if he had witnessed anything unusual in the stratosphere over Laramie. Deshler said he had, and surmised it was from a volcanic eruption, but had not identified the volcano. Bourassa then told him of the Nabro eruption and invited Deshler to contribute his aerosol measurements in Laramie to a paper on the effects of the eruption.
Deshler, who has conducted previous aerosol measurement projects on several continents and countries — including Antarctica, Brazil, Sweden and New Zealand — agreed to participate. Deshler’s Laramie measurements relied on a National Science Foundation grant to measure stratospheric aerosol and a balloon launch facility, built in 1971 and owned by UW, at Laramie Regional Airport.
The balloons, which resemble giant jellyfish at the surface, are released partially inflated and carry measuring instruments, which weigh between 50 and 150 pounds. In flight, the balloon instruments collect measurements every 10 seconds. In real time, the instruments transmit measurements of particles of various sizes back to the airport facility. The balloon fully inflates to a diameter of approximately 120 feet when it reaches an altitude of 100,000 feet, Deshler said.
At that height, helium has expanded to completely fill the balloon, as the pressure outside decreases on ascent. At ceiling, the balloon is torn open by the pressure inside, Deshler said. The balloon starts to collapse and the instruments, outfitted with a parachute, descend rapidly. A mechanism fires a small charge and cuts a line, separating the balloon from the parachute. A team is sent out to retrieve the balloon, parachute and instruments, which include GPS tracking and a backup locating beacon, Deshler said.