Taking Stock of the Atmosphere
ARM-ACME VI field campaign will chart changes in greenhouse gas levels
For the next year, a Cessna 206 aircraft from the Atmospheric Radiation Measurement (ARM) Climate Research Facility will sweep through the skies multiple times, skimming 500 feet above the Earth’s surface and soaring up to 17,500 feet, allowing scientists to gain an accurate picture of trace gas concentrations in the atmosphere over the ARM Southern Great Plains (SGP) facility.
The flights will help the ARM Airborne Carbon Measurements VI (ARM-ACME VI) team inventory carbon dioxide, methane, and other greenhouse gases in the region. Building on results of previous ARM-ACME campaigns, the findings will create a detailed record of atmospheric changes in the region and help validate climate models and satellite measurements.
"These measurements we're making are the most intensive measurements made in the United States," said Sebastien Biraud from U.S. Department of Energy’s (DOE) Lawrence Berkeley National Laboratory, who is leading the campaign. "We know that the atmosphere is changing with time and what we are trying to do is document those changes."
In addition, the data will help scientists understand the intricate interactions between the land and the atmosphere and, consequently, how land management practices impact trace gas levels.
"If we can understand what controls the flows, or exchanges, of carbon dioxide, water, and energy between the land and the atmosphere, we can do a better job of predicting those exchanges in the future," said Margaret Torn, the co-principal investigator for the ARM-ACME V campaign from Lawrence Berkeley National Laboratory.
A Holistic View of the Atmosphere
During each flight in the campaign period, which started on October 1, the scientists take air samples at different heights above the SGP facility so that they can measure the concentrations of the various trace gases at different altitudes. At higher elevations, the measurements are representative of a larger region than those of lower elevations due to circulation effects from a variety of sources. "So sampling at varied elevations enables us to look at the big picture and the fine details simultaneously," Biraud said.
It is a data collection effort that began in 2002, when scientists collected air samples above the SGP, as part of the In-situ Aerosol Profiles campaign supported by the ARM Facility. In 2008, when this project ended, the ARM-ACME project began using the aerial platform for its measurements.
"What is really unique about this study is that we have been taking these highly accurate measurements over the course of so many years," said Beat Schmid, Technical Director of the ARM Aerial Facility at the Pacific Northwest National Laboratory.
In addition to the ARM-ACME campaigns, NASA’s Orbiting Carbon Observatory (OCO-2) satellite mission provides spaced-based observations of atmospheric carbon dioxide and a network of towers in the south-central region record ground-based measurements.
"So you have the bird's eye view from the satellite, you get the aerial view from the planes, and you have the ground measurements, also." Biraud said. "They all work together to contribute to getting a big picture view of the atmosphere."
Understanding the Connections Between Land and Air
The data from this big picture view will help scientists understand how plants affect the atmosphere and the duration of droughts or storms.
"Many people thought that soil moisture controlled clouds and convection, but we are showing that plants are the gatekeepers to flows of moisture," Torn said. "It is plant roots that convey the water from the soil to the atmosphere, and unless we understand how plants function we can't predict the clouds and rainfall as accurately."
In the previous five years, the SGP has experienced severe droughts that have affected farmers and cattle ranchers. But these droughts also mean less water evaporates back into the atmosphere. "That makes the atmosphere drier and it even less likely to rain," Torn said.
Consequently, the scientists are using measurements of carbon dioxide and water to understand how lack of ground moisture impacts the atmosphere and drives this vicious cycle. Understanding such connections between the land and the air means that scientists can better determine the impact of land use practices on the atmosphere, Torn said.
"Agriculture is the single largest land use change in the SGP," Torn said. "We are finding that land use has a profound influence on the annual and seasonal cycle of carbon in the atmosphere."
Such highly detailed and precise data can provide information that will help create more accurate climate models, and validate the findings from satellites and ground-based instrumentation. "Ultimately, any global statement has to come from models or satellites," Schmid said. "And if you validate that model at several places, you can develop a trust that the model is accurate."
Mapping Methane’s Role
In the ARM-ACME VI campaign, the scientists are also focusing their attention on methane emissions. As a potent greenhouse gas, methane contributes significantly to climate warming.
"We've been making measurements and have started to see the levels of methane begin to rise," Biraud said. "That is the beauty of these frequent measurements—if you are not collecting data, you simply miss what is going on."
Now the team plans to investigate this trend by determining the exact nature and location of these emissions. Since 2006, oil and gas drilling has proliferated in the region, which may be contributing to the increase in methane emission.
"There is a lot of uncertainty in the sources and sinks of atmospheric greenhouse gases, like methane," Torn said. "This research is helping to narrow the confidence gap and provide solid science that will help understand the environmental impacts of energy use."
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The ARM Climate Research Facility is a national scientific user facility funded through the U.S. Department of Energy's Office of Science. The ARM Facility is operated by nine Department of Energy national laboratories, including Lawrence Berkeley National Laboratory in California.