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Checks and Balances
Daniel Jacob, of Harvard University Daniel Jacob, of Harvard University in Cambridge, Mass., plans flights during the ARTAS field campaign in Fairbanks, Alaska. Credit: NASA
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In his endeavors to study pollution sources in the Arctic and the implications for Arctic ecosystems and for climate, Harvard University professor and project scientist Daniel Jacob relies on NASA satellite data for much of his research.

"The Arctic is a major receptor for northern mid-latitudes pollution and is experiencing particularly rapid climate change," Jacob explains.

Jacob is currently involved in research based out of Alaska with Harvard's Atmospheric Chemistry Modeling Group in conjunction with NASA's Arctic Research of the Troposphere from Aircraft and Satellites (ARCTAS) campaign and other international initiatives. Jacob says he and his team are gathering data on greenhouse gases, atmospheric particles, various air pollutants and chemically reactive species that play a critical role in the removal of long-lived gases from the atmosphere.

"I would like to achieve better understanding of pollution sources to the Arctic and of the chemical evolution of the pollution once over the Arctic," says Jacob of what he hopes to accomplish with his research. This sentiment is shared among the many research partners participating -- academia, government and industry alike—that have come together in a truly global effort: the International Polar Year (IPY) studies.

To ensure every partner's effort to obtain data, one interesting facet of Jacob's fieldwork is to act as what could be likened to a checks-and-balances system. He makes daily decisions on aircraft flights and flight plans.

Comparing the flight planning Jacob does to a checks-and-balances system may sound simple enough; however, it is anything but.

Flight planning for a campaign such as ARCTAS requires keeping in mind several science goals coupled with multiple approaches to gathering the right data at the right time. In general, the science goals would include collecting samples to characterize chemical composition and satellite validation. Satellite validation requires Jacob to plan some flights to occur in coincidence with the passing of one of NASA's satellites as it is taking measurements.

To align the airplane and satellite to collect data, Jacob engages in a dynamic process that changes daily depending upon meteorological conditions. Day-to-day flight planning begins with matching multiple mission objectives with a flight plan that best meets the science goals.

NASA TC4 mission data from August 2007 Like the aircraft flight path described for the ARCTAS campaign, the NASA TC-4 mission in August 2007 included the spiral path used to obtain data coincident with satellite readings. Credit: NASA
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Jacob leads a flight planning team that will base its decisions on computer model- generated forecasts of atmospheric chemical composition, the timing of future satellite overpasses, the latest data obtained from most recent flights, as well as practical considerations such as surface weather conditions, the range of the aircraft, air traffic limitations and safety concerns.

"The main objectives in a campaign like this are to characterize chemical composition, to better understand the chemical and physical processes that occur over the Arctic, and to assess satellite measurements of the polar environment," explains Duncan Fairlie, a research scientist with NASA Langley Research Center's Science Directorate in Hampton, Va. "To cover as many objectives as possible, they need to get as many flights in as they can."

Scientists and flight planners like Jacob must combine this complex information each day and track it as the information available changes from moment to moment. Flight plans are modified as new information becomes available. In fact, a flight plan may not be fully known until as close as 24 hours before takeoff. Once underway, adjustments may still be necessary because research flights require unusual patterns.

Chemical aging is yet another factor to consider in planning as the Arctic pollution plumes researchers want to sample change and can even dissipate in only two to three days. Despite the urgency in collecting these samples, potentially extreme polar weather changes can halt a day's campaign flight entirely.

Some targeted locations will have Jacob planning relatively even, low-level flight legs to gather data such as the surface chemistry over sea ice. Others will involve coordinating patterns that spiral up, taking in-situ samples from around a satellite's field of view. Next, another even flight path at a higher altitude that would lead the plane to intersect with another remote measurement, spiraling down once again to gain as much coincident data as possible.

"The flights and satellites both sample the atmosphere," says Fairlie. "They take as many readings as they can of both vertical profiles and horizontal structure. The plane flies in one-dimension. The satellite measurements provide another dimension, and ground measurements and observations yet another."

The plane samples the air with its suite of instruments reading any number of atmospheric constituents: gases such as ozone and particles such as sulfate or organic aerosols. The airborne sensors take readings "in-situ," meaning the mounted probes all along the outside of the fuselage sample the air directly in a targeted location and store the measurements in real-time.

Some satellite instruments, such as lidar, read the light scattered back from atmospheric aerosols, and the data are subsequently downloaded to NASA's massive archives for processing. Scientists and researchers then combine these data sets -- from different viewing platforms and different instruments -- to create multidimensional views of the atmosphere.

"We are comparing our aircraft observations to measurements from other aircraft, and measurements from satellites and ground stations," says Jacob. "The aircraft campaign provides precious satellite validation data."

Providing compatible, complementary, validated data is critical to the ultimate success of the research resulting from campaigns like ARCTAS. Reliable data lead to trusted research results.

From the extensive IPY initiative, scientists are able to compare and combine data collected by more than 60 participating countries. As IPY moves forward into 2009, the volumes of data that build will open the door for reliable opportunities to research and understand the rapid changes in the Arctic and implications for climate.
Denise M. Stefula
NASA's Langley Research Center