Jet-setting for science

HIPPO team takes to the skies again this summer

It’s a daunting itinerary that unfortunately does not come with frequent flier miles: Boulder-Anchorage-Northern Polar Regions-Hawaii-American Samoa-New Zealand-Southern Polar Regions-Australia-Saipan-Midway Island-Anchorage-Northern Polar Regions-Boulder.

This summer, a group of researchers from EOL and science institutions around the nation will take the Gulfstream V (HIAPER) on two whirlwind tours of the Pacific. The HIPPO (HIAPER Pole-to-Pole Observations) field project consists of five missions in all, beginning in 2009.  Next up is the fourth mission, which runs June 14–July 10 and focuses on sampling the western Pacific and Australia (see map, below). The fifth and final mission, scheduled for August 9­–September 9, will take a slightly different route that returns via the central Pacific.

Two men working on instrument beneath the aircraft's wing.
Brent Kidd (left) assists Kurt Zrubek (both EOL) in repairing HIAPER’s cloud droplet probe in Kona, Hawaii, on a maintenance day during HIPPO III. The probe had developed a loose connection but was successfully repaired to full functionality. (Image by Pavel Romashkin.)

An ambitious project, HIPPO seeks to make the most extensive airborne measurements of carbon dioxide and other greenhouse gases to date. Sampling as much of the atmosphere in the Pacific Basin as possible, from 85°N down to 67°S, will give scientists a longitudinal snapshot of Earth's atmosphere that lends itself to improving our understanding of a wide range of atmospheric species.

The five missions all follow similar flight paths but at different times of year, in order to compile a collection of seasonal snapshots of greenhouse gas concentrations. The team is constructing vertical as well as latitudinal cross sections, with HIAPER dipping as low as 1,000 feet (300 meters) and soaring as high as 47,000 ft (14,000 m).

The findings will help scientists determine where and when greenhouse gases enter and leave the atmosphere, a critical prerequisite for taking steps to curb global warming. It will also shine light on questions such as why atmospheric levels of methane, a potent greenhouse gas, have tripled since the Industrial Age and are on the rise again after leveling off in the 1990s. And researchers will be able to analyze other gases and particles in the atmosphere that can affect temperatures by influencing clouds or the amount of solar heat that reaches Earth's surface.

“Some of the biggest questions that we have about where our carbon dioxide is going focus on northern forests, tropical forests, and different regions of the ocean,” explains Britt Stephens, one of HIPPO’s co-principal investigators. “By taking this aircraft and flying from Boulder to as far north out of Anchorage as we can, all the way down the Pacific to as far south out of New Zealand as we can, we’ve been able to cover an enormous distance and see the influence of carbon dioxide from all of these different regions.”

The first three HIPPO missions, which occurred during the Northern Hemisphere’s fall, winter, and early spring, are already providing interesting results. The team noted significant variations in carbon dioxide distributions and concentrations on each mission. Observations also showed a more widespread, uniform distribution of black carbon than anticipated, with greater-than-expected levels found at high latitudes in the Northern Hemisphere. Additionally, concentrations of nitrous oxide, the third most important long-lived anthropogenic greenhouse gas (after carbon dioxide and methane), were higher than expected in the mid- and upper tropical troposphere.

About a half dozen EOL staff will be aboard HIAPER during the two missions this summer. A typical day includes several hours of pre-flight preparation, an 8-9 hour flight, and an hour of post-flight operations—followed by additional hours of analyzing data and sending it back to NCAR over often-slow Internet connections. “For the scientists on board, it’s a very exciting time, but also very exhausting,” Britt says. “Watching all the data come up in the real-time displays is extremely engaging but not nearly as relaxing as an in-flight movie.”

After HIPPO’s field component wraps up this summer, the number crunching begins. Britt estimates that there is a decade’s worth or more of work to be done. “The exciting part for me is all the collaborators pouring in, eager to work on the data—we’ve been making it widely available and it’s been well received,” he says, adding that demonstrating HIAPER’s ability to undertake this sort of experiment should motivate researchers to make similar use of the aircraft in other disciplines.


A map of the HIPPO IV route.
The proposed HIPPO IV route. The route originally included stops in the Philippines and Japan that were cancelled due to the earthquake in Japan.