A research aircraft is born: The NSF/NCAR Gulfstream-V flies high (and far)
During a few memorable days in early 2006, a small group of pilots and scientists left NCAR’s Research Aviation Facility (RAF) near Boulder in the morning, took part in a field campaign in eastern California by day, and returned to Colorado before midnight. The flights served as testimony to the impressive range and speed of a new Gulfstream-V aircraft based at NCAR and dedicated to environmental science. T-REX, the Terrain-induced Rotor Experiment, marked the first major deployment for the NSF/NCAR G-V, also known as HIAPER, the High-performance Instrumented Airborne Platform for Environmental Research.
T-REX was both a success on its own terms and the fulfillment of years of work readying the $81 million G-V aircraft for demanding research sorties. The G-V’s ability to fly at altitudes up to 51,000 feet made the aircraft ideal for probing the high-level features studied in T-REX, and the plane’s cruising range of nearly 7,000 miles allowed participants to commute to work. Thanks to improvements in long-distance communication, the G-V operations center was also based at RAF. This allowed many NCAR scientists to stay involved from Colorado as the project unfolded in California.
When upper-level winds from the Pacific Ocean slam into the Sierra Nevada range, they often produce mountain waves, a type of atmospheric gravity wave that can propagate and “break” into the stratosphere at heights of more than 16 kilometers (10 miles). The strong wind shear and turbulence in these waves can play havoc with aircraft. A mountain wave may also produce a rotor, a huge rolling-pin–shaped zone of high turbulence with weak east-to-west winds across the valley floor and howling west-to-east winds higher up. Although the general structure of breaking gravity waves and rotors has been known for decades, the details remained fuzzy.
Led by scientific project director Vanda Grubiši? (Desert Research Institute), researchers studied the mountain-generated flow from several perspectives during T-REX. HIAPER joined the University of Wyoming King Air and the U.K. Facility for Airborne Atmospheric Measurements BAe146 aircraft. The planes deployed dropsondes and aimed cloud radars into the rotors and waves. From the ground, lidars, radars, automated weather stations, wind profilers, and balloons sampled the airflow.
“We’re discovering what the relation is between the rotors and waves close to the mountain tops and what the rotors look like closer to the ground. While the rotors are the focus of this study, we are learning a lot about the waves in the upper troposphere and lower stratosphere as well.” says Grubišic.
T-REX shed light on chemical processes at altitude, especially the ways in which breaking waves can help foster the mixing of constituents between the troposphere and stratosphere, the atmosphere’s two lowest layers. The project could also help improve turbulence forecasts for aviation, according to Ronald Smith (Yale University), one of the principal investigators. “I believe that within a few years we could see the measurements and forecast-model tests from T-REX translated into improved forecasts of turbulence in the troposphere and stratosphere, which will have a direct impact on commercial aviation,” says Smith.
It’s hard to imagine anyone more gratified by T-REX than principal investigator Joachim Kuettner. The UCAR scientist first explored mountain waves in Germany in the 1930s as part of his doctoral research. At the helm of an open sailplane, he set world records for glider altitude. In the 1950s, Kuettner led the Sierra Waves Project. At age 96, Kuettner found himself again exploring the region’s mountain airflow, this time aboard the G-V. He’s long been familiar with rotors, but this experiment offered the most in-depth sampling of the phenomenon in Kuettner’s eight decades of research on mountain flow. “I’ve always wanted to explore the rotors,” he said as the project got under way. “It’s taken me this long.”
The G-V’s second major project pushed the aircraft closer to its top range and took full advantage of its strengths. Conducted early in 2007, PACDEX (the Pacific Dust Experiment) was led by scientists at NCAR and Scripps Institution of Oceanography. The project is a far-reaching study of plumes of airborne dust and pollutants that originate in Asia and journey to North America.
“We were able to find a wide variety of plumes from Asia at various locations across the ocean, including a number of encounters with the plumes in large-scale storm clouds,” says NCAR’s Jeffrey Stith. “The long-range capabilities of the aircraft allowed us to gain an ocean-wide perspective.”
As Asia’s economies boom, scientists are increasingly turning their attention to the plumes, which pack a combination of industrial emissions (including soot, smog, and trace metals) and dust. The plumes are lofted by storms that originate in regions such as Central Asia’s Gobi Desert. To study the plumes on their long trek across the Pacific, the G-V carried an array of instruments, including some newly designed for the aircraft, that enabled scientists to collect data on clouds and bring dust, pollutants, and cloud particles into the aircraft for study.
While many airborne particles, such as sulfates, cool the planet by blocking solar radiation from reaching Earth, others, such as black carbon, can have a warming effect. Overall, the particles may mask up to half of the global warming effect of greenhouse gases. Warming in the coming decades will be strongly influenced by how particle emissions change, particularly in Asia. The plumes also affect temperature and precipitation by interacting with huge cloud systems across the Pacific that reflect enormous amounts of sunlight and help regulate global climate.
In their first look at PACDEX data, the researchers discovered that some plumes spanned as little as a few hundred feet in height. “We found pollution layers in very thin vertical regions, which may be one of the reasons why it is challenging to model these effects,” Stith says.
Black carbon showed up in PACDEX at very high altitudes, according to Scripps principal investigator Veerabhadran Ramanathan. “That worries me greatly, because the higher [the aerosols] are, the longer are their lifetimes in the atmosphere and the greater are their impacts on climate,” he says. Ramanathan notes that a black carbon aerosol at 10 km (6 mi) may have a climate warming factor two to three times greater than at 1 km (0.6 mi). The team also saw dust and black carbon occurring simultaneously at the higher altitudes. “Theory suggests that this combination will enhance the warming effects of the black carbon even more,” Ramanathan says.
Layering | A window | A research aircraft is born