The $81.5 million HIAPER aircraft, owned by the National Science Foundation and operated by the National Center for Atmospheric Research (NCAR), will fly over treacherous whirlwinds, known as rotors, as they form above California's Sierra Nevada mountain range.

HIAPER (High-performance Instrumented Airborne Platform for Environmental Research) will embark on a series of 10-hour flights that will take it from its base at Jefferson County Airport in Colorado to California's Owens Valley during next month's Terrain-Induced Rotor Experiment, or T-REX. The aircraft will explore the mountain waves that form over the Sierra Nevada and are associated with the rotors, as well as study the impacts of the waves on atmospheric regions as high as the stratosphere. The research will lead to better prediction of these aviation hazards.

Rotors, which form on the lee side of high, steep mountains beneath the cresting waves of air, have contributed to a number of aircraft accidents, but scientists know little about their structure and evolution. They are common in the Sierras because the area has the steepest topography in the continental United States. Owens Valley sits some 10,000 feet directly below the highest peaks of the adjacent mountains.

"From a scientific point of view, this will be a fantastic part of the atmosphere to be flying around in because of the mountain waves, the turbulence, and the movements of air masses," says NCAR scientist Jorgen Jensen. "With our advanced instrument payload and our flight paths, the amount of data we will collect will be absolutely unprecedented for describing airflow over mountains."

HIAPER, a highly instrumented Gulfstream V that is capable of reaching an altitude of 51,000 feet and cruising for 7,000 miles, is ideally suited for the experiment.

"HIAPER's first science campaign, on the origin and evolution of rotors, could not have been done without the long-range capabilities of the aircraft," says Margaret Leinen, NSF assistant director for geosciences. "In addition, the communications and data capabilities of HIAPER will allow the entire science team of T-REX to participate in the experiment, whether or not they are actually flying on board. "

James Huning, the program manager for HIAPER at the National Science Foundation, adds, "The project will help forecasters predict when and where rotors are most likely to occur and the degree of their intensity, as well as the nature of the mountain waves, or gravity waves, that crest high above rotors and cause strong turbulence. Without HIAPER, this understanding would not be possible."

NCAR's Earth Observing Laboratory will oversee T-REX field operations from Bishop, California, and manage the resulting data.

"The results of this project should help pilots by enabling computer models to be more effective in forecasting turbulent conditions associated with mountain waves," explains Richard Dirks, NCAR field operations director.

Project details

The international research team of about 60 scientists, led by scientific project director Vanda Grubi�ic of the Desert Research Institute in Reno, Nevada, will study the rotors from several perspectives. On the ground, researchers will probe them with radars, lidars (laser-based radars), automated weather stations, wind profilers, and balloons. Researchers aboard HIAPER will observe the rotors from above and release dropsondes (instruments that contain temperature, wind, and other sensors) into the most turbulent areas. Two other aircraft from the University of Wyoming and a team of British government agencies, flying at lower elevations, will also gather data and aim cloud radars into the rotors.

The data they retrieve should help researchers understand the three-dimensional nature of the rotors. The project will help forecasters predict when and where rotors are most likely to occur and the degree of their intensity, as well as the nature of the mountain waves, or gravity waves, that crest high above the rotors and cause strong turbulence as well.

"Rotors have intrigued scientists since the 19th century, and frustrated pilots since they started flying near the mountains," Grubi�ic says. "With the newest advances in airborne measurements, remote sensing, and atmospheric numerical modeling, we are now in a position to tackle some basic scientific questions on the evolution, structure, and predictability of rotors and also breaking mountain waves. We expect T-REX results to help improve aviation safety near mountainous terrain."

Scientists will also study the pollutants and particles that are moved around by the waves and affect climate and air quality. By flying as high as the lower stratosphere, HIAPER will enable researchers to gather data about the distribution of chemicals high in the atmosphere after they get rearranged by mountain waves.

A research veteran

The T-REX team will include veteran NCAR scientist Joachim Kuettner, who first explored the newly discovered mountain waves in Germany in the 1930s at the helm of an open sailplane. Now 96, Kuettner is a principal investigator on T-Rex. "I've always wanted to explore the rotors," he says. "It's taken me this long."

Related Links
US National Science Foundation
US National Center for Atmospheric Research