BAe-146; photo courtesy FAAM
Of course spacecraft and astronauts and robot rovers are sexy. So are scientific submarines and their dives to the deep seafloor. But today I want to speak up for research aircraft and the plucky geniuses who maintain and fly them. They penetrate hurricanes; they peek high above thunderstorm complexes at night for a glimpse of sprites; they fly over the El Niños and the poles.
Most of all, aircraft are an indispensable part of our effort to understand Earth’s climate and the atmosphere that sustains it. They’re worthy of graphic-novel treatment, if there’s an artist out there who’s up for it. Here’s the story line: Next week three of the world’s best scientific aircraft will team up on a six-week mission, called CONTRAST, to explore a key part of the world’s climate system.
The tropical western Pacific, south of Guam, is the opposite of Antarctica: the warmest part of the ocean. As we shiver through winter, the atmosphere above the Western Pacific Warm Pool is at its most active. The region acts like an immense chimney, with thunderstorms and other deep convective disturbances pushing huge quantities of air some 20 kilometers straight up from the sea surface. Some of this air bursts into the quiet stratosphere, where it stays for years and spreads outward across the entire world. The West Pacific chimney is where most of the stratosphere’s input of surface air happens. Models of global climate need to account for the influence of this great engine of air, but its makeup is poorly known.
One notable ingredient of oceanic air is a set of organic bromine compounds emitted by sea life. Although these gases usually are swiftly neutralized by ozone within 100 meters of the sea surface, the western Pacific chimney is active enough to funnel bromine into the upper atmosphere, where it erodes the stratospheric ozone layer that protects us from damaging ultraviolet radiation. Volcanoes also inject bromine into the stratosphere, but in the Pacific chimney we can study the same process all the way up from the sea surface without dealing with a volcano’s dangers.
Three state-of-the-art aircraft will team up for CONTRAST (CONvective TRansport of Active Species in the Tropics). Two have human crews while the third, the high-altitude star, is a robot. Between them, they can cover the whole altitude range of this energetic region from the wavetops well into the stratosphere.
The British research aircraft BAe-146, part of the Facility for Airborne Atmospheric Measurements, will handle the low-altitude portion up to about 6 kilometers (20,000 feet). A large plane that can carry 18 people, its focus will be on the rising clouds, where exceptionally low ozone levels allow the bromine gases (and related iodine gases) to survive far beyond their normal lives. Its data will help fill in a large gap between the sea surface and the top of the chimney. Just as important will be the differences it discovers between air inside and outside clouds.
Tackling the middle part will be the National Science Foundation’s High-Performance Instrumented Airborne Platform for Environmental Research (HIAPER), a modified Gulfstream business jet that can reach over 15 kilometers (51,000 feet). Its previous special mission was observing sprites over the Midwest last summer. It will continue the BAe-146′s measurements upward in the atmosphere. It will also gather data during the night as well as the day, because the chemical reactions in the air change dramatically when the sun goes down.
HIAPER; photo courtesy Carlye Calvin, UCAR
The high extreme, between 14 and 19 kilometers (up to 62,000 feet) will be handled by a large robot plane, NASA’s Global Hawk, as part of the ATTREX (Airborne Tropical TRopopause EXperiment) project. This heavily instrumented, pilotless observing platform is stationed at Edwards Air Force Base and has been in use for barely a year. It can make 30-hour flights that exceed the safe limits of any human pilot. Global Hawk will deal with the stratosphere, ranging widely around the West Pacific chimney to trace its injected air and study how it changes.
Global Hawk; NASA photo by C. Fratello
All three aircraft will also be measuring temperature, humidity, and the usual suspects among atmospheric gases: ozone, water vapor, carbon dioxide, methane, nitrogen oxides and more. Each gas has its own story in the stratosphere that must be accounted for in global climate models. The mission is summed up in this diagram.
The three CONTRAST aircraft will cover the vertical range of the tropical troposphere. CPT, cold point tropopause; TTL, tropopause transition layer; CBL, convective boundary layer. Diagram by Diane Pendlebury, Univ. Toronto
You can follow this all-star team as it takes on the Chimney during CONTRAST from January 14 to February 28 on NASA’s Aircraft Tracker: the BAe-146 is “FAAM BAE-146,” HIAPER is “NSF/NCAR G-V,” and Global Hawk is “Global Hawk AV6.” Give the aircraft some respect!