Could the night sky itself be used as a lab for one of the Earth’s most elusive atmospheric enigmas?
NASA is trying an unconventional triple-rocket launch Monday night from its Wallops Flight Facility in Virginia, launching the Turbulent Oxygen Mixing Experiment Plus TOMEX+ into the mesopause, a cold, turbulent region at 53 to 65 miles altitude. This area, where the mesosphere and the thermosphere converge, is the coldest part of the atmosphere, with temperatures dropping to almost minus 148 degrees Fahrenheit. It is also an area of intense mixing, where energy from the lower atmosphere travels upward and induces turbulence that can increase drag on satellites in a silent but dramatic fashion.
In contrast to the stratosphere and troposphere, the mesopause is inaccessible to balloons and beneath satellites’ direct line of sight. Sounding rockets, since they are able to target specific altitudes for short but high-intensity measurements, are among the limited instruments that can pierce it. TOMEX+ will deploy them in a synchronized cascade: two rockets will emit colored vapor tracers composed of barium, lithium, and aluminum compounds, the same substances used in fireworks, and a third rocket will deploy a laser-based lidar system to follow their trajectory.
The tracers, when released, will create glowing clouds visible on the ground. As they shear and stretch out in the turbulence and winds, high-speed cameras and airborne instruments will monitor their formation. The lidar on the third rocket, resonating at a wavelength that excited naturally occurring atomic sodium in the upper atmosphere created by dust that is being kicked up by meteors, will make the sodium layer fluoresce. The light band is a natural motion tracker, which displays fine-scale wave structure and turbulent eddies in three dimensions.
Measurements of this type are critical to the determination of atmospheric turbulence’s physics. At these heights, turbulent mixing shapes the density structure of the upper atmosphere and consequently the aerodynamic drag low-Earth orbit satellites encounter. Over time, even small drag variations can change satellite orbits, reducing mission duration or necessitating expensive orbital maneuvers. These have been shown to be related in long-term investigations to mesopause turbulence caused by wave activity propagating from the lower atmosphere and influenced by trends in stratospheric ozone and upper-atmosphere greenhouse gas–caused cooling.
The TOMEX+ mission is an improved version of the 2000 flight TOMEX with the addition of more technology. The lidar instrument, which was previously only on the ground, will now be sent from a rocket platform to measure over a much greater volume. By combining imaging of tracer clouds with wind and density profiles from lidar, scientists hope to produce the best 3D mapping to date of turbulence at the edge of space.
The chemical tracers themselves are released in limited amounts and quickly disperse. NASA points out that the chemicals are not toxic to humans or the environment. Their bright colors greens due to barium, reds due to lithium are a spin-off of their atomic emission spectra, similar to the chemistry of fireworks. To observers along sections of the U.S. East Coast, witness these radiant clouds shining in the evening sky, a fleeting event that is also an experiment of high accuracy.
Mesopause turbulence has applications beyond Earth. Martian upper atmosphere and Venusian upper atmosphere processes are the same, where energy transfer between atmospheric layers impacts climate and weather. With greater insight into the origin and dissipation of turbulence, TOMEX+ data could enhance satellite drag forecasting and global circulation models employed in climate studies.
Previous launches had been scrubbed by Hurricane Erin, which generated dicey recovery weather in the Atlantic. Now that the atmosphere is willing to cooperate, the launch window now is open as of 10 p.m. Eastern and runs into early morning. The success in the mission will paint the sky with transient ribbons of color as well as light up the clandestine machinery of a boundary layer that bridges Earth’s weather to the void of space.
