From the ground, the dance of the northern lights, or aurora borealis, can look peaceful. But those shimmering sheets of colored lights are the product of violent collisions between Earth’s atmosphere and particles from the Sun. Understanding the contribution that aurora make to the total amount of energy that enters and leaves Earth’s geospace system is one of the major goals of the NASA-funded AZURE (Auroral Zone Upwelling Rocket Experiment) mission. On April 5, 2019, the mission was successfully conducted from the Andøya Space Center in Norway: two Black Brant XI-A sounding rockets were launched at 6:14 and 6:16 p.m. EDT carrying scientific instruments and visible gas tracers — trimethyl aluminum (TMA) and a barium/strontium mixture, which ionizes when exposed to sunlight.
Colorful clouds formed by the release of vapors from the two AZURE rockets allow scientists to measure auroral winds. Image credit: Lee Wingfield / NASA.
AZURE is the first of eight sounding rocket missions launching over the next two years as part of an international collaboration of scientists known as The Grand Challenge Initiative – Cusp.
These missions will launch from the Andøya and Svalbard rocket ranges in Norway to study the processes occurring inside the Earth’s polar cusp — where the planet’s magnetic field lines bend down into the atmosphere and allow particles from space to intermingle with those of Earthly origin — and nearby auroral oval.
“AZURE will study the flow of particles in the ionosphere, the electrically charged layer of the atmosphere that acts as Earth’s interface to space, focusing specifically on the E and F regions,” NASA scientists said.
“The E region — so-named by early radio pioneers that discovered the region was electrically charged, and so could reflect radio waves — lies between 56 to 93 miles (90-150 km) above Earth’s surface. The F region resides just above it, between 93 to 310 miles (150-500 km) altitude.”
“The E and F regions contain free electrons that have been ejected from their atoms by the energizing input of the Sun’s rays, a process called photoionization. After nightfall, without the energizing input of the Sun to keep them separated, electrons recombine with the positively charged ions they left behind, lowering the regions’ overall electron density. The daily cycle of ionization and recombination makes the E and F regions especially turbulent and complex.”
“AZURE will focus specifically on measuring the vertical winds in these regions, which create a tumultuous particle soup that re-distributes the energy, momentum and chemical constituents of the atmosphere.”
On April 5, two AZURE rockets released visible gas tracers over the Norwegian Sea at 71 through 150 miles (114-241 km) altitude.
These mixtures, using substances similar to those found in fireworks, created colorful clouds that allow the researchers to track the flow of neutral and charged particles with the auroral wind.
“By tracking the movement of these colorful clouds via ground-based photography and triangulating their moment-by-moment position in 3D, AZURE will provide valuable data on the vertical and horizontal flow of particles in two key regions of the ionosphere over a range of different altitudes,” the scientists said.
