The NASA-funded Auroral Zone Upwelling Rocket Experiment, or AZURE is the first of eight sounding rocket missions to be launched over the course of next two years with the aim of studying the auroral winds at the poles.
The northern lights, or aurora borealis, are beautiful when seen from ground up, but the scenario is completely different in the atmosphere where particles from the Sun collide violently with Earth’s atmosphere. The sounding rocket missions will be studying the contribution that aurora make to the total amount of energy that enters and leaves Earth’s geospace system — referred to as auroral forcing.
All of the eight sounding rocket missions geared towards understanding the auroral winds will be launched from the Andøya and Svalbard rocket ranges in Norway.
According to mission scientists, 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. 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 above Earth’s surface. The F region resides just above it, between 93 to 310 miles 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.
To better understand the forces at play, in early March the AZURE team will launch two sounding rockets near-simultaneously from the Andøya Space Center in Norway. Waiting to launch until the conditions are just right, the rockets will fly up into space, making measurements of the atmospheric density and temperature with instruments on the rockets and deploying visible tracers, trimethyl aluminum (TMA) and a barium/strontium mixture, which ionizes when exposed to sunlight.
These mixtures create colorful clouds that allow researchers to track the flow of neutral and charged particles, respectively. The tracers will be released at altitudes 71 to 155 miles high and pose no hazard to residents in the region.
By tracking the movement of these colorful clouds via ground-based photography and triangulating their moment-by-moment position in three dimensions, 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.
Such measurements are critical if we are to truly understand the effects of the mysterious yet beautiful aurora. The results will be key to a better understanding of the effects of auroral forcing on the atmosphere, including how and where the auroral energy is deposited.