High above Earth, thin veils of metallic haze drift through the edge of space. Known as sporadic E layers, these high-altitude “clouds” form from the vaporized dust of burnt-up meteors, earning their name from the unpredictable way they emerge and then dissipate.
Though invisible to the eye, sporadic E layers make their presence known to the radio signals we rely on for long-distance communication. When present, sporadic E can send those signals ping-ponging off in unexpected directions, rendering the technology temporarily unreliable.
Scientists have long sought a fuller understanding of these radio-disrupting clouds, but until recently, they had only sampled them one narrow slice at a time. The rocket, called the sporadic E Electrodynamics Demonstration, or SpEED Demon for short, launched from NASA’s Wallops Flight Facility in Virginia on Aug. 24, 2022, and demonstrated the first concurrent, multi-point view inside sporadic E. Its results, from a team led by Embry-Riddle Aeronautical University, are described in a new study in the Journal of Geophysical Research: Space Physics.
Sporadic E layers form in the ionosphere, a region of the upper atmosphere beginning around 40 miles (60 kilometers) up where the neutral gases begin to transform into plasma, or ionized gas. Some of the particles there come from meteors, which burn up and leave behind traces of iron, magnesium, and other metals. These metals occasionally clump into dense, cloud-like sheets — the sporadic E layers — that reflect radio waves.
“Sporadic E layers are, in one sense, giant mirrors of radio frequency waves in the sky,” said Aroh Barjatya, the mission’s principal investigator and a professor of engineering physics at Embry-Riddle in Daytona Beach, Florida.
When a sporadic E layer forms, signals meant to travel out to space can ricochet back toward the ground. Air traffic controllers and marine radio users may pick up distant transmissions as though they were nearby, and radars scanning beyond the horizon can register so-called “ghosts,” or false targets.
“The biggest source of error in the GPS in your phone, for example, is from the plasma in the ionosphere, and sporadic E layers can contribute to this uncertainty,” said Henry Valentine, the study’s lead author, who conducted the work at Embry-Riddle and is now a researcher at the U.S. Naval Research Laboratory.
Because sporadic E layers hover around 60 miles (100 kilometers) up — too high for weather balloons, too low for satellites — and form and dissipate unpredictably, they have long been challenging to study. The SpEED Demon mission provides the first detailed look at their internal structure.