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. Now, new results from a NASA sounding rocket — a suborbital research rocket — that flew five detectors through one of these layers simultaneously reveal unexpected complexity in the layer for the first time.
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 effects reach everyday technology, too.
“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 the province of sounding rockets, which can be launched on short notice to catch one in the act. But a single rocket flies a single path, taking measurements only along a line. Barjatya likens the situation to viewing a scene through a crack in a wall. One can only observe what is happening along that narrow slit, missing out on the crucial context of whatever is occurring to the left or right of one’s view.
The SpEED Demon mission changed that. The mission was the first to deploy ejectable probes, called dropsondes, inside a sporadic E layer. Once inside, the rocket released four dropsondes that flew away from the main payload and from one another, each measuring the plasma along its own track and beaming its measurements back to ground stations. Together with the main payload, the probes sampled the layer in a total of five places at the same moment.
“Now with multiple sensors, we’ve turned that crack into a picket fence,” Barjatya said.
The data revealed surprising complexity inside the sporadic E layer. Rather than a smooth, dense pancake of metallic particles, the layer that SpEED Demon flew through appeared uneven and structured, shaped by turbulent winds moving through the neutral air around it.
“A lot of times you think of sporadic E as this single sharp density layer, but what we saw in ours is it’s interacting with neutral wind and these swirling atmospheric turbulences,” Valentine said. “Rather than a flat pancake, it’s closer to a cinnamon roll.”
On the way down, the layer even split into two distinct peaks. The team found that shape was consistent with modulation by Kelvin-Helmholtz billows, the curling, wave-like instability that produces breaking-wave patterns in ordinary clouds. Because the flight was unable to measure the local winds and electric fields directly, the researchers are careful to call the billow explanation plausible rather than confirmed.
The SpEED Demon mission was designed as a technology demonstration — a test of whether the dropsonde technique would work at all. It did, and the team was quick to apply it again. Barjatya’s team used a similar multi-probe strategy to launch rockets into the paths of the October 2023 annular eclipse and April 2024 total solar eclipse, studying how the sudden darkness disturbed the upper atmosphere. In June 2025, they flew SpEED Demon’s most direct descendant, Sporadic-E ElectroDynamics, or SEED, into sporadic E layers from Kwajalein Atoll in the Marshall Islands, studying them at lower latitudes. Papers from those missions are in preparation.
After years of study, sporadic E layers are no longer as unpredictable as they once were. “They have a seasonality to them, with peak occurrence happening in the local summer,” Barjatya said.
Questions about how and when they form are increasingly fine-grained. The new deployable multi-point rocket sensor methodology, along with ground-based measurements, is likely to bring the picture even closer to completion. “The science community as a whole is now in its final stretches of fully understanding these giant radio frequency mirrors in the sky,” Barjatya said.
By Miles Hatfield
NASA’s Goddard Space Flight Center, Greenbelt, Md.
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Source: science.nasa.gov
