High above Earth, a thin metallic haze forms at the edge of space. These high-altitude “clouds,” known as sporadic E layers, are created from vaporized meteor dust and are named for their unpredictable appearance and disappearance. New findings from a NASA sounding rocket equipped with five simultaneous detectors have revealed the unexpected structure and complexity of these mysterious ionospheric layers.
Although sporadic E layers are invisible to the human eye, they can significantly affect radio communications. When these dense sheets of ionized metal form, they may reflect radio signals in unexpected directions, temporarily reducing the reliability of long-range communication systems.
Scientists have long worked to understand how sporadic E layers form and change. Until recently, researchers could measure only one narrow path through a layer at a time. That changed on August 24, 2022, when NASA launched the Sporadic-E Electrodynamics Demonstration mission, known as Speed Demon, from NASA’s Wallops Flight Facility in Virginia. The mission provided the first simultaneous, multi-point measurements inside a sporadic E layer. A team led by Embry-Riddle Aeronautical University describes the results in a new study published in the Journal of Geophysical Research: Space Physics.
Sporadic E layers form in the ionosphere, a region of Earth’s upper atmosphere that begins roughly 40 miles (60 kilometers) above the surface. In the ionosphere, neutral gases are transformed into plasma, or electrically charged gases. Some of the particles in this region originate from meteors, which burn up as they enter the atmosphere and leave behind metals such as iron and magnesium. These metals can collect into dense, cloud-like sheets capable of reflecting radio waves.
“The sporadic E layer is, in a sense, a giant mirror for high-frequency waves in the sky,” said Aroo Barjatya, the mission’s principal investigator and a professor of engineering physics at Embry-Riddle Aeronautical University in Daytona Beach, Florida.
When sporadic E layers develop, radio signals that would normally travel into space can bounce back toward Earth. Air traffic controllers and maritime radio users may receive distant transmissions as if they originated nearby. Radar systems scanning beyond the horizon may also detect “ghost” targets, or false objects. The effects can even influence everyday navigation technology.
“For example, the largest source of error in cellphone GPS is due to ionospheric plasma, and sporadic E layers can contribute to this uncertainty,” said Henry Valentine, the study’s lead author. Valentine conducted the research at Embry-Riddle and is now a research scientist at the U.S. Naval Research Laboratory.
Sporadic E layers typically form about 60 miles (100 kilometers) above Earth—too high for weather balloons and too low for satellites. Because they can appear and disappear unpredictably, researchers have often relied on sounding rockets, which can be launched quickly when the layers are detected. However, a single rocket follows only one path and collects measurements along a narrow line. Barjatya compares this limited view to looking through a crack in a wall: Researchers can see what is directly in front of them but miss what is happening to either side.
The Speed Demon mission changed that approach. It became the first mission to release deployable probes, called dropsondes, directly into a sporadic E layer. After reaching the layer, the rocket released four dropsondes that moved away from the main payload and from one another. Each probe measured plasma along its own trajectory and transmitted the data to a ground station. Together with the primary payload, the mission sampled the sporadic E layer at five locations simultaneously.
“We used multiple sensors to turn that crack into a picket fence,” Barjatya said.
The measurements revealed that sporadic E layers are far more complex than previously thought. Instead of forming a smooth, uniformly dense sheet of metallic particles, the layer observed by Speed Demon appeared uneven and highly structured. The shape seemed to be influenced by turbulent flows moving through the surrounding neutral atmosphere.
“Often we think of sporadic E as this single sharp, dense layer, but what we observed is that it’s interacting with neutral winds and swirling atmospheric turbulence,” Valentine said. “It’s more like a cinnamon roll than a flat pancake.”
During the rocket’s descent, the sporadic E layer sometimes split into two distinct peaks. The researchers found that this shape is consistent with the influence of Kelvin-Helmholtz waves—curling atmospheric instabilities that can create wave-like patterns similar to those seen in breaking clouds. Because the mission did not directly measure local winds and electric fields, the team considers this explanation plausible but not yet confirmed.
Speed Demon was initially designed as a technology demonstration to determine whether dropsonde measurements could be successfully deployed in the ionosphere. The mission succeeded, and researchers soon applied the same multi-probe strategy to other missions. Barjatya’s team launched rockets during the annular solar eclipse in October 2023 and the total solar eclipse in April 2024 to study how sudden darkness affects the upper atmosphere. In June 2025, the team launched the mission’s direct successor, Sporadic-E ElectroDynamics, or SEED, from Kwajalein Atoll in the Marshall Islands to study sporadic E layers at lower latitudes. Research papers from these missions are in preparation.
After decades of research, sporadic E layers are no longer considered entirely unpredictable. Scientists now know that they follow seasonal patterns and occur most frequently during the local summer, Barjatya said.
However, many questions remain about how sporadic E layers form, evolve and influence radio signals. Advanced multipoint rocket sensors, combined with ground-based observations, could help scientists develop a more complete understanding of these high-altitude structures and their effects on communications, navigation and radar systems.
“The entire scientific community is now in the final stages of fully understanding the giant high-frequency mirrors in our sky,” Barjatya said.
By Miles Hatfield
NASA’s Goddard Space Flight Center, Greenbelt, Maryland
Source: science.nasa.gov