Summary
Scientists in Antarctica have discovered that invisible showers of energetic electrons, a kind of ‘silent aurora’, bombard our atmosphere for hours after the visible light show fades. They used a powerful radar to detect these events, revealing they are far more common and long-lasting than previously thought.
Quick Facts
The study used the SuperDARN radar at Syowa Station, Antarctica.
These energy showers are called Energetic Electron Precipitation (EEP).
EEP events cause a form of radio blackout in the upper atmosphere.
They are most common in winter, occurring on over 50% of days.
The invisible energy can continue raining down for 2-4 hours after sunrise.
The average event detected by the radar lasted for over two hours.
The Discovery: Listening for a Silent Storm
At the remote Syowa Station in Antarctica, scientists were using a powerful high-frequency radar called SuperDARN to study the upper atmosphere. They noticed something peculiar: sometimes, their radar signal would just vanish. Both the signal they sent out and the background radio noise from space would suddenly go quiet. They realized this wasn’t an equipment failure; something in the atmosphere was absorbing the radio waves. By cross-referencing their data with an all-sky camera, they found a match: these radio blackouts happened during pulsating auroras. These are faint, patchy auroras caused by showers of high-energy electrons. The team had found a new way to track these invisible energy storms, even when clouds or daylight made the aurora impossible to see.
We can use the radar to detect this high frequency radio wave attenuation in the D region during energetic electron precipitation events.
— Emma C. Bland, Lead Author
The Science Explained Simply
Energetic Electron Precipitation (EEP) is like an invisible rain of high-speed electrons from space. Guided by Earth’s magnetic field, these particles funnel down towards the poles and slam into our atmosphere. While lower-energy electrons create the beautiful auroras we see at about 100-300 km altitude, these higher-energy electrons dive deeper, down into the D-region (60-90 km). Here, they crash into air molecules, knocking their electrons loose. This process, called ionization, creates a dense layer of charged particles. For high-frequency radio waves, like those used by the SuperDARN radar, this dense layer acts like a thick foam wall, absorbing the signal completely instead of letting it pass through or bounce back. This is why both the radar’s echo and the cosmic background noise disappear.
The Aurora Connection
Think of EEP as the powerful, invisible cousin of the aurora. While the Northern and Southern Lights are the beautiful, visible result of particles hitting our atmosphere, EEP represents a more intense energy transfer. This study specifically linked the radar blackouts to pulsating auroras, a type of aurora known to be driven by these energetic electrons. The most amazing discovery was what happened at dawn. As the sun rose, the camera would stop seeing the faint pulsating aurora. But the radar showed that the radio blackout—the EEP event—continued for another 2 to 4 hours! This means the energy kept pouring into our atmosphere long after the visible light show ended. This ‘invisible afterglow’ constantly affects the chemistry of our upper atmosphere, creating molecules that can impact the ozone layer.
The postmidnight and morning sector occurrence rates reach approximately 50% in the winter and 15% in the summer.
— Bland et al., 2019
A Peek Inside the Research
The scientists developed a clever detection method using two clues from the SuperDARN radar. The first clue was a sharp drop in backscatter power. This is the signal that bounces off the ionosphere and returns to the radar; if it disappears, it means it was absorbed on its way up and back. The second clue was a simultaneous drop in the background noise. This is the natural radio static from space, like lightning on other planets. If this background static also disappears, it confirms that a layer in our atmosphere is absorbing *all* incoming radio waves. When both clues appeared together, the team knew an EEP event was happening. They validated this method by perfectly matching the start times of these ‘double drops’ with the appearance of pulsating auroras in an all-sky camera located right next to the radar.
Key Takeaways
Specialized radars can detect invisible space weather events that optical cameras miss.
Energetic electrons create a dense layer in the D-region of our atmosphere that absorbs radio waves.
The effects of an aurora can persist as an 'invisible afterglow' of energy long after the lights disappear.
EEP has a strong seasonal cycle, peaking in the polar winter.
Understanding EEP is crucial for modeling its impact on atmospheric chemistry, like ozone depletion.
Sources & Further Reading
Frequently Asked Questions
Q: Is this EEP stuff the same as the Northern Lights?
A: They are two sides of the same coin! The Northern Lights (aurora) are the visible light created by lower-energy particles. EEP is caused by higher-energy particles that penetrate deeper into the atmosphere, and while it’s associated with a faint type of aurora, its main effects (like radio absorption) are invisible to our eyes.
Q: Why does this only happen near the North and South Poles?
A: Earth’s magnetic field acts like a giant shield, but it has funnels at the North and South Poles. Energetic particles from the Sun and space get trapped by this field and are guided down these funnels into the polar atmosphere, which is why auroras and EEP events are concentrated there.
Q: Does this invisible energy storm affect us?
A: Yes, it can. EEP events can disrupt high-frequency (HF) radio communications, which are still used by aircraft on polar routes. Scientists are also studying the long-term chemical effects, as EEP produces nitrogen oxides (NOx) that can contribute to ozone destruction in the polar stratosphere.
Q: Why do more of these events happen in winter?
A: The polar atmosphere is different in the continuous darkness of winter. The lack of sunlight changes the chemistry and density at high altitudes, which can enhance the effects of EEP. Winter is the prime season for these invisible energy showers, with the radar detecting them on more than half the days.
