Speed Demons of the Sky: Fast-Moving Auroral Surges

By the end of this article, you will understand how scientists discovered a lightning-fast type of aurora, and how they use magnetic fingerprints to tell different space storms apart.

In 2013, researchers set up a massive network of all-sky cameras and magnetometers across northern Europe. They weren’t just taking pretty pictures; they were hunting for dynamic changes in the night sky. During a moderate space weather event, they observed a Surprise: a series of glowing green surges shooting eastward. These weren’t standard auroras. They were Eastward-Expanding Auroral Surges (EEAS). The team tracked these surges moving across the sky in 15-minute intervals, perfectly synced with invisible magnetic pulses detected on the ground. They had caught a completely unique, highly energetic phase of a space storm in action.

Original Paper: ‘Eastward-expanding auroral surges observed in the post-midnight sector’

The dynamic behavior of the EEAS is very similar for all three events, which occurred intermittently at intervals of about 15 min.
— Dr. Yoshimasa Tanaka

Here is the Salient Idea: This is NOT an ‘omega band’ aurora, even though it looks like one. Omega bands are large, glowing waves that drift slowly. The EEAS is entirely distinct because of its speed and timing. While omega bands stroll across the sky at about 1 kilometer per second during the end of a space storm, an EEAS rockets across at 3 to 4 kilometers per second right at the beginning. Even weirder, the electrical currents inside an EEAS spin counterclockwise—completely backwards compared to the smooth, clockwise spin of an omega band. This is a chaotic, high-speed surge, not a lazy glowing river.

The difference in the ionospheric current… may be attributed to a large temporal variation in the surge structure.
— Research Team

Why do these speedsters exist? It all comes back to Earth’s magnetic field. When the solar wind stretches Earth’s magnetic tail too far, it snaps back, firing energy toward the poles. This creates a substorm. As the energy hits the atmosphere, it creates a massive electrical circuit called a substorm current wedge. The extreme speed of the EEAS is actually the visual footprint of this magnetic wedge rapidly expanding eastward. By studying these high-speed auroras, we are literally watching the physical boundaries of Earth’s protective magnetic shield stretch and snap in real time.

The fast eastward propagation speed… is consistent with the speed of eastward expansion fronts of the substorm current wedge.
— Research Team

To prove these surges were unique, the scientists couldn’t just use cameras. They had to measure the invisible. They used magnetometers—highly sensitive electronic compasses that track fluctuations in magnetic fields. When an EEAS passed overhead, the magnetometers spiked, showing magnetic pulsations every 4 to 6 minutes. By combining the video of the glowing gas with the magnetic data of the invisible electrical currents, they could map out a 3D picture of the storm. It is a brilliant example of using multiple tools to uncover the hidden physics of the night sky.

It is necessary to analyze data from ground-based imager and magnetometer networks to study the spatiotemporal development…
— Dr. Yoshimasa Tanaka

Q: Why do these fast auroras only happen after midnight?
A: The shape of Earth’s magnetic field gets stretched into a long tail on the night side by the solar wind. When that tail ‘snaps’ back, the explosive energy is directed straight toward the midnight and post-midnight sections of the globe.