A previously undetected solar storm struck Earth on November 20th, causing a temporary, but noticeable, spike in geomagnetic activity and contributing to aurora displays at mid-latitudes. The event underscores the challenges of space weather forecasting, as these “stealth” coronal mass ejections (CMEs) are notoriously difficult to observe before they reach our planet.
What Happened?
Unlike typical CMEs – which are often preceded by visible flares and bright coronal emissions – this storm unfolded quietly. The storm arrived without a clear signal, but was detected after its effects began to disrupt conditions in the solar wind surrounding Earth. At approximately 9:20 a.m. EST (1420 GMT), the magnetic field strength jumped from a normal 4-6 nanoteslas to 18 nanoteslas, while solar wind speeds climbed to 400-500 km/s.
This transient event coincided with a high-speed stream flowing from a coronal hole on the sun, enhancing geomagnetic activity enough to push auroras further south than usual, with reports coming in from places like Maine and Denmark.
The Problem With Stealth CMEs
The difficulty in detecting these storms lies in their faint signatures. Stealth CMEs emerge from quiet regions of the sun, lacking the bright flares or dramatic loops that typically accompany solar eruptions. As space weather physicist Tamitha Skov noted, these events “have no signature in on-disk or coronagraph imagery,” meaning they are only discovered once they interact with Earth.
A 2021 study highlighted that stealth CMEs can still produce significant magnetic disturbances in space despite their subtle origins. This poses a serious forecasting problem, as current detection methods often miss these events entirely.
Why This Matters
The increasing frequency of stealth CMEs during the declining phase of the sun’s 11-year cycle adds another layer of complexity to space weather prediction. While this particular storm was minor, stronger undetected eruptions could disrupt satellite operations, power grids, and communication systems.
“Space weather events can have significant impacts on technology in space and on Earth,” says NOAA’s Space Weather Prediction Center. “Improved forecasting is critical to mitigating these risks.”
The ability to reliably detect and predict these stealth eruptions remains a key challenge for scientists, requiring more advanced monitoring techniques and a deeper understanding of the sun’s quiet regions.
This event serves as a reminder that even seemingly calm periods of solar activity can harbor hidden threats. Continued research into stealth CMEs is essential for protecting our increasingly vulnerable technological infrastructure.
