In April 2023, an unexpectedly strong solar storm caught scientists and the world by surprise. On April 23, Earth was struck by a geomagnetic storm that created vivid auroras visible as far south as southern Texas. The source of this disturbance was a coronal mass ejection (CME), a cloud of energetic particles and magnetic fields ejected from the Sun. What made this particular storm unusual was the fact that the CME was preceded by a relatively weak solar flare, leading scientists to anticipate only a minor disruption. However, the storm turned out to be far more intense than expected.
The Mystery Behind The Storm’s Strength
Researchers from NASA and other space agencies have worked extensively to understand why some solar storms, like the one in April 2023, cause more significant impacts than others. According to a study published in The Astrophysical Journal, the CME’s orientation relative to Earth was a key factor in the storm’s unexpected strength. Scientists noted a large coronal hole near the CME’s origin. Coronal holes are regions where solar wind flows at higher-than-normal speeds, influencing the movement of CMEs.
The research, led by Evangelos Paouris of the Johns Hopkins Applied Physics Laboratory, explains that the fast solar wind from the coronal hole acted like an “air current,” shifting the CME from its original path. This change brought the CME closer to Earth’s orbital plane, making it interact more intensely with Earth’s magnetic field. The result was a stronger storm than anticipated. The study concluded that the CME’s magnetic fields, which were oriented opposite to Earth’s, allowed more solar energy to flow into Earth’s atmosphere, amplifying the storm’s effects.
Surprising Effects On Earth’s Thermosphere
NASA’s GOLD (Global-scale Observations of Limb and Disk) mission provided another fascinating insight during the April 2023 geomagnetic storm. GOLD’s spacecraft measured the temperature in Earth’s thermosphere, a layer of the upper atmosphere between 85 and 120 miles above the surface. The results were striking: temperatures soared during the storm, but then plummeted to significantly lower levels once the event subsided.
After the storm, the thermosphere cooled by 90 to 198 degrees Fahrenheit, dropping from a temperature range of about 980 to 1,070°F to a cooler range of 870 to 980°F. This cooling effect was unprecedented and was the first time that such widespread temperature drops had been observed following a strong geomagnetic event.
According to Xuguang Cai from the University of Colorado, who led the GOLD research, the temperature drop is critical because it impacts satellite and space debris behavior. Cooler temperatures cause the thermosphere to contract and reduce its density at satellite altitudes, ultimately decreasing drag. This means satellites and debris can stay in orbit longer than expected, potentially increasing the risk of collisions in space.
New Technology For Predicting Solar Storms
Understanding the full scope of solar storms is not just a matter of academic curiosity. Predicting when and how a CME will affect Earth is vital for protecting space-based infrastructure, such as satellites, GPS systems, and communication networks. To improve these predictions, NASA is turning to machine learning. A new technique, known as GeoCME, utilizes artificial intelligence to identify patterns in images of CMEs captured by NASA’s SOHO (Solar and Heliospheric Observatory) spacecraft.
GeoCME was trained using historical CME data, allowing the machine learning model to predict the likelihood of a CME triggering a geomagnetic storm. The system has shown remarkable accuracy, predicting the outcomes of 21 CMEs and correctly identifying the non-geoeffective nature of most other events. Jack Ireland, a heliophysicist at NASA’s Goddard Space Flight Center, remarked on the promising potential of machine learning in improving CME predictions.
Early Warnings Could Save Valuable Time
The May 2024 geomagnetic superstorm, the most intense in over 20 years, underscored the importance of real-time predictions for solar storms. During this event, NASA’s STEREO (Solar Terrestrial Relations Observatory) spacecraft played a crucial role in measuring the magnetic structure of CMEs as they passed by Earth. A significant finding from the event was that STEREO-A, a spacecraft located closer to the Sun than the typical monitoring point at Lagrange Point 1 (L1), could have provided an earlier warning by more than two hours.
The results, published in Space Weather, demonstrated that positioning spacecraft closer to the Sun could offer more advanced predictions about the intensity of solar storms, giving critical time to prepare and protect Earth’s infrastructure. This observation is particularly notable as it’s the first time a spacecraft positioned closer to the Sun than L1 has tracked such an event.