Historic solar wind event reveals Alfvén wings in Earth’s magnetosphere

New research published in Geophysical Research Letters reveals an unprecedented solar wind event observed by NASA’s Magnetospheric Multiscale (MMS) mission on April 24, 2023, when a massive coronal mass ejection (CME), with a low plasma beta of 0.01, caused Earth’s magnetosphere to lose its typical tail and form Alfvén wings. This event, lasting about two hours, provides new insights into space weather processes and the interaction between CME plasma and Earth’s magnetic field.

• The results show that the magnetosphere transforms from its typical windsock-like configuration to having wings that magnetically connect our planet to the Sun. The wings are highways for Earth’s plasma to be lost to the Sun, and for the plasma from the footpoints of the Sun’s erupted flux rope to access Earth’s ionosphere.
• The work indicates highly dynamic generation and interaction of the wing filaments, shedding new light on how sub-Alfvénic plasma wind may impact astrophysical bodies in our solar and other stellar systems.

A team of scientists from NASA’s Magnetospheric Multiscale (MMS) mission, including researchers Li‐Jen Chen and colleagues, observed a hitherto unheard-of solar wind event. Their research, recently published in Geophysical Research Letters, has come up with new details about space weather and its impact on Earth’s magnetic environment.

In April 2023 Earth’s magnetosphere which acts as a protective shield against solar and cosmic radiation, underwent an unusual and significant upheaval when a massive CME destroyed the magnetosphere’s usual elongated tail.

This CME, with a low plasma beta of 0.01, caused major changes in the magnetosphere’s structure. The traditional tail structure was replaced by intricate Alfvén wings which are complex magnetic structures, which connected the Earth’s magnetosphere directly to the recently erupted region of the Sun, serving as a plasma transportation highway. 

The disturbance took place in the Earth’s magnetosphere, which is known to extend into space and interact with solar wind. The MMS spacecraft, which is strategically positioned to explore the interplay between solar wind and the Earth’s magnetic field, conducted observations from space. The data collected from this vantage point revealed important information about the event’s influence on the magnetosphere.

This significant event occurred on April 24, 2023, and for approximately two hours the CME disrupted the normal structure of the Earth’s magnetosphere, revealing rapid changes in the magnetic field and plasma environment.

The CME’s low plasma beta was the primary cause of this amazing event. Beta, which measures the ratio of plasma to magnetic pressure, was extremely low during this CME. This environment allowed for faster magnetic reconnection and more intense plasma energization than is generally observed. As a result, Earth’s bow shock—a protective border in the magnetosphere—was briefly removed, allowing the CME’s plasma and magnetic fields to interact directly with the magnetosphere.

“The terrestrial bow shock disappears, leaving the magnetosphere exposed directly to the cold CME plasma and the strong magnetic field from the Sun’s corona. Our results show that the magnetosphere transforms from its typical windsock-like configuration to having wings that magnetically connect our planet to the Sun,” the researchers stated.

NASA’s MMS mission detected an unusual type of magnetosphere interaction with unshocked low-beta CME plasma. This interaction was characterized by the creation of Alfvén wings, which were complex magnetic structures that connected the magnetosphere to the Sun’s erupting flux rope. The MMS spacecraft found cold CME ions on closed field lines, most likely caused by a mechanism known as dual-wing reconnection. This reconnection featured the draped Interplanetary Magnetic Field (IMF) merging with Earth’s magnetic field lines at the cusps of northern dawn and southern twilight. The end effect was the formation of Alfvén wings, which acted as dynamic pathways for plasma transfer between Earth and the Sun.

The CME’s high Alfvén speed caused the bow shock in the magnetosphere to dissipate, allowing the solar plasma to interact directly with the Earth’s magnetic field. The cold CME ions detected on the closed field lines gave more evidence of this interaction, emphasizing the magnetosphere’s complex and dynamic reaction to such solar wind disruptions.

“The reported measurements advance our knowledge of CME interaction with planetary magnetospheres, and open new opportunities to understand how sub-Alfvénic plasma flows impact astrophysical bodies such as Mercury, moons of Jupiter, and exoplanets close to their host stars,” the researchers concluded.

The solar wind disturbance reported on April 24, 2023, has profoundly challenged the understanding of the Earth’s magnetosphere. The loss of the typical magnetospheric tail and the introduction of Alfvén wings demonstrate the active nature of space weather interactions.

These findings improve the understanding of Earth’s space environment and draw interesting parallels with other celestial bodies, such as Jupiter’s moon Ganymede.

References:

¹ Earth’s Alfvén Wings Driven by the April 2023 Coronal Mass Ejection – Li Jen Chen et al. – AGU Geophysical Research Letters – July 24, 2024 – https://doi.org/10.1029/2024GL108894 – OPEN ACCESS

Harsha Borah

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