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Simulation claims to find solutions to a central mystery in space physics

Simulation finds solutions to a central mystery in space physics
Simplified schematics showing the events within the tail current sheet leading to the eruption of the tail-wide plasmoid. a, The situation within Fig. 1b, showing the two local reconnection regions Earthward and tailward of the dominant x line. Magnetic field topology is given, with ⊙ and ⊗ symbols representing outward and inward directions with respect to the plane and corresponding to Bz > 0 and Bz < 0, respectively. b, The situation within Fig. 1c, where the dusk flank local flux rope is mainly Earthward of the dominant x line. The flapping begins. c, The situation within Fig. 1d, where the flapping waves have evolved into the strong central fold in the noon–midnight meridional plane. The flux ropes have grown and moved tailwards and towards the center of the plasma sheet. d, The situation within Fig. 1g, where the large tail-wide plasmoid has been formed from the two local flank flux ropes. Their merging in the center current sheet was enabled by the current disruption within the central fold. In all panels, the position of the dominant x line is a result of a competition between two x lines. The one that is stronger diverts flow, and hence the global flow reversal changes position. Credit: Palmroth et al., Nature Geoscience (2023). DOI: 10.1038/s41561-023-01206-2.

How are plasma eruptions in near-Earth space formed? Vlasiator, a model designed at the University of Helsinki for simulating near-Earth space, demonstrated that the two central theories on the occurrence of eruptions are simultaneously valid: eruptions are explained by both magnetic reconnection and kinetic instabilities.

Rapid plasma eruptions known as plasmoids take place on the nightside of the magnetosphere. Plasmoids are also associated with the sudden brightening of the aurora. The research group at the University of Helsinki investigates and simulates these difficult-to-predict eruptions in near-Earth space using the Vlasiator model.

"The phenomena associated with plasmoids cause the most intense but the least predictable magnetic disturbances, which can cause, for example, disturbances in ," says Professor of Computational Space Physics Minna Palmroth from the University of Helsinki. "These eruptions occur on a daily basis, in varying sizes, in the 'tail' of the magnetosphere."

Palmroth is also the director of the Center of Excellence in Research of Sustainable Space, and the principal investigator for the Vlasiator simulation.

"The chain of events leading to plasmoids is one of the longest-standing unresolved questions in space physics: solutions have been sought for it since the 1960s," Palmroth says.

Near-Earth space is a unique place for understanding plasma eruptions

Two competing lines of thinking have been proposed to explain the course of events, the first asserting that severs a part of the magnetotail into a plasmoid. According to the other explanation, kinetic instabilities disrupt the current sheet (a wide, thin distribution of electric current) maintaining the tail, which eventually results in the ejection of a plasmoid. Arguments about the primacy of these two phenomena have been ongoing for decades.

"It now appears that the causalities are in fact more complex than previously understood," Palmroth says.

The Vlasiator simulation, which requires the processing power of a supercomputer, modeled near-Earth space for the first time in six dimensions and on a scale corresponding to the size of the magnetosphere. The 6D modeling was successful in describing the physics phenomena underlying both paradigms.

"It was a difficult technical challenge that no one else has been able to model," Palmroth says. Behind the achievement is more than 10 years of software development.

Consequently, the study was able to demonstrate that both magnetic reconnection and kinetic instabilities explain the functioning of the magnetotail. The associated with these seemingly contradictory theories actually both take place, and simultaneously.

The finding helps to understand how plasma eruptions can occur. This helps in designing spacecraft and equipment, observing these events for further research, and improving the predictability of space weather by improving the understanding of near-Earth space.

The paper is published in the journal Nature Geoscience.

More information: Minna Palmroth et al, Magnetotail plasma eruptions driven by magnetic reconnection and kinetic instabilities Nature Geoscience (2023). DOI: 10.1038/s41561-023-01206-2.

Journal information: Nature Geoscience

Citation: Simulation claims to find solutions to a central mystery in space physics (2023, June 29) retrieved 26 February 2024 from
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