Different than expected: When a solar storm hits the Earth’s magnetic field, it triggers a previously undetected interaction, measured data reveal. Energy-rich waves initially race towards the Earth’s poles and make the protective screen vibrate like a cylinder. But then some of the reflected waves generate a countercurrent that repels the solar wind and locally creates a standing wave at the boundary layer, the researchers report in the journal Nature Communications.
The Earth’s magnetic field is the most important to us protective shield Against high-energy radiation and streams of particles from space. A dense “cage” made of magnetic field lines keeps much of the solar wind, solar storms and solid cosmic rays away. But this does not leave our magnetic field without a trace: if a solar storm hits it, it vibrates as a result of the collision. like a drum. Standing waves are generated at the boundary layer, the magnetic stop period. These vibrations can be Make it heardn.
wave propagation pattern
But as we can now see, some previously undetected processes still occur in the magnetic field. Until now it was assumed that the vibrations at the magnetic field boundary move mainly away from the Sun. If a solar storm hits the outer limits of Earth’s magnetic field, it generates shock waves of rapidly charged particles that race toward Earth’s poles, according to current models. At the boundary layer, low-frequency waves arise that also move away from the Sun, albeit much slower – according to the current model.
However, there are notes that do not fit into this simple picture. NASA’s THEMIS satellites recently provided some measurement data indicating skew currents and normal oscillations especially at magnetic field boundaries. Martin Archer of Imperial College London and colleagues have now studied what this is about and how it is generated using THEMIS data and models.
Eigenmode detects countercurrent
The result was surprising: analysis of the waveforms showed that it is clear that not all the energy of the vibrations of the solar shock wave is transferred to the side facing away from the sun. Instead, there is a region where the waves are reflected from the polar ionosphere and thus move against the current. In an area directly opposite the Sun, the energy flow of these reflected waves is as strong as the main flow of waves moving toward the tail.
In other words, the reflected waves and the shock wave of the solar wind cancel each other out. “This means that the wave energy remains locally trapped at the magnetic field boundary and an azimuthal fixed wave is generated,” the team said. They compare it to trying to climb an escalator against the direction of travel: “Even though you put in a lot of effort, you can’t get out of place,” Archer explains.
© Martin Archer/CCMC, NASA
Incomplete common forms
But this means that the current model of deflecting shock waves on the sun-facing side is incomplete. “The natural oscillations on the magnetic stop surface do not match the well-established model,” the scientists say. Because, contrary to what was believed, some waves of the magnetic field move against the current. At the point closest to the Sun on the day side of the Earth, this countercurrent is just as strong as the solar wind, and therefore causes a standing wave there.
“This effect is important for our ideas about the radiation belt, ionospheric dynamics, polar lights, and other dynamical regimes,” Archer and colleagues write. (Nature Communications, 2021; doi: 10.1038/s41467-021-25923-7)
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