Alfvén wave

An Alfvén wave is a magnetohydrodynamic disturbance that travels along magnetic-field lines through a conducting fluid. Magnetic tension supplies the restoring force, while the plasma moves with the field.

Magnetic tension: The restoring force produced when a magnetic field is bent or stretched. Bent field lines pull plasma back toward alignment, restoring the wave disturbance.
Solar wind: The continuous stream of charged particles flowing outward from the Sun’s atmosphere. Alfvénic fluctuations are widespread in the solar wind and help characterize its dynamics.
Hannes Alfvén: Swedish physicist who developed magnetohydrodynamics and predicted the wave now bearing his name. His 1942 analysis identified transverse waves in conducting fluids with magnetic fields.
Parker Solar Probe: A NASA spacecraft launched in 2018 to study the Sun’s outer atmosphere and near-Sun environment. Its measurements found large Alfvénic magnetic and velocity fluctuations close to the Sun.
Alfvén speed: The characteristic speed of transverse magnetic disturbances in a conducting fluid, set by magnetic-field strength and mass density. It gives the propagation speed along the background magnetic field.
Solar corona: The Sun’s outer atmosphere, extending millions of kilometers into space and reaching very high temperatures. Alfvén-wave energy is a proposed contributor to coronal heating and solar-wind acceleration.
Magnetohydrodynamic wave: A wave arising from the coupled dynamics of a conducting fluid and its magnetic field. Alfvén waves are one fundamental mode within this broader family.
Alfvénic switchback: A rapid reversal in the solar-wind magnetic-field direction accompanied by correlated plasma motion. Switchbacks are observed as large-amplitude, nonlinear Alfvénic structures in the solar wind.
Magnetohydrodynamics: A continuum theory describing the coupled behavior of electrically conducting fluids and magnetic fields. Its equations describe Alfvén waves when plasma is treated as a conducting fluid.
Coronal heating problem: The unresolved question of how the Sun’s tenuous corona reaches temperatures far above its surface. Dissipation of Alfvénic energy is one candidate source of the required heat.

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