Spectral line

Quantum mechanics

Shock wave

Magnetic field

Helioseismology

Magnetohydrodynamics

Computational physics

Shock (circulatory)

Nuclear physics

Astrophysics

Atomic physics

Plasma

Classical mechanics

Dissipation

Thermodynamics

Physics

Sunspot

Astronomy

Magnetohydrodynamic drive

Solar atmosphere

Internal medicine

Chromosphere

Medicine

Mechanics

Thermalisation

Nature Physics

Magneto-hydrodynamic (MHD) Alfv\'en waves have been a focus of laboratory plasma physics and astrophysics for over half a century. Their unique nature makes them ideal energy transporters, and while the solar atmosphere provides preferential conditions for their existence, direct detection has proved difficult as a result of their evolving and dynamic observational signatures. The viability of Alfv\'en waves as a heating mechanism relies upon the efficient dissipation and thermalization of the wave energy, with direct evidence remaining elusive until now. Here we provide the first observational evidence of Alfv\'en waves heating chromospheric plasma in a sunspot umbra through the formation of shock fronts. The magnetic field configuration of the shock environment, alongside the tangential velocity signatures, distinguish them from conventional umbral flashes. Observed local temperature enhancements of 5% are consistent with the dissipation of mode-converted Alfv\'en waves driven by upwardly propagating magneto-acoustic oscillations, providing an unprecedented insight into the behaviour of Alfv\'en waves in the solar atmosphere and beyond.

Alfvén wave dissipation in the solar chromosphere