Chromospheric and Coronal Wave Generation in a Magnetic Flux Sheath

TL;DR

This study uses advanced simulations to demonstrate how magnetic pumping in flux concentrations excites slow magneto-acoustic waves, which can heat the chromosphere and drive dynamic fibrils.

Contribution

It reveals a self-consistent mechanism for wave generation in magnetic flux tubes, linking convective downdrafts to chromospheric and coronal wave phenomena.

Findings

Downflows inside flux slabs generate upward propagating waves.

Shock waves form at chromospheric heights, lifting the transition region.

Oscillations with a period of about 4 mHz are observed inside flux tubes.

Abstract

Using radiation magnetohydrodynamic simulations of the solar atmospheric layers from the upper convection zone to the lower corona, we investigate the self-consistent excitation of slow magneto-acoustic body waves (slow modes) in a magnetic flux concentration. We find that the convective downdrafts in the close surroundings of a two-dimensional flux slab "pump" the plasma inside it in the downward direction. This action produces a downflow inside the flux slab, which encompasses ever higher layers, causing an upwardly propagating rarefaction wave. The slow mode, excited by the adiabatic compression of the downflow near the optical surface, travels along the magnetic field in the upward direction at the tube speed. It develops into a shock wave at chromospheric heights, where it dissipates, lifts the transition region, and produces an offspring in the form of a compressive wave that propagates further into the corona. In the wake of downflows and propagating shock waves, the atmosphere inside the flux slab in the chromosphere and higher tends to oscillate with a period of $\nu\approx 4$~mHz. We conclude that this process of "magnetic pumping" is a most plausible mechanism for the direct generation of longitudinal chromospheric and coronal compressive waves within magnetic flux concentrations, and it may provide an important heat source in the chromosphere. It may also be responsible for certain types of dynamic fibrils.