Coupling the solar surface and the corona: coronal rotation, Alfv\'en wave-driven polar plumes

TL;DR

This study introduces a simple parametrized model for chromospheric reflectivity to better understand how surface rotation influences the solar corona and polar plume formation driven by Alfvén waves.

Contribution

It presents a novel approximation for chromospheric reflectivity in simulations, elucidating its role in angular momentum transfer and polar plume dynamics.

Findings

High chromospheric reflectivity is essential for accurate angular momentum transfer.

Polar plumes remain stable over a range of reflectivity values.

Total reflection leads to bursty and disruptive polar plumes.

Abstract

The dynamical response of the solar corona to surface and sub-surface perturbations depends on the chromospheric stratification, and specifically on how efficiently these layers reflect or transmit incoming Alfv\'en waves. While it would be desirable to include the chromospheric layers in the numerical simulations used to study such phenomena, that is most often not feasible. We defined and tested a simple approximation allowing the study of coronal phenomena while taking into account a parametrised chromospheric reflectivity. We addressed the problems of the transmission of the surface rotation to the corona and that of the generation of polar plumes by Alfv\'en waves (Pinto et al., 2010, 2011). We found that a high (yet partial) effective chromospheric reflectivity is required to properly describe the angular momentum balance in the corona and the way the surface differential rotation is transmitted upwards. Alfv\'en wave-driven polar plumes maintain their properties for a wide range of values for the reflectivity, but they become bursty (and eventually disrupt) when the limit of total reflection is attained.