Turbulent Suppression of Alfvénic Wave Resonances in Coronal Loops

Abstract Alfvénic wave turbulence is a leading mechanism for explaining the heating of the solar corona and the acceleration of the solar wind. Alfvénic waves are observed to be prevalent throughout the inner corona. An intriguing aspect of the observed waves is that active-region loops show decayless standing Alfvénic oscillations, while quiet-Sun loops show only propagating Alfvénic waves. Given the weaker rates of resonant damping found in the quiet Sun (compared to those estimated from decaying oscillations of active-region loops), the reason for the lack of observed standing oscillations is unclear. We suggest that this may be due to the presence of efficient (or strong) Alfvénic wave turbulence in the quiet Sun, which limits the ability of waves to form resonant oscillations in the coronal cavity. To test this idea, we model the coronal velocity fluctuations using a previously developed 3D reduced magnetohydrodynamic model. In this model, we implement a semi-realistic profile for atmospheric plasma conditions along the magnetic field and a homogeneous plasma perpendicular to the magnetic field. Results are presented for different models of the background atmosphere that effectively have different levels of coronal turbulence. For the Alfvénic waves in the simulation, we see that resonant modes are present when the coronal turbulence is in a weak regime. However, decreasing the nonlinear timescale leads to a faster development of turbulence. This can suppress the presence of standing modes when the nonlinear timescale is comparable to or shorter than the Alfvén travel time.