Potential evidence for the onset of alfvénic turbulence in trans-equatorial coronal loops

Doppler-shift oscillations with a broad range of frequencies are found to propagate along the loop with a speed of about 500 km s-1. The power spectrum of perturbations travelling up from both loop footpoints is remarkably symmetric, probably due to the almost perfect north-south alignment of the loop system.

Compared to the power spectrum at the footpoints of the loop, the Fourier power at the apex appears to be higher in the high-frequency part of the spectrum than expected from theoretical models. We suggest this excess high-frequency power could be tentative evidence for the onset of a cascade of the low-to-mid frequency waves into (Alfvénic) turbulence.