The Magnetic Power Spectra of Decaying Active Regions: New Evidence for the Large-Scale Magnetic Flux Bundle Submergence?

Using the magnetic power spectrum approach, we explore the magnetic energy changes at different spatial scales in four moderate-size decaying active regions (ARs). We find the dominant energy variations to take place at large spatial scales while the energy at low scales changes insignificantly. The analysis of the energy transfer function allows us to conclude that the direct turbulent cascade might occur occasionally and does not significantly contribute to the flux budget. Instead, we confirm the turbulent erosion, along with turbulent diffusion, to be the dominant mechanisms of the AR decay. We also reveal a gradual monotonous convergence of two coherent sunspots of opposite magnetic polarities as the decay proceeds. The sunspots exhibit magnetic connection seen as plasma loops in UV images. We suppose that the convergence is a result of an AR-size \(\Omega \)-loop submergence beneath the photosphere.