Abstract
Recent observations with the Atmospheric Imaging Assembly (AIA) instrument on the SDO spacecraft have revealed the existence of decayless coronal kink oscillations. These transverse oscillations are not connected to any external phenomena like flares or coronal mass ejections, and show significantly lower amplitudes than the externally excited decaying oscillations. Numerical studies have managed to reproduce such decayless oscillations in the form of footpoint driven standing waves in coronal loops, and to treat them as a possible mechanism for wave heating of the solar corona. Our aim is to investigate the correlation between the observed amplitudes of the oscillations and input the energy flux from different drivers. We perform 3D MHD simulations in single, straight, density-enhanced coronal flux tubes for different drivers, in the presence of gravity. Synthetic images at different spectral lines are constructed with the use of the FoMo code. The development of the Kelvin-Helmholtz instability leads to mixing of plasma between the flux tube and the hot corona. Once the KHI is fully developed, the amplitudes of the decayless oscillations show only a weak correlation with the driver strength. We find that low amplitude decayless kink oscillations may correspond to significant energy fluxes of the order of the radiative losses for the Quiet Sun. A clear correlation between the input energy flux and the observed amplitudes from our synthetic imaging data cannot be established. Stronger drivers lead to higher vales of the line width estimated energy fluxes. Finally, estimations of the energy fluxes by spectroscopic data are affected by the LOS angle, favoring combined analysis of imaging and spectroscopic data for single oscillating loops.
Highlights
Over the past 20 years, observations of the Sun have shown the existence of waves and oscillations throughout the solar corona (Aschwanden, 2006; De Moortel and Nakariakov, 2012)
Once the standing mode is initiated, we have the gradual development of the KH instability and the expansion of the flux tube cross-section (Karampelas et al, 2017)
As expected for loops with turbulent cross-sections (Karampelas et al, 2019), the development of the KH instability and the spatially extended transverse wave induced Kelvin-Helmholtz (TWIKH) rolls lead to extensive mixing of the loop with the surrounding plasma
Summary
Over the past 20 years, observations of the Sun have shown the existence of waves and oscillations throughout the solar corona (Aschwanden, 2006; De Moortel and Nakariakov, 2012). The discovery of transverse magnetohydrodynamic (MHD) standing (Aschwanden et al, 1999; Nakariakov et al, 1999) waves in coronal loops, and propagating waves in open magnetic field structures (Verwichte et al, 2005) has lead to many observational and numerical studies The ubiquity of such waves has Simulated Decayless Oscillations been established in prominence threads (Okamoto et al, 2007), coronal loops (McIntosh et al, 2011), as well as greater areas of the corona (Tomczyk et al, 2007; Tomczyk and McIntosh, 2009; Thurgood et al, 2014; Morton et al, 2016), renewing the interest on the effects of these waves in the solar atmosphere. Recent simulations of coronal loop waves (Pagano and De Moortel, 2017, 2019; Pagano et al, 2018) have not reported sufficient heating to balance the radiative losses
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