Excitation of vertical kink waves in a solar coronal arcade loop by a periodic driver

Abstract

Aims. We study an oscillatory driver as a possible excitation mechanism of vertical kink loop oscillations in the ideal MHD regime. Methods. We consider a solar coronal magnetic arcade with a dense photospheric layer. The two-dimensional numerical model that we implement includes the effects of nonlinearity and line curvature on the excitation and attenuation of fast magnetosonic kink waves. We investigate the effects of a driven sinusoidal pressure pulse and compare it with the impulsive excitation by a pressure pulse that impacts the overlying loop. Results. Our numerical simulations reveal wave signatures that are reminiscent of vertical loop oscillations seen in TRACE observational data. Conclusions. We conclude that attenuation of vertical kink oscillations can be reduced to the value observed by adopting an oscillatory instead of an impulsive excitation. An oscillatory driver also naturally explains why only a small subset of all loops is excited to oscillate transversally in an active region.

Decaying and decayless transverse oscillations of a coronal loop

“…Ballai et al (2008) have found that kink oscillations generated by a harmonic driver have a dominant period belonging to that of the driver, while for a non-harmonic driver (modelling a shock wave) the generated oscillations are of natural periods only. Similar conclusions were reached in Selwa et al (2010), where the authors pointed out that in the case of an oscillatory driver with a given frequency, only a small subset of loops will start to oscillate, i.e. those whose typical period matches that of the driver.…”

“…Standing kink oscillations can be excited by an impulsive, flare-generated driver (e.g. McLaughlin & Ofman 2008), by a periodic driver associated with a coronal wave (Ballai et al 2008;Selwa et al 2010), or directly from reconnection . Alternative mechanisms, e.g.…”

Excitation of vertical coronal loop oscillations by plasma condensations

“…Aschwanden et al 1999;Verwichte et al 2004), while the source of excitation of the vertical oscillations remains unclear. They are usually explained by placing an external driver below the loop, by the reconnection process or by footpoint motion (Brady & Arber 2005;Gruszecki & Murawski 2008;Selwa et al 2010;White et al 2013). Subsonic siphon flows have also been proposed as a possible excitation mechanism (Ofman et al 2012).…”

Numerical simulations for MHD coronal seismology

“…Hood et al 2005;McLaughlin et al 2011), vertical kink modes (e.g. Gruszecki et al 2006;Wasiljew & Murawski 2009;Selwa et al 2010), oscillations in active regions (e.g. McLaughlin & Ofman 2008;Selwa et al 2011;Pascoe et al 2009;Pascoe & De Moortel 2014), fine structuring (e.g.…”