Leakage of photospheric acoustic waves into non-magnetic solar atmosphere

Abstract

Aims. This paper aims to look at the propagation of synthetic photospheric oscillations from a point source into a two-dimensional non-magnetic solar atmosphere. It takes a particular interest in the leakage of 5-min global oscillations into the atmosphere, and aims to complement efforts on the driving of chromospheric dynamics (e.g. spicules and waves) by 5-min oscillations. Methods. A model solar atmosphere is constructed based on realistic temperature and gravitational stratification. The response of this atmosphere to a wide range of adiabatic periodic velocity drivers is numerically investigated in the hydrodynamic approximation. Results. The findings of this modelling are threefold. Firstly, high-frequency waves are shown to propagate from the lower atmosphere across the transition region experiencing relatively low reflection and transmitting energy into the corona. Secondly, it is demonstrated that driving the upper solar photosphere with a harmonic piston driver at around the 5 min period may generate three separate standing modes with similar periods in the chromosphere and transition region. In the cavity formed by the chromosphere and bounded by regions of low cut-off period at the photospheric temperature minimum and the transition region this is caused by reflection, while at either end of this region in the lower chromosphere and transition region the standing modes are caused by resonant excitation. Finally, the transition region becomes a guide for horizontally propagating surface waves for a wide range of driver periods, and in particular at those periods which support chromospheric standing waves. Crucially, these findings are the results of a combination of a chromospheric cavity and resonant excitation in the lower atmosphere and transition region.

Numerical simulations of magnetoacoustic oscillations in a gravitationally stratified solar corona

“…The coincidence of the observed periods of coronal and photospheric oscillations logically leads to the idea that the photospheric oscillations leak into the corona along inclined magnetic fields (De Pontieu et al 2005;Erdélyi et al 2007;Fedun et al 2009). However, Murawski and Zaqarashvili (2010) and Zaqarashvili et al (2011) suggested that the observed periodicity in the solar corona is caused by quasi-periodic rebound shocks, originating from nonlinear wakes in the stratified atmosphere.…”

Phase relations for seismology of photospheric flux tubes

“…We also want to point out that this model omits important physics, e.g. density stratification (Osterbrock 1961;Rosenthal et al 2002;Erdélyi et al 2007), but the idea is to use a very simple model to illustrate the possibility of photospheric seismology.…”

Acoustic oscillations in the field-free, gravitationally stratified cavities under solar bipolar magnetic canopies

“…We showed that the field-free cavity regions under the magnetic canopy can trap high-frequency acoustic oscillations, leading to the observed increased high-frequency power in the photosphere, while the lower-frequency oscillations are channeled upwards in the form of magneto-acoustic waves (Erdélyi et al 2007;Srivastava et al 2008). However, those calculations have been performed without taking the gravitational stratification into account, which is important at the photospheric level.…”