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Direct propagation of photospheric acoustic p-modes into non-magnetic solar atmosphere  

Chris Malins   Submitted: 2007-02-27 05:26

One of the dominant types of coherent signals in Doppler velocity in the solar photosphere are p-modes with periods with a power peak of about 300 seconds. The propagation (or leakage) of these p-mode signals into the higher solar atmosphere is one of the key drivers of oscillatory motions in the higher solar chromosphere and corona. This paper examines numerically the direct propagation of acoustic waves driven harmonically at the photosphere, into the non-magnetic solar atmosphere. Erdelyi et al (2007) investigated the acoustic response to a single point source driver. In this follow-up work we generalise this previous study to more structured coherent photospheric drivers mimicking solar global oscillations. Driving with a pair of point drivers separated in space, reflection at the transition region causes cavity oscillations in the lower chromosphere, and amplification and resonance of waves at the transition region generate strong surface oscillations. Driving at the photosphere with a horizontally widely coherent velocity signal it is demonstrated again thst cavity modes are caused in the chromosphere, surface waves at the transition region, and even in the absence of a magnetic field it is shown that fine-structures are generated extending from a dynamic transition region into the lower corona.

Authors: C. Malins, R. Erdelyi
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Publication Status: Accepted
Last Modified: 2007-08-16 10:10
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Leakage of photospheric acoustic waves into non-magnetic solar atmosphere  

Chris Malins   Submitted: 2006-12-12 05:39

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-minute global oscillations into the atmosphere, and aims to complement efforts on the driving of chromospheric dynamics (eg. spicules and waves) by 5-minute oscillations. Method: 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 minute 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.

Authors: Erdelyi, R.; Malins, C.; DePontieu, B.; Toth, G.
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Publication Status: A&A(submitted)
Last Modified: 2007-04-02 11:32
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Direct propagation of photospheric acoustic p-modes into non-magnetic solar atmosphere
Leakage of photospheric acoustic waves into non-magnetic solar atmosphere

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