Leakage of photospheric acoustic waves into non-magnetic solar atmosphere
Solar Physics and Space Plasma Research Centre (SPRC), Department of Applied Mathematics, University of Sheffield, The Hicks Building, Hounsfield Road, Sheffield S3 7RH, UK e-mail: [robertus;c.malins]@sheffield.ac.uk
2 Department of Atomic Physics, Eötvös Loránd University, Pázmány Péter sétány 1/A, Budapest 1117, Hungary e-mail: email@example.com
3 Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Org. ADBS, Building 252, Palo Alto, CA 94304n, USA e-mail: firstname.lastname@example.org
Accepted: 3 March 2007
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.
Key words: hydrodynamics / methods: numerical / Sun: chromosphere / Sun: oscillations / Sun: atmosphere / Sun: transition region
© ESO, 2007