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Floweffect on resonant absorption of pmodes in sunspots R. Erd'elyi

Summary: Flow­effect on resonant absorption of p­modes in sunspots
R. Erd'elyi
Armagh Observatory, Armagh, College Hill, Armagh, BT61 9DG N.
Abstract. The effect of an equilibrium flow on resonant absorption of
p­mode oscillations in sunspots is studied in compressible viscous MHD.
We show that an equilibrium shear flow can significantly influence the
absorption suffered by the acoustic driving waves.
1. Interaction of p­modes with sunspots
Braun et al. (1987) carried out a series of observations designed to probe the
nature of sunspots by detecting their influence on high­degree p­mode oscilla­
tions in the photosphere. Braun el al. decomposed the p­mode oscillations in
the photospheric surroundings of several sunspots into waves travelling radially
towards and outwards from each spot. By comparing the power difference be­
tween the incoming and outgoing waves they found that sunspots can absorb up
to 50 \Gamma 60% of the acoustic wave energy. The effect is present in p­modes with
wavelength on a large scale (with respect to the radius of the spots). For more
details see e.g. Braun et al. 1987, 1988, 1990, 1992; Braun & Duwall 1990.
The loss of power of p­mode oscillations, as a physical mechanism, might
be modelled by the classical picture of resonant absorption: a periodic external


Source: Armagh Observatory


Collections: Physics