Surface waves as the origin of the Evershed phenomenon

Details Surface waves as the origin of the Evershed phenomenon Surface waves as the origin of the Evershed phenomenon

Jul 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...274..478b&link_type=abstract

Astronomy and Astrophysics, Vol. 274, p. 478 (1993)

Astronomy and Astrophysics

Astrophysics

16

Sun: Magnetic Fields, Sunspots, Line: Profiles, Mhd

Scientific paper

We investigate the spectral signature of magnetoacoustic-gravity surface waves (MAGS-waves), which we expect to exist at the interface between the lower boundary of the magnetic field of the sunspot penumbra and the non-magnetic gas below. MAGS-waves have a number of properties that make them attractive candidates for explaining the photo spheric Evershed effect: 1. Since they transport only energy but no mass, they resolve the problem of mass conservation at the outer penumbral boundary. 2. Since they are restricted to magnetic interfaces, they are only (or dominantly) present in the penumbra and absent in the umbra. 3. The phase relation between the temperature, the horizontal, and vertical velocity perturbations leads to line shifts and asymmetries in observations at the limb, but none at disc centre. 4. The amplitude of the velocity perturbation drops approximately exponentially with height, in good agreement with observations. 5. Waves travelling in opposite directions with respect to the observer produce oppositely directed line shifts and asymmetries, making it straightforward to explain the opposite shifts and asymmetries observed in the limb-side and centre-side penumbra.

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