Infrared lines as probes of solar magnetic features. 7: On the nature of the Evershed effect in sunspots

Details Infrared lines as probes of solar magnetic features. 7: On the nature of the Evershed effect in sunspots Infrared lines as probes of solar magnetic features. 7: On the nature of the Evershed effect in sunspots

Mar 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...283..221s&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 283, no. 1, p. 221-231

Astronomy and Astrophysics

Astrophysics

71

Infrared Spectra, Line Spectra, Penumbras, Solar Limb, Solar Magnetic Field, Sunspots, Solar Spectra, Spectrum Analysis, Steady Flow

Scientific paper

Stokes I and V profiles of 1.56 micron lines are observed in sunspots and their surroundings near the solar limb. An analysis of these observations confirms that the magnetic field of the sunspots continues beyond their visible boundaries in the form of an extensive, low-lying (supernumbral) canopy. We also find that the V profiles, which are only formed above the canopy base, exhibit the Evershed effect with line shifts of 0.5-2 km/s, while the non-magnetic material below the canopy is at rest. The deduced geometry of the flow outside the sunspot suggests a resolution of the long standing dispute about the existence or not of an Evershed flow outside the visible sunspot. In addition, the low density of the gas above the canopy base implies that the mass flux in the magnetic canopy is much smaller (approximately equals 10%) than the mass flux in the penumbra, where the 1.5 micron lines exhibit wavelength shifts of approximately 4 km/s. The present observations cast doubt on the standard interpretation of the photospheric Evershed effect in terms of a steady flow, in particular if it is driven by the siphon-flow mechanism.

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