Abstract
The radial variation of the Evershed flow in two small sunspots (NOAA 8737 and NOAA 9145) is studied by means of two-dimensional spectrograms of high spatial resolution. We nd a systematic decrease of the flow velocity with photospheric height and a shift of the velocity maximum towards larger penumbral radii in higher layers but no clear correlation between flow velocity and continuum intensity. At the outer penumbral boundaries the Evershed flow ceases abruptly and even downward directed flow velocities in the deepest probed photospheric layers were found. Furthermore, granules adjacent to the penumbral boundary show a systematic redshift of their spot-side parts which is attributed to fast, eventually supersonic, downflows between them and the penumbral boundary.
Highlights
Since its discovery (Evershed 1909) the Evershed effect is a controversial topic in solar physics
We find a systematic decrease of the flow velocity with photospheric height and a shift of the velocity maximum towards larger penumbral radii in higher layers but no clear correlation between flow velocity and continuum intensity
These findings are contradicted by observations of Wiehr & Stellmacher (1989) and Lites et al (1990) who did not find a correlation between continuum intensity and flow velocity
Summary
Since its discovery (Evershed 1909) the Evershed effect is a controversial topic in solar physics. A widely accepted explanation for this result is that the Evershed flow is concentrated in dark almost horizontal flow channels (inclination angle φ = 6◦−11◦, see Shine et al 1995) whereas in the bright filaments the matter is at rest. This theory is supported by observations of the penumbral magnetic field. Recent observations of Schlichenmaier & Schmidt (2000) and Westendorp Plaza et al (2001b) show that the inclination of the Evershed flow channels becomes larger than 90◦ in the outer penumbra which means that the matter turns back below the photosphere in a relatively flat angle. We present new insights into the geometry of the Evershed flow from the analysis of high spatial resolution data
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