Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...290..972r&link_type=abstract
Astronomy and Astrophysics 290, 972-982 (1994)
Astronomy and Astrophysics
Astrophysics
69
Sun: Sunspots, Activity, Magnetic Fields, Photosphere
Scientific paper
We present the results of high resolution observations of the Evershed effect, with emphasis on the variation of the Evershed velocities in time. Using a tunable narrow band filter we recorded time sequences of the two dimensional penumbral velocity field. The Evershed velocities are clearly non-stationary. Velocity packets are observed propagating radially outward towards the penumbral boundary and into the adjacent quiet photosphere. The propagation speed ranges from 2 to 5.5km/s, with an average of 3.2+/-1.1km/s. This pattern repeats in a quasi periodic way on a time scale of order 15 min. Subsequent velocity packets are separated in space by =~2000-3000km in the radial direction. At a photospheric height of =~160km we measure an average maximum Doppler velocity of 4.7+/-0.6km/s. The Doppler velocity seems to have less variance than propagation speed of the moving velocity features. Both wave phenomena and transient siphon flows are discussed as possible explanations for the observed time dependence of the Evershed effect. On a time scale of 1h we find no observational evidence for the proposed interchange convection process.
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