Volume 397, Number 2, January II 2003
|Page(s)||757 - 764|
|Published online||17 December 2002|
On the time variability of the Evershed effect
The Institute for Solar Physics of the Royal Swedish Academy of Sciences, AlbaNova University Center, 10691 Stockholm, Sweden
Corresponding author: firstname.lastname@example.org
Accepted: 14 October 2002
The time variability of the Evershed effect in the penumbra of a sunspot is studied from a time series of high-spatial resolution spectrograms covering the wings of the K line accompanied by K slit-jaw images obtained with the Swedish Vacuum Solar Telescope. Simultaneous G-band observations from the Dutch Open Telescope are used to study the penumbral scene around the spectrograph slit on the photospheric level. Four spectral lines are selected to probe the Evershed effect at different heights in the penumbral atmosphere. The Evershed flow is found to show variations on a time scale of 8–14 min which is a confirmation of earlier observations from tunable filter instruments. The largest amplitudes in the variation are found where the Evershed flow is strongest. No systematic height dependence is found for the propagation of the velocity variations. On several occasions, an increase in the Evershed signal is associated with an intensity increase. In the weak Evershed signal detected in bright filaments, no significant variability is found. As an alternative to the interpretation of temporal enhancements in the flow speed, it is speculated that temporal height variations of a flow channel hosting a steady Evershed flow can explain the observed variations in the Evershed effect.
Key words: sunspots / Sun: photosphere
© ESO, 2003
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.