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Astron. Astrophys. 349, 941-955 (1999)

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Dynamics of solar magnetic elements

M. Sigwarth *  1, K.S. Balasubramaniam 2, M. Knölker 3 and W. Schmidt 1

1 Kiepenheuer-Institut für Sonnenphysik, Schöneckstrasse 6, D-79104 Freiburg i. Br., Germany (sigwarth@sunspot.noao.edu; wolfgang@kis.uni-freiburg.de)
2 National Solar Observatory/Sacramento Peak, National Optical Astronomy Observatories, and Air Force Research Laboratory, Space Hazards Branch, Sunspot, NM 88349-0062, USA (bala@sunspot.noao.edu)
3 High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO 80307-3000, USA (knoe@hao.ucar.edu)

Received 27 April 1999 / Accepted 30 June 1999

Abstract

We present observational results that demonstrate a strong increase in the dynamic behavior of magnetic elements at the solar photosphere, when observed at high spatial and temporal resolution. The HAO/NSO Advanced Stokes Polarimeter was used to obtain an extensive set of high resolution Stokes-V spectra from network, intranetwork and active region magnetic fields at a low noise level. We performed a statistical analysis of Doppler shifts and asymmetries of the V spectra of FeI 630.15 and 630.25 nm to obtain information on the dynamics of magnetic elements of different sizes. The spatial resolution of 0.8-1 arcsec in combination with high polarimetric precision allowed us to investigate Stokes-V spectra of magnetic elements down to a size of [FORMULA] 150 km. The Doppler velocity within magnetic elements as well as the amplitude and area asymmetries of the Stokes-V profiles show a strong dependence on the size of the magnetic elements as well as on the granular velocity in their vicinity. Applying an absolute velocity calibration we find that the smallest magnetic features have velocities of up to 5 km s-1 in both up- and downflows whereas for larger elements or clusters of several flux tubes the velocities become smaller and more uniform. The V-profile asymmetries are larger (both positive and negative) for small fill fraction than for higher fill fraction within the resolution element. Averaged over all individual profiles, there remains a positive amplitude and area asymmetry and a downflow exceeding 0.5 km s-1. The properties of spatially and temporally integrated V profiles are consistent with results from FTS-observations. Our observations are in qualitative agreement with results from numerical MHD simulations.

Key words: Sun: magnetic fields – Sun: photosphere – polarization – magnetic fields – methods: observational – techniques: polarimetric

* Current address: NSO/SP, Sunspot, NM 88349-0062, USA

Send offprint requests to: M. Sigwarth

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© European Southern Observatory (ESO) 1999

Online publication: September 13, 1999
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