Bibcode
Guglielmino, S. L.; Martínez-Pillet, V.; Bonet, J. A.; del Toro Iniesta, J. Carlos; Bellot Rubio, L. R.; Solanki, S. K.; Schmidt, W.; Gandorfer, A.; Barthol, P.; Knölker, M.
Bibliographical reference
The Astrophysical Journal, Volume 745, Issue 2, article id. 160 (2012).
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2
2012
Journal
Citations
40
Refereed citations
34
Description
We report on the photospheric evolution of an intermediate-scale (≈4
Mm footpoint separation) magnetic bipole, from emergence to decay,
observed in the quiet Sun at high spatial (0farcs3) and temporal (33 s)
resolution. The observations were acquired by the Imaging Magnetograph
Experiment imaging magnetograph during the first science flight of the
SUNRISE balloon-borne solar observatory. The bipole flux content is 6
× 1017 Mx, representing a structure bridging the gap
between granular scale bipoles and the smaller ephemeral regions.
Footpoints separate at a speed of 3.5 km s-1 and reach
a maximum distance of 4.5 Mm before the field dissolves. The evolution
of the bipole is revealed to be very dynamic: we found a proper motion
of the bipole axis and detected a change of the azimuth angle of 90°
in 300 s, which may indicate the presence of some writhe in the emerging
structure. The overall morphology and behavior are in agreement with
previous analyses of bipolar structures emerging at the granular scale,
but we also found several similarities with emerging flux structures at
larger scales. The flux growth rate is 2.6 × 1015 Mx
s-1, while the mean decay rate is one order of
magnitude smaller. We describe in some detail the decay phase of the
bipole footpoints that includes break up into smaller structures, and
interaction with preexisting fields leading to cancellation, but it
appears to be dominated by an as-yet unidentified diffusive process that
removes most of the flux with an exponential flux decay curve. The
diffusion constant (8 × 102 km2
s-1) associated with this decay is similar to the
values used to describe the large-scale diffusion in flux transport
models.
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