Resistive flux emergence in undulatory flux tubes |
|
Etienne Pariat Submitted: 2004-06-22 01:19
During its January 2000 flight, the {em Flare Genesis Experiment}
observed the gradual emergence of a bipolar active region, by recording
a series of high resolution photospheric vector magnetograms
and images in the blue wing of the Hα line. Previous analyses
of these data revealed the occurence of many small scale transient
Hα brightenings identified as Ellerman bombs (EBs). They occure
during the flux emergence, and many of them are located near moving
magnetic dipoles in which the vector magnetic field is nearly tangential
to the photosphere.
A linear force-free field extrapolation of one of
the magnetograms was performed to study the
magnetic topology of small-scale EBs and their possible role in the
flux emergence process.
We found that 23 out of 47 EBs are co-spatial with Bald Patches (BPs), while 15
are located at the footpoint of
very flat separatrix field lines passing through a distant BP.
We conclude that EB can be due to magnetic reconnection, not only
at BP locations, but also along their separatrices, occurring in the
low chromosphere.
The topological analysis reveals, for the first time,
that many EBs/BPs are linked by a hierarchy of elongated flux tubes
showing aperiodic spatial undulations, whose wavelengths are typically
above the threshold of the Parker instability.
These findings suggest that arch filament systems and coronal loops do not
result from the smooth emergence of large-scale Omega-loops from below
the photosphere, but rather from the rise of undulatory flux tubes
whose upper parts emerge due to the Parker instability, and whose
dipped lower parts emerge
due to magnetic reconnection. Ellerman bombs
are then the signature of this resistive emergence of undulatory
flux tubes.
Authors: E. Pariat, G. Aulanier, B. Schmieder, M.K. Georgoulis, D.M. Rust and P.N. Bernasconi
Projects: None,TRACE
|
Publication Status: ApJ (in press)
Last Modified: 2004-06-22 01:19
|
 
 
 
 
|
|