Plenty of highly dynamic small-scale activities exist in the low solar atmosphere,
and they are of great significance to understand corona and chromosphere heating and
even the origin of large-scale activity. A great many of these small-scale activities are
considered to be heated by magnetic reconnection in the low solar atmosphere, that is
triggered by the magnetic flux emergence (MFE) process. Ellerman bombs (EBs) and
Ultraviolet (UV) bursts are such common brightening phenomena. In this paper, we
combine the studies of magnetic flux emergence process with the small-scale activities
in the lower atmosphere, and discuss the formation process and fine structures of the
small-scale activities triggered by the MFE. The main research method applied in this
work is magneto-hydrodynamic (MHD) simulations. This paper includes two parts. In
the first part, we present the two-dimensional (2D) MHD simulation results about the
MFE process, which verify the two-step emergence process of magnetic flux and are
roughly consistent with the previous theoretical research. In addition, we also explore the
instability of MFE, and find a series of appropriate parameters that cause the magnetic
field lines to rise to chromosphere or higher altitudes, which provide fundamental bases
for the following three-dimensional (3D) MHD simulations. In the second part, we
focus on the study of “The Ellerman bomb and Ultraviolet burst triggered sucessively
by an emerging magnetic flux rope ”. We have studied the emerging process of an initial
un-twisted magnetic flux rope based on 3D MHD simulations. The EB-like and UV
burst-like activities successively appear in the U-shaped part of the undulating magnetic
fields triggered by Parker Instability. The EB-like activity starts to appear earlier and
lasts for about 80 seconds. Six minutes later, a much hotter UV burst-like event starts to
appear and lasts for about 60 seconds. Along the direction vertical to the solar surface,
both the EB and UV burst start in the low chromosphere, but the UV burst extends
to a higher altitude in the up chromosphere. The regions with apparent temperature
increase in the EB and UV burst are both located inside the small twisted flux ropes
generated in magnetic reconnection processes, which are consistent with the previous 2D simulations that most hot regions are usually located inside the magnetic islands.
However, the twisted flux rope corresponding to the EB is only strongly heated after it
floats up to an altitude much higher than the reconnection site during that period. Our
analyses show that the EB is heated by the shocks driven by the strong horizontal flows
at two sides of the U-shaped magnetic fields. The twisted flux rope corresponding to
the UV burst is heated by the driven magnetic reconnection process.
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