162 research outputs found
Effects of Coronal Density and Magnetic Field Distributions on a Global Solar EUV Wave
We investigate a global extreme-ultraviolet (EUV) wave associated with a
coronal mass ejection (CME)-driven shock on 2017 September 10. The EUV wave is
transmitted by north- and south-polar coronal holes (CHs), which is observed by
the Solar Dynamics Observatory (SDO) and Solar Terrestrial Relations
Observatory A (STEREO-A) from opposite sides of the Sun. We obtain key findings
on how the EUV wave interacts with multiple coronal structures, and on its
connection with the CME-driven shock: (1) the transmitted EUV wave is still
connected with the shock that is incurvated to the Sun, after the shock has
reached the opposite side of the eruption; (2) the south CH transmitted EUV
wave is accelerated inside an on-disk, low-density region with closed magnetic
fields, which implies that an EUV wave can be accelerated in both open and
closed magnetic field regions; (3) part of the primary EUV wavefront turns
around a bright point (BP) with a bipolar magnetic structure when it approaches
a dim, low-density filament channel near the BP; (4) the primary EUV wave is
diffused and apparently halted near the boundaries of remote active regions
(ARs) that are far from the eruption, and no obvious AR related secondary waves
are detected; (5) the EUV wave extends to an unprecedented scale of ~360{\deg}
in latitudes, which is attributed to the polar CH transmission. These results
provide insights into the effects of coronal density and magnetic field
distributions on the evolution of an EUV wave, and into the connection between
the EUV wave and the associated CME-driven shock.Comment: 16 pages, 8 figures, and 3 animations available at
http://doi.org/10.13140/RG.2.2.12408.29442 ,
http://doi.org/10.13140/RG.2.2.25830.06723 , and
http://doi.org/10.13140/RG.2.2.19119.18088 ; published in Ap
An adaptive finite element method for distributed elliptic optimal control problems with variable energy regularization
We analyze the finite element discretization of distributed elliptic optimal
control problems with variable energy regularization, where the usual
norm regularization term with a constant regularization parameter
is replaced by a suitable representation of the energy norm in
involving a variable, mesh-dependent regularization parameter
. It turns out that the error between the computed finite element
state and the desired state (target) is
optimal in the norm provided that behaves like the
local mesh size squared. This is especially important when adaptive meshes are
used in order to approximate discontinuous target functions. The adaptive
scheme can be driven by the computable and localizable error norm between the finite element
state and the target . The numerical
results not only illustrate our theoretical findings, but also show that the
iterative solvers for the discretized reduced optimality system are very
efficient and robust
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