42 research outputs found
A Comprehensive Method of Estimating Electric Fields from Vector Magnetic Field and Doppler Measurements
Photospheric electric fields, estimated from sequences of vector magnetic
field and Doppler measurements, can be used to estimate the flux of magnetic
energy (the Poynting flux) into the corona and as time-dependent boundary
conditions for dynamic models of the coronal magnetic field. We have modified
and extended an existing method to estimate photospheric electric fields that
combines a poloidal-toroidal (PTD) decomposition of the evolving magnetic field
vector with Doppler and horizontal plasma velocities. Our current, more
comprehensive method, which we dub the "{\bf P}TD-{\bf D}oppler-{\bf F}LCT {\bf
I}deal" (PDFI) technique, can now incorporate Doppler velocities from
non-normal viewing angles. It uses the \texttt{FISHPACK} software package to
solve several two-dimensional Poisson equations, a faster and more robust
approach than our previous implementations. Here, we describe systematic,
quantitative tests of the accuracy and robustness of the PDFI technique using
synthetic data from anelastic MHD (\texttt{ANMHD}) simulations, which have been
used in similar tests in the past. We find that the PDFI method has less than
error in the total Poynting flux and a error in the helicity flux
rate at a normal viewing angle ) and less than and
errors respectively at large viewing angles (). We compare our
results with other inversion methods at zero viewing angle, and find that our
method's estimates of the fluxes of magnetic energy and helicity are comparable
to or more accurate than other methods. We also discuss the limitations of the
PDFI method and its uncertainties.Comment: 56 pages, 10 figures, ApJ (in press
Photospheric Electric Fields and Energy Fluxes in the Eruptive Active Region NOAA 11158
How much electromagnetic energy crosses the photosphere in evolving solar
active regions? With the advent of high-cadence vector magnetic field
observations, addressing this fundamental question has become tractable. In
this paper, we apply the "PTD-Doppler-FLCT-Ideal" (PDFI) electric field
inversion technique of Kazachenko et al. (2014) to a 6-day HMI/SDO vector
magnetogram and Doppler velocity sequence, to find the electric field and
Poynting flux evolution in active region NOAA 11158, which produced an X2.2
flare early on 2011 February 15. We find photospheric electric fields ranging
up to V/cm. The Poynting fluxes range from to
ergscms, mostly positive, with the largest contribution to
the energy budget in the range of -
ergscms. Integrating the instantaneous energy flux over
space and time, we find that the total magnetic energy accumulated above the
photosphere from the initial emergence to the moment before the X2.2 flare to
be ergs, which is partitioned as and
ergs, respectively, between free and potential energies.
Those estimates are consistent with estimates from preflare non-linear
force-free field (NLFFF) extrapolations and the Minimum Current Corona
estimates (MCC), in spite of our very different approach. This study of
photospheric electric fields demonstrates the potential of the PDFI approach
for estimating Poynting fluxes and opens the door to more quantitative studies
of the solar photosphere and more realistic data-driven simulations of coronal
magnetic field evolution.Comment: 51 pages, 10 figures, accepted by ApJ on August 11, 201
Solar Atmospheric Heating Due to Small-scale Events in an Emerging Flux Region
We investigate the thermal, kinematic and magnetic structure of small-scale
heating events in an emerging flux region (EFR). We use high-resolution
multi-line observations (including Ca II 8542~\AA, Ca II K, and Fe I 6301~\AA
line pair) of an EFR located close to the disk center from the CRISP and
CHROMIS instruments at the Swedish 1-m Solar Telescope. We perform non-LTE
inversions of multiple spectral lines to infer the temperature, velocity, and
magnetic field structure of the heating events. Additionally, we use the
data-driven Coronal Global Evolutionary Model to simulate the evolution of the
3D magnetic field configuration above the events and understand their dynamics.
Furthermore, we analyze the differential emission measure to gain insights into
the heating of the coronal plasma in the EFR. Our analysis reveals the presence
of numerous small-scale heating events in the EFR, primarily located at
polarity inversion lines of bipolar structures. These events not only heat the
lower atmosphere but also significantly heat the corona. The data-driven
simulations, along with the observed enhancement of currents and Poynting flux,
suggest that magnetic reconnection in the lower atmosphere is likely
responsible for the observed heating at these sites.Comment: 20 pages, 15 figures, accepted for publication in the Ap
Modeling a Coronal Mass Ejection from an Extended Filament Channel. I. Eruption and Early Evolution
We present observations and modeling of the magnetic field configuration, morphology, and dynamics of a large-scale, high-latitude filament eruption observed by the Solar Dynamics Observatory. We analyze the 2015 July 9-10 filament eruption and the evolution of the resulting coronal mass ejection (CME) through the solar corona. The slow streamer-blowout CME leaves behind an elongated post-eruption arcade above the extended polarity inversion line that is only poorly visible in extreme ultraviolet (EUV) disk observations and does not resemble a typical bright flare-loop system. Magnetohydrodynamic (MHD) simulation results from our data-inspired modeling of this eruption compare favorably with the EUV and white-light coronagraph observations. We estimate the reconnection flux from the simulation's flare-arcade growth and examine the magnetic-field orientation and evolution of the erupting prominence, highlighting the transition from an erupting sheared-arcade filament channel into a streamer-blowout flux-rope CME. Our results represent the first numerical modeling of a global-scale filament eruption where multiple ambiguous and complex observational signatures in EUV and white light can be fully understood and explained with the MHD simulation. In this context, our findings also suggest that the so-called stealth CME classification, as a driver of unexpected or "problem" geomagnetic storms, belongs more to a continuum of observable/nonobservable signatures than to separate or distinct eruption processes.Peer reviewe
Quantifying Properties of Photospheric Magnetic Cancellations in the Quiet Sun Internetwork
We analyzed spectropolarimetric data from the Swedish 1-meter Solar Telescope
to investigate physical properties of small-scale magnetic cancellations in the
quiet Sun photosphere. Specifically, we looked at the full Stokes polarization
profiles along the Fe I 557.6 nm and of the Fe I 630.1 nm lines measured by
CRisp Imaging SpectroPolarimeter (CRISP) to study temporal evolution of the
line-of-sight (LOS) magnetic field during 42.5 minutes of quiet Sun evolution.
From this magnetogram sequence, we visually identified 38 cancellation events.
We then used Yet Another Feature Tracking Algorithm (YAFTA) to characterize
physical properties of these magnetic cancellations. We found on average
Mx of magnetic flux cancelled in each event with an average
cancellation rate of Mx s. The derived cancelled flux
is associated with strong downflows, with an average speed of
km s. Our results show that the average
lifetime of each event is minutes with an average of initial
magnetic flux being cancelled. Our estimates of magnetic fluxes provide a lower
limit since studied magnetic cancellation events have magnetic field values
that are very close to the instrument noise level. We observed no horizontal
magnetic fields at the cancellation sites and therefore can not conclude
whether the events are associated structures that could cause magnetic
reconnection.Comment: 19 pages, 18 figures, 2 tables, accepted into ApJ on 06/08/202