98 research outputs found
Global MHD Simulations of the Time-Dependent Corona
We describe, test, and apply a technique to incorporate full-sun, surface
flux evolution into an MHD model of the global solar corona. Requiring only
maps of the evolving surface flux, our method is similar to that of Lionello et
al. (2013), but we introduce two ways to correct the electric field at the
lower boundary to mitigate spurious currents. We verify the accuracy of our
procedures by comparing to a reference simulation, driven with known flows and
electric fields. We then present a thermodynamic MHD calculation lasting one
solar rotation driven by maps from the magnetic flux evolution model of
Schrijver & DeRosa (2003). The dynamic, time-dependent nature of the model
corona is illustrated by examining the evolution of the open flux boundaries
and forward modeled EUV emission, which evolve in response to surface flows and
the emergence and cancellation flux. Although our main goal is to present the
method, we briefly investigate the relevance of this evolution to properties of
the slow solar wind, examining the mapping of dipped field lines to the
topological signatures of the "S-Web" and comparing charge state ratios
computed in the time-dependently driven run to a steady state equivalent.
Interestingly, we find that driving on its own does not significantly improve
the charge states ratios, at least in this modest resolution run that injects
minimal helicity. Still, many aspects of the time-dependently driven model
cannot be captured with traditional steady-state methods, and such a technique
may be particularly relevant for the next generation of solar wind and CME
models
SuNeRF: Validation of a 3D Global Reconstruction of the Solar Corona Using Simulated EUV Images
Extreme Ultraviolet (EUV) light emitted by the Sun impacts satellite
operations and communications and affects the habitability of planets.
Currently, EUV-observing instruments are constrained to viewing the Sun from
its equator (i.e., ecliptic), limiting our ability to forecast EUV emission for
other viewpoints (e.g. solar poles), and to generalize our knowledge of the
Sun-Earth system to other host stars. In this work, we adapt Neural Radiance
Fields (NeRFs) to the physical properties of the Sun and demonstrate that
non-ecliptic viewpoints could be reconstructed from observations limited to the
solar ecliptic. To validate our approach, we train on simulations of solar EUV
emission that provide a ground truth for all viewpoints. Our model accurately
reconstructs the simulated 3D structure of the Sun, achieving a peak
signal-to-noise ratio of 43.3 dB and a mean absolute relative error of 0.3\%
for non-ecliptic viewpoints. Our method provides a consistent 3D reconstruction
of the Sun from a limited number of viewpoints, thus highlighting the potential
to create a virtual instrument for satellite observations of the Sun. Its
extension to real observations will provide the missing link to compare the Sun
to other stars and to improve space-weather forecasting.Comment: Accepted at Machine Learning and the Physical Sciences workshop,
NeurIPS 202
Coronal Hole Detection and Open Magnetic Flux
Many scientists use coronal hole (CH) detections to infer open magnetic flux. Detection techniques differ in the areas that they assign as open, and may obtain different values for the open magnetic flux. We characterize the uncertainties of these methods, by applying six different detection methods to deduce the area and open flux of a near-disk center CH observed on 2010 September 19, and applying a single method to five different EUV filtergrams for this CH. Open flux was calculated using five different magnetic maps. The standard deviation (interpreted as the uncertainty) in the open flux estimate for this CH ≈ 26%. However, including the variability of different magnetic data sources, this uncertainty almost doubles to 45%. We use two of the methods to characterize the area and open flux for all CHs in this time period. We find that the open flux is greatly underestimated compared to values inferred from in situ measurements (by 2.2–4 times). We also test our detection techniques on simulated emission images from a thermodynamic MHD model of the solar corona. We find that the methods overestimate the area and open flux in the simulated CH, but the average error in the flux is only about 7%. The full-Sun detections on the simulated corona underestimate the model open flux, but by factors well below what is needed to account for the missing flux in the observations. Under-detection of open flux in coronal holes likely contributes to the recognized deficit in solar open flux, but is unlikely to resolve it
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