Session 4 - Data-driven modeling of solar atmosphere and solar explosive events

Conveners: Meng Jin (LMSAL), Véronique Delouille (ROB)
Wednesday 31/10, 09:00 - 11:30

We have witnessed rapid increase in solar data especially in the SDO era, which is not only utilized for extensive model validation, but also dramatically facilitates the development of data-driven models across multiple scales and different domains. This session welcomes presentations of all kinds of data-driven modeling efforts to understand the dynamics of the solar atmosphere from convection zone into the heliosphere and the ideas/discussions of the current challenges of data-driven models. In particular, we encourage modeling results which are directly relevant to the forthcoming solar and heliosphere missions (e.g., Parker Solar Probe and Solar Orbiter).

Plenary speaker: Maria Kazachenko (SSL/Berkeley)

Talks

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Wednesday October 31, 09:00 - 10:30

09:00	Data-driven Models of the Solar Corona Magnetic Fields: Review	Kazachenko, M	Invited Oral
	Maria Kazachenko
	UC Berkeley, CU Boulder, National Solar Observatory
	The advent of high-cadence, large-scale photospheric vector magnetic field and Doppler velocity measurements from the Solar Dynamics Observatory and progress in the computational techniques facilitated development of the time-dependent data-driven models of the coronal magnetic fields. In this talk I will first review current state and challenges of these models. I will then describe recent progress of the Coronal Global Evolutionary Model (CGEM), a collaborative effort between UC Berkeley, Lockheed Martin and Stanford University that computes electric fields in the photosphere to drive a 3D non-potential model of the solar corona magnetic fields.
09:30	Ellerman bombs and UV bursts: reconnection at different atmospheric layers?	Hansteen, V	Oral
	Viggo Hansteen
	Rosseland Centre for Solar Physics, University of Oslo
	The emergence of magnetic flux through the photosphere and into the outer solar atmosphere produces, amongst many other phenomena, the appearance of Ellerman bombs (EBs) in the photosphere. EBs are observed in the wings of H(alpha) and are highly likely to be due to reconnection in the photosphere, below the chromospheric canopy. But signs of the reconnection process are also observed in several other spectral lines, typical of the chromosphere or transition region. An example are the UV bursts observed in the transition region lines of Si IV. In this work we analyze high cadence coordinated observations between the 1-m Swedish Solar Telescope and the IRIS spacecraft in order to study the possible relationship between reconnection events at different layers in the atmosphere, and in particular, the timing history between them. High cadence, high resolution H-alpha images from the SST provide us with the positions, timings and trajectories of Ellerman bombs in an emerging flux region. Simultaneous co-aligned IRIS slit-jaw images at 1400 and 1330 A and detailed Si IV spectra from the fast spectrograph raster allow us to study the possible transition region counterparts of those photospheric Ellerman bombs. We complement these observations with numerical models of Ellerman bombs and UV bursts. Our main goal is to study whether there is a temporal and spatial relationship between the appearance of an EB and the appearance of a UV burst.
09:45	The role of small-scale photospheric motions in coronal magnetic energy buildup and explosive release	Dahlin, J	Oral
	Joel Dahlin [1][2],Spiro Antiochos [1],C. Richard DeVore [1]
	[1]NASA GSFC [2]UCAR
	CMEs/eruptive flares are spectacular examples of explosive solar activity resulting from magnetic self-organization in the corona. Recent theory and modeling studies have demonstrated a mechanism by which small-scale stochastic flows (e.g., photospheric convection) trigger an inverse cascade that concentrates coronal magnetic structure at polarity inversion lines to form highly sheared filament channels. We report on new 3D MHD simulations of an eruptive flare driven by this process of ‘helicity condensation’. Energy buildup occurs in the form of a sheared arcade that explosively erupts via magnetic breakout. Interestingly, the magnetic shear above the PIL undergoes a three-phase evolution: an initial increase in response to the driving followed by a decrease as the magnetic structure expands outward, concluding with a sharp increase upon the onset of flare reconnection and fast downflows. We discuss implications of our results for SDO observations of CMEs/eruptive flares. Our simulations are especially relevant to the many SDO observations of eruptions from circular filament channels. We also discuss future opportunities for data-driven modeling of the magnetic energy build up leading to explosive solar activity, and for possible application to space weather prediction. This work was supported by the NASA LWS, H-SR and ISFM programs.
10:00	Energy transport and heating by torsional Alfven waves in the quiet-Sun atmosphere	Soler, R	Oral
	Roberto Soler[1], Jaume Terradas[1], Ramon Oliver[1], Jose Luis Ballester[1]
	[1]University of the Balearic Islands
	High-resolution observations with instruments on board SDO have revealed the ubiquitous presence of Alfv\'en waves in the solar atmosphere. These waves are believed to play an important role in the transfer of energy from the photosphere to the overlying corona and solar wind, and in the heating of the partially ionized chromosphere. Here we perform numerical computations to investigate the energy transport and dissipation associated to torsional Alfv\'en waves propagating in magnetic flux tubes that expand from the photosphere to the corona in quiet-Sun conditions. We place a broadband driver at the photosphere that contains a spectrum of frequencies ranging from 0.1 mHz to 300 mHz and injects a wave energy flux of $10^7$~erg~cm$^{-2}$~s$^{-1}$. We consider Ohm's magnetic diffusion and ion-neutral collisions as dissipation mechanisms in the chromosphere. We find that only a small fraction of the driven flux, $\sim 10^5$~erg~cm$^{-2}$~s$^{-1}$, is able to reach coronal heights, but it may be sufficient to partly compensate the total coronal energy loss. The reason for the small energy transmittance is the combined effect of reflection and dissipation. Low wave frequencies are reflected at the transition region, while high wave frequencies are dissipated producing an efficient enough heating to balance chromospheric radiative losses.
10:15	Simulation of dynamics of hot plasma in postflare loops	Shestov, S	Oral
	Sergei Shestov[1,2], Andrei Zhukov[1,3], Tom Van Doorsselaere[4]
	[1]Solar-Terrestrial Centre of Excellence - SIDC, Royal Observatory of Belgium, Brussels, Belgium; [2]Lebedev Physical Institute, Moscow, Russia; [3] Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, Russia; [4] Centre for Mathematical Plasma Astrophysics (CmPA), KU Leuven, Leuven, Belgium
	We investigate dynamics of hot plasma in postflare coronal loops using state of the art MHD modeling and calculating synthetic images/fluxes in various SDO channels and other spectral bands – GOES and Mg XII 8.42 A spectral line. Our aim is to investigate dynamics of evaporation and condensation/draining of hot plasma in postflare loops. We use 2D and 3D MHD simulations, start with loop-like initial magnetic field and realistic plasma parameters. For the solving of MHD equations we use MPI-AMRVAC code with gravity, thermal conduction and radiative loses. We apply arbitrary heating in the chromosphere which mimic chromospheric heating by the energetic electrons from the reconnection region. The plasma starts to evaporate and soon fills the overlying magnetic loop system. The particular observed characteristics –, temperature, density, flow, and their dynamics strongly depend on applied physical condition. In particular, strength of magnetic field plays important role, as well as heating rate and the size of the heated region. To constrain the possible range of parameters we calculate synthetic images/fluxes in various EUV and X-ray channels with the use of FoMo code. We compare calculated images with observational data (we chose one large-scale and one small-scale loop associated with ~B-class flares) and identify the most probable physical conditions, in which synthetic data match observations. We were able to find heating regimes to match the observations; beside we see several interesting features that can be revealed only in 2D or 3D modeling.

Wednesday October 31, 11:00 - 11:30

11:00	Variation of Doppler velocity with non-thermal line width in a gravitationally stratified plasma	Pant, V	Oral
	Vaibhav Pant[1], Norbert Magyar[1], Tom Van Doorsselaere[1], Richard Morton[2]
	[1]Centre for mathematical Plasma Astrophysics (CmPA), KU Leuven, [2]Northumbria University
	Magnetohydrodynamic (MHD) waves are ubiquitous in the solar atmosphere. These waves play an important role in the heating of solar corona. Recently, an apparent discrepancy is observed in the Alfvénic wave amplitudes measured by the Coronal Multi-channel Polarimeter (CoMP) compared to those measured by the Hinode and the Solar Dynamics Observatory (SDO). This discrepancy was attributed to a large line-of-sight superposition and low spatial resolution of the CoMP, which may lead to low wave amplitudes and large non-thermal line widths. A wedge-shape correlation is also observed between root mean square Doppler velocity and mean non-thermal line width. We investigate this scenario by performing a 3D MHD simulation of a gravitationally stratified transversely inhomogenous plasma subjected to the unidirectionally propagating MHD waves. Here, we present the results of this simulation forward modelled with the FoMo for Fe XIII (10747~\AA) emission line to study the variation of Doppler velocities with non-thermal line widths. We perform the random integration over different line-of-sights angles across and along the simulation box. We degrade the spatial resolution of the simulation box to the spatial resolution of the CoMP and compare Doppler velocities and non-thermal line widths at different heights. We compare our results with previous studies as well as with observations made by the CoMP and find a fairly good match between them.
11:15	Understanding Heating Properties of Active Region Loops through Forward Modeling and Machine Learning	Barnes, W	Oral
	Will Barnes[1], Stephen Bradshaw[1], Nicki Viall[2], Stuart Mumford[3]
	[1]Rice University, [2]NASA Goddard Space Flight Center, [3]University of Sheffield
	Understanding how loops in active regions are heated is a critical step in solving the coronal heating problem. In particular, constraining the frequency at which individual strands are reenergized can shed light on what mechanism releases energy from the highly-stressed magnetic field into the coronal plasma (Klimchuk, 2015). To address this problem, we forward model time-dependent AIA intensity maps for active region NOAA 1158 using a combination of loop hydrodynamics (Bradshaw & Cargill, 2013), potential field extraplations derived from HMI magnetograms, and detailed atomic physics. We model the AIA intensity for a range of heating frequencies and constrain the total energy input based on both observed active region flux and the magnetic field strengths derived from the field extrapolation. We then apply the timelag method of Viall & Klimchuk (2012) to compute cross-correlations for all possible channel pairs for every pixel in our synthesized active region. For a given channel pair, the delay which maximizes the cross-correlation provides a proxy for the cooling time between the two channels in a given pixel. We apply this same technique to twelve hours of AIA observations of NOAA 1158. To make meaningful comparisons between our synthetic and observed data, we train a random forest classifier on the synthesized timelags and apply it to our observed timelags in order to classify the heating frequency in each pixel of the active region. This approach allows us to easily and efficiently incorporate every channel pair in deciding which heating model is most consistent with our observed timelags in the context of our model. We also compute emission measure distributions from our modeled and observed intensities using the method of Hannah & Kontar (2012), as any successful heating model should be able to reproduce multiple observational signatures. Furthermore, we apply this analysis to several more active regions from the catalog compiled by Warren et al. (2012). In order to efficiently analyze this large time-dependent, multi-wavelength data, we use the Dask Python library (Dask Development Team, 2016) for out-of-core data processing in order to take advantage of multiple computing cores when preparing and analyzing the data. Such an approach provides a pipeline for processing a many hours of full-disk, level 1 images into a series of timelag maps in a matter of a few hours. This novel combination of distributed and parallel data processing, detailed forward modeling, and machine learning allows us to survey active region heating properties at an unprecedented scale.

Posters

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e-Posters

Observations and Modeling of a High-Latitude, Extended Filament Channel Eruption	Lynch, B
B. J. Lynch[1], E. Palmerio[2], M. D. Kazachenko[1,3], J. Pomoell[2], E. K. J. Kilpua[2]
[1] Space Science Laboratory, Univ. of California-Berkeley, Berkeley, CA, USA, [2] Department of Physics, Univ. of Helsinki, Helsinki, Finland, [3] Laboratory Atmospheric Space Physics, Univ. of Colorado, Boulder, CO, USA
We present observations and modeling of the magnetic field configuration, morphology, and dynamics of a high-latitude, extended filament channel eruption observed by SDO. We analyze the 2015 July 10 filament eruption by quantifying a number of physical properties of the CME source region and the CME's evolution through the corona. The resulting slow streamer blowout CME gives rise to the formation of an extended post-eruption arcade above the polarity inversion line that is only poorly visible in disk observations and does not resemble the typical bright post-eruption loop systems. We estimate the reconnection flux from this "stealthy" flare arcade growth and examine the magnetic field orientation and evolution of the erupting prominence. We present preliminary results from our data-inspired numerical MHD modeling of this event and their comparison to the SDO/AIA observations, focusing on the transition from an erupting sheared-arcade prominence to a slow streamer blowout flux rope CME. The ambiguous on-disk signatures in certain wavelengths suggest that the "stealth CME" phenomenon (and classification) may be more of a continuum of observable or non-observable signatures rather than a distinct type of eruption. As such, these CME events may also be problematic for space weather forecasting.
Eruptions from quiet Sun coronal bright points: Observations & Modeling	Madjarska-theissen, M
Maria S. Madjarska[1], Klaus Galsgaard[2], Chauzhou Mou[3]
[1]Max Planck Institute for Solar System Research, Goettingen, Germany, [2] Niels Bohr Institute, Copenhagen, Denmark, [3]Institute of Space Sciences, Shandong University, Weihai, China
We present a two part study that aims first to observationally explore in full detail the morphological and dynamical evolution of eruptions from coronal bright points (CBPs) in the context of the full lifetime evolution of 11 CBPs. Next, we employ data-driven modelling based on a relaxation code to reproduce the time evolution of the magnetic field of these eruptive CBPs, and provide an insight on the possible causes for destabilisation and eruption. Observations of the full lifetime of CBPs in data taken with the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory in four passbands He II 304 Å, Fe IX/X 171 Å, Fe XII 193 Å, and Fe XVIII 94 Å are investigated for the occurrence of plasma ejections, micro-flaring, mini-filament eruptions and mini coronal mass ejections (mini-CMEs). Data from the Helioseismic and Magnetic Imager are analysed to study the longitudinal photospheric magnetic field evolution associated with the CBPs and related eruptions. The magnetic structure of each CBP is then evolved in time using the relaxation approach, based on a time series of HMI magnetograms. This results in a series of Non-Linear Force Free Field Extrapolations (NLFFF). The time series is initiated with a potential field extrapolation based on a HMI magnetogram well before the eruptions, and evolved in time as a response to the changes in the magnetic field distribution in the photosphere. This time series of NLFFF field solutions is analysed for the local and global magnetic field structure in the vicinity of the eruption sites.
Research on Solar Drivers of Space-weather: Sun-Earth connection of magnetic flux ropes	Vemareddy, P
P. Vemareddy [1], P. Demoulin[2]
[1] Indian Indian Institute of Astrophysics, Bengaluru, India [2] Observatory de Paris, Meudon, LESIA, Paris
I present few representative results of the research on solar drivers of space weather carried out in the past two years. The objectives include how local plasma evolution leads to formation of magnetic flux ropes (MFRs), its eruption and heliospheric evolution. To show this scenario of Sun-earth connection of an MFR, we undertook an eruption event involving clear flux rope signatures on the Sun, and studied its formation, initiation, driving mechanisms. Further, we extended our earlier studies on helicity flux transport in emerging ARs, sun-earth connections of MFR, and sunspot rotation as a driver of major solar eruptions. In an emerging AR, the helicity being pumped by flux emergence and plasma motions revealed that the flux tube is likely having opposite signs of helicity along its length. These results suggest that the ARs with a predominant sign of helicity flux launch CMEs at some point of time, however, the AR with successive injection of opposite helicity exhibits cancellation of coronal helicity leading to field reconfiguration and dissipation of energy heating the corona. The sun-earth connection of a CME is probed by in-situ observations, which delineates the source region magnetic signatures in the magnetic cloud. On the other hand, a rotating sunspot in AR 12158 is proved to have built flux rope like sigmoidal structure by injecting twist, which is apparently co-temporal with the occurrence of two major CMEs.

p-Posters

Soft X-ray (0.1 – 2.5 nm) Spectral Emission Lines Associated with AR 12713 Observed with Rocket EVE/SAM Instrument on June 18, 2018	Didkovsky, L
Leonid Didkovsky[1], Tom Woods[2], Phil Chamberlin[2], Andrew Jones[2]
[1]University of Southern California, Space Sciences Center (USA), [2]University of Colorado in Boulder, Laboratory for Atmospheric and Space Physics (USA)
Some observations of soft X-ray emission spectral lines associated with AR 12713 are reported in a wavelength range of about 0.1 to 2.5 nm. The spectra were received from a modified EVE/SAM instrument during sounding rocket flight (NASA 36.336 US) launched on June 18, 2018 from the White Sands Missile Range, NM. The modification of the SAM instrument consisted in assembling on it a diffraction transmission grating, which creates a number of spectra from a bright solar disk object like an AR. Such spectra with a good spatial resolution (AR only) and sufficient spectral resolution may help us to model solar reference spectra for more accurate calculations of absolute solar irradiance in soft X-ray.
Global Magnetohydrodynamics Simulation of EUV Waves and Shocks from the X8.2 Eruptive Flare on 2017 September 10	Jin, M
Meng Jin[1,2], Wei Liu[1], Mark Cheung[1], Nariaki Nitta[1], Ward Manchester[3], Leon Ofman[4], Cooper Downs[5], Vahe Petrosian[6], Nicola Omodei[6]
[1]LMSAL, [2]SETI Institute, [3]University of Michigan, [4]NASA Goddard Space Flight Center, [5]Predictive Science Inc., [6]Stanford University
As one of the largest flare-CME eruptions during solar cycle 24, the 2017 September 10 X8.2 flare event is associated with spectacular global EUV waves that transverse almost the entire visible solar disk, a CME with speed > 3000 km/s, which is one of the fastest CMEs ever recorded, and >100 MeV Gamma-ray emission lasting for more than 12 hours. All these unique observational features pose new challenge on current numerical models to reproduce the multi-wavelength observations. To take this challenge, we simulate the September 10 event using a global MHD model (AWSoM: Alfven Wave Solar Model) within the Space Weather Modeling Framework and initiate CMEs by Gibson-Low flux rope. We conduct detailed comparisons of the synthesized EUV images with SDO/AIA observations of global EUV waves. We find that the simulated EUV wave morphology and kinematics are sensitive to the orientation of the initial flux rope introduced to the source active region. An orientation with the flux-rope axis in the north-south direction produces the best match to the observations, which suggests that EUV waves may potentially be used to constrain the flux-rope geometry for such limb or behind-the-limb eruptions that lack good magnetic field observations. We also compare observed and simulated EUV intensities in multiple AIA channels to perform thermal seismology of the global corona. Furthermore, we track the 3D CME-driven shock surface in the simulation and derive the time-varying shock parameters together with the dynamic magnetic connectivity between the shock and the surface of the Sun, with which we discuss the role of CME-driven shocks in the long-duration Gamma-ray events.
Fast velocities of flare ribbon kernels and ribbon elongation in a quiescent filament eruption of 2012 August 31 observed by SDO/AIA	Lorincik, J
Juraj Lörinčík[1][2], Jaroslav Dudík[1], Jana Kašparová[1], Guillaume Aulanier[3], Alena Zemanová[1], Elena Dzifčáková[1]
[1]Astronomical Institute, CAS, Ondřejov, Czech Republic; [2]Institute of Astronomy, Charles University, Prague, Czech Republic; [3]LESIA, Observatoire de Paris, Meudon, France
We report on SDO observations of an eruption of a quiescent filament from 2012 August 31. In the 1600 \AA{} filter channel of AIA, flare ribbons were observed to elongate at velocities up to 480 km s^{-1} and flare kernels move along a ribbon at velocity of $\approx$ 260 km s^{-1}. In order to investigate the emission observed in the 1600 \AA{} channel, we used synthetic spectra modeled using CHIANTI and RADYN models of flare atmospheres with beam parameters constrained using fits of \textit{RHESSI} spectra. We found out that depending on parameters of heating of a flare model, thickness of a region where the emission of the 1600 \AA{} filter channel originates ranges between 10^{-2} and 10^{2} km. Information on dimensions of the formation region were then utilized to estimate densities in flare ribbons using inversions of the emission measure. These were found to range between 10^{10} – 4.10^{12} cm^{-3} for flare atmospheres heated by beams of different parameters. Together with B_{LOS} data from \textit{SDO}/HMI, diagnosed densities were used to calculate Alfvén velocities in observed ribbons. These can be as small as 17 km s^{-1} for flare ribbons observed in region of weak magnetic field at latter stages of heating. This finding suggests that elongation of ribbons and motion of kernels might not be related to waves. Motions along the PIL are well-described in the 3D model of solar eruptions of Aulanier et al. 2013 (A&A, 543, 110). However, EUV observations of flare loops revealed that velocity of their apparent slipping motion is much lower than velocity of elongation of a ribbon, which is observed in a close vicinity. Therefore, observed phenomena can not be directly related to super-Alvénic regime of magnetic slipping reconnection introduced in the 3D model.
On the extrapolation of magneto-hydro-static equilibria on the sun: model and tests	Zhu, X
Xiaoshuai Zhu[1], Thomas Wiegelmann[1]
[1] Max Planck Institute for Solar System Research
Modeling the interface region between solar photosphere and corona is challenging, because the relative importance of magnetic and plasma forces change by several orders of magnitude. While the solar corona can be modeled by the force-free assumption, we need to take care about plasma forces (pressure gradient and gravity) in photosphere and chromosphere, here within the magneto-hydro-static (MHS) model. We solve the MHS equations with the help of an optimization principle and use vector magnetogram as boundary condition. Positive pressure and density are ensured by replacing them with two new basic variables. The Lorentz force during optimization is used to update the plasma pressure on the bottom boundary, which makes the new extrapolation works even without pressure measurement on the photosphere. Our code is tested by using a linear MHS model as reference. From the detailed analyses, we find that the newly developed MHS extrapolation not only recovers the plasma distribution at high accuracy. but also gives the better fit magnetic field than the nonlinear force-free extrapolation.
What can we learn from impulsively generated waves observed by SDO/AIA?	Ofman, L
Leon Ofman[1], Wei Liu[2], Tongjiang Wang[3]
[1]NASA Goddard Space Flight Center and CUA, Greenbelt, MD, USA, [2]Lockheed Martin Space and Astrophysics Lab. and Stanford U. and BAERI, Palo Alto, CA, USA
Since the launch of the SDO/AIA instrument in 2010, various types of MHD waves in the solar corona have been observed in unprecedented detail. Notable examples include quasi-periodic fast propagating (QFP) waves in active regions, global EUV waves in the large-scale corona, standing kink and slow magnetosonic waves in coronal loops. The observed waves are generated by impulsive events, such as flares and CMEs, and can range in two orders of magnitude in phase speed from ~100 km/s to >1000 km/s, depending on their types and polarizations. The amplitude of the waves ranges from linear (i.e., with the velocity amplitude being small compared to the phase speed) to nonlinear regimes with shock-like features. The observations of the waves combined with MHD modeling provide a unique means of understanding the propagation/reflection/refraction of the waves and their interactions with coronal structures. We will present recent SDO/AIA observations of impulsively generated coronal waves and related MHD modeling results. We will also present applications of coronal seismology using these waves to determine the magnetic and thermal properties of various coronal structures.