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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Influence of Photospheric Magnetic Conditions on the Catastrophic Behaviors of Flux Ropes in Solar Active Regions

Since only the magnetic conditions at the photosphere can be routinely observed in current observations, it is of great significance to determine the influences of photospheric magnetic conditions on solar eruptive activities. Previous studies about catastrophe indicated that the magnetic system consisting of a flux rope in a partially open bipolar field is subject to catastrophe, but not if the bipolar field is completely closed under the same specified photospheric conditions. In order to investigate the influence of the photospheric magnetic conditions on the catastrophic behavior of this system, we expand upon the 2.5-dimensional ideal magnetohydrodynamic model in Cartesian coordinates to simulate the evolution of the equilibrium states of the system under different photospheric flux distributions. Our simulation results reveal that a catastrophe occurs only when the photospheric flux is not concentrated too much toward the polarity inversion line and the source regions of the bipolar field are not too weak; otherwise no catastrophe occurs. As a result, under certain photospheric conditions, a catastrophe could take place in a completely closed configuration, whereas it ceases to exist in a partially open configuration. This indicates that whether the background field is completely closed or partially open is not the only necessary condition for the existence of catastrophe, and that the photospheric conditions also play a crucial role in the catastrophic behavior of the flux rope system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Sub-photospheric Shocks in Relativistic Explosions

This paper examines the mechanism of internal shocks in opaque relativistic outflows, in particular in cosmological gamma-ray bursts. The shocks produce neutrino emission and affect the observed photospheric radiation from the explosion. They develop from internal compressive waves and can be of different types depending on the composition of the outflow. (1) Shocks in “photon gas,” with negligible plasma inertia, have a unique structure determined by the force-free condition—zero radiation flux in the plasma rest frame. Radiation dominance over plasma inertia suppresses the formation of collisionless shocks mediated by collective electromagnetic fields. (2) If the outflow is sufficiently magnetized, a strong collisionless subshock develops, which is embedded in a thicker radiation-mediated structure. (3) Waves in outflows with a free neutron component lead to dissipation through nuclear collisions. At large optical depths, shocks have a thickness comparable to the neutron free path, with embedded radiation-mediated and collisionless subshocks. The paper also presents first-principles simulations of magnetized flows filled with photons, demonstrating the formation of shocks and their structure. Simple estimates show that magnetized sub-photospheric shocks are efficient producers of photons and have a great impact on the observed photospheric radiation. The shock structure changes as the outflow expands toward its photosphere. The dissipation is accompanied by strong e{sup ±} pair creation, and the e{sup ±}-dressed shock carries the photosphere with it up to two decades in radius, emitting a strong pulse of nonthermal radiation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The Polarization Signature of Photospheric Magnetic Fields in 3D MHD Simulations and Observations at Disk Center

Before using three-dimensional (3D) magnetohydrodynamical (MHD) simulations of the solar photosphere in the determination of elemental abundances, one has to ensure that the correct amount of magnetic flux is present in the simulations. The presence of magnetic flux modifies the thermal structure of the solar photosphere, which affects abundance determinations and the solar spectral irradiance. The amount of magnetic flux in the solar photosphere also constrains any possible heating in the outer solar atmosphere through magnetic reconnection. We compare the polarization signals in disk-center observations of the solar photosphere in quiet-Sun regions with those in Stokes spectra computed on the basis of 3D MHD simulations having average magnetic flux densities of about 20, 56, 112, and 224 G. This approach allows us to find the simulation run that best matches the observations. The observations were taken with the Hinode SpectroPolarimeter (SP), the Tenerife Infrared Polarimeter (TIP), the Polarimetric Littrow Spectrograph (POLIS), and the GREGOR Fabry–Pèrot Interferometer (GFPI), respectively. We determine characteristic quantities of full Stokes profiles in a few photospheric spectral lines in the visible (630 nm) and near-infrared (1083 and 1565 nm). We find that the appearance of abnormal granulation in intensity maps of degraded simulations can be traced back to an initially regular granulation pattern with numerous bright points in the intergranular lanes before the spatial degradation. The linear polarization signals in the simulations are almost exclusively related to canopies of strong magnetic flux concentrations and not to transient events of magnetic flux emergence. We find that the average vertical magnetic flux density in the simulation should be less than 50 G to reproduce the observed polarization signals in the quiet-Sun internetwork. A value of about 35 G gives the best match across the SP, TIP, POLIS, and GFPI observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Investigation of Relationship between High-energy X-Ray Sources and Photospheric and Helioseismic Impacts of X1.8 Solar Flare of 2012 October 23

The X-class solar flare of 2012 October 23 generated continuum photospheric emission and a strong helioseismic wave (“sunquake”) that points to an intensive energy release in the dense part of the solar atmosphere. We study properties of the energy release with high temporal and spatial resolutions, using photospheric data from the Helioseismic Magnetic Imager (HMI) on board Solar Dynamics Observatory , and hard X-ray observations made by RHESSI . For this analysis we use level-1 HMI data (filtergrams), obtained by scanning the Fe i line (6731 Å) with the time cadence of ∼3.6 s and spatial resolution of ∼0.″5 per pixel. It is found that the photospheric disturbances caused by the flare spatially coincide with the region of hard X-ray emission but are delayed by ≲4 s. This delay is consistent with predictions of the flare hydrodynamics RADYN models. However, the models fail to explain the magnitude of variations observed by the HMI. The data indicate that the photospheric impact and helioseismic wave might be caused by the electron energy flux, which is substantially higher than that in the current flare radiative hydrodynamic models.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

TRACING p -MODE WAVES FROM THE PHOTOSPHERE TO THE CORONA IN ACTIVE REGIONS

Atmosphere above sunspots is abundant with different types of waves. Among these waves are running penumbral waves in the chromosphere, quasi-periodic oscillations in the lower coronal loops, and recently reported running waves in sunspots’ photosphere, all of which were interpreted as magnetoacoustic waves by some authors. Are these waves in different atmospheric layers related to each other, what is the nature of these waves, and where are the ultimate sources of these waves? Applying a time–distance helioseismic analysis over a suite of multi-wavelength observations above a sunspot, we demonstrate that the helioseismic p -mode waves are able to channel up from the photosphere through the chromosphere and transition region into the corona, and that the magnetoacoustic waves observed in different atmospheric layers are a same wave originating from the photosphere but exhibiting differently under different physical conditions. We also show waves of different frequencies travel along different paths, which can be used to derive the physical properties of the atmosphere above sunspots. Our numerical simulation of traveling of waves from a subphotospheric source qualitatively resembles the observed properties of the waves and offers an interpretation of the shapes of the wavefronts above the photosphere.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

NASA’s Pandora SmallSat Mission: Simulating the Impact of Stellar Photospheric Heterogeneity and Its Correction

Stellar photospheric heterogeneity is a dominant astrophysical systematic impacting exoplanet transmission spectroscopy. NASA’s Pandora SmallSat Mission is designed to address this challenge through contemporaneous visible-band photometry and near-infrared spectroscopy of exoplanet host stars. Here, we present an end-to-end simulation study quantifying Pandora’s ability to infer stellar photospheric properties and correct stellar contamination using out-of-transit observations. We construct eight representative stellar activity scenarios and generate 160 simulated Pandora datasets, incorporating time-dependent stellar spectra, instrument response, and noise. Given accurate models, Bayesian retrievals of joint visible photometry (0.4–0.7 μm) and near-infrared spectroscopy (0.9–1.6 μm, R ≈ 120) recover photospheric temperatures with typical uncertainties of ≈30 K, with no significant bias. Models with two spectral components (i.e., a quiescent photosphere and spots) are strongly favored in 95% of cases; one-component models are preferred when true spot filling factors fall below a detection threshold of ≈0.3%. We propagate the true and inferred stellar parameters to compute true, inferred, and residual contamination signals under physically motivated spot geometries. For simple spot distributions, contamination signals of 10 2 –10 3 ppm are reduced to ≲10 ppm—well below Pandora’s expected transmission spectroscopy precision (30–100 ppm). For more complex spot distributions, geometric degeneracies limit deterministic corrections, leaving residual contamination at the 10 3 ppm level that must be mitigated using additional constraints, such as spot-crossing events and joint stellar–planetary retrievals of transmission spectra. These results define regimes in which stellar contamination can be corrected from stellar observations alone and show how Pandora stellar observations can identify cases where additional information is required.

Astronomy and AstroPhysics↗
DOE OSTI2022

Black Hole to Photosphere: 3D GRMHD Simulations of Collapsars Reveal Wobbling and Hybrid Composition Jets

Long-duration γ-ray bursts (GRBs) accompany the collapse of massive stars and carry information about the central engine. However, no 3D models have been able to follow these jets from their birth via black hole (BH) to the photosphere. We present the first such 3D general-relativity magnetohydrodynamic simulations, which span over six orders of magnitude in space and time. The collapsing stellar envelope forms an accretion disk, which drags inwardly the magnetic flux that accumulates around the BH, becomes dynamically important, and launches bipolar jets. The jets reach the photosphere at ~10 12 cm with an opening angle θ j ~ 6° and a Lorentz factor Γ j ≲ 30, unbinding ≳90% of the star. We find that (i) the disk–jet system spontaneously develops misalignment relative to the BH rotational axis. As a result, the jet wobbles with an angle θ t ~ 12°, which can naturally explain quiescent times in GRB lightcurves. The effective opening angle for detection θ j + θ t suggests that the intrinsic GRB rate is lower by an order of magnitude than standard estimates. This suggests that successful GRBs are rarer than currently thought and emerge in only ~0.1% of supernovae Ib/c, implying that jets are either not launched or choked inside most supernova Ib/c progenitors. (ii) The magnetic energy in the jet decreases due to mixing with the star, resulting in jets with a hybrid composition of magnetic and thermal components at the photosphere, where ~10% of the gas maintains magnetization σ ≳ 0.1. This indicates that both a photospheric component and reconnection may play a role in the prompt emission.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

THE EFFECTS OF TRANSIENTS ON PHOTOSPHERIC AND CHROMOSPHERIC POWER DISTRIBUTIONS

We have observed a quiet-Sun region with the Swedish 1 m Solar Telescope equipped with the CRISP Imaging SpectroPolarimeter. High-resolution, high-cadence, H α line scanning images were taken to observe different layers of the solar atmosphere from the photosphere to upper chromosphere. We study the distribution of power in different period bands at different heights. Power maps of the upper photosphere and the lower chromosphere show suppressed power surrounding the magnetic-network elements, known as “magnetic shadows.” These also show enhanced power close to the photosphere, traditionally referred to as “power halos.” The interaction between acoustic waves and inclined magnetic fields is generally believed to be responsible for these two effects. In this study we explore whether small-scale transients can influence the distribution of power at different heights. We show that the presence of transients, like mottles, Rapid Blueshifted Excursions (RBEs), and Rapid Redshifted Excursions (RREs), can strongly influence the power maps. The short and finite lifetime of these events strongly affects all power maps, potentially influencing the observed power distribution. We show that Doppler-shifted transients like RBEs and RREs that occur ubiquitously can have a dominant effect on the formation of the power halos in the quiet Sun. For magnetic shadows, transients like mottles do not seem to have a significant effect on the power suppression around 3 minutes, and wave interaction may play a key role here. Our high-cadence observations reveal that flows, waves, and shocks manifest in the presence of magnetic fields to form a nonlinear magnetohydrodynamic system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

MODELING THE SUN’S SMALL-SCALE GLOBAL PHOTOSPHERIC MAGNETIC FIELD

We present a new model for the Sun’s global photospheric magnetic field during a deep minimum of activity, in which no active regions emerge. The emergence and subsequent evolution of small-scale magnetic features across the full solar surface is simulated, subject to the influence of a global supergranular flow pattern. Visually, the resulting simulated magnetograms reproduce the typical structure and scale observed in quiet Sun magnetograms. Quantitatively, the simulation quickly reaches a steady state, resulting in a mean field and flux distribution that are in good agreement with those determined from observations. A potential coronal magnetic field is extrapolated from the simulated full Sun magnetograms to consider the implications of such a quiet photospheric magnetic field on the corona and inner heliosphere. The bulk of the coronal magnetic field closes very low down, in short connections between small-scale features in the simulated magnetic network. Just 0.1% of the photospheric magnetic flux is found to be open at 2.5 R {sub ⊙}, around 10–100 times less than that determined for typical Helioseismic and Magnetic Imager synoptic map observations. If such conditions were to exist on the Sun, this would lead to a significantly weaker interplanetary magnetic field than is currently observed, and hence a much higher cosmic ray flux at Earth.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

( Hinode Hinode) and IRIS observations of the magnetohydrodynamic waves propagating from the photosphere to the chromosphere in a sunspot

Magnetohydrodynamic (MHD) waves have been considered as energy sources for heating the solar chromosphere and the corona. Although MHD waves have been observed in the solar atmosphere, there are a lack of quantitative estimates on the energy transfer and dissipation in the atmosphere. We performed simultaneous Hinode and Interface Region Imaging Spectrograph observations of a sunspot umbra to derive the upward energy fluxes at two different atmospheric layers (photosphere and lower transition region) and estimate the energy dissipation. The observations revealed some properties of the observed periodic oscillations in physical quantities, such as their phase relations, temporal behaviors, and power spectra, making a conclusion that standing slow-mode waves are dominant at the photosphere with their high-frequency leakage, which is observed as upward waves at the chromosphere and the lower transition region. Our estimates of upward energy fluxes are 2.0×10{sup 7} erg cm{sup −2} s{sup −1} at the photospheric level and 8.3×10{sup 4} erg cm{sup −2} s{sup −1} at the lower transition region level. The difference between the energy fluxes is larger than the energy required to maintain the chromosphere in the sunspot umbrae, suggesting that the observed waves can make a crucial contribution to the heating of the chromosphere in the sunspot umbrae. In contrast, the upward energy flux derived at the lower transition region level is smaller than the energy flux required for heating the corona, implying that we may need another heating mechanism. We should, however, note a possibility that the energy dissipated at the chromosphere might be overestimated because of the opacity effect.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

PIXEL ANALYSIS OF PHOTOSPHERIC SPECTRAL DATA. I. PLASMA DYNAMICS

Recent observations of the photosphere using high spatial and temporal resolution show small dynamic features at or below the current resolving limits. A new pixel dynamics method has been developed to analyze spectral profiles and quantify changes in line displacement, width, asymmetry, and peakedness of photospheric absorption lines. The algorithm evaluates variations of line profile properties in each pixel and determines the statistics of such fluctuations averaged over all pixels in a given region. The method has been used to derive statistical characteristics of pixel fluctuations in observed quiet-Sun regions, an active region with no eruption, and an active region with an ongoing eruption. Using Stokes I images from the Vector Spectromagnetograph (VSM) of the Synoptic Optical Long-term Investigations of the Sun (SOLIS) telescope on 2012 March 13, variations in line width and peakedness of Fe i 6301.5 Å are shown to have a distinct spatial and temporal relationship with an M7.9 X-ray flare in NOAA 11429. This relationship is observed as stationary and contiguous patches of pixels adjacent to a sunspot exhibiting intense flattening in the line profile and line-center displacement as the X-ray flare approaches peak intensity, which is not present in area scans of the non-eruptive active region. The analysis of pixel dynamics allows one to extract quantitative information on differences in plasma dynamics on sub-pixel scales in these photospheric regions. The analysis can be extended to include the Stokes parameters and study signatures of vector components of magnetic fields and coupled plasma properties.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

ARE INTERNETWORK MAGNETIC FIELDS IN THE SOLAR PHOTOSPHERE HORIZONTAL OR VERTICAL?

Using many observations obtained during 2007 with the Spectro-Polarimeter of the Hinode Solar Optical Telescope , we explore the angular distribution of magnetic fields in the quiet internetwork regions of the solar photosphere. Our work follows from the insight of Stenflo, who examined only linear polarization signals in photospheric lines, thereby avoiding complications of the analysis arising from the differing responses to linear and circular polarization. We identify and isolate regions of a strong polarization signal that occupy only a few percent of the observed quiet Sun area yet contribute most to the net linear polarization signal. The center-to-limb variation of the orientation of linear polarization in these strong signal regions indicates that the associated magnetic fields have a dominant vertical orientation. In contrast, the great majority of the solar disk is occupied by much weaker linear polarization signals. The orientation of the linear polarization in these regions demonstrates that the field orientation is dominantly horizontal throughout the photosphere. We also apply our analysis to Stokes profiles synthesized from the numerical MHD simulations of Rempel as viewed at various oblique angles. The analysis of the synthetic data closely follows that of the observations, lending confidence to using the simulations as a guide for understanding the physical origins of the center-to-limb variation of linear polarization in the quiet Sun area.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

A STUDY OF SOLAR PHOTOSPHERIC TEMPERATURE GRADIENT VARIATION USING LIMB DARKENING MEASUREMENTS

The variation in area of quiet magnetic network measured over the sunspot cycle should modulate the spatially averaged photospheric temperature gradient, since temperature declines with optical depth more gradually in magnetic flux tube atmospheres. Yet, limb darkening measurements show no dependence upon activity level, even at an rms precision of 0.04%. We study the sensitivity of limb darkening to changes in area filling factor using a 3D MHD model of the magnetized photosphere. The limb darkening change expected from the measured 11-year area variation lies below the level of measured limb darkening variations, for a reasonable range of magnetic flux in quiet network and internetwork regions. So the remarkably constant limb darkening observed over the solar activity cycle is not inconsistent with the measured 11-year change in area of quiet magnetic network. Our findings offer an independent constraint on photospheric temperature gradient changes reported from measurements of the solar spectral irradiance from the Spectral Irradiance Monitor, and recently, from wavelength-differential spectrophotometry using the Solar Optical Telescope aboard the HINODE spacecraft.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Photospheric Origin of Three-minute Oscillations in a Sunspot

The origin of the three-minute oscillations of intensity and velocity observed in the chromosphere of sunspot umbrae is still unclear. We investigated the spatio-spectral properties of the 3 minute oscillations of velocity in the photosphere of a sunspot umbra as well as those in the low chromosphere using the spectral data of the Ni i λ 5436, Fe i λ 5435, and Na i D{sub 2} λ 5890 lines taken by the Fast Imaging Solar Spectrograph of the 1.6 m New Solar Telescope at the Big Bear Solar Observatory. As a result, we found a local enhancement of the 3 minute oscillation power in the vicinities of a light bridge (LB) and numerous umbral dots (UDs) in the photosphere. These 3 minute oscillations occurred independently of the 5 minute oscillations. Through wavelet analysis, we determined the amplitudes and phases of the 3 minute oscillations at the formation heights of the spectral lines, and they were found to be consistent with the upwardly propagating slow magnetoacoustic waves in the photosphere with energy flux large enough to explain the chromospheric oscillations. Our results suggest that the 3 minute chromospheric oscillations in this sunspot may have been generated by magnetoconvection occurring in the LB and UDs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Height-dependent Velocity Structure of Photospheric Convection in Granules and Intergranular Lanes with Hinode /SOT

The solar photosphere is the visible surface of the Sun, where many bright granules, surrounded by narrow dark intergranular lanes, are observed everywhere. The granular pattern is a manifestation of convective motion at the photospheric level, but its velocity structure in the height direction is poorly understood observationally. Applying bisector analysis to a photospheric spectral line recorded by the Hinode Solar Optical Telescope, we derived the velocity structure of the convective motion in granular regions and intergranular lanes separately. The amplitude of motion of the convective material decreases from 0.65 to 0.40 km s{sup −1} as the material rises in granules, whereas the amplitude of motion increases from 0.30 to 0.50 km s{sup −1} as it descends in intergranular lanes. These values are significantly larger than those obtained in previous studies using bisector analysis. The acceleration of descending materials with depth is not predicted from the convectively stable condition in a stratified atmosphere. Such convective instability can be developed more efficiently by radiative cooling and/or a gas pressure gradient, which can control the dynamical behavior of convective material in intergranular lanes. Our analysis demonstrated that bisector analysis is a useful method for investigating the long-term dynamic behavior of convective material when a large number of pixels is available. In addition, one example is the temporal evolution of granular fragmentation, in which downflowing material develops gradually from a higher layer downward.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Access I. An optical transmission spectrum of GJ 1214B reveals a heterogeneous stellar photosphere

GJ 1214b is the most studied sub-Neptune exoplanet to date. Recent measurements have shown its near-infrared transmission spectrum to be flat, pointing to a high-altitude opacity source in the exoplanet's atmosphere, either equilibrium condensate clouds or photochemical hazes. Many photometric observations have been reported in the optical by different groups, though simultaneous measurements spanning the entire optical regime are lacking. We present an optical transmission spectrum (4500–9260 Å) of GJ 1214b in 14 bins, measured with Magellan/IMACS repeatedly over three transits. We measure a mean planet-to-star radius ratio of R{sub p}/R{sub s}=0.1146±2×10{sup −4} and mean uncertainty of σ(R{sub p}/R{sub s})=8.7×10{sup −4} in the spectral bins. The optical transit depths are shallower on average than observed in the near-infrared. We present a model for jointly incorporating the effects of a composite photosphere and atmospheric transmission through the exoplanet's limb (the CPAT model), and use it to examine the cases of absorber and temperature heterogeneities in the stellar photosphere. We find the optical and near-infrared measurements are best explained by the combination of (1) photochemical haze in the exoplanetary atmosphere with a mode particle size r = 0.1 μm and haze-forming efficiency f{sub haze}=10% and (2) faculae in the unocculted stellar disk with a temperature contrast ΔT=354{sub −46}{sup +46} K, assuming 3.2% surface coverage. The CPAT model can be used to assess potential contributions of heterogeneous stellar photospheres to observations of exoplanet transmission spectra, which will be important for searches for spectral features in the optical.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Propagation of Torsional Alfvén Waves from the Photosphere to the Corona: Reflection, Transmission, and Heating in Expanding Flux Tubes

It has been proposed that Alfvén waves play an important role in the energy propagation through the solar atmospheric plasma and its heating. Here we theoretically investigate the propagation of torsional Alfvén waves in magnetic flux tubes expanding from the photosphere up to the low corona and explore the reflection, transmission, and dissipation of wave energy. We use a realistic variation of the plasma properties and the magnetic field strength with height. Dissipation by ion–neutral collisions in the chromosphere is included using a multifluid partially ionized plasma model. Considering the stationary state, we assume that the waves are driven below the photosphere and propagate to the corona, while they are partially reflected and damped in the chromosphere and transition region. The results reveal the existence of three different propagation regimes depending on the wave frequency: low frequencies are reflected back to the photosphere, intermediate frequencies are transmitted to the corona, and high frequencies are completely damped in the chromosphere. The frequency of maximum transmissivity depends on the magnetic field expansion rate and the atmospheric model, but is typically in the range of 0.04–0.3 Hz. Magnetic field expansion favors the transmission of waves to the corona and lowers the reflectivity of the chromosphere and transition region compared to the case with a straight field. As a consequence, the chromospheric heating due to ion–neutral dissipation systematically decreases when the expansion rate of the magnetic flux tube increases.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

A NEW TECHNIQUE FOR THE PHOTOSPHERIC DRIVING OF NON-POTENTIAL SOLAR CORONAL MAGNETIC FIELD SIMULATIONS

In this paper, we develop a new technique for driving global non-potential simulations of the Sun’s coronal magnetic field solely from sequences of radial magnetic maps of the solar photosphere. A primary challenge to driving such global simulations is that the required horizontal electric field cannot be uniquely determined from such maps. We show that an “inductive” electric field solution similar to that used by previous authors successfully reproduces specific features of the coronal field evolution in both single and multiple bipole simulations. For these cases, the true solution is known because the electric field was generated from a surface flux-transport model. The match for these cases is further improved by including the non-inductive electric field contribution from surface differential rotation. Then, using this reconstruction method for the electric field, we show that a coronal non-potential simulation can be successfully driven from a sequence of ADAPT maps of the photospheric radial field, without including additional physical observations which are not routinely available.

79 ASTRONOMY AND ASTROPHYSICS↗