Fe XIII Research Articles

Coronagraphic Observations of Si x λ14301 and Fe xiii λ10747 Linearly Polarized Spectra Using the SOLARC Telescope

Abstract The forbidden Si x emission line at 14301 Å has been identified as a potentially valuable polarized diagnostic for solar coronal magnetic fields; however, the only polarized Si x measurements achieved to date have been during eclipses and at comparatively low spatial and spectral resolution. Here we report spectropolarimetric observations of both the Si x 14301 Å and more well-established Fe xiii 10747 Å coronal lines acquired with the 0.45 m aperture SOLARC coronagraph atop Haleakalā. Using its fiber-based integral field spectropolarimeter, we derive observations sampled at radial intervals of 0.05 (i.e., ∼50″) with a spectral resolving power of ≈36,000. Results for both lines, which represent averages over different active and nonactive regions of the corona, indicate a relatively flat radial variation for the line widths and line centers and a factor of ≈2–3 decrease in polarized brightness between 1.05 and 1.45 . Averaging over all the measurements the mean and standard deviations of line properties for Si x 14301 Å and Fe xiii 10747 Å are, respectively, FWHM of 3.0 ± 0.4 Å and 1.6 ± 0.1 Å, line-integrated polarized brightness of 0.07 ± 0.03 and 0.3 ± 0.3 erg s−2 cm−2 sr−1, where the uncertainty quoted reflects a large sample variance, and line center wavelengths 14300.7 ± 0.2 Å and 10746.3 ± 0.1 Å. The polarized brightness for both lines may be underestimated by up to a factor of 5 due to limitations in the photometric calibration. When accounting for this uncertainty we find consistency between our observations and previous measurements of the two lines as well as theoretical calculations and affirm the potential of the Si x line as a polarized diagnostic of the solar corona.

Non-equilibrium Ionization Effects on Extreme-ultraviolet Emissions Modulated by Standing Sausage Modes in Coronal Loops

Abstract Forward-modeling the emission properties in various passbands is important for confidently identifying magnetohydrodynamic waves in the structured solar corona. We examine how non-equilibrium ionization (NEI) affects the extreme-ultraviolet (EUV) emissions modulated by standing fast sausage modes (FSMs) in coronal loops, taking the Fe ix 171 Å and Fe xii 193 Å emission lines as examples. Starting with the expressions for linear FSMs in straight cylinders, we synthesize the specific intensities and spectral profiles for the two spectral lines by incorporating the self-consistently derived ionic fractions in the relevant contribution functions. We find that relative to the case where equilibrium ionization (EI) is assumed, NEI considerably impacts the intensity modulations, but shows essentially no effect on the Doppler velocities or widths. Furthermore, NEI may affect the phase difference between intensity variations and those in Doppler widths for Fe xii 193 Å when the line of sight is oblique to the loop axis. While this difference is 180° when EI is assumed, it is ∼90° when NEI is incorporated for the parameters we choose. We conclude that in addition to viewing angles and instrumental resolutions, NEI further complicates the detection of FSMs in spectroscopic measurements of coronal loops in the EUV passband.

Impacts of EUV Wavefronts on Coronal Structures in Homologous Coronal Mass Ejections

Abstract Large-scale propagating fronts are frequently observed during solar eruptions, yet whether or not they are waves is an open question, partly because the propagation is modulated by coronal structures, whose magnetic fields we still cannot measure. However, when a front impacts coronal structures, an opportunity arises for us to look into the magnetic properties of both interacting parties in the low-β corona. Here we studied large-scale EUV fronts accompanying three coronal mass ejections (CMEs), each originating from a kinking rope-like structure in the NOAA active region (AR) 12371. These eruptions were homologous and the surrounding coronal structures remained stationary. Hence we treated the events as one observed from three different viewing angles, and found that the primary front directly associated with the CME consistently transmits through (1) a polar coronal hole, (2) the ends of a crescent-shaped equatorial coronal hole, leaving a stationary front outlining its AR-facing boundary, and (3) two quiescent filaments, producing slow and diffuse secondary fronts. The primary front also propagates along an arcade of coronal loops and slows down due to foreshortening at the far side, where local plasma heating is indicated by an enhancement in 211 Å (Fe xiv) but a dimming in 193 Å (Fe xii) and 171 Å (Fe ix). The strength of coronal magnetic field is therefore estimated to be ∼2 G in the polar coronal hole and ∼4 G in the coronal arcade neighboring the AR. These observations substantiate the wave nature of the primary front and shed new light on slow fronts.

Helicity Removal and Coronal Fe xii Stalks: Evidence That the Axial Field Is Not Ejected but Resubmerged

Abstract The magnetic/current helicity of the coronal field is closely associated with the presence of a nonpotential axial component directed along the photospheric polarity inversion line (PIL), which is also the source of the axial/toroidal field in flux ropes and coronal mass ejections (CMEs). To better understand the role of this axial component in the evolution of coronal helicity, we use Fe xii 19.3 nm images and longitudinal magnetograms from the Solar Dynamics Observatory to track active regions (ARs) and their filament channels as they decay due to flux transport processes. We find that the Fe xii loop legs or “stalks,” initially oriented almost perpendicular to the PIL, become closely aligned with it after ∼1–4 rotations; this alignment is attributed to the progressive cancellation of the transverse field component at the PIL. As the AR flux continues to decay, the PIL becomes ever more distorted and the directions of the stalks are increasingly randomized. These observations suggest that most of the original axial field in ARs is not expelled in CMEs, but instead pinches off after the eruptions and becomes concentrated at the PIL. Because the twist of the field decreases, however, the helicity itself decreases, with CMEs removing a significant fraction of it in the form of disconnected flux ropes. Like most of the AR flux, the bulk of the axial field is eventually canceled/resubmerged, brought to the equator by the subsurface meridional flow, and annihilated (along with the remaining helicity) by merging with its opposite-handed counterpart from the other hemisphere.

Incorporating Uncertainties in Atomic Data into the Analysis of Solar and Stellar Observations: A Case Study in Fe xiii

Abstract Information about the physical properties of astrophysical objects cannot be measured directly but is inferred by interpreting spectroscopic observations in the context of atomic physics calculations. Ratios of emission lines, for example, can be used to infer the electron density of the emitting plasma. Similarly, the relative intensities of emission lines formed over a wide range of temperatures yield information on the temperature structure. A critical component of this analysis is understanding how uncertainties in the underlying atomic physics propagate to the uncertainties in the inferred plasma parameters. At present, however, atomic physics databases do not include uncertainties on the atomic parameters and there is no established methodology for using them even if they did. In this paper we develop simple models for uncertainties in the collision strengths and decay rates for Fe xiii and apply them to the interpretation of density-sensitive lines observed with the EUV (extreme ultraviolet) Imagining spectrometer (EIS) on Hinode. We incorporate these uncertainties in a Bayesian framework. We consider both a pragmatic Bayesian method where the atomic physics information is unaffected by the observed data, and a fully Bayesian method where the data can be used to probe the physics. The former generally increases the uncertainty in the inferred density by about a factor of 5 compared with models that incorporate only statistical uncertainties. The latter reduces the uncertainties on the inferred densities, but identifies areas of possible systematic problems with either the atomic physics or the observed intensities.

Polar Coronal Plumes as Tornado-like Jets

Abstract We examine the dynamical behavior of white-light polar-plume structures in the inner corona that are observed from the ground during total solar eclipses, based on their extreme ultraviolet (EUV) hot and cool emission line counterparts observed from space. EUV observations from Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) of a sequence of rapidly varying coronal hole structures are analyzed. Evidence of events showing acceleration in the 1.25 Mk line of Fe xii at 193 Å is given. The structures along the plume show an outward velocity of about 140 km s−1 that can be interpreted as an upward propagating wave in the 304 Å and 171 Å lines; higher speeds are seen in 193 Å (up to 1000 km s−1). The ejection of the cold He ii plasma is delayed by about 4 minutes in the lowest layer and is delayed more than 12 minutes in the highest level compared to the hot 193 Å behavior. A study of the dynamics using time-slice diagrams reveals that a large amount of fast ejected material originates from below the plume, at the footpoints. The release of plasma material appears to come from a cylinder with quasi-parallel edge-enhanced walls. After the initial phase of a longitudinal acceleration, the speed substantially reduces, and the ejecta disperse into the environment. Finally, the detailed temporal and spatial relationships between the cool and hot components were studied with simultaneous multiwavelength observations, using more AIA data. The outward-propagating perturbation of the presumably magnetic walls of polar plumes supports the suggestion that Alfvén waves propagate outwardly along these radially extended walls.

Measurements of the effective electron density in an electron beam ion trap using extreme ultraviolet spectra and optical imaging.

In an electron beam ion trap (EBIT), the ions are not confined to the electron beam, but rather oscillate in and out of the beam. As a result, the ions do not continuously experience the full density of the electron beam. To determine the effective electron density, n e,eff, experienced by the ions, the electron beam size, the nominal electron density n e, and the ion distribution around the beam, i.e., the so-called ion cloud, must be measured. We use imaging techniques in the extreme ultraviolet (EUV) and optical to determine these. The electron beam width is measured using 3d → 3p emission from Fe xii and xiii between 185 and 205 Å. These transitions are fast and the EUV emission occurs only within the electron beam. The measured spatial emission profile and variable electron current yield a nominal electron density range of n e ∼ 1011-1013 cm-3. We determine the size of the ion cloud using optical emission from metastable levels of ions with radiative lifetimes longer than the ion orbital periods. The resulting emission maps out the spatial distribution of the ion cloud. We find a typical electron beam radius of ∼60 μm and an ion cloud radius of ∼300 μm. These yield a spatially averaged effective electron density, n e,eff, experienced by the ions in EBIT spanning ∼ 5 × 109-5 × 1011 cm-3.

Predicting the COSIE-C Signal from the Outer Corona up to 3 Solar Radii

Abstract We present estimates of the signal to be expected in quiescent solar conditions, as would be obtained with the COronal Spectrographic Imager in the EUV in its coronagraphic mode (COSIE-C). COSIE-C has been proposed to routinely observe the relatively unexplored outer corona, where we know that many fundamental processes affecting both the lower corona and the solar wind are taking place. The COSIE-C spectral band, 186–205 Å, is well-known as it has been observed with Hinode EIS. We present Hinode EIS observations that we obtained in 2007 out to 1.5 R ⊙, to show that this spectral band in quiescent streamers is dominated by Fe xii and Fe xi and that the ionization temperature is nearly constant. To estimate the COSIE-C signal in the 1.5–3.1 R ⊙ region we use a model based on CHIANTI atomic data and SoHO UVCS observations in the Si xii and Mg x coronal lines of two quiescent 1996 streamers. We reproduce the observed EUV radiances with a simple density model, photospheric abundances, and a constant temperature of 1.4 MK. We show that other theoretical or semi-empirical models fail to reproduce the observations. We find that the coronal COSIE-C signal at 3 R ⊙ should be about 5 counts/s per 3.″1 pixel in quiescent streamers. This is unprecedented and opens up a significant discovery space. We also briefly discuss stray light and the visibility of other solar features. In particular, we present UVCS observations of an active region streamer, indicating increased signal compared to the quiet Sun cases.

Predictions of DKIST/DL-NIRSP Observations for an Off-limb Kink-unstable Coronal Loop

Abstract Synthetic intensity maps are generated from a 3D kink-unstable flux rope simulation using several DKIST/DL-NIRSP spectral lines to make a prediction of the observational signatures of energy transport and release. The reconstructed large field-of-view intensity mosaics and single tile sit-and-stare high-cadence image sequences show detailed, fine-scale structure and exhibit signatures of wave propagation, redistribution of heat, flows, and fine-scale bursts. These fine-scale bursts are present in the synthetic Doppler velocity maps and can be interpreted as evidence for small-scale magnetic reconnection at the loop boundary. The spectral lines reveal the different thermodynamic structures of the loop, with the hotter lines showing the loop interior and braiding and the cooler lines showing the radial edges of the loop. The synthetic observations of DL-NIRSP are found to preserve the radial expansion, and hence the loop radius can be measured accurately. The electron number density can be estimated using the intensity ratio of the Fe xiii lines at 10747 and 10798 Å. The estimated density from this ratio is correct to within ±10% during the later phases of the evolution; however, it is less accurate initially when line-of-sight density inhomogeneities contribute to the Fe xiii intensity, resulting in an overprediction of the density by ≈30%. The identified signatures are all above a conservative estimate for instrument noise and therefore will be detectable. In summary, we have used forward modeling to demonstrate that the coronal off-limb mode of DKIST/DL-NIRSP will be able to detect multiple independent signatures of a kink-unstable loop and observe small-scale transient features including loop braiding/twisting and small-scale reconnection events occurring at the radial edge of the loop.

Energy Levels, Lifetimes, and Transition Rates for P-like Ions from Cr x to Zn xvi from Large-scale Relativistic Multiconfiguration Calculations

Abstract The fully relativistic multiconfiguration Dirac–Hartree–Fock method is used to compute excitation energies and lifetimes for the 143 lowest states of the , 3s3p 4, , 3s3p 33d, 3p 5, configurations in P-like ions from Cr x to Zn xvi. Multipole (E1, M1, E2, M2) transition rates, line strengths, oscillator strengths, and branching fractions among these states are also given. Valence–valence and core–valence electron correlation effects are systematically accounted for using large basis function expansions. Computed excitation energies are compared with the NIST ASD and CHIANTI compiled values and previous calculations. The mean average absolute difference, removing obvious outliers, between computed and observed energies for the 41 lowest identified levels in Fe xii, is only 0.057%, implying that the computed energies are accurate enough to aid identification of new emission lines from the Sun and other astrophysical sources. The amount of energy and transition data of high accuracy are significantly increased for several P-like ions of astrophysics interest, where experimental data are still very scarce.

Diagnosing the Magnetic Field Structure of a Coronal Cavity Observed during the 2017 Total Solar Eclipse

Abstract We present an investigation of a coronal cavity observed above the western limb in the coronal red line Fe x 6374 Å using a telescope of Peking University and in the green line Fe xiv 5303 Å using a telescope of Yunnan Observatories, Chinese Academy of Sciences, during the total solar eclipse on 2017 August 21. A series of magnetic field models is constructed based on the magnetograms taken by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory (SDO) one week before the eclipse. The model field lines are then compared with coronal structures seen in images taken by the Atmospheric Imaging Assembly on board SDO and in our coronal red line images. The best-fit model consists of a flux rope with a twist angle of 3.1π, which is consistent with the most probable value of the total twist angle of interplanetary flux ropes observed at 1 au. Linear polarization of the Fe xiii 10747 Å line calculated from this model shows a “lagomorphic” signature that is also observed by the Coronal Multichannel Polarimeter of the High Altitude Observatory. We also find a ring-shaped structure in the line-of-sight velocity of Fe xiii 10747 Å, which implies hot plasma flows along a helical magnetic field structure, in the cavity. These results suggest that the magnetic structure of the cavity is a highly twisted flux rope, which may erupt eventually. The temperature structure of the cavity has also been investigated using the intensity ratio of Fe xiii 10747 Å and Fe x 6374 Å.

Optical design of visible emission line coronagraph on Indian space solar mission Aditya-L1

The ground based observations of the coronal emission lines using a coronagraph are affected by the short duration of clear sky and varying sky transparency. These conditions do not permit to study small amplitude variations in the coronal emission reliably necessary to investigate the process or processes involved in heating the coronal plasma and dynamics of solar corona. The proposed Visible Emission Line Coronagraph (VELC) over comes these limitations and will provide continuous observation 24 h a day needed for detailed studies of solar corona and drivers for space weather predictions. VELC payload onboard India’s Aditya-L1 space mission is an internally occulted solar coronagraph for studying the temperature, velocity, density and heating of solar corona. To achieve the proposed science goals, an instrument which is capable of carrying out simultaneous imaging, spectroscopy and spectro-polarimetric observations of the solar corona close to the solar limb is required. VELC is designed with salient features of (a) Imaging solar corona at 500 nm with an angular resolution of 5 arcsec over a FOV of 1.05Ro to 3Ro (Ro:Solar radius) (b) Simultaneous multi-slit spectroscopy at 530.3 nm [Fe XIV],789.2 nm [Fe XI] and 1074.7 nm [Fe XIII] with spectral dispersion of 28mA, 31mA and 202mA per pixel respectively, over a FOV of 1.05Ro to 1.5Ro. (c) Multi-slit dual beam spectro-polarimetry at 1074.7 nm. All the components of instrument have been optimized in view of the scientific objectives and requirements of space payloads. In this paper we present the details of optical configuration and the expected performance of the payload.

Electron-density-sensitive Line Ratios of Fe xiii– xvi from Laboratory Sources Compared to CHIANTI

Abstract We present electron-density-sensitive line ratios for Fe xiii– xvi measured in the spectral wavelength range of 200–440 Å and an electron density range of (1–4) × 1013 cm−3. The results provide a test at the high-density limit of density-sensitive line ratios useful for astrophysical studies. The measurements were performed on the National Spherical Torus Experiment-Upgrade, where electron densities were measured independently by the laser Thomson scattering diagnostic. Spectra were collected with a flat-field grazing-incidence spectrometer, which provided a spectral resolution of up to 0.3 Å, i.e., high resolution across the broad wavelength range. The response of the instrument was relatively calibrated using spectroscopic techniques in order to improve accuracy. The line ratios are compared to other laboratory sources and the latest version of CHIANTI (8.0.2), and an agreement within 30% is found.

Coronal magnetic field measurements using forbidden emission lines

AbstractThe polarization measurement of coronal forbidden emission lines is the most promising method of determining the direction of magnetic fields in the corona. A classical theory for the forbidden lines was presented in Megha et al. (2017) for the case of arbitrary strength magnetic fields. Here we apply that theoretical formalism to study the effect of density distributions, magnetic field configurations, and velocity fields on the Stokes profiles formed in corona. For illustrations we use the atomic parameters of the [Fe xiii] 10747 Å coronal forbidden line.

Using a New Infrared Si x Coronal Emission Line for Discriminating between Magnetohydrodynamic Models of the Solar Corona During the 2006 Solar Eclipse

Abstract During the 2006 March 29 total solar eclipse, coronal spectropolarimetric measurements were obtained over a 6 × 6 R ☉ field of view with a 1–2 μm spectral range. The data yielded linearly polarized measurements of the Fe xiii 1.075 μm, He i 1.083 μm, and for the first time, of the Si x 1.430 μm emission lines. To interpret the measurements, we used forward-integrated synthetic emission from two magnetohydrodynamic models for the same Carrington rotation with different heating functions and magnetic boundary conditions. Observations of the Fe xiii 1.075/Si x 1.430 line ratio allowed us to discriminate between two models of the corona, with the observations strongly favoring the warmer model. The observed polarized amplitudes for the Si x 1.430 μm line are around 7%, which is three times higher than the predicted values from available atomic models for the line. This discrepancy indicates a need for a closer look at some of the model assumptions for the collisional coefficients, as well as new polarized observations of the line to rule out any unknown systematic effect in the present data. All but two near-limb fibers show correlated bright He i 1.083 μm and H i 1.282 μm emission, which likely indicates cool prominence emission that is non-localized by the strongly defocused optics. One of the distant fibers located at 1.5 R ☉ detected a weak He i 1.083 μm intensity signal consistent with previous eclipse measurements around 3 × 10−7 B ☉ . However, given the limitations of these observations, it is not possible to completely remove contamination that is due to emission from prominence material that is not obscured by the lunar limb.

The Plasma Parameters and Geometry of Cool and Warm Active Region Loops

Abstract How the solar corona is heated to high temperatures remains an unsolved mystery in solar physics. In the present study we analyze observations of 50 whole active region loops taken with the Extreme-ultraviolet Imaging Spectrometer on board the Hinode satellite. Eleven loops were classified as cool loops (<1 MK) and 39 as warm loops (1–2 MK). We study their plasma parameters, such as densities, temperatures, filling factors, nonthermal velocities, and Doppler velocities. We combine spectroscopic analysis with linear force-free magnetic field extrapolation to derive the 3D structure and positioning of the loops, their lengths and heights, and the magnetic field strength along the loops. We use density-sensitive line pairs from Fe xii, Fe xiii, Si x, and Mg vii ions to obtain electron densities by taking special care of intensity background subtraction. The emission measure loci method is used to obtain the loop temperatures. We find that the loops are nearly isothermal along the line of sight. Their filling factors are between 8% and 89%. We also compare the observed parameters with the theoretical Rosner–Tucker–Vaiana (RTV) scaling law. We find that most of the loops are in an overpressure state relative to the RTV predictions. In a follow-up study, we will report a heating model of a parallel-cascade-based mechanism and will compare the model parameters with the loop plasma and structural parameters derived here.

Neon-like Iron Ion Lines Measured in NIFS/Large Helical Device (LHD) and Hinode/EUV Imaging Spectrometer (EIS)

Abstract Line intensities emerging from the Ne-sequence iron ion (Fe xvii) are measured in the laboratory, by the Large Helical Device at the National Institute for Fusion Science, and in the solar corona by the EUV Imaging Spectrometer (EIS) on board the Hinode mission. The intensity ratios of Fe xvii λ 204.6/λ 254.8 are derived in the laboratory by unblending the contributions of the Fe xiii and xii line intensities. They are consistent with theoretical predictions and solar observations, the latter of which endorses the in-flight radiometric calibrations of the EIS instrument. The still remaining temperature-dependent behavior of the line ratio suggests the contamination of lower-temperature iron lines that are blended with the λ 204.6 line.

Hanle-Zeeman Scattering Matrix for Magnetic Dipole Transitions

Abstract The polarization of the light that is scattered by the coronal ions is influenced by the anisotropic illumination from the photosphere and the magnetic field structuring in the solar corona. The properties of the coronal magnetic fields can be well studied by understanding the polarization properties of coronal forbidden emission lines that arise from magnetic dipole (M1) transitions in the highly ionized atoms that are present in the corona. We present the classical scattering theory of the forbidden lines for a more general case of arbitrary-strength magnetic fields. We derive the scattering matrix for M1 transitions using the classical magnetic dipole model of Casini & Lin and applying the scattering matrix approach of Stenflo. We consider a two-level atom model and neglect collisional effects. The scattering matrix so derived is used to study the Stokes profiles formed in coronal conditions in those regions where the radiative excitations dominate collisional excitations. To this end, we take into account the integration over a cone of an unpolarized radiation from the solar disk incident on the scattering atoms. Furthermore, we also integrate along the line of sight to calculate the emerging polarized line profiles. We consider radial and dipole magnetic field configurations and spherically symmetric density distributions. For our studies we adopt the atomic parameters corresponding to the [Fe xiii] 10747 Å coronal forbidden line. We also discuss the nature of the scattering matrix for M1 transitions and compare it with that for the electric dipole (E1) transitions.

Study on Precursor Activity of the X1.6 Flare in the Great AR 12192 with SDO, IRIS, and Hinode

Abstract The physical properties and their contribution to the onset of a solar flare are still uncleare even though chromospheric brightening is considered a precursor phenomenon of a flare. Many studies suggested that photospheric magnetic field changes cause destabilization of large-scale coronal structure. We aim to understand how a small photospheric change contributes to a flare and to reveal how the intermediary chromosphere behaves in the precursor phase. We analyzed the precursor brightening of the X1.6 flare on 2014 October 22 in the AR 12192 using the Interface Region Imaging Spectrograph (IRIS) and Hinode/EUV Imaging Spectrometer (EIS) data. We investigated a localized jet with the strong precursor brightening, and compared the intensity, Doppler velocity, and line width in C ii, Mg ii k, and Si iv lines by IRIS and He ii, Fe xii, and Fe xv lines by Hinode/EIS. We also analyzed the photospheric magnetic field and chromospheric/coronal structures using the Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager and Atmospheric Imaging Assembly. We found a significant blueshift (∼100 km s−1), which is related to the strong precursor brightening over a characteristic magnetic field structure, and the blueshift was observed at all of the temperatures. This might indicate that the flow is accelerated by Lorentz force. Moreover, the large-scale coronal loop that connects the foot points of the flare ribbons was destabilized just after the precursor brightening with the blueshift. It suggests that magnetic reconnection locally occurred in the lower chromosphere and it triggered magnetic reconnection of the X1.6 flare in the corona.

The Great Solar Active Region NOAA 12192: Helicity Transport, Filament Formation, and Impact on the Polar Field

Abstract The solar active region (AR), NOAA 12192, appeared in 2014 October as the largest AR in 24 years. Here we examine the counterintuitive nature of two diffusion-driven processes in the region: the role of helicity buildup in the formation of a major filament, and the relationship between the effects of supergranular diffusion and meridional flow on the AR and on the polar field. Quantitatively, calculations of current helicity and magnetic twist from Helioseismic and Magnetic Imager (HMI) vector magnetograms indicate that, though AR 12192 emerged with negative helicity, positive helicity from subsequent flux emergence, consistent with the hemispheric sign-preference of helicity, increased over time within large-scale, weak-field regions such as those near the polarity inversion line (PIL). Morphologically, Atmospheric Imaging Assembly observations of filament barbs, sigmoidal patterns, and bases of Fe xii stalks initially exhibited signatures of negative helicity, and the long filament that subsequently formed had a strong positive helicity consistent with the helicity buildup along the PIL. We find from full-disk HMI magnetograms that AR 12192's leading positive flux was initially closer to the equator but, owing either to the region’s magnetic surroundings or to its asymmetric flux density distribution, was transported poleward more quickly on average than its trailing negative flux, contrary to the canonical pattern of bipole flux transport. This behavior caused the AR to have a smaller effect on the polar fields than expected and enabled the formation of the very long neutral line where the filament formed.