Determination of Coronal Magnetic Fields from Vector Magnetograms

NASA Technical Reports Server (NTRS)

Mikic, Zoran

1997-01-01

During the course of the present contract we developed an 'evolutionary technique' for the determination of force-free coronal magnetic fields from vector magnetograph observations. The method can successfully generate nonlinear force- free fields (with non-constant-a) that match vector magnetograms. We demonstrated that it is possible to determine coronal magnetic fields from photospheric measurements, and we applied it to vector magnetograms of active regions. We have also studied theoretical models of coronal fields that lead to disruptions. Specifically, we have demonstrated that the determination of force-free fields from exact boundary data is a well-posed mathematical problem, by verifying that the computed coronal field agrees with an analytic force-free field when boundary data for the analytic field are used; demonstrated that it is possible to determine active-region coronal magnetic fields from photospheric measurements, by computing the coronal field above active region 5747 on 20 October 1989, AR6919 on 15 November 1991, and AR7260 on 18 August 1992, from data taken with the Stokes Polarimeter at Mees Solar Observatory, University of Hawaii; started to analyze active region 7201 on 19 June 1992 using measurements made with the Advanced Stokes Polarimeter at NSO/Sac Peak; investigated the effects of imperfections in the photospheric data on the computed coronal magnetic field; documented the coronal field structure of AR5747 and compared it to the morphology of footpoint emission in a flare, showing that the 'high- pressure' H-alpha footpoints are connected by coronal field lines; shown that the variation of magnetic field strength along current-carrying field lines is significantly different from the variation in a potential field, and that the resulting near-constant area of elementary flux tubes is consistent with observations; begun to develop realistic models of coronal fields which can be used to study flare trigger mechanisms; demonstrated that magnetic nonequilibrium can disrupt sheared coronal arcades, and that helmet streamers can disrupt, leading to coronal mass ejections. Our model has significantly extended the realism with which the coronal magnetic field can be inferred from actual observations. In a subsequent contract awarded by NASA, we have continued to apply and improve the evolutionary technique, to study the physical properties of active regions, and to develop theoretical models of magnetic fields.

Determination of coronal magnetic fields from vector magnetograms

NASA Technical Reports Server (NTRS)

Mikic, Zoran

1993-01-01

This report covers technical progress during the second year of the contract entitled 'Determination of Coronal Magnetic Fields from Vector Magnetograms,' NASW-4728, between NASA and Science Applications International Corporation, and covers the period January 1, 1993 to December 31, 1993. Under this contract SAIC has conducted research into the determination of coronal magnetic fields from vector magnetograms, including the development and application of algorithms to determine force-free coronal fields above selected observations of active regions. The contract began on June 30, 1992 and has a completion date of December 31, 1994. This contract is a continuation of work started in a previous contract, NASW-4571, which covered the period November 15, 1990 to December 14, 1991. During this second year we have concentrated on studying additional active regions and in using the estimated coronal magnetic fields to compare to coronal features inferred from observations.

PHYSICAL CONDITIONS OF CORONAL PLASMA AT THE TRANSIT OF A SHOCK DRIVEN BY A CORONAL MASS EJECTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Susino, R.; Bemporad, A.; Mancuso, S., E-mail: susino@oato.inaf.it

2015-10-20

We report here on the determination of plasma physical parameters across a shock driven by a coronal mass ejection using white light (WL) coronagraphic images and radio dynamic spectra (RDS). The event analyzed here is the spectacular eruption that occurred on 2011 June 7, a fast CME followed by the ejection of columns of chromospheric plasma, part of them falling back to the solar surface, associated with a M2.5 flare and a type-II radio burst. Images acquired by the Solar and Heliospheric Observatory/LASCO coronagraphs (C2 and C3) were employed to track the CME-driven shock in the corona between 2–12 R{submore » ⊙} in an angular interval of about 110°. In this interval we derived two-dimensional (2D) maps of electron density, shock velocity, and shock compression ratio, and we measured the shock inclination angle with respect to the radial direction. Under plausible assumptions, these quantities were used to infer 2D maps of shock Mach number M{sub A} and strength of coronal magnetic fields at the shock's heights. We found that in the early phases (2–4 R{sub ⊙}) the whole shock surface is super-Alfvénic, while later on (i.e., higher up) it becomes super-Alfvénic only at the nose. This is in agreement with the location for the source of the observed type-II burst, as inferred from RDS combined with the shock kinematic and coronal densities derived from WL. For the first time, a coronal shock is used to derive a 2D map of the coronal magnetic field strength over intervals of 10 R{sub ⊙} altitude and ∼110° latitude.« less

Higher-speed coronal mass ejections and their geoeffectiveness

NASA Astrophysics Data System (ADS)

Singh, A. K.; Bhargawa, Asheesh; Tonk, Apeksha

2018-06-01

We have attempted to examine the ability of coronal mass ejections to cause geoeffectiveness. To that end, we have investigated total 571 cases of higher-speed (> 1000 km/s) coronal mass ejection events observed during the years 1996-2012. On the basis of angular width (W) of observance, events of coronal mass ejection were further classified as front-side or halo coronal mass ejections (W = 360°); back-side halo coronal mass ejections (W = 360°); partial halo (120°< W < 360°) and non-halo (W < 120°). From further analysis, we found that front halo coronal mass ejections were much faster and more geoeffective in comparison of partial halo and non-halo coronal mass ejections. We also inferred that the front-sided halo coronal mass ejections were 67.1% geoeffective while geoeffectiveness of partial halo coronal mass ejections and non-halo coronal mass ejections were found to be 44.2% and 56.6% respectively. During the same period of observation, 43% of back-sided CMEs showed geoeffectiveness. We have also investigated some events of coronal mass ejections having speed > 2500 km/s as a case study. We have concluded that mere speed of coronal mass ejection and their association with solar flares or solar activity were not mere criterion for producing geoeffectiveness but angular width of coronal mass ejections and their originating position also played a key role.

Slowly moving disturbances in the X-ray corona

NASA Technical Reports Server (NTRS)

Rust, D. M.; Svestka, Z.

1979-01-01

Sequences of soft X-ray pictures, taken aboard Skylab between May and November, 1973, have made it possible to detect slowly moving disturbances originating in disrupted filaments and causing subsequent brightenings of distant coronal structures. With speeds decreasing from approximately 400 km/sec shortly after the filament disruption to approximately 10 km/sec four or five hours later, these disturbances appear to be identical with slow waves earlier inferred by Bruzel (1952, 1969), Oehman (1953), and Yajima (1971) from chromospheric observations.

Critical Magnetic Field Strengths for Unipolar Solar Coronal Plumes in Quiet Regions and Coronal Holes?

NASA Astrophysics Data System (ADS)

Avallone, E. A.; Tiwari, S. K.; Panesar, N. K.; Moore, R. L.

2017-12-01

Coronal plumes are sporadic fountain-like structures that are bright in coronal emission. Each is a magnetic funnel rooted in a strong patch of dominant-polarity photospheric magnetic flux surrounded by a predominantly-unipolar magnetic network, either in a quiet region or a coronal hole. The heating processes that make plumes bright evidently involve the magnetic field in the base of the plume, but remain mysterious. Raouafi et al. (2014) inferred from observations that plume heating is a consequence of magnetic reconnection in the base, whereas Wang et al. (2016) showed that plume heating turns on/off from convection-driven convergence/divergence of the base flux. While both papers suggest that the base magnetic flux in their plumes is of mixed polarity, these papers provide no measurements of the abundance and strength of the evolving base flux or consider whether a critical magnetic field strength is required for a plume to become noticeably bright. To address plume production and evolution, we track the plume luminosity and the abundance and strength of the base magnetic flux over the lifetimes of six coronal plumes, using Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) 171 Å images and SDO/Helioseismic and Magnetic Imager (HMI) line-of-sight magnetograms. Three of these plumes are in coronal holes, three are in quiet regions, and each plume exhibits a unipolar base flux. We track the base magnetic flux over each plume's lifetime to affirm that its convergence and divergence respectively coincide with the appearance and disappearance of the plume in 171 Å images. We tentatively find that plume formation requires enough convergence of the base flux to surpass a field strength of ˜300-500 Gauss, and that quiet Sun and coronal-hole plumes both exhibit the same behavior in the response of their luminosity in 171 Å to the strength of the magnetic field in the base.

Coronal and Prominence Plasmas

NASA Technical Reports Server (NTRS)

Poland, Arthur I. (Editor)

1986-01-01

Various aspects of solar prominences and the solar corona are discussed. The formation of prominences, prominence diagnostics and structure, prominence dissappearance, large scale coronal structure, coronal diagnostics, small scale coronal structure, and non-equilibrium/coronal heating are among the topics covered.

A Two-Fluid, MHD Coronal Model

NASA Technical Reports Server (NTRS)

Suess, Steven T.; Wang, A.-H.; Wu, S. T.; Poletto, G.; McComas, D. J.

1998-01-01

We describe first results from a numerical two-fluid MHD model of the global structure of the solar corona. The model is two-fluid in the sense that it accounts for the collisional energy exchange between protons and electrons. As in our single-fluid model, volumetric heat and momentum sources are required to produce high speed wind from coronal holes, low speed wind above streamers, and mass fluxes similar to the empirical solar wind. By specifying different proton and electron heating functions we obtain a high proton temperature in the coronal hole and a relatively low proton temperature in the streamer (in comparison with the electron temperature). This is consistent with inferences from SOHO/UVCS, and with the Ulysses/SWOOPS proton and electron temperature measurements which we show from the fast latitude scan. The density in the coronal hole between 2 solar radii and 5 solar radii (2RS and 5RS) is similar to the density reported from SPARTAN 201-01 measurements by Fisher and Guhathakurta. The proton mass flux scaled to 1 AU is 2.4 x 10(exp 8)/sq cm s, which is consistent with Ulysses observations. Inside the closed field region, the density is sufficiently high so that the simulation gives equal proton and electron temperatures due to the high collision rate. In open field regions (in the coronal hole and above the streamer) the proton and electron temperatures differ by varying amounts. In the streamer, the temperature and density are similar to those reported empirically by Li et al and the plasma beta is larger than unity everywhere above approx. 1.5 R(sub s), as it is in all other MHD coronal streamer models.

An Alternative Interpretation of the Relationship between the Inferred Open Solar Flux and the Interplanetary Magnetic Field

NASA Technical Reports Server (NTRS)

Riley, Pete

2007-01-01

Photospheric observations at the Wilcox Solar Observatory (WSO) represent an uninterrupted data set of 32 years and are therefore unique for modeling variations in the magnetic structure of the corona and inner heliosphere over three solar cycles. For many years, modelers have applied a latitudinal correction factor to these data, believing that it provided a better estimate of the line-of-sight magnetic field. Its application was defended by arguing that the computed open flux matched observations of the interplanetary magnetic field (IMF) significantly better than the original WSO correction factor. However, no physically based argument could be made for its use. In this Letter we explore the implications of using the constant correction factor on the value and variation of the computed open solar flux and its relationship to the measured IMF. We find that it does not match the measured IMF at 1 AU except at and surrounding solar minimum. However, we argue that interplanetary coronal mass ejections (ICMEs) may provide sufficient additional magnetic flux to the extent that a remarkably good match is found between the sum of the computed open flux and inferred ICME flux and the measured flux at 1 AU. If further substantiated, the implications of this interpretation may be significant, including a better understanding of the structure and strength of the coronal field and I N providing constraints for theories of field line transport in the corona, the modulation of galactic cosmic rays, and even possibly terrestrial climate effects.

Large-Scale Coronal Heating from "Cool" Activity in the Solar Magnetic Network

NASA Technical Reports Server (NTRS)

Falconer, D. A.; Moore, R. L.; Porter, J. G.; Hathaway, D. H.

1999-01-01

In Fe XII images from SOHO/EIT, the quiet solar corona shows structure on scales ranging from sub-supergranular (i.e., bright points and coronal network) to multi-supergranular (large-scale corona). In Falconer et al 1998 (Ap.J., 501, 386) we suppressed the large-scale background and found that the network-scale features are predominantly rooted in the magnetic network lanes at the boundaries of the supergranules. Taken together, the coronal network emission and bright point emission are only about 5% of the entire quiet solar coronal Fe XII emission. Here we investigate the relationship between the large-scale corona and the network as seen in three different EIT filters (He II, Fe IX-X, and Fe XII). Using the median-brightness contour, we divide the large-scale Fe XII corona into dim and bright halves, and find that the bright-half/dim half brightness ratio is about 1.5. We also find that the bright half relative to the dim half has 10 times greater total bright point Fe XII emission, 3 times greater Fe XII network emission, 2 times greater Fe IX-X network emission, 1.3 times greater He II network emission, and has 1.5 times more magnetic flux. Also, the cooler network (He II) radiates an order of magnitude more energy than the hotter coronal network (Fe IX-X, and Fe XII). From these results we infer that: 1) The heating of the network and the heating of the large-scale corona each increase roughly linearly with the underlying magnetic flux. 2) The production of network coronal bright points and heating of the coronal network each increase nonlinearly with the magnetic flux. 3) The heating of the large-scale corona is driven by widespread cooler network activity rather than by the exceptional network activity that produces the network coronal bright points and the coronal network. 4) The large-scale corona is heated by a nonthermal process since the driver of its heating is cooler than it is. This work was funded by the Solar Physics Branch of NASA's office of Space Science through the SR&T Program and the SEC Guest Investigator Program.

A STEREO Survey of Magnetic Cloud Coronal Mass Ejections Observed at Earth in 2008–2012

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wood, Brian E.; Wu, Chin-Chun; Howard, Russell A.

We identify coronal mass ejections (CMEs) associated with magnetic clouds (MCs) observed near Earth by the Wind spacecraft from 2008 to mid-2012, a time period when the two STEREO spacecraft were well positioned to study Earth-directed CMEs. We find 31 out of 48 Wind MCs during this period can be clearly connected with a CME that is trackable in STEREO imagery all the way from the Sun to near 1 au. For these events, we perform full 3D reconstructions of the CME structure and kinematics, assuming a flux rope (FR) morphology for the CME shape, considering the full complement ofmore » STEREO and SOHO imaging constraints. We find that the FR orientations and sizes inferred from imaging are not well correlated with MC orientations and sizes inferred from the Wind data. However, velocities within the MC region are reproduced reasonably well by the image-based reconstruction. Our kinematic measurements are used to provide simple prescriptions for predicting CME arrival times at Earth, provided for a range of distances from the Sun where CME velocity measurements might be made. Finally, we discuss the differences in the morphology and kinematics of CME FRs associated with different surface phenomena (flares, filament eruptions, or no surface activity).« less

Large-scale solar magnetic fields and H-alpha patterns

NASA Technical Reports Server (NTRS)

Mcintosh, P. S.

1972-01-01

Coronal and interplanetary magnetic fields computed from measurements of large-scale photospheric magnetic fields suffer from interruptions in day-to-day observations and the limitation of using only measurements made near the solar central meridian. Procedures were devised for inferring the lines of polarity reversal from H-alpha solar patrol photographs that map the same large-scale features found on Mt. Wilson magnetograms. These features may be monitored without interruption by combining observations from the global network of observatories associated with NOAA's Space Environment Services Center. The patterns of inferred magnetic fields may be followed accurately as far as 60 deg from central meridian. Such patterns will be used to improve predictions of coronal features during the next solar eclipse.

IS FLUX ROPE A NECESSARY CONDITION FOR THE PROGENITOR OF CORONAL MASS EJECTIONS?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ouyang, Y.; Yang, K.; Chen, P. F., E-mail: chenpf@nju.edu.cn

2015-12-10

A magnetic flux rope structure is believed to exist in most coronal mass ejections (CMEs). However, it has been long debated whether the flux rope exists before eruption or if it is formed during eruption via magnetic reconnection. The controversy has continued because of our lack of routine measurements of the magnetic field in the pre-eruption structure, such as solar filaments. However, recently an indirect method was proposed to infer the magnetic field configuration based on the sign of helicity and the bearing direction of the filament barbs. In this paper, we apply this method to two erupting filament events, one onmore » 2014 September 2 and the other on 2011 March 7, and find that the first filament is supported by a magnetic flux rope and the second filament is supported by a sheared arcade, i.e., the first one is an inverse-polarity filament and the second one is a normal-polarity filament. With the identification of the magnetic configurations in these two filaments, we stress that a flux rope is not a necessary condition for the pre-CME structure.« less

Coronal loop seismology using damping of standing kink oscillations by mode coupling. II. additional physical effects and Bayesian analysis

NASA Astrophysics Data System (ADS)

Pascoe, D. J.; Anfinogentov, S.; Nisticò, G.; Goddard, C. R.; Nakariakov, V. M.

2017-04-01

Context. The strong damping of kink oscillations of coronal loops can be explained by mode coupling. The damping envelope depends on the transverse density profile of the loop. Observational measurements of the damping envelope have been used to determine the transverse loop structure which is important for understanding other physical processes such as heating. Aims: The general damping envelope describing the mode coupling of kink waves consists of a Gaussian damping regime followed by an exponential damping regime. Recent observational detection of these damping regimes has been employed as a seismological tool. We extend the description of the damping behaviour to account for additional physical effects, namely a time-dependent period of oscillation, the presence of additional longitudinal harmonics, and the decayless regime of standing kink oscillations. Methods: We examine four examples of standing kink oscillations observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). We use forward modelling of the loop position and investigate the dependence on the model parameters using Bayesian inference and Markov chain Monte Carlo (MCMC) sampling. Results: Our improvements to the physical model combined with the use of Bayesian inference and MCMC produce improved estimates of model parameters and their uncertainties. Calculation of the Bayes factor also allows us to compare the suitability of different physical models. We also use a new method based on spline interpolation of the zeroes of the oscillation to accurately describe the background trend of the oscillating loop. Conclusions: This powerful and robust method allows for accurate seismology of coronal loops, in particular the transverse density profile, and potentially reveals additional physical effects.

Alfven Waves in the Solar Corona

NASA Astrophysics Data System (ADS)

Tomczyk, S.; McIntosh, S. W.; Keil, S. L.; Judge, P. G.; Schad, T.; Seeley, D. H.; Edmondson, J.

2007-12-01

We present observations of the coronal intensity, line-of-sight velocity, and linear polarization obtained in the FeXIII 1074.7 nm coronal emission line with the Coronal Multi-channel Polarimeter (CoMP) instrument. Analysis of these observations reveal ubiquitous upward propagating waves with phase speeds of 1-4 Mm/s and trajectories consistent with the direction of the magnetic field inferred from the linear polarization measurements. We can definitively identify these as Alfvén waves. An estimate of the energy carried by the waves that we spatially resolve indicates that they are unable to heat the solar corona, however, unresolved waves may carry sufficient energy.

Coronal Heating, Spicules, and Solar-B

NASA Technical Reports Server (NTRS)

Moore, Ron; Falconer, David; Porter, Jason; Hathaway, David; Yamauchi, Yohei

2003-01-01

Falconer et al. investigated the heating of the quiet corona by measuring the increase of coronal luminosity with the amount of the magnetic flux in the underlying network at solar minimum when there were no active regions on the face of the Sun. The coronal luminosity was measured from Fe IX/X - Fe XII pairs of coronal images from SOHO/EIT, under the assumption that practically all of the coronal luminosity in these very quiet regions came from plasma in the temperature range 0.9 x 10(exp 6) K is less than or equal to T is less than or equal to 1.3 x 10(exp 6) K. The network magnetic flux content was measured from SOHO/MDI magnetograms. It was found that luminosity of the corona in these quiet regions increased roughly in proportion to the square root of the magnetic flux content of the network and roughly in proportion to the length of the perimeter of the network flux clumps. From 1) this result; 2) the observed occurrence of many fine-scale explosive events (e.g., spicules) at the edges of network flux clumps; and 3) a demonstration that it is energetically feasible for the heating of the corona in quiet regions to be driven by explosions of granule-sized sheared-core magnetic bipoles embedded in the edges of the network flux clumps, Falconer et al. infer that in quiet regions that are not influenced by active regions the corona is mainly heated by such magnetic activity in the edges of the network flux clumps. From their observational results together with their feasibility analysis, Falconer et al. predict that 1) At the edges of the network flux clumps there are many transient sheared core bipoles of the size and lifetime of granules and having transverse field strengths greater than approx. 100 G; 2) Approx. 30 of these bipoles are present per supergranule; and 3) Most spicules are produced by explosions of these bipoles. The photospheric vector magnetograms, chromospheric filtergrams, and EUV spectra from Solar-B are expected to have sufficient sensitivity, spatial resolution, and cadence to test these predictions. The Falconer et al. (2003) inferred mixed-polarity magnetic flux at the base of spicules is compatible with the observed magnetic structure of Ha macrospicules recently found by Yamuchi et al. (2003).

Characteristics of the Time Variable Component of the Coronal Heating Process

NASA Technical Reports Server (NTRS)

Habbal, Shadia R.; Poland, Art (Technical Monitor)

2001-01-01

The goal of the proposed study was to explore the non-steady nature of the coronal heating processes and its manifestations in the inner corona and interplanetary space by coordinating coronal SOHO observations in white light, ultraviolet, and extreme ultraviolet, with complementary radio occultation measurements during an unprecedented and rare coincidence of a total solar eclipse with the superior conjunction of a planetary spacecraft, Galileo, in February 1998. In addition, radio occultation measurements by the Mars Global Surveyor spacecraft in May 1998 spanned the inner heliosphere observed by coronal SOHO instruments and probing it to within 0.5 R(sub S), above the solar surface. Inferences of physical properties derived from these simultaneous observations were subsequently used in solar wind model computations to yield the range of plasma parameters characteristic of the fast and slow solar wind.

Determining the Evolution and Propagation of CME Flux Ropes from the Sun to Earth

NASA Astrophysics Data System (ADS)

Palmerio, E.; Kilpua, E.; Mierla, M.; Rodriguez, L.; Isavnin, A.; Zhukov, A.

2017-12-01

Coronal mass ejections (CMEs) are the main drivers of space weather phenomena at the Earth. They form in the solar atmosphere as helical magnetic field structures known as flux ropes. The key parameter that defines the ability of a CME to drive geomagnetic storms is the North-South magnetic field component. One of the most significant problems in current long-term space weather forecasts is that there is no practical method to measure the magnetic structure of CMEs routinely in the corona. The magnetic structure of erupting flux ropes can however be inferred based on the properties of the CME's source region characteristics, e.g.filament details, coronal EUV arcades, X-ray/EUV sigmoids, taking into account nearby coronal and photospheric features. These proxies are useful for reconstructing the "instrinsic flux rope type" at the time of the eruption. However, the knowledge of the flux rope's magnetic structure at the Sun does not always imply a successful prediction of the magnetic structure at the Earth. This is because CMEs can change their orientation due to deflections, rotations, and deformations. We present here examples of CMEs for which we have determined their magnetic structure when launched from the Sun by using a synthesis of indirect proxies based on multiwavelength remote-sensing observations. When compared to their in situ counterparts, these CMEs present a different magnetic configuration, implying a high amount of rotation of their central axis during their propagation. We study the early evolution of these CMEs both on the solar disk and in coronagraph images though different techniques, e.g. forward modelling and tie-pointing technique. When possible, we study the CME structure in situ at other planets. We aim at determining where the rotation occurs and the rate of rotation during the CME evolution from the Sun to Earth, and possibly estimating the causes of such a high amount of rotation.

Automated Coronal Loop Identification using Digital Image Processing Techniques

NASA Astrophysics Data System (ADS)

Lee, J. K.; Gary, G. A.; Newman, T. S.

2003-05-01

The results of a Master's thesis study of computer algorithms for automatic extraction and identification (i.e., collectively, "detection") of optically-thin, 3-dimensional, (solar) coronal-loop center "lines" from extreme ultraviolet and X-ray 2-dimensional images will be presented. The center lines, which can be considered to be splines, are proxies of magnetic field lines. Detecting the loops is challenging because there are no unique shapes, the loop edges are often indistinct, and because photon and detector noise heavily influence the images. Three techniques for detecting the projected magnetic field lines have been considered and will be described in the presentation. The three techniques used are (i) linear feature recognition of local patterns (related to the inertia-tensor concept), (ii) parametric space inferences via the Hough transform, and (iii) topological adaptive contours (snakes) that constrain curvature and continuity. Since coronal loop topology is dominated by the magnetic field structure, a first-order magnetic field approximation using multiple dipoles provides a priori information that has also been incorporated into the detection process. Synthesized images have been generated to benchmark the suitability of the three techniques, and the performance of the three techniques on both synthesized and solar images will be presented and numerically evaluated in the presentation. The process of automatic detection of coronal loops is important in the reconstruction of the coronal magnetic field where the derived magnetic field lines provide a boundary condition for magnetic models ( cf. , Gary (2001, Solar Phys., 203, 71) and Wiegelmann & Neukirch (2002, Solar Phys., 208, 233)). . This work was supported by NASA's Office of Space Science - Solar and Heliospheric Physics Supporting Research and Technology Program.

TRANSITION-REGION/CORONAL SIGNATURES AND MAGNETIC SETTING OF SUNSPOT PENUMBRAL JETS: HINODE (SOT/FG), Hi-C, AND SDO/AIA OBSERVATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tiwari, Sanjiv K.; Moore, Ronald L.; Winebarger, Amy R.

2016-01-10

Penumbral microjets (PJs) are transient narrow bright features in the chromosphere of sunspot penumbrae, first characterized by Katsukawa et al. using the Ca ii H-line filter on Hinode's Solar Optical Telescope (SOT). It was proposed that the PJs form as a result of reconnection between two magnetic components of penumbrae (spines and interspines), and that they could contribute to the transition region (TR) and coronal heating above sunspot penumbrae. We propose a modified picture of formation of PJs based on recent results on the internal structure of sunspot penumbral filaments. Using data of a sunspot from Hinode/SOT, High Resolution Coronalmore » Imager, and different passbands of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, we examine whether PJs have signatures in the TR and corona. We find hardly any discernible signature of normal PJs in any AIA passbands, except for a few of them showing up in the 1600 Å images. However, we discovered exceptionally stronger jets with similar lifetimes but bigger sizes (up to 600 km wide) occurring repeatedly in a few locations in the penumbra, where evidence of patches of opposite-polarity fields in the tails of some penumbral filaments is seen in Stokes-V images. These tail PJs do display signatures in the TR. Whether they have any coronal-temperature plasma is unclear. We infer that none of the PJs, including the tail PJs, directly heat the corona in active regions significantly, but any penumbral jet might drive some coronal heating indirectly via the generation of Alfvén waves and/or braiding of the coronal field.« less

North-South Asymmetry in the Magnetic Deflection of Polar Coronal Jets

NASA Astrophysics Data System (ADS)

Nisticò, Giuseppe; Zimbardo, Gaetano; Bothmer, Volker; Patsourakos, Spiros

Solar jets observed with the Extreme Ultra-Violet Imager (EUVI) and CORonagraphs (COR) instruments aboard the STEREO mission provide a tool to probe and understand the magnetic structure of the corona. Since the corona is an environment where the magnetic pressure is greater than the kinetic pressure, the magnetic field controls the dynamics of plasma and, on average, jets during their propagation trace the magnetic field lines. We discuss the North-South asymmetry of the magnetic field of the Sun as inferred from measurements of the deflection of polar coronal hole jets when they propagate throughout the corona. We measured the position angle at 1 and at 2 solar radii for the 79 jets of the catalogue of Nisticò et al. (2009), based on the STEREO ultraviolet and visible observations, and we found that the propagation is not radial. The average jet deflection is studied both in the plane perpendicular to the line of sight, and, for a reduced number of jets in the three dimensional (3D) space. We find that the magnetic deflection of jets is larger in the North than in the South, with an asymmetry which is consistent with the N-S asymmetry of the heliospheric magnetic field inferred from the Ulysses in situ measurements, and gives clues to the study of the large scale solar magnetic field.

Coronal magnetic structure and the latitude and longitude distribution of energetic particles, 1-5 AU

NASA Technical Reports Server (NTRS)

Roelof, E. C.; Mitchell, D. G.

1979-01-01

The relation of the coronal magnetic field structure to the distribution of approximately 1 MeV protons in interplanetary space between 1 and 5 AU is discussed. After ordering the interplanetary data by its estimated coronal emission source location in heliographic coordinates, the multispacecraft measured proton fluxes are compared with coronal magnetic field structure infrared as observed in soft X-ray photographs and potential field calculations. Evidence for the propagation and possible acceleration of solar flare protons on high magnetic loop structure in the corona is presented. Further, it is shown that corotating proton flux enhancements are associated with regions of low coronal X-ray emission (including coronal holes), usually in association with solar wind stream structure.

Mapping the Solar Wind from its Source Region into the Outer Corona

NASA Technical Reports Server (NTRS)

Esser, Ruth

1998-01-01

Knowledge of the radial variation of the plasma conditions in the coronal source region of the solar wind is essential to exploring coronal heating and solar wind acceleration mechanisms. The goal of the present proposal is to determine as many plasma parameters in that region as possible by coordinating different observational techniques, such as Interplanetary Scintillation Observations, spectral line intensity observations, polarization brightness measurements and X-ray observations. The inferred plasma parameters are then used to constrain solar wind models.

Dispersive Evolution of Nonlinear Fast Magnetoacoustic Wave Trains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pascoe, D. J.; Goddard, C. R.; Nakariakov, V. M., E-mail: D.J.Pascoe@warwick.ac.uk

2017-10-01

Quasi-periodic rapidly propagating wave trains are frequently observed in extreme ultraviolet observations of the solar corona, or are inferred by the quasi-periodic modulation of radio emission. The dispersive nature of fast magnetohydrodynamic waves in coronal structures provides a robust mechanism to explain the detected quasi-periodic patterns. We perform 2D numerical simulations of impulsively generated wave trains in coronal plasma slabs and investigate how the behavior of the trapped and leaky components depend on the properties of the initial perturbation. For large amplitude compressive perturbations, the geometrical dispersion associated with the waveguide suppresses the nonlinear steepening for the trapped wave train.more » The wave train formed by the leaky components does not experience dispersion once it leaves the waveguide and so can steepen and form shocks. The mechanism we consider can lead to the formation of multiple shock fronts by a single, large amplitude, impulsive event and so can account for quasi-periodic features observed in radio spectra.« less

A Two-Fluid, MHD Coronal Model

NASA Technical Reports Server (NTRS)

Suess, S. T.; Wang, A.-H.; Wu, S. T.; Poletto, G.; McComas, D. J.

1999-01-01

We describe first results from a numerical two-fluid MHD model of the global structure of the solar Corona. The model is two-fluid in the sense that it accounts for the collisional energy exchange between protons and electrons. As in our single-fluid model, volumetric heat and Momentum sources are required to produce high speed wind from Corona] holes, low speed wind above streamers, and mass fluxes similar to the empirical solar wind. By specifying different proton and electron heating functions we obtain a high proton temperature in the coronal hole and a relatively low proton temperature above the streamer (in comparison with the electron temperature). This is consistent with inferences from SOHO/UltraViolet Coronagraph Spectrometer instrument (UVCS), and with the Ulysses/Solar Wind Observations Over the Poles of the Sun instrument (SWOOPS) proton and electron temperature measurements which we show from the fast latitude scan. The density in the coronal hole between 2 and 5 solar radii (2 and 5 R(sub S)) is similar to the density reported from SPARTAN 201.-01 measurements by Fisher and Guhathakurta [19941. The proton mass flux scaled to 1 AU is 2.4 x 10(exp 8)/sq cm s, which is consistent with Ulysses observations. Inside the closed field region, the density is sufficiently high so that the simulation gives equal proton and electron temperatures due to the high collision rate. In open field regions (in the coronal hole and above the streamer) the proton and electron temperatures differ by varying amounts. In the streamer the temperature and density are similar to those reported empirically by Li et al. [1998], and the plasma beta is larger than unity everywhere above approx. 1.5 R(sub S), as it is in all other MHD coronal streamer models [e.g., Steinolfson et al., 1982; also G. A. Gary and D. Alexander, Constructing the coronal magnetic field, submitted to Solar Physics, 1998].

Near-Sun and 1 AU magnetic field of coronal mass ejections: a parametric study

NASA Astrophysics Data System (ADS)

Patsourakos, S.; Georgoulis, M. K.

2016-11-01

Aims: The magnetic field of coronal mass ejections (CMEs) determines their structure, evolution, and energetics, as well as their geoeffectiveness. However, we currently lack routine diagnostics of the near-Sun CME magnetic field, which is crucial for determining the subsequent evolution of CMEs. Methods: We recently presented a method to infer the near-Sun magnetic field magnitude of CMEs and then extrapolate it to 1 AU. This method uses relatively easy to deduce observational estimates of the magnetic helicity in CME-source regions along with geometrical CME fits enabled by coronagraph observations. We hereby perform a parametric study of this method aiming to assess its robustness. We use statistics of active region (AR) helicities and CME geometrical parameters to determine a matrix of plausible near-Sun CME magnetic field magnitudes. In addition, we extrapolate this matrix to 1 AU and determine the anticipated range of CME magnetic fields at 1 AU representing the radial falloff of the magnetic field in the CME out to interplanetary (IP) space by a power law with index αB. Results: The resulting distribution of the near-Sun (at 10 R⊙) CME magnetic fields varies in the range [0.004, 0.02] G, comparable to, or higher than, a few existing observational inferences of the magnetic field in the quiescent corona at the same distance. We also find that a theoretically and observationally motivated range exists around αB = -1.6 ± 0.2, thereby leading to a ballpark agreement between our estimates and observationally inferred field magnitudes of magnetic clouds (MCs) at L1. Conclusions: In a statistical sense, our method provides results that are consistent with observations.

On the structure of solar and stellar coronae - Loops and loop heat transport

NASA Technical Reports Server (NTRS)

Litwin, Christof; Rosner, Robert

1993-01-01

We discuss the principal constraints on mechanisms for structuring and heating the outer atmospheres - the coronae - of stars. We argue that the essential cause of highly localized heating in the coronae of stars like the sun is the spatially intermittent nature of stellar surface magnetic fields, and that the spatial scale of the resulting coronal structures is related to the spatial structure of the photospheric fields. We show that significant constraints on coronal heating mechanisms derive from the observed variations in coronal emission, and, in addition, show that the observed structuring perpendicular to coronal magnetic fields imposes severe constraints on mechanisms for heat dispersal in the low-beta atmosphere. In particular, we find that most of commonly considered mechanisms for heat dispersal, such as anomalous diffusion due to plasma turbulence or magnetic field line stochasticity, are much too slow to account for the observed rapid heating of coronal loops. The most plausible mechanism appears to be reconnection at the interface between two adjacent coronal flux bundles. Based on a model invoking hyperresistivity, we show that such a mechanism naturally leads to dominance of isolated single bright coronal loops and to bright coronal plasma structures whose spatial scale transverse to the local magnetic field is comparable to observed dimensions of coronal X-ray loops.

Mapping the Solar Wind from its Source Region into the Outer Corona

NASA Technical Reports Server (NTRS)

Esser, Ruth

1997-01-01

Knowledge of the radial variation of the plasma conditions in the coronal source region of the solar wind is essential to exploring coronal heating and solar wind acceleration mechanisms. The goal of the proposal was to determine as many plasma parameters in the solar wind acceleration region and beyond as possible by coordinating different observational techniques, such as Interplanetary Scintillation Observations, spectral line intensity observations, polarization brightness measurements and X-ray observations. The inferred plasma parameters were then used to constrain solar wind models.

Heliocentric Distance of Coronal Mass Ejections at the Time of Energetic Particle Release: Revisiting the Ground Level Enhancement Events of Solar Cycle 23

NASA Technical Reports Server (NTRS)

Gopalswamy, Natchimuthuk

2011-01-01

Using the kinematics of coronal mass ejections (CMEs), onset time of soft X-ray flares, and the finite size of the pre-eruption CME structure, we derive the heliocentric distane at which the energetic particles during the ground level enhancement (GLE) events of Solar Cycle 23. We find that the GLE particles are released when the CMEs reach an average heliocentric distance of approx.3.25 solar radii (Rs). From this we infer that the shocks accelerating the particles are located at similar heights. Type II radio burst observations indicate that the CMEs are at much lower distances (average approx.1.4 Rs) when the CME-driven shock first forms. The shock seems to travel approx.1.8 Rs over a period of approox.30 min on the average before releasing the GLE particles. In deriving these results, we made three assumptions that have observational support: (i) the CME lift off occurs from an initial distance of about 1.25 Rs; (ii) the flare onset and CME onset are one and the same because these are two different manifestations of the same eruption; and (iii) the CME has positive acceleration from the onset to the first appearance in the coronagraphic field of view (2.5 to 6 Rs). Observations of coronal cavities in eclipse pictures and in coronagraphic images justify the assumption (i). The close relationship between the flare reconnection magnetic flux and the azimuthal flux of interplanetary magnetic clouds justify assumption (ii) consistent with the standard model (CSHKP) of solar eruption. Coronagraphic observations made close to the solar surface indicate a large positive acceleration of CMEs to a heliocentric distance of approx.3 Rs before they start slowing down due to the drag force. The inferred acceleration (approx.1.5 km/s/s) is consistent with reported values in the literature.

Using coronal seismology to estimate the magnetic field strength in a realistic coronal model

NASA Astrophysics Data System (ADS)

Chen, F.; Peter, H.

2015-09-01

Aims: Coronal seismology is used extensively to estimate properties of the corona, e.g. the coronal magnetic field strength is derived from oscillations observed in coronal loops. We present a three-dimensional coronal simulation, including a realistic energy balance in which we observe oscillations of a loop in synthesised coronal emission. We use these results to test the inversions based on coronal seismology. Methods: From the simulation of the corona above an active region, we synthesise extreme ultraviolet emission from the model corona. From this, we derive maps of line intensity and Doppler shift providing synthetic data in the same format as obtained from observations. We fit the (Doppler) oscillation of the loop in the same fashion as done for observations to derive the oscillation period and damping time. Results: The loop oscillation seen in our model is similar to imaging and spectroscopic observations of the Sun. The velocity disturbance of the kink oscillation shows an oscillation period of 52.5 s and a damping time of 125 s, which are both consistent with the ranges of periods and damping times found in observations. Using standard coronal seismology techniques, we find an average magnetic field strength of Bkink = 79 G for our loop in the simulation, while in the loop the field strength drops from roughly 300 G at the coronal base to 50 G at the apex. Using the data from our simulation, we can infer what the average magnetic field derived from coronal seismology actually means. It is close to the magnetic field strength in a constant cross-section flux tube, which would give the same wave travel time through the loop. Conclusions: Our model produced a realistic looking loop-dominated corona, and provides realistic information on the oscillation properties that can be used to calibrate and better understand the result from coronal seismology. A movie associated with Fig. 1 is available in electronic form at http://www.aanda.org

A Universal Model for Solar Eruptions

NASA Astrophysics Data System (ADS)

Wyper, Peter; Antiochos, Spiro K.; DeVore, C. Richard

2017-08-01

We present a universal model for solar eruptions that encompasses coronal mass ejections (CMEs) at one end of the scale, to coronal jets at the other. The model is a natural extension of the Magnetic Breakout model for large-scale fast CMEs. Using high-resolution adaptive mesh MHD simulations conducted with the ARMS code, we show that so-called blowout or mini-filament coronal jets can be explained as one realisation of the breakout process. We also demonstrate the robustness of this “breakout-jet” model by studying three realisations in simulations with different ambient field inclinations. We conclude that magnetic breakout supports both large-scale fast CMEs and small-scale coronal jets, and by inference eruptions at scales in between. Thus, magnetic breakout provides a unified model for solar eruptions. P.F.W was supported in this work by an award of a RAS Fellowship and an appointment to the NASA Postdoctoral Program. C.R.D and S.K.A were supported by NASA’s LWS TR&T and H-SR programs.

Interplanetary Coronal Mass Ejection effects on thermospheric density as inferred from International Space Station orbital data

NASA Astrophysics Data System (ADS)

Mendaza, T.; Blanco-Ávalos, J. J.; Martín-Torres, J.

2017-11-01

The solar activity induces long term and short term periodical variations in the dynamics and composition of Earth's atmosphere. The Sun also shows non periodical (i.e., impulsive) activity that reaches the planets orbiting around it. In particular, Interplanetary Coronal Mass Ejections (ICMEs) reach Earth and interact with its magnetosphere and upper neutral atmosphere. Nevertheless, the interaction with the upper atmosphere is not well characterized because of the absence of regular and dedicated in situ measurements at high altitudes; thus, current descriptions of the thermosphere are based on semi empirical models. In this paper, we present the total neutral mass densities of the thermosphere retrieved from the orbital data of the International Space Station (ISS) using the General Perturbation Method, and we applied these densities to routinely compiled trajectories of the ISS in low Earth orbit (LEO). These data are explicitly independent of any atmospheric model. Our density values are consistent with atmospheric models, which demonstrates that our method is reliable for the inference of thermospheric density. We have inferred the thermospheric total neutral density response to impulsive solar activity forcing from 2001 to the end of 2006 and determined how solar events affect this response. Our results reveal that the ISS orbital parameters can be used to infer the thermospheric density and analyze solar effects on the thermosphere.

Thermodynamic Structure of Collision-Dominated Expanding Plasma: Heating of Interplanetary Coronal Mass Injections

NASA Technical Reports Server (NTRS)

Liu, Y.; Richardson, J. D.; Belcher, J. W.; Kasper, J. C.; Elliott, H. A.

2006-01-01

We investigate the thermodynamic structure of interplanetary coronal mass ejections (ICMEs) using combined surveys of the ejecta between 0.3 and 20 AU. ICMEs are shown to have a moderate expansion in the solar wind compared with theoretical predictions. The expansion seems to be governed by a polytrope with gamma approx. 1.3 in this distance range. We find that Coulomb collisions are important contributors to the ion-ion equilibration process in the ICME plasma. The alpha-proton differential speed quickly drops to below 10 km/s due to strong Coulomb collisions. However, the two species of particles are far from thermal equilibrium with a temperature ratio T(sub alpha/T(sub p) = 4-6, suggestive of a preferential heating of alpha particles. The plasma heating rate as a function of heliocentric &stance required for the temperature profile is deduced by taking into account the expansion and energy transfer between protons and alphas via Coulomb collisions. The turbulence dissipation rate is also inferred from the inertial range power spectrum of magnetic fluctuations within ICMEs. Comparison of the turbulence dissipation rate with the required heating rate shows that turbulence dissipation seems sufficient to explain the ICME heating. Sources powering the turbulence are also investigated by examining the instabilities induced by temperature anisotropies and energy deposition by pickup ions.

IRIS Observations of Coronal Rain and Prominences: Return Flows of the Chromosphere-Corona Mass Cycle

NASA Astrophysics Data System (ADS)

Liu, Wei; Berger, Thomas; Antolin, Patrick; Schrijver, Karel

2014-06-01

It has recently been recognized that a mass cycle (e.g., Berger et al. 2011; McIntosh et al. 2012) between the hot, tenuous solar corona and the cool, dense chromosphere underneath it plays an important role in the mass budget and dynamic evolution of the solar atmosphere. Although the corona ultimately loses mass through the solar wind and coronal mass ejections, a fraction of its mass returns to the chromosphere in coronal rain, downflows of prominences, and other as-yet unidentified processes. We present here analysis of joint observations of IRIS, SDO/AIA, and Hinode/SOT of such phenomena. By utilizing the wide temperature coverage (logT: 4 - 7) provided by these instruments combined, we track the coronal cooling sequence (e.g., Schrijver 2001; Liu et al. 2012; Berger et al. 2012) leading to the formation of such material at transition region or chromospheric temperatures (logT: 4 - 5) in the million-degree corona. We compare the cooling times with those expected from the radiative cooling instability. We also measure the kinematics and densities of such downflows and infer their mass fluxes, which are compared to the upward mass fluxes into the corona, e.g., those associated with spicules and flux emergence. Special attention is paid to coronal rain formed near cusp-shaped portions of coronal loops, funnel-shaped prominences at dips of coronal loops, and their respective magnetic environments. With the information about where and when such catastrophic cooling events take place, we discuss the implications for the enigmatic coronal heating mechanisms (e.g., Antolin et al. 2010).

Current Sheet Evolution In The Aftermath Of A CME Event

NASA Technical Reports Server (NTRS)

Bemporad, A.; Poletto, G.; Seuss, S. T.; Schwardron, N. A.; Elliott, H. A.; Raymond, J. C.

2006-01-01

We report on SOHO UVCS observations of the coronal restructuring following a coronal mass ejection (CME) on 2002 November 26, at the time of a SOHO-Ulysses quadrature campaign. Starting about 1.5 hr after a CME in the northwest quadrant, UVCS began taking spectra at 1.7 R, covering emission from both cool and hot plasma. Observations continued, with occasional gaps, for more than 2 days. Emission in the 974.8 A line of [Fe XVIII], indicating temperatures above 6 x 10(exp 6) K, was observed throughout the campaign in a spatially limited location. Comparison with EIT images shows the [Fe XVIII] emission to overlie a growing post-flare loop system formed in the aftermath of the CME. The emission most likely originates in a current sheet overlying the arcade. Analysis of the [Fe XVIII] emission allows us to infer the evolution of physical parameters in the current sheet over the entire span of our observations: in particular, we give the temperature versus time in the current sheet and estimate its density. At the time of the quadrature, Ulysses was directly above the location of the CME and intercepted the ejecta. High ionization state Fe was detected by the Ulysses SWICS throughout the magnetic cloud associated with the CME, although its rapid temporal variation suggests bursty, rather than smooth, reconnection in the coronal current sheet. The SOHO-Ulysses data set provided us with the unique opportunity of analyzing a current sheet structure from its lowest coronal levels out to its in situ properties. Both the remote and in situ observations are compared with predictions of theoretical CME models.

Comparison of CME radial velocities from a flux rope model and an ice cream cone model

NASA Astrophysics Data System (ADS)

Kim, T.; Moon, Y.; Na, H.

2011-12-01

Coronal Mass Ejections (CMEs) on the Sun are the largest energy release process in the solar system and act as the primary driver of geomagnetic storms and other space weather phenomena on the Earth. So it is very important to infer their directions, velocities and three-dimensional structures. In this study, we choose two different models to infer radial velocities of halo CMEs since 2008 : (1) an ice cream cone model by Xue et al (2005) using SOHO/LASCO data, (2) a flux rope model by Thernisien et al. (2009) using the STEREO/SECCHI data. In addition, we use another flux rope model in which the separation angle of flux rope is zero, which is morphologically similar to the ice cream cone model. The comparison shows that the CME radial velocities from among each model have very good correlations (R>0.9). We will extending this comparison to other partial CMEs observed by STEREO and SOHO.

Tensor-product kernel-based representation encoding joint MRI view similarity.

PubMed

Alvarez-Meza, A; Cardenas-Pena, D; Castro-Ospina, A E; Alvarez, M; Castellanos-Dominguez, G

2014-01-01

To support 3D magnetic resonance image (MRI) analysis, a marginal image similarity (MIS) matrix holding MR inter-slice relationship along every axis view (Axial, Coronal, and Sagittal) can be estimated. However, mutual inference from MIS view information poses a difficult task since relationships between axes are nonlinear. To overcome this issue, we introduce a Tensor-Product Kernel-based Representation (TKR) that allows encoding brain structure patterns due to patient differences, gathering all MIS matrices into a single joint image similarity framework. The TKR training strategy is carried out into a low dimensional projected space to get less influence of voxel-derived noise. Obtained results for classifying the considered patient categories (gender and age) on real MRI database shows that the proposed TKR training approach outperforms the conventional voxel-wise sum of squared differences. The proposed approach may be useful to support MRI clustering and similarity inference tasks, which are required on template-based image segmentation and atlas construction.

Using Prominence Mass Inferences in Different Coronal Lines to Obtain the He/H Abundance

NASA Technical Reports Server (NTRS)

Gilbert, Holly; Kilper, Gary; Alexander, David; Kucera, Therese

2008-01-01

In a previous study we developed a new technique for deriving prominence mass by observing how much coronal radiation in the Fe XI1 (lambda 195) spectral line is absorbed by prominence material. In the present work we apply this method, which allows us to consider the effects of both foreground and background radiation in our calculations, to a sample of prominences absorbing in a coronal line that ionizes both H and He (h < 504 Angstroms), and a line that ionizes only H (504 Angstroms < lambda < 911 Angstroms). This approach, first suggested by Kucera et al. (1998), permits the determination of the abundance ratio [He I]/[H I] of neutral helium and hydrogen in the prominence. This ratio should depend on how the prominence is formed, on its current thermodynamic state, and on its dynamical evolution. Thus, it may provide useful insights into the formation and evolution of prominences.

Using Prominence Mass Inferences in Different Coronal Lines to Obtain the He/H Abundance

NASA Technical Reports Server (NTRS)

Gilbert, Holly; Kilper, Gary; Alexander, David; Kucera, Therese

2009-01-01

In a previous study we developed a new technique for deriving prominence mass by observing how much coronal radiation in the Fe XII (lambda195) spectral Line is absorbed by prominence material. In the present work we apply this method. which allows us to consider the effects of both foreground and background radiation in our calculations, to a sample of prominences absorbing in a coronal line that ionizes both H and He (lambda < 504 Angstroms), and a line that ionizes only H (504 Angstroms < lambda < 911 Angstroms). This approach, first suggested by Mucera et al. (1998). permits the determination of the abundance ratio [He I]/[H I] of neutral helium and hydrogen in the prominence. This ratio should depend on how the prominence is formed, on its current thermodynamic state, and on its dynamical evolution. Thus, it may provide useful insights into the formation and evolution of prominences.

Spatiotemporal Analysis of Coronal Loops Using Seismology of Damped Kink Oscillations and Forward Modeling of EUV Intensity Profiles

NASA Astrophysics Data System (ADS)

Pascoe, D. J.; Anfinogentov, S. A.; Goddard, C. R.; Nakariakov, V. M.

2018-06-01

The shape of the damping profile of kink oscillations in coronal loops has recently allowed the transverse density profile of the loop to be estimated. This requires accurate measurement of the damping profile that can distinguish the Gaussian and exponential damping regimes, otherwise there are more unknowns than observables. Forward modeling of the transverse intensity profile may also be used to estimate the width of the inhomogeneous layer of a loop, providing an independent estimate of one of these unknowns. We analyze an oscillating loop for which the seismological determination of the transverse structure is inconclusive except when supplemented by additional spatial information from the transverse intensity profile. Our temporal analysis describes the motion of a coronal loop as a kink oscillation damped by resonant absorption, and our spatial analysis is based on forward modeling the transverse EUV intensity profile of the loop under the isothermal and optically thin approximations. We use Bayesian analysis and Markov chain Monte Carlo sampling to apply our spatial and temporal models both individually and simultaneously to our data and compare the results with numerical simulations. Combining the two methods allows both the inhomogeneous layer width and density contrast to be calculated, which is not possible for the same data when each method is applied individually. We demonstrate that the assumption of an exponential damping profile leads to a significantly larger error in the inferred density contrast ratio compared with a Gaussian damping profile.

ATM observations - X-ray results. [solar coronal structure from Skylab experiments

NASA Technical Reports Server (NTRS)

Vaiana, G. S.; Zombeck, M.; Krieger, A. S.; Timothy, A. F.

1976-01-01

Preliminary results of the solar X-ray observations from Skylab are reviewed which indicate a highly structured nature for the corona, with closed magnetic-loop structures over a wide range of size scales. A description of the S-054 experiments is provided, and values are given for the parameters - including size, density, and temperature - describing a variety of typical coronal features. The structure and evolution of active regions, coronal holes, and bright points are discussed.

Influence of the remaining coronal structure on the resistance of teeth with intraradicular retainer.

PubMed

Pereira, Jefferson Ricardo; Neto, Tatiany de Mendonça; Porto, Vinícius de Carvalho; Pegoraro, Luiz Fernando; do Valle, Accácio Lins

2005-01-01

The aim of this study was to compare the resistance of endodontically treated teeth with intraradicular retainer different amounts of remaining coronal structure. Fifty freshly extracted maxillary canines were endodontically treated and randomly assigned to five groups (n=10), as follows: group 1 (control) = teeth with custom cast post and core; group 2 = teeth without remaining coronal structure; group 3, 4 and 5 = teeth with 1 mm, 2 mm and 3 mm of remaining coronal structure, respectively. All specimens in groups 2 to 5 were restored with prefabricated post and resin core. The teeth were embedded in acrylic resin and the fracture strength was measured on a universal testing machine at 45 degrees to the long axis of the tooth until failure. Data were analyzed statistically by one-way analysis of variance and Tukey's test. There was no significant differences (p>0.05) between the control group and group 2, and between groups 3, 4 and 5 (p>0.05). Control group and group 2 had significantly higher resistance strength than groups 3, 4 and 5 (p<0.00001). The findings of this study showed that teeth without remaining coronal structure had significantly higher fracture strength than those with remaining coronal structure (1 mm, 2 mm and 3 mm). When the dental crown was not completely removed, the amount of remaining coronal dentin did not significantly affect the fracture strength of endodontically treated teeth with intraradicular retainer.

Repeated Structures Found After the Solar Maximum in the Butterfly Diagrams of Coronal Holes

NASA Astrophysics Data System (ADS)

Hofer, M. Y.; Storini, M.

2003-09-01

The influence of the solar cycle evolution on the coronal hole space-time distribution is well known, for polar as well as for equatorial isolated sources of high speed solar wind. Among them the long-lived coronal holes occurrence from the sunspot cycle 21 on is investigated, using the coronal hole catalogue based on HeI (1083 nm) observations (Sanchez-Ibarra and Barraza-Paredes). In at least these two solar cycles (n. 21 and n. 22) a similar structure in the latitude-time diagram of coronal holes is found. The area occurs shortly after the solar maximum at around ~35° heliolatitude and consists of over several Carrington Rotations stable coronal holes (>5 Carr. Rot.s). The diagonal disappears 2-3 years later at the helioequator. Furthermore, the analysis results in a close relation between long-lived isolated coronal holes and the soft X-class flares.

Coronal Structures in Cool Stars: XMM-NEWTON Hybrid Stars and Coronal Evolution

NASA Technical Reports Server (NTRS)

Dupree, Andrea K.; Mushotzky, Richard (Technical Monitor)

2003-01-01

This program addresses the evolution of stellar coronas by comparing a solar-like corona in the supergiant Beta Dra (G2 Ib-IIa) to the corona in the allegedly more evolved state of a hybrid star, alpha TrA (K2 II-III). Because the hybrid star has a massive wind, it appears likely that the corona will be cooler and less dense as the magnetic loop structures are no longer closed. By analogy with solar coronal holes, when the topology of the magnetic field is configured with open magnetic structures, both the coronal temperature and density are lower than in atmospheres dominated by closed loops. The hybrid stars assume a pivotal role in the definition of coronal evolution, atmospheric heating processes and mechanisms to drive winds of cool stars. We are attempting to determine if this model of coronal evolution is correct by using XMM-NEWTON RGS spectra for the 2 targets we were allocated through the Guest Observer program.

Standing Kink modes in three-dimensional coronal loops

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pascoe, D. J.; De Moortel, I., E-mail: dpascoe@mcs.st-andrews.ac.uk

2014-04-01

So far, the straight flux tube model proposed by Edwin and Roberts is the most commonly used tool in practical coronal seismology, in particular, to infer values of the (coronal) magnetic field from observed, standing kink mode oscillations. In this paper, we compare the period predicted by this basic model with three-dimensional (3D) numerical simulations of standing kink mode oscillations, as the period is a crucial parameter in the seismological inversion to determine the magnetic field. We perform numerical simulations of standing kink modes in both straight and curved 3D coronal loops and consider excitation by internal and external drivers.more » The period of oscillation for the displacement of dense coronal loops is determined by the loop length and the kink speed, in agreement with the estimate based on analytical theory for straight flux tubes. For curved coronal loops embedded in a magnetic arcade and excited by an external driver, a secondary mode with a period determined by the loop length and external Alfvén speed is also present. When a low number of oscillations is considered, these two periods can result in a single, non-resolved (broad) peak in the power spectrum, particularly for low values of the density contrast for which the two periods will be relatively similar. In that case (and for this particular geometry), the presence of this additional mode would lead to ambiguous seismological estimates of the magnetic field strength.« less

Comparison of magnetic helicity close to the sun and in magnetic clouds

NASA Astrophysics Data System (ADS)

Rust, D.

Magnetic helicity is present in the solar atmosphere - as inferred from vector magnetograph measurements, solar filaments, S-shaped coronal structures known as sigmoids, and sunspot whorls. I will survey the possible solar sources of this magnetic helicity. Included are fieldline footpoint motions, effects of Coriolis forces, effects of convection, shear associated with differential rotation, and, of course, the internal dynamo. Besides the survey of possible local mechanisms for helicity generation, I will consider the global view of the flow of helicity from the sun into interplanetary space. The principal agents by which the sun sheds helicity are coronal mass ejections (CMEs). They are often associated with interplanetary magnetic clouds (MCs), whose fields are regularly probed with sensitive spacecraft magnetometers. MCs yield more direct measurements of helicity. They show that each MC carries helicity away from the sun. A major issue in solar-heliospheric research is whether the amount of helicity that MCs carry away in a solar cycle can be accounted for by the helicity generation mechanisms proposed so far. The NASA Solar and Heliospheric Physics Program supports this work under grants NAG5- 7921 and NAG 5-11584.

Fifteen years in the high-energy life of the solar-type star HD 81809. XMM-Newton observations of a stellar activity cycle

NASA Astrophysics Data System (ADS)

Orlando, S.; Favata, F.; Micela, G.; Sciortino, S.; Maggio, A.; Schmitt, J. H. M. M.; Robrade, J.; Mittag, M.

2017-09-01

Context. The modulation of the activity level of solar-like stars is commonly revealed by cyclic variations in their chromospheric indicators, such as the Ca II H&K S-index, similarly to what is observed in our Sun. However, while the variation of solar activity is also reflected in the cyclical modulation of its coronal X-ray emission, similar behavior has only been discovered in a few stars other than the Sun. Aims: The data set of the long-term XMM-Newton monitoring program of HD 81809 is analyzed to study its X-ray cycle, investigate if the latter is related to the chromospheric cycle, infer the structure of the corona of HD 81809, and explore if the coronal activity of HD 81809 can be ascribed to phenomena similar to solar activity and, therefore, considered an extension of the solar case. Methods: We analyzed the observations of HD 81809 performed with XMM-Newton with a regular cadence of six months from 2001 to 2016, which represents one of the longest available observational baseline ( 15 yr) for a solar-like star with a well-studied chromospheric cycle (with a period of 8 yr). We investigated the modulation of coronal luminosity and temperature and its relation with the chromospheric cycle. We interpreted the data in terms of a mixture of solar-like coronal regions, adopting a method originally proposed to study the Sun as an X-ray star. Results: The observations show a well-defined regular cyclic modulation of the X-ray luminosity that reflects the activity level of HD 81809. The data covers approximately two cycles of coronal activity; the modulation has an amplitude of a factor of 5 (excluding evident flares, as in the June 2002 observation) and a period of 7.3 ± 1.5 yr, which is consistent with that of the chromospheric cycle. We demonstrate that the corona of HD 81809 can be interpreted as an extension of the solar case and can be modeled with a mixture of solar-like coronal regions along the whole cycle. The activity level is mainly determined by varying coverage of very bright active regions, similar to cores of active regions observed in the Sun. Evidence of unresolved significant flaring activity is present especially in the proximity of cycle maxima.

On the Role of Interchange Reconnection in the Generation of the Slow Solar Wind

NASA Astrophysics Data System (ADS)

Edmondson, J. K.

2012-11-01

The heating of the solar corona and therefore the generation of the solar wind, remain an active area of solar and heliophysics research. Several decades of in situ solar wind plasma observations have revealed a rich bimodal solar wind structure, well correlated with coronal magnetic field activity. Therefore, the reconnection processes associated with the large-scale dynamics of the corona likely play a major role in the generation of the slow solar wind flow regime. In order to elucidate the relationship between reconnection-driven coronal magnetic field structure and dynamics and the generation of the slow solar wind, this paper reviews the observations and phenomenology of the solar wind and coronal magnetic field structure. The geometry and topology of nested flux systems, and the (interchange) reconnection process, in the context of coronal physics is then explained. Once these foundations are laid out, the paper summarizes several fully dynamic, 3D MHD calculations of the global coronal system. Finally, the results of these calculations justify a number of important implications and conclusions on the role of reconnection in the structural dynamics of the coronal magnetic field and the generation of the solar wind.

Thermodynamics of the Solar Corona and Evolution of the Solar Magnetic Field as Inferred from the Total Solar Eclipse Observations of 11 July 2010

NASA Technical Reports Server (NTRS)

Habbal, Shadia Rifai; Druckmueller, Miloslav; Morgan, Huw; Ding, Adalbert; Johnson, Judd; Druckmuellerova, Hana; Daw, Adrian; Arndt, Martina B.; Dietzel, Martin; Saken, Jon

2011-01-01

We report on multi-wavelength observations of the corona taken simultaneously in broadband white light, and in seven spectral lines, H-alpha 656.3 nm, Fe IX 435.9 nm, Fe X 637.4 nm, Fe XI 789.2 nm, Fe XIII 1074.7 nm, Fe XIV 530.3 nm and Ni XV 670.2 nm. The observations were made during the total solar eclipse of 11 July 2010 from the atoll of Tatakoto in French Polynesia. Simultaneous imaging with narrow bandpass filters in each of these spectral lines and in their corresponding underlying continua maximized the observing time during less than ideal observing conditions and yielded outstanding quality data. The application of two complementary image processing techniques revealed the finest details of coronal structures at 1" resolution in white light, and 6.5" in each of the spectral lines. This comprehensive wavelength coverage confirmed earlier eclipse findings that the solar corona has a clear two-temperature structure: The open field lines, expanding outwards from the solar surface, are characterized by electron temperatures near 1 X 10(exp 6) K, while the hottest plasma around 2X 10(exp 6) K resides in loop-like structures forming the bulges of streamers. The first images of the corona in the forbidden lines of Fe IX and Ni XV, showed that there was very little coronal plasma at temperatures below 5 X 10(exp 5) K and above 2.5X 10(exp 6) K. The data also enabled temperature differentiations as low as 0:2 X 10(exp 6) K in different density structures. These observations showed how the passage of CMEs through the corona, prior to totality, produced large scale ripples and very sharp streaks, which could be identified with distinct temperatures for the first time. The ripples were most prominent in emission from spectral lines associated with temperatures around 10(exp 6) K. The most prominent streak was associated with a conical-shaped void in the emission from the coolest line of Fe IX and from the hottest line of Ni XV. A prominence, which erupted prior to totality, appeared in the shape of a hook in the cooler lines of Fe X and Fe XI, spanning 0.5 R(solar) in extent starting at a heliocentric distance of 1.3 R(solar), with a complex trail of hot and cool twisted structures connecting it to the solar surface. Simultaneous Fe X 17.4 nm observations from space by Proba2/SWAP provided an ideal opportunity for comparing emission from a coronal forbidden line, namely Fe X 637.4 nm, with a space-based EUV allowed line. Comparison of the Fe X 17.4 nm and 637.4 nm emission provided the first textbook example of the role of radiative excitation in extending the detectability of coronal emission to much larger heliocentric distances than its collisionally excited component. These eclipse observations demonstrate the unique capabilities of coronal forbidden lines for exploring the evolution of the coronal magnetic field in the heliocentric distance range of 1 - 3 R(solar), which is currently inaccessible to any space-borne or ground-based observatory.

A Study of the 2012 January 19 Complex Type II Radio Burst Using Wind, SOHO, and STEREO Observations*

NASA Technical Reports Server (NTRS)

Teklu, T. B.; Gholap, A. V.; Gopalswamy, N.; Yashiro, S.; Makela, P.; Akiyama, S.; Thakur, N.; Xie, H.

2016-01-01

We report on a case study of the complex type II radio burst of 2012 January 19 and its association with a white-light coronal mass ejection (CME). The complexity can be described as the appearance of an additional type II burst component and strong intensity variation. The dynamic spectrum shows a pair of type II bursts with fundamental harmonic structures, one confined to decameter-hectometric (DH) wavelengths and the other extending to kilometric (km) wavelengths. By comparing the speeds obtained from white-light images with that speed of the shock inferred from the drift rate, we show that the source of the short-lived DH component is near the nose.

A Multiwavelength Study of Coronal Structure: A Simultaneous Observation from NIXT and YOHKOH

NASA Technical Reports Server (NTRS)

Golub, Leon

1998-01-01

Solar soft X-ray images taken simultaneously by the Yohkoh and the Normal Incidence X-ray Telescope (NIXT) reveal significantly different coronal structures. Coronal loops are more clearly seen in the Yohkoh images, and the isolated island-like structures seen in the NIXT image have been found to correspond to the footpoints of the Yohkoh loops. The difference is due to the difference in the temperature response of the telescopes: NIXT is sensitive to temperatures ranging from 0.9 to 3 MK, while Yohkoh is more sensitive to temperatures above 2.5 MK. The morphological differences reflect the multi-temperature (1-5 MK) nature of the solar coronal plasmas.

DICHOTOMY OF SOLAR CORONAL JETS: STANDARD JETS AND BLOWOUT JETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moore, Ronald L.; Cirtain, Jonathan W.; Sterling, Alphonse C.

2010-09-01

By examining many X-ray jets in Hinode/X-Ray Telescope coronal X-ray movies of the polar coronal holes, we found that there is a dichotomy of polar X-ray jets. About two thirds fit the standard reconnection picture for coronal jets, and about one third are another type. We present observations indicating that the non-standard jets are counterparts of erupting-loop H{alpha} macrospicules, jets in which the jet-base magnetic arch undergoes a miniature version of the blowout eruptions that produce major coronal mass ejections. From the coronal X-ray movies we present in detail two typical standard X-ray jets and two typical blowout X-ray jetsmore » that were also caught in He II 304 A snapshots from STEREO/EUVI. The distinguishing features of blowout X-ray jets are (1) X-ray brightening inside the base arch in addition to the outside bright point that standard jets have, (2) blowout eruption of the base arch's core field, often carrying a filament of cool (T {approx} 10{sup 4} - 10{sup 5} K) plasma, and (3) an extra jet-spire strand rooted close to the bright point. We present cartoons showing how reconnection during blowout eruption of the base arch could produce the observed features of blowout X-ray jets. We infer that (1) the standard-jet/blowout-jet dichotomy of coronal jets results from the dichotomy of base arches that do not have and base arches that do have enough shear and twist to erupt open, and (2) there is a large class of spicules that are standard jets and a comparably large class of spicules that are blowout jets.« less

ANALYSIS OF CORONAL RAIN OBSERVED BY IRIS , HINODE /SOT, AND SDO /AIA: TRANSVERSE OSCILLATIONS, KINEMATICS, AND THERMAL EVOLUTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kohutova, P.; Verwichte, E., E-mail: p.kohutova@warwick.ac.uk

Coronal rain composed of cool plasma condensations falling from coronal heights along magnetic field lines is a phenomenon occurring mainly in active region coronal loops. Recent high-resolution observations have shown that coronal rain is much more common than previously thought, suggesting its important role in the chromosphere-corona mass cycle. We present the analysis of MHD oscillations and kinematics of the coronal rain observed in chromospheric and transition region lines by the Interface Region Imaging Spectrograph (IRIS) , the Hinode Solar Optical Telescope (SOT), and the Solar Dynamics Observatory ( SDO) Atmospheric Imaging Assembly (AIA). Two different regimes of transverse oscillationsmore » traced by the rain are detected: small-scale persistent oscillations driven by a continuously operating process and localized large-scale oscillations excited by a transient mechanism. The plasma condensations are found to move with speeds ranging from few km s{sup −1} up to 180 km s{sup −1} and with accelerations largely below the free-fall rate, likely explained by pressure effects and the ponderomotive force resulting from the loop oscillations. The observed evolution of the emission in individual SDO /AIA bandpasses is found to exhibit clear signatures of a gradual cooling of the plasma at the loop top. We determine the temperature evolution of the coronal loop plasma using regularized inversion to recover the differential emission measure (DEM) and by forward modeling the emission intensities in the SDO /AIA bandpasses using a two-component synthetic DEM model. The inferred evolution of the temperature and density of the plasma near the apex is consistent with the limit cycle model and suggests the loop is going through a sequence of periodically repeating heating-condensation cycles.« less

Using observations of slipping velocities to test the hypothesis that reconnection heats the active region corona

NASA Astrophysics Data System (ADS)

Yang, Kai; Longcope, Dana; Guo, Yang; Ding, Mingde

2017-08-01

Numerous proposed coronal heating mechanisms have invoked magnetic reconnection in some role. Testing such a mechanism requires a method of measuring magnetic reconnection coupled with a prediction of the heat delivered by reconnection at the observed rate. In the absence of coronal reconnection, field line footpoints move at the same velocity as the plasma they find themselves in. The rate of coronal reconnection is therefore related to any discrepancy observed between footpoint motion and that of the local plasma — so-called slipping motion. We propose a novel method to measure this velocity discrepancy by combining a sequence of non-linear force-free field extrapolations with maps of photospheric velocity. We obtain both from a sequence of vector magnetograms of an active region (AR). We then propose a method of computing the coronal heating produced under the assumption the observed slipping velocity was due entirely to coronal reconnection. This heating rate is used to predict density and temperature at points along an equilibrium loop. This, in turn, is used to synthesize emission in EUV and SXR bands. We perform this analysis using a sequence of HMI vector magnetograms of a particular AR and compare synthesized images to observations of the same AR made by SDO. We also compare differential emission measure inferred from those observations to that of the modeled corona.

Evolution and Activity in the Solar Corona: A Comparison of Coronal and Chromospheric Structures Seen in Soft X-Rays, White Light and H-Alpha Emission

NASA Technical Reports Server (NTRS)

Bagenal, Fran

2001-01-01

The work completed under this project, 'Evolution and Activity in the Solar Corona: A Comparison of Coronal and Chromospheric Structures Seen in Soft X-Rays, White Light and H-Alpha Emission', includes the following presentations: (1) Analysis of H-alpha Observations of High-altitude Coronal Condensations; (2) Multi-spectral Imaging of Coronal Activity; (3) Measurement and Modeling of Soft X-ray Loop Arcades; (4) A Study of the Origin and Dynamics of CMEs; and various poster presentations and thesis dissertations.

Flux Cancelation: The Key to Solar Eruptions

NASA Technical Reports Server (NTRS)

Panesar, Navdeep K.; Sterling, Alphonse; Moore, Ronald; Chakrapani, Prithi; Innes, Davina; Schmit, Don; Tiwari, Sanjiv

2017-01-01

Solar coronal jets are magnetically channeled eruptions that occur in all types of solar environments (e.g. active regions, quiet-Sun regions and coronal holes). Recent studies show that coronal jets are driven by the eruption of small-scare filaments (minifilaments). Once the eruption is underway magnetic reconnection evidently makes the jet spire and the bright emission in the jet base. However, the triggering mechanism of these eruptions and the formation mechanism of the pre-jet minifilaments are still open questions. In this talk, mainly using SDO/AIA (Solar Dynamics Observatory / Atmospheric Imaging Assembly) and SDO/HIM (Solar Dynamics Observatory / Helioseismic and Magnetic Imager) data, first I will address the question: what triggers the jet-driving minifilament eruptions in different solar environments (coronal holes, quiet regions, active regions)? Then I will talk about the magnetic field evolution that produces the pre-jet minifilaments. By examining pre-jet evolutionary changes in line-of-sight HMI magnetograms while examining concurrent EUV (Extreme Ultra-Violet) images of coronal and transition-region emission, we find clear evidence that flux cancelation is the main process that builds pre-jet minifilaments, and is also the main process that triggers the eruptions. I will also present results from our ongoing work indicating that jet-driving minifilament eruptions are analogous to larger-scare filament eruptions that make flares and CMEs (Coronal Mass Ejections). We find that persistent flux cancellation at the neutral line of large-scale filaments often triggers their eruptions. From our observations we infer that flux cancelation is the fundamental process from the buildup and triggering of solar eruptions of all sizes.

Three-Dimensional MHD Modeling of The Solar Corona and Solar Wind: Comparison with The Wang-Sheeley Model

NASA Technical Reports Server (NTRS)

Usmanov, A. V.; Goldstein, M. L.

2003-01-01

We present simulation results from a tilted-dipole steady-state MHD model of the solar corona and solar wind and compare the output from our model with the Wang-Sheeley model which relates the divergence rate of magnetic flux tubes near the Sun (inferred from solar magnetograms) to the solar wind speed observed near Earth and at Ulysses. The boundary conditions in our model specified at the coronal base and our simulation region extends out to 10 AU. We assumed that a flux of Alfven waves with amplitude of 35 km per second emanates from the Sun and provides additional heating and acceleration for the coronal outflow in the open field regions. The waves are treated in the WKB approximation. The incorporation of wave acceleration allows us to reproduce the fast wind measurements obtained by Ulysses, while preserving reasonable agreement with plasma densities typically found at the coronal base. We find that our simulation results agree well with Wang and Sheeley's empirical model.

Results from CoMStOC - The Coronal Magnetic Structures Observing Campaign

NASA Technical Reports Server (NTRS)

Schmelz, J. T.; Holman, G. D.

1991-01-01

The Coronal Magnetic Structures Observing Campaign (CoMStOC) was designed to measure the magnetic field strength and determine its structure in the solar corona. Simultaneous soft X-ray and microwave observations were taken by the Solar Maximum Mission's X-ray Polychromator (XRP) and the Very Large Array (VLA) on four days in the campaign period (Nov 25 to Dec 21, 1987). XRP maps in soft X-ray resonance lines formed at different coronal temperatures provide accurate temperature and emission measure diagnostics. VLA maps at several frequencies in the 20 cm and 6 cm bands yield information on microwave structure, spectrum and polarization. The combined data set separates contributions from the two dominant microwave emission mechanisms, thermal bremsstrahlung and gyroresonance. Where gyroresonance dominates, the coronal magnetic field strength has been determined with the aid of theoretical modeling.

Results from CoMStOC - The Coronal Magnetic Structures Observing Campaign

NASA Astrophysics Data System (ADS)

Schmelz, J. T.; Holman, G. D.

The Coronal Magnetic Structures Observing Campaign (CoMStOC) was designed to measure the magnetic field strength and determine its structure in the solar corona. Simultaneous soft X-ray and microwave observations were taken by the Solar Maximum Mission's X-ray Polychromator (XRP) and the Very Large Array (VLA) on four days in the campaign period (Nov 25 to Dec 21, 1987). XRP maps in soft X-ray resonance lines formed at different coronal temperatures provide accurate temperature and emission measure diagnostics. VLA maps at several frequencies in the 20 cm and 6 cm bands yield information on microwave structure, spectrum and polarization. The combined data set separates contributions from the two dominant microwave emission mechanisms, thermal bremsstrahlung and gyroresonance. Where gyroresonance dominates, the coronal magnetic field strength has been determined with the aid of theoretical modeling.

Application of a magnetograph and X-ray telescope to the study of coronal structure variations

NASA Technical Reports Server (NTRS)

Rust, D. M.

1980-01-01

The application of magnetographs and X-ray imaging techniques to determine the magnitude, structure, origin, and evolution of the solar coronal magnetic field is examined. The spatial and temporal resolution of the X-ray telescope is discussed and a comparison of ground based magnetogram sequences versus a magnetograph in space is presented. Skylab photographs of the evolution of transient coronal holes are provided.

Do changes in coronal emission structure imply magnetic reconnection

NASA Technical Reports Server (NTRS)

Nolte, J. T.; Gerassimenko, M.; Krieger, A. S.; Petrasso, R. D.; Svestka, Z.; Wentzel, D. G.

1977-01-01

Several physical processes that can affect the emission from structures in the corona are investigated on the basis of images of coronal X-ray and XUV emission structures. Changes in emission accompanied by little or no change in large-scale magnetic structure are examined, and three theoretically distinct processes by which magnetic structure can change are discussed: reconfiguration of potential (current-free) fields, reconfiguration of frozen-in fields, and reconfiguration by magnetic-field-line reconnection. The possibility is considered of determining by observation whether a change in emission results from a magnetic change and, if so, what kind of magnetic change has occurred. It is concluded that changes in coronal emission structure do not necessarily imply magnetic reconnection.

LOFAR observations of the quiet solar corona

NASA Astrophysics Data System (ADS)

Vocks, C.; Mann, G.; Breitling, F.; Bisi, M. M.; Dąbrowski, B.; Fallows, R.; Gallagher, P. T.; Krankowski, A.; Magdalenić, J.; Marqué, C.; Morosan, D.; Rucker, H.

2018-06-01

Context. The quiet solar corona emits meter-wave thermal bremsstrahlung. Coronal radio emission can only propagate above that radius, Rω, where the local plasma frequency equals the observing frequency. The radio interferometer LOw Frequency ARray (LOFAR) observes in its low band (10-90 MHz) solar radio emission originating from the middle and upper corona. Aims: We present the first solar aperture synthesis imaging observations in the low band of LOFAR in 12 frequencies each separated by 5 MHz. From each of these radio maps we infer Rω, and a scale height temperature, T. These results can be combined into coronal density and temperature profiles. Methods: We derived radial intensity profiles from the radio images. We focus on polar directions with simpler, radial magnetic field structure. Intensity profiles were modeled by ray-tracing simulations, following wave paths through the refractive solar corona, and including free-free emission and absorption. We fitted model profiles to observations with Rω and T as fitting parameters. Results: In the low corona, Rω < 1.5 solar radii, we find high scale height temperatures up to 2.2 × 106 K, much more than the brightness temperatures usually found there. But if all Rω values are combined into a density profile, this profile can be fitted by a hydrostatic model with the same temperature, thereby confirming this with two independent methods. The density profile deviates from the hydrostatic model above 1.5 solar radii, indicating the transition into the solar wind. Conclusions: These results demonstrate what information can be gleaned from solar low-frequency radio images. The scale height temperatures we find are not only higher than brightness temperatures, but also than temperatures derived from coronograph or extreme ultraviolet (EUV) data. Future observations will provide continuous frequency coverage. This continuous coverage eliminates the need for local hydrostatic density models in the data analysis and enables the analysis of more complex coronal structures such as those with closed magnetic fields.

Identification and analysis of structures in the corona from X-ray photography

NASA Technical Reports Server (NTRS)

Vaiana, G. S.; Krieger, A. S.; Timothy, A. F.

1973-01-01

This paper summarizes the results of a program of rocket observations of the solar corona with grazing incidence X-ray telescopes. A series of five flights of a Kanigen-surfaced telescope with a few arc seconds resolution, together with the first flight of a newer telescope have resulted in the identification of six classes of coronal structures observable in the X-ray photographs. These are: active regions, active region interconnections, large loop structures associated with unipolar magnetic regions, coronal holes, coronal bright points, and the structures surrounding filament cavities. Two solar flares have been observed. The methods involved in deriving coronal temperature and density information from X-ray photographs are described and the analysis of a bright active region (McMath plage 11035) observed at the west limb on November 24, 1970 is presented as an example of these techniques.

Unresolved fine-scale structure in solar coronal loop-tops

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scullion, E.; Van der Voort, L. Rouppe; Wedemeyer, S.

2014-12-10

New and advanced space-based observing facilities continue to lower the resolution limit and detect solar coronal loops in greater detail. We continue to discover even finer substructures within coronal loop cross-sections, in order to understand the nature of the solar corona. Here, we push this lower limit further to search for the finest coronal loop substructures, through taking advantage of the resolving power of the Swedish 1 m Solar Telescope/CRisp Imaging Spectro-Polarimeter (CRISP), together with co-observations from the Solar Dynamics Observatory/Atmospheric Image Assembly (AIA). High-resolution imaging of the chromospheric Hα 656.28 nm spectral line core and wings can, under certainmore » circumstances, allow one to deduce the topology of the local magnetic environment of the solar atmosphere where its observed. Here, we study post-flare coronal loops, which become filled with evaporated chromosphere that rapidly condenses into chromospheric clumps of plasma (detectable in Hα) known as a coronal rain, to investigate their fine-scale structure. We identify, through analysis of three data sets, large-scale catastrophic cooling in coronal loop-tops and the existence of multi-thermal, multi-stranded substructures. Many cool strands even extend fully intact from loop-top to footpoint. We discover that coronal loop fine-scale strands can appear bunched with as many as eight parallel strands within an AIA coronal loop cross-section. The strand number density versus cross-sectional width distribution, as detected by CRISP within AIA-defined coronal loops, most likely peaks at well below 100 km, and currently, 69% of the substructure strands are statistically unresolved in AIA coronal loops.« less

The First Empirical Determination of the Fe10+ and Fe13+ Freeze-in Distances in the Solar Corona

NASA Astrophysics Data System (ADS)

Boe, Benjamin; Habbal, Shadia; Druckmüller, Miloslav; Landi, Enrico; Kourkchi, Ehsan; Ding, Adalbert; Starha, Pavel; Hutton, Joseph

2018-06-01

Heavy ions are markers of the physical processes responsible for the density and temperature distribution throughout the fine-scale magnetic structures that define the shape of the solar corona. One of their properties, whose empirical determination has remained elusive, is the “freeze-in” distance (R f ) where they reach fixed ionization states that are adhered to during their expansion with the solar wind. We present the first empirical inference of R f for {Fe}}{10+} and {Fe}}{13+} derived from multi-wavelength imaging observations of the corresponding Fe XI ({Fe}}{10+}) 789.2 nm and Fe XIV ({Fe}}{13+}) 530.3 nm emission acquired during the 2015 March 20 total solar eclipse. We find that the two ions freeze-in at different heliocentric distances. In polar coronal holes (CHs) R f is around 1.45 R ⊙ for {Fe}}{10+} and below 1.25 R ⊙ for {Fe}}{13+}. Along open field lines in streamer regions, R f ranges from 1.4 to 2 R ⊙ for {Fe}}{10+} and from 1.5 to 2.2 R ⊙ for {Fe}}{13+}. These first empirical R f values: (1) reflect the differing plasma parameters between CHs and streamers and structures within them, including prominences and coronal mass ejections; (2) are well below the currently quoted values derived from empirical model studies; and (3) place doubt on the reliability of plasma diagnostics based on the assumption of ionization equilibrium beyond 1.2 R ⊙.

The Three-part Structure of a Filament-unrelated Solar Coronal Mass Ejection

NASA Astrophysics Data System (ADS)

Song, H. Q.; Cheng, X.; Chen, Y.; Zhang, J.; Wang, B.; Li, L. P.; Li, B.; Hu, Q.; Li, G.

2017-10-01

Coronal mass ejections (CMEs) often exhibit the typical three-part structure in the corona when observed with white-light coronagraphs, I.e., the bright leading front, dark cavity, and bright core, corresponding to a high-low-high density sequence. As CMEs result from eruptions of magnetic flux ropes (MFRs), which can possess either lower (e.g., coronal-cavity MFRs) or higher (e.g., hot-channel MFRs) density compared to their surroundings in the corona, the traditional opinion regards the three-part structure as the manifestations of coronal plasma pileup (high density), coronal-cavity MFR (low density), and filament (high density) contained in the trailing part of MFR, respectively. In this paper, we demonstrate that filament-unrelated CMEs can also exhibit the classical three-part structure. The observations were made from different perspectives through an event that occurred on 2011 October 4. The CME cavity corresponds to the low-density zone between the leading front and the high-density core, and it is obvious in the low corona and gradually becomes fuzzy when propagating outward. The bright core corresponds to a high-density structure that is suggested to be an erupting MFR. The MFR is recorded from both edge-on and face-on perspectives, exhibiting different morphologies that are due to projection effects. We stress that the zone (MFR) with lower (higher) density in comparison to the surroundings can appear as the dark cavity (bright core) when observed through white-light coronagraphs, which is not necessarily the coronal-cavity MFR (erupted filament).

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

NASA Astrophysics Data System (ADS)

Chen, Yajie; Tian, Hui; Su, Yingna; Qu, Zhongquan; Deng, Linhua; Jibben, Patricia R.; Yang, Zihao; Zhang, Jingwen; Samanta, Tanmoy; He, Jiansen; Wang, Linghua; Zhu, Yingjie; Zhong, Yue; Liang, Yu

2018-03-01

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.

The Fate of Cool Material in the Hot Corona: Solar Prominences and Coronal Rain

NASA Astrophysics Data System (ADS)

Liu, Wei; Antolin, Patrick; Sun, Xudong; Vial, Jean-Claude; Berger, Thomas

2017-08-01

As an important chain of the chromosphere-corona mass cycle, some of the million-degree hot coronal mass undergoes a radiative cooling instability and condenses into material at chromospheric or transition-region temperatures in two distinct forms - prominences and coronal rain (some of which eventually falls back to the chromosphere). A quiescent prominence usually consists of numerous long-lasting, filamentary downflow threads, while coronal rain consists of transient mass blobs falling at comparably higher speeds along well-defined paths. It remains puzzling why such material of similar temperatures exhibit contrasting morphologies and behaviors. We report recent SDO/AIA and IRIS observations that suggest different magnetic environments being responsible for such distinctions. Specifically, in a hybrid prominence-coronal rain complex structure, we found that the prominence material is formed and resides near magnetic null points that favor the radiative cooling process and provide possibly a high plasma-beta environment suitable for the existence of meandering prominence threads. As the cool material descends, it turns into coronal rain tied onto low-lying coronal loops in a likely low-beta environment. Such structures resemble to certain extent the so-called coronal spiders or cloud prominences, but the observations reported here provide critical new insights. We will discuss the broad physical implications of these observations for fundamental questions, such as coronal heating and beyond (e.g., in astrophysical and/or laboratory plasma environments).

Characterizing the Background Corona with SDO/AIA

NASA Technical Reports Server (NTRS)

Napier, Kate; Alexander, Caroline; Winebarger, Amy

2014-01-01

Characterizing the nature of the solar coronal background would enable scientists to more accurately determine plasma parameters, and may lead to a better understanding of the coronal heating problem. Because scientists study the 3D structure of the Sun in 2D, any line-of-sight includes both foreground and background material, and thus, the issue of background subtraction arises. By investigating the intensity values in and around an active region, using multiple wavelengths collected from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) over an eight-hour period, this project aims to characterize the background as smooth or structured. Different methods were employed to measure the true coronal background and create minimum intensity images. These were then investigated for the presence of structure. The background images created were found to contain long-lived structures, including coronal loops, that were still present in all of the wavelengths, 131, 171, 193, 211, and 335 A. The intensity profiles across the active region indicate that the background is much more structured than previously thought.

Flux Cancelation: The Key to Solar Eruptions

NASA Technical Reports Server (NTRS)

Panesar, Navdeep K.; Sterling, Alphonse; Moore, Ronald; Chakrapani, Prithi; Innes, Davina; Schmit, Don; Tiwari, Sanjiv

2017-01-01

Solar coronal jets are magnetically channeled eruptions that occur in all types of solar environments (e.g. active regions, quiet-Sun regions and coronal holes). Recent studies show that coronal jets are driven by the eruption of small-scare filaments (minifilaments). Once the eruption is underway magnetic reconnection evidently makes the jet spire and the bright emission in the jet base. However, the triggering mechanism of these eruptions and the formation mechanism of the pre-jet minifilaments are still open questions. In this talk, mainly using SDOAIA and SDOHIM data, first I will address the question: what triggers the jet-driving minifilament eruptions in different solar environments (coronal holes, quiet regions, active regions)? Then I will talk about the magnetic field evolution that produces the pre-jet minifilaments. By examining pre-jet evolutionary changes in line-of-sight HMI magnetograms while examining concurrent EUV images of coronal and transition-region emission, we find clear evidence that flux cancelation is the main process that builds pre-jet minifilaments, and is also the main process that triggers the eruptions. I will also present results from our ongoing work indicating that jet-driving minifilament eruptions are analogous to larger-scare filament eruptions that make flares and CMEs. We find that persistent flux cancellation at the neutral line of large-scale filaments often triggers their eruptions. From our observations we infer that flux cancelation is the fundamental process from the buildup and triggering of solar eruptions of all sizes.

Flux Cancelation: The Key to Solar Eruptions

NASA Technical Reports Server (NTRS)

Panesar, Navdeep K.; Sterling, Alphonse; Moore, Ronald; Chakrapani, Prithi; Innes, Davina; Schmit, Don; Tiwari, Sanjiv

2017-01-01

Solar coronal jets are magnetically channeled eruptions that occur in all types of solar environments (e.g. active regions, quiet-Sun regions and coronal holes). Recent studies show that coronal jets are driven by the eruption of small-scale filaments (minifilaments). Once the eruption is underway magnetic reconnection evidently makes the jet spire and the bright emission in the jet base. However, the triggering mechanism of these eruptions and the formation mechanism of the pre-jet minifilaments are still open questions. In this talk, mainly using SDO/AIA and SDO/HMI data, first I will address the question: what triggers the jet-driving minifilament eruptions in different solar environments (coronal holes, quiet regions, active regions)? Then I will talk about the magnetic field evolution that produces the pre-jet minifilaments. By examining pre-jet evolutionary changes in line-of-sight HMI magnetograms while examining concurrent EUV images of coronal and transition-region emission, we find clear evidence that flux cancellation is the main process that builds pre-jet minifilaments, and is also the main process that triggers the eruptions. I will also present results from our ongoing work indicating that jet-driving minifilament eruptions are analogous to larger-scale filament eruptions that make flares and CMEs. We find that persistent flux cancellation at the neutral line of large-scale filaments often triggers their eruptions. From our observations we infer that flux cancellation is the fundamental process for the buildup and triggering of solar eruptions of all sizes.

Coronal sounding with Ulysses - Preliminary results from the first solar conjunction

NASA Technical Reports Server (NTRS)

Paetzold, M.; Bird, M. K.; Volland, H.; Edenhofer, P.; Asmar, S. W.; Brenkle, J. P.

1992-01-01

Radio-sounding observations of the solar corona between 4 and 115 solar radii were performed during the first superior solar conjunction phase of the Ulysses spacecraft in August/September 1991. As a first result of this Solar Corona Experiment, the total electron content inferred from dual-frequency ranging observations is presented here as a function of solar distance.

Phenomena Associated with EIT Waves

NASA Technical Reports Server (NTRS)

Thompson, B. J.; Biesecker, D. A.; Gopalswamy, N.; Fisher, Richard R. (Technical Monitor)

2002-01-01

We discuss phenomena associated with 'EIT Wave' transients. These phenomena include coronal mass ejections, flares, EUV/SXR dimmings, chromospheric waves, Moreton waves, solar energetic particle events, energetic electron events, and radio signatures. Although the occurrence of many phenomena correlate with the appearance of EIT waves, it is difficult to infer which associations are causal. The presentation will include a discussion of correlation surveys of these phenomena.

Imaging spectroscopy of type U and J solar radio bursts with LOFAR

NASA Astrophysics Data System (ADS)

Reid, Hamish A. S.; Kontar, Eduard P.

2017-10-01

Context. Radio U-bursts and J-bursts are signatures of electron beams propagating along magnetic loops confined to the corona. The more commonly observed type III radio bursts are signatures of electron beams propagating along magnetic loops that extend into interplanetary space. Given the prevalence of solar magnetic flux to be closed in the corona, why type III bursts are more frequently observed than U-bursts or J-bursts is an outstanding question. Aims: We use Low-Frequency Array (LOFAR) imaging spectroscopy between 30-80 MHz of low-frequency U-bursts and J-bursts, for the first time, to understand why electron beams travelling along coronal loops produce radio emission less often. Radio burst observations provide information not only about the exciting electron beams but also about the structure of large coronal loops with densities that are too low for standard extreme ultraviolet (EUV) or X-ray analysis. Methods: We analysed LOFAR images of a sequence of two J-bursts and one U-burst. The different radio source positions were used to model the spatial structure of the guiding magnetic flux tube and then deduce the energy range of the exciting electron beams without the assumption of a standard density model. We also estimated the electron density along the magnetic flux rope and compared it to coronal models. Results: The radio sources infer a magnetic loop that is 1 solar radius in altitude with the highest frequency sources starting around 0.6 solar radii. Electron velocities were found between 0.13 c and 0.24 c with the front of the electron beam travelling faster than the back of the electron beam. The velocities correspond to energy ranges within the beam from 0.7-11 keV to 0.7-43 keV. The density along the loop is higher than typical coronal density models and the density gradient is smaller. Conclusions: We found that a more restrictive range of accelerated beam and background plasma parameters can result in U-bursts or J-bursts, causing type III bursts to be more frequently observed. The large instability distances required before Langmuir waves are produced by some electron beams, and the small magnitude of the background density gradients makes closed loops less facilitative for radio emission than loops that extend into interplanetary space.

Comparison of Damping Mechanisms for Transverse Waves in Solar Coronal Loops

NASA Astrophysics Data System (ADS)

Montes-Solís, María; Arregui, Iñigo

2017-09-01

We present a method to assess the plausibility of alternative mechanisms to explain the damping of magnetohydrodynamic transverse waves in solar coronal loops. The considered mechanisms are resonant absorption of kink waves in the Alfvén continuum, phase mixing of Alfvén waves, and wave leakage. Our methods make use of Bayesian inference and model comparison techniques. We first infer the values for the physical parameters that control the wave damping, under the assumption of a particular mechanism, for typically observed damping timescales. Then, the computation of marginal likelihoods and Bayes factors enable us to quantify the relative plausibility between the alternative mechanisms. We find that, in general, the evidence is not large enough to support a single particular damping mechanism as the most plausible one. Resonant absorption and wave leakage offer the most probable explanations in strong damping regimes, while phase mixing is the best candidate for weak/moderate damping. When applied to a selection of 89 observed transverse loop oscillations, with their corresponding measurements of damping timescales and taking into account data uncertainties, we find that positive evidence for a given damping mechanism is only available in a few cases.

Comparison of Damping Mechanisms for Transverse Waves in Solar Coronal Loops

DOE Office of Scientific and Technical Information (OSTI.GOV)

Montes-Solís, María; Arregui, Iñigo, E-mail: mmsolis@iac.es

We present a method to assess the plausibility of alternative mechanisms to explain the damping of magnetohydrodynamic transverse waves in solar coronal loops. The considered mechanisms are resonant absorption of kink waves in the Alfvén continuum, phase mixing of Alfvén waves, and wave leakage. Our methods make use of Bayesian inference and model comparison techniques. We first infer the values for the physical parameters that control the wave damping, under the assumption of a particular mechanism, for typically observed damping timescales. Then, the computation of marginal likelihoods and Bayes factors enable us to quantify the relative plausibility between the alternativemore » mechanisms. We find that, in general, the evidence is not large enough to support a single particular damping mechanism as the most plausible one. Resonant absorption and wave leakage offer the most probable explanations in strong damping regimes, while phase mixing is the best candidate for weak/moderate damping. When applied to a selection of 89 observed transverse loop oscillations, with their corresponding measurements of damping timescales and taking into account data uncertainties, we find that positive evidence for a given damping mechanism is only available in a few cases.« less

Dichotomy of Solar Coronal Jets: Standard Jets and Blowout Jets

NASA Technical Reports Server (NTRS)

Moore, R. L.; Cirtain, J. W.; Sterling, A. C.; Falconer, D. A.

2010-01-01

By examining many X-ray jets in Hinode/XRT coronal X-ray movies of the polar coronal holes, we found that there is a dichotomy of polar X-ray jets. About two thirds fit the standard reconnection picture for coronal jets, and about one third are another type. We present observations indicating that the non-standard jets are counterparts of erupting-loop H alpha macrospicules, jets in which the jet-base magnetic arch undergoes a miniature version of the blowout eruptions that produce major CMEs. From the coronal X-ray movies we present in detail two typical standard X-ray jets and two typical blowout X-ray jets that were also caught in He II 304 Angstrom snapshots from STEREO/EUVI. The distinguishing features of blowout X-ray jets are (1) X-ray brightening inside the base arch in addition to the outside bright point that standard jets have, (2) blowout eruption of the base arch's core field, often carrying a filament of cool (T 10(exp 4) - 10(exp 5) K) plasma, and (3) an extra jet-spire strand rooted close to the bright point. We present cartoons showing how reconnection during blowout eruption of the base arch could produce the observed features of blowout X-ray jets. We infer that (1) the standard-jet/blowout-jet dichotomy of coronal jets results from the dichotomy of base arches that do not have and base arches that do have enough shear and twist to erupt open, and (2) there is a large class of spicules that are standard jets and a comparably large class of spicules that are blowout jets.

Coronal Seismology: The Search for Propagating Waves in Coronal Loops

NASA Astrophysics Data System (ADS)

Schad, Thomas A.; Seeley, D.; Keil, S. L.; Tomczyk, S.

2007-05-01

We report on Doppler observations of the solar corona obtained in the Fe XeXIII 1074.7nm coronal emission line with the HAO Coronal Multi-Channel Polarimeter (CoMP) mounted on the NSO Coronal One Shot coronagraph located in the Hilltop Facility of NSO/Sacramento Peak. The COMP is a tunable filtergraph instrument that records the entire corona from the edge of the occulting disk at approximately 1.03 Rsun out to 1.4 Rsun with a spatial resolution of about 4” x 4”. COMP can be rapidly scanned through the spectral line while recording orthogonal states of linear and circular polarization. The two dimensional spatial resolution allows us to correlate temporal fluctuations observed in one part of the corona with those seen at other locations, in particular along coronal loops. Using cross spectral analysis we find that the observations reveal upward propagating waves that are characterized by Doppler shifts with rms velocities of 0.3 km/s, peak wave power in the 3-5 mHz frequency range, and phase speeds 1-3 Mm/s. The wave trajectories are consistent with the direction of the magnetic field inferred from the linear polarization measurements. We discuss the phase and coherence of these waves as a function of height in the corona and relate our findings to previous observations. The observed waves appear to be Alfvenic in character. "Thomas Schad was supported through the National Solar Observatory Research Experiences for Undergraduate (REU) site program, which is co-funded by the Department of Defense in partnership with the National Science Foundation REU Program." Daniel Seeley was supported through the National Solar Observatory Research Experience for Teachers (RET) site program, which is funded by the National Science Foundation RET program.

Stereoscopy and Tomography of Coronal Structures

NASA Astrophysics Data System (ADS)

de Patoul, J.

2012-04-01

The hot solar corona consists of a low density plasma, which is highly structured by the magnetic field. To resolve and study the corona, several solar Ultraviolet (UV) and X-ray telescopes are operated with high spatial and temporal resolution. EUV (Extreme UV) image sequences of the lower solar corona have revealed a wide variety of structures with sizes ranging from the Sun's diameter to the limit of the angular resolution. Active regions can be observed with enhanced temperature and density, as well as 'quiet' regions, coronal holes with lower density and numerous other transient phenomena such as plumes, jets, bright points, flares, filaments, coronal mass ejections, all structured by the coronal magnetic field. In this work, we analyze polar plumes in a sequence of Solar EUV images taken nearly simultaneously by the three telescopes on board of the spacecraft STEREO/SECCHI A and B, and SOHO/EIT. Plumes appear in EUV images as elongated objects starting on the surface of the Sun extending super-radially into the corona. Their formation and contribution to the fast solar wind and other coronal phenomena are still under debate. Knowledge of the polar plume 3-D geometry can help to understand some of the physical processes in the solar corona. In this dissertation we develop new techniques for the characterization of polar plume structures in solar coronal images (Part II) then we analyze these structures using the techniques (Part III): We design a new technique capable of automatically identifying plumes in solar EUV images close to the limb at 1.01-1.39 Ro. This plume identification is based on a multi-scale Hough-wavelet analysis. We show that the method is well adapted to identifying the location, width and orientation of plumes. Starting from Hough-wavelet analysis, we elaborate on two other techniques to determine 3-D plume localization and structure: (i) tomography employing data from a single spacecraft over more than half a rotation and (ii) stereoscopy from simultaneous data observed by two or more spacecrafts. For tomography, we consider the filtered back projection method for which we incorporate the differential rotation of the Sun. For stereoscopy, we use three view directions for a conventional stereoscopic triangulation. These multi-scale Hough-wavelet analyses, stereoscopy and tomography extensions have been applied for the first time in a coronal plumes study. The temporal evolution of the mean orientation of plumes from May 2007 to April 2008 is then analyzed and discussed. Since the plume orientation is assumed to follow the coronal magnetic field, this analysis reveals: (i) a mean orientation of plumes more horizontal than for a dipole magnetic field, (ii) an asymmetry of the coronal open polar cap magnetic field from the solar rotation axis by up to 6° and (iii) a variation of these orientation and asymmetry over the year. Finally, with the help of the reconstructed 3-D geometry of the plumes, we study in detail their temporal evolution as well as the shape and size of their cross sections. The study reveals: (i) different lifetimes of plumes from 2-3 days up to 9 days and (ii) the presence of both near-circular plume cross sections and plumes with curtain-like structures. Also discussed is the plumes positions and their relation to other coronal phenomena such as coronal holes and jets. Plumes are found to be located inside coronal holes, and jets could explain the intensity enhancement within the plumes.

Newborn Coronal Holes Associated with the Disappearance of Polarity Reversal Boundaries (P46)

NASA Astrophysics Data System (ADS)

Shelke, R.

2006-11-01

rajendra_shelke@yahoo.co.in Coronal holes play an important role in the occurrence of various kinds of solar events. The geomagnetic activity, coronal transients, type II radio bursts, and soft X ray blowouts have shown their strong association with coronal holes (Webb et al., 1978; Shelke and Pande, 1985; Bhatnagar, 1996; Hewish and Bravo, 1986). Recently, Shelke (2006) has linked the onset of interplanetary erupting stream disturbances with the evolutionary changes in the coronal holes. The present study reveals that there exists some physical relationship between the formation of new coronal holes and the disappearance of polarity reversal boundaries with or without the overlying prominences. About 124 new coronal holes are found to emerge at the locations where polarity reversal boundaries existed prior to their disappearance. Among them, nearly 66% and 18% newborn coronal holes have been associated with disappearing prominences and disappearing small unipolar magnetic regions (UMRs) with encircled polarity reversal boundaries respectively. Coronal holes and quiescent prominences are stable solar features that last for many solar rotations. A coronal hole is indicative of a radial magnetic field of a predominant magnetic polarity at the photosphere, whereas solar prominence overlying the polarity reversal boundary straddles both the polarities of a bipolar magnetic region. The new coronal hole emerges on the Sun, owing to the changes in magnetic field configuration leading to the opening of closed magnetic structure into the corona. The mechanism that leads to the eruption of polarity reversal boundaries with or without prominences seems to be interlinked with the mechanism that converts bipolar magnetic regions into unipolar magnetic regions characterizing coronal holes. The fundamental activity for the onset of erupting polarity reversal boundary seems to be the opening of preexisting closed magnetic structures into a new coronal hole, which can support mass motion including erupting prominence.

MASC: Magnetic Activity of the Solar Corona

NASA Astrophysics Data System (ADS)

Auchere, Frederic; Fineschi, Silvano; Gan, Weiqun; Peter, Hardi; Vial, Jean-Claude; Zhukov, Andrei; Parenti, Susanna; Li, Hui; Romoli, Marco

We present MASC, an innovative payload designed to explore the magnetic activity of the solar corona. It is composed of three complementary instruments: a Hard-X-ray spectrometer, a UV / EUV imager, and a Visible Light / UV polarimetric coronagraph able to measure the coronal magnetic field. The solar corona is structured in magnetically closed and open structures from which slow and fast solar winds are respectively released. In spite of much progress brought by two decades of almost uninterrupted observations from several space missions, the sources and acceleration mechanisms of both types are still not understood. This continuous expansion of the solar atmosphere is disturbed by sporadic but frequent and violent events. Coronal mass ejections (CMEs) are large-scale massive eruptions of magnetic structures out of the corona, while solar flares trace the sudden heating of coronal plasma and the acceleration of electrons and ions to high, sometimes relativistic, energies. Both phenomena are most probably driven by instabilities of the magnetic field in the corona. The relations between flares and CMEs are still not understood in terms of initiation and energy partition between large-scale motions, small-scale heating and particle acceleration. The initiation is probably related to magnetic reconnection which itself results magnetic topological changes due to e.g. flux emergence, footpoints motions, etc. Acceleration and heating are also strongly coupled since the atmospheric heating is thought to result from the impact of accelerated particles. The measurement of both physical processes and their outputs is consequently of major importance. However, despite its fundamental importance as a driver for the physics of the Sun and of the heliosphere, the magnetic field of our star’s outer atmosphere remains poorly understood. This is due in large part to the fact that the magnetic field is a very difficult quantity to measure. Our knowledge of its strength and orientation is primarily based on extrapolations from photospheric observations, not from direct measurements. These extrapolations require strong assumptions on critical but unobserved quantities and thus fail to accurately reproduce the complex topologies inferred from remote-sensing observations of coronal structures in white light, EUV, and X-rays. Direct measurements of the coronal magnetic field are also clearly identified by the international heliophysics community as a key element susceptible to lead to major breakthroughs in the understanding of our star. MASC is thus designed to answer the following top-level scientific questions: 1. What is the global magnetic field configuration in the corona? 2. What is the role of the magnetic field in the triggering of flares and CMEs? 3. What is the role of the magnetic field in the acceleration mechanisms of the solar winds? 4. What is the energy spectrum and in particular what are the highest energies to which charged particles can be accelerated in the solar corona? MASC will address these fundamental questions with a suite of instruments composed of an X-ray spectrometer, a UV / EUV imager, and a coronagraph working in the visible and at Lyman alpha. The spectrometer will provide information on the energetics of solar flares, in particular at very high energies of accelerated particles. The UV / EUV imager will provide constraints on the temperature of the flaring and non-flaring corona. The coronagraph will provide the number density of free electrons in the corona, maps of the outflow velocity of neutral hydrogen, and measurements of the coronal magnetic field, via the Hanle effect. These measurements will be performed at all steps of the flare-CME processes, thus providing a detailed picture of the solar coronal dynamics in the quiet and eruptive periods.

Feel the Burn, Part II: Quantifying and mapping spectral, spatial, and temporal structures of the transition region under hot and cold coronal regions

NASA Astrophysics Data System (ADS)

Atwood, Shane; Kankelborg, Charles C.

2017-08-01

The coronal volume is filled with magnetic field, yet only part of that volume has sufficient volume to exhibit hot X-ray loops. Using XRT and AIA images, we identify footpoints of hot coronal loops. We then use IRIS rasters to compare the spatial, temporal, and spectral structure of these relatively "heated" and "unheated" regions. We seek a signature of upward-propagating energy that could be associated with hot active region loops.

The Three-part Structure of a Filament-unrelated Solar Coronal Mass Ejection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, H. Q.; Chen, Y.; Wang, B.

Coronal mass ejections (CMEs) often exhibit the typical three-part structure in the corona when observed with white-light coronagraphs, i.e., the bright leading front, dark cavity, and bright core, corresponding to a high-low-high density sequence. As CMEs result from eruptions of magnetic flux ropes (MFRs), which can possess either lower (e.g., coronal-cavity MFRs) or higher (e.g., hot-channel MFRs) density compared to their surroundings in the corona, the traditional opinion regards the three-part structure as the manifestations of coronal plasma pileup (high density), coronal-cavity MFR (low density), and filament (high density) contained in the trailing part of MFR, respectively. In this paper,more » we demonstrate that filament-unrelated CMEs can also exhibit the classical three-part structure. The observations were made from different perspectives through an event that occurred on 2011 October 4. The CME cavity corresponds to the low-density zone between the leading front and the high-density core, and it is obvious in the low corona and gradually becomes fuzzy when propagating outward. The bright core corresponds to a high-density structure that is suggested to be an erupting MFR. The MFR is recorded from both edge-on and face-on perspectives, exhibiting different morphologies that are due to projection effects. We stress that the zone (MFR) with lower (higher) density in comparison to the surroundings can appear as the dark cavity (bright core) when observed through white-light coronagraphs, which is not necessarily the coronal-cavity MFR (erupted filament).« less

Comparing Spatial Distributions of Solar Prominence Mass Derived from Coronal Absorption

NASA Technical Reports Server (NTRS)

Gilbert, Holly; Kilper, Gary; Alexander, David; Kucera, Therese

2010-01-01

In the present work we extend the use of this mass-inference technique to a sample of prominences observed in at least two coronal lines. This approach, in theory, allows a direct calculation of prominence mass and helium abundance and how these properties vary spatially and temporally. Our motivation is two-fold: to obtain a He(exp 0)/H(exp 0) abundance ratio, and to determine how the relative spatial distribution of the two species varies in prominences. The first of these relies on the theoretical expectation that the amount of absorption at each EUV wavelength is well-characterized. However, in this work we show that due to a saturation of the continuum absorption in the 625 A and 368 A lines (which have much higher opacity compared to 195 A-) the uncertainties in obtaining the relative abundances are too high to give meaningful estimates. This is an important finding because of its impact on future studies in this area. The comparison of the spatial distribution of helium and hydrogen presented here augments previous observational work indicating that cross-field diffusion of neutrals is an important mechanism for mass loss. Significantly different loss timescales for neutral He and H (helium drains much more rapidly than hydrogen) can impact prominence structure, and both the present and past studies suggest this mechanism is playing a role in structure and possibly dynamics. Section 2 of this paper contains a description of the observations and Section 3 summarizes the method used to infer mass along with the criteria imposed in choosing prominences appropriate for this study. Section 3 also contains a discussion of the problems due to limitations of the available data and the implications for determining relative abundances. We present our results in Section 4, including plots of radial-like scans of prominence mass in different lines to show the spatial distribution of the different species. The last section contains a discussion summarizing the importance of the qualitative results found in this work. The Appendix provides a detailed derivation of how to obtain prominence mass and helium abundance (A 1) and includes the data for all prominences studied (A2).

Evaluating Uncertainties in Coronal Electron Temperature and Radial Speed Measurements Using a Simulation of the Bastille Day Eruption

NASA Astrophysics Data System (ADS)

Reginald, Nelson; St. Cyr, Orville; Davila, Joseph; Rastaetter, Lutz; Török, Tibor

2018-05-01

Obtaining reliable measurements of plasma parameters in the Sun's corona remains an important challenge for solar physics. We previously presented a method for producing maps of electron temperature and speed of the solar corona using K-corona brightness measurements made through four color filters in visible light, which were tested for their accuracies using models of a structured, yet steady corona. In this article we test the same technique using a coronal model of the Bastille Day (14 July 2000) coronal mass ejection, which also contains quiet areas and streamers. We use the coronal electron density, temperature, and flow speed contained in the model to determine two K-coronal brightness ratios at (410.3, 390.0 nm) and (423.3, 398.7 nm) along more than 4000 lines of sight. Now assuming that for real observations, the only information we have for each line of sight are these two K-coronal brightness ratios, we use a spherically symmetric model of the corona that contains no structures to interpret these two ratios for electron temperature and speed. We then compare the interpreted (or measured) values for each line of sight with the true values from the model at the plane of the sky for that same line of sight to determine the magnitude of the errors. We show that the measured values closely match the true values in quiet areas. However, in locations of coronal structures, the measured values are predictably underestimated or overestimated compared to the true values, but can nevertheless be used to determine the positions of the structures with respect to the plane of the sky, in front or behind. Based on our results, we propose that future white-light coronagraphs be equipped to image the corona using four color filters in order to routinely create coronal maps of electron density, temperature, and flow speed.

Comment on: Polar Plumes and Fine-scale Coronal Structures - On the Interpretation of Coronal Radio Sounding Data by Patzold and Bird

NASA Technical Reports Server (NTRS)

Woo, R.; Habbal, S. R.

1998-01-01

Radio occultation measurements, which probe electron density over a wide dynamic range with high sensitivity and high spatial and temporal resolution reveal a solar corona permeated by a hierarchy of filamentary structures.

Classification and Physical parameters EUV coronal jets with STEREO/SECCHI.

NASA Astrophysics Data System (ADS)

Nistico, Giuseppe; Bothmer, Volker; Patsourakos, Spiro; Zimbardo, Gaetano

In this work we present observations of EUV coronal jets, detected with the SECCHI (Sun Earth Connection Coronal and Heliospheric Investigation) imaging suites of the two STEREO spacecraft. Starting from catalogues of polar and equatorial coronal hole jets (Nistico' et al., Solar Phys., 259, 87, 2009; Ann. Geophys. in press), identified from simultaneous EUV and white-light coronagraph observations, taken during the time period March 2007 to April 2008 when solar activity was at minimum, we perfom a detailed study of some events. A basic char-acterisation of the magnetic morphology and identification of the presence of helical structure were established with respect to recently proposed models for their origin and temporal evo-lution. A classification of the events with respect to previous jet studies shows that amongst the 79 events, identified into polar coronal holes, there were 37 Eiffel tower -type jet events commonly interpreted as a small-scale ( 35 arcsec) magnetic bipole reconnecting with the ambi-ent unipolar open coronal magnetic fields at its looptops, 12 lambda-type jet events commonly interpreted as reconnection with the ambient field happening at the bipoles footpoints. Five events were termed micro-CME type jet events because they resembled classical three-part structured coronal mass ejections (CMEs) but on much smaller scales. The remainig 25 cases could not be uniquely classified. Thirty-one of the total number of events exhibited a helical magnetic field structure, indicative for a torsional motion of the jet around its axis of propaga-tion. The jet events are found to be also present in equatorial coronal holes. We also present the 3-D reconstruction, temperature, velocity, and density measurements of a number of jets during their evolution.

Morphology of Pseudostreamers and Solar Wind Properties

NASA Astrophysics Data System (ADS)

Panasenco, Olga; Velli, Marco

2016-05-01

The solar dynamo and photospheric convection lead to three main types of structures extending from the solar surface into the corona - active regions, solar filaments (prominences when observed at the limb) and coronal holes. These structures exist over a wide range of scales, and are interlinked with each other in evolution and dynamics. Active regions can form clusters of magnetic activity and the strongest overlie sunspots. In the decay of active regions, the boundaries separating opposite magnetic polarities (neutral lines) develop the specific structures called filament channels above which filaments form. In the presence of flux imbalance decaying active regions can also give birth to lower latitude coronal holes. The accumulation of magnetic flux at coronal hole boundaries also creates the conditions for filament formation: polar crown filaments are permanently present at the boundaries of the polar coronal holes. Middle-latitude and equatorial coronal holes - the result of active region evolution - can create pseudostreamers (PSs) if other coronal holes of the same polarity are present. While helmet streamers form between open fields of opposite polarities, the pseudostreamer, characterized by a smaller coronal imprint, typically shows a more prominent straight ray or stalk extending from the corona. The pseudostreamer base at photospheric heights is multipolar; often one observes tripolar magnetic configurations with two neutral lines - where filaments can form - separating the coronal holes. Here we discuss the specific role of filament channels on pseudostreamer topology and on solar wind properties. 1D numerical analysis of PSs shows that the properties of the solar wind from around PSs depend on the presence/absence of filament channels, number of channels and chirality at the PS base low in the corona.

Solar Coronal Loop Dynamics Near the Null Point Above Active Region NOAA 2666

NASA Astrophysics Data System (ADS)

Filippov, B.

2018-06-01

We analyse observations of a saddle-like structure in the corona above the western limb of the Sun on 2017 July 18. The structure was clearly outlined by coronal loops with typical coronal temperature no more than 1 MK. The dynamics of loops showed convergence towards the centre of the saddle in the vertical direction and divergence in the horizontal direction. The event is a clear example of smooth coronal magnetic field reconnection. No heating manifestations in the reconnection region or magnetically connected areas were observed. Potential magnetic field calculations, which use as the boundary condition the SDO/HMI magnetogram taken on July 14, showed the presence of a null point at the height of 122 arcsec above the photosphere just at the centre of the saddle structure. The shape of field lines fits the fan-spine magnetic configuration above NOAA 2666.

Flow properties of the solar wind obtained from white light data, Ulysses observations and a two-fluid model

NASA Technical Reports Server (NTRS)

Habbal, Shadia Rifai; Esser, Ruth; Guhathakurta, Madhulika; Fisher, Richard

1995-01-01

Using the empirical constraints provided by observations in the inner corona and in interplanetary space. we derive the flow properties of the solar wind using a two fluid model. Density and scale height temperatures are derived from White Light coronagraph observations on SPARTAN 201-1 and at Mauna Loa, from 1.16 to 5.5 R, in the two polar coronal holes on 11-12 Apr. 1993. Interplanetary measurements of the flow speed and proton mass flux are taken from the Ulysses south polar passage. By comparing the results of the model computations that fit the empirical constraints in the two coronal hole regions, we show how the effects of the line of sight influence the empirical inferences and subsequently the corresponding numerical results.

Plasma properties and magnetic field structure of the solar corona, based on coordinated Max 1991 observations from SERTS, the VLA, and magnetographs

NASA Technical Reports Server (NTRS)

Brosius, Jeffrey W.

1995-01-01

The purposes of this investigation are to use existing, calibrated, coaligned sets of coordinated multiwaveband observations of the Sun to determine the coronal magnetic field strength and structure, and interpret the collective observations in terms of a self-consistent model of the coronal plasma and magnetic field. This information is vital to understanding processes such as coronal heating, solar wind acceleration, pre-flare energy storage, and active region evolution. Understanding these processes is the central theme of Max '91, the NASA-supported series of solar observing campaigns under which the observations acquired for this work were obtained. The observations came from NASA/GSFC's Solar EUV Rocket Telescope and Spectrograph (SERTS), the Very Large Array (VLA), and magnetographs. The technique of calculating the coronal magnetic field is to establish the contributions to the microwave emission from the two main emission mechanisms: thermal bremsstrahlung and thermal gyroemission. This is done by using the EUV emission to determine values of the coronal plasma quantities needed to calculate the thermal bremsstrahlung contribution to the microwave emission. Once the microwave emission mechanism(s) are determined, the coronal magnetic field can be calculated. A comparison of the coronal magnetic field derived from the coordinated multiwaveband observations with extrapolations from photospheric magnetograms will provide insight into the nature of the coronal magnetic field.

Characterizing the True Background Corona with SDO/AIA

NASA Technical Reports Server (NTRS)

Napier, Kate; Winebarger, Amy; Alexander, Caroline

2014-01-01

Characterizing the nature of the solar coronal background would enable scientists to more accurately determine plasma parameters, and may lead to a better understanding of the coronal heating problem. Because scientists study the 3D structure of the Sun in 2D, any line of sight includes both foreground and background material, and thus, the issue of background subtraction arises. By investigating the intensity values in and around an active region, using multiple wavelengths collected from the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) over an eight-hour period, this project aims to characterize the background as smooth or structured. Different methods were employed to measure the true coronal background and create minimum intensity images. These were then investigated for the presence of structure. The background images created were found to contain long-lived structures, including coronal loops, that were still present in all of the wavelengths, 193 Angstroms,171 Angstroms,131 Angstroms, and 211 Angstroms. The intensity profiles across the active region indicate that the background is much more structured than previously thought.

Bright points and ejections observed on the sun by the KORONAS-FOTON instrument TESIS

NASA Astrophysics Data System (ADS)

Ulyanov, A. S.; Bogachev, S. A.; Kuzin, S. V.

2010-10-01

Five-second observations of the solar corona carried out in the FeIX 171 Å line by the KORONAS-FOTON instrument TESIS are used to study the dynamics of small-scale coronal structures emitting in and around coronal bright points. The small-scale structures of the lower corona display complex dynamics similar to those of magnetic loops located at higher levels of the solar corona. Numerous detected oscillating structures with sizes below 10 000 km display oscillation periods from 50 to 350 s. The period distributions of these structures are different for P < 150 s and P > 150 s, which implies that different oscillation modes are excited at different periods. The small-scale structures generate numerous flare-like events with energies 1024-1026 erg (nanoflares) and with a spatial density of one event per arcsecond or more observed over an area of 4 × 1011 km2. Nanoflares are not associated with coronal bright points, and almost uniformly cover the solar disk in the observation region. The ejections of solar material from the coronal bright points demonstrate velocities of 80-110 km/s.

Simulating multi-spacecraft Heliospheric Imager observations for tomographic reconstruction of interplanetary CMEs

NASA Astrophysics Data System (ADS)

Barnes, D.

2017-12-01

The multiple, spatially separated vantage points afforded by the STEREO and SOHO missions provide physicists with a means to infer the three-dimensional structure of the solar corona via tomographic imaging. The reconstruction process combines these multiple projections of the optically thin plasma to constrain its three-dimensional density structure and has been successfully applied to the low corona using the STEREO and SOHO coronagraphs. However, the technique is also possible at larger, inter-planetary distances using wide-angle imagers, such as the STEREO Heliospheric Imagers (HIs), to observe faint solar wind plasma and Coronal Mass Ejections (CMEs). Limited small-scale structure may be inferred from only three, or fewer, viewpoints and the work presented here is done so with the aim of establishing techniques for observing CMEs with upcoming and future HI-like technology. We use simulated solar wind densities to compute realistic white-light HI observations, with which we explore the requirements of such instruments for determining solar wind plasma density structure via tomography. We exploit this information to investigate the optimal orbital characteristics, such as spacecraft number, separation, inclination and eccentricity, necessary to perform the technique with HIs. Further to this we argue that tomography may be greatly enhanced by means of improved instrumentation; specifically, the use of wide-angle imagers capable of measuring polarised light. This work has obvious space weather applications, serving as a demonstration for potential future missions (such as at L1 and L5) and will prove timely in fully exploiting the science return from the upcoming Solar Orbiter and Parker Solar Probe missions.

Hybrid Stars and Coronal Evolution

NASA Technical Reports Server (NTRS)

Mushotzky, Richard (Technical Monitor); Dupree, Andrea K.

2004-01-01

This program addresses the evolution of stellar coronas by comparing a solar-like corona in the supergiant Dra (G2 Ib-IIa) to the corona in the allegedly more evolved state of a hybrid star, TrA (K2 11-111). Because the hybrid star has a massive wind, it appears likely that the corona will be cooler and less dense as the magnetic loop structures are no longer closed. By analogy with solar coronal holes, when the topology of the magnetic field is configured with open magnetic structures, both the coronal temperature and density are lower than in atmospheres dominated by closed loops. The hybrid stars assume a pivotal role in the definition of coronal evolution, atmospheric heating processes and mechanisms to drive winds of cool stars.

The Solar Wind from Pseudostreamers and their Environs: Opportunities for Observations with Parker Solar Probe and Solar Orbiter

NASA Astrophysics Data System (ADS)

Panasenco, O.; Velli, M.; Panasenco, A.; Lionello, R.

2017-12-01

The solar dynamo and photospheric convection lead to three main types of structures extending from the solar surface into the corona - active regions, solar filaments (prominences when observed at the limb) and coronal holes. These structures exist over a wide range of scales, and are interlinked with each other in evolution and dynamics. Active regions can form clusters of magnetic activity and the strongest overlie sunspots. In the decay of active regions, the boundaries separating opposite magnetic polarities (neutral lines) develop specific structures called filament channels above which filaments form. In the presence of flux imbalance decaying active regions can also give birth to lower latitude coronal holes. The accumulation of magnetic flux at coronal hole boundaries also creates conditions for filament formation: polar crown filaments are permanently present at the boundaries of the polar coronal holes. Mid-latitude and equatorial coronal holes - the result of active region evolution - can create pseudostreamers if other coronal holes of the same polarity are present. While helmet streamers form between open fields of opposite polarities, the pseudostreamer, characterized by a smaller coronal imprint, typically shows a more prominent straight ray or stalk extending from the corona. The pseudostreamer base at photospheric heights is multipolar; often one observes tripolar magnetic configurations with two neutral lines - where filaments can form - separating the coronal holes. Here we discuss the specific role of filament channels on pseudostreamer topology and on solar wind properties. 1D numerical analysis of pseudostreamers shows that the properties of the solar wind from around PSs depend on the presence/absence of filament channels, number of channels and chirality at thepseudostreamer base low in the corona. We review and model possible coronal magnetic configurations and solar wind plasma properties at different distances from the solar surface that may be observed by Parker Solar Probe and Solar Orbiter.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Antolin, P.; Verwichte, E., E-mail: patrick.antolin@astro.uio.no, E-mail: erwin.verwichte@warwick.ac.uk

The condensations composing coronal rain, falling down along loop-like structures observed in cool chromospheric lines such as H{alpha} and Ca II H, have long been a spectacular phenomenon of the solar corona. However, considered a peculiar sporadic phenomenon, it has not received much attention. This picture is rapidly changing due to recent high-resolution observations with instruments such as the Hinode/Solar Optical Telescope (SOT), CRISP of the Swedish 1-m Solar Telescope, and the Solar Dynamics Observatory. Furthermore, numerical simulations have shown that coronal rain is the loss of thermal equilibrium of loops linked to footpoint heating. This result has highlighted themore » importance that coronal rain can play in the field of coronal heating. In this work, we further stress the importance of coronal rain by showing the role it can play in the understanding of the coronal magnetic field topology. We analyze Hinode/SOT observations in the Ca II H line of a loop in which coronal rain puts in evidence in-phase transverse oscillations of multiple strand-like structures. The periods, amplitudes, transverse velocities, and phase velocities are calculated, allowing an estimation of the energy flux of the wave and the coronal magnetic field inside the loop through means of coronal seismology. We discuss the possible interpretations of the wave as either standing or propagating torsional Alfven or fast kink waves. An estimate of the plasma beta parameter of the condensations indicates a condition that may allow the often observed separation and elongation processes of the condensations. We also show that the wave pressure from the transverse wave can be responsible for the observed low downward acceleration of coronal rain.« less

Cometary compact H II regions are stellar-wind bow shocks

NASA Technical Reports Server (NTRS)

Van Buren, Dave; Mac Low, Mordecai-Mark; Wood, Douglas O. S.; Churchwell, ED

1990-01-01

Comet-shaped H II regions, like G34.3 + 0.2, are easily explained as bow shocks created by wind-blowing massive stars moving supersonically through molecular clouds. The required velocities of the stars through dense clumps are less than about 10 km/s, comparable to the velocity dispersion of stars in OB associations. An analytic model of bow shocks matches the gross characteristics seen in the radio continuum and the velocity structure inferred from hydrogen recombination and molecular line observations. The champagne flow model cannot account for these structures. VLBI observations of masers associated with the shells of cometary compact H II regions should reveal tailward proper motions predominantly parallel to the shell, rather than perpendicular. It is predicted that over a decade baseline, high signal-to-noise VLA observations of this class of objects will show headward pattern motion in the direction of the symmetry axis, but not expansion. Finally, shock-generated and coronal infrared lines are also predicted.

Temperature Structure of a Coronal Cavity

NASA Technical Reports Server (NTRS)

Kucera, T. A.; Gibson, S. E.; Schmit, D. J.

2011-01-01

we analyze the temperature structure of a coronal cavity observed in Aug. 2007. coronal cavities are long, low-density structures located over filament neutral lines and are often seen as dark elliptical features at the solar limb in white light, EUV and x-rays. when these structures erupt they form the cavity portions of CMEs. It is important to establish the temperature structure of cavities in order to understand the thermodynamics of cavities in relation to their three-dimensional magnetic structure. To analyze the temperature we compare temperature ratios of a series of iron lines observed by the Hinode/EUv Imaging spectrometer (EIS). We also use those lines to constrain a forward model of the emission from the cavity and streamer. The model assumes a coronal streamer with a tunnel-like cavity with elliptical cross-section and a Gaussian variation of height along the tunnel lenth. Temperature and density can be varied as a function of altitude both in the cavity and streamer. The general cavity morphology and the cavity and streamer density have already been modeled using data from STEREO's SECCHI/EUVI and Hinode/EIS (Gibson et al 2010 and Schmit & Gibson 2011).

Solar and stellar coronal plasmas

NASA Technical Reports Server (NTRS)

Golub, L.

1985-01-01

Progress made in describing and interpreting coronal plasma processes and the relationship between the solar corona and its stellar counterparts is reported. Topics covered include: stellar X-ray emission, HEAO 2 X-ray survey of the Pleiades, closed coronal structures, X-ray survey of main-sequence stars with shallow convection zones, implications of the 1400 MHz flare emission, and magnetic field stochasticity.

The Influence of the Solar Coronal Radiation on Coronal Plasma Structures, I: Determination of the Incident Coronal Radiation

NASA Astrophysics Data System (ADS)

Brown, Gerrard M.; Labrosse, Nicolas

2018-02-01

Coronal structures receive radiation not only from the solar disc, but also from the corona. This height-dependent incident radiation plays a crucial role in the excitation and the ionisation of the illuminated plasma. The aim of this article is to present a method for computing the detailed incident radiation coming from the solar corona, which is perceived at a point located at an arbitrary height. The coronal radiation is calculated by integrating the radiation received at a point in the corona over all of the corona visible from this point. The emission from the corona at all wavelengths of interest is computed using atomic data provided by CHIANTI. We obtain the spectrum illuminating points located at varying heights in the corona at wavelengths between 100 and 912 Å when photons can ionise H or He atoms and ions in their ground states. As expected, individual spectral lines will contribute most at the height within the corona where the local temperature is closest to their formation temperature. As there are many spectral lines produced by many ions, the coronal intensity cannot be assumed to vary in the same way at all wavelengths and so must be calculated for each separate height that is to be considered. This code can be used to compute the spectrum from the corona illuminating a point at any given height above the solar surface. This brings a necessary improvement to models where an accurate determination of the excitation and ionisation states of coronal plasma structures is crucial.

Structure and Dynamics of Coronal Plasma

NASA Technical Reports Server (NTRS)

Golub, Leon

1998-01-01

Brief summaries of the four published papers produced within the present performance period of NASA Grant NAGW-4081 are presented. The full text of the papers are appended to the report. The first paper titled "Coronal Structures Observed in X-rays and H-alpa Structures" was published in the Kofu Symposium proceedings. The study analyzes cool and hot behavior of two x-ray events, a small flare and a surge. It was found that a large H-alpha surge appears in x-rays as a very weak event, while a weak H-alpha feature corresponds to the brightest x-ray emission on the disk at the time of the observation. Calculations of the heating necessary to produce these signatures, and implications for the driving and heating mechanisms of flares vs. surges are presented. The second paper "Differential Magnetic Field Shear in an Active Region" has been published in The Astrophysical Journal. The study compared the three dimensional extrapolation of magnetic fields with the observed coronal structure in an active region. Based on the fit between observed coronal structure throughout the volume of the region and the calculated magnetic field configurations, the authors propose a differential magnetic field shear model for this active region. The decreasing field shear in the outer portions of the AR may indicate a continual relaxation of the magnetic field with time, corresponding to a net transport of helicity outward. The third paper "Difficulties in Observing Coronal Structure" has been published in the journal Solar Physics. This paper discusses the evidence that the temperature and density structure of the corona are far more complicated than had previously been thought. The discussion is based on five studies carried out by the group on coronal plasma properties, showing that any one x-ray instrument does see all of the plasma present in the corona, that hot and cool material may appear to be co-spatial at a given location in the corona, and that simple magnetic field extrapolations provide only a poor fit to the observed structure. The fourth paper "Analysis and Comparison of Loop Structures Imaged with NIXT and Yohkoh/SXT" has been published in Astronomy and Astrophysics. This paper analyzes and compares a variety of coronal loops, deriving loop pressure and emission measure from loop models. They are able to determine the volume filling factor in the corona, which is found to be in the range 0.001 to 0.01 for compact loops, and of order 1 for large structures. The small values suggest highly filamented structures, especially at lower temperatures.

Tethered Prominence-CME Systems Captured during the 2012 November 13 and 2013 November 3 Total Solar Eclipses

NASA Astrophysics Data System (ADS)

Druckmüller, Miloslav; Habbal, Shadia R.; Alzate, Nathalia; Emmanouilidis, Constantinos

2017-12-01

We report on white light observations of high latitude tethered prominences acquired during the total solar eclipses of 2012 November 13 and 2013 November 3, at solar maximum, with a field of view spanning several solar radii. Distinguished by their pinkish hue, characteristic of emission from neutral hydrogen and helium, the four tethered prominences were akin to twisted flux ropes, stretching out to the limit of the field of view, while remaining anchored at the Sun. Cotemporal observations in the extreme ultraviolet from the Solar Dynamics Observatory (SDO/AIA) clearly showed that the pinkish emission from the cool (≈ {10}4-{10}5 K) filamentary prominences was cospatial with the 30.4 nm He II emission, and was directly linked to filamentary structures emitting at coronal temperatures ≥slant {10}6 K in 17.1 and 19.3 nm. The tethered prominences evolved from typical tornado types. Each one formed the core of different types of coronal mass ejections (CMEs), as inferred from coordinated LASCO C2, C3, and STEREO A and B coronagraph observations. Two of them evolved into a series of faint, unstructured puffs. One was a normal CME. The most striking one was a “light-bulb” type CME, whose three-dimensional structure was confirmed from all four coronagraphs. These first uninterrupted detections of prominence-CME systems anchored at the Sun, and stretching out to at least the edge of the field of view of LASCO C3, provide the first observational confirmation for the source of counter-streaming electron fluxes measured in interplanetary CMEs, or ICMEs.

Measurements of Photospheric and Chromospheric Magnetic Fields

NASA Astrophysics Data System (ADS)

Lagg, Andreas; Lites, Bruce; Harvey, Jack; Gosain, Sanjay; Centeno, Rebecca

2017-09-01

The Sun is replete with magnetic fields, with sunspots, pores and plage regions being their most prominent representatives on the solar surface. But even far away from these active regions, magnetic fields are ubiquitous. To a large extent, their importance for the thermodynamics in the solar photosphere is determined by the total magnetic flux. Whereas in low-flux quiet Sun regions, magnetic structures are shuffled around by the motion of granules, the high-flux areas like sunspots or pores effectively suppress convection, leading to a temperature decrease of up to 3000 K. The importance of magnetic fields to the conditions in higher atmospheric layers, the chromosphere and corona, is indisputable. Magnetic fields in both active and quiet regions are the main coupling agent between the outer layers of the solar atmosphere, and are therefore not only involved in the structuring of these layers, but also for the transport of energy from the solar surface through the corona to the interplanetary space. Consequently, inference of magnetic fields in the photosphere, and especially in the chromosphere, is crucial to deepen our understanding not only for solar phenomena such as chromospheric and coronal heating, flares or coronal mass ejections, but also for fundamental physical topics like dynamo theory or atomic physics. In this review, we present an overview of significant advances during the last decades in measurement techniques, analysis methods, and the availability of observatories, together with some selected results. We discuss the problems of determining magnetic fields at smallest spatial scales, connected with increasing demands on polarimetric sensitivity and temporal resolution, and highlight some promising future developments for their solution.

Coronal Current Sheet Evolution in the Aftermath of a CME

NASA Technical Reports Server (NTRS)

Bemporad, A.; Poletto, G.; Suess, S. T.; Ko, Y.-K.; Schwadron, N. A.; Elliott, H. A.; Raymond, J. C.

2005-01-01

We report on SOHO-UVCS observations of coronal restructuring following a Coronal Mass Ejection (CME) on November 26, 2002, at the time of a SOHO-Ulysses quadrature campaign. Starting about 3 hours after the CME, which was directed towards Ulysses, UVCS began taking spectra at 1.7 solar radii, covering emission from both cool and hot plasma. Observations continued, with occasional gaps, for more than 2 days. Emission in the 974.8 Angstrom line of [Fe XVIII], indicating temperatures above 6x10(6) K, was observed throughout the campaign in a spatially limited location. Comparison with EIT images shows the [Fe XVIII] emission to overlie a growing post-flare loop system formed in the aftermath of the CME. The emission most likely originates in a current sheet overlying the arcade. Analysis of the [Fe XVIII] emission allows us to infer the evolution of physical parameters in the current sheet over the entire span of our observations: in particular, we give the temperature vs. time in the current sheet and estimate the density. Ulysses was directly above the location of the CME and intercepted the ejecta. High ionization state Fe was detected by SWICS throughout the magnetic cloud associated with the CME, although the rapid temporal variation suggests bursty, rather than smooth, reconnection in the coronal current sheet. Both the remote and in situ observations are compared with predictions of theoretical CME models.

The role of the large-scale coronal magnetic field in the eruption of prominence/cavity systems

NASA Astrophysics Data System (ADS)

de Toma, G.; Gibson, S. E.; Fan, Y.; Torok, T.

2013-12-01

Prominence/cavity systems are large-scale coronal structures that can live for many weeks and even months and often end their life in the form of large coronal eruptions. We investigate the role of the surrounding ambient coronal field in stabilizing these systems against eruption. In particular, we examine the extent to which the decline with height of the external coronal magnetic field influences the evolution of these coronal systems and their likelihood to erupt. We study prominence/cavity systems during the rising phase of cycle 24 in 2010-2013, when a significant number of CMEs were associated with polar crown or large filament eruptions. We use EUV observations from SDO/AIA to identify stable and eruptive coronal cavities, and SDO/HMI magnetograms as boundary conditions to PFSS extrapolation to derive the ambient coronal field. We compute the decay index of the potential field for the two groups and find that systematic differences exist between eruptive and non-eruptive systems.

Hanle Effect Diagnostics of the Coronal Magnetic Field: A Test Using Realistic Magnetic Field Configurations

NASA Astrophysics Data System (ADS)

Raouafi, N.-E.; Solanki, S. K.; Wiegelmann, T.

2009-06-01

Our understanding of coronal phenomena, such as coronal plasma thermodynamics, faces a major handicap caused by missing coronal magnetic field measurements. Several lines in the UV wavelength range present suitable sensitivity to determine the coronal magnetic field via the Hanle effect. The latter is a largely unexplored diagnostic of coronal magnetic fields with a very high potential. Here we study the magnitude of the Hanle-effect signal to be expected outside the solar limb due to the Hanle effect in polarized radiation from the H I Lyα and β lines, which are among the brightest lines in the off-limb coronal FUV spectrum. For this purpose we use a magnetic field structure obtained by extrapolating the magnetic field starting from photospheric magnetograms. The diagnostic potential of these lines for determining the coronal magnetic field, as well as their limitations are studied. We show that these lines, in particular H I Lyβ, are useful for such measurements.

Research in solar plasma theory

NASA Technical Reports Server (NTRS)

Vanhoven, Gerard

1992-01-01

The main thrust and significance of our research results are presented. The topics covered include: (1) coronal structure and dynamics; (2) coronal heating; (3) filament formation; and (4) flare energy release.

Coronal Heating and the Magnetic Flux Content of the Network

NASA Technical Reports Server (NTRS)

Falconer, D. A.; Moore, R. L.; Porter, J. G.; Hathaway, D. H.; Rose, M. Franklin (Technical Monitor)

2001-01-01

Previously, from analysis of SOHO coronal images in combination with Kitt Peak magnetograms, we found that the quiet corona is the sum of two components: the large-scale corona and the coronal network. The large-scale corona consists of all coronal-temperature (T approximately 10(exp 6) K) structures larger than supergranules (greater than approximately 30,000 kilometers). The coronal network (1) consists of all coronal-temperature structures smaller than supergranules, (2) is rooted in and loosely traces the photospheric magnetic network, (3) has its brightest features seated on polarity dividing lines (neutral lines) in the network magnetic flux, and (4) produces only about 5% of the total coronal emission in quiet regions. The heating of the coronal network is apparently magnetic in origin. Here, from analysis of EIT coronal images of quiet regions in combination with magnetograms of the same quiet regions from SOHO/MDI and from Kitt Peak, we examine the other 95% of the quiet corona and its relation to the underlying magnetic network. We find: (1) Dividing the large-scale corona into its bright and dim halves divides the area into bright "continents" and dark "oceans" having spans of 2-4 supergranules. (2) These patterns are also present in the photospheric magnetograms: the network is stronger under the bright half and weaker under the dim half. (3) The radiation from the large-scale corona increases roughly as the cube root of the magnetic flux content of the underlying magnetic network. In contrast, the coronal radiation from an active region increases roughly linearly with the magnetic flux content of the active region. We assume, as is widely held, that nearly all of the large-scale corona is magnetically rooted in the network. Our results suggest that either the coronal heating in quiet regions has a large non-magnetic component, or, if the heating is predominantly produced via the magnetic field, the mechanism is significantly different than in active regions.

Observational Analysis of Coronal Fans

NASA Technical Reports Server (NTRS)

Talpeanu, D.-C.; Rachmeler, L; Mierla, Marilena

2017-01-01

Coronal fans (see Figure 1) are bright observational structures that extend to large distances above the solar surface and can easily be seen in EUV (174 angstrom) above the limb. They have a very long lifetime and can live up to several Carrington rotations (CR), remaining relatively stationary for many months. Note that they are not off-limb manifestation of similarly-named active region fans. The solar conditions required to create coronal fans are not well understood. The goal of this research was to find as many associations as possible of coronal fans with other solar features and to gain a better understanding of these structures. Therefore, we analyzed many fans and created an overview of their properties. We present the results of this statistical analysis and also a case study on the longest living fan.

Disruption of a coronal streamer by an eruptive prominence and coronal mass ejection

NASA Technical Reports Server (NTRS)

Illing, R. M. E.; Hundhausen, A. J.

1986-01-01

The coronal mass ejection of August 18, 1980 is analyzed using images from the coronagraph on the Solar Maximum Mission (SMM) satellite. The event occurred at the site of a large coronal helmet streamer and evolved into the three-part structure of a bright frontal shell, followed by a relatively dark space surrounding a bright filamentary core as seen in many mass ejections of the SMM epoch. The bright core can be identified as material from a prominence whose eruption was observed from the ground. The mass of the frontal shell is equal to that of the coronal helmet streamer, indicating that the shell is the coronal material previously in the helmet streamer, displaced and set into motion by the erupting prominence and surrounding cavity. The mass ejected in the bright core (or prominences) is estimated to be 50 percent larger than the 'coronal' material in the front loop.

The Origins of Magnetic Structure in the Corona and Wind

NASA Technical Reports Server (NTRS)

Antiochos, Spiro K.

2010-01-01

One of the most important and most puzzling features of the coronal magnetic field is that it appears to have smooth magnetic structure with little evidence for non-potentiality except at two special locations: photospheric polarity inversions lines. (non-potentiality observed as a filament channel) and coronal hole boundaries, (observed as the slow solar wind). This characteristic feature of the closed-field corona is highly unexpected given that its magnetic field is continuously tangled by photospheric motions. Although reconnection can eliminate some of the injected structure, it cannot destroy the helicity, which should build up to produce observable complexity. I propose that an inverse cascade process transports the injected helicity from the interior of closed flux regions to their boundaries inversion lines and coronal holes, creating both filament channels and the slow wind. We describe how the helicity is injected and transported and calculate the relevant rates. I argue that one process, helicity transport, can explain both the observed lack and presence of structure in the coronal magnetic field. This work has been supported by the NASA HTP, SR&T, and LWS programs.

Subphotospheric current systems and flares

NASA Technical Reports Server (NTRS)

Hudson, Hugh S.

1987-01-01

Subphotospheric current systems inferred from recent vector magnetograph observations imply the existence of electric currents penetrating the photosphere and thus flowing deep in the solar convection zone. These currents presumably originate in an internal dynamo that supplies the observed photospheric magnetic fields through the buoyant motions of the initially deeply-buried flux tubes. The coronal fields resulting from this process therefore must carry slowly-varying currents driven by emfs remote from the surface. These currents may then drive solar-flare energy release. This paper discusses the consequences of such a deep origin of the coronal parallel currents. Simple estimates for a large active region suggest a mean current-closure depth of not less than 10,000 km, with a subphotospheric inductance of not less than 100 H and a subphotospheric stored energy of not less than 10 to the 33rd ergs.

Coronal energy distribution and X-ray activity in the small scale magnetic field of the quiet sun

NASA Technical Reports Server (NTRS)

Habbal, S. R.

1992-01-01

The energy distribution in the small-scale magnetic field that pervades the solar surface, and its relationship to X-ray/coronal activity are discussed. The observed emission from the small scale structures, at temperatures characteristic of the chromosphere, transition region and corona, emanates from the boundaries of supergranular cells, within coronal bright points. This emission is characterized by a strong temporal and spatial variability with no definite pattern. The analysis of simultaneous, multiwavelength EUV observations shows that the spatial density of the enhanced as well as variable emission from the small scale structures exhibits a pronounced temperature dependence with significant maxima at 100,000 and 1,000,000 K. Within the limits of the spatial (1-5 arcsec) and temporal (1-5 min) resolution of data available at present, the observed variability in the small scale structure cannot account for the coroal heating of the quiet sun. The characteristics of their emission are more likely to be an indicator of the coronal heating mechanisms.

Forward Modeling of a Coronal Cavity

NASA Technical Reports Server (NTRS)

Kucera, T. A.; Gibson, S. E.; Schmit, D. J.

2011-01-01

We apply a forward model of emission from a coronal cavity in an effort to determine the temperature and density distribution in the cavity. Coronal cavities are long, low-density structures located over filament neutral lines and are often seen as dark elliptical features at the solar limb in white light, EUV and X-rays. When these structures erupt they form the cavity portions of CMEs The model consists of a coronal streamer model with a tunnel-like cavity with elliptical cross-section and a Gaussian variation of height along the tunnel length. Temperature and density can be varied as a function of altitude both in the cavity and streamer. We apply this model to a cavity observed in Aug. 2007 by a wide array of instruments including Hinode/EIS, STEREO/EUVI and SOHO/EIT. Studies such as these will ultimately help us understand the the original structures which erupt to become CMEs and ICMES, one of the prime Solar Orbiter objectives.

Coronal Hole Coming Around

NASA Image and Video Library

2016-12-06

A substantial coronal hole began to rotate into view over the past few days (Dec. 1-2, 2016). Coronal holes are magnetically open areas of the sun's magnetic field structure that spew streams of high speed solar wind into space. In about a week or so that coronal hole might send streams of particles in the direction of Earth. Often times these streams can interact with Earth's magnetosphere and generate aurora. The images were taken in a wavelength of extreme ultraviolet light. Movies are available at http://photojournal.jpl.nasa.gov/catalog/PIA21208

EUV lines observed with EIS/Hinode in a solar prominence

NASA Astrophysics Data System (ADS)

Labrosse, N.; Schmieder, B.; Heinzel, P.; Watanabe, T.

2011-07-01

Context. During a multi-wavelength observation campaign with Hinode and ground-based instruments, a solar prominence was observed for three consecutive days as it crossed the western limb of the Sun in April 2007. Aims: We report on observations obtained on 26 April 2007 using EIS (Extreme ultraviolet Imaging Spectrometer) on Hinode. They are analysed to provide a qualitative diagnostic of the plasma in different parts of the prominence. Methods: After correcting for instrumental effects, the rasters at different wavelengths are presented. Several regions within the same prominence are identified for further analysis. Selected profiles for lines with formation temperatures between log (T) = 4.7 and log (T) = 6.3, as well as their integrated intensities, are given. The profiles of coronal, transition region, and He ii lines are discussed. We pay special attention to the He ii line, which is blended with coronal lines. Results: Some quantitative results are obtained by analysing the line profiles. They confirm that depression in EUV lines can be interpreted in terms of two mechanisms: absorption of coronal radiation by the hydrogen and neutral helium resonance continua, and emissivity blocking. We present estimates of the He ii line integrated intensity in different parts of the prominence according to different scenarios for the relative contribution of absorption and emissivity blocking to the coronal lines blended with the He ii line. We estimate the contribution of the He ii 256.32 Å line to the He ii raster image to vary between ~44% and 70% of the raster's total intensity in the prominence according to the different models used to take into account the blending coronal lines. The inferred integrated intensities of the He ii 256 Å line are consistent with the theoretical intensities obtained with previous 1D non-LTE radiative transfer calculations, yielding a preliminary estimate of the central temperature of 8700 K, a central pressure of 0.33 dyn cm-2, and a column mass of 2.5 × 10-4 g cm-2. The corresponding theoretical hydrogen column density (1020 cm-2) is about two orders of magnitude higher than those inferred from the opacity estimates at 195 Å. The non-LTE calculations indicate that the He ii 256.32 Å line is essentially formed in the prominence-to-corona transition region by resonant scattering of the incident radiation. The movie associated to Fig. 2 is available in electronic form at http://www.aanda.org

Structure and Dynamics of Coronal Plasmas

NASA Technical Reports Server (NTRS)

Golub, Leon

1997-01-01

During the past year this grant has funded research in the interaction between magnetic fields and the hot plasma in the solar outer atmosphere. The following is a brief summary of the published papers, abstracts and talks which have been supported. The paper 'Coronal Structures Observed in X-rays and H-alpha Structures' was published in the Kofu Symposium proceedings. The study analyzes cool and hot behavior of two x-ray events, a small flare and a surge. We find that a large H-alpha surge appears in x-rays as a very weak event, while a weak H-alpha feature corresponds to the brightest x-ray emission on the disk at the time of the observation. Calculations of the heating necessary to produce these signatures, and implications for the driving and heating mechanisms of flares vs. surges are presented. A copy of the paper is appended to this report. The paper 'Differential Magnetic Field Shear in an Active Region' has been published in The Astrophysical Journal. We have compared the 3D extrapolation of magnetic fields with the observed coronal structure in an active region. Based on the fit between observed coronal structure throughout the volume of the region and the calculated magnetic field configurations, we propose a differential magnetic field shear model for this active region. The decreasing field shear in the outer portions of the AR may indicate a continual relaxation of the magnetic field with time, corresponding to a net transport of helicity outward. The paper 'Difficulties in Observing Coronal Structure' has been accepted for publication in the journal Solar Physics. In this paper we discuss the evidence that the temperature and density structure of the corona are far more complicated than had previously been thought. The discussion is based on five studies carried out by our group on coronal plasma properties, showing that any one x-ray instrument does see all of the plasma present in the corona, that hot and cool material may appear to be co-spatial at a given location in the corona, and that simple magnetic field extrapolations provide only a poor fit to the observed structure. A copy of the paper is appended to this report.

Relation of large-scale coronal X-ray structure and cosmic rays. I - Sources of solar wind streams as defined by X-ray emission and H-alpha absorption features

NASA Technical Reports Server (NTRS)

Krieger, A. S.; Nolte, J. T.; Sullivan, J. D.; Lazarus, A. J.; Mcintosh, P. S.; Gold, R. E.; Roelof, E. C.

1975-01-01

The large-scale structure of the corona and the interplanetary medium during Carrington rotations 1601-1607 is discussed relative to recurrent high-speed solar wind streams and their coronal sources. Only streams A, C, D, and F recur on more than one rotation. Streams A and D are associated with coronal holes, while C and F originate in the high corona (20-50 solar radii) over faint X-ray emissions. The association of the streams with holes is confirmed by earlier findings that there are no large equatorial holes without an associated high-speed stream and that the area of the equatorial region of coronal holes is highly correlated with the maximum velocity observed in the associated stream near 1 AU.

The structure and evolution of coronal holes

NASA Technical Reports Server (NTRS)

Timothy, A. F.; Krieger, A. S.; Vaiana, G. S.

1975-01-01

Soft X-ray observations of coronal holes are analyzed to determine the structure, temporal evolution, and rotational properties of those features as well as possible mechanisms which may account for their almost rigid rotational characteristics. It is shown that coronal holes are open features with a divergent magnetic-field configuration resulting from a particular large-scale magnetic-field topology. They are apparently formed when the successive emergence and dispersion of active-region fields produce a swath of unipolar field founded by fields of opposite polarity, and they die when large-scale field patterns emerge which significantly distort the original field configuration. Two types of holes are described (compact and elongated), and three possible rotation mechanisms are considered: a rigidly rotating subphotospheric phenomenon, a linking of high and low latitudes by closed field lines, and an interaction between moving coronal material and open field lines.

Extreme-ultraviolet observations of global coronal wave rotation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Attrill, G. D. R.; Long, D. M.; Green, L. M.

2014-11-20

We present evidence of global coronal wave rotation in EUV data from SOHO/EIT, STEREO/EUVI, and SDO/AIA. The sense of rotation is found to be consistent with the helicity of the source region (clockwise for positive helicity, anticlockwise for negative helicity), with the source regions hosting sigmoidal structures. We also study two coronal wave events observed by SDO/AIA where no clear rotation (or sigmoid) is observed. The selected events show supporting evidence that they all originate with flux rope eruptions. We make comparisons across this set of observations (both with and without clear sigmoidal structures). On examining the magnetic configuration ofmore » the source regions, we find that the nonrotation events possess a quadrupolar magnetic configuration. The coronal waves that do show a rotation originate from bipolar source regions.« less

Internal and External Reconnection Series Homologous Solar Flares

NASA Technical Reports Server (NTRS)

Sterling, Alphonse C.; Moore, Ronald L.

2001-01-01

Using data from the extreme ultraviolet imaging telescope (EIT) on SOHO and the soft X-ray telescope (SXT) on Yohkoh, we examine a series of morphologically homologous solar flares occurring in National Oceanic and Atmospheric Administration (NOAA) active region 8210 over May 1-2, 1998. An emerging flux region (EFR) impacted against a sunspot to the west and next to a coronal hole to the east is the source of the repeated flaring. An SXT sigmoid parallels the EFR's neutral line at the site of the initial flaring in soft X rays. In EIT each flaring episode begins with the formation of a crinkle pattern external to the EFR. These EIT crinkles move out from, and then in toward, the EFR with velocities approx. 20 km/ s. A shrinking and expansion of the width of the coronal hole coincides with the crinkle activity, and generation and evolution of a postflare loop system begins near the time of crinkle formation. Using a schematic based on magnetograms of the region, we suggest that these observations are consistent with the standard reconnection-based model for solar eruptions but are modified by the presence of the additional magnetic fields of the sunspot and coronal hole. In the schematic, internal reconnection begins inside of the EFR-associated fields, unleashing a flare, postflare loops, and a coronal mass ejection (CME). External reconnection, first occurring between the escaping CME and the coronal hole field and second occurring between fields formed as a result of the first external reconnection, results in the EIT crinkles and changes in the coronal hole boundary. By the end of the second external reconnection, the initial setup is reinstated; thus the sequence can repeat, resulting in morphologically homologous eruptions. Our inferred magnetic topology is similar to that suggested in the "breakout model" of eruptions although we cannot determine if our eruptions are released primarily by the breakout mechanism (external reconnection) or, alternatively, primarily by the internal reconnection.

The Solar Wind Source Cycle: Relationship to Dynamo Behavior

NASA Astrophysics Data System (ADS)

Luhmann, J. G.; Li, Y.; Lee, C. O.; Jian, L. K.; Petrie, G. J. D.; Arge, C. N.

2017-12-01

Solar cycle trends of interest include the evolving properties of the solar wind, the heliospheric medium through which the Sun's plasmas and fields interact with Earth and the planets -including the evolution of CME/ICMEs enroute. Solar wind sources include the coronal holes-the open field regions that constantly evolve with solar magnetic fields as the cycle progresses, and the streamers between them. The recent cycle has been notably important in demonstrating that not all solar cycles are alike when it comes to contributions from these sources, including in the case of ecliptic solar wind. In particular, it has modified our appreciation of the low latitude coronal hole and streamer sources because of their relative prevalence. One way to understand the basic relationship between these source differences and what is happening inside the Sun and on its surface is to use observation-based models like the PFSS model to evaluate the evolution of the coronal field geometry. Although the accuracy of these models is compromised around solar maximum by lack of global surface field information and the sometimes non-potential evolution of the field related to more frequent and widespread emergence of active regions, they still approximate the character of the coronal field state. We use these models to compare the inferred recent cycle coronal holes and streamer belt sources of solar wind with past cycle counterparts. The results illustrate how (still) hemispherically asymmetric weak polar fields maintain a complex mix of low-to-mid latitude solar wind sources throughout the latest cycle, with a related marked asymmetry in the hemispheric distribution of the ecliptic wind sources. This is likely to be repeated until the polar field strength significantly increases relative to the fields at low latitudes, and the latter symmetrize.

TRIGGER MECHANISM OF SOLAR SUBFLARES IN A BRAIDED CORONAL MAGNETIC STRUCTURE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tiwari, Sanjiv K.; Alexander, Caroline E.; Winebarger, Amy R.

Fine-scale braiding of coronal magnetic loops by continuous footpoint motions may power coronal heating via nanoflares, which are spontaneous fine-scale bursts of internal reconnection. An initial nanoflare may trigger an avalanche of reconnection of the braids, making a microflare or larger subflare. In contrast to this internal triggering of subflares, we observe external triggering of subflares in a braided coronal magnetic field observed by the High-resolution Coronal Imager (Hi-C). We track the development of these subflares using 12 s cadence images acquired by SDO/AIA in 1600, 193, 94 Å, and registered magnetograms of SDO/HMI, over four hours centered on the Hi-Cmore » observing time. These data show numerous recurring small-scale brightenings in transition-region emission happening on polarity inversion lines where flux cancellation is occurring. We present in detail an example of an apparent burst of reconnection of two loops in the transition region under the braided coronal field which is appropriate for releasing a short reconnected loop downward and a longer reconnected loop upward. The short loop presumably submerges into the photosphere, participating in observed flux cancellation. A subflare in the overlying braided magnetic field is apparently triggered by the disturbance of the braided field by the reconnection-released upward loop. At least 10 subflares observed in this braided structure appear to be triggered this way. How common this external trigger mechanism for coronal subflares is in other active regions, and how important it is for coronal heating in general, remain to be seen.« less

INFERRING THE STRUCTURE OF THE SOLAR CORONA AND INNER HELIOSPHERE DURING THE MAUNDER MINIMUM USING GLOBAL THERMODYNAMIC MAGNETOHYDRODYNAMIC SIMULATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Riley, Pete; Lionello, Roberto; Linker, Jon A., E-mail: pete@predsci.com, E-mail: lionel@predsci.com, E-mail: linkerj@predsci.com

Observations of the Sun’s corona during the space era have led to a picture of relatively constant, but cyclically varying solar output and structure. Longer-term, more indirect measurements, such as from {sup 10}Be, coupled by other albeit less reliable contemporaneous reports, however, suggest periods of significant departure from this standard. The Maunder Minimum was one such epoch where: (1) sunspots effectively disappeared for long intervals during a 70 yr period; (2) eclipse observations suggested the distinct lack of a visible K-corona but possible appearance of the F-corona; (3) reports of aurora were notably reduced; and (4) cosmic ray intensities atmore » Earth were inferred to be substantially higher. Using a global thermodynamic MHD model, we have constructed a range of possible coronal configurations for the Maunder Minimum period and compared their predictions with these limited observational constraints. We conclude that the most likely state of the corona during—at least—the later portion of the Maunder Minimum was not merely that of the 2008/2009 solar minimum, as has been suggested recently, but rather a state devoid of any large-scale structure, driven by a photospheric field composed of only ephemeral regions, and likely substantially reduced in strength. Moreover, we suggest that the Sun evolved from a 2008/2009-like configuration at the start of the Maunder Minimum toward an ephemeral-only configuration by the end of it, supporting a prediction that we may be on the cusp of a new grand solar minimum.« less

Initiation of Coronal Mass Ejections

NASA Technical Reports Server (NTRS)

Moore, Ronald L.; Sterling, Alphonse C.

2005-01-01

This paper is a synopsis of the initiation of the strong-field magnetic explosions that produce large, fast coronal mass ejections. Cartoons based on observations are used to describe the inferred basic physical processes and sequences that trigger and drive the explosion. The magnetic field that explodes is a sheared-core bipole that may or may not be embedded in surrounding strong magnetic field, and may or may not contain a flux rope before it starts to explode. We describe three different mechanisms that singly or in combination trigger the explosion: (1) runaway internal tether-cutting reconnection, (2) runaway external tether-cutting reconnection, and (3) ideal MHD instability or loss or equilibrium. For most eruptions, high-resolution, high-cadence magnetograms and chromospheric and coronal movies (such as from TRACE and/or Solar-B) of the pre-eruption region and of the onset of the eruption and flare are needed to tell which one or which combination of these mechanisms is the trigger. Whatever the trigger, it leads to the production of an erupting flux rope. Using a simple model flux rope, we demonstrate that the explosion can be driven by the magnetic pressure of the expanding flux rope, provided the shape of the expansion is "fat" enough.

Magnetic Field-Line Lengths in Interplanetary Coronal Mass Ejections Inferred From Energetic Electron Events (Postprint)

DTIC Science & Technology

2012-05-03

ENERGETIC ELECTRON EVENTS (POSTPRINT) S.W. Kahler, et al. 03 May 2012 Technical Paper APPROVED FOR PUBLIC RELEASE...REPORT DATE (DD-MM-YYYY) 03-05-2012 2. REPORT TYPE Technical Paper 3. DATES COVERED (From - To) 1 Oct 2007 – 13 Jul 2011 4. TITLE AND SUBTITLE...AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT NUMBER ir Force Research Laboratory Space Vehicles Directorate 3550 Aberdeen Ave SE

The Coronal Monsoon: Thermal Nonequilibrium Revealed by Periodic Coronal Rain

NASA Astrophysics Data System (ADS)

Auchère, Frédéric; Froment, Clara; Soubrié, Elie; Antolin, Patrick; Oliver, Ramon; Pelouze, Gabriel

2018-02-01

We report on the discovery of periodic coronal rain in an off-limb sequence of Solar Dynamics Observatory/Atmospheric Imaging Assembly images. The showers are co-spatial and in phase with periodic (6.6 hr) intensity pulsations of coronal loops of the sort described by Auchère et al. and Froment et al. These new observations make possible a unified description of both phenomena. Coronal rain and periodic intensity pulsations of loops are two manifestations of the same physical process: evaporation/condensation cycles resulting from a state of thermal nonequilibrium. The fluctuations around coronal temperatures produce the intensity pulsations of loops, and rain falls along their legs if thermal runaway cools the periodic condensations down and below transition-region temperatures. This scenario is in line with the predictions of numerical models of quasi-steadily and footpoint heated loops. The presence of coronal rain—albeit non-periodic—in several other structures within the studied field of view implies that this type of heating is at play on a large scale.

Lifecycle of a large-scale polar coronal pseudostreamer/cavity system

NASA Astrophysics Data System (ADS)

Guennou, Chloé; Auchere, Frederic; Seaton, Daniel; Rachmeler, Laurel

2016-07-01

Coronal cavities, tunnel-like areas of rarefied density, provide important information about the magnetic structures that support prominences. The magnetic energy is stored through the twisted or shared magnetic field, ultimately released through Coronal Mass Ejections (CME). To be able to forecast these energetic releases of material and prevent potential terrestrial consequences, the understanding of the cavity 3D morphology, magnetic and thermal properties are essential. The prominences embedded in the cavity only trace a small part of the magnetic field, whereas the much larger cavity provides more information about the magnetic field morphology. As a result, a clear understanding of the coronal volume of the cavity significantly advances our understanding of both the pre-eruption equilibrium and the triggers of such eruptions. Determining both morphological and thermodynamical coronal structures is difficult due to the optically thin nature of the plasma. Observations are subject to integration along the line-of-sight (LOS). This effect can strongly complicate both the derivation and the interpretation of important physical quantities. One way to deduce the 3D structure is with Solar Rotational Tomography (SRT). The 3D plasma emissivity is estimated from EUV/white light images taken from different viewpoints. Physical properties can be then derived using Differential Emission Measure analysis from multi-wavelength 3D reconstructions. We applied this technique to an exceptional large-scale coronal pseudostreamer/cavity system in the southern polar region of the solar corona that was visible for approximately a year starting in February 2014. It is unusual to see such a large closed-field structure embedded within the open polar coronal hole. We investigate this structure to document its formation, evolution and eventually its shrinking process using data from both the PROBA2/SWAP and SDO/AIA EUV imagers. We found that the cavity temperature is extremely stable with time and is essentially at a similar or slightly hotter temperature than the surrounding pseudostreamer. Two regimes in cavity thermal properties were observed: during the first 5 months of observation, we found lower density depletion and highly multi-thermal plasma, while after the pseudostreamer became stable and slowly shrank, the depletion was more pronounced and the plasma was less multithermal. As the thermodynamic properties are strongly correlated with the magnetic structure, these results provide constraints on both the trigger of CMEs and the processes that maintain cavities stability for such a long lifetime.

Resonant electrodynamic heating of stellar coronal loops: An LRC circuit analogue

NASA Technical Reports Server (NTRS)

Ionson, J. A.

1980-01-01

The electrodynamic coupling of stellar coronal loops to underlying beta velocity fields. A rigorous analysis revealed that the physics can be represented by a simple yet equivalent LRC circuit analogue. This analogue points to the existence of global structure oscillations which resonantly excite internal field line oscillations at a spatial resonance within the coronal loop. Although the width of this spatial resonance, as well as the induced currents and coronal velocity field, explicitly depend upon viscosity and resistivity, the resonant form of the generalized electrodynamic heating function is virtually independent of irreversibilities. This is a classic feature of high quality resonators that are externally driven by a broad band source of spectral power. Applications to solar coronal loops result in remarkable agreement with observations.

The temperature structure, mass, and energy flow in the corona and inner solar wind

NASA Technical Reports Server (NTRS)

Withbroe, George L.

1988-01-01

Remote-sensing and in situ data are used to constrain a radiative energy balance model in order to study the radial variations of coronal temperatures, densities, and outflow speeds in several types of coronal holes and in an unstructured quiet region of the corona. A one-fluid solar wind model is used which takes into account the effects of radiative and inward conductive losses in the low corona and the chromospheric-coronal transition region. The results show that the total nonradiative energy input in magnetically open coronal regions is 5 + or - 10 to the 5th ergs/sq cm, and that most of the energy heating the coronal plasma is dissipated within 2 solar radii of the solar surface.

Coronal partings

NASA Astrophysics Data System (ADS)

Nikulin, Igor F.; Dumin, Yurii V.

2016-02-01

The basic observational properties of "coronal partings"-the special type of quasi-one-dimensional magnetic structures, identified by a comparison of the coronal X-ray and EUV images with solar magnetograms-are investigated. They represent the channels of opposite polarity inside the unipolar large-scale magnetic fields, formed by the rows of magnetic arcs directed to the neighboring sources of the background polarity. The most important characteristics of the partings are discussed. It can be naturally assumed that-from the evolutionary and spatial points of view-the partings can transform into the coronal holes and visa versa. The classes of global, intersecting, and complex partings are identified.

AN INVESTIGATION OF TIME LAG MAPS USING THREE-DIMENSIONAL SIMULATIONS OF HIGHLY STRATIFIED HEATING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Winebarger, Amy R.; Lionello, Roberto; Downs, Cooper

2016-11-10

The location and frequency of coronal energy release provide a significant constraint on the coronal heating mechanism. The evolution of the intensity observed in coronal structures found from time lag analysis of Atmospheric Imaging Assembly (AIA) data has been used to argue that heating must occur sporadically. Recently, we have demonstrated that quasi-steady, highly stratified (footpoint) heating can produce results qualitatively consistent with the evolution of observed coronal structures. The goals of this paper are to demonstrate that time lag analysis of 3D simulations of footpoint heating are qualitatively consistent with time lag analysis of observations and to use themore » 3D simulations to further understand whether time lag analysis is a useful tool in defining the evolution of coronal structures. We find the time lag maps generated from simulated data are consistent with the observed time lag maps. We next investigate several example points. In some cases, the calculated time lag reflects the evolution of a unique loop along the line of sight, though there may be additional evolving structures along the line of sight. We confirm that using the multi-peak AIA channels can produce time lags that are difficult to interpret. We suggest using a different high temperature channel, such as an X-ray channel. Finally, we find that multiple evolving structures along the line of sight can produce time lags that do not represent the physical properties of any structure along the line of sight, although the cross-correlation coefficient of the lightcurves is high. Considering the projected geometry of the loops may reduce some of the line-of-sight confusion.« less

Study of the solar corona using radio and space observations

NASA Technical Reports Server (NTRS)

Dulk, G. A.

1984-01-01

The physics of coronal transients, the characteristics of radiation and accelerated particles at the time of flares, and the density/temperature structure of the transition region and corona and the coronal magnetic field are investigated.

Coronal Heating Observed with Hi-C

NASA Technical Reports Server (NTRS)

Winebarger, Amy R.

2013-01-01

The recent launch of the High-Resolution Coronal Imager (Hi-C) as a sounding rocket has offered a new, different view of the Sun. With approx 0.3" resolution and 5 second cadence, Hi-C reveals dynamic, small-scale structure within a complicated active region, including coronal braiding, reconnection regions, Alfven waves, and flows along active region fans. By combining the Hi-C data with other available data, we have compiled a rich data set that can be used to address many outstanding questions in solar physics. Though the Hi-C rocket flight was short (only 5 minutes), the added insight of the small-scale structure gained from the Hi-C data allows us to look at this active region and other active regions with new understanding. In this talk, I will review the first results from the Hi-C sounding rocket and discuss the impact of these results on the coronal heating problem.

The Role of Magnetic Reconnection in Solar Activity

NASA Technical Reports Server (NTRS)

Antiochos, Spiro; DeVore, C. R.

2008-01-01

The central challenge in solar/heliospheric physics is to understand how the emergence and transport of magnetic flux at the photosphere drives the structure and dynamics that we observe in the corona and heliosphere. This presentation focuses on the role of magnetic reconnection in determining solar/heliospheric activity. We demonstrate that two generic properties of the photospheric magnetic and velocity fields are responsible for the ubiquitous reconnection in the corona. First, the photospheric velocities are complex, which leads to the injection of energy and helicity into the coronal magnetic fields and to the efficient, formation of small-scale structure. Second, the flux distribution at the photosphere is multi-polar, which implies that topological discontinuities and, consequently, current sheets, must be present in the coronal magnetic field. We: present numerical simulations showing that photospherically-driven reconnection is responsible for the heating and dynamics of coronal plasma, and for the topology of the coronal/heliospheric magnetic field.

Study of the Source Regions of Coronal Mass Ejections Using Yohkoh SXT Data

NASA Technical Reports Server (NTRS)

Webb, David F.; Kahler, Stephen W.

1997-01-01

The scientific objective of the program was to better understand how CMEs (Coronal Mass Ejections) are initiated at the sun by examining structures on the disk which are related to the origins of CMEs. CMEs represent important disruptions of large-scale structures of closed magnetic fields in the corona, and result in significant disturbances of the interplanetary medium and near-Earth space. The program pertained to NASA's objectives of understanding the physics of solar activity and the structured and evolution of the corona, and the results are being applied to understanding CMEs currently being observed by SOHO near the sun and by WIND and Ulysses in the heliosphere. Three general areas of research were pursued in the program. One was to use Yohkoh soft X-ray telescope (SXT) images of eruptive events visible against the solar disk to examine the coronal structures and the boundaries of the large-scale magnetic fields considered to be involved in coronal mass ejections (CMEs). The second area involved a survey and study of SXT X-ray arcade events which exhibit dimming, or the possible depletion of coronal material above and possibly before onset of the bright long-duration event (LDE). Finally, we studied the SXT data during periods when white light CMEs were observed the HAO Mauna Loa K-coronameter and, conversely, we examined the white light data during periods when expanding X-ray loops were observed at the limb.

Closed coronal structures. V - Gasdynamic models of flaring loops and comparison with SMM observations

NASA Technical Reports Server (NTRS)

Peres, G.; Serio, S.; Vaiana, G.; Acton, L.; Leibacher, J.; Rosner, R.; Pallavicini, R.

1983-01-01

A time-dependent one-dimensional code incorporating energy, momentum and mass conservation equations, and taking the entire solar atmospheric structure into account, is used to investigate the hydrodynamic response of confined magnetic structures to strong heating perturbations. Model calculation results are compared with flare observations which include the light curves of spectral lines formed over a wide range of coronal flare temperatures, as well as determinations of Doppler shifts for the high temperature plasma. It is shown that the numerical simulation predictions are in good overall agreement with the observed flare coronal plasma evolution, correctly reproducing the temporal profile of X-ray spectral lines and their relative intensities. The predicted upflow velocities support the interpretation of the blueshifts as due to evaporation of chromospheric material.

Alfvén Waves in the Solar Corona

NASA Astrophysics Data System (ADS)

Tomczyk, S.; McIntosh, S. W.; Keil, S. L.; Judge, P. G.; Schad, T.; Seeley, D. H.; Edmondson, J.

2007-08-01

Alfvén waves, transverse incompressible magnetic oscillations, have been proposed as a possible mechanism to heat the Sun’s corona to millions of degrees by transporting convective energy from the photosphere into the diffuse corona. We report the detection of Alfvén waves in intensity, line-of-sight velocity, and linear polarization images of the solar corona taken using the FeXIII 1074.7-nanometer coronal emission line with the Coronal Multi-Channel Polarimeter (CoMP) instrument at the National Solar Observatory, New Mexico. Ubiquitous upward propagating waves were seen, with phase speeds of 1 to 4 megameters per second and trajectories consistent with the direction of the magnetic field inferred from the linear polarization measurements. An estimate of the energy carried by the waves that we spatially resolved indicates that they are too weak to heat the solar corona; however, unresolved Alfvén waves may carry sufficient energy.

Constraints on Variability of Brightness and Surface Magnetism on Time Scales of Decades to Centuries in the Sun and Sun-Like Stars: A Source of Potential Terrestrial Climate Variability

NASA Technical Reports Server (NTRS)

Baliunas, Sallie L.; Sharber, James (Technical Monitor)

2003-01-01

The following summarizes the most important, results of our research: (1) Conciliation of solar and stellar photometric variability; (2) Demonstration of an inverse correlation between the global temperature of the terrestrial lower troposphere, inferred from the NASA Microwave Sounding Unit (MSU)) radiometers, and the total area of the Sun covered by coronal holes from January 1979 to present (up to May 2000); (3) Identification of a possible climate mechanism amplifying the impact of solar ultraviolet irradiance variations; (4) Exploration of natural variability in an ocean-atmosphere climate model; (5) Presentation of a review of the sun's coronal influence on the terrestrial space environment; (6) Quantification of stellar variability as an influence on the analysis of periodic radial velocities that imply the presence of a planetary companion.

The Structure of Coronal Loops

NASA Technical Reports Server (NTRS)

Antiochos, Spiro K.

2009-01-01

It is widely believed that the simple coronal loops observed by XUV imagers, such as EIT, TRACE, or XRT, actually have a complex internal structure consisting of many (perhaps hundreds) of unresolved, interwoven "strands". According to the nanoflare model, photospheric motions tangle the strands, causing them to reconnect and release the energy required to produce the observed loop plasma. Although the strands, themselves, are unresolved by present-generation imagers, there is compelling evidence for their existence and for the nanoflare model from analysis of loop intensities and temporal evolution. A problem with this scenario is that, although reconnection can eliminate some of the strand tangles, it cannot destroy helicity, which should eventually build up to observable scales. we consider, therefore, the injection and evolution of helicity by the nanoflare process and its implications for the observed structure of loops and the large-scale corona. we argue that helicity does survive and build up to observable levels, but on spatial and temporal scales larger than those of coronal loops. we discuss the implications of these results for coronal loops and the corona, in general .

The structure of the inner heliosphere from Pioneer Venus and IMP observations

NASA Technical Reports Server (NTRS)

Gazis, P. R.; Barnes, A.; Mihalov, J. D.; Lazarus, A. J.

1992-01-01

The IMP 8 and Pioneer Venus Orbiter (PVO) spacecraft explore the region of heliographic latitudes between 8 deg N and 8 deg S. Solar wind observations from these spacecraft are used to construct synoptic maps of solar wind parameters in this region. These maps provide an explicit picture of the structure of high speed streams near 1 AU and how that structure varies with time. From 1982 until early 1985, solar wind parameters varied little with latitude. During the last solar minimum, the solar wind developed strong latitudinal structure; high speed streams were excluded from the vicinity of the solar equator. Synoptic maps of solar wind speed are compared with maps of the coronal source surface magnetic field. This comparison reveals the expected correlation between solar wind speed near 1 AU, the strength of the coronal magnetic field, and distance from the coronal neutral line.

Wave Propagation Around Coronal Structures: Stratification, Buoyancy, Small Scale Formation

NASA Astrophysics Data System (ADS)

Tomlinson, S. M.; Rappazzo, F.; Velli, M.

2017-12-01

We study the propagation of waves in a coronal medium characterized by stratification and structure in density. temperature and magnetic field. It is well known that average gradients affect the propagation of Alfvén and other MHD waves via reflection, phase mixing, resonant absorption and other coupling phenomena. Here we discuss how the interplay of propagation on inhomogeneous, stratified structures with nonlinear interactions may lead to interesting effects including preferential heating, buoyancy, and plasma acceleration.

An observation of prominence condensation out of a coronal void

NASA Astrophysics Data System (ADS)

Wagner, W. J.; Newkirk, G., Jr.; Schmidt, H. U.

1983-02-01

Photographic averaging of cine-camera data-frames from the 7 March 1970 eclipse provided a record of the inner white light corona with unusually high resolution for low-contrast features. The authors report that a coronal void, similar to high corona structures associated with prominence formation (MacQueen et al., 1983), extended low into the corona. During eclipse totality, a coronal rain prominence condensed from the base of the void.

Simultaneous Solar Maximum Mission (SMM) and very large array observations of solar active regions

NASA Technical Reports Server (NTRS)

Lang, K. R.

1986-01-01

The research deals mainly with Very Large Array and Solar Maximum Mission observations of the ubiquitous coronal loops that dominate the structure of the low corona. As illustrated, the observations of thermal cyclotron lines at microwave wavelengths provide a powerful new method of accurately specifying the coronal magnetic field strength. Processes are delineated that trigger solar eruptions from coronal loops, including preburst heating and the magnetic interaction of coronal loops. Evidence for coherent burst mechanisms is provided for both the Sun and nearby stars, while other observations suggest the presence of currents that may amplify the coronal magnetic field to unexpectedly high levels. The existence is reported of a new class of compact, variable moving sources in regions of apparently weak photospheric field.

Characteristics of shocks in the solar corona, as inferred from radio, optical, and theoretical investigations

NASA Technical Reports Server (NTRS)

Maxwell, A.; Dryer, M.

1982-01-01

Solar radio bursts of spectral type II provide one of the chief diagnostics for the propagation of shocks through the solar corona. Radio data on the shocks are compared with computer models for propagation of fast-mode MHD shocks through the solar corona. Data on coronal shocks and high-velocity ejecta from solar flares are then discussed in terms of a general model consisting of three main velocity regimes.

The quiet sun

NASA Technical Reports Server (NTRS)

Gibson, E. G.

1973-01-01

An up-to-date textbook of solar physics is presented. The solar structure and processes, and the interior are described along with the photosphere, the chromosphere, and the corona. The strongest Fraunhofer lines, visible coronal lines, and coronal UV, XUV, and X-ray lines are listed.

Relation of large-scale coronal X-ray structure and cosmic rays. II - Coronal control of interplanetary injection of 300 keV protons

NASA Technical Reports Server (NTRS)

Roelof, E. C.; Gold, R. E.; Krimigis, S. M.; Krieger, A. S.; Nolte, J. T.; Mcintosh, P. S.; Lazarus, A. J.; Sullivan, J. D.

1975-01-01

We report the striking coronal control of low-energy solar particles from the solar flare of September 7, 1973. The flare was at S18, W46 (Carrington longitude 188 deg) in McMath Plage Region 12307. We find strong intensity gradients in heliolongitude (about 10% per deg) that are nearly identical in protons, helium, and medium nuclei at energies about 0.5 MeV/nuc, as well as relativistic electrons and 3 MeV protons. This pervasive gradient occurs at longitudes over bright X-ray emission structures east of the flare site which interconnect large-scale chromospheric polarity regions identifiable in H-alpha filtergrams.

A comparison of coronal X-ray structures of active regions with magnetic fields computed from photospheric observations

NASA Technical Reports Server (NTRS)

Poletto, G.; Vaiana, G. S.; Zombeck, M. V.; Krieger, A. S.; Timothy, A. F.

1975-01-01

The appearances of several X-ray active regions observed on March 7, 1970 and June 15, 1973 are compared with the corresponding coronal magnetic-field topology. Coronal fields have been computed from measurements of the longitudinal component of the underlying magnetic fields, based on the current-free hypothesis. An overall correspondence between X-ray structures and calculated field lines is established, and the magnetic counterparts of different X-ray features are also examined. A correspondence between enhanced X-ray emission and the location of compact closed field lines is suggested. Representative magnetic-field values calculated under the assumption of current-free fields are given for heights up to 200 sec.

Solar wind ion composition and charge states

NASA Technical Reports Server (NTRS)

vonSteiger, R.

1995-01-01

The solar wind, a highly tenuous plasma streaming from the Sun into interplanetary space at supersonic speed, is roughly composed of 95% hydrogen and 5% helium by number. All other, heavy elements contribute less than 0.1% by number and thus are truly test particles Nevertheless, these particles provide valuable information not present in the main components. We first discuss the importance of the heavy ions as tracers for processes in the solar atmosphere. Specifically, their relative abundances are found to be different in the solar wind as compared to the photosphere. This fractionation, which is best organized as a function of the first ionization time (FIT) of the elements under solar surface conditions, provides information on the structure of the chromosphere. where it is imparted on the partially ionized material by an atom-ion separation mechanism. Moreover, the charge states of the heavy ions can be used to infer the coronal temperature, since they are frozen-in near the altitude where the expansion time scale overcomes the ionization/recombination time scales. Next, we review the published values of ion abundances in the solar wind, concentrating on the recent results of the SWICS instrument on Ulysses. About 8 elements and more than 20 charge states can be routinely analyzed by this sensor. There is clear evidence that both the composition and the charge state distribution is significantly different in the fast solar wind from the south polar coronal hole, traversed by Ulysses in 1993/94, as compared to the solar wind normally encountered near the ecliptic plane. The fractionation between low- and high-FIT elements is reduced, and the charge states indicate a lower, more uniform coronal temperature in the hole. Finally, we discuss these results in the framework of existing theoretical models of the chromosphere and corona, attempting to identify differences between the low- and high-latitude regions of the solar atmosphere.

Comparing Temporally-Separated Solar Wind Structures at 1 AU (STEREO A and OMNI)

NASA Astrophysics Data System (ADS)

Galvin, A. B.; Farrugia, C. J.; Jian, L. K.

2017-12-01

One may use the longitudinal coverage of different spacecraft assets, or the same asset over sequential Carrington Rotations, to study the solar wind behavior from long-lived structures (coronal holes, active regions), or occasionally observe the extent of transient structures (Farrugia et al., 2011). This is of interest as the evolution of the extent and persistence of interplanetary coronal mass ejections (ICMEs) and of stream interaction regions (SIRs) have implications for space weather forecasting. One challenge is that one must be aware of the temporal evolution of the structure on the Sun and the affect of `sampling' different solar sources due to different solar latitudes of the in-situ spacecraft observations. Here we look at case studies of recent event time intervals during 2015-2017 where solar wind emanating from long-lived coronal-hole structures are observed both at STEREO A and at near-Earth assets (OMNI2). The observations are taken at similar solar latitudes and longitudes but temporally separated by several days or weeks.

MAVEN Observations of Magnetic Flux Ropes with a Strong Field Amplitude in the Martian Magnetosheath During the ICME Passage on 8 March 2015

NASA Technical Reports Server (NTRS)

Hara, Takuya; Luhmann, Janet G.; Halekas, Jasper S.; Espley, Jared R.; Seki, Kanako; Brain, David A.; Hasegawa, Hiroshi; McFadden, James P.; Mitchell, David L.; Mazelle, Christian;

Flux-Rope Structure of Coronal Mass Ejections

NASA Technical Reports Server (NTRS)

Gopalswamy, N.; Nieves-Chinchilla, T.; Hidalgo, M.; Zhang, J.; Riley, P.; van Driel-Gesztelyi, L.; Mandrini, C. H.

2013-01-01

This Topical Issue (TI) of Solar Physics, devoted to the study of flux-rope structure in coronal mass ejections (CMEs), is based on two Coordinated Data Analysis Workshops (CDAWs) held in 2010 (20-23 September in Dan Diego, California, USA) and 2011 (5-9 September in Alcala, Spain). The primary purpose of the CDAWs was to address the question whether all CMEs have a flux rope structure. Each CDAW was attended by about 50 scientists interested in the origin, propagation, and interplanetary manifestation of CME phenomena.

Evidence for the Magnetic Breakout Model in an Equatorial Coronal-hole Jet

NASA Astrophysics Data System (ADS)

Kumar, Pankaj; Karpen, Judith T.; Antiochos, Spiro K.; Wyper, Peter F.; DeVore, C. Richard; DeForest, Craig E.

2018-02-01

Small, impulsive jets commonly occur throughout the solar corona, but are especially visible in coronal holes. Evidence is mounting that jets are part of a continuum of eruptions that extends to much larger coronal mass ejections and eruptive flares. Because coronal-hole jets originate in relatively simple magnetic structures, they offer an ideal testbed for theories of energy buildup and release in the full range of solar eruptions. We analyzed an equatorial coronal-hole jet observed by the Solar Dynamics Observatory (SDO)/AIA on 2014 January 9 in which the magnetic-field structure was consistent with the embedded-bipole topology that we identified and modeled previously as an origin of coronal jets. In addition, this event contained a mini-filament, which led to important insights into the energy storage and release mechanisms. SDO/HMI magnetograms revealed footpoint motions in the primary minority-polarity region at the eruption site, but show negligible flux emergence or cancellation for at least 16 hr before the eruption. Therefore, the free energy powering this jet probably came from magnetic shear concentrated at the polarity inversion line within the embedded bipole. We find that the observed activity sequence and its interpretation closely match the predictions of the breakout jet model, strongly supporting the hypothesis that the breakout model can explain solar eruptions on a wide range of scales.

Evidence for the Magnetic Breakout Model in an Equatorial Coronal-Hole Jet

NASA Technical Reports Server (NTRS)

Kumar, Pankaj; Karpen, Judith T.; Antiochos, Spiro K.; Wyper, Peter F.; Devore, C. Richard; DeForest, Craig E.

2018-01-01

Small, impulsive jets commonly occur throughout the solar corona, but are especially visible in coronal holes. Evidence is mounting that jets are part of a continuum of eruptions that extends to much larger coronal mass ejections and eruptive flares. Because coronal-hole jets originate in relatively simple magnetic structures, they offer an ideal testbed for theories of energy buildup and release in the full range of solar eruptions. We analyzed an equatorial coronal-hole jet observed by the Solar Dynamics Observatory (SDO)/AIA (Atmospheric Imaging Assembly)) on 2014 January 9 in which the magnetic-field structure was consistent with the embedded-bipole topology that we identified and modeled previously as an origin of coronal jets. In addition, this event contained a mini-filament, which led to important insights into the energy storage and release mechanisms. SDO/HMI (Solar Dynamics Observatory/Helioseismic and Magnetic Imager) magnetograms revealed footpoint motions in the primary minority-polarity region at the eruption site, but show negligible flux emergence or cancellation for at least 16 hours before the eruption. Therefore, the free energy powering this jet probably came from magnetic shear concentrated at the polarity inversion line within the embedded bipole. We find that the observed activity sequence and its interpretation closely match the predictions of the breakout jet model, strongly supporting the hypothesis that the breakout model can explain solar eruptions on a wide range of scales.

Geometry of solar coronal rays

NASA Astrophysics Data System (ADS)

Filippov, B. P.; Martsenyuk, O. V.; Platov, Yu. V.; Den, O. E.

2016-02-01

Coronal helmet streamers are the most prominent large-scale elements of the solar corona observed in white light during total solar eclipses. The base of the streamer is an arcade of loops located above a global polarity inversion line. At an altitude of 1-2 solar radii above the limb, the apices of the arches sharpen, forming cusp structures, above which narrow coronal rays are observed. Lyot coronagraphs, especially those on-board spacecrafts flying beyond the Earth's atmosphere, enable us to observe the corona continuously and at large distances. At distances of several solar radii, the streamers take the form of fairly narrow spokes that diverge radially from the Sun. This radial direction displays a continuous expansion of the corona into the surrounding space, and the formation of the solar wind. However, the solar magnetic field and solar rotation complicate the situation. The rotation curves radial streams into spiral ones, similar to water streams flowing from rotating tubes. The influence of the magnetic field is more complex and multifarious. A thorough study of coronal ray geometries shows that rays are frequently not radial and not straight. Coronal streamers frequently display a curvature whose direction in the meridional plane depends on the phase of the solar cycle. It is evident that this curvature is related to the geometry of the global solar magnetic field, which depends on the cycle phase. Equatorward deviations of coronal streamers at solar minima and poleward deviations at solar maxima can be interpreted as the effects of changes in the general topology of the global solar magnetic field. There are sporadic temporal changes in the coronal rays shape caused by remote coronal mass ejections (CMEs) propagating through the corona. This is also a manifestation of the influence of the magnetic field on plasma flows. The motion of a large-scale flux rope associated with a CME away from the Sun creates changes in the structure of surrounding field lines, which are similar to the kink propagation along coronal rays. Careful analysis of these events could give us valuable information about the coronal plasma.

X-ray observations of characteristic structures and time variations from the solar corona - Preliminary results from Skylab.

NASA Technical Reports Server (NTRS)

Vaiana, G. S.; Davis, J. M.; Giacconi, R.; Krieger, A. S.; Silk, J. K.; Timothy, A. F.; Zombeck, M.

1973-01-01

Examples taken from the S-054 X-ray telescope observations made during the first Skylab mission show the hot coronal plasma tracing the configuration of the magnetic fields. The high spectral resolution and sensitivity of the instrument has enabled the following two facts to be more firmly established: (1) that the 'quiet homogeneous corona' is in fact highly structured and that the structures observed appear to be the results of dispersed active region magnetic fields; and (2) that numerous bright points are distributed randomly on the disk. Their presence at high latitudes may play a role in solar cycle models. In addition, the capability of Skylab for studying time evolution has enabled the restructuring of coronal features to be seen at times of high activity, indicating a restructuring of the coronal magnetic fields.

Planned Visible Emission Line Space Solar Coronagraph on-board Aditya-1

NASA Astrophysics Data System (ADS)

Singh, Jagdev

2012-07-01

An imaging visible emission line internally occulted coronagraph using 20 cm off axis parabolic mirror has been designed and planned to be launched in 2014. The coronagraph will have the facility to take images of the solar simultaneously, in the green [Fe xiv] and the red [Fe x] emission lines up to 1.5 solar radii with a frequency of about 3 Hz using 0.5 nm pass band filters and the images in continuum at 580 nm up to 3 solar radii. The satellite has been named as Aditya-1 and the scientific objectives of this payload are: (i) to investigate the existence of intensity oscillations for the study of wave driven coronal heating, (ii) to study the dynamics and formation of coronal loops and temperature structure of the coronal features, (iii) to study the origin, cause and acceleration of Coronal Mass Ejections (CME's) and other solar active features, and (iv) Coronal magnetic field topology and the 3-dimensional structures of the CMEs using polarization information. The fabrication of the pay load will be done in the laboratories of LEOS, SAC, ISAC, IIA and USO and launched by ISRO. Here we shall discuss the design and the realization of the mission.

Determination of temperature maps of EUV coronal hole jets

NASA Astrophysics Data System (ADS)

Nisticò, Giuseppe; Patsourakos, Spiros; Bothmer, Volker; Zimbardo, Gaetano

2011-11-01

Coronal hole jets are fast ejections of plasma occurring within coronal holes, observed at Extreme-UltraViolet (EUV) and X-ray wavelengths. Recent observations of jets by the STEREO and Hinode missions show that they are transient phenomena which occur at much higher rates than large-scale impulsive phenomena like flares and Coronal Mass Ejections (CMEs). In this paper we describe some typical characteristics of coronal jets observed by the SECCHI instruments of STEREO spacecraft. We show an example of 3D reconstruction of the helical structure for a south pole jet, and present how the angular distribution of the jet position angles changes from the Extreme-UltraViolet-Imager (EUVI) field of view to the CORonagraph1 (COR1) (height ∼2.0 R⊙ heliocentric distance) field of view. Then we discuss a preliminary temperature determination for the jet plasma by using the filter ratio method at 171 and 195 Å and applying a technique for subtracting the EUV background radiation. The results show that jets are characterized by electron temperatures ranging between 0.8 and 1.3 MK. We present the thermal structure of the jet as temperature maps and we describe its thermal evolution.

Helmet and active streamers from radio observations

NASA Technical Reports Server (NTRS)

Avignon, Y.; Axisa, F.; Martres, M. J.; Pick, M.; Simon, P.

1972-01-01

Large coronal regions disconnected from any calcium plages and identified by their thermal emission at 169 mHz play a basic role in the sector structure of the interplanetary medium. It was concluded that these coronal regions are to be interpreted as streamers.

Comment on: The Pioneer 6 Faraday Rotation Transients -- On the Interpretation of Coronal Faraday Rotation Data, by Patzold and Bird

NASA Technical Reports Server (NTRS)

Woo, R.

1998-01-01

The detection of coronal streamers in Doppler scintillation measurements revealed for the first time that variations in radio occultation measurements near the Sun could be caused by quasi-stationary raylike structures.

Structure and dynamics of coronal plasmas

NASA Technical Reports Server (NTRS)

Golub, Leon (Principal Investigator)

1996-01-01

Progress for the period July 1995 - June 1996 included work on the differential magnetic field shear in an active region; observations and modeling of the solar chromosphere seen in soft X-ray absorption by NIXT; and modeling magnetic flux emergence. These were the subjects of three papers. The plans for the current year include projects on a converging flux model for point-like brightenings around sunspots, and difficulties in observing coronal structure.

Driving extreme variability: Measuring the evolving coronæ and evidence for jet launching in AGN

NASA Astrophysics Data System (ADS)

Wilkins, D. R.

2016-05-01

Relativistically blurred reflection from the accretion disc provides a powerful probe of the extreme environments close to supermassive black holes; the inner regions of the accretion flow and the corona that produces the intense X-ray continuum. Techniques by which the geometry and extent of the corona can be measured through the observed X-ray spectrum are reviewed along with the evolution in the structure of the corona that is seen to accompany variations in the X-ray luminosity both on long and short timescales. Detailed analyses of the narrow line Seyfert 1 galaxies Mrk 335 and 1H 0707-495, over observations with XMM-Newton as well as Suzaku and NuSTAR spanning nearly a decade reveal that increases in the X-ray luminosity coincide with an expansion of the corona to cover a larger area of the inner accretion disc. Underlying this long timescale variability lie more complex patterns of behaviour on short timescales. Flares in the X-ray emission during a low flux state of Mrk 335 observed in 2013 and 2014 are found to mark a reconfiguration of the corona while there is evidence that the flares were caused by a vertical collimation and ejection of coronal material, reminiscent of an aborted jet-launching event. Measurements of the corona and reflecting accretion disc are combined to infer the conditions on the inner disc that lead to the flaring event.

Disruption of Helmet Streamers by Current Emergence

NASA Technical Reports Server (NTRS)

Guo, W. P.; Wu, S. T.; Tandberg-Hanssen, E.

1996-01-01

We have investigated the dynamic response of a coronal helmet streamer to the emergence from below of a current with its magnetic field in a direction opposite to the overlying streamer field. Once the emerging current moves into the closed region of the streamer, a current sheet forms between the emerging field and the streamer field, because the preexisting field and the newly emerging field have opposite polarities. Thus magnetic reconnection will occur at the flanks of the emerged structure where the current density is maximum. If the emerging current is large enough, the energy contained in the current and the reconnection will promptly disrupt the streamer. If the emerging current is small, the streamer will experience a stage of slow evolution. In this stage, slow magnetic reconnection occurring at the flanks of the emerged structure leads to the degeneration of the emerged current to a neutral point. Above this point, a new magnetic bubble will form. The resulting configuration resembles an inverse-polarity prominence. Depending on the initial input energy of the current, the resulting structure will either remain in situ, forming a quasi-static structure, or move upward, forming a coronal transient similar to coronal jets. The numerical method used in this paper can be used to construct helmet streamers containing a detached magnetic structure in their closed field region. The quasi-static solution may serve as a preevent corona for studying coronal mass ejection initiation.

The Magnetic Structure of H-Alpha Macrospicules in Solar Coronal Holes

NASA Technical Reports Server (NTRS)

Yamauchi, Y.; Moore, R. L.; Suess, S. T.; Wang, H.; Sakuri, T.

2003-01-01

Measurements by Ulysses in the high-speed polar solar wind have shown the wind to carry some fine-scale structures in which the magnetic field reverses direction by having a switchback fold in it. The lateral span of these magnetic switchbacks, translated to the Sun, is of the scale of the lanes and cells of the magnetic network in which the open magnetic flux of the polar coronal hole and polar solar wind are rooted. This suggests that the magnetic switchbacks might be formed from network-scale magnetic loops that erupt into the corona and then undergo reconnection with the open field. This possibility motivated us to undertake the study reported here of the structure of H-alpha macrospicules observed at the limb in polar coronal holes, to determine whether a significant fraction of these eruptions appear to be erupting loops. From a search of the polar-coronal holes in 6 days of image-processed full-disk H-alpha movies from Big Bear Solar Observatory, we found a total of 35 macrospicules. Nearly all of these (32) were of one or the other of two different forms: 15 were in the form of an erupting loop, and 17 were in the form of a single-column spiked jet. The erupting-loop macrospicules are appropriate for producing the magnetic switchbacks in the polar wind. The spiked-jet macrospicules show the appropriate structure and evolution to be driven by reconnection between network-scale closed field (a network bipole) and the open field rooted against the closed field. This evidence for reconnection in a large fraction of our macrospicules (1) suggests that many spicules may be generated by similar but smaller reconnection events, and (2) supports the view that coronal heating and solar wind acceleration in coronal holes and in quiet regions and corona are driven by explosive reconnection events in the magnetic network.

The Magnetic Structure of H-alpha Macrospicules in Solar Coronal Holes

NASA Technical Reports Server (NTRS)

Yamauchi, Y.; Moore, R. L.; Suess, S. T.; Wang, H.; Sakurai, T.

2004-01-01

Measurements by Ulysses in the high-speed polar solar wind have shown the wind to carry some fine-scale structures in which the magnetic field reverses direction by having a switchback fold in it. The lateral span of these magnetic switchbacks, translated back to the Sun, is of the scale of the lanes and cells of the magnetic network in which the open magnetic field of the polar coronal hole and polar solar wind are rooted. This suggests that the magnetic switchbacks might be formed from network-scale magnetic loops that erupt into the corona and then undergo reconnection with the open field. This possibility motivated us to undertake the study reported here of the structure of Ha macrospicules observed at the limb in polar coronal holes, to determine whether a significant fraction of these eruptions appear to be erupting loops. From a search of the polar coronal holes in 6 days of image- processed full-disk Ha movies from Big Bear Solar Observatory, we found a total of 35 macrospicules. Nearly all of these (32) were of one or the other of two different forms: 15 were in the form of an erupting loop, and 17 were in the form of a single column spiked jet. The erupting-loop macrospicules are appropriate for producing the magnetic switchbacks in the polar wind. The spiked-jet macrospicules show the appropriate structure and evolution to be driven by reconnection between network-scale closed field (a network bipole) and the open field rooted against the closed field. This evidence for reconnection in a large fraction of our macrospicules (1) suggests that many spicules may be generated by similar but smaller reconnection events and (2) supports the view that coronal heating and solar wind acceleration in coronal holes and in quiet regions are driven by explosive reconnection events in the magnetic network.

Evolutionary diversification of secondary mechanoreceptor cells in tunicata.

PubMed

Rigon, Francesca; Stach, Thomas; Caicci, Federico; Gasparini, Fabio; Burighel, Paolo; Manni, Lucia

2013-06-04

Hair cells are vertebrate secondary sensory cells located in the ear and in the lateral line organ. Until recently, these cells were considered to be mechanoreceptors exclusively found in vertebrates that evolved within this group. Evidence of secondary mechanoreceptors in some tunicates, the proposed sister group of vertebrates, has recently led to the hypothesis that vertebrate and tunicate secondary sensory cells share a common origin. Secondary sensory cells were described in detail in two tunicate groups, ascidians and thaliaceans, in which they constitute an oral sensory structure called the coronal organ. Among thaliaceans, the organ is absent in salps and it has been hypothesised that this condition is due to a different feeding system adopted by this group of animals. No information is available as to whether a comparable structure exists in the third group of tunicates, the appendicularians, although different sensory structures are known to be present in these animals. We studied the detailed morphology of appendicularian oral mechanoreceptors. Using light and electron microscopy we could demonstrate that the mechanosensory organ called the circumoral ring is composed of secondary sensory cells. We described the ultrastructure of the circumoral organ in two appendicularian species, Oikopleura dioica and Oikopleura albicans, and thus taxonomically completed the data collection of tunicate secondary sensory cells. To understand the evolution of secondary sensory cells in tunicates, we performed a cladistic analysis using morphological data. We constructed a matrix consisting of 19 characters derived from detailed ultrastructural studies in 16 tunicate species and used a cephalochordate and three vertebrate species as outgroups. Our study clearly shows that the circumoral ring is the appendicularian homologue of the coronal organ of other tunicate taxa. The cladistic analysis enabled us to reconstruct the features of the putative ancestral hair cell in tunicates, represented by a simple monociliated cell. This cell successively differentiated into the current variety of oral mechanoreceptors in the various tunicate lineages. Finally, we demonstrated that the inferred evolutionary changes coincide with major transitions in the feeding strategies in each respective lineage.

Structure and evolution of the large scale solar and heliospheric magnetic fields. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Hoeksema, J. T.

1984-01-01

Structure and evolution of large scale photospheric and coronal magnetic fields in the interval 1976-1983 were studied using observations from the Stanford Solar Observatory and a potential field model. The solar wind in the heliosphere is organized into large regions in which the magnetic field has a componenet either toward or away from the sun. The model predicts the location of the current sheet separating these regions. Near solar minimum, in 1976, the current sheet lay within a few degrees of the solar equator having two extensions north and south of the equator. Soon after minimum the latitudinal extent began to increase. The sheet reached to at least 50 deg from 1978 through 1983. The complex structure near maximum occasionally included multiple current sheets. Large scale structures persist for up to two years during the entire interval. To minimize errors in determining the structure of the heliospheric field particular attention was paid to decreasing the distorting effects of rapid field evolution, finding the optimum source surface radius, determining the correction to the sun's polar field, and handling missing data. The predicted structure agrees with direct interplanetary field measurements taken near the ecliptic and with coronameter and interplanetary scintillation measurements which infer the three dimensional interplanetary magnetic structure. During most of the solar cycle the heliospheric field cannot be adequately described as a dipole.

Coronal Heating and the Magnetic Flux Content of the Network

NASA Technical Reports Server (NTRS)

Falconer, D. A.; Moore, R. L.; Porter, J. G.; Hathaway, D. H.; Whitaker, Ann F. (Technical Monitor)

2001-01-01

Previously, from analysis of SOHO/EIT coronal images in combination with Kitt Peak magnetograms (Falconer et al 1998, ApJ, 501, 386-396), we found that the quiet corona is the sum of two components: the e-scale corona and the coronal network. The large-scale corona consists of all coronal-temperature (T approx. 10(exp 6) K) structures larger than supergranules (>approx.30,000 km). The coronal network (1) consists of all coronal-temperature structures smaller than supergranules, (2) is rooted in and loosely traces the photospheric magnetic network, (3) has its brightest features seated on polarity dividing fines (neutral lines) in the network magnetic flux, and (4) produces only about 5% of the total coronal emission in quiet regions. The heating of the coronal network is apparently magnetic in origin. Here, from analysis of EIT coronal images of quiet regions in combination with magnetograms of the same quiet regions from SOHO/MDI and from Kitt Peak, we examine the other 95% of the quiet corona and its relation to the underlying magnetic network. We find: (1) Dividing the large-scale corona into its bright and dim halves divides the area into bright "continents" and dark "oceans" having spans of 2-4 supergranules. (2) These patterns are also present in the photospheric magnetograms: the network is stronger under the bright half and weaker under the dim half. (3) The radiation from the large-scale corona increases roughly as the cube root of the magnetic flux content of the underlying magnetic network. In contrast, Fisher et A (1998, ApJ, 508, 985-998) found that the coronal radiation from an active region increases roughly linearly with the magnetic flux content of the active region. We assume, as is widely held, that nearly all of the large-scale corona is magnetically rooted in the network. Our results, together with the result of Fisher et al (1999), suggest that either the coronal heating in quiet regions has a large non-magnetic component, or, if the heating is predominantly produced via the magnetic field, the mechanism is significantly different than in active regions. This work is funded by NASA's Office of Space Science through the Solar Physics Supporting Research and Technology Program and the Sun-Earth Connection Guest Investigator Program.

The cyclical variation of energy flux and photospheric magnetic field strength from coronal holes

NASA Technical Reports Server (NTRS)

Webb, D. F.; Davis, J. M.

1985-01-01

The average soft X-ray emission from coronal holes observed on images obtained during rocket flights from 1974 to 1981 is measured. The variation of this emission over the solar cycle was then compared with photospheric magnetic flux measurements within coronal holes over the same period. It was found that coronal hole soft X-ray emission could be detected and that this emission appeared to increase with the rise of the sunspot cycle from activity minimum to maximum. These quantitative results confirmed previous suggestions that the coronal brightness contrast between holes and large-scale structure decreased during this period of the cycle. Gas pressures at the hole base were estimated for assumed temperatures and found to vary from about 0.03 dyne/sq cm in 1974 to 0.35 dyne/sq cm in 1981. The increase in coronal hole X-ray emission was accompanied by a similar trend in the surface magnetic flux of near-equatorial holes between 1975 and 1980 (Harvey et al., 1982).

REVIEWS OF TOPICAL PROBLEMS: Coronal magnetic loops

NASA Astrophysics Data System (ADS)

Zaitsev, Valerii V.; Stepanov, Alexander V.

2008-11-01

The goal of this review is to outline some new ideas in the physics of coronal magnetic loops, the fundamental structural elements of the atmospheres of the Sun and flaring stars, which are involved in phenomena such as stellar coronal heating, flare energy release, charged particle acceleration, and the modulation of optical, radio, and X-ray emissions. The Alfvén-Carlqvist view of a coronal loop as an equivalent electric circuit allows a good physical understanding of loop processes. Describing coronal loops as MHD-resonators explains various ways in which flaring emissions from the Sun and stars are modulated, whereas modeling them by magnetic mirror traps allows one to describe the dynamics and emission of high-energy particles. Based on these approaches, loop plasma and fast particle parameters are obtained and models for flare energy release and stellar corona heating are developed.

Bayesian coronal seismology

NASA Astrophysics Data System (ADS)

Arregui, Iñigo

2018-01-01

In contrast to the situation in a laboratory, the study of the solar atmosphere has to be pursued without direct access to the physical conditions of interest. Information is therefore incomplete and uncertain and inference methods need to be employed to diagnose the physical conditions and processes. One of such methods, solar atmospheric seismology, makes use of observed and theoretically predicted properties of waves to infer plasma and magnetic field properties. A recent development in solar atmospheric seismology consists in the use of inversion and model comparison methods based on Bayesian analysis. In this paper, the philosophy and methodology of Bayesian analysis are first explained. Then, we provide an account of what has been achieved so far from the application of these techniques to solar atmospheric seismology and a prospect of possible future extensions.

Acceleration of the Fast Solar Wind by Solitary Waves in Coronal Holes

NASA Technical Reports Server (NTRS)

Ofman, Leon

2001-01-01

The purpose of this investigation is to develop a new model for the acceleration of the fast solar wind by nonlinear. time-dependent multidimensional MHD simulations of waves in solar coronal holes. Preliminary computational studies indicate that nonlinear waves are generated in coronal holes by torsional Alfv\\'{e}n waves. These waves in addition to thermal conduction may contribute considerably to the accelerate the solar wind. Specific goals of this proposal are to investigate the generation of nonlinear solitary-like waves and their effect on solar wind acceleration by numerical 2.5D MHD simulation of coronal holes with a broad range of plasma and wave parameters; to study the effect of random disturbances at the base of a solar coronal hole on the fast solar wind acceleration with a more advanced 2.5D MHD model and to compare the results with the available observations; to extend the study to a full 3D MHD simulation of fast solar wind acceleration with a more realistic model of a coronal hole and solar boundary conditions. The ultimate goal of the three year study is to model the, fast solar wind in a coronal hole, based on realistic boundary conditions in a coronal hole near the Sun, and the coronal hole structure (i.e., density, temperature. and magnetic field geometry,) that will become available from the recently launched SOHO spacecraft.

Acceleration of the Fast Solar Wind by Solitary Waves in Coronal Holes

NASA Technical Reports Server (NTRS)

Ofman, Leon

2000-01-01

The purpose of this investigation is to develop a new model for the acceleration of the fast solar wind by nonlinear, time-dependent multidimensional MHD simulations of waves in solar coronal holes. Preliminary computational studies indicate that solitary-like waves are generated in coronal holes nonlinearly by torsional Alfven waves. These waves in addition to thermal conduction may contribute considerably to the accelerate the solar wind. Specific goals of this proposal are to investigate the generation of nonlinear solitary-like waves and their effect on solar wind acceleration by numerical 2.5D MHD simulation of coronal holes with a broad range of plasma and wave parameters; to study the effect of random disturbances at the base of a solar coronal hole on the fast solar wind acceleration with a more advanced 2.5D MHD model and to compare the results with the available observations; to extend the study to a full 3D MHD simulation of fast solar wind acceleration with a more realistic model of a coronal hole and solar boundary conditions. The ultimate goal of the three year study is to model the fast solar wind in a coronal hole, based on realistic boundary conditions in a coronal hole near the Sun, and the coronal hole structure (i.e., density, temperature, and magnetic field geometry) that will become available from the recently launched SOHO spacecraft.

Effect of remaining coronal structure on the resistance to fracture of crowned endodontically treated maxillary first premolars.

PubMed

Nissan, Joseph; Barnea, Eitan; Bar Hen, Doron; Assif, David

2008-09-01

Endodontically treated maxillary first premolars present a restorative challenge. The objective of the present study was to assess the resistance to fracture of crowned endodontically treated maxillary first premolars under simulated occlusal load, while preserving various degrees of remaining coronal structure. The study consisted of 50 intact maxillary first premolars with bifurcated roots and similar root diameter and length, randomly divided into 5 equal experimental groups. All dowels were luted with Flexi-Flow titanium-reinforced composite resin cement. TiCore titanium-reinforced composite resin was used to fabricate the core. Complete cast crowns were fabricated and cemented with zinc phosphate cement. Forces at fracture and mode of failure were recorded. Statistically significant differences (P < .05) were found among mean failure forces for all tested groups in their resistance to fracture under load with the Kruskal-Wallias test and among all combinations of the 5 groups (Z = -1.56/-2.34; P > .05) with the Mann-Whitney test. This indicates that crowned maxillary first premolars with varying degrees of remaining coronal structure differ significantly in their resistance to fracture under occlusal load. There was increased protection against fracture under occlusal loads with more remaining tooth structure. Within the limitations of this study, remaining coronal structure influenced the fracture resistance of crowned endodontically treated maxillary first premolars. Preservation of tooth structure is important for its protection against fracture under occlusal loads and may influence the tooth prognosis.

An investigation of coronal active region loop structures using AS&E rocket X-ray images

NASA Technical Reports Server (NTRS)

Webb, D. F.

1983-01-01

Simultaneous high spatial resolution observations at 6 cm in soft X-rays, in photospheric magnetograms, and in optical filtergrams were used to compare the most intense sources of centimetric emission in two active regions to coronal loops, sunspots, chromospheric structures, and photospheric magnetic fields. Results show that the majority of the bright microwave components are not associated with sunspots or X-ray emission. A nonthermal mechanism appears necessary to explain the brightest microwave components, discrete regions of continuous particle acceleration may be common in active regions. Studies of the plasma parameters of selected loops imply that the radio emission is consistent with gyro-resonance absorption at the third and fourth harmonic, at least from part of each loop. Results are presented for: (1) X-ray and microwave observations of active regions; (2) comparison of coronal holes observed in soft X-rays and Hel 10830 A spectrosheliograms; and (3) the reappearance of polar coronal holes and the evolution of the solar magnetic field.

SIMULATIONS OF THE KELVIN–HELMHOLTZ INSTABILITY DRIVEN BY CORONAL MASS EJECTIONS IN THE TURBULENT CORONA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gómez, Daniel O.; DeLuca, Edward E.; Mininni, Pablo D.

Recent high-resolution Atmospheric Imaging Assembly/Solar Dynamics Observatory images show evidence of the development of the Kelvin–Helmholtz (KH) instability, as coronal mass ejections (CMEs) expand in the ambient corona. A large-scale magnetic field mostly tangential to the interface is inferred, both on the CME and on the background sides. However, the magnetic field component along the shear flow is not strong enough to quench the instability. There is also observational evidence that the ambient corona is in a turbulent regime, and therefore the criteria for the development of the instability are a priori expected to differ from the laminar case. To studymore » the evolution of the KH instability with a turbulent background, we perform three-dimensional simulations of the incompressible magnetohydrodynamic equations. The instability is driven by a velocity profile tangential to the CME–corona interface, which we simulate through a hyperbolic tangent profile. The turbulent background is generated by the application of a stationary stirring force. We compute the instability growth rate for different values of the turbulence intensity, and find that the role of turbulence is to attenuate the growth. The fact that KH instability is observed sets an upper limit on the correlation length of the coronal background turbulence.« less

Theoretical quantification of shock-timing sensitivities for direct-drive inertial confinement fusion implosions on OMEGA

NASA Astrophysics Data System (ADS)

Cao, D.; Boehly, T. R.; Gregor, M. C.; Polsin, D. N.; Davis, A. K.; Radha, P. B.; Regan, S. P.; Goncharov, V. N.

2018-05-01

Using temporally shaped laser pulses, multiple shocks can be launched in direct-drive inertial confinement fusion implosion experiments to set the shell on a desired isentrope or adiabat. The velocity of the first shock and the times at which subsequent shocks catch up to it are measured through the velocity interferometry system for any reflector diagnostic [T. R. Boehly et al., Phys. Plasmas 18, 092706 (2011)] on OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. Simulations reproduce these velocity and shock-merger time measurements when using laser pulses designed for setting mid-adiabat (α ˜ 3) implosions, but agreement degrades for lower-adiabat (α ˜ 1) designs. Simulation results indicate that the shock timing discrepancy is most sensitive to details of the density and temperature profiles in the coronal plasma, which influences the laser energy coupled into the target, and only marginally sensitive to the target offset and beam power imbalance. To aid in verifying the coronal profile's influence, a new technique under development to infer coronal profiles using x-ray self-emission imaging [A. K. Davis et al., Bull. Am. Phys. Soc. 61, BAPS.2016.DPP.NO8.7 (2016)] can be applied to the pulse shapes used in shock-timing experiments.

An Innovative Approach for Management of Vertical Coronal Fracture in Molar: Case Report

PubMed Central

Kathuria, Ambica; Kavitha, M.; Ravishankar, P.

2012-01-01

Unlike anterior teeth, acute exogenous trauma is an infrequent cause of posterior coronal vertical tooth fractures. Endodontic and restorative management of such fractures is a great challenge for the clinician. Newer advancements in adhesive techniques can provide successful intracoronal splinting of such teeth to reinforce the remaining tooth structure. This paper describes the diagnosis and management of a case of complicated vertical coronal fracture in mandibular first molar induced by a traffic accident. PMID:22567453

Solar and interplanetary dynamics; Proceedings of the Symposium, Harvard University, Cambridge, Mass., August 27-31, 1979

NASA Technical Reports Server (NTRS)

Dryer, M. (Editor); Tandberg-Hanssen, E.

1980-01-01

The symposium focuses on solar phenomena as the source of transient events propagating through the solar system, and theoretical and observational assessments of the dynamic processes involved in these events. The topics discussed include the life history of coronal structures and fields, coronal and interplanetary responses to long time scale phenomena, solar transient phenomena affecting the corona and interplanetary medium, coronal and interplanetary responses to short time scale phenomena, and future directions.

Small-scale filament eruptions as the driver of X-ray jets in solar coronal holes.

PubMed

Sterling, Alphonse C; Moore, Ronald L; Falconer, David A; Adams, Mitzi

2015-07-23

Solar X-ray jets are thought to be made by a burst of reconnection of closed magnetic field at the base of a jet with ambient open field. In the accepted version of the 'emerging-flux' model, such a reconnection occurs at a plasma current sheet between the open field and the emerging closed field, and also forms a localized X-ray brightening that is usually observed at the edge of the jet's base. Here we report high-resolution X-ray and extreme-ultraviolet observations of 20 randomly selected X-ray jets that form in coronal holes at the Sun's poles. In each jet, contrary to the emerging-flux model, a miniature version of the filament eruptions that initiate coronal mass ejections drives the jet-producing reconnection. The X-ray bright point occurs by reconnection of the 'legs' of the minifilament-carrying erupting closed field, analogous to the formation of solar flares in larger-scale eruptions. Previous observations have found that some jets are driven by base-field eruptions, but only one such study, of only one jet, provisionally questioned the emerging-flux model. Our observations support the view that solar filament eruptions are formed by a fundamental explosive magnetic process that occurs on a vast range of scales, from the biggest mass ejections and flare eruptions down to X-ray jets, and perhaps even down to smaller jets that may power coronal heating. A similar scenario has previously been suggested, but was inferred from different observations and based on a different origin of the erupting minifilament.

Solar Coronal Heating and the Magnetic Flux Content of the Network

NASA Technical Reports Server (NTRS)

Falconer, D. A.; Moore, R. L.; Porter, J. G.; Hathaway, D. H.

2003-01-01

We investigate the heating of the quiet corona by measuring the increase of coronal luminosity with the amount of magnetic flux in the underlying network at solar minimum when there were no active regions on the face of the Sun. The coronal luminosity is measured from Fe IX/X-Fe XII pairs of coronal images from SOHO/EIT. The network magnetic flux content is measured from SOHO/MDI magnetograms. We find that the luminosity of the corona in our quiet regions increases roughly in proportion to the square root of the magnetic flux content of the network and roughly in proportion to the length of the perimeter of the network magnetic flux clumps. From (1) this result, (2) other observations of many fine-scale explosive events at the edges of network flux clumps, and (3) a demonstration that it is energetically feasible for the heating of the corona in quiet regions to be driven by explosions of granule-sized sheared-core magnetic bipoles embedded in the edges of network flux clumps, we infer that in quiet regions that are not influenced by active regions the corona is mainly heated by such magnetic activity in the edges of the network flux clumps. Our observational results together with our feasibility analysis allow us to predict that (1) at the edges of the network flux clumps there are many transient sheared-core bipoles of the size and lifetime of granules and having transverse field strengths > approx. 100 G, (2) approx. 30 of these bipoles are present per supergranule, and (3) most spicules are produced by explosions of these bipoles.

Solar Coronal Heating and the Magnetic Flux Content of the Network

NASA Technical Reports Server (NTRS)

Moore, R. L.; Falconer, D. A.; Porter, J. G.; Hathaway, D. H.

2003-01-01

We investigate the heating of the quiet corona by measuring the increase of coronal luminosity with the amount of magnetic flux in the underlying network at solar minimum when there were no active regions on the face of the Sun. The coronal luminosity is measured from Fe IX/X-Fe XII pairs of coronal images from SOHO/EIT. The network magnetic flux content is measured from SOHO/MDI magnetograms. We find that the luminosity of the corona in our quiet regions increases roughly in proportion to the square root of the magnetic flux content of the network and roughly in proportion to the length of the perimeter of the network magnetic flux clumps. From (1) this result, (2) other observations of many fine-scale explosive events at the edges of network flux clumps, and (3) a demonstration that it is energetically feasible for the heating of the corona in quiet regions to be driven by explosions of granule-sized sheared-core magnetic bipoles embedded in the edges of network flux clumps, we infer that in quiet regions that are not influenced by active regions the corona is mainly heated by such magnetic activity in the edges of the network flux clumps. Our observational results together with our feasibility analysis allow us to predict that (1) at the edges of the network flux clumps there are many transient sheared-core bipoles of the size and lifetime of granules and having transverse field strengths greater than approximately - 100 G, (2) approximately 30 of these bipoles are present per supergranule, and (3) most spicules are produced by explosions of these bipoles.

Magnetohydrodynamic Simulations for Studying Solar Flare Trigger Mechanism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muhamad, J.; Kusano, K.; Inoue, S.

In order to understand the flare trigger mechanism, we conduct three-dimensional magnetohydrodynamic simulations using a coronal magnetic field model derived from data observed by the Hinode satellite. Several types of magnetic bipoles are imposed into the photospheric boundary of the Nonlinear Force-free Field model of Active Region (AR) NOAA 10930 on 2006 December 13, to investigate what kind of magnetic disturbance may trigger the flare. As a result, we confirm that certain small bipole fields, which emerge into the highly sheared global magnetic field of an AR, can effectively trigger a flare. These bipole fields can be classified into twomore » groups based on their orientation relative to the polarity inversion line: the so-called opposite polarity, and reversed shear structures, as suggested by Kusano et al. We also investigate the structure of the footpoints of reconnected field lines. By comparing the distribution of reconstructed field lines and observed flare ribbons, the trigger structure of the flare can be inferred. Our simulation suggests that the data-constrained simulation, taking into account both the large-scale magnetic structure and small-scale magnetic disturbance (such as emerging fluxes), is a good way to discover a flare-producing AR, which can be applied to space weather prediction.« less

Geometrical Properties of Coronal Mass Ejections

NASA Astrophysics Data System (ADS)

Cremades, Hebe; Bothmer, Volker

Based on the SOHO/LASCO dataset, a collection of "structured" coronal mass ejections (CMEs) has been compiled within the period 1996-2002, in order to analyze their three-dimensional configuration. These CME events exhibit white-light fine structures, likely indicative of their possible 3D topology. From a detailed investigation of the associated low coronal and photospheric source regions, a generic scheme has been deduced, which considers the white-light topology of a CME projected in the plane of the sky as being primarily dependent on the orientation and position of the source region's neutral line on the solar disk. The obtained results imply that structured CMEs are essentially organized along a symmetry axis, in a cylindrical manner. The measured dimensions of the cylinder's base and length yield a ratio of 1.6. These CMEs seem to be better approximated by elliptic cones, rather than by the classical ice cream cone, characterized by a circular cross section.

Solar wind and coronal structure near sunspot minimum - Pioneer and SMM observations from 1985-1987

NASA Technical Reports Server (NTRS)

Mihalov, J. D.; Barnes, A.; Hundhausen, A. J.; Smith, E. J.

1990-01-01

Changes in solar wind speed and magnetic polarity observed at the Pioneer spacecraft are discussed here in terms of the changing magnetic geometry implied by SMM coronagraph observations over the period 1985-1987. The pattern of recurrent solar wind streams, the long-term average speed, and the sector polarity of the interplanetary magnetic field all changed in a manner suggesting both a temporal variation, and a changing dependence on heliographic latitude. Coronal observations during this epoch show a systematic variation in coronal structure and the magnetic structure imposed on the expanding solar wind. These observations suggest interpretation of the solar wind speed variations in terms of the familiar model where the speed increases with distance from a nearly flat interplanetary current sheet, and where this current sheet becomes aligned with the solar equatorial plane as sunspot minimum approaches, but deviates rapidly from that orientation after minimum.

Understanding the Global Structure and Evolution of Coronal Mass Ejections in the Solar Wind

NASA Technical Reports Server (NTRS)

Riley, Pete

2004-01-01

This report summarizes the technical progress made during the first six months of the second year of the NASA Living with a Star program contract Understanding the global structure and evolution of coronal mass ejections in the solar wind, between NASA and Science Applications International Corporation, and covers the period November 18, 2003 - May 17,2004. Under this contract SAIC has conducted numerical and data analysis related to fundamental issues concerning the origin, intrinsic properties, global structure, and evolution of coronal mass ejections in the solar wind. During this working period we have focused on a quantitative assessment of 5 flux rope fitting techniques. In the following sections we summarize the main aspects of this work and our proposed investigation plan for the next reporting period. Thus far, our investigation has resulted in 6 refereed scientific publications and we have presented the results at a number of scientific meetings and workshops.

Chromospheric and Coronal Structure of Polar Plumes. 1; Magnetic Structure and Radiative Energy Balance

NASA Technical Reports Server (NTRS)

Allen, Maxwell J.; Oluseyi, Hakeem M.; Walker, Arthur B. C.; Hoover, Richard B.; Barbee, Troy W., Jr.

1997-01-01

The Multi-Spectral Solar Telescope Array (MSSTA), a rocket-borne solar observatory, was successfully launched from White Sands Missile Range, New Mexico, on May 13, 1991 at 19:05 UT. The telescope systems onboard the MSSTA obtained several full disk solar images in narrow bandpasses centered around strong soft X-ray, EUV, and FUV emission lines. Each telescope was designed to be sensitive to the coronal plasmas at a particular temperature, for seven temperatures ranging from 20,000 K to 4,000,000 K. We report here on the images obtained during the initial flight of the MSSTA, and on the chromospheric and coronal structure of polar plumes observed over both poles of the Sun. We have also co-aligned the MSSTA images with Kitt Peak magnetograms taken on the same day. We are able to positively identify the magnetic structures underlying the polar plumes we analyze as unipolar. We discuss the plume observations and present a radiative energy balance model derived from them.

Fading Coronal Structure and the Onset of Turbulence in the Young Solar Wind

NASA Technical Reports Server (NTRS)

DeForest, C. E.; Matthaeus, W. H.; Viall, N. M.; Cranmer, S. R.

2016-01-01

Above the top of the solar corona, the young, slow solar wind transitions from low-beta, magnetically structured flow dominated by radial structures to high-beta, less structured flow dominated by hydrodynamics. This transition, long inferred via theory, is readily apparent in the sky region close to 10deg from the Sun in processed, background-subtracted solar wind images. We present image sequences collected by the inner Heliospheric Imager instrument on board the Solar-Terrestrial Relations Observatory (STEREO/HI1) in 2008 December, covering apparent distances from approximately 4deg to 24deg from the center of the Sun and spanning this transition in the large-scale morphology of the wind. We describe the observation and novel techniques to extract evolving image structure from the images, and we use those data and techniques to present and quantify the clear textural shift in the apparent structure of the corona and solar wind in this altitude range. We demonstrate that the change in apparent texture is due both to anomalous fading of the radial striae that characterize the corona and to anomalous relative brightening of locally dense puffs of solar wind that we term "flocculae." We show that these phenomena are inconsistent with smooth radial flow, but consistent with the onset of hydrodynamic or magnetohydrodynamic instabilities leading to a turbulent cascade in the young solar wind.

FADING CORONAL STRUCTURE AND THE ONSET OF TURBULENCE IN THE YOUNG SOLAR WIND

DOE Office of Scientific and Technical Information (OSTI.GOV)

DeForest, C. E.; Matthaeus, W. H.; Viall, N. M.

Above the top of the solar corona, the young, slow solar wind transitions from low- β , magnetically structured flow dominated by radial structures to high- β , less structured flow dominated by hydrodynamics. This transition, long inferred via theory, is readily apparent in the sky region close to 10° from the Sun in processed, background-subtracted solar wind images. We present image sequences collected by the inner Heliospheric Imager instrument on board the Solar-Terrestrial Relations Observatory ( STEREO /HI1) in 2008 December, covering apparent distances from approximately 4° to 24° from the center of the Sun and spanning this transitionmore » in the large-scale morphology of the wind. We describe the observation and novel techniques to extract evolving image structure from the images, and we use those data and techniques to present and quantify the clear textural shift in the apparent structure of the corona and solar wind in this altitude range. We demonstrate that the change in apparent texture is due both to anomalous fading of the radial striae that characterize the corona and to anomalous relative brightening of locally dense puffs of solar wind that we term “flocculae.” We show that these phenomena are inconsistent with smooth radial flow, but consistent with the onset of hydrodynamic or magnetohydrodynamic instabilities leading to a turbulent cascade in the young solar wind.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Antolin, P.; Vissers, G.; Shibata, K., E-mail: antolin@astro.uio.n, E-mail: g.j.m.vissers@astro.uio.n, E-mail: shibata@kwasan.kyoto-u.ac.j

Reported observations in H{alpha}, Ca II H, and K or other chromospheric lines of coronal rain trace back to the days of the Skylab mission. Corresponding to cool and dense plasma, coronal rain is often observed falling down along coronal loops in active regions. A physical explanation for this spectacular phenomenon has been put forward thanks to numerical simulations of loops with footpoint-concentrated heating, a heating scenario in which cool condensations naturally form in the corona. This effect has been termed 'catastrophic cooling' and is the predominant explanation for coronal rain. In this work, we further investigate the link betweenmore » this phenomenon and the heating mechanisms acting in the corona. We start by analyzing observations of coronal rain at the limb in the Ca II H line performed by the Hinode satellite, and derive interesting statistical properties concerning the dynamics. We then compare the observations with 1.5-dimensional MHD simulations of loops being heated by small-scale discrete events concentrated toward the footpoints (that could come, for instance, from magnetic reconnection events), and by Alfven waves generated at the photospheric level. Both our observation and simulation results suggest that coronal rain is a far more common phenomenon than previously thought. Also, we show that the structure and dynamics of condensations are far more sensitive to the internal pressure changes in loops than to gravity. Furthermore, it is found that if a loop is predominantly heated from Alfven waves, coronal rain is inhibited due to the characteristic uniform heating they produce. Hence, coronal rain may not only point to the spatial distribution of the heating in coronal loops but also to the agent of the heating itself. We thus propose coronal rain as a marker for coronal heating mechanisms.« less

Energy Input Flux in the Global Quiet-Sun Corona

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mac Cormack, Cecilia; Vásquez, Alberto M.; López Fuentes, Marcelo

We present first results of a novel technique that provides, for the first time, constraints on the energy input flux at the coronal base ( r ∼ 1.025 R {sub ⊙}) of the quiet Sun at a global scale. By combining differential emission measure tomography of EUV images, with global models of the coronal magnetic field, we estimate the energy input flux at the coronal base that is required to maintain thermodynamically stable structures. The technique is described in detail and first applied to data provided by the Extreme Ultraviolet Imager instrument, on board the Solar TErrestrial RElations Observatory mission,more » and the Atmospheric Imaging Assembly instrument, on board the Solar Dynamics Observatory mission, for two solar rotations with different levels of activity. Our analysis indicates that the typical energy input flux at the coronal base of magnetic loops in the quiet Sun is in the range ∼0.5–2.0 × 10{sup 5} (erg s{sup −1} cm{sup −2}), depending on the structure size and level of activity. A large fraction of this energy input, or even its totality, could be accounted for by Alfvén waves, as shown by recent independent observational estimates derived from determinations of the non-thermal broadening of spectral lines in the coronal base of quiet-Sun regions. This new tomography product will be useful for the validation of coronal heating models in magnetohydrodinamic simulations of the global corona.« less

The nature of micro CMEs within coronal holes

NASA Astrophysics Data System (ADS)

Bothmer, Volker; Nistico, Giuseppe; Zimbardo, Gaetano; Patsourakos, Spiros; Bosman, Eckhard

Whilst investigating the origin and characteristics of coronal jets and large-scale CMEs identi-fied in data from the SECCHI (Sun Earth Connection Coronal and Heliospheric Investigation) instrument suites on board the two STEREO satellites, we discovered transient events that originated in the low corona with a morphology resembling that of typical three-part struc-tured coronal mass ejections (CMEs). However, the CMEs occurred on considerably smaller spatial scales. In this presentation we show evidence for the existence of small-scale CMEs from inside coronal holes and present quantitative estimates of their speeds and masses. We interprete the origin and evolution of micro CMEs as a natural consequence of the emergence of small-scale magnetic bipoles related to the Sun's ever changing photospheric magnetic flux on various scales and their interactions with the ambient plasma and magnetic field. The analysis of CMEs is performed within the framework of the EU Erasmus and FP7 SOTERIA projects.

Coronal Magnetism and Forward Solarsoft Idl Package

NASA Astrophysics Data System (ADS)

Gibson, S. E.

2014-12-01

The FORWARD suite of Solar Soft IDL codes is a community resource for model-data comparison, with a particular emphasis on analyzing coronal magnetic fields. FORWARD may be used both to synthesize a broad range of coronal observables, and to access and compare to existing data. FORWARD works with numerical model datacubes, interfaces with the web-served Predictive Science Inc MAS simulation datacubes and the Solar Soft IDL Potential Field Source Surface (PFSS) package, and also includes several analytic models (more can be added). It connects to the Virtual Solar Observatory and other web-served observations to download data in a format directly comparable to model predictions. It utilizes the CHIANTI database in modeling UV/EUV lines, and links to the CLE polarimetry synthesis code for forbidden coronal lines. FORWARD enables "forward-fitting" of specific observations, and helps to build intuition into how the physical properties of coronal magnetic structures translate to observable properties.

3D electron density distributions in the solar corona during solar minima: assessment for more realistic solar wind modeling

NASA Astrophysics Data System (ADS)

de Patoul, J.; Foullon, C.; Riley, P.

2015-12-01

Knowledge of the electron density distribution in the solar corona put constraints on the magnetic field configurations for coronal modeling, and on initial conditions for solar wind modeling. We work with polarized SOHO/LASCO-C2 images from the last two recent minima of solar activity (1996-1997 and 2008-2010), devoid of coronal mass ejections. We derive the 4D electron density distributions in the corona by applying a newly developed time-dependent tomographic reconstruction method. First we compare the density distributions obtained from tomography with magnetohydrodynamic (MHD) solutions. The tomography provides more accurate distributions of electron densities in the polar regions, and we find that the observed density varies with the solar cycle in both polar and equatorial regions. Second, we find that the highest-density structures do not always correspond to the predicted large-scale heliospheric current sheet or its helmet streamer but can follow the locations of pseudo-streamers. We conclude that tomography offers reliable density distribution in the corona, reproducing the slow time evolution of coronal structures, without prior knowledge of the coronal magnetic field over a full rotation. Finally, we suggest that the highest-density structures show a differential rotation well above the surface depending on how it is magnetically connected to the surface. Such valuable information on the rotation of large-scale structures could help to connect the sources of the solar wind to their in-situ counterparts in future missions such as Solar Orbiter and Solar Probe Plus. This research combined with the MHD coronal modeling efforts has the potential to increase the reliability for future space weather forecasting.

Internal and External reconnection in a Series of Homologous Solar Flares

NASA Technical Reports Server (NTRS)

Sterling, Alphonse C.; Moore, Ronald L.; Rose, M. Franklin (Technical Monitor)

2000-01-01

Using data from the Extreme Ultraviolet Telescope (EIT) on SOHO and the Soft X-ray Telescope (SXT) on Yohkoh, we examine a series of morphologically homologous solar flares occurring in NOAA AR 8210 over May 1-2, 1998. An emerging flux region (EFR) impacted against a sunspot to the west and next to a coronal hole to the east is the source of the repeated flaring. An SXT sigmoid parallels the EFR's neutral line at the site of the initial flaring in soft X-rays. In EIT, each flaring episode begins with the formation of a crinkle pattern external to the EFR. These EIT crinkles move out from, and then in toward, the EFR with velocities approximately 20 km/s. A shrinking and expansion of the width of the coronal hole coincides with the crinkle activity, and generation and evolution of a postflare loop system begins near the. time of crinkle formation. Using a schematic based on magnetograms of the region, we suggest that these observations are consistent with the standard reconnection-based model for solar eruptions, but modified by the presence of the additional magnetic fields of the sunspot and coronal hole. In the schematic, internal reconnection begins inside of the EFR-associated fields, unleashing a flare, postflare loops, and a CME. External reconnection, first occurring between the escaping CME and the coronal hole field, and second occurring between fields formed as a result of the first external reconnection, results in the EIT crinkles and changes in the coronal hole boundary. By the end of the second external reconnection, the initial setup is reinstated; thus the sequence can repeat, resulting in morphologically homologous eruptions. Our inferred magnetic topology is similar to that suggested in the "breakout model" of eruptions [Antiochos, 1998], although we cannot determine if our eruptions are released primarily by the breakout mechanism (external reconnection) or, alternatively, are released primarily by the internal reconnection.

The COronal Solar Magnetism Observatory (COSMO) Large Aperture Coronagraph

NASA Astrophysics Data System (ADS)

Tomczyk, Steve; Gallagher, Dennis; Wu, Zhen; Zhang, Haiying; Nelson, Pete; Burkepile, Joan; Kolinksi, Don; Sutherland, Lee

2013-04-01

The COSMO is a facility dedicated to observing coronal and chromospheric magnetic fields. It will be located on a mountaintop in the Hawaiian Islands and will replace the current Mauna Loa Solar Observatory (MLSO). COSMO will provide unique observations of the global coronal magnetic fields and its environment to enhance the value of data collected by other observatories on the ground (e.g. SOLIS, BBO NST, Gregor, ATST, EST, Chinese Giant Solar Telescope, NLST, FASR) and in space (e.g. SDO, Hinode, SOHO, GOES, STEREO, Solar-C, Solar Probe+, Solar Orbiter). COSMO will employ a fleet of instruments to cover many aspects of measuring magnetic fields in the solar atmosphere. The dynamics and energy flow in the corona are dominated by magnetic fields. To understand the formation of CMEs, their relation to other forms of solar activity, and their progression out into the solar wind requires measurements of coronal magnetic fields. The large aperture coronagraph, the Chromospheric and Prominence Magnetometer and the K-Coronagraph form the COSMO instrument suite to measure magnetic fields and the polarization brightness of the low corona used to infer electron density. The large aperture coronagraph will employ a 1.5 meter fuse silica singlet lens, birefringent filters, and a spectropolarimeter to cover fields of view of up to 1 degree. It will observe the corona over a wide range of emission lines from 530.3 nm through 1083.0 nm allowing for magnetic field measurements over a wide range of coronal temperatures (e.g. FeXIV at 530.3 nm, Fe X at 637.4 nm, Fe XIII at 1074.7 and 1079.8 nm. These lines are faint and require the very large aperture. NCAR and NSF have provided funding to bring the large aperture coronagraph to a preliminary design review state by the end of 2013. As with all data from Mauna Loa, the data products from COSMO will be available to the community via the Mauna Loa website: http://mlso.hao.ucar.edu

Simultaneous Extreme-Ultraviolet Explorer and Optical Observations of Ad Leonis: Evidence for Large Coronal Loops and the Neupert Effect in Stellar Flares

NASA Technical Reports Server (NTRS)

Hawley, Suzanne L.; Fisher, George H.; Simon, Theodore; Cully, Scott L.; Deustua, Susana E.; Jablonski, Marek; Johns-Krull, Christopher; Pettersen, Bjorn R.; Smith, Verne; Spiesman, William J.;

First analysis of solar structures in 1.21 mm full-disc ALMA image of the Sun

NASA Astrophysics Data System (ADS)

Brajša, R.; Sudar, D.; Benz, A. O.; Skokić, I.; Bárta, M.; Pontieu, B. De; Kim, S.; Kobelski, A.; Kuhar, M.; Shimojo, M.; Wedemeyer, S.; White, S.; Yagoubov, P.; Yan, Y.

2018-05-01

Context. Various solar features can be seen in emission or absorption on maps of the Sun in the millimetre and submillimetre wavelength range. The recently installed Atacama Large Millimetre/submillimetre Array (ALMA) is capable of observing the Sun in that wavelength range with an unprecedented spatial, temporal and spectral resolution. To interpret solar observations with ALMA, the first important step is to compare solar ALMA maps with simultaneous images of the Sun recorded in other spectral ranges. Aims: The first aim of the present work is to identify different structures in the solar atmosphere seen in the optical, infrared, and EUV parts of the spectrum (quiet Sun, active regions, prominences on the disc, magnetic inversion lines, coronal holes and coronal bright points) in a full-disc solar ALMA image. The second aim is to measure the intensities (brightness temperatures) of those structures and to compare them with the corresponding quiet Sun level. Methods: A full-disc solar image at 1.21 mm obtained on December 18, 2015, during a CSV-EOC campaign with ALMA is calibrated and compared with full-disc solar images from the same day in Hα line, in He I 1083 nm line core, and with various SDO images (AIA at 170 nm, 30.4 nm, 21.1 nm, 19.3 nm, and 17.1 nm and HMI magnetogram). The brightness temperatures of various structures are determined by averaging over corresponding regions of interest in the calibrated ALMA image. Results: Positions of the quiet Sun, active regions, prominences on the disc, magnetic inversion lines, coronal holes and coronal bright points are identified in the ALMA image. At the wavelength of 1.21 mm, active regions appear as bright areas (but sunspots are dark), while prominences on the disc and coronal holes are not discernible from the quiet Sun background, despite having slightly less intensity than surrounding quiet Sun regions. Magnetic inversion lines appear as large, elongated dark structures and coronal bright points correspond to ALMA bright points. Conclusions: These observational results are in general agreement with sparse earlier measurements at similar wavelengths. The identification of coronal bright points represents the most important new result. By comparing ALMA and other maps, it was found that the ALMA image was oriented properly and that the procedure of overlaying the ALMA image with other images is accurate at the 5 arcsec level. The potential of ALMA for physics of the solar chromosphere is emphasised.

Evidence for magnetic energy storage in coronal active regions

NASA Technical Reports Server (NTRS)

Krieger, A. S.; De Feiter, L. D.; Vaiana, G. S.

1976-01-01

Examination of X-ray images obtained by the S-054 X-ray spectrographic telescope on Skylab shows the presence of some atypical X-ray-emitting coronal structures in active regions which are not consistent with potential extrapolations of photospheric magnetic fields. Analysis of the observed temporal changes in the X-ray-emitting active-region structures demonstrates that the majority of these consist of brightness changes representing temperature (and perhaps density) variations of the material in the loops.

Ultra-fine-scale filamentary structures in the Outer Corona and the Solar Magnetic Field

NASA Technical Reports Server (NTRS)

Woo, Richard

2006-01-01

Filamentary structures following magnetic field lines pervade the Sun's atmosphere and offer us insight into the solar magnetic field. Radio propagation measurements have shown that the smallest filamentary structures in the solar corona are more than 2 orders of magnitude finer than those seen in solar imaging. Here we use radio Doppler measurements to characterize their transverse density gradient and determine their finest scale in the outer corona at 20-30 R(circled dot operator), where open magnetic fields prevail. Filamentary structures overly active regions have the steepest gradient and finest scale, while those overlying coronal holes have the shallowest gradient and least finest scale. Their organization by the underlying corona implies that these subresolution structures extend radially from the entire Sun, confirming that they trace the coronal magnetic field responsible for the radial expansion of the solar wind. That they are rooted all over the Sun elucidates the association between the magnetic field of the photosphere and that of the corona, as revealed by the similarity between the power spectra of the photospheric field and the coronal density fluctuations. This association along with the persistence of filamentary structures far from the Sun demonstrate that subresolution magnetic fields must play an important role not only in magnetic coupling of the photosphere and corona, but also in coronal heating and solar wind acceleration through the process of small-scale magnetic reconnection. They also explain why current widely used theoretical models that extrapolate photospheric magnetic fields into the corona do not predict the correct source of the solar wind.

An Extreme-ultraviolet Wave Generating Upward Secondary Waves in a Streamer-like Solar Structure

NASA Astrophysics Data System (ADS)

Zheng, Ruisheng; Chen, Yao; Feng, Shiwei; Wang, Bing; Song, Hongqiang

2018-05-01

Extreme-ultraviolet (EUV) waves, spectacular horizontally propagating disturbances in the low solar corona, always trigger horizontal secondary waves (SWs) when they encounter the ambient coronal structure. We present the first example of upward SWs in a streamer-like structure after the passing of an EUV wave. This event occurred on 2017 June 1. The EUV wave happened during a typical solar eruption including a filament eruption, a coronal mass ejection (CME), and a C6.6 flare. The EUV wave was associated with quasi-periodic fast propagating (QFP) wave trains and a type II radio burst that represented the existence of a coronal shock. The EUV wave had a fast initial velocity of ∼1000 km s‑1, comparable to high speeds of the shock and the QFP wave trains. Intriguingly, upward SWs rose slowly (∼80 km s‑1) in the streamer-like structure after the sweeping of the EUV wave. The upward SWs seemed to originate from limb brightenings that were caused by the EUV wave. All of the results show that the EUV wave is a fast-mode magnetohydrodynamic (MHD) shock wave, likely triggered by the flare impulses. We suggest that part of the EUV wave was probably trapped in the closed magnetic fields of the streamer-like structure, and upward SWs possibly resulted from the release of slow-mode trapped waves. It is believed that the interplay of the strong compression of the coronal shock and the configuration of the streamer-like structure is crucial for the formation of upward SWs.

Exploration of the Characteristics of the Time Variable Component of the Coronal Heating Process

NASA Technical Reports Server (NTRS)

Wagner, William (Technical Monitor); Habbal, Shadia R.

2003-01-01

By coordinating coronal SOHO observations in white light, ultraviolet, extreme ultraviolet, with radio occultation measurements, and complementing these with modeling, two break-throughs were achieved from this funding: (1) The discovery that minor ions are accelerated much faster than protons in the fast solar wind, and (2) that the imprint of coronal density structures is carried outwards from the Sun into the solar wind. Three refereed papers and one invited review, published in the proceedings of the conference, resulted from this funding. A summary of each is given.

Coronal Heating: Testing Models of Coronal Heating by Forward-Modeling the AIA Emission of the Ansample of Coronal Loops

NASA Astrophysics Data System (ADS)

Malanushenko, A. V.

2015-12-01

We present a systemic exploration of the properties of coronal heating, by forward-modeling the emission of the ensemble of 1D quasi-steady loops. This approximations were used in many theoretical models of the coronal heating. The latter is described in many such models in the form of power laws, relating heat flux through the photosphere or volumetric heating to the strength of the magnetic field and length of a given field line. We perform a large search in the parameter space of these power laws, amongst other variables, and compare the resulting emission of the active region to that observed by AIA. We use a recently developed magnetic field model which uses shapes of coronal loops to guide the magnetic model; the result closely resembles observed structures by design. We take advantage of this, by comparing, in individual sub-regions of the active region, the emission of the active region and its synthetic model. This study allows us to rule out many theoretical models and formulate predictions for the heating models to come.

The Magnetic Origins of Solar Activity

NASA Technical Reports Server (NTRS)

Antiochos, S. K.

2012-01-01

The defining physical property of the Sun's corona is that the magnetic field dominates the plasma. This property is the genesis for all solar activity ranging from quasi-steady coronal loops to the giant magnetic explosions observed as coronal mass ejections/eruptive flares. The coronal magnetic field is also the fundamental driver of all space weather; consequently, understanding the structure and dynamics of the field, especially its free energy, has long been a central objective in Heliophysics. The main obstacle to achieving this understanding has been the lack of accurate direct measurements of the coronal field. Most attempts to determine the magnetic free energy have relied on extrapolation of photospheric measurements, a notoriously unreliable procedure. In this presentation I will discuss what measurements of the coronal field would be most effective for understanding solar activity. Not surprisingly, the key process for driving solar activity is magnetic reconnection. I will discuss, therefore, how next-generation measurements of the coronal field will allow us to understand not only the origins of space weather, but also one of the most important fundamental processes in cosmic and laboratory plasmas.

Determination of plasma parameters from soft X-ray images for coronal holes /open magnetic field configurations/ and coronal large-scale structures /extended closed-field configurations/

NASA Technical Reports Server (NTRS)

Maxson, C. W.; Vaiana, G. S.

1977-01-01

In connection with high-quality solar soft X-ray images the 'quiet' features of the inner corona have been separated into two sharply different components, including the strongly reduced emission areas or coronal holes (CH) and the extended regions of looplike emission features or large-scale structures (LSS). Particular central meridian passage observations of the prominent CH1 on August 21, 1973, are selected for a quantitative study. Histogram photographic density distributions for full-disk images at other central meridian passages of CH 1 are also presented, and the techniques of converting low photographic density data to deposited energy are discussed, with particular emphasis on the problems associated with the CH data.

Recent perspectives in solar physics - Elemental composition, coronal structure and magnetic fields, solar activity

NASA Technical Reports Server (NTRS)

Newkirk, G., Jr.

1975-01-01

Elemental abundances in the solar corona are studied. Abundances in the corona, solar wind and solar cosmic rays are compared to those in the photosphere. The variation in silicon and iron abundance in the solar wind as compared to helium is studied. The coronal small and large scale structure is investigated, emphasizing magnetic field activity and examining cosmic ray generation mechanisms. The corona is observed in the X-ray and EUV regions. The nature of coronal transients is discussed with emphasis on solar-wind modulation of galactic cosmic rays. A schematic plan view of the interplanetary magnetic field during sunspot minimum is given showing the presence of magnetic bubbles and their concentration in the region around 4-5 AU by a fast solar wind stream.

Observations and Numerical Models of Solar Coronal Heating Associated with Spicules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pontieu, B. De; Martinez-Sykora, J.; Moortel, I. De

Spicules have been proposed as significant contributors to the mass and energy balance of the corona. While previous observations have provided a glimpse of short-lived transient brightenings in the corona that are associated with spicules, these observations have been contested and are the subject of a vigorous debate both on the modeling and the observational side. Therefore, it remains unclear whether plasma is heated to coronal temperatures in association with spicules. We use high-resolution observations of the chromosphere and transition region (TR) with the Interface Region Imaging Spectrograph and of the corona with the Atmospheric Imaging Assembly on board themore » Solar Dynamics Observatory to show evidence of the formation of coronal structures associated with spicular mass ejections and heating of plasma to TR and coronal temperatures. Our observations suggest that a significant fraction of the highly dynamic loop fan environment associated with plage regions may be the result of the formation of such new coronal strands, a process that previously had been interpreted as the propagation of transient propagating coronal disturbances. Our observations are supported by 2.5D radiative MHD simulations that show heating to coronal temperatures in association with spicules. Our results suggest that heating and strong flows play an important role in maintaining the substructure of loop fans, in addition to the waves that permeate this low coronal environment.« less

Distribution of Plasmoids in Post-Coronal Mass Ejection Current Sheets

NASA Astrophysics Data System (ADS)

Bhattacharjee, A.; Guo, L.; Huang, Y.

2013-12-01

Recently, the fragmentation of a current sheet in the high-Lundquist-number regime caused by the plasmoid instability has been proposed as a possible mechanism for fast reconnection. In this work, we investigate this scenario by comparing the distribution of plasmoids obtained from Large Angle and Spectrometric Coronagraph (LASCO) observational data of a coronal mass ejection event with a resistive magnetohydrodynamic simulation of a similar event. The LASCO/C2 data are analyzed using visual inspection, whereas the numerical data are analyzed using both visual inspection and a more precise topological method. Contrasting the observational data with numerical data analyzed with both methods, we identify a major limitation of the visual inspection method, due to the difficulty in resolving smaller plasmoids. This result raises questions about reports of log-normal distributions of plasmoids and other coherent features in the recent literature. Based on nonlinear scaling relations of the plasmoid instability, we infer a lower bound on the current sheet width, assuming the underlying mechanism of current sheet broadening is resistive diffusion.

Energetic particle abundances in solar electron events

NASA Technical Reports Server (NTRS)

Reames, D. V.; Cane, H. V.; Von Rosenvinge, T. T.

1990-01-01

The results of a comprehensive search of the ISEE 3 energetic particle data for solar electron events with associated increases in elements with atomic number Z = 6 or greater are reported. A sample of 90 such events was obtained. The events support earlier evidence of a bimodal distribution in Fe/O or, more clearly, in Fe/C. Most of the electron events belong to the group that is Fe-rich in comparison with the coronal abundance. The Fe-rich events are frequently also He-3-rich and are associated with type III and type V radio bursts and impulsive solar flares. Fe-poor events are associated with type IV bursts and with interplanetary shocks. With some exceptions, event-to-event enhancements in the heavier elements vary smoothly with Z and with Fe/C. In fact, these variations extend across the full range of events despite inferred differences in acceleration mechanism. The origin of source material in all events appears to be coronal and not photospheric.

The Origin of Sequential Chromospheric Brightenings

NASA Astrophysics Data System (ADS)

Kirk, M. S.; Balasubramaniam, K. S.; Jackiewicz, J.; Gilbert, H. R.

2017-06-01

Sequential chromospheric brightenings (SCBs) are often observed in the immediate vicinity of erupting flares and are associated with coronal mass ejections. Since their initial discovery in 2005, there have been several subsequent investigations of SCBs. These studies have used differing detection and analysis techniques, making it difficult to compare results between studies. This work employs the automated detection algorithm of Kirk et al. (Solar Phys. 283, 97, 2013) to extract the physical characteristics of SCBs in 11 flares of varying size and intensity. We demonstrate that the magnetic substructure within the SCB appears to have a significantly smaller area than the corresponding Hα emission. We conclude that SCBs originate in the lower corona around 0.1 R_{⊙} above the photosphere, propagate away from the flare center at speeds of 35 - 85 km s^{-1}, and have peak photosphere magnetic intensities of 148±2.9 G. In light of these measurements, we infer SCBs to be distinctive chromospheric signatures of erupting coronal mass ejections.

FORWARD MODELING OF STANDING KINK MODES IN CORONAL LOOPS. I. SYNTHETIC VIEWS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Ding; Doorsselaere, Tom Van, E-mail: DYuan2@uclan.ac.uk

2016-04-15

Kink magnetohydrodynamic (MHD) waves are frequently observed in various magnetic structures of the solar atmosphere. They may contribute significantly to coronal heating and could be used as a tool to diagnose the solar plasma. In this study, we synthesize the Fe ix λ171.073 Å emission of a coronal loop supporting a standing kink MHD mode. The kink MHD wave solution of a plasma cylinder is mapped into a semi-torus structure to simulate a curved coronal loop. We decompose the solution into a quasi-rigid kink motion and a quadrupole term, which dominate the plasma inside and outside of the flux tube, respectively.more » At the loop edges, the line of sight integrates relatively more ambient plasma, and the background emission becomes significant. The plasma motion associated with the quadrupole term causes spectral line broadening and emission suppression. The periodic intensity suppression will modulate the integrated intensity and the effective loop width, which both exhibit oscillatory variations at half of the kink period. The quadrupole term can be directly observed as a pendular motion at the front view.« less

Corotating solar wind structures and recurrent trains of enhanced diurnal variation in galactic cosmic rays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yeeram, T.; Ruffolo, D.; Sáiz, A.

Data from the Princess Sirindhorn Neutron Monitor at Doi Inthanon, Thailand, with a vertical cutoff rigidity of 16.8 GV, were utilized to determine the diurnal anisotropy (DA) of Galactic cosmic rays (GCRs) near Earth during solar minimum conditions between 2007 November and 2010 November. We identified trains of enhanced DA over several days, which often recur after a solar rotation period (∼27 days). By investigating solar coronal holes as identified from synoptic maps and solar wind parameters, we found that the intensity and anisotropy of cosmic rays are associated with the high-speed streams (HSSs) in the solar wind, which aremore » in turn related to the structure and evolution of coronal holes. An enhanced DA was observed after the onset of some, but not all, HSSs. During time periods of recurrent trains, the DA was often enhanced or suppressed according to the sign of the interplanetary magnetic field B, which suggests a contribution from a mechanism involving a southward gradient in the GCR density, n, and a gradient anisotropy along B × ∇n. In one non-recurrent and one recurrent sequence, an HSS from an equatorial coronal hole was merged with that from a trailing mid-latitude extension of a polar coronal hole, and the slanted HSS structure in space with suppressed GCR density can account for the southward GCR gradient. We conclude that the gradient anisotropy is a source of temporary changes in the GCR DA under solar minimum conditions, and that the latitudinal GCR gradient can sometimes be explained by the coronal hole morphology.« less

The correlation of fractal structures in the photospheric and the coronal magnetic field

NASA Astrophysics Data System (ADS)

Dimitropoulou, M.; Georgoulis, M.; Isliker, H.; Vlahos, L.; Anastasiadis, A.; Strintzi, D.; Moussas, X.

2009-10-01

Context: This work examines the relation between the fractal properties of the photospheric magnetic patterns and those of the coronal magnetic fields in solar active regions. Aims: We investigate whether there is any correlation between the fractal dimensions of the photospheric structures and the magnetic discontinuities formed in the corona. Methods: To investigate the connection between the photospheric and coronal complexity, we used a nonlinear force-free extrapolation method that reconstructs the 3d magnetic fields using 2d observed vector magnetograms as boundary conditions. We then located the magnetic discontinuities, which are considered as spatial proxies of reconnection-related instabilities. These discontinuities form well-defined volumes, called here unstable volumes. We calculated the fractal dimensions of these unstable volumes and compared them to the fractal dimensions of the boundary vector magnetograms. Results: Our results show no correlation between the fractal dimensions of the observed 2d photospheric structures and the extrapolated unstable volumes in the corona, when nonlinear force-free extrapolation is used. This result is independent of efforts to (1) bring the photospheric magnetic fields closer to a nonlinear force-free equilibrium and (2) omit the lower part of the modeled magnetic field volume that is almost completely filled by unstable volumes. A significant correlation between the fractal dimensions of the photospheric and coronal magnetic features is only observed at the zero level (lower limit) of approximation of a current-free (potential) magnetic field extrapolation. Conclusions: We conclude that the complicated transition from photospheric non-force-free fields to coronal force-free ones hampers any direct correlation between the fractal dimensions of the 2d photospheric patterns and their 3d counterparts in the corona at the nonlinear force-free limit, which can be considered as a second level of approximation in this study. Correspondingly, in the zero and first levels of approximation, namely, the potential and linear force-free extrapolation, respectively, we reveal a significant correlation between the fractal dimensions of the photospheric and coronal structures, which can be attributed to the lack of electric currents or to their purely field-aligned orientation.

Current systems of coronal loops in 3D MHD simulations

NASA Astrophysics Data System (ADS)

Warnecke, J.; Chen, F.; Bingert, S.; Peter, H.

2017-11-01

Aims: We study the magnetic field and current structure associated with a coronal loop. Through this we investigate to what extent the assumptions of a force-free magnetic field break down and where they might be justified. Methods: We analyze a three-dimensional (3D) magnetohydrodynamic (MHD) model of the solar corona in an emerging active region with the focus on the structure of the forming coronal loops. The lower boundary of this simulation is taken from a model of an emerging active region. As a consequence of the emerging magnetic flux and the horizontal motions at the surface a coronal loop forms self-consistently. We investigate the current density along magnetic field lines inside (and outside) this loop and study the magnetic and plasma properties in and around this loop. The loop is defined as the bundle of field lines that coincides with enhanced emission in extreme UV. Results: We find that the total current along the emerging loop changes its sign from being antiparallel to parallel to the magnetic field. This is caused by the inclination of the loop together with the footpoint motion. Around the loop, the currents form a complex non-force-free helical structure. This is directly related to a bipolar current structure at the loop footpoints at the base of the corona and a local reduction of the background magnetic field (I.e., outside the loop) caused by the plasma flow into and along the loop. Furthermore, the locally reduced magnetic pressure in the loop allows the loop to sustain a higher density, which is crucial for the emission in extreme UV. The action of the flow on the magnetic field hosting the loop turns out to also be responsible for the observed squashing of the loop. Conclusions: The complex magnetic field and current system surrounding it can only be modeled in 3D MHD models where the magnetic field has to balance the plasma pressure. A one-dimensional coronal loop model or a force-free extrapolation cannot capture the current system and the complex interaction of the plasma and the magnetic field in the coronal loop, despite the fact that the loop is under low-β conditions.

CME Interaction with Large-Scale Coronal Structures

NASA Technical Reports Server (NTRS)

Gopalswarny, Nat

2012-01-01

This talk presents some key observations that highlight the importance of CME interaction with other large scale structures such as CMEs and coronal holes . Such interactions depend on the phase of the solar cycle: during maximum, CMEs are ejected more frequently, so CME-CME interaction becomes dominant. During the rise phase, the polar coronal holes are strong, so the interaction between polar coronal holes and CMEs is important, which also leads to a possible increase in the number of interplanetary CMEs observed as magnetic clouds. During the declining phase, there are more equatorial coronal holes, so CMEs originating near these coronal holes are easily deflected. CMEs can be deflected toward and away from the Sun-Earth line resulting in interesting geospace consequences. For example, the largest geomagnetic storm of solar cycle 23 was due to a CME that was deflected towards the Sun-earth line from E22. CME deflection away from the Sun-Earth line diminishes the chance of a CME producing a geomagnetic storm. CME interaction in the coronagraphic field of view was first identified using enhanced radio emission, which is an indication of acceleration of low energy (approx.10 keV) electrons in the interaction site. CME interaction, therefore, may also have implications for proton acceleration. For example, solar energetic particle events typically occur with a higher intensity, whenever multiple CMEs occur in quick succession from the same source region. CME deflection may also have implications to the arrival of energetic particles to earth because magnetic connectivity may be changed by the interaction. I illustrate the above points using examples from SOHO, STEREO, Wind, and ACE data .

Report on New Mission Concept Study: Stereo X-Ray Corona Imager Mission

NASA Technical Reports Server (NTRS)

Liewer, Paulett C.; Davis, John M.; DeJong, E. M.; Gary, G. Allen; Klimchuk, James A.; Reinert, R. P.

1998-01-01

Studies of the three-dimensional structure and dynamics of the solar corona have been severely limited by the constraint of single viewpoint observations. The Stereo X-Ray Coronal Imager (SXCI) mission will send a single instrument, an X-ray telescope, into deep space expressly to record stereoscopic images of the solar corona. The SXCI spacecraft will be inserted into a approximately 1 AU heliocentric orbit leading Earth by approximately 25 deg at the end of nine months. The SXCI X-ray telescope forms one element of a stereo pair, the second element being an identical X-ray telescope in Earth orbit placed there as part of the NOAA GOES program. X-ray emission is a powerful diagnostic of the corona and its magnetic fields, and three dimensional information on the coronal magnetic structure would be obtained by combining the data from the two X-ray telescopes. This information can be used to address the major solar physics questions of (1) what causes explosive coronal events such as coronal mass ejections (CMEs), eruptive flares and prominence eruptions and (2) what causes the transient heating of coronal loops. Stereoscopic views of the optically thin corona will resolve some ambiguities inherent in single line-of-sight observations. Triangulation gives 3D solar coordinates of features which can be seen in the simultaneous images from both telescopes. As part of this study, tools were developed for determining the 3D geometry of coronal features using triangulation. Advanced technologies for visualization and analysis of stereo images were tested. Results of mission and spacecraft studies are also reported.

Solar Active Region Coronal Jets. II. Triggering and Evolution of Violent Jets

NASA Astrophysics Data System (ADS)

Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David A.; Panesar, Navdeep K.; Martinez, Francisco

2017-07-01

We study a series of X-ray-bright, rapidly evolving active region coronal jets outside the leading sunspot of AR 12259, using Hinode/X-ray telescope, Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI), and Interface Region Imaging Spectrograph (IRIS) data. The detailed evolution of such rapidly evolving “violent” jets remained a mystery after our previous investigation of active region jets. The jets we investigate here erupt from three localized subregions, each containing a rapidly evolving (positive) minority-polarity magnetic-flux patch bathed in a (majority) negative-polarity magnetic-flux background. At least several of the jets begin with eruptions of what appear to be thin (thickness ≲ 2\\prime\\prime ) miniature-filament (minifilament) “strands” from a magnetic neutral line where magnetic flux cancelation is ongoing, consistent with the magnetic configuration presented for coronal-hole jets in Sterling et al. (2016). Some jets strands are difficult/impossible to detect, perhaps due to, e.g., their thinness, obscuration by surrounding bright or dark features, or the absence of erupting cool-material minifilaments in those jets. Tracing in detail the flux evolution in one of the subregions, we find bursts of strong jetting occurring only during times of strong flux cancelation. Averaged over seven jetting episodes, the cancelation rate was ˜ 1.5× {10}19 Mx hr-1. An average flux of ˜ 5× {10}18 Mx canceled prior to each episode, arguably building up ˜1028-1029 erg of free magnetic energy per jet. From these and previous observations, we infer that flux cancelation is the fundamental process responsible for the pre-eruption build up and triggering of at least many jets in active regions, quiet regions, and coronal holes.

An observationally-driven kinetic approach to coronal heating

NASA Astrophysics Data System (ADS)

Moraitis, K.; Toutountzi, A.; Isliker, H.; Georgoulis, M.; Vlahos, L.; Chintzoglou, G.

2016-11-01

Aims: Coronal heating through the explosive release of magnetic energy remains an open problem in solar physics. Recent hydrodynamical models attempt an investigation by placing swarms of "nanoflares" at random sites and times in modeled one-dimensional coronal loops. We investigate the problem in three dimensions, using extrapolated coronal magnetic fields of observed solar active regions. Methods: We applied a nonlinear force-free field extrapolation above an observed photospheric magnetogram of NOAA active region (AR) 11 158. We then determined the locations, energy contents, and volumes of "unstable" areas, namely areas prone to releasing magnetic energy due to locally accumulated electric current density. Statistical distributions of these volumes and their fractal dimension are inferred, investigating also their dependence on spatial resolution. Further adopting a simple resistivity model, we inferred the properties of the fractally distributed electric fields in these volumes. Next, we monitored the evolution of 105 particles (electrons and ions) obeying an initial Maxwellian distribution with a temperature of 10 eV, by following their trajectories and energization when subjected to the resulting electric fields. For computational convenience, the length element of the magnetic-field extrapolation is 1 arcsec, or 725 km, much coarser than the particles' collisional mean free path in the low corona (0.1-1 km). Results: The presence of collisions traps the bulk of the plasma around the unstable volumes, or current sheets (UCS), with only a tail of the distribution gaining substantial energy. Assuming that the distance between UCS is similar to the collisional mean free path we find that the low active-region corona is heated to 100-200 eV, corresponding to temperatures exceeding 2 MK, within tens of seconds for electrons and thousands of seconds for ions. Conclusions: Fractally distributed, nanoflare-triggening fragmented UCS in the active-region corona can heat electrons and ions with minor enhancements of the local resistivity. This statistical result is independent from the nature of the extrapolation and the spatial resolution of the modeled active-region corona. This finding should be coupled with a complete plasma treatment to determine whether a quasi-steady temperature similar to that of the ambient corona can be maintained, either via a kinetic or via a hybrid, kinetic and fluid, plasma treatment. The finding can also be extended to the quiet solar corona, provided that the currently undetected nanoflares are frequent enough to account for the lower (compared to active regions) energy losses in this case.

Radiative transfer of X-rays in the solar corona

NASA Technical Reports Server (NTRS)

Acton, L. W.

1978-01-01

The problem of resonance scattering of X-ray emission lines in the solar corona is investigated. For the resonance lines of some helium-like ions, significant optical depths are reached over distances small compared with the size of typical coronal features. A general integral equation for the transfer of resonance-line radiation under solar coronal conditions is derived. This expression is in a form useful for modeling the complex three-dimensional temperature and density structure of coronal active regions. The transfer equation is then cast in a form illustrating the terms which give rise to the attenuation or enhancement of the resonance-line intensity. The source function for helium-like oxygen (O VII) under coronal conditions is computed and discussed in terms of the relative importance of scattering.

Three-dimensional geometry of coronal loops inferred by the Principal Component Analysis

NASA Astrophysics Data System (ADS)

Nisticò, Giuseppe; Nakariakov, Valery

We propose a new method for the determination of the three dimensional (3D) shape of coronal loops from stereoscopy. The common approach requires to find a 1D geometric curve, as circumference or ellipse, that best-fits the 3D tie-points which sample the loop shape in a given coordinate system. This can be easily achieved by the Principal Component (PC) analysis. It mainly consists in calculating the eigenvalues and eigenvectors of the covariance matrix of the 3D tie-points: the eigenvalues give a measure of the variability of the distribution of the tie-points, and the corresponding eigenvectors define a new cartesian reference frame directly related to the loop. The eigenvector associated with the smallest eigenvalues defines the normal to the loop plane, while the other two determine the directions of the loop axes: the major axis is related to the largest eigenvalue, and the minor axis with the second one. The magnitude of the axes is directly proportional to the square roots of these eigenvalues. The technique is fast and easily implemented in some examples, returning best-fitting estimations of the loop parameters and 3D reconstruction with a reasonable small number of tie-points. The method is suitable for serial reconstruction of coronal loops in active regions, providing a useful tool for comparison between observations and theoretical magnetic field extrapolations from potential or force-free fields.

Diagnostics of the solar corona from comparison between Faraday rotation measurements and magnetohydrodynamic simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Le Chat, G.; Cohen, O.; Kasper, J. C.

Polarized natural radio sources passing behind the Sun experience Faraday rotation as a consequence of the electron density and magnetic field strength in coronal plasma. Since Faraday rotation is proportional to the product of the density and the component of the magnetic field along the line of sight of the observer, a model is required to interpret the observations and infer coronal structures. Faraday rotation observations have been compared with relatively ad hoc models of the corona. Here for the first time we compare these observations with magnetohydrodynamic (MHD) models of the solar corona driven by measurements of the photosphericmore » magnetic field. We use observations made with the NRAO Very Large Array of 34 polarized radio sources occulted by the solar corona between 5 and 14 solar radii. The measurements were made during 1997 May, and 2005 March and April. We compare the observed Faraday rotation values with values extracted from MHD steady-state simulations of the solar corona. We find that (1) using a synoptic map of the solar magnetic field just one Carrington rotation off produces poorer agreements, meaning that the outer corona changes in the course of one month, even in solar minimum; (2) global MHD models of the solar corona driven by photospheric magnetic field measurements are generally able to reproduce Faraday rotation observations; and (3) some sources show significant disagreement between the model and the observations, which appears to be a function of the proximity of the line of sight to the large-scale heliospheric current sheet.« less

Latitude dependence of solar wind velocity observed at not less than 1 AU

NASA Technical Reports Server (NTRS)

Mitchell, D. G.; Roelof, E. C.; Wolfe, J. H.

1981-01-01

The large-scale solar wind velocity structure in the outer heliosphere has been systematically analyzed for Carrington rotations 1587-1541 (March 1972 to April 1976). Spacecraft data were taken from Imp 7/8 at earth, Pioneer 6, 8, and 9 near 1 AU, and Pioneer 10 and 11 between 1.6 and 5 AU. Using the constant radial velocity solar wind approximation to map all of the velocity data to its high coronal emission heliolongitude, the velocity structure observed at different spacecraft was examined for latitudinal dependence and compared with coronal structure in soft X-rays and H-alpha absorption features. The constant radial velocity approximation usually remains self-consistent in decreasing or constant velocity solar wind out to 5 AU, enabling us to separate radial from latitudinal propagation effects. Several examples of sharp nonmeridional stream boundaries in interplanetary space (about 5 deg latitude in width), often directly associated with features in coronal X-rays and H-alpha were found.

Solar--geophysical data. Prompt reports. [Number 405, May 1978. Data for A/pril 1978--March 1978

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coffey, H.E.

1978-05-01

This prompt report provides data for April 1978 on alert period, daily solar indices, solar flares, solar radio waves, solar x-ray radiation, coronal holes, inferred IP magnetic field polarities, mean solar magnetic field, solar wind measurements, geomagnetic substorms, and magnetograms of geomagnetic storm. It also provides data for March 1978 on daily solar activity center, sudden ionospheric disturbances, solar x-ray radiation, solar radio waves, cosmic rays, geomagnetic indices and radio propagation indices. A new data page lists the North American magnetometer network.

Conditions for the formation of prominences as inferred from optical observations

NASA Technical Reports Server (NTRS)

Martin, Sara F.

1990-01-01

It is suggested that three conditions, if dynamically maintained for a sufficient period of time, will result in the formation of a solar prominence. These conditions are the presence of a coronal arcade that connects the magnetic fields on opposite sides of a prominence; the existence of a long-term (hours to days) converging flow of small patches of opposite-polarity magnetic flux toward a common-polarity inversion zone; and the cancellation of encountered patches of magnetic flux of opposite polarity at a photospheric polarity inversion boundary.

V.L.A. Observations of Solar-Active Regions. I. The Slowly Varying Component,

DTIC Science & Technology

1980-08-01

bremsstrahlung accounts for the highly polarized radiation. In this situation the magnetic energy 2 % 4 -3 density of H /(8T) 10 erg cm vastly exceeds the...equipartition value inferred from the virial theorem, for the thermal kinetic energy density in -3 the "coronal condensations" is 3N kT 5 erg cm . It...Boston: D. Reidel). Kundu, M.R., 1959a, Ann. Ap., 22, 1. Kundu, M.R., 1959b, "Etude Interferometrique des Sources d’Activite Solaire sur 3 cm de

Can Thermal Nonequilibrium Explain Coronal Loops?

NASA Technical Reports Server (NTRS)

Klimchuk, James A.; Karpen, Judy T.; Antiochos, Spiro K.

2010-01-01

Any successful model of coronal loops must explain a number of observed properties. For warm (approx. 1 MK) loops, these include: 1. excess density, 2. flat temperature profile, 3. super-hydrostatic scale height, 4. unstructured intensity profile, and 5. 1000-5000 s lifetime. We examine whether thermal nonequilibrium can reproduce the observations by performing hydrodynamic simulations based on steady coronal heating that decreases exponentially with height. We consider both monolithic and multi-stranded loops. The simulations successfully reproduce certain aspects of the observations, including the excess density, but each of them fails in at least one critical way. -Xonolithic models have far too much intensity structure, while multi-strand models are either too structured or too long-lived. Storms of nanoflares remain the only viable explanation for warm loops that has been proposed so far. Our results appear to rule out the widespread existence of heating that is both highly concentrated low in the corona and steady or quasi-steady (slowly varying or impulsive with a rapid cadence). Active regions would have a very different appearance if the dominant heating mechanism had these properties. Thermal nonequilibrium may nonetheless play an important role in prominences and catastrophic cooling e(veen.gts..,coronal rain) that occupy a small fraction of the coronal volume. However, apparent inconsistencies between the models and observations of cooling events have yet to be understood.

Feel the Burn: What accounts for spatial variations in coronal heating?

NASA Astrophysics Data System (ADS)

Atwood, Shane; Kankelborg, Charles C.

2016-05-01

The coronal volume is filled with magnetic field, yet only part of that volume has sufficient heating to exhibit hot x-ray loops. How does the Sun decide where the heat goes? Using XRT and AIA images and HMI magnetograms, we identify footpoints of hot coronal loops, and magnetically similar regions underlying relatively unheated corona. We then use IRIS rasters and sit-and-stare observations to compare the spatial, temporal, and spectral structure of these relatively ``heated’’ and ``unheated’’ regions. We seek a signature of upward propagating energy that could be associated with hot active region loops.

Predicting Ly-alpha intensities in coronal streamers

NASA Technical Reports Server (NTRS)

Noci, Giancarlo; Poletto, Giannina; Suess, Steven T.; Wang, A.-H.; Wu, S. T.

1992-01-01

SOHO (Solar and Heliospheric Observatory) UVCS (Ultraviolet Coronagraph Spectrometer) will make long term observations of coronal streamers in UV lines, providing a new tool for the analysis of structures which have been known for decades but are still far from being adequately described. Work to evaluate the Lyman alpha brightness of coronal streamers is reported, adopting the streamer models obtained, via a time dependent numerical relaxation technique. This will yield understanding on the role of geometric versus physical factors in determining the streamer lyman alpha intensity and provide guidelines for UVCS observational operations. Future prospects along this line of research are summarized.

Quasi-static evolution of coronal magnetic fields

NASA Technical Reports Server (NTRS)

Longcope, D. W.; Sudan, R. N.

1992-01-01

A formalism is developed to describe the purely quasi-static part of the evolution of a coronal loop driven by its footpoints. This is accomplished under assumptions of a long, thin loop. The quasi-static equations reveal the possibility for sudden 'loss of equilibrium' at which time the system evolves dynamically rather than quasi-statically. Such quasi-static crises produce high-frequency Alfven waves and, in conjunction with Alfven wave dissipation models, form a viable coronal heating mechanism. Furthermore, an approximate solution to the quasi-static equations by perturbation method verifies the development of small-scale spatial current structure.

Fast Breakdown as Coronal/Ionization Waves?

NASA Astrophysics Data System (ADS)

Krehbiel, P. R.; Petersen, D.; da Silva, C. L.

2017-12-01

Studies of high-power narrow bipolar events (NBEs) have shown they are produced by a newly-recognized breakdown process called fast positive breakdown (FPB, Rison et al., 2016, doi:10.1038/ncomms10721). The breakdown was inferred to be produced by a system of positive streamers that propagate at high speed ( ˜3-6 x 107 m/s) due to occurring in a localized region of strong electric field. The polarity of the breakdown was determined from broadband interferometer (INTF) observations of the propagation direction of its VHF radiation, which was downward into the main negative charge region of a normally-electrified storm. Subsequent INTF observations being conducted in at Kennedy Space Center in Florida have shown a much greater incidence of NBEs than in New Mexico. Among the larger dataset have been clear-cut instances of some NBEs being produced by upward breakdown that would be of negative polarity. The speed and behavior of the negative breakdown is the same as that of the fast positive, leading to it being termed fast negative breakdown (FNB). The similarity (not too mention its occurrence) is surprising, given the fact that negative streamers and breakdown develops much differently than that of positive breakdown. The question is how this happens. In this study, we compare fast breakdown characteristics to well-known streamer properties as inferred from laboratory experiments and theoretical analysis. Additionally, we begin to explore the possibility that both polarities of fast breakdown are produced by what may be called coronal or ionization waves, in which the enhanced electric field produced by streamer or coronal breakdown of either polarity propagates away from the advancing front at the speed of light into a medium that is in a metastable condition of being at the threshold of hydrometeor-mediated corona onset or other ionization processes. The wave would develop at a faster speed than the streamer breakdown that gives rise to it, and thus would be somewhat analogous to a phase velocity. Once started, the breakdown would tend to be polarity independent. The main difference would be that FNB would be more difficult to initiate and therefore less common, which agrees with current observations.

Characteristics of EUV Coronal Jets Observed with STEREO/SECCHI

NASA Astrophysics Data System (ADS)

Nisticò, G.; Bothmer, V.; Patsourakos, S.; Zimbardo, G.

2009-10-01

In this paper we present the first comprehensive statistical study of EUV coronal jets observed with the SECCHI (Sun Earth Connection Coronal and Heliospheric Investigation) imaging suites of the two STEREO spacecraft. A catalogue of 79 polar jets is presented, identified from simultaneous EUV and white-light coronagraph observations, taken during the time period March 2007 to April 2008, when solar activity was at a minimum. The twin spacecraft angular separation increased during this time interval from 2 to 48 degrees. The appearances of the coronal jets were always correlated with underlying small-scale chromospheric bright points. A basic characterization of the morphology and identification of the presence of helical structure were established with respect to recently proposed models for their origin and temporal evolution. Though each jet appeared morphologically similar in the coronagraph field of view, in the sense of a narrow collimated outward flow of matter, at the source region in the low corona the jet showed different characteristics, which may correspond to different magnetic structures. A classification of the events with respect to previous jet studies shows that amongst the 79 events there were 37 Eiffel tower-type jet events, commonly interpreted as a small-scale (˜35 arc sec) magnetic bipole reconnecting with the ambient unipolar open coronal magnetic fields at its loop tops, and 12 lambda-type jet events commonly interpreted as reconnection with the ambient field happening at the bipole footpoints. Five events were termed micro-CME-type jet events because they resembled the classical coronal mass ejections (CMEs) but on much smaller scales. The remaining 25 cases could not be uniquely classified. Thirty-one of the total number of events exhibited a helical magnetic field structure, indicative for a torsional motion of the jet around its axis of propagation. A few jets are also found in equatorial coronal holes. In this study we present sample events for each of the jet types using both, STEREO A and STEREO B, perspectives. The typical lifetimes in the SECCHI/EUVI ( Extreme UltraViolet Imager) field of view between 1.0 to 1.7 R ⊙ and in SECCHI/COR1 field of view between 1.4 to 4 R ⊙ are obtained, and the derived speeds are roughly estimated. In summary, the observations support the assumption of continuous small-scale reconnection as an intrinsic feature of the solar corona, with its role for the heating of the corona, particle acceleration, structuring and acceleration of the solar wind remaining to be explored in more detail in further studies.

Studying the Kinematic Behavior of Coronal Mass Ejections and Other Solar Phenomena using the Time-Convolution Mapping Method

NASA Astrophysics Data System (ADS)

Hess Webber, Shea A.; Thompson, Barbara J.; Kwon, Ryun Young; Ireland, Jack

2018-01-01

An improved understanding of the kinematic properties of CMEs and CME-associated phenomena has several impacts: 1) a less ambiguous method of mapping propagating structures into their inner coronal manifestations, 2) a clearer view of the relationship between the “main” CME and CME-associated brightenings, and 3) an improved identification of the heliospheric sources of shocks, Type II bursts, and SEPs. We present the results of a mapping technique that facilitates the separation of CMEs and CME-associated brightenings (such as shocks) from background corona. The Time Convolution Mapping Method (TCMM) segments coronagraph data to identify the time history of coronal evolution, the advantage being that the spatiotemporal evolution profiles allow users to separate features with different propagation characteristics. For example, separating “main” CME mass from CME-associated brightenings or shocks is a well-known obstacle, which the TCMM aids in differentiating. A TCMM CME map is made by first recording the maximum value each individual pixel in the image reaches during the traversal of the CME. Then the maximum value is convolved with an index to indicate the time that the pixel reached that value. The TCMM user is then able to identify continuous “kinematic profiles,” indicating related kinematic behavior, and also identify breaks in the profiles that indicate a discontinuity in kinematic history (i.e. different structures or different propagation characteristics). The maps obtained from multiple spacecraft viewpoints (i.e., STEREO and SOHO) can then be fit with advanced structural models to obtain the 3D properties of the evolving phenomena. We will also comment on the TCMM's further applicability toward the tracking of prominences, coronal hole boundaries and coronal cavities.

Electron trapping in evolving coronal structures during a large gradual hard X-ray/radio burst

NASA Technical Reports Server (NTRS)

Bruggmann, G.; Vilmer, N.; Klein, K.-L.; Kane, S. R.

1994-01-01

Gradual hard X-ray/radio bursts are characterized by their long duration, smooth time profile, time delays between peaks at different hard X-ray energies and microwaves, and radiation from extended sources in the low and middle corona. Their characteristic properties have been ascribed to the dynamic evolution of the accelerated electrons in coronal magnetic traps or to the separate acceleration of high-energy electrons in a 'second step' process. The information available so far was drawn from quality considerations of time profiles or even only from the common occurrence of emissions in different spectral ranges. This paper presents model computations of the temporal evolution of hard X-ray and microwave spectra, together with a qualitative discussion of radio lightcurves over a wide spectral range, and metric imaging observations. The basis hypothesis investigated is that the peculiar 'gradual' features can be related to the dynamical evolution of electrons injected over an extended time interval in a coronal trap, with electrons up to relativistic energies being injected simultaneously. The analyzed event (26 April. 1981) is particularly challenging to this hypothesis because of the long time delays between peaks at different X-ray energies and microwave frequencies. The observations are shown to be consistent with the hypothesis, provided that the electrons lose their energy by Coulomb collisions and possibly betatron deceleration. The access of the electrons to different coronal structures varies in the course of the event. The evolution and likely destabilization of part of the coronal plasma-magnetic field configuration is of crucial influence in determining the access to these structures and possibly the dynamical evolution of the trapped electrons through betatron deceleration in the late phase of the event.

An Airborne Infrared Spectrometer for Solar Eclipse Observations

NASA Astrophysics Data System (ADS)

Samra, Jenna; DeLuca, Edward E.; Golub, Leon; Cheimets, Peter; Philip, Judge

2016-05-01

The airborne infrared spectrometer (AIR-Spec) is an innovative solar spectrometer that will observe the 2017 solar eclipse from the NSF/NCAR High-Performance Instrumented Airborne Platform for Environmental Research (HIAPER). AIR-Spec will image five infrared coronal emission lines to determine whether they may be useful probes of coronal magnetism.The solar magnetic field provides the free energy that controls coronal heating, structure, and dynamics. Energy stored in coronal magnetic fields is released in flares and coronal mass ejections and ultimately drives space weather. Therefore, direct coronal field measurements have significant potential to enhance understanding of coronal dynamics and improve solar forecasting models. Of particular interest are observations of field lines in the transitional region between closed and open flux systems, providing important information on the origin of the slow solar wind.While current instruments routinely observe only the photospheric and chromospheric magnetic fields, AIR-Spec will take a step toward the direct observation of coronal fields by measuring plasma emission in the infrared at high spatial and spectral resolution. During the total solar eclipse of 2017, AIR-Spec will observe five magnetically sensitive coronal emission lines between 1.4 and 4 µm from the HIAPER Gulfstream V at an altitude above 14.9 km. The instrument will measure emission line intensity, width, and Doppler shift, map the spatial distribution of infrared emitting plasma, and search for waves in the emission line velocities.AIR-Spec consists of an optical system (feed telescope, grating spectrometer, and infrared detector) and an image stabilization system, which uses a fast steering mirror to correct the line-of-sight for platform perturbations. To ensure that the instrument meets its research goals, both systems are undergoing extensive performance modeling and testing. These results are shown with reference to the science requirements.

The effects of large- and small-scale density structures on the radio from coronal streamers

NASA Astrophysics Data System (ADS)

Thejappa, G.; Kundu, M. R.

1994-01-01

The radio observations of the coronal streamers obtained using Clark Lake radioheliograph at 73.8, 50.0, and 38.5 MHz during a period of minimum activity in September 1986 are presented. Streamers appear to correlate with two prominent disk sources whose intensites fluctuated randomly. The variations in half-power diameter of the radio Sun are found to correspond with the variations in the white-light extents of the coronal streamers. It appears that the shape of the radio Sun is not a function of the phase of the solar cycle; instead it depends on the relative positions of the streamers in the corona. The observed peak brightness temperatures, TB, of the streamers are found to be very low, being approximately equal to 6 x 104 K. We compute the brightness temperature distribution along the equator by tracing the rays in the coronal plasma. The rays are deflected away by the streamers before reaching the critical density level, whereas they penetrate deeper into the coronal hole for small angles between the line of sight and the streamer axis. As a consequence, it is found that the streamers and coronal holes appear in the calculated equatorial brightness distribution as irregular brightness depressions and enhancements, respectively. The fine structures are found to disappear when the scattering due to small-scale density inhomogeneities is included in the ray-tracing calculations. The required relative level of density fluctuations, epsilon1 = (delta N)/N, is found to be greater than 12% to reduce the peak brightness temperature from 106 K to 6 x 104 K for all the three frequencies.

Nonlinear Force-free Coronal Magnetic Stereoscopy

NASA Astrophysics Data System (ADS)

Chifu, Iulia; Wiegelmann, Thomas; Inhester, Bernd

2017-03-01

Insights into the 3D structure of the solar coronal magnetic field have been obtained in the past by two completely different approaches. The first approach are nonlinear force-free field (NLFFF) extrapolations, which use photospheric vector magnetograms as boundary condition. The second approach uses stereoscopy of coronal magnetic loops observed in EUV coronal images from different vantage points. Both approaches have their strengths and weaknesses. Extrapolation methods are sensitive to noise and inconsistencies in the boundary data, and the accuracy of stereoscopy is affected by the ability of identifying the same structure in different images and by the separation angle between the view directions. As a consequence, for the same observational data, the 3D coronal magnetic fields computed with the two methods do not necessarily coincide. In an earlier work (Paper I) we extended our NLFFF optimization code by including stereoscopic constrains. The method was successfully tested with synthetic data, and within this work, we apply the newly developed code to a combined data set from SDO/HMI, SDO/AIA, and the two STEREO spacecraft. The extended method (called S-NLFFF) contains an additional term that monitors and minimizes the angle between the local magnetic field direction and the orientation of the 3D coronal loops reconstructed by stereoscopy. We find that when we prescribe the shape of the 3D stereoscopically reconstructed loops, the S-NLFFF method leads to a much better agreement between the modeled field and the stereoscopically reconstructed loops. We also find an appreciable decrease by a factor of two in the angle between the current and the magnetic field. This indicates the improved quality of the force-free solution obtained by S-NLFFF.

A New View of the Origin of the Solar Wind

NASA Technical Reports Server (NTRS)

Woo, Richard; Habbal, Shadia Rifai

1999-01-01

This paper uses white-light measurements made by the SOHO LASCO coronagraph and HAO Mauna Loa Mk III K-coronameter to illustrate the new view of solar wind structure deduced originally from radio occultation measurements. It is shown that the density profile closest to the Sun at 1.15 Ro, representing the imprint of the Sun, is carried essentially radially into interplanetary space by small-scale raylike structures that permeate the solar corona and which have only been observed by radio occultation measurements. The only exception is the small volume of interplanetary space occupied by the heliospheric plasma sheet that evolves from coronal streamers within a few solar radii of the Sun. The radial preservation of the density profile also implies that a significant fraction of field lines which extend into interplanetary space originate from the quiet Sun, and are indistinguishable in character from those emanating from polar coronal holes. The white-light measurements dispel the long-held belief that the boundaries of polar coronal holes diverge significantly, and further support the view originally proposed that the fast solar wind originates from the quiet Sun as well as polar coronal holes.

Acquisition of thin coronal sectional dataset of cadaveric liver.

PubMed

Lou, Li; Liu, Shu Wei; Zhao, Zhen Mei; Tang, Yu Chun; Lin, Xiang Tao

2014-04-01

To obtain the thin coronal sectional anatomic dataset of the liver by using digital freezing milling technique. The upper abdomen of one Chinese adult cadaver was selected as the specimen. After CT and MRI examinations verification of absent liver lesions, the specimen was embedded with gelatin in stand erect position and frozen under profound hypothermia, and the specimen was then serially sectioned from anterior to posterior layer by layer with digital milling machine in the freezing chamber. The sequential images were captured by means of a digital camera and the dataset was imported to imaging workstation. The thin serial section of the liver added up to 699 layers with each layer being 0.2 mm in thickness. The shape, location, structure, intrahepatic vessels and adjacent structures of the liver was displayed clearly on each layer of the coronal sectional slice. CT and MR images through the body were obtained at 1.0 and 3.0 mm intervals, respectively. The methodology reported here is an adaptation of the milling methods previously described, which is a new data acquisition method for sectional anatomy. The thin coronal sectional anatomic dataset of the liver obtained by this technique is of high precision and good quality.

On the Rates of Coronal Mass Ejections: Remote Solar and In Situ Observations

NASA Technical Reports Server (NTRS)

Riley, Pete; Schatzman, C.; Cane, H. V.; Richardson, I. G.; Gopalswamy, N.

2006-01-01

We compare the rates of coronal mass ejections (CMEs) as inferred from remote solar observations and interplanetary CMEs (ICMEs) as inferred from in situ observations at both 1 AU and Ulyssses from 1996 through 2004. We also distinguish between those ICMEs that contain a magnetic cloud (MC) and those that do not. While the rates of CMEs and ICMEs track each other well at solar minimum, they diverge significantly in early 1998, during the ascending phase of the solar cycle, with the remote solar observations yielding approximately 20 times more events than are seen at 1 AU. This divergence persists through 2004. A similar divergence occurs between MCs and non-MC ICMEs. We argue that these divergences are due to the birth of midlatitude active regions, which are the sites of a distinct population of CMEs, only partially intercepted by Earth, and we present a simple geometric argument showing that the CME and ICME rates are consistent with one another. We also acknowledge contributions from (1) an increased rate of high-latitude CMEs and (2) focusing effects from the global solar field. While our analysis, coupled with numerical modeling results, generally supports the interpretation that whether one observes a MC within an ICME is sensitive to the trajectory of the spacecraft through the ICME (i.e., an observational selection effect), one result directly contradicts it. Specifically, we find no systematic offset between the latitudinal origin of ICMEs that contain MCs at 1 AU in the ecliptic plane and that of those that do not.

Modeling a simple coronal streamer during whole sun month

NASA Technical Reports Server (NTRS)

Gibson, S. E.; Bagenal, F.; Biesecker, D.; Guhathakurta, M.; Hoeksema, J. T.; Thompson, B. J.

1997-01-01

The solar minimum streamer structure observed during the whole sun month was modeled. The Van de Hulst inversion was used in order to determine the coronal electron density profiles and scale-height temperature profiles. The axisymmetric magnetostatic model of Gibson, Bagenal and Low was also used. The density, temperature, and magnetic field distribution were quantified using both coronal white light data and photospheric magnetic field data from the Wilcox Solar Observatory. The densities and temperatures obtained by the Van de Hulst and magnetostatic models are compared to the magnetic field predicted by the magnetostatic model to a potential field extrapolated from the photosphere.

Developing a tooth restorability index.

PubMed

McDonald, Ailbhe; Setchell, Derrick

2005-01-01

It is generally agreed that the inherent strength of a tooth is dependent on the remaining dentine. It therefore seems logical that preservation of coronal dentine is important to the survival of intra- and extra-coronal restorations. The clinical assessment of the amount of dentine needed for functional requirements and the strategic value of remaining tooth structure is currently based on clinical opinion. This paper discusses what recommendations have been published and proposes an index that may be useful in assessing the restorability of a tooth. An index used to assess the amount and contribution of remaining coronal dentine to resistance and retention form could be of value in treatment planning.

Empirical scaling laws for coronal heating

NASA Technical Reports Server (NTRS)

Golub, L.

1983-01-01

The origins and uses of scaling laws in studies of stellar outer atmospheres are reviewed with particular emphasis on the properties of coronal loops. Some evidence is presented for a fundamental structuring of the solar corona and the thermodynamics of scaling laws are discussed. It is found that magnetic field-related scaling laws can be obtained by relating coronal pressure, temperature, and magnetic field strength. Available data validate this method. Some parameters of the theory, however, must be treated as adjustable, and it is considered necessary to examine data from other stars in order to determine the validity of the parameters. Using detailed observational data, the applicability of single loop models is examined.

Neutral Hydrogen and Its Emission Lines in the Solar Corona

NASA Astrophysics Data System (ADS)

Vial, Jean-Claude; Chane-Yook, Martine

2016-12-01

Since the Lyman-α rocket observations of Gabriel ( Solar Phys. 21, 392, 1971), it has been realized that the hydrogen (H) lines could be observed in the corona and that they offer an interesting diagnostic for the temperature, density, and radial velocity of the coronal plasma. Moreover, various space missions have been proposed to measure the coronal magnetic and velocity fields through polarimetry in H lines. A necessary condition for such measurements is to benefit from a sufficient signal-to-noise ratio. The aim of this article is to evaluate the emission in three representative lines of H for three different coronal structures. The computations have been performed with a full non-local thermodynamic-equilibrium (non-LTE) code and its simplified version without radiative transfer. Since all collisional and radiative quantities (including incident ionizing and exciting radiation) are taken into account, the ionization is treated exactly. Profiles are presented at two heights (1.05 and 1.9 solar radii, from Sun center) in the corona, and the integrated intensities are computed at heights up to five solar radii. We compare our results with previous computations and observations ( e.g. Lα from Ultraviolet Coronal Spectrometer) and find a rough (model-dependent) agreement. Since the Hα line is a possible candidate for ground-based polarimetry, we show that in order to detect its emission in various coronal structures, it is necessary to use a very narrow (less than 2 Å wide) bandpass filter.

A SOLAR CORONAL JET EVENT TRIGGERS A CORONAL MASS EJECTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Jiajia; Wang, Yuming; Shen, Chenglong

2015-11-10

In this paper, we present multi-point, multi-wavelength observations and analysis of a solar coronal jet and coronal mass ejection (CME) event. Employing the GCS model, we obtained the real (three-dimensional) heliocentric distance and direction of the CME and found it to propagate at a high speed of over 1000 km s{sup −1}. The jet erupted before the CME and shared the same source region. The temporal and spacial relationship between these two events lead us to the possibility that the jet triggered the CME and became its core. This scenario hold the promise of enriching our understanding of the triggeringmore » mechanism of CMEs and their relations to coronal large-scale jets. On the other hand, the magnetic field configuration of the source region observed by the Solar Dynamics Observatory (SDO)/HMI instrument along with the off-limb inverse Y-shaped configuration observed by SDO/AIA in the 171 Å passband provide the first detailed observation of the three-dimensional reconnection process of a large-scale jet as simulated in Pariat et al. The eruption process of the jet highlights the importance of filament-like material during the eruption of not only small-scale X-ray jets, but likely also of large-scale EUV jets. Based on our observations and analysis, we propose the most probable mechanism for the whole event, with a blob structure overlaying the three-dimensional structure of the jet, to describe the interaction between the jet and the CME.« less

HiRISE/NEOCE: an ESA M5 formation flying proposed mission combining high resolution and coronagraphy for ultimate observations of the chromosphere, corona and interface

NASA Astrophysics Data System (ADS)

Damé, Luc; Von Fay-Siebenburgen Erdélyi, Robert

2016-07-01

The global understanding of the solar environment through the magnetic field emergence and dissipation, and its influence on Earth, is at the centre of the four major thematics addressed by HiRISE/NEOCE (High Resolution Imaging and Spectroscopy Explorer/New Externally Occulted Coronagraph Experiment). They are interlinked and also complementary: the internal structure of the Sun determines the surface activity and dynamics that trigger magnetic field structuring which evolution, variation and dissipation will, in turn, explain the coronal heating onset and the major energy releases that feed the influence of the Sun on Earth. The 4 major themes of HiRISE/NEOCE are: - fine structure of the chromosphere-corona interface by 2D spectroscopy in FUV at very high resolution; - coronal heating roots in inner corona by ultimate externally-occulted coronagraphy; - resolved and global helioseismology thanks to continuity and stability of observing at L1 Lagrange point; - solar variability and space climate with a global comprehensive view of UV variability as well. Recent missions have shown the definite role of waves and of the magnetic field deep in the inner corona, at the chromosphere-corona interface, where dramatic changes occur. The dynamics of the chromosphere and corona is controlled by the emerging magnetic field, guided by the coronal magnetic field. Accordingly, the direct measurement of the chromospheric and coronal magnetic fields is of prime importance. This is implemented in HiRISE/NEOCE, to be proposed for ESA M5 ideally placed at the L1 Lagrangian point, providing FUV imaging and spectro-imaging, EUV and XUV imaging and spectroscopy, and ultimate coronagraphy by a remote external occulter (two satellites in formation flying 375 m apart minimizing scattered light) allowing to characterize temperature, densities and velocities up to the solar upper chromosphere, transition zone and inner corona with, in particular, 2D very high resolution multi-spectral imaging-spectroscopy and direct coronal magnetic field measurement: a unique set of tools to understand the structuration and onset of coronal heating. We give a detailed account of the major scientific objectives, and present the ESA M5 proposed mission profile and model payload (in particular of the SuperASPIICS package of visible, NIR and UV, Lyman-Alpha and OVI, coronagraphs).

A Multiscale Vision Model applied to analyze EIT images of the solar corona

NASA Astrophysics Data System (ADS)

Portier-Fozzani, F.; Vandame, B.; Bijaoui, A.; Maucherat, A. J.; EIT Team

2001-07-01

The large dynamic range provided by the SOHO/EIT CCD (1 : 5000) is needed to observe the large EUV zoom of coronal structures from coronal homes up to flares. Histograms show that often a wide dynamic range is present in each image. Extracting hidden structures in the background level requires specific techniques such as the use of the Multiscale Vision Model (MVM, Bijaoui et al., 1998). This method, based on wavelet transformations optimizes detection of various size objects, however complex they may be. Bijaoui et al. built the Multiscale Vision Model to extract small dynamical structures from noise, mainly for studying galaxies. In this paper, we describe requirements for the use of this method with SOHO/EIT images (calibration, size of the image, dynamics of the subimage, etc.). Two different areas were studied revealing hidden structures: (1) classical coronal mass ejection (CME) formation and (2) a complex group of active regions with its evolution. The aim of this paper is to define carefully the constraints for this new method of imaging the solar corona with SOHO/EIT. Physical analysis derived from multi-wavelength observations will later complete these first results.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chesny, D. L.; Oluseyi, H. M.; Orange, N. B.

Ubiquitous solar atmospheric coronal and transition region bright points (BPs) are compact features overlying strong concentrations of magnetic flux. Here, we utilize high-cadence observations from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory to provide the first observations of extreme ultraviolet quiet-Sun (QS) network BP activity associated with sigmoidal structuring. To our knowledge, this previously unresolved fine structure has never been associated with such small-scale QS events. This QS event precedes a bi-directional jet in a compact, low-energy, and low-temperature environment, where evidence is found in support of the typical fan-spine magnetic field topology. As in active regionsmore » and micro-sigmoids, the sigmoidal arcade is likely formed via tether-cutting reconnection and precedes peak intensity enhancements and eruptive activity. Our QS BP sigmoid provides a new class of small-scale structuring exhibiting self-organized criticality that highlights a multi-scaled self-similarity between large-scale, high-temperature coronal fields and the small-scale, lower-temperature QS network. Finally, our QS BP sigmoid elevates arguments for coronal heating contributions from cooler atmospheric layers, as this class of structure may provide evidence favoring mass, energy, and helicity injections into the heliosphere.« less

Hinode observations and 3D magnetic structure of an X-ray bright point

NASA Astrophysics Data System (ADS)

Alexander, C. E.; Del Zanna, G.; Maclean, R. C.

2011-02-01

Aims: We present complete Hinode Solar Optical Telescope (SOT), X-Ray Telescope (XRT)and EUV Imaging Spectrometer (EIS) observations of an X-ray bright point (XBP) observed on the 10, 11 of October 2007 over its entire lifetime (~12 h). We aim to show how the measured plasma parameters of the XBP change over time and also what kind of similarities the X-ray emission has to a potential magnetic field model. Methods: Information from all three instruments on-board Hinode was used to study its entire evolution. XRT data was used to investigate the structure of the bright point and to measure the X-ray emission. The EIS instrument was used to measure various plasma parameters over the entire lifetime of the XBP. Lastly, the SOT was used to measure the magnetic field strength and provide a basis for potential field extrapolations of the photospheric fields to be made. These were performed and then compared to the observed coronal features. Results: The XBP measured ~15´´ in size and was found to be formed directly above an area of merging and cancelling magnetic flux on the photosphere. A good correlation between the rate of X-ray emission and decrease in total magnetic flux was found. The magnetic fragments of the XBP were found to vary on very short timescales (minutes), however the global quasi-bipolar structure remained throughout the lifetime of the XBP. The potential field extrapolations were a good visual fit to the observed coronal loops in most cases, meaning that the magnetic field was not too far from a potential state. Electron density measurements were obtained using a line ratio of Fe XII and the average density was found to be 4.95 × 109 cm-3 with the volumetric plasma filling factor calculated to have an average value of 0.04. Emission measure loci plots were then used to infer a steady temperature of log Te [ K] ~ 6.1. The calculated Fe XII Doppler shifts show velocity changes in and around the bright point of ±15 km s-1 which are observed to change on a timescale of less than 30 min.

Creation of current filaments in the solar corona

NASA Technical Reports Server (NTRS)

Mikic, Z.; Schnack, D. D.; Van Hoven, G.

1989-01-01

It has been suggested that the solar corona is heated by the dissipation of electric currents. The low value of the resistivity requires the magnetic field to have structure at very small length scales if this mechanism is to work. In this paper it is demonstrated that the coronal magnetic field acquires small-scale structure through the braiding produced by smooth, randomly phased, photospheric flows. The current density develops a filamentary structure and grows exponentially in time. Nonlinear processes in the ideal magnetohydrodynamic equations produce a cascade effect, in which the structure introduced by the flow at large length scales is transferred to smaller scales. If this process continues down to the resistive dissipation length scale, it would provide an effective mechanism for coronal heating.

Mini-filament Eruption as the Initiation of a Jet along Coronal Loops

NASA Astrophysics Data System (ADS)

Hong, Junchao; Jiang, Yunchun; Yang, Jiayan; Yang, Bo; Xu, Zhe; Xiang, Yongyuan

2016-10-01

Minifilament eruptions (MFEs) and coronal jets are different types of solar small-scale explosive events. We report an MFE observed at the New Vacuum Solar Telescope (NVST). As seen in the NVST Hα images, during the rising phase, the minifilament erupts outward orthogonally to its length, accompanied with a flare-like brightening at the bottom. Afterward, dark materials are found to possibly extend along the axis of the expanded filament body. The MFE is analogous to large filament eruptions. However, a simultaneous observation of the Solar Dynamics Observatory shows that a jet is initiated and flows out along nearby coronal loops during the rising phase of the MFE. Meanwhile, small hot loops, which connect the original eruptive site of the minifilament to the footpoints of the coronal loops, are formed successively. A differential emission measure analysis demonstrates that, on the top of the new small loops, a hot cusp structure exists. We conjecture that the magnetic fields of the MFE interact with magnetic fields of the coronal loops. This interaction is interpreted as magnetic reconnection that produces the jet and the small hot loops.

Coronal Jets in Closed Magnetic Regions on the Sun

NASA Astrophysics Data System (ADS)

Wyper, Peter Fraser; DeVore, C. R.

2015-04-01

Coronal jets are dynamic, collimated structures observed in solar EUV and X-ray emission. They appear predominantly in the open field of coronal holes, but are also observed in areas of closed field, especially active regions. A common feature of coronal jets is that they originate from the field above a parasitic polarity of opposite sign to the surrounding field. Some process - such as instability onset or flux emergence - induces explosive reconnection between the closed “anemone” field and the surrounding open field that generates the jet. The lesser number of coronal jets in closed-field regions suggests a possible stabilizing effect of the closed configuration with respect to coronal jet formation. If the scale of the jet region is small compared with the background loop length, as in for example type II spicules, the nearby magnetic field may be treated as locally open. As such, one would expect that if a stabilizing effect exists it becomes most apparent as the scale of the anemone region approaches that of the background coronal loops.To investigate if coronal jets are indeed suppressed along shorter coronal loops, we performed a number of simulations of jets driven by a rotation of the parasitic polarity (as in the previous open-jet calculations by Pariat et. al 2009, 2010, 2015) embedded in a large-scale closed bipolar field. The simulations were performed with the state of the art Adaptively Refined Magnetohydrodynamics Solver. We will report here how the magnetic configuration above the anemone region determines the nature of the jet, when it is triggered, and how much of the stored magnetic energy is released. We show that regions in which the background field and the parasitic polarity region are of comparable scale naturally suppress explosive energy release. We will also show how in the post-jet relaxation phase a combination of confined MHD waves and weak current layers are generated by the jet along the background coronal loops, both of which may have implications for coronal heating.This work was supported by an appointment to the NASA Postdoctoral Program (P.F.W.) and by NASA’s Living With a Star Targeted Research and Technology program (C.R.D.).

Detection of Propagating Fast Sausage Waves through Detailed Analysis of a Zebra-pattern Fine Structure in a Solar Radio Burst

NASA Astrophysics Data System (ADS)

Kaneda, K.; Misawa, H.; Iwai, K.; Masuda, S.; Tsuchiya, F.; Katoh, Y.; Obara, T.

2018-03-01

Various magnetohydrodynamic (MHD) waves have recently been detected in the solar corona and investigated intensively in the context of coronal heating and coronal seismology. In this Letter, we report the first detection of short-period propagating fast sausage mode waves in a metric radio spectral fine structure observed with the Assembly of Metric-band Aperture Telescope and Real-time Analysis System. Analysis of Zebra patterns (ZPs) in a type-IV burst revealed a quasi-periodic modulation in the frequency separation between the adjacent stripes of the ZPs (Δf ). The observed quasi-periodic modulation had a period of 1–2 s and exhibited a characteristic negative frequency drift with a rate of 3–8 MHz s‑1. Based on the double plasma resonance model, the most accepted generation model of ZPs, the observed quasi-periodic modulation of the ZP can be interpreted in terms of fast sausage mode waves propagating upward at phase speeds of 3000–8000 km s‑1. These results provide us with new insights for probing the fine structure of coronal loops.

Observations of the birth of a small coronal hole

NASA Technical Reports Server (NTRS)

Solodyna, C. V.; Krieger, A. S.; Nolte, J. T.

1977-01-01

Using soft X-ray data from the S-054 X-ray spectrographic telescope aboard Skylab, we observed temporal changes in the emission structure of the X-ray corona associated with the birth of a small coronal hole. Designated as CH6, this coronal hole was born near the equator in a time interval less than 9-1/2 hr. By constructing a light curve for a point near the center of CH6, we observed a sudden 40% decrease in X-ray emission associated with the birth of this coronal hole. On a time scale of hours, the growth of CH6 in area proceeded faster than the average rate predicted by the diffusion of solar fields. The short term decay of CH6 followed the diffusive rate to within experimental uncertainty. On a time scale of one rotation, the subsequent development of CH6 was not consistent with steady growth at the average rate predicted by diffusion.

Hi-C and AIA observations of transverse magnetohydrodynamic waves in active regions

NASA Astrophysics Data System (ADS)

Morton, R. J.; McLaughlin, J. A.

2013-05-01

The recent launch of the High resolution Coronal imager (Hi-C) provided a unique opportunity of studying the EUV corona with unprecedented spatial resolution. We utilize these observations to investigate the properties of low-frequency (50-200 s) active region transverse waves, whose omnipresence had been suggested previously. The five-fold improvement in spatial resolution over SDO/AIA reveals coronal loops with widths 150-310 km and that these loops support transverse waves with displacement amplitudes <50 km. However, the results suggest that wave activity in the coronal loops is of low energy, with typical velocity amplitudes <3 km s-1. An extended time-series of SDO data suggests that low-energy wave behaviour is typical of the coronal structures both before and after the Hi-C observations. Appendix A and five movies associated to Figs. A.2-A.6 are available in electronic form at http://www.aanda.org

Solar coronal magnetic field topology inferred from high resolution optical and x-ray movies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tarbell, T.; Frank, Z.; Hurlburt, N.

1993-01-01

The authors are using high resolution digital movies of solar active regions in optical and X-ray wavelengths to study solar flares and other transients. The optical movies were collected at the Swedish Solar Observatory on La Palma using the Lockheed tunable filtergraph system, in May-July, 1992. They include longitudinal and transverse magnetograms, H-alpha Doppler and intensity images at many wavelengths, Ca K, Na D, and white light images. Simultaneous X-ray images from Yohkoh are available much of the time. Several ways to establish the connectivity of some coronal magnetic field lines are being explored. Some of the clues available are:more » magnetic footpoint polarities and transverse field direction; H-alpha fibrils and loops seen in several wavelengths; proper motion and Dopper shifts of blobs moving along field lines; footprint brightening in micro-flares; spreading of flare ribbons during gradual phases of flares; X-ray morphology and correlations with H-alpha; and draining of flare loops. Examples of each of these will be shown on video.« less

Slow twists of solar magnetic flux tubes and the polar magnetic field of the sun

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, M.A.; Hollweg, J.V.

The solar wind model of Weber and Davis (1967) is generalized to compute the heliospheric magnetic field resulting from solar rotation or a steady axisymmetric twist including a geometrical expansion which is more rapid than spherical. The calculated increase in the ratio of the toroidal to poloidal field components with heliocentric radial distance r clarifies an expression derived recently by Jokipii and Kota (1989). Magnetic field components transverse to r do not in general grow to dominate the radial component at large r. The analysis also yield expressions for the Poynting flux associated with the steady twists. These results aremore » regarded as indicative of the Poynting flux associated with very low frequency Alfven waves, and it is shown how the Poynting flux and the spatial evolution of the wave amplitude differ from the usual WKB result. It is found that the low-frequency Poynting flux at the base of a coronal hole can be about 50 percent larger than the WKB flux inferred from spectral observations of coronal motions (e.g. Hassler et al., 1988).« less

Beam-induced pressure gradients in the early phase of proton-heated solar flares

NASA Technical Reports Server (NTRS)

Tamres, David H.; Canfield, Richard C.; Mcclymont, A. N.

1986-01-01

The pressure gradient induced in a coronal loop by proton beam momentum deposition is calculated and compared with the thermal pressure gradient arising from nonuniform deposition of beam energy; it is assumed that the transfer of momentum and energy from beam to target occurs via the Coulomb interaciton. Results are presented for both a low mean energy and a high mean energy proton beam injected at the loop apex and characterized by a power-law energy spectrum. The present treatment takes account of the breakdown of the cold target approximation for the low-energy proton beam in the corona, where the thermal speed of target electrons exceeds the beam speed. It is found that proton beam momentum deposition plays a potentially significant role in flare dynamics only in the low mean energy case and only in the corona, where it may dominate the acceleration of target material for as long as several tens of seconds. This conclusion suggest that the presence of low-energy nonthermal protons may be inferred from velocity-sensitive coronal observations in the early impulsive phase.

Coronae of Stars with Supersolar Elemental Abundances

NASA Technical Reports Server (NTRS)

Peretz, Uria; Behar, Ehud; Drake, Stephen A.

2015-01-01

Coronal elemental abundances are known to deviate from the photospheric values of their parent star, with the degree of deviation depending on the first ionization potential (FIP). This study focuses on the coronal composition of stars with supersolar photospheric abundances. We present the coronal abundances of six such stars: 11 LMi, iota Hor, HR 7291, tau Boo, and alpha Cen A and B. These stars all have high-statistics X-ray spectra, three of which are presented for the first time. The abundances we measured were obtained using the line-resolved spectra of the Reflection Grating Spectrometer (RGS) in conjunction with the higher throughput EPIC-pn camera spectra onboard the XMM-Newton observatory. A collisionally ionized plasma model with two or three temperature components is found to represent the spectra well. All elements are found to be consistently depleted in the coronae compared to their respective photospheres. For 11 LMi and tau Boo no FIP effect is present, while iota Hor, HR 7291, and alpha Cen A and B show a clear FIP trend. These conclusions hold whether the comparison is made with solar abundances or the individual stellar abundances. Unlike the solar corona, where low-FIP elements are enriched, in these stars the FIP effect is consistently due to a depletion of high-FIP elements with respect to actual photospheric abundances. A comparison with solar (instead of stellar) abundances yields the same fractionation trend as on the Sun. In both cases, a similar FIP bias is inferred, but different fractionation mechanisms need to be invoked.

Observation of a metric type N solar radio burst

DOE PAGES

Kong, Xiangliang; Chen, Yao; Feng, Shiwei; ...

2016-10-10

Type III and type-III-like radio bursts are produced by energetic electron beams guided along coronal magnetic fields. As a variant of type III bursts, Type N bursts appear as the letter "N" in the radio dynamic spectrum and reveal a magnetic mirror effect in coronal loops. Here, we report a well-observed N-shaped burst consisting of three successive branches at metric wavelength with both fundamental and harmonic components and a high brightness temperature (>10 9 K). We verify the burst as a true type N burst generated by the same electron beam from three aspects of the data. First, durations ofmore » the three branches at a given frequency increase gradually and may be due to the dispersion of the beam along its path. Second, the flare site, as the only possible source of non-thermal electrons, is near the western feet of large-scale closed loops. Third, the first branch and the following two branches are localized at different legs of the loops with opposite senses of polarization. We also find that the sense of polarization of the radio burst is in contradiction to the O-mode and there exists a fairly large time delay (~3–5 s) between the fundamental and harmonic components. Possible explanations accounting for these observations are presented. Finally, assuming the classical plasma emission mechanism, we can infer coronal parameters such as electron density and magnetic field near the radio source and make diagnostics on the magnetic mirror process.« less

Evidence for Precursors of the Coronal Hole Jets in Solar Bright Points

NASA Astrophysics Data System (ADS)

Bagashvili, Salome R.; Shergelashvili, Bidzina M.; Japaridze, Darejan R.; Kukhianidze, Vasil; Poedts, Stefaan; Zaqarashvili, Teimuraz V.; Khodachenko, Maxim L.; De Causmaecker, Patrick

2018-03-01

A set of 23 observations of coronal jet events that occurred in coronal bright points has been analyzed. The focus was on the temporal evolution of the mean brightness before and during coronal jet events. In the absolute majority of the cases either single or recurrent coronal jets (CJs) were preceded by slight precursor disturbances observed in the mean intensity curves. The key conclusion is that we were able to detect quasi-periodical oscillations with characteristic periods from sub-minute up to 3–4 minute values in the bright point brightness that precedes the jets. Our basic claim is that along with the conventionally accepted scenario of bright-point evolution through new magnetic flux emergence and its reconnection with the initial structure of the bright point and the coronal hole, certain magnetohydrodynamic (MHD) oscillatory and wavelike motions can be excited and these can take an important place in the observed dynamics. These quasi-oscillatory phenomena might play the role of links between different epochs of the coronal jet ignition and evolution. They can be an indication of the MHD wave excitation processes due to the system entropy variations, density variations, or shear flows. It is very likely a sharp outflow velocity transverse gradients at the edges between the open and closed field line regions. We suppose that magnetic reconnections can be the source of MHD waves due to impulsive generation or rapid temperature variations, and shear flow driven nonmodel MHD wave evolution (self-heating and/or overreflection mechanisms).

Observations and Modeling of Transition Region and Coronal Heating Associated with Spicules

NASA Astrophysics Data System (ADS)

De Pontieu, B.; Martinez-Sykora, J.; De Moortel, I.; Chintzoglou, G.; McIntosh, S. W.

2017-12-01

Spicules have been proposed as significant contributorsto the coronal energy and mass balance. While previous observationshave provided a glimpse of short-lived transient brightenings in thecorona that are associated with spicules, these observations have beencontested and are the subject of a vigorous debate both on the modelingand the observational side so that it remains unclear whether plasmais heated to coronal temperatures in association with spicules. We use high-resolution observations of the chromosphere and transition region with the Interface Region Imaging Spectrograph (IRIS) and ofthe corona with the Atmospheric Imaging Assembly (AIA) onboard theSolar Dynamics Observatory (SDO) to show evidence of the formation of coronal structures as a result of spicular mass ejections andheating of plasma to transition region and coronaltemperatures. Our observations suggest that a significant fraction of the highly dynamic loop fan environment associated with plage regions may be the result of the formation of such new coronal strands, a process that previously had been interpreted as the propagation of transient propagating coronal disturbances (PCD)s. Our observationsare supported by 2.5D radiative MHD simulations that show heating tocoronal temperatures in association with spicules. Our results suggest that heating and strong flows play an important role in maintaining the substructure of loop fans, in addition to the waves that permeate this low coronal environment. Our models also matches observations ofTR counterparts of spicules and provides an elegant explanation forthe high apparent speeds of these "network jets".

Determination of the structure and heating mechanisms of coronal loops from soft X-ray observations with the solar probe. [grazing incidence telescope

NASA Technical Reports Server (NTRS)

Davis, J. M.; Krieger, A. S.

1978-01-01

High resolution soft X-ray imaging from the solar probe is justified in terms of the expected scientific returns which include the determination of the temperature and density structure of a coronal loop. The advantages of the grazing incidence telescope over the multiple pinhole camera are discussed. An instrument package is described which includes a grazing incidence mirror, a thermal prefilter, a three position filter wheel and a focal plane detector baselined as an 800 by 800 back-illuminated charge coupled device. The structural assembly together with the data processing equipment would draw heavily on the designs being developed for the Solar Polar Mission.

Population mechanisms for the He(+) n = 3 levels determined from measurements of the solar 1640 A emission

NASA Technical Reports Server (NTRS)

Seely, J. F.; Feldman, U.

1985-01-01

The 1640 A line profile is analyzed using solar data obtained by the NRL slit spectrograph on Skylab. Data from coronal hole regions, quiet sun regions, active regions, prominence regions, and flare regions are presented. The relative densities of 3s, 3p, and 3d levels are determined from the data, and the dominant population mechanisms for these levels are inferred using a rate equation model for the He(+) ion. The relative importance of collisional excitation, radiative recombination, and photoexcitation is determined for each of the solar regions.

An observational search for large-scale organization of five-minute oscillations on the sun. [coronal holes or sector structure relationships

NASA Technical Reports Server (NTRS)

Dittmer, P. H.; Scherrer, P. H.; Wilcox, J. M.

1978-01-01

The large-scale solar velocity field has been measured over an aperture of radius 0.8 solar radii on 121 days between April and September, 1976. Measurements are made in the line Fe I 5123.730 A, employing a velocity subtraction technique similar to that of Severny et al. (1976). Comparisons of the amplitude and frequency of the five-minute resonant oscillation with the geomagnetic C9 index and magnetic sector boundaries show no evidence of any relationship between the oscillations and coronal holes or sector structure.

Structure and dynamics of the coronal magnetic field

NASA Technical Reports Server (NTRS)

VanHoven, Gerard; Schnack, Dalton D.

1996-01-01

The last few years have seen a marked increase in the sophistication of models of the solar corona. This has been brought about by a confluence of three key elements. First, the collection of high-resolution observations of the Sun, both in space and time, has grown tremendously. The SOHO (Solar Heliospheric Observatory) mission is providing additional correlated high-resolution magnetic, white-light and spectroscopic observations. Second, the power and availability of supercomputers has made two- and three-dimensional modeling routine. Third, the sophistication of the models themselves, both in their geometrical realism and in the detailed physics that has been included, has improved significantly. The support from our current Space Physics Theory grant has allowed us to exploit this confluence of capabilities. We have carried out direct comparisons between observations and models of the solar corona. The agreement between simulated coronal structure and observations has verified that the models are mature enough for detailed analysis, as we will describe. The development of this capability is especially timely, since observations obtained from three space missions that are underway (Ulysses, WIND and SOHO) offer an opportunity for significant advances in our understanding of the corona and heliosphere. Through this interplay of observations and theory we can improve our understanding of the Sun. Our achievements thus far include progress modeling the large-scale structure of the solar corona, three-dimensional models of active region fields, development of emerging flux and current, formation and evolution of coronal loops, and coronal heating by current filaments.

SHOCK CONNECTIVITY IN THE 2010 AUGUST AND 2012 JULY SOLAR ENERGETIC PARTICLE EVENTS INFERRED FROM OBSERVATIONS AND ENLIL MODELING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bain, H. M.; Luhmann, J. G.; Li, Y.

During periods of increased solar activity, coronal mass ejections (CMEs) can occur in close succession and proximity to one another. This can lead to the interaction and merger of CME ejecta as they propagate in the heliosphere. The particles accelerated in these shocks can result in complex solar energetic particle (SEP) events, as observing spacecraft form both remote and local shock connections. It can be challenging to understand these complex SEP events from in situ profiles alone. Multipoint observations of CMEs in the near-Sun environment, from the Solar Terrestrial Relations Observatory –Sun Earth Connection Coronal and Heliospheric Investigation and themore » Solar and Heliospheric Observatory Large Angle and Spectrometric Coronagraph, greatly improve our chances of identifying the origin of these accelerated particles. However, contextual information on conditions in the heliosphere, including the background solar wind conditions and shock structures, is essential for understanding SEP properties well enough to forecast their characteristics. Wang–Sheeley–Arge WSA-ENLIL + Cone modeling provides a tool to interpret major SEP event periods in the context of a realistic heliospheric model and to determine how much of what is observed in large SEP events depends on nonlocal magnetic connections to shock sources. We discuss observations of the SEP-rich periods of 2010 August and 2012 July in conjunction with ENLIL modeling. We find that much SEP activity can only be understood in the light of such models, and in particular from knowing about both remote and local shock source connections. These results must be folded into the investigations of the physics underlying the longitudinal extent of SEP events, and the source connection versus diffusion pictures of interpretations of SEP events.« less

New Techniques Used in Modeling the 2017 Total Solar Eclipse: Energizing and Heating the Large-Scale Corona

NASA Astrophysics Data System (ADS)

Downs, Cooper; Mikic, Zoran; Linker, Jon A.; Caplan, Ronald M.; Lionello, Roberto; Torok, Tibor; Titov, Viacheslav; Riley, Pete; Mackay, Duncan; Upton, Lisa

2017-08-01

Over the past two decades, our group has used a magnetohydrodynamic (MHD) model of the corona to predict the appearance of total solar eclipses. In this presentation we detail recent innovations and new techniques applied to our prediction model for the August 21, 2017 total solar eclipse. First, we have developed a method for capturing the large-scale energized fields typical of the corona, namely the sheared/twisted fields built up through long-term processes of differential rotation and flux-emergence/cancellation. Using inferences of the location and chirality of filament channels (deduced from a magnetofrictional model driven by the evolving photospheric field produced by the Advective Flux Transport model), we tailor a customized boundary electric field profile that will emerge shear along the desired portions of polarity inversion lines (PILs) and cancel flux to create long twisted flux systems low in the corona. This method has the potential to improve the morphological shape of streamers in the low solar corona. Second, we apply, for the first time in our eclipse prediction simulations, a new wave-turbulence-dissipation (WTD) based model for coronal heating. This model has substantially fewer free parameters than previous empirical heating models, but is inherently sensitive to the 3D geometry and connectivity of the coronal field---a key property for modeling/predicting the thermal-magnetic structure of the solar corona. Overall, we will examine the effect of these considerations on white-light and EUV observables from the simulations, and present them in the context of our final 2017 eclipse prediction model.Research supported by NASA's Heliophysics Supporting Research and Living With a Star Programs.

Predicting the magnetic vectors within coronal mass ejections arriving at Earth: 2. Geomagnetic response

NASA Astrophysics Data System (ADS)

Savani, N. P.; Vourlidas, A.; Richardson, I. G.; Szabo, A.; Thompson, B. J.; Pulkkinen, A.; Mays, M. L.; Nieves-Chinchilla, T.; Bothmer, V.

2017-02-01

This is a companion to Savani et al. (2015) that discussed how a first-order prediction of the internal magnetic field of a coronal mass ejection (CME) may be made from observations of its initial state at the Sun for space weather forecasting purposes (Bothmer-Schwenn scheme (BSS) model). For eight CME events, we investigate how uncertainties in their predicted magnetic structure influence predictions of the geomagnetic activity. We use an empirical relationship between the solar wind plasma drivers and Kp index together with the inferred magnetic vectors, to make a prediction of the time variation of Kp (Kp(BSS)). We find a 2σ uncertainty range on the magnetic field magnitude (|B|) provides a practical and convenient solution for predicting the uncertainty in geomagnetic storm strength. We also find the estimated CME velocity is a major source of error in the predicted maximum Kp. The time variation of Kp(BSS) is important for predicting periods of enhanced and maximum geomagnetic activity, driven by southerly directed magnetic fields, and periods of lower activity driven by northerly directed magnetic field. We compare the skill score of our model to a number of other forecasting models, including the NOAA/Space Weather Prediction Center (SWPC) and Community Coordinated Modeling Center (CCMC)/SWRC estimates. The BSS model was the most unbiased prediction model, while the other models predominately tended to significantly overforecast. The True skill score of the BSS prediction model (TSS = 0.43 ± 0.06) exceeds the results of two baseline models and the NOAA/SWPC forecast. The BSS model prediction performed equally with CCMC/SWRC predictions while demonstrating a lower uncertainty.

Radio Emmision during the interaction of two Interplanetary Coronal Mass Ejections

NASA Astrophysics Data System (ADS)

Lara, Alejandro; Niembro, Tatiana; González, Ricardo

2016-07-01

We show that some sporadic radio emission observed by the WIND/WAVES experiment in the decametric/kilometric bands are due to the interaction of two interplanetary Coronal Mass Ejections. We have performed hydrodynamic simulations of the evolution of two consecutive Coronal Mass ejections in the interplanetary medium. With these simulations it is possible to follow the density evolution of the merged structure, and therefore, compute the frequency limits of the possible plasma emission. We study four well documented ICME interaction events, and found radio emission at the time and frequencies predicted by the simulations. This emission may help to anticipate the complexity of the merged region before it reaches one AU.

Observations of solar active regions and solar flares by OSO-7

NASA Technical Reports Server (NTRS)

Neupert, W. M.

1977-01-01

Contributions made to the physics of coronal active regions and flares by the extreme ultraviolet and soft X-ray spectroheliograph on OSO-7 were discussed. Coronal structures above active regions were discussed from the point of view of their morphology and physical properties, including their relationship to photospheric and coronal magnetic fields. OSO-7 also recorded flares with sufficient spatial and temporal resolution to record, in some instances for the first time, the extreme ultraviolet and soft X-ray emission associated with such chromospheric phenomena as filament activation and the emergence of satellite sunspots. Flare phenomena were reviewed in terms of the several stages of evolution typically associated with the event.

Reconciling CME Kinematics using Radio and White-light Observations from STEREO and SOHO

NASA Astrophysics Data System (ADS)

Gopalswamy, Nat; Yashiro, Seiji; Xie, Hong; Makela, Pertti; Akiyama, Sachiko; Reiner, Michael; MacDowall, Robert

2014-05-01

We study the characteristics of nonthermal radio emission associated with coronal mass ejections (CMEs) observed by STEREO, SOHO, and Wind spacecraft. In particular, we examine three backside CMEs associated with type II radio bursts at frequencies below 16 MHz. These bursts are known to be excellent indicators of solar energetic particle events. We use the universal drift rate spectrum of type II radio bursts and the inferred density scale heights in the corona and interplanetary medium o estimate the speed of the shock waves that produce the type II radio bursts. We find that the radio bursts can provide an accurate estimate of the CME speeds. We consider three backside events and a cannibalism event to show the usefulness of radio dynamic spectrum in inferring CME kinematics. We use radio direction finding technique to show that CME-CME interaction results in enhanced nonthermal radio emission. The radio data also provide constraints on the particle acceleration mechanisms and the reason for the energetic particles observed at wide-ranging longitudes. Finally we infer the shape and extent of the shock associated with one of the biggest solar energetic particle events in the space era.

The Connection Between Solar Coronal Cavities and Solar Filaments

NASA Astrophysics Data System (ADS)

Zawadzki, B.; Karna, N.; Prchlik, J.; Reeves, K.; Kempton, D.; Angryk, R.

2017-12-01

Filaments are structures in the solar corona made up of relatively cool, dense, partially ionized plasma. Coronal cavities, circular or elliptical regions of low plasma density, are observed above prominences on the solar limb when viewed in EUV and white light coronal images. Since most filament/cavity eruptions lead to a coronal mass ejection (CME), determining the likelihood of an eruption event will improve our ability to predict space weather. We examine SDO/AIA cavity metadata and HEK filament metadata to determine which cavities are associated with which filaments from 2012 to 2015. Our study involved 140 cavities and 368 filaments that appeared poleward of +-30 degrees. We categorized the cavities and filaments based on the stability of the structures, defined by whether or not the cavity and filament exist long enough to track fully across the solar disk. Using these categories we perform a statistical study on various filament qualities within the metadata. Our findings indicate that filaments with cavities are observed more often at high latitude in compared to filaments without cavities. Moreover, our study indicates that a statistically significant difference exists between the filament length and tilt distributions for certain categories. This work supported by the NSF-REU solar physics program at SAO, grant number AGS-1560313, and the NSF-DIBBS project, grant number ACI-1443061.

Comparison of a modified mid-coronal sectioning technique and Wilson's technique when conducting eye and brain examinations in rabbit teratology studies.

PubMed

Ziejewski, Mary K; Solomon, Howard M; Rendemonti, Joyce; Stanislaus, Dinesh

2015-02-01

There are two methods used when examining fetal rabbit eyes and brain in teratology studies. One method employs prior fixation before serial sectioning (Wilson's technique) and the other uses fresh tissue (mid-coronal sectioning). We modified the mid-coronal sectioning technique to include removal of eyes and brain for closer examination and to increase the number of structures that can be evaluated and compared it to the Wilson's technique. We found that external examination of the head, in conjunction with either sectioning method, is equally sensitive in identifying developmental defects. We evaluated 40,401 New Zealand White (NZW) and Dutch-Belted (DB) rabbit fetuses for external head alterations, of which 28,538 fetuses were further examined for eye and brain alterations using the modified mid-coronal sectioning method (16,675 fetuses) or Wilson's technique (11,863 fetuses). The fetuses were from vehicle control or drug-treated pregnant rabbits in embryo-fetal development studies conducted to meet international regulatory requirements for the development of new drugs. Both methods detected the more common alterations (microphthalmia and dilated lateral cerebral ventricles) and other less common findings (changes in size and/or shape of eye and brain structures). While both methods are equally sensitive at detecting common and rare developmental defects, the modified mid-coronal sectioning technique eliminates the use of chemicals and concomitant fixation artifacts that occur with the Wilson's technique and allows for examination of 100% intact fetuses thereby increasing potential for detecting eye and brain alterations as these findings occur infrequently in rabbits. © 2015 Wiley Periodicals, Inc.

CLASP/SJ Observations of Rapid Time Variations in the Ly α Emission in a Solar Active Region

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ishikawa, Shin-nosuke; Kubo, Masahito; Katsukawa, Yukio

The Chromospheric Ly α SpectroPolarimeter (CLASP) is a sounding rocket experiment launched on 2015 September 3 to investigate the solar chromosphere and transition region. The slit-jaw (SJ) optical system captured Ly α images with a high time cadence of 0.6 s. From the CLASP/SJ observations, many variations in the solar chromosphere and transition region emission with a timescale of <1 minute were discovered. In this paper, we focus on the active region within the SJ field of view and investigate the relationship between short (<30 s) temporal variations in the Ly α emission and the coronal structures observed by Solarmore » Dynamics Observatory/Atmospheric Imaging Assembly (AIA). We compare the Ly α temporal variations at the coronal loop footpoints observed in the AIA 211 Å (≈2 MK) and AIA 171 Å (≈0.6 MK) channels with those in the regions with bright Ly α features without a clear association with the coronal loop footpoints. We find more short (<30 s) temporal variations in the Ly α intensity in the footpoint regions. Those variations did not depend on the temperature of the coronal loops. Therefore, the temporal variations in the Ly α intensity at this timescale range could be related to the heating of the coronal structures up to temperatures around the sensitivity peak of 171 Å. No signature was found to support the scenario that these Ly α intensity variations were related to the nanoflares. Waves or jets from the lower layers (lower chromosphere or photosphere) are possible causes for this phenomenon.« less

Exploring the fine structure at the limb in coronal holes

NASA Technical Reports Server (NTRS)

Karovska, Magarita; Blundell, Solon F.; Habbal, Shadia Rifai

1994-01-01

The fine structure of the solar limb in coronal holes is explored at temperatures ranging from 10(exp 4) to 10(exp 6) K. An image enhancement algorithm orignally developed for solar eclipse observations is applied to a number of simultaneous multiwavelength observations made with the Harvard Extreme Ultraviolet Spectrometer experiment on Skylab. The enhanced images reveal the presence of filamentary structures above the limb with a characteristic separation of approximately 10 to 15 sec . Some of the structures extend from the solar limb into the corona to at least 4 min above the solar limb. The brightness of these structures changes as a function of height above the limb. The brightest emission is associated with spiculelike structures in the proximity of the limb. The emission characteristic of high-temperature plasma is not cospatial with the emission at lower temperatures, indicating the presence of different temperature plasmas in the field of view.

Cyclic Evolution of Coronal Fields from a Coupled Dynamo Potential-Field Source-Surface Model.

PubMed

Dikpati, Mausumi; Suresh, Akshaya; Burkepile, Joan

The structure of the Sun's corona varies with the solar-cycle phase, from a near spherical symmetry at solar maximum to an axial dipole at solar minimum. It is widely accepted that the large-scale coronal structure is governed by magnetic fields that are most likely generated by dynamo action in the solar interior. In order to understand the variation in coronal structure, we couple a potential-field source-surface model with a cyclic dynamo model. In this coupled model, the magnetic field inside the convection zone is governed by the dynamo equation; these dynamo-generated fields are extended from the photosphere to the corona using a potential-field source-surface model. Assuming axisymmetry, we take linear combinations of associated Legendre polynomials that match the more complex coronal structures. Choosing images of the global corona from the Mauna Loa Solar Observatory at each Carrington rotation over half a cycle (1986 - 1991), we compute the coefficients of the associated Legendre polynomials up to degree eight and compare with observations. We show that at minimum the dipole term dominates, but it fades as the cycle progresses; higher-order multipolar terms begin to dominate. The amplitudes of these terms are not exactly the same for the two limbs, indicating that there is a longitude dependence. While both the 1986 and the 1996 minimum coronas were dipolar, the minimum in 2008 was unusual, since there was a substantial departure from a dipole. We investigate the physical cause of this departure by including a North-South asymmetry in the surface source of the magnetic fields in our flux-transport dynamo model, and find that this asymmetry could be one of the reasons for departure from the dipole in the 2008 minimum.

The Role of Magnetic Helicity in Structuring the Solar Corona

NASA Technical Reports Server (NTRS)

Knizhnik, K. J.; Antiochos, S. K.; DeVore, C. R.

2017-01-01

Two of the most widely observed and striking features of the Suns magnetic field are coronal loops, which are smooth and laminar, and prominences or filaments, which are strongly sheared. Loops are puzzling because they show little evidence of tangling or braiding, at least on the quiet Sun, despite the chaotic nature of the solar surface convection. Prominences are mysterious because the origin of their underlying magnetic structure filament channels is poorly understood at best. These two types of features would seem to be quite unrelated and wholly distinct. We argue that, on the contrary, they are inextricably linked and result from a single process: the injection of magnetic helicity into the corona by photospheric motions and the subsequent evolution of this helicity by coronal reconnection. In this paper, we present numerical simulations of the response of a Parker (1972) corona to photospheric driving motions that have varying degrees of helicity preference. We obtain four main conclusions: (1) in agreement with the helicity condensation model of Antiochos (2013), the inverse cascade of helicity by magnetic reconnection in the corona results in the formation of filament channels localized about polarity inversion lines; (2) this same process removes most complex fine structure from the rest of the corona, resulting in smooth and laminar coronal loops; (3) the amount of remnant tangling in coronal loops is inversely dependent on the net helicity injected by the driving motions; and (4) the structure of the solar corona depends only on the helicity preference of the driving motions and not on their detailed time dependence. We discuss the implications of our results for high-resolution observations of the corona.

3D ELECTRON DENSITY DISTRIBUTIONS IN THE SOLAR CORONA DURING SOLAR MINIMA: ASSESSMENT FOR MORE REALISTIC SOLAR WIND MODELING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patoul, Judith de; Foullon, Claire; Riley, Pete, E-mail: j.depatoul@exeter.ac.uk, E-mail: c.foullon@exeter.ac.uk, E-mail: rileype@saic.com

Knowledge of the electron density distribution in the solar corona put constraints on the magnetic field configurations for coronal modeling and on initial conditions for solar wind modeling. We work with polarized SOHO/LASCO-C2 images from the last two recent minima of solar activity (1996–1997 and 2008–2010), devoid of coronal mass ejections. The goals are to derive the 4D electron density distributions in the corona by applying a newly developed time-dependent tomographic reconstruction method and to compare the results between the two solar minima and with two magnetohydrodynamic models. First, we confirm that the values of the density distribution in thermodynamic models aremore » more realistic than in polytropic ones. The tomography provides more accurate distributions in the polar regions, and we find that the density in tomographic and thermodynamic solutions varies with the solar cycle in both polar and equatorial regions. Second, we find that the highest-density structures do not always correspond to the predicted large-scale heliospheric current sheet or its helmet streamer but can follow the locations of pseudo-streamers. We deduce that tomography offers reliable density distributions in the corona, reproducing the slow time evolution of coronal structures, without prior knowledge of the coronal magnetic field over a full rotation. Finally, we suggest that the highest-density structures show a differential rotation well above the surface depending on how they are magnetically connected to the surface. Such valuable information on the rotation of large-scale structures could help to connect the sources of the solar wind to their in situ counterparts in future missions such as Solar Orbiter and Solar Probe Plus.« less

Coronal Magnetography of Solar Active Regions Using Coordinated SOHO/CDS and VLA Observations

NASA Technical Reports Server (NTRS)

Brosius, Jeffrey W.

1999-01-01

The purpose of this project is to apply the coronal magnetographic technique to SOHO (Solar Heliospheric Observatory) /CDS (Coronal Diagnostic Spectrometer) EUV (Extreme Ultraviolet Radiation) and coordinated VLA microwave observations of solar active regions to derive the strength and structure of the coronal magnetic field. A CDS observing plan was developed for obtaining spectra needed to derive active region differential emission measures (DEMs) required for coronal magnetography. VLA observations were proposed and obtained. SOHO JOP 100 was developed, tested, approved, and implemented to obtain coordinated CDS (Coronal Diagnostic Spectrometer)/EIT (Ultraviolet Imaging Telescope)/ VLA (Very Large Array)/ TRACE (Transition Region and Coronal Explorer)/ SXT (Solar X Ray Telescope) observations of active regions on April 12, May 9, May 13, and May 23. Analysis of all four data sets began, with heaviest concentration on COS data. It is found that 200-pixel (14 A in NIS1) wavelength windows are appropriate for extracting broadened Gaussian line profile fit parameters for lines including Fe XIV at 334.2, Fe XVI at 335.4, Fe XVI at 360.8, and Mg IX at 368.1 over the 4 arcmin by 4 arcmin CDS field of view. Extensive efforts were focused on learning and applying were focused on learning and applying CDS software, and including it in new IDL procedures to carry out calculations relating to coronal magnetography. An important step is to extract Gaussian profile fits to all the lines needed to derive the DEM in each spatial pixel of any given active region. The standard CDS absolute intensity calibration software was applied to derived intensity images, revealing that ratios between density-insensitive lines like Fe XVI 360.8/335.4 yield good agreement with theory. However, the resulting absolute intensities of those lines are very high, indicating that revisions to the CDS absolute intensity calibrations remain to be included in the CDS software, an essential step to deriving reliable coronal magnetograms. With lessons learned and high quality data obtained during the past year, coronal magnetography will be successfully pursued under my new SOHO GI program.

Activity associated with the solar origin of coronal mass ejections

NASA Technical Reports Server (NTRS)

Webb, D. F.; Hundhausen, A. J.

1987-01-01

Solar coronal mass ejections (CMEs) observed in 1980 with the HAO Coronagraph/Polarimeter on the Solar Maximum Mission (SMM) satellite are compared with other forms of solar activity that might be physically related to the ejections. The solar phenomena checked and the method of association used were intentionally patterned after those of Munro et al.'s (1979) analysis of mass ejections observed with the Skylab coronagraph to facilitate comparison of the two epochs. Comparison of the results reveals that the types and degree of CME associations are similar near solar activity minimum and at maximum. For both epochs, most CMEs with associations had associated eruptive prominences, and the proportions of association of all types of activity were similar. A high percentage of association between SMM CMEs and X-ray long duration events is also found, in agreement with Skylab results. It is concluded that most CMEs are the result of the destabilization and eruption of a prominence and its overlying coronal structure, or of a magnetic structure capable of supporting a prominence.

The magnetic connectivity of coronal shocks from behind-the-limb flares to the visible solar surface during γ-ray events

NASA Astrophysics Data System (ADS)

Plotnikov, I.; Rouillard, A. P.; Share, G. H.

2017-12-01

Context. The observation of >100 MeV γ-rays in the minutes to hours following solar flares suggests that high-energy particles interacting in the solar atmosphere can be stored and/or accelerated for long time periods. The occasions when γ-rays are detected even when the solar eruptions occurred beyond the solar limb as viewed from Earth provide favorable viewing conditions for studying the role of coronal shocks driven by coronal mass ejections (CMEs) in the acceleration of these particles. Aims: In this paper, we investigate the spatial and temporal evolution of the coronal shocks inferred from stereoscopic observations of behind-the-limb flares to determine if they could be the source of the particles producing the γ-rays. Methods: We analyzed the CMEs and early formation of coronal shocks associated with γ-ray events measured by the Fermi-Large Area Telescope (LAT) from three eruptions behind the solar limb as viewed from Earth on 2013 Oct. 11, 2014 Jan. 06 and Sep. 01. We used a 3D triangulation technique, based on remote-sensing observations to model the expansion of the CME shocks from above the solar surface to the upper corona. Coupling the expansion model to various models of the coronal magnetic field allowed us to derive the time-dependent distribution of shock Mach numbers and the magnetic connection of particles produced by the shock to the solar surface visible from Earth. Results: The reconstructed shock fronts for the three events became magnetically connected to the visible solar surface after the start of the flare and just before the onset of the >100 MeV γ-ray emission. The shock surface at these connections also exhibited supercritical Mach numbers required for significant particle energization. The strongest γ-ray emissions occurred when the flanks of the shocks were connected in a quasi-perpendicular geometry to the field lines reaching the visible surface. Multipoint, in situ, measurements of solar energetic particles (SEPs) were consistent with the production of these SEPs by the same shock processes responsible for the γ-rays. The fluxes of protons in space and at the Sun were highest for the 2014 Sep. 01, which had the fastest moving shock. Conclusions: This study provides further evidence that high-energy protons producing time-extended high-energy γ-ray emission likely have the same CME-shock origin as solar energetic particles measured in interplanetary space.

On the Link between the Release of Solar Energetic Particles Measured at Widespread Heliolongitudes and the Properties of the Associated Coronal Shocks

NASA Astrophysics Data System (ADS)

Lario, D.; Kwon, R.-Y.; Riley, P.; Raouafi, N. E.

2017-10-01

Under the paradigm that the main agents in the acceleration of solar energetic particles (SEPs) are shocks initially driven by coronal mass ejections, we analyze whether the properties of the shocks in the corona inferred from combining extreme-ultraviolet (EUV) and white-light (WL) observations from multiple vantage points together with magnetohydrodynamic (MHD) simulations of the corona can be used to determine the release of SEPs into different regions of the heliosphere and hence determine the longitudinal extent of the SEP events. We analyze the SEP events observed on 2011 November 3, 2013 April 11, and 2014 February 25 over a wide range of heliolongitudes. MHD simulations provide the characteristics of the background medium where shocks propagate, in particular the Alfvén and sound speed profiles that allow us to determine both the extent of the EUV waves in the low corona and the fast magnetosonic Mach number (M FM) of the shocks. The extent of the EUV waves in the low corona is controlled by this background medium and does not coincide with the extent of the SEP events in the heliosphere. Within the uncertainties of (I) the extent and speed of the shock inferred from EUV and WL images and (II) the assumptions made in the MHD models, we follow the evolution of M FM at the region of the shock magnetically connected to each spacecraft. The estimated release times of the first SEPs measured by each spacecraft does not coincide with the time when the M FM at this region exceeds a given threshold.

On the Link between the Release of Solar Energetic Particles Measured at Widespread Heliolongitudes and the Properties of the Associated Coronal Shocks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lario, D.; Kwon, R.-Y.; Raouafi, N. E.

Under the paradigm that the main agents in the acceleration of solar energetic particles (SEPs) are shocks initially driven by coronal mass ejections, we analyze whether the properties of the shocks in the corona inferred from combining extreme-ultraviolet (EUV) and white-light (WL) observations from multiple vantage points together with magnetohydrodynamic (MHD) simulations of the corona can be used to determine the release of SEPs into different regions of the heliosphere and hence determine the longitudinal extent of the SEP events. We analyze the SEP events observed on 2011 November 3, 2013 April 11, and 2014 February 25 over a widemore » range of heliolongitudes. MHD simulations provide the characteristics of the background medium where shocks propagate, in particular the Alfvén and sound speed profiles that allow us to determine both the extent of the EUV waves in the low corona and the fast magnetosonic Mach number ( M {sub FM}) of the shocks. The extent of the EUV waves in the low corona is controlled by this background medium and does not coincide with the extent of the SEP events in the heliosphere. Within the uncertainties of (i) the extent and speed of the shock inferred from EUV and WL images and (ii) the assumptions made in the MHD models, we follow the evolution of M {sub FM} at the region of the shock magnetically connected to each spacecraft. The estimated release times of the first SEPs measured by each spacecraft does not coincide with the time when the M {sub FM} at this region exceeds a given threshold.« less

ANALYSIS AND MODELING OF TWO FLARE LOOPS OBSERVED BY AIA AND EIS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Y.; Ding, M. D.; Qiu, J.

2012-10-10

We analyze and model an M1.0 flare observed by SDO/AIA and Hinode/EIS to investigate how flare loops are heated and evolve subsequently. The flare is composed of two distinctive loop systems observed in extreme ultraviolet (EUV) images. The UV 1600 A emission at the feet of these loops exhibits a rapid rise, followed by enhanced emission in different EUV channels observed by the Atmospheric Imaging Assembly (AIA) and the EUV Imaging Spectrometer (EIS). Such behavior is indicative of impulsive energy deposit and the subsequent response in overlying coronal loops that evolve through different temperatures. Using the method we recently developed,more » we infer empirical heating functions from the rapid rise of the UV light curves for the two loop systems, respectively, treating them as two big loops with cross-sectional area of 5'' by 5'', and compute the plasma evolution in the loops using the EBTEL model. We compute the synthetic EUV light curves, which, with the limitation of the model, reasonably agree with observed light curves obtained in multiple AIA channels and EIS lines: they show the same evolution trend and their magnitudes are comparable by within a factor of two. Furthermore, we also compare the computed mean enthalpy flow velocity with the Doppler shift measurements by EIS during the decay phase of the two loops. Our results suggest that the two different loops with different heating functions as inferred from their footpoint UV emission, combined with their different lengths as measured from imaging observations, give rise to different coronal plasma evolution patterns captured both in the model and in observations.« less

Coronal O VI emission observed with UVCS/SOHO during solar flares: Comparison with soft X-ray observations

NASA Astrophysics Data System (ADS)

Mancuso, S.; Giordano, S.; Raymond, J. C.

2016-06-01

In this work, we derive the O VI 1032 Å luminosity profiles of 58 flares, during their impulsive phase, based on off-limb measurements by the Ultraviolet Coronagraph Spectrometer (UVCS) aboard the SOlar and Heliospheric Observatory (SOHO). The O VI luminosities from the transition region plasma (here defined as the region with temperatures 5.0 ≤ log T (K) ≤ 6.0) were inferred from the analysis of the resonantly scattered radiation of the O VI coronal ions. The temperature of maximum ionization for O VI is log Tmax (K) = 5.47. By comparison with simultaneous soft X-ray measurements, we investigate the likely source (chromospheric evaporation, footpoint emission, or heated prominence ejecta) for the transition region emission observed during the impulsive phase. In our study, we find evidence of the main characteristics predicted by the evaporation scenario. Specifically, most O VI flares precede the X-ray peaks typically by several minutes with a mean of 3.2 ± 0.1 min, and clear correlations are found between the soft X-ray and transition region luminosities following power laws with indices ~ 0.7 ± 0.3. Overall, the results are consistent with transition region emission originating from chromospheric evaporation; the thermal X-ray emission peaks after the emission from the evaporation flow as the loops fill with hot plasma. Finally, we were able to infer flow speeds in the range ~20-100 km s-1 for one-third of the events, 14 of which showed speeds between 60 and 80 km s-1. These values are compatible with those found through direct spectroscopic observations at transition region temperatures by the EUV Imaging Spectrometer (EIS) on board Hinode.

Space Oddities: The Search For Ephemeral Coronal Holes

NASA Astrophysics Data System (ADS)

O'Connor, Rachel E.; Pesnell, W. Dean; Kirk, Michael S.; Karna, Nishu

2016-10-01

Ephemeral coronal holes are short-lived, volatile counterparts to equatorial coronal holes. Very little is known about their characteristics and behavior aside from their definition: open, unipolar magnetic field lines resulting in darkened regions of the corona. The first exemplar of this phenomenon was observed by NASA's Solar Dynamics Observatory (SDO) on October 26, 2010, which spurred our search for other occurrences in order to understand the frequency and evolution of these phenomena. To accomplish this, we visually evaluated SDO 211 Å images on a 12-hour cadence between June 2010 and June 2016. Each compact and isolated dim region we encountered was flagged as a potential ephemeral coronal hole for further analysis. This preliminary effort resulted in 149 candidate holes. For further analysis of their characteristics, we applied a strict definition criterion of an ephemeral coronal hole. This criterion was a set of four factors that were created in order to ensure events being observed were isolated, individual events- the candidates had to be dark relative to the surrounding material, not influenced by a nearby eruption, not obviously connected to other coronal hole structures, and their lifetime had to occur completely within the disk crossing. This criterion was designed so that events could be completely analyzed, from beginning to end, to better understand the origins. Application of this criterion eliminated all candidates but 5 of the original 149. True ephemeral coronal holes are rare occurrences, appearing only five times in six years. Future research in this area is needed to both locate additional events and study the underlying driving forces behind these rare phenomena.

MINI-FILAMENT ERUPTION AS THE INITIATION OF A JET ALONG CORONAL LOOPS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Junchao; Jiang, Yunchun; Yang, Jiayan

Minifilament eruptions (MFEs) and coronal jets are different types of solar small-scale explosive events. We report an MFE observed at the New Vacuum Solar Telescope (NVST). As seen in the NVST H α images, during the rising phase, the minifilament erupts outward orthogonally to its length, accompanied with a flare-like brightening at the bottom. Afterward, dark materials are found to possibly extend along the axis of the expanded filament body. The MFE is analogous to large filament eruptions. However, a simultaneous observation of the Solar Dynamics Observatory shows that a jet is initiated and flows out along nearby coronal loopsmore » during the rising phase of the MFE. Meanwhile, small hot loops, which connect the original eruptive site of the minifilament to the footpoints of the coronal loops, are formed successively. A differential emission measure analysis demonstrates that, on the top of the new small loops, a hot cusp structure exists. We conjecture that the magnetic fields of the MFE interact with magnetic fields of the coronal loops. This interaction is interpreted as magnetic reconnection that produces the jet and the small hot loops.« less

A gigantic coronal jet ejected from a compact active region in a coronal hole

NASA Technical Reports Server (NTRS)

Shibata, K.; Nitta, N.; Strong, K. T.; Matsumoto, R.; Yokoyama, T.; Hirayama, T.; Hudson, H.; Ogawara, Y.

1994-01-01

A gigantic coronal jet greater than 3 x 10(exp 5) km long (nearly half the solar radius) has been found with the soft X-ray telescope (SXT) on board the solar X-ray satellite, Yohkoh. The jet was ejected on 1992 January 11 from an 'anemone-type' active region (AR) appearing in a coronal hole and is one of the largest coronal X-ray jets observed so far by SXT. This gigantic jet is the best observed example of many other smaller X-ray jets, because the spatial structures of both the jet and the AR located at its base are more easily resolved. The range of apparent translational velocities of the bulk of the jet was between 90 and 240 km s(exp -1), with the corresponding kinetic energy estimated to be of order of 10(exp 28) ergs. A detailed analysis reveals that the jet was associated with a loop brightening (a small flare) that occurred in the active region. Several features of this observation suggest and are consistent with a magnetic reconnection mechanism for the production of such a 'jet-loop-brightening' event.

Loop models of low coronal structures observed by the Normal Incidence X-Ray Telescope (NIXT)

NASA Technical Reports Server (NTRS)

Peres, G.; Reale, F.; Golub, L.

1994-01-01

The X-ray pictures obtained with the Normal Incidence X-Ray Telescope (NIXT), apart from the ubiquitous coronal loops well known from previous X-ray observations, show a new and peculiar morphology: in many active regions there are wide and apparently low-lying areas of intense emission which resemble H alpha plages. By means of hydrostatic models of coronal arches, we analyze the distribution of temperature, density, emission measure, and plasma emissivity in the spectral band to which NIXT is sensitive, and we show that the above morphology can be explained by the characteristics of high pressure loops having a thin region of high surface brightness at the base. We therefore propose that this finding might help to identify high-pressure X-ray emitting coronal regions in NIXT images, and it is in principle applicable to any imaging instrument which has high sensitivity to 10(exp 4) - 10(exp 6) K plasma within a narrow coronal-temperature passband. As a more general result of this study, we propose that the comparison of NIXT observations with models of stationary loops might provide a new diagnostic: the determination of the loop plasma pressure from measurements of brightness distribution along the loop.

Temperature, density and magnetic field structure of the corona during the total eclipse of 1999 August 11

NASA Astrophysics Data System (ADS)

Habbal, S. R.; Johnson, J.; Nisenson, P.; Woo, R.; Fineschi, S.; Esser, R.; Wood, C. H.; Hale, J.; Forman, M. A.; Johnson, J. A.; Jabbour, J.

2000-05-01

The goal of the eclipse expedition of the Harvard-Smithsonian Center for Astrophysics on 1999 August 11 to Ayn Diwar in Syria was to explore the temperature, density and magnetic structure of the corona through simultaneous imaging in the Fe X 6374, XIV 5303 and XI 7892 Angstroms lines, the Hα 6563 Angstroms line, and the polarized brightness or white light. Polarization measurements were made in the Fe XIV 5303 Angstroms and Hα 6563 Angstroms lines to yield the direction of the coronal magnetic field. Inferences of the temperature distribution were made from the three iron lines, while density profiles were derived from the polarized brightness measurements. Supporting space based observations were acquired with LASCO and UVCS on SOHO. The comprehensive diagnostic resulting from the analysis of the observations of the close-to-spherically symmetric corona of 1999 August 11 approaching solar maximum will be presented. Funding for this research was provided by NSF grant ATM 9521733 to the Smithsonian Astrophysical Observatory. We acknowledge the generous hospitality and support bestowed upon the team by the Syrian Ministry of Higher Education to conduct the experiment in Syria. The digitization of the photographic film was made with the help of Dr. J. Thornton and S. Sarafian from the Image Science Laboratory at Polaroid Corporation.

A coronal hole and its identification as the source of a high velocity solar wind stream

NASA Technical Reports Server (NTRS)

Krieger, A. S.; Timothy, A. F.; Roelof, E. C.

1973-01-01

X-ray images of the solar corona showed a magnetically open structure in the low corona which extended from N20W20 to the south pole. Analysis of the measured X-ray intensities shows the density scale heights within the structure to be typically a factor of two less than that in the surrounding large scale magnetically closed regions. The structure is identified as a coronal hole. Wind measurements for the appropriate period were traced back to the sun by the method of instantaneous ideal spirals. A striking agreement was found between the Carrington longitude of the solar source of a recurrent high velocity solar wind stream and the position of the hole.

Probing Twisted Magnetic Field Using Microwave Observations in an M Class Solar Flare on 11 February, 2014

NASA Astrophysics Data System (ADS)

Sharykin, I. N.; Kuznetsov, A. A.; Myshyakov, I. I.

2018-02-01

This work demonstrates the possibility of magnetic-field topology investigations using microwave polarimetric observations. We study a solar flare of GOES M1.7 class that occurred on 11 February, 2014. This flare revealed a clear signature of spatial inversion of the radio-emission polarization sign. We show that the observed polarization pattern can be explained by nonthermal gyrosynchrotron emission from the twisted magnetic structure. Using observations of the Reuven Ramaty High Energy Solar Spectroscopic Imager, Nobeyama Radio Observatory, Radio Solar Telescope Network, and Solar Dynamics Observatory, we have determined the parameters of nonthermal electrons and thermal plasma and identified the magnetic structure where the flare energy release occurred. To reconstruct the coronal magnetic field, we use nonlinear force-free field (NLFFF) and potential magnetic-field approaches. Radio emission of nonthermal electrons is simulated by the GX Simulator code using the extrapolated magnetic field and the parameters of nonthermal electrons and thermal plasma inferred from the observations; the model radio maps and spectra are compared with observations. We have found that the potential-magnetic-field approach fails to explain the observed circular polarization pattern; on the other hand, the Stokes-V map is successfully explained by assuming nonthermal electrons to be distributed along the twisted magnetic structure determined by the NLFFF extrapolation approach. Thus, we show that the radio-polarization maps can be used for diagnosing the topology of the flare magnetic structures where nonthermal electrons are injected.

Very large array faraday rotation studies of the coronal plasma

NASA Astrophysics Data System (ADS)

Kooi, Jason Earl

Knowledge of the coronal magnetic field is crucial for understanding (1) the heating mechanism(s) of the solar corona, (2) the acceleration of the fast solar wind, and (3) the structure and dynamics of coronal mass ejections (CMEs). Observation of Faraday rotation (FR) is one of the best remote-sensing techniques for determining plasma properties in the corona and can provide information on the plasma structure of a CME shortly after launch, shedding light on the initiation process. I used the Karl G. Jansky Very Large Array (VLA) to make sensitive Faraday rotation measurements to investigate the general plasma structure of the corona, properties of coronal plasma inhomogeneities and waves, and transients associated with coronal mass ejections. To enhance my measurements of FR transients, I also developed an algorithm in the Common Astronomy Software Applications (CASA) package to mitigate ionospheric Faraday rotation. In August, 2011, I made FR observations at 5.0 and 6.1 GHz of the radio galaxy 3C 228 through the solar corona at heliocentric distances of 4.6-5.0 solar radii using the VLA. Observations at 5.0 GHz permit measurements deeper in the corona than previous VLA observations at 1.4 and 1.7 GHz. These FR observations provided unique information on the magnetic field in this region of the corona. My data on 3C 228 provide two lines of sight (separated by 46 arcseconds, 33,000 km in the corona). I detected three periods during which there appeared to be a difference in the Faraday rotation measure between these two closely spaced lines of sight, which I used to estimate coronal currents; these values (ranging from 2.6 to 4.1 GA) are several orders of magnitude below that which is necessary for significant coronal heating (assuming the Spitzer resistivity). I also used the data to determine upper limits (3.3 and 6.4 rad/m2 along the two lines of sight) on FR fluctuations caused by coronal waves. These upper limits are comparable to and, thus, not inconsistent with the theoretical models for Alfven wave heating of the corona by Hollweg et al. (2010). To support the needs of the low frequency radioastronomical community as well as my own research of coronal FR transients, I developed a new calibration algorithm for CASA that uses GPS-based global ionosphere maps of the Total Electron Content (TEC) to mitigate ionospheric Faraday rotation. The Earth's ionosphere introduces direction- and time-dependent effects over a range of physical and temporal scales and so is a major source for unmodeled phase offsets for low frequency radioastronomical observations. It has become common practice to use global ionospheric models derived from the Global Positioning System (GPS) to provide a means of externally calibrating low frequency data. However, CASA, which was developed to meet the data post-processing needs of next generation telescopes such as the VLA and the Atacama Large Millimeter/submillimeter Array (ALMA), did not have the capability to make ionospheric corrections before I implemented this calibration algorithm. I investigated several data centers as potential sources for global ionospheric models and chose the International Global Navigation Satellite System Service data product because data from other sources are generally too sparse to use without additional interpolation schemes. I employed these ionospheric corrections in reducing VLA observations made in August, 2012, at 1-2 GHz of a "constellation'' of radio sources through the solar corona at heliocentric distances that ranged from 5-15 solar radii. Of the nine sources observed, three were occulted by CMEs: 0842+1835, 0900+1832, and 0843+1547. In addition to my radioastronomical observations, which represent one of the first active hunts for CME Faraday rotation since Bird et al. (1985) and the first active hunt using the VLA, I obtained white-light coronagraph images from the LASCO/C3 instrument aboard SOHO to determine the Thomson scattering brightness, BT. BT is proportional to the electron plasma density and provides a means to independently estimate the plasma density and determine its contribution to the observed Faraday rotation. A constant density force-free flux rope embedded in the background corona was used to model the effects of the CMEs on BT and FR. In the case of 0842+1835, the flux rope model underestimated the peak value in BT and did not reproduce the decreasing BT inside the inner cavity region of the CME; however, there was satisfactory agreement between the model and the observed FR. The single flux rope model successfully reproduces both the observed BT and FR profiles for 0900+1832. 0843+1547 was occulted by two CMEs. Therefore, I modeled observations of 0843+1547 using two flux ropes embedded in the background corona. The two flux rope model successfully reproduces both BT and FR profiles for 0843+1547 and, in particular, the two flux rope model successfully replicates the appropriate slope in FR before and after occultation by the second CME and predicts the observed change in sign to FR > 0 at the end of the observing session. I briefly discuss the plasma densities (6-22 x 10 3 cm-3) and axial magnetic field strengths (2-12 mG) inferred from my models and compare them to the modeling work of Liu et al. (2007) and Jensen et al. (2008), as well as previous CME FR observations by Bird et al. (1985).

Dynamics of Large-scale Coronal Structures as Imaged during the 2012 and 2013 Total Solar Eclipses

NASA Astrophysics Data System (ADS)

Alzate, Nathalia; Habbal, Shadia R.; Druckmüller, Miloslav; Emmanouilidis, Constantinos; Morgan, Huw

2017-10-01

White light images acquired at the peak of solar activity cycle 24, during the total solar eclipses of 2012 November 13 and 2013 November 3, serendipitously captured erupting prominences accompanied by CMEs. Application of state-of-the-art image processing techniques revealed the intricate details of two “atypical” large-scale structures, with strikingly sharp boundaries. By complementing the processed white light eclipse images with processed images from co-temporal Solar Dynamics Observatory/AIA and SOHO/LASCO observations, we show how the shape of these atypical structures matches the shape of faint CME shock fronts, which traversed the inner corona a few hours prior to the eclipse observations. The two events were not associated with any prominence eruption but were triggered by sudden brightening events on the solar surface accompanied by sprays and jets. The discovery of the indelible impact that frequent and innocuous transient events in the low corona can have on large-scale coronal structures was enabled by the radial span of the high-resolution white light eclipse images, starting from the solar surface out to several solar radii, currently unmatched by any coronagraphic instrumentation. These findings raise the interesting question as to whether large-scale coronal structures can ever be considered stationary. They also point to the existence of a much larger number of CMEs that goes undetected from the suite of instrumentation currently observing the Sun.

X ray microscope/telescope test and alignment

NASA Technical Reports Server (NTRS)

Walker, Arthur B. C.; Hoover, Richard B.

1991-01-01

The tasks performed by the Center for Applied Optics (CAO) in support of the Normal Incidence Multilayer X-Ray Optics Program are detailed. The Multi-Spectral Solar Telescope Array (MSSTA) was launched on a Terrier-boosted Black Brant sounding rocket from White Sands Missile Range on 13 May 1991. High resolution images of the sun in the soft x ray to extreme ultraviolet (EUV) regime were obtained with normal-incidence Cassegrain, Ritchey-Chretien, and Herschelian telescopes mounted in the sounding rocket. MSSTA represents the first use of multilayer optics to study a very broad range of x ray and EUV solar emissions. Energy-selective properties of multilayer-coated optics allow distinct groups of emission lines to be isolated in the solar corona and transition region. Features of the near and far coronal structures including magnetic loops of plasmas, coronal plumes, coronal holes, faint structures, and cool prominences are visible in these images. MSSTA successfully obtained unprecedented information regarding the structure and dynamics of the solar atmosphere in the temperature range of 10(exp 4)-10(exp 7) K. The performance of the MSSTA has demonstrated a unique combination of ultra-high spatial resolution and spectral differentiation by use of multilayer optics.

Semi-empirical models of the wind in cool supergiant stars

NASA Technical Reports Server (NTRS)

Kuin, N. P. M.; Ahmad, Imad A.

1988-01-01

A self-consistent semi-empirical model for the wind of the supergiant in zeta Aurigae type systems is proposed. The damping of the Alfven waves which are assumed to drive the wind is derived from the observed velocity profile. Solution of the ionization balance and energy equation gives the temperature structure for given stellar magnetic field and wave flux. Physically acceptable solutions of the temperature structure place limits on the stellar magnetic field. A crude formula for a critical mass loss rate is derived. For a mass loss rate below the critical value the wind cannot be cool. Comparison between the observed and the critical mass loss rate suggests that the proposed theory may provide an explanation for the coronal dividing line in the Hertzsprung-Russell diagram. The physical explanation may be that the atmosphere has a cool wind, unless it is physically impossible to have one. Stars which cannot have a cool wind release their nonthermal energy in an outer atmosphere at coronal temperatures. It is possible that in the absence of a substantial stellar wind the magnetic field has less incentive to extend radially outward, and coronal loop structures may become more dominant.

Pictorial essay of ultrasound-reconstructed coronal plane images of the uterus in different uterine pathologies.

PubMed

Grigore, Mihaela; Grigore, Anamaria; Gafitanu, Dumitru; Furnica, Cristina

2018-04-01

Imaging in the major planes (horizontal, coronal, and sagittal) of the uterus is important for determining anatomy and allowing the findings to be standardized, and for evaluating and diagnosing different pathological conditions in clinical practice. Examination of the coronal plane is an important step in identifying uterine pathologies and their relationships to the endometrial canal. Three-dimensional (3D) ultrasound reveals the normal anatomy better and improves the depiction of abnormal anatomy, as the coronal plane of the uterus can easily be obtained using 3D reconstruction techniques. Our pictorial essay demonstrates that adding 3D ultrasound to a routine gynecological workup can be beneficial for clinicians, enabling a precise diagnosis to be made. In addition, the volumes obtained and stored by 3D ultrasound can allow students or residents to become more familiar with normal and abnormal pelvic structures. Clin. Anat. 31:373-379, 2018. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Parametric Transformation Analysis

NASA Technical Reports Server (NTRS)

Gary, G. Allan

2003-01-01

Because twisted coronal features are important proxies for predicting solar eruptive events, and, yet not clearly understood, we present new results to resolve the complex, non-potential magnetic field configurations of active regions. This research uses free-form deformation mathematics to generate the associated coronal magnetic field. We use a parametric representation of the magnetic field lines such that the field lines can be manipulated to match the structure of EUV and SXR coronal loops. The objective is to derive sigmoidal magnetic field solutions which allows the beta greater than 1 regions to be included, aligned and non-aligned electric currents to be calculated, and the Lorentz force to be determined. The advantage of our technique is that the solution is independent of the unknown upper and side boundary conditions, allows non-vanishing magnetic forces, and provides a global magnetic field solution, which contains high- and low-beta regimes and is consistent with all the coronal images of the region. We show that the mathematical description is unique and physical.

Corrugation Instability of a Coronal Arcade

NASA Astrophysics Data System (ADS)

Klimushkin, D. Y.; Nakariakov, V. M.; Mager, P. N.; Cheremnykh, O. K.

2017-12-01

We analyse the behaviour of linear magnetohydrodynamic perturbations of a coronal arcade modelled by a half-cylinder with an azimuthal magnetic field and non-uniform radial profiles of the plasma pressure, temperature, and the field. Attention is paid to the perturbations with short longitudinal (in the direction along the arcade) wavelengths. The radial structure of the perturbations, either oscillatory or evanescent, is prescribed by the radial profiles of the equilibrium quantities. Conditions for the corrugation instability of the arcade are determined. It is established that the instability growth rate increases with decreases in the longitudinal wavelength and the radial wave number. In the unstable mode, the radial perturbations of the magnetic field are stronger than the longitudinal perturbations, creating an almost circularly corrugated rippling of the arcade in the longitudinal direction. For coronal conditions, the growth time of the instability is shorter than one minute, decreasing with an increase in the temperature. Implications of the developed theory for the dynamics of coronal active regions are discussed.

Macrospicule Jets in On-Disk Coronal Holes

NASA Technical Reports Server (NTRS)

Adams, M. L.; Sterling, A. C.; Moore, R. L.

2014-01-01

We examine the magnetic structure and dynamics of multiple jets found in coronal holes close to or on disk center. All data are from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO). We report on observations of six jets in an equatorial coronal hole spanning 2011 February 27 and 28. We show the evolution of these jets in AIA 193 A, examine the magnetic field configuration, and postulate the probable trigger mechanism of these events. We recently reported on another jet in the same coronal hole on 2011 February 27, approximately 13:04 Universal Time (Adams et al 2014, Astrophysical Journal, 783: 11); this jet is a previously-unrecognized variety of blowout jet. In this variety, the reconnection bright point is not made by interchange reconnection of initially-closed erupting field in the base of the jet with ambient open field. Instead, there is a miniature filament-eruption flare arcade made by internal reconnection of the legs of the erupting field.

Formation of a White-Light Jet Within a Quadrupolar Magnetic Configuration

NASA Astrophysics Data System (ADS)

Filippov, Boris; Koutchmy, Serge; Tavabi, Ehsan

2013-08-01

We analyze multi-wavelength and multi-viewpoint observations of a large-scale event viewed on 7 April 2011, originating from an active-region complex. The activity leads to a white-light jet being formed in the outer corona. The topology and evolution of the coronal structures were imaged in high resolution using the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). In addition, large field-of-view images of the corona were obtained using the Sun Watcher using Active Pixel System detector and Image Processing (SWAP) telescope onboard the PRoject for Onboard Autonomy (PROBA2) microsatellite, providing evidence for the connectivity of the coronal structures with outer coronal features that were imaged with the Large Angle Spectrometric Coronagraph (LASCO) C2 on the S olar and Heliospheric Observatory (SOHO). The data sets reveal an Eiffel-tower type jet configuration extending into a narrow jet in the outer corona. The event starts from the growth of a dark area in the central part of the structure. The darkening was also observed in projection on the disk by the Solar TErrestrial RElations Observatory-Ahead (STEREO-A) spacecraft from a different point of view. We assume that the dark volume in the corona descends from a coronal cavity of a flux rope that moved up higher in the corona but still failed to erupt. The quadrupolar magnetic configuration corresponds to a saddle-like shape of the dark volume and provides a possibility for the plasma to escape along the open field lines into the outer corona, forming the white-light jet.

2010 August 1–2 Sympathetic Eruptions. II. Magnetic Topology of the MHD Background Field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Titov, Viacheslav S.; Mikić, Zoran; Török, Tibor

Using a potential field source-surface (PFSS) model, we recently analyzed the global topology of the background coronal magnetic field for a sequence of coronal mass ejections (CMEs) that occurred on 2010 August 1–2. Here we repeat this analysis for the background field reproduced by a magnetohydrodynamic (MHD) model that incorporates plasma thermodynamics. As for the PFSS model, we find that all three CME source regions contain a coronal hole (CH) that is separated from neighboring CHs by topologically very similar pseudo-streamer structures. However, the two models yield very different results for the size, shape, and flux of the CHs. Wemore » find that the helmet-streamer cusp line, which corresponds to a source-surface null line in the PFSS model, is structurally unstable and does not form in the MHD model. Our analysis indicates that, generally, in MHD configurations, this line instead consists of a multiple-null separator passing along the edge of disconnected-flux regions. Some of these regions are transient and may be the origin of the so-called streamer blobs. We show that the core topological structure of such blobs is a three-dimensional “plasmoid” consisting of two conjoined flux ropes of opposite handedness, which connect at a spiral null point of the magnetic field. Our analysis reveals that such plasmoids also appear in pseudo-streamers on much smaller scales. These new insights into the coronal magnetic topology provide some intriguing implications for solar energetic particle events and for the properties of the slow solar wind.« less

2010 August 1-2 Sympathetic Eruptions. II. Magnetic Topology of the MHD Background Field

NASA Astrophysics Data System (ADS)

Titov, Viacheslav S.; Mikić, Zoran; Török, Tibor; Linker, Jon A.; Panasenco, Olga

2017-08-01

Using a potential field source-surface (PFSS) model, we recently analyzed the global topology of the background coronal magnetic field for a sequence of coronal mass ejections (CMEs) that occurred on 2010 August 1-2. Here we repeat this analysis for the background field reproduced by a magnetohydrodynamic (MHD) model that incorporates plasma thermodynamics. As for the PFSS model, we find that all three CME source regions contain a coronal hole (CH) that is separated from neighboring CHs by topologically very similar pseudo-streamer structures. However, the two models yield very different results for the size, shape, and flux of the CHs. We find that the helmet-streamer cusp line, which corresponds to a source-surface null line in the PFSS model, is structurally unstable and does not form in the MHD model. Our analysis indicates that, generally, in MHD configurations, this line instead consists of a multiple-null separator passing along the edge of disconnected-flux regions. Some of these regions are transient and may be the origin of the so-called streamer blobs. We show that the core topological structure of such blobs is a three-dimensional “plasmoid” consisting of two conjoined flux ropes of opposite handedness, which connect at a spiral null point of the magnetic field. Our analysis reveals that such plasmoids also appear in pseudo-streamers on much smaller scales. These new insights into the coronal magnetic topology provide some intriguing implications for solar energetic particle events and for the properties of the slow solar wind.

A comprehensive visual rating scale of brain magnetic resonance imaging: application in elderly subjects with Alzheimer's disease, mild cognitive impairment, and normal cognition.

PubMed

Jang, Jae-Won; Park, So Young; Park, Young Ho; Baek, Min Jae; Lim, Jae-Sung; Youn, Young Chul; Kim, SangYun

2015-01-01

Brain magnetic resonance imaging (MRI) shows cerebral structural changes. However, a unified comprehensive visual rating scale (CVRS) has seldom been studied. Thus, we combined brain atrophy and small vessel disease scales and used an MRI template as a CVRS. The aims of this study were to design a simple and reliable CVRS, validate it by investigating cerebral structural changes in clinical groups, and made comparison to the volumetric measurements. Elderly subjects (n = 260) with normal cognition (NC, n = 65), mild cognitive impairment (MCI, n = 101), or Alzheimer's disease (AD, n = 94) were evaluated with brain MRI according to the CVRS of brain atrophy and small vessel disease. Validation of the CVRS with structural changes, neuropsychological tests, and volumetric analyses was performed. The CVRS revealed a high intra-rater and inter-rater agreement and it reflected the structural changes of subjects with NC, MCI, and AD better than volumetric measures (CVRS-coronal: F = 13.5, p < 0.001; CVRS-axial: F = 19.9, p < 0.001). The area under the receiver operation curve (aROC) of the CVRS showed higher accuracy than volumetric analyses. (NC versus MCI aROC: CVRS-coronal, 0.777; CVRS-axial, 0.773; MCI versus AD aROC: CVRS-coronal, 0.680; CVRS-axial, 0.681). The CVRS can be used clinically to conveniently measure structural changes of brain. It reflected cerebral structural changes of clinical groups and correlated with the age better than volumetric measures.

[Ultraviolet spectroscopic study on the fine structures in the solar polar hole].

PubMed

Zhang, Min; Wang, Dong; Liu, Guo-Hong

2014-07-01

Fine structures in the south solar polar coronal hole were observed by N IV line of SOHO/SUMER spectrograph. The scales of the fine structures range spatially range from 1 arcsec to several arcsecs, temporally from 1 min to several minutes, and parts of them are in strip shape along the slit direction. The line-of-sight velocity of them is up to tens of km x s(-1) with red and blue shift intercrossed occasionally, which appear periodically as long as 100 minutes in some regions. Part of the fine structures can be clearly observed at the Ne V III line with higher formation temperature in the same spectral window. The time and location of some fine structures with high velocity in the Ne V III spectrum are almost the same as that in N IV spectrum, but they are extended and diffused in the Ne V III spectrum. Some fine structures have non-Gaussian profiles with the line-of-sight Doppler velocities up to 150 km x s(-1) in the N IV blue/red wings, which is similar with the explosive events in the transition region. In the past, explosive events are small-scale dynamic phenomena often observed in the quiet-sun (QS) region, while their properties in coronal holes (CHs) remain unclear. Here, we find the EE-like events with strong dynamics in the south solar polar coronal hole by N IV line of SOHO/SUMER spectrograph.

NEOCE: a new external occulting coronagraph experiment for ultimate observations of the chromosphere, corona and interface

NASA Astrophysics Data System (ADS)

Damé, Luc; Fineschi, Silvano; Kuzin, Sergey; Von Fay-Siebenburgen, Erdélyi Robert

Several ground facilities and space missions are currently dedicated to the study of the Sun at high resolution and of the solar corona in particular. However, and despite significant progress with the advent of space missions and UV, EUV and XUV direct observations of the hot chromosphere and million-degrees coronal plasma, much is yet to be achieved in the understanding of these high temperatures, fine dynamic dissipative structures and of the coronal heating in general. Recent missions have shown the definite role of a wide range of waves and of the magnetic field deep in the inner corona, at the chromosphere-corona interface, where dramatic and physically fundamental changes occur. The dynamics of the chromosphere and corona is controlled and governed by the emerging magnetic field. Accordingly, the direct measurement of the chromospheric and coronal magnetic fields is of prime importance. The solar corona consists of many localised loop-like structures or threads with the plasmas brightening and fading independently. The plasma evolution in each thread is believed to be related to the formation of filaments, each one being dynamic, in a non-equilibrium state. The mechanism sustaining this dynamics, oscillations or waves (Alfvén or other magneto-plasma waves), requires both very high-cadence, multi-spectral observations, and high resolution and coronal magnetometry. This is foreseen in the future Space Mission NEOCE (New External Occulting Coronagraph Experiment), the ultimate new generation high-resolution coronagraphic heliospheric mission, to be proposed for ESA M4. NEOCE, an evolution of the HiRISE mission, is ideally placed at the L5 Lagrangian point (for a better follow-up of CMEs), and provides FUV imaging and spectro-imaging, EUV and XUV imaging and spectroscopy, and ultimate coronagraphy by a remote external occulter (two satellites in formation flying 375 m apart minimizing scattered light) allowing to characterize temperature, densities and velocities up to the solar upper chromosphere, transition zone and inner corona with, in particular, 2D very high resolution multi-spectral imaging-spectroscopy and direct coronal magnetic field measurement: a unique set of tools to understand the structuration and onset of coronal heating. We give a detailed account of the proposed mission profile, and its major scientific objectives and model payload (in particular of the SuperASPIICS package of visible, NIR and UV, Lyman-Alpha and OVI, coronagraphs).

Diagnosing the Prominence-Cavity Connection in the Solar Corona

NASA Astrophysics Data System (ADS)

Schmit, D. J.

The energetic equilibrium of the corona is described by a balance of heating, thermal conduction, and radiative cooling. Prominences can be described by the thermal instability of coronal energy balance which leads to the formation of cool condensations. Observationally, the prominence is surrounded by a density depleted elliptical structure known as a cavity. In this dissertation, we use extreme ultraviolet remote sensing observations of the prominence-cavity system to diagnose the static and dynamic properties of these structures. The observations are compared with numerical models for the time-dependent coronal condensation process and the time-independent corona-prominence magnetic field. To diagnose the density of the cavity, we construct a three-dimensional structural model of the corona. This structural model allows us to synthesize extreme ultraviolet emission in the corona in a way that incorporates the projection effects which arise from the optically thin plasma. This forward model technique is used to constrain a radial density profile simultaneously in the cavity and the streamer. We use a χ2 minimization to find the density model which best matches a density sensitive line ratio (observed with Hinode/Extreme ultraviolet Imaging Spectrometer) and the white light scattered intensity (observed with Mauna Loa Solar Observatory MK4 coronagraph). We use extreme ultraviolet spectra and spectral images to diagnose the dynamics of the prominence and the surrounding corona. Based on the doppler shift of extreme ultraviolet coronal emission lines, we find that there are large regions of flowing plasma which appear to occur within cavities. These line of sight flows have speeds of 10 km/s-1 and projected spatial scales of 100 Mm. Using the Solar Dynamics Observatory Atmospheric Imaging Assembly (SDO/AIA) dataset, we observe dynamic emission from the prominence-cavity system. The SDO/AIA dataset observes multiple spectral bandpasses with different temperature sensitivities. Time-dependent changes in the observed emission in these bandpass images represent changes in the thermodynamic properties of the emitting plasma. We find that the coronal region surrounding the prominence exhibits larger intensity variations (over tens of hours of observations) as compared to the streamer region. This variability is particularly strong in the cool coronal emission of the 171Å bandpass. We identify the source of this variability as strong brightening events that resemble concave-up loop segments and extend from the cool prominence plasma. Magnetic field lines are the basic structural building block of the corona. Energy and pressure balance in the corona occur along magnetic field lines. The large-scale extreme ultraviolet emission we observe in the corona is a conglomerate of many coronal loops projected along a line of sight. In order to calculate the plasma properties at a particular point in the corona, we use one-dimensional models for energy and pressure balance along field lines. In order to predict the extreme ultraviolet emission along a particular line of sight, we project these one-dimensional models onto the three-dimensional magnetic configuration provided by a MHD model for the coronal magnetic field. These results have allowed us to the establish the first comprehensive picture on the magnetic and energetic interaction of the prominence and the cavity. While the originally hypothesis that the cavity supplies mass to the prominence proved inaccurate, we cannot simply say that these structures are not related. Rather our findings suggest that the prominence and the cavity are distinct magnetic substructures that are complementary regions of a larger whole, specifically a magnetic flux rope. (Abstract shortened by UMI.).

Blowout Jets: Hinode X-Ray Jets that Don't Fit the Standard Model

NASA Technical Reports Server (NTRS)

Moore, Ronald L.; Cirtain, Jonathan W.; Sterling, Alphonse C.; Falconer, David A.

2010-01-01

Nearly half of all H-alpha macrospicules in polar coronal holes appear to be miniature filament eruptions. This suggests that there is a large class of X-ray jets in which the jet-base magnetic arcade undergoes a blowout eruption as in a CME, instead of remaining static as in most solar X-ray jets, the standard jets that fit the model advocated by Shibata. Along with a cartoon depicting the standard model, we present a cartoon depicting the signatures expected of blowout jets in coronal X-ray images. From Hinode/XRT movies and STEREO/EUVI snapshots in polar coronal holes, we present examples of (1) X-ray jets that fit the standard model, and (2) X-ray jets that do not fit the standard model but do have features appropriate for blowout jets. These features are (1) a flare arcade inside the jet-base arcade in addition to the small flare arcade (bright point) outside that standard jets have, (2) a filament of cool (T is approximately 80,000K) plasma that erupts from the core of the jetbase arcade, and (3) an extra jet strand that should not be made by the reconnection for standard jets but could be made by reconnection between the ambient unipolar open field and the opposite-polarity leg of the filament-carrying flux-rope core field of the erupting jet-base arcade. We therefore infer that these non-standard jets are blowout jets, jets made by miniature versions of the sheared-core-arcade eruptions that make CMEs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chifu, Iulia; Wiegelmann, Thomas; Inhester, Bernd, E-mail: chifu@mps.mpg.de

Insights into the 3D structure of the solar coronal magnetic field have been obtained in the past by two completely different approaches. The first approach are nonlinear force-free field (NLFFF) extrapolations, which use photospheric vector magnetograms as boundary condition. The second approach uses stereoscopy of coronal magnetic loops observed in EUV coronal images from different vantage points. Both approaches have their strengths and weaknesses. Extrapolation methods are sensitive to noise and inconsistencies in the boundary data, and the accuracy of stereoscopy is affected by the ability of identifying the same structure in different images and by the separation angle betweenmore » the view directions. As a consequence, for the same observational data, the 3D coronal magnetic fields computed with the two methods do not necessarily coincide. In an earlier work (Paper I) we extended our NLFFF optimization code by including stereoscopic constrains. The method was successfully tested with synthetic data, and within this work, we apply the newly developed code to a combined data set from SDO /HMI, SDO /AIA, and the two STEREO spacecraft. The extended method (called S-NLFFF) contains an additional term that monitors and minimizes the angle between the local magnetic field direction and the orientation of the 3D coronal loops reconstructed by stereoscopy. We find that when we prescribe the shape of the 3D stereoscopically reconstructed loops, the S-NLFFF method leads to a much better agreement between the modeled field and the stereoscopically reconstructed loops. We also find an appreciable decrease by a factor of two in the angle between the current and the magnetic field. This indicates the improved quality of the force-free solution obtained by S-NLFFF.« less

Large-Scale Coronal Heating from the Solar Magnetic Network

NASA Technical Reports Server (NTRS)

Falconer, David A.; Moore, Ronald L.; Porter, Jason G.; Hathaway, David H.

1999-01-01

In Fe 12 images from SOHO/EIT, the quiet solar corona shows structure on scales ranging from sub-supergranular (i.e., bright points and coronal network) to multi- supergranular. In Falconer et al 1998 (Ap.J., 501, 386) we suppressed the large-scale background and found that the network-scale features are predominantly rooted in the magnetic network lanes at the boundaries of the supergranules. The emission of the coronal network and bright points contribute only about 5% of the entire quiet solar coronal Fe MI emission. Here we investigate the large-scale corona, the supergranular and larger-scale structure that we had previously treated as a background, and that emits 95% of the total Fe XII emission. We compare the dim and bright halves of the large- scale corona and find that the bright half is 1.5 times brighter than the dim half, has an order of magnitude greater area of bright point coverage, has three times brighter coronal network, and has about 1.5 times more magnetic flux than the dim half These results suggest that the brightness of the large-scale corona is more closely related to the large- scale total magnetic flux than to bright point activity. We conclude that in the quiet sun: (1) Magnetic flux is modulated (concentrated/diluted) on size scales larger than supergranules. (2) The large-scale enhanced magnetic flux gives an enhanced, more active, magnetic network and an increased incidence of network bright point formation. (3) The heating of the large-scale corona is dominated by more widespread, but weaker, network activity than that which heats the bright points. This work was funded by the Solar Physics Branch of NASA's office of Space Science through the SR&T Program and the SEC Guest Investigator Program.

Hi-C Observations of an Active Region Corona, and Investigation of the Underlying Magnetic Structure

NASA Technical Reports Server (NTRS)

Tiwari, S. K.; Alexander, C. E.; Winebarger, A.; Moore, R. L.

2014-01-01

The solar corona is much hotter (>=10(exp 6) K) than its surface (approx 6000 K), puzzling astrophysicists for several decades. Active region (AR) corona is again hotter than the quiet Sun (QS) corona by a factor of 4-10. The most widely accepted mechanism that could heat the active region corona is the energy release by current dissipation via reconnection of braided magnetic field structure, first proposed by E. N. Parker three decades ago. The first observational evidence for this mechanism has only recently been presented by Cirtain et al. by using High-resolution Coronal Imager (Hi-C) observations of an AR corona at a spatial resolution of 0.2 arcsec, which is required to resolve the coronal loops, and was not available before the rocket flight of Hi-C in July 2012. The Hi-C project is led by NASA/MSFC. In the case of the QS, work done by convection/granulation on the inter-granular feet of the coronal field lines translates into the heat observed in the corona. In the case of the AR, as here, there could be flux emergence, cancellation/submergence, or shear flows generating large stress and tension in coronal field loops which is released as heat in the corona. We are currently investigating the changes taking place in photospheric feet of the magnetic field involved with brightenings in the Hi-C AR corona. For this purpose, we are also using SDO/AIA data of +/- 2 hours around the 5 minutes Hi-C flight. In the present talk, I will first summarize some of the results of the Hi-C observations and then present some results from our recent analysis on what photospheric processes feed the magnetic energy that dissipates into heat in coronal loops.

The Faraday rotation experiment. [solar corona

NASA Technical Reports Server (NTRS)

Volland, H.; Levy, G. S.; Bird, M. K.; Stelzried, C. T.; Seidel, B. L.

1984-01-01

The magnetized plasma of the solar corona was remotely sounded using the Faraday rotation effect. The solar magnetic field together with the electrons of the coronal plasma cause a measurable Faraday rotation effect, since the radio waves of Helios are linearly polarized. The measurement is performed at the ground stations. Alfven waves traveling from the Sun's surface through the corona into interplanetary space are observed. Helios 2 signals penetrating through a region where coronal mass is ejected show wavelike structures.

Measuring Temperature-Dependent Propagating Disturbances in Coronal Fan Loops Using Multiple SDO-AIA Channels and Surfing Transform Technique

NASA Technical Reports Server (NTRS)

Uritskiy, Vadim M.; Davila, Joseph M.; Viall, Nicholeen M.; Ofman, Leon

2013-01-01

A set of co-aligned high resolution images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) is used to investigate propagating disturbances (PDs) in warm fan loops at the periphery of a non-flaring active region NOAA AR 11082. To measure PD speeds at multiple coronal temperatures, a new data analysis methodology is proposed enabling quantitative description of sub visual coronal motions with low signal-to-noise ratios of the order of 0.1. The technique operates with a set of one-dimensional surfing signals extracted from position-timeplots of several AIA channels through a modified version of Radon transform. The signals are used to evaluate a two-dimensional power spectral density distribution in the frequency - velocity space which exhibits a resonance in the presence of quasi-periodic PDs. By applying this analysis to the same fan loop structures observed in several AIA channels, we found that the traveling velocity of PDs increases with the temperature of the coronal plasma following the square root dependence predicted for the slow mode magneto-acoustic wave which seems to be the dominating wave mode in the studied loop structures. This result extends recent observations by Kiddie et al. (2012) to a more general class of fan loop systems not associated with sunspots and demonstrating consistent slow mode activity in up to four AIA channels.

Signatures Of Coronal Heating Driven By Footpoint Shuffling: Closed and Open Structures.

NASA Astrophysics Data System (ADS)

Velli, M. C. M.; Rappazzo, A. F.; Dahlburg, R. B.; Einaudi, G.; Ugarte-Urra, I.

2017-12-01

We have previously described the characteristic state of the confined coronal magnetic field as a special case of magnetically dominated magnetohydrodynamic (MHD) turbulence, where the free energy in the transverse magnetic field is continuously cascaded to small scales, even though the overall kinetic energy is small. This coronal turbulence problem is defined by the photospheric boundary conditions: here we discuss recent numerical simulations of the fully compressible 3D MHD equations using the HYPERION code. Loops are forced at their footpoints by random photospheric motions, energizing the field to a state with continuous formation and dissipation of field-aligned current sheets: energy is deposited at small scales where heating occurs. Only a fraction of the coronal mass and volume gets heated at any time. Temperature and density are highly structured at scales that, in the solar corona, remain observationally unresolved: the plasma of simulated loops is multithermal, where highly dynamical hotter and cooler plasma strands are scattered throughout the loop at sub-observational scales. We will also compare Reduced MHD simulations with fully compressible simulations and photospheric forcings with different time-scales compared to the Alfv'en transit time. Finally, we will discuss the differences between the closed field and open field (solar wind) turbulence heating problem, leading to observational consequences that may be amenable to Parker Solar Probe and Solar Orbiter.

First 2017-total-eclipse results from the Williams College team

NASA Astrophysics Data System (ADS)

Pasachoff, J.; Dantowitz, R.; Rusin, V.; Seiradakis, J. H.; Voulgaris, A.; Seaton, D. B.; Davis, A. B.; Lu, M.; Sliski, D.; Ladd, E. F.; Economou, T.; Peñaloza-Murillo, M. A.; Nagle-McNaughton, T.

2017-12-01

We report on a wide range of observations we carried out during the total solar eclipse of August 21, 2017. Our main site was on the campus of Willamette University, Salem, Oregon, at which we had a variety of telescopes, spectrographs, cameras, a grism, and terrestrial-atmospheric measuring devices. Our goals included differentiating between models of coronal heating through measuring power-spectra of coronal loops in the [Fe XIV] and [Fe X] emission lines at multi-Hertz cadence with a frame-transfer CCD and otherwise; following coronal structure over the solar-activity cycle; comparing the results of a full-MHD prediction with actual coronal streamers; studying the dynamics of coronal plumes given the minimum phase of the solar-activity cycle; measuring the variation of the corona over the solar-activity cycle from our continuing measurements of the green-line/red-line intensity ratio; studying a variety of additional coronal emisson lines; high-resolution coronal imaging compared with overlapping images from space coronagraphs aboard SoHO and STEREO; comparing with AIA/SDO, HMO/SDO, SUVI/GOES-16, and SWAP/PROBA2 space images; and more. Our research has been supported in large part by grants from the Committee for Research and Exploration of the National Geographic Society and from the Solar Terrestrial Program of the Atmospheric and Geospace Sciences Division of the National Science Foundation, with additional support from Sigma Xi. Additional support for undergraduate participation came from the NSF, the NASA Massachusetts Space Grant Consortium, and the Clare Booth Luce Foundation, with travel support from the Freeman Foote Fund, the Rob Spring Fund, the Brandi Fund, and other sources at Williams College.

The wide skirt of the bashful ballerina: Hemispheric asymmetry of the heliospheric magnetic field in the inner and outer heliosphere

NASA Astrophysics Data System (ADS)

Mursula, K.; Virtanen, I.

2012-04-01

We reanalyze the observations of the heliospheric magnetic field (HMF) made by the Pioneer 10 and 11 and Voyager 1 and 2 heliospheric probes since 1972, and calculate the HMF sector occurrence ratios and tangential component strengths in the different regions of the heliosphere. Observations at the distant probes and at 1 AU show a very consistent picture of the HMF sector structure in the entire heliosphere, and even beyond the termination shock. Pioneer 11 and Voyager 1 show that the development of northern polar coronal holes was very systematic and active during all the four solar minima since mid-1970s. On the other hand, Voyager 2 observations show a less systematic and delayed development of southern coronal holes in 1980s, 1990s and 2000s. This delay in the evolution of southern coronal holes with respect to the rapid and systematic evolution of northern coronal holes leads to a larger extent of northern coronal holes and a southward shift of the heliospheric current sheet (the bashful ballerina phenomenon) for a few years in the late declining phase of each solar cycle. HMF observations of the probes also directly verify the HCS southward shift, supporting earlier observations at 1-2 AU by the Ulysses probe and Earth-orbiting satellites and extending them into the more distant heliosphere. Although the evidence for the connection between the temporal difference in the evolution of polar coronal holes and the bashful ballerina times is based only on three solar cycles, this may be a common pattern for solar coronal hole evolution since the southward shift of the HCS has occurred at least since solar cycle 16.

The wide skirt of the bashful ballerina: Hemispheric asymmetry of the heliospheric magnetic field in the inner and outer heliosphere

NASA Astrophysics Data System (ADS)

Mursula, K.; Virtanen, I. I.

2012-08-01

We reanalyze the observations of the heliospheric magnetic field (HMF) made by the Pioneer 10 and 11 and Voyager 1 and 2 heliospheric probes since 1972, and calculate the HMF sector occurrence ratios and tangential component strengths in the different regions of the heliosphere. Observations at the distant probes and at 1 AU show a very consistent picture of the HMF sector structure in the entire heliosphere, and even beyond the termination shock. HMF observations by the probes also support the southward shift of the heliospheric current sheet (the bashful ballerina phenomenon), which is observed earlier at 1-2 AU by the Ulysses probe and Earth-orbiting satellites, and verify the HCS shift over a wide range of radial distances until the distant heliosphere. Pioneer 11 and Voyager 1 show that the development of northern polar coronal holes was very systematic and active during all the four solar minima since mid-1970s, while Voyager 2 observations show a less systematic and delayed development of southern coronal holes in 1980s, 1990s and 2000s. This delay in the evolution of southern coronal holes with respect to the rapid and systematic evolution of northern coronal holes leads to a larger extent of northern coronal holes and the southward shift of the HCS for a few years in the late declining phase of each solar cycle. Although evidence for the connection between the different evolution of polar coronal holes and the bashful ballerina phenomenon is obtained here only for three solar cycles, this may be a common pattern for solar coronal hole evolution since the southward shift of the HCS has occurred at least since solar cycle 16.

The plasma filling factor of coronal bright points. II. Combined EIS and TRACE results

NASA Astrophysics Data System (ADS)

Dere, K. P.

2009-04-01

Aims: In a previous paper, the volumetric plasma filling factor of coronal bright points was determined from spectra obtained with the Extreme ultraviolet Imaging Spectrometer (EIS). The analysis of these data showed that the median plasma filling factor was 0.015. One interpretation of this result was that the small filling factor was consistent with a single coronal loop with a width of 1-2´´, somewhat below the apparent width. In this paper, higher spatial resolution observations with the Transition Region and Corona Explorer (TRACE) are used to test this interpretation. Methods: Rastered spectra of regions of the quiet Sun were recorded by the EIS during operations with the Hinode satellite. Many of these regions were simultaneously observed with TRACE. Calibrated intensities of Fe xii lines were obtained and images of the quiet corona were constructed from the EIS measurements. Emission measures were determined from the EIS spectra and geometrical widths of coronal bright points were obtained from the TRACE images. Electron densities were determined from density-sensitive line ratios measured with EIS. A comparison of the emission measure and bright point widths with the electron densities yielded the plasma filling factor. Results: The median electron density of coronal bright points is 3 × 109 cm-3 at a temperature of 1.6 × 106 K. The volumetric plasma filling factor of coronal bright points was found to vary from 3 × 10-3 to 0.3 with a median value of 0.04. Conclusions: The current set of EIS and TRACE coronal bright-point observations indicate the median value of their plasma filling factor is 0.04. This can be interpreted as evidence of a considerable subresolution structure in coronal bright points or as the result of a single completely filled plasma loop with widths on the order of 0.2-1.5´´ that has not been spatially resolved in these measurements.

Hemispheric asymmetry in coronal hole evolution: Cause of the bashful ballerina?

NASA Astrophysics Data System (ADS)

Mursula, K.; Tlatov, A.; Virtanen, I.

2012-12-01

The magnetic hemisphere prevalent in the solar northern hemisphere has been shown to cover a larger area than in the south for about three years in the declining phase of several solar cycles. Correspondingly, the average field intensity is weaker in the northern hemisphere and the heliospheric current sheet (HCS) is shifted southward at these times. This phenomenon, now called the bashful ballerina, has been verified using several databases and methods, including the in situ observations of the heliospheric magnetic field (HMF) at 1 AU by the OMNI data base, at about 2 AU by the Ulysses probe, and at different radial distances by the Voyager 1 and 2 and Pioneer 10 and 11 probes. The Ulysses observations show that the mean southward shift of the HCS was about 2 degrees in the declining phase of both cycle 22 and cycle 23, although the polar strengths were very different between the two cycles. The HMF observations by the Voyager and Pioneer probes show a very consistent structure of HMF sectors and HCS location in the entire heliosphere, and even beyond the termination shock. Moreover, they suggest a systematic difference in the development of northern and southern polar coronal holes. While the northern coronal holes developed very systematically during all the four solar minima since mid-1970s, the evolution of southern coronal holes was less systematic and delayed with respect to the northern hemisphere. This delay in the evolution of southern coronal holes leads to a larger extent of northern coronal holes and a southward shift of the heliospheric current sheet (the bashful ballerina phenomenon) for a few years in the declining phase of the solar cycle. Here we study direct observations of solar coronal holes and verify this difference in the evolution of coronal holes between the two solar hemispheres, which explains the bashful ballerina phenomenon.

Force-Free Magnetic Fields Calculated from Automated Tracing of Coronal Loops with AIA/SDO

NASA Astrophysics Data System (ADS)

Aschwanden, M. J.

2013-12-01

One of the most realistic magnetic field models of the solar corona is a nonlinear force-free field (NLFFF) solution. There exist about a dozen numeric codes that compute NLFFF solutions based on extrapolations of photospheric vector magnetograph data. However, since the photosphere and lower chromosphere is not force-free, a suitable correction has to be applied to the lower boundary condition. Despite of such "pre-processing" corrections, the resulting theoretical magnetic field lines deviate substantially from observed coronal loop geometries. - Here we developed an alternative method that fits an analytical NLFFF approximation to the observed geometry of coronal loops. The 2D coordinates of the geometry of coronal loop structures observed with AIA/SDO are traced with the "Oriented Coronal CUrved Loop Tracing" (OCCULT-2) code, an automated pattern recognition algorithm that has demonstrated the fidelity in loop tracing matching visual perception. A potential magnetic field solution is then derived from a line-of-sight magnetogram observed with HMI/SDO, and an analytical NLFFF approximation is then forward-fitted to the twisted geometry of coronal loops. We demonstrate the performance of this magnetic field modeling method for a number of solar active regions, before and after major flares observed with SDO. The difference of the NLFFF and the potential field energies allows us then to compute the free magnetic energy, which is an upper limit of the energy that is released during a solar flare.

Classical Heat-Flux Measurements in Coronal Plasmas from Collective Thomson-Scattering Spectra

NASA Astrophysics Data System (ADS)

Henchen, R. J.; Hu, S. X.; Katz, J.; Froula, D. H.; Rozmus, W.

2016-10-01

Collective Thomson scattering was used to measure heat flux in coronal plasmas. The relative amplitude of the Thomson-scattered power into the up- and downshifted electron plasma wave features was used to determine the flux of electrons moving along the temperature gradient at three to four times the electron thermal velocity. Simultaneously, the ion-acoustic wave features were measured. Their relative amplitude was used to measure the flux of the return-current electrons. The frequencies of these ion-acoustic and electron plasma wave features provide local measurements of the electron temperature and density. These spectra were obtained at five locations along the temperature gradient in a laser-produced blowoff plasma. These measurements of plasma parameters are used to infer the Spitzer-Härm flux (qSH = - κ∇Te ) and are in good agreement with the values of the heat flux measured from the scattering-feature asymmetries. Additional experiments probed plasma waves perpendicular to the temperature gradient. The data show small effects resulting from heat flux compared to probing waves along the temperature gradient. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Non-thermal recombination - a neglected source of flare hard X-rays and fast electron diagnostics (Corrigendum)

NASA Astrophysics Data System (ADS)

Brown, J. C.; Mallik, P. C. V.; Badnell, N. R.

2010-06-01

Brown and Mallik (BM) recently claimed that non-thermal recombination (NTR) can be a dominant source of flare hard X-rays (HXRs) from hot coronal and chromospheric sources. However, major discrepancies between the thermal continua predicted by BM and by the Chianti database as well as RHESSI flare data, led us to discover substantial errors in the heuristic expression used by BM to extend the Kramers expressions beyond the hydrogenic case. Here we present the relevant corrected expressions and show the key modified results. We conclude that, in most cases, NTR emission was overestimated by a factor of 1-8 by BM but is typically still large enough (as much as 20-30% of the total emission) to be very important for electron spectral inference and detection of electron spectral features such as low energy cut-offs since the recombination spectra contain sharp edges. For extreme temperature regimes and/or if the Fe abundance were as high as some values claimed, NTR could even be the dominant source of flare HXRs, reducing the electron number and energy budget, problems such as in the extreme coronal HXR source cases reported by e.g. Krucker et al.

Future space missions and ground observatory for measurements of coronal magnetic fields

NASA Astrophysics Data System (ADS)

Fineschi, Silvano; Gibson, Sarah; Bemporad, Alessandro; Zhukov, Andrei; Damé, Luc; Susino, Roberto; Larruquert, Juan

2016-07-01

This presentation gives an overview of the near-future perspectives for probing coronal magnetism from space missions (i.e., SCORE and ASPIICS) and ground-based observatory (ESCAPE). Spectro-polarimetric imaging of coronal emission-lines in the visible-light wavelength-band provides an important diagnostics tool of the coronal magnetism. The interpretation in terms of Hanle and Zeeman effect of the line-polarization in forbidden emission-lines yields information on the direction and strength of the coronal magnetic field. As study case, this presentation will describe the Torino Coronal Magnetograph (CorMag) for the spectro-polarimetric observation of the FeXIV, 530.3 nm, forbidden emission-line. CorMag - consisting of a Liquid Crystal (LC) Lyot filter and a LC linear polarimeter. The CorMag filter is part of the ESCAPE experiment to be based at the French-Italian Concordia base in Antarctica. The linear polarization by resonance scattering of coronal permitted line-emission in the ultraviolet (UV)can be modified by magnetic fields through the Hanle effect. Space-based UV spectro-polarimeters would provide an additional tool for the disgnostics of coronal magnetism. As a case study of space-borne UV spectro-polarimeters, this presentation will describe the future upgrade of the Sounding-rocket Coronagraphic Experiment (SCORE) to include new generation, high-efficiency UV polarizer with the capability of imaging polarimetry of the HI Lyman-α, 121.6 nm. SCORE is a multi-wavelength imager for the emission-lines, HeII 30.4 nm and HI 121.6 nm, and visible-light broad-band emission of the polarized K-corona. SCORE has flown successfully in 2009. The second lauch is scheduled in 2016. Proba-3 is the other future solar mission that would provide the opportunity of diagnosing the coronal magnetic field. Proba-3 is the first precision formation-flying mission to launched in 2019). A pair of satellites will fly together maintaining a fixed configuration as a 'large rigid structure' in space. The paired satellites will together form a 150-m long solar coronagraph (ASPIICS) to study the Sun's faint corona closer to the solar limb than has ever before been achieved. High-resolution imaging in polarized visible-light of shock waves generated by Coronal Mass Ejections would provide a diagnostics of the magnetic field in the pre-shock ambient corona.

Coronal Bright Points Associated with Minifilament Eruptions

NASA Astrophysics Data System (ADS)

Hong, Junchao; Jiang, Yunchun; Yang, Jiayan; Bi, Yi; Li, Haidong; Yang, Bo; Yang, Dan

2014-12-01

Coronal bright points (CBPs) are small-scale, long-lived coronal brightenings that always correspond to photospheric network magnetic features of opposite polarity. In this paper, we subjectively adopt 30 CBPs in a coronal hole to study their eruptive behavior using data from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory. About one-quarter to one-third of the CBPs in the coronal hole go through one or more minifilament eruption(s) (MFE(s)) throughout their lifetimes. The MFEs occur in temporal association with the brightness maxima of CBPs and possibly result from the convergence and cancellation of underlying magnetic dipoles. Two examples of CBPs with MFEs are analyzed in detail, where minifilaments appear as dark features of a cool channel that divide the CBPs along the neutral lines of the dipoles beneath. The MFEs show the typical rising movements of filaments and mass ejections with brightenings at CBPs, similar to large-scale filament eruptions. Via differential emission measure analysis, it is found that CBPs are heated dramatically by their MFEs and the ejected plasmas in the MFEs have average temperatures close to the pre-eruption BP plasmas and electron densities typically near 109 cm-3. These new observational results indicate that CBPs are more complex in dynamical evolution and magnetic structure than previously thought.

MAGNETIC BRAIDING AND PARALLEL ELECTRIC FIELDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilmot-Smith, A. L.; Hornig, G.; Pontin, D. I.

2009-05-10

The braiding of the solar coronal magnetic field via photospheric motions-with subsequent relaxation and magnetic reconnection-is one of the most widely debated ideas of solar physics. We readdress the theory in light of developments in three-dimensional magnetic reconnection theory. It is known that the integrated parallel electric field along field lines is the key quantity determining the rate of reconnection, in contrast with the two-dimensional case where the electric field itself is the important quantity. We demonstrate that this difference becomes crucial for sufficiently complex magnetic field structures. A numerical method is used to relax a braided magnetic field towardmore » an ideal force-free equilibrium; the field is found to remain smooth throughout the relaxation, with only large-scale current structures. However, a highly filamentary integrated parallel current structure with extremely short length-scales is found in the field, with the associated gradients intensifying during the relaxation process. An analytical model is developed to show that, in a coronal situation, the length scales associated with the integrated parallel current structures will rapidly decrease with increasing complexity, or degree of braiding, of the magnetic field. Analysis shows the decrease in these length scales will, for any finite resistivity, eventually become inconsistent with the stability of the coronal field. Thus the inevitable consequence of the magnetic braiding process is a loss of equilibrium of the magnetic field, probably via magnetic reconnection events.« less

Solar X-ray Astronomy Sounding Rocket Program

NASA Technical Reports Server (NTRS)

Moses, J. Daniel

1989-01-01

Several broad objectives were pursued by the development and flight of the High Resolution Soft X-Ray Imaging Sounding Rocket Payload, followed by the analysis of the resulting data and by comparison with both ground based and space based observations from other investigators. The scientific objectives were: to study the thermal equilibrium of active region loop systems by analyzing the X-ray observations to determine electron temperatures, densities, and pressures; by recording the changes in the large scale coronal structures from the maximum and descending phases of Cycle 21 to the ascending phase of Cycle 22; and to extend the study of small scale coronal structures through the minimum of Cycle 21 with new emphasis on correlative observations.

The behaviour of post-retained core materials supported by coronal tooth structure in vitro.

PubMed

Russell, M D; Masood, M; Cunningham, L

1997-11-01

This study was designed to investigate the effect of retaining coronal tooth substance on the performance of post-retained core materials, and to compare the fracture resistance of the system with an intact tooth prepared to similar dimensions. Ten teeth restored with post-retained silver amalgam, and 10 teeth restored with silver-glass cermet, all with a retained single wall of coronal tooth substance, were compared with 10 unrestored teeth prepared to similar dimensions when subjected to a shearing load. The results showed no statistically significant difference between the unrestored teeth and those restored with a silver-glass cermet. Whilst the teeth restored with silver amalgam had a significantly higher fracture resistance (P > 0.01) there was greater tendency to root fracture.

Dynamics of Coronal Structures Captured During the 2012 and 2013 Total Solar Eclipses

NASA Astrophysics Data System (ADS)

Alzate, N.; Habbal, S. R.; Druckmuller, M.

2017-12-01

White light eclipse images taken during total solar eclipses provide a very high dynamic range spanning tens of solar radii starting from the solar surface. They capture the instantaneous state of the corona, including dynamic events. We present observations of the 2012 November 13 and 2013 November 3 total solar eclipses, taken by Constantinos Emmanouilidis, in which we captured high latitude tethered prominences accompanied by CMEs, as well as several `atypical' large scale structures, spanning a few solar radii above the solar surface. By complementing the eclipse observations with co-temporaneous SDO/AIA, STEREO/EUVI and SOHO/LASCO observations, we show how the shape of the atypical structures outlines the shape of faint CME shock fronts, driven by flaring activities. The tethered prominences were imaged from their anchor at the solar surface out to several solar radii. The SDO/AIA 30.4, 17.1 and 19.3 nm emission clearly show how a direct link between the cool (104 - 105 K) filamentary emission from prominence material, and the filamentary structures emitting at coronal temperatures (> 106 K), is unmistakably present. The observed survival of these tethered systems out to the field of view of LASCO C3, establishes the likely origin of counter-streaming electrons associated with CMEs observed in interplanetary space (ICMEs). They also provide new insights for CME-initiation models associated with prominence eruptions. Our work highlights the uniqueness of eclipse observations in identifying the impact of transit events on large-scale coronal structures.

Fluxes of MeV particles at Earth's orbit and their relationship with the global structure of the solar corona: Observations from SOHO

NASA Technical Reports Server (NTRS)

Posner, A.; Bothmer, V.; Kunow, H.; Heber, B.; Mueller-Mellin, R.; Delaboudiniere, J.-P.; Thompson, B. J.; Brueckner, G. E.; Howard, R. A.; Michels, D. J.

1997-01-01

The SOHO satellite, launched on 2 December 1995, combines a unique set of instruments which allow comparative studies of the interior of the sun, the outer corona and solar to be carried out. In its halo orbit around the L1 Lagrangian point of the sun-earth system, SOHO's comprehensive suprathermal and energetic particle analyzer (COSTEP) measures in situ energetic particles in the energy range of 44 keV/particle to greater than 53 MeV/n. The MeV proton, electron and helium nuclei measurements from the COSTEP electron proton helium instrument (EPHIN) were used to investigate the relationships of intensity increases of these particle species with the large-scale structures of the solar corona and heliosphere, including temporal variations. Coronal observatons are provided by the large angle spectroscopic coronagraph (LASCO) and the extreme ultraviolet imaging telescope (EIT). It was found that during times of minimum solar activity, intensity increases of the particles have two well defined sources: corotating interaction regions (CIRs) in the heliosphere related to coronal holes at the sun and coronal mass ejections.

FORWARD MODELING OF STANDING KINK MODES IN CORONAL LOOPS. II. APPLICATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Ding; Doorsselaere, Tom Van, E-mail: DYuan2@uclan.ac.uk

2016-04-15

Magnetohydrodynamic waves are believed to play a significant role in coronal heating, and could be used for remote diagnostics of solar plasma. Both the heating and diagnostic applications rely on a correct inversion (or backward modeling) of the observables into the thermal and magnetic structures of the plasma. However, due to the limited availability of observables, this is an ill-posed issue. Forward modeling is designed to establish a plausible mapping of plasma structuring into observables. In this study, we set up forward models of standing kink modes in coronal loops and simulate optically thin emissions in the extreme ultraviolet bandpasses,more » and then adjust plasma parameters and viewing angles to match three events of transverse loop oscillations observed by the Solar Dynamics Observatory/Atmospheric Imaging Assembly. We demonstrate that forward models could be effectively used to identify the oscillation overtone and polarization, to reproduce the general profile of oscillation amplitude and phase, and to predict multiple harmonic periodicities in the associated emission intensity and loop width variation.« less

THE INSTABILITY AND NON-EXISTENCE OF MULTI-STRANDED LOOPS WHEN DRIVEN BY TRANSVERSE WAVES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Magyar, N.; Van Doorsselaere, T., E-mail: norbert.magyar@wis.kuleuven.be

2016-06-01

In recent years, omni-present transverse waves have been observed in all layers of the solar atmosphere. Coronal loops are often modeled as a collection of individual strands in order to explain their thermal behavior and appearance. We perform three-dimensional (3D) ideal magnetohydrodynamics simulations to study the effect of a continuous small amplitude transverse footpoint driving on the internal structure of a coronal loop composed of strands. The output is also converted into synthetic images, corresponding to the AIA 171 and 193 Å passbands, using FoMo. We show that the multi-stranded loop ceases to exist in the traditional sense of themore » word, because the plasma is efficiently mixed perpendicularly to the magnetic field, with the Kelvin–Helmholtz instability acting as the main mechanism. The final product of our simulation is a mixed loop with density structures on a large range of scales, resembling a power-law. Thus, multi-stranded loops are unstable to driving by transverse waves, and this raises strong doubts on the usability and applicability of coronal loop models consisting of independent strands.« less

Digging into the corona: A modeling framework trained with Sun-grazing comet observations

NASA Astrophysics Data System (ADS)

Jia, Y. D.; Pesnell, W. D.; Bryans, P.; Downs, C.; Liu, W.; Schwartz, S. J.

2017-12-01

Images of comets diving into the low corona have been captured a few times in the past decade. Structures visible at various wavelengths during these encounters indicate a strong variation of the ambient conditions of the corona. We combine three numerical models: a global coronal model, a particle transportation model, and a cometary plasma interaction model into one framework to model the interaction of such Sun-grazing comets with plasma in the low corona. In our framework, cometary vapors are ionized via multiple channels and then captured by the coronal magnetic field. In seconds, these ions are further ionized into their highest charge state, which is revealed by certain coronal emission lines. Constrained by observations, we apply our framework to trace back to the local conditions of the ambient corona, and their spatial/time variation over a broad range of scales. Once trained by multiple stages of the comet's journey in the low corona, we illustrate how this framework can leverage these unique observations to probe the structure of the solar corona and solar wind.

3D Studies of the Solar Corona and its Evolution with SOHO/EIT

NASA Astrophysics Data System (ADS)

Portier-Fozzani, F.

This thesis deals with 3D evolution of coronal structures based upon the ultraviolet telescope of SOHO : EIT. Anaglyphs and incertainties on a complete stereovision reconstruction are described. Stereoscopic methods for loop reconstruction were successfully made to find 3D parameters. With dynamical stereoscopy, physical conditions were derived for 30 loops of temperature around 1MK. A method which is able to derive twist variation were also built. Emerging loops were found highly twisted and they detwist as they grow. According to helicity conservation, this correspond to a transfert of twist into expansion. Long time twist evolution of magnetic flux tubes are followed in relation with flares as relaxation. Interaction between magnetic field lines were analysed. An example of reconnection between open and closed field line were observed. Other interactions were found with multi-wavelength observations : coronal holes borders (and thus CH) are better defined when an active region nearby is growing. Other imaging techniques were used to better take profit as possible of SOHO/EIT. A multiscale vision model (MVM) was applied with success to show small coronal structures evolutions hidden by the noise level.

Hi-C Observations of an Active Region Corona, and Investigation of the Underlying Magnetic Structure

NASA Technical Reports Server (NTRS)

Tiwari, Sanjiv K.; Alexander, Caroline E.; Winebarger, Amy R.; Moore, Ronald L.

2014-01-01

Hi-C: first observational evidence of field line braiding in the AR corona; NLFFF extrapolations support. Flux emergence and/or cancellation in the coronal braided region generate large stresses and tension in the coronal field loops which is released as heat in the corona. The field in these sub-regions are highly sheared and have apparent high speed plasma flows, therefore, the contribution from shearing flows to power the coronal and transition region heating can not be ruled out! The spatial resolution of Hi-­C is five times better than AIA. The cadence of Hi-C is 2.5 - 6 times better than AIA. The 193 Å was selected because of the strong emission line of Fe XII (peak formation temperature of 1.5 MK). Hi-­C collected data for 345 s @ 5.4 s cadence. The Hi-C target region was NOAA AR 11520; 11 July 2012, 18:51-18:57 UT. NLFFF extrapolation confirms the braided structure, and free magnetic energy estimates in the given volume.

The solar corona as probed by comet Lovejoy (C/2011 W3)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raymond, J. C.; McCauley, P. I.; Cranmer, S. R.

2014-06-20

Extreme-ultraviolet images of Comet Lovejoy (C/2011 W3) from the Atmospheric Imaging Assembly show striations related to the magnetic field structure in both open and closed magnetic regions. The brightness contrast implies coronal density contrasts of at least a factor of six between neighboring flux tubes over scales of a few thousand kilometers. These density structures imply variations in the Alfvén speed on a similar scale. They will drastically affect the propagation and dissipation of Alfvén waves, and that should be taken into account in models of coronal heating and solar wind acceleration. In each striation, the cometary emission moves alongmore » the magnetic field and broadens with time. The speed and the rate of broadening are related to the parallel and perpendicular components of the velocities of the cometary neutrals when they become ionized. We use a magnetohydrodynamic model of the coronal magnetic field and the theory of pickup ions to compare the measurements with theoretical predictions, in particular with the energy lost to Alfvén waves as the cometary ions isotropize.« less

Remote Sensing Measurements of the Corona with the Solar Probe

NASA Technical Reports Server (NTRS)

Habbal, Shadia Rifai; Woo, Richard

1996-01-01

Remote sensing measurements of the solar corona are indespensible for the exploration of the source and acceleration regions of the solar wind which are inaccessible to in situ plasma, paritcles and field experiments.Furthermore, imaging the solar disk and coronal from the unique vantage point of the trajectory and the proximity of the Solar Probe spacecraft, will provide the first ever opportunity to explore the small scale structures within coronal holes and streamers from viewing angles and with spatial resolutions never attained before.

The solar atmosphere and the structure of active regions

NASA Technical Reports Server (NTRS)

Sturrock, P. A.

1974-01-01

The existence of 'holes' in the corona is reported characterized by abnormally low densities and temperatures. It was found that such coronal holes appear to be the source of high-velocity, enhanced-density streams in the solar wind as observed at the earth's orbit. It was further noted that coronal holes appear to be associated with regions of diverging magnetic fields in the corona. Models were developed to accomplish the objective for the principal energy flows in the transition region and corona.

Global Magnetohydrodynamic Modeling of the Solar Corona

NASA Technical Reports Server (NTRS)

Linker, Jon A.

1998-01-01

The coronal magnetic field defines the structure of the solar corona, the position of the heliospheric current sheet, the regions of fast and slow solar wind, and the most likely sites of coronal mass ejections. There are few measurements of the magnetic fields in the corona, but the line-of-sight component of the global magnetic fields in the photosphere have been routinely measured for many years (for example, at Stanford's Wilcox Solar Observatory, and at the National Solar Observatory at Kitt Peak). The SOI/MDI instrument is now providing high-resolution full-disk magnetograms several times a day. Understanding the large-scale structure of the solar corona and inner heliosphere requires accurately mapping the measured photospheric magnetic field into the corona and outward. Ideally, a model should not only extrapolate the magnetic field, but should self-consistently reconstruct both the plasma and magnetic fields in the corona and solar wind. Support from our NASA SR&T contract has allowed us to develop three-dimensional magnetohydrodynamic (MHD) computations of the solar corona that incorporate observed photospheric magnetic fields into the boundary conditions. These calculations not only describe the magnetic field in the corona and interplanetary spice, but also predict the plasma properties as well. Our computations thus far have been successful in reproducing many aspects of both coronal and interplanetary data, including the structure of the streamer belt, the location of coronal hole boundaries, and the position and shape of the heliospheric current sheet. The most widely used technique for extrapolating the photospheric magnetic field into the corona and heliosphere are potential field models, such as the potential field source-surface model (PFSS),and the potential field current-sheet (PFCS) model

THE ROLE OF MAGNETIC HELICITY IN STRUCTURING THE SOLAR CORONA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Knizhnik, K. J.; Antiochos, S. K.; DeVore, C. R.

Two of the most widely observed and striking features of the Sun's magnetic field are coronal loops, which are smooth and laminar, and prominences or filaments, which are strongly sheared. Loops are puzzling because they show little evidence of tangling or braiding, at least on the quiet Sun, despite the chaotic nature of the solar surface convection. Prominences are mysterious because the origin of their underlying magnetic structure—filament channels—is poorly understood at best. These two types of features would seem to be quite unrelated and wholly distinct. We argue that, on the contrary, they are inextricably linked and result frommore » a single process: the injection of magnetic helicity into the corona by photospheric motions and the subsequent evolution of this helicity by coronal reconnection. In this paper, we present numerical simulations of the response of a Parker (1972) corona to photospheric driving motions that have varying degrees of helicity preference. We obtain four main conclusions: (1) in agreement with the helicity condensation model of Antiochos (2013), the inverse cascade of helicity by magnetic reconnection in the corona results in the formation of filament channels localized about polarity inversion lines; (2) this same process removes most complex fine structure from the rest of the corona, resulting in smooth and laminar coronal loops; (3) the amount of remnant tangling in coronal loops is inversely dependent on the net helicity injected by the driving motions; and (4) the structure of the solar corona depends only on the helicity preference of the driving motions and not on their detailed time dependence. We discuss the implications of our results for high-resolution observations of the corona.« less

Coronal Loops: Observations and Modeling of Confined Plasma.

PubMed

Reale, Fabio

Coronal loops are the building blocks of the X-ray bright solar corona. They owe their brightness to the dense confined plasma, and this review focuses on loops mostly as structures confining plasma. After a brief historical overview, the review is divided into two separate but not independent parts: the first illustrates the observational framework, the second reviews the theoretical knowledge. Quiescent loops and their confined plasma are considered and, therefore, topics such as loop oscillations and flaring loops (except for non-solar ones, which provide information on stellar loops) are not specifically addressed here. The observational section discusses the classification, populations, and the morphology of coronal loops, its relationship with the magnetic field, and the loop stranded structure. The section continues with the thermal properties and diagnostics of the loop plasma, according to the classification into hot, warm, and cool loops. Then, temporal analyses of loops and the observations of plasma dynamics, hot and cool flows, and waves are illustrated. In the modeling section, some basics of loop physics are provided, supplying fundamental scaling laws and timescales, a useful tool for consultation. The concept of loop modeling is introduced and models are divided into those treating loops as monolithic and static, and those resolving loops into thin and dynamic strands. More specific discussions address modeling the loop fine structure and the plasma flowing along the loops. Special attention is devoted to the question of loop heating, with separate discussion of wave (AC) and impulsive (DC) heating. Large-scale models including atmosphere boxes and the magnetic field are also discussed. Finally, a brief discussion about stellar coronal loops is followed by highlights and open questions.

New Images of the Solar Corona

NASA Astrophysics Data System (ADS)

Gurman, Joseph B.; Thompson, Barbara J.; Newmark, Jeffrey A.; Deforest, Craig E.

In 1.5 years of operation, The Extreme Ultraviolet Imaging Telescope (EIT) on SOHO has obtained over 40,000 images of the Sun in four wavebands between 171 Angstroms and 304 Angstroms, with spatial resolution limited only by the pixel scale of 2.59 arcsec. These images, and in particular compilations of time series of images into digital movies, have changed several of our ideas about the corona at temperatures of 0.9 - 2.5 MK. For the first time, we are able to see outflow in polar plumes and microjets inputting momentum into the high-speed, polar wind flow. For the first time, in conjunction with the LASCO coronagraphs and ground-based He I imagers, we have been able to see all the structures involved in coronal mass ejections (CMEs), from the surface of the Sun to 30 solar radii above it. In several cases, we have been able to observe directly the dramatic Moreton waves emanating from the active region where the CMEs originate, and radiating across virtually the entire visible hemisphere of the Sun. We interpret these large-scale coronal disturbances as fast-mode waves. Such events appear in the SOHO-LASCO coronagraphs as earthward-directed, and several have been detected by solar wind monitoring experiments on SOHO and other spacecraft. We have been able to view a variety of small-scale phenomena as well, including motions in prominences and filaments, macrospicular and polar microjet eruptions, and fine structures in the polar crown filament belt. The multi-wavelength capability of EIT makes it possible to determine the temperature of the coronal plasma and, here, too, we have been afforded a novel view: the heating in coronal active regions occurs over a considerably larger area than the high-density loops structures alone (i.e., bright features) would indicate.

Distribution of electric currents in sunspots from photosphere to corona

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gosain, Sanjay; Démoulin, Pascal; López Fuentes, Marcelo

2014-09-20

We present a study of two regular sunspots that exhibit nearly uniform twist from the photosphere to the corona. We derive the twist parameter in the corona and in the chromosphere by minimizing the difference between the extrapolated linear force-free field model field lines and the observed intensity structures in the extreme-ultraviolet images of the Sun. The chromospheric structures appear more twisted than the coronal structures by a factor of two. Further, we derive the vertical component of electric current density, j{sub z} , using vector magnetograms from the Hinode Solar Optical Telescope (SOT). The spatial distribution of j{sub z}more » has a zebra pattern of strong positive and negative values owing to the penumbral fibril structure resolved by Hinode/SOT. This zebra pattern is due to the derivative of the horizontal magnetic field across the thin fibrils; therefore, it is strong and masks weaker currents that might be present, for example, as a result of the twist of the sunspot. We decompose j{sub z} into the contribution due to the derivatives along and across the direction of the horizontal field, which follows the fibril orientation closely. The map of the tangential component has more distributed currents that are coherent with the chromospheric and coronal twisted structures. Moreover, it allows us to map and identify the direct and return currents in the sunspots. Finally, this decomposition of j{sub z} is general and can be applied to any vector magnetogram in order to better identify the weaker large-scale currents that are associated with coronal twisted/sheared structures.« less

APPARENT CROSS-FIELD SUPERSLOW PROPAGATION OF MAGNETOHYDRODYNAMIC WAVES IN SOLAR PLASMAS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaneko, T.; Yokoyama, T.; Goossens, M.

2015-10-20

In this paper we show that the phase-mixing of continuum Alfvén waves and/or continuum slow waves in the magnetic structures of the solar atmosphere as, e.g., coronal arcades, can create the illusion of wave propagation across the magnetic field. This phenomenon could be erroneously interpreted as fast magnetosonic waves. The cross-field propagation due to the phase-mixing of continuum waves is apparent because there is no real propagation of energy across the magnetic surfaces. We investigate the continuous Alfvén and slow spectra in two-dimensional (2D) Cartesian equilibrium models with a purely poloidal magnetic field. We show that apparent superslow propagation acrossmore » the magnetic surfaces in solar coronal structures is a consequence of the existence of continuum Alfvén waves and continuum slow waves that naturally live on those structures and phase-mix as time evolves. The apparent cross-field phase velocity is related to the spatial variation of the local Alfvén/slow frequency across the magnetic surfaces and is slower than the Alfvén/sound velocities for typical coronal conditions. Understanding the nature of the apparent cross-field propagation is important for the correct analysis of numerical simulations and the correct interpretation of observations.« less

The Effects of Differential Rotation on the Magnetic Structure of the Solar Corona: MHD Simulations

NASA Technical Reports Server (NTRS)

Lionello, Roberto; Riley, Pete; Linker, Jon A.; Mikic, Zoran

2004-01-01

Coronal holes are magnetically open regions from which the solar wind streams. Magnetic reconnection has been invoked to reconcile the apparently rigid rotation of coronal holes with the differential rotation of magnetic flux in the photosphere. This mechanism might also be relevant to the formation of the slow solar wind, the properties of which seem to indicate an origin from the opening of closed magnetic field lines. We have developed a global MHD model to study the effect of differential rotation on the coronal magnetic field. Starting from a magnetic flux distribution similar to that of Wang et al., which consists of a bipolar magnetic region added to a background dipole field, we applied differential rotation over a period of 5 solar rotations. The evolution of the magnetic field and of the boundaries of coronal holes are in substantial agreement with the findings of Wang et al.. We identified examples of interchange reconnection and other changes of topology of the magnetic field. Possible consequences for the origin of the slow solar wind are also discussed.

The Brazilian decimetric array and space weather

NASA Astrophysics Data System (ADS)

Sawant, Hanumant S.; Gopalswamy, Natchimuthuk; Rosa, Reinaldo R.; Sych, Robert A.; Anfinogentov, Sergey A.; Fernandes, Francisco C. R.; Cecatto, José R.; Costa, Joaquim E. R.

2011-07-01

We report on the development and current status of the Brazilian Decimetric Array (BDA), which will play a vital role in filling the existing gaps in imaging the Sun at decimetric wavelengths. The BDA will operate in the following radio bands: 1.2-1.7, 2.8, and 5.6 GHz with high spatial and temporal resolutions. BDA can observe flares and coronal mass ejections (CMEs) in a spectral range poorly covered in the past, thus providing important information to space weather science. The smallest baseline of 9 m employed by the BDA combined with high sensitivity will readily identify large-scale structures such as coronal holes and provide information on wave flows from them. New methods are being developed to analyze the solar-disk data with high time resolution by using tomographic and spatial PWF techniques that can readily identify coronal holes in their initial stage. Efforts are also being made to analyze the BDA data in real time in conjunction with SOHO data for a better understanding of CMEs and coronal holes. This paper provides a brief description of the BDA, and the new techniques of data analysis.

Origins of the Solar Wind

NASA Technical Reports Server (NTRS)

Warren, Harry; Gurman, Joseph (Technical Monitor)

2002-01-01

This paper presented the differential emission measure analysis of SUMER observations of a coroner streamer. We found that: The coroner streamer is isothermal at all heights. This suggests that the loops comprising the streamer must have very flat temperature profiles. The coroner streamer is "overdense" relative to the predictions of hydrostatic equilibrium at most heights. At the lowest heights the streamer is actually "underdense". The SUMER temperature measurements are not consistent with those derived from simultaneous SXT observations. SXT indicates systematically higher temperatures as well as a strong temperature gradient. These SUMER measurements yield somewhat lower temperatures and no gradient in the temperature with height. Previous work has suggested that there may be a hot component to the streamer that is preferentially observed with SXT. Our analysis shows that high temperature emission lines would be observed with SUMER if this were true and thus discounts this possibility. We suggested that scattered light in SXT might produce spurious temperature measurements. The temperature and density structure of this coroner streamer are very similar to "TRACE" active region loops (flat temperature profiles, overdense relative to uniform heating, and relatively cool temperatures).

A clinically oriented comprehensive pictorial review of canine elbow anatomy.

PubMed

Constantinescu, Gheorghe M; Constantinescu, Ileana A

2009-02-01

The clinically oriented canine elbow anatomy in its complexity earned a high importance in surgery especially after multiple imaging modalities have been used in the benefit of diagnosis and treatment of canine elbow disorders. The bony, joint, and muscular structures, the arteries, the veins and the nerves supplying the elbow are described and illustrated in textbooks and atlases in the context of the comparative anatomy. Nevertheless, there is no publication focused on all of these structures described together from the skin to the bones in a systematic and topographic order, nor through cross and/or sagittal and coronal sections. The figures used in this article are original and drawn after dissection, cross, sagittal, and coronal sections of the elbow structures. The sections are correlated to the multiple imaging modalities shown in the next article.

Physics of magnetic flux ropes

NASA Astrophysics Data System (ADS)

Russell, C. T.; Priest, E. R.; Lee, L. C.

The present work encompasses papers on the structure, waves, and instabilities of magnetic flux ropes (MFRs), photospheric flux tubes (PFTs), the structure and heating of coronal loops, solar prominences, coronal mass ejections and magnetic clouds, flux ropes in planetary ionospheres, the magnetopause, magnetospheric field-aligned currents and flux tubes, and the magnetotail. Attention is given to the equilibrium of MFRs, resistive instability, magnetic reconnection and turbulence in current sheets, dynamical effects and energy transport in intense flux tubes, waves in solar PFTs, twisted flux ropes in the solar corona, an electrodynamical model of solar flares, filament cooling and condensation in a sheared magnetic field, the magnetopause, the generation of twisted MFRs during magnetic reconnection, ionospheric flux ropes above the South Pole, substorms and MFR structures, evidence for flux ropes in the earth magnetotail, and MFRs in 3D MHD simulations.

Microflaring in Low-Lying Core Fields and Extended Coronal Heating in the Quiet Sun

NASA Technical Reports Server (NTRS)

Porter, Jason G.; Falconer, D. A.; Moore, Ronald L.

1999-01-01

We have previously reported analyses of Yohkoh SXT data examining the relationship between the heating of extended coronal loops (both within and stemming from active regions) and microflaring in core fields lying along neutral lines near their footpoints (J. G. Porter, D. A. Falconer, and R. L. Moore 1998, in Solar Jets and Coronal Plumes, ed. T. Guyenne, ESA SP-421, and references therein). We found a surprisingly poor correlation of intensity variations in the extended loops with individual microflares in the compact heated areas at their feet, despite considerable circumstancial evidence linking the heating processes in these regions. Now, a study of Fe XII image sequences from SOHO EIT show that similar associations of core field structures with the footpoints of very extended coronal features can be found in the quiet Sun. The morphology is consistent with the finding of Wang et al. (1997, ApJ 484, L75) that polar plumes are rooted at sites of mixed polarity in the magnetic network. We find that the upstairs/downstairs intensity variations often follow the trend, identified in the active region observations, of a weak correspondence. Apparently much of the coronal heating in the extended loops is driven by a type of core field magnetic activity that is "cooler" than the events having the coronal signature of microflares, i.e., activity that results in little heating within the core fields themselves. This work was funded by the Solar Physics Branch of NASA's Office of Space Science through the SR&T Program and the SEC Guest Investigator Program.

OBSERVATIONAL SIGNATURES OF CORONAL LOOP HEATING AND COOLING DRIVEN BY FOOTPOINT SHUFFLING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dahlburg, R. B.; Taylor, B. D.; Einaudi, G.

The evolution of a coronal loop is studied by means of numerical simulations of the fully compressible three-dimensional magnetohydrodynamic equations using the HYPERION code. The footpoints of the loop magnetic field are advected by random motions. As a consequence, the magnetic field in the loop is energized and develops turbulent nonlinear dynamics characterized by the continuous formation and dissipation of field-aligned current sheets: energy is deposited at small scales where heating occurs. Dissipation is nonuniformly distributed so that only a fraction of the coronal mass and volume gets heated at any time. Temperature and density are highly structured at scalesmore » that, in the solar corona, remain observationally unresolved: the plasma of our simulated loop is multithermal, where highly dynamical hotter and cooler plasma strands are scattered throughout the loop at sub-observational scales. Numerical simulations of coronal loops of 50,000 km length and axial magnetic field intensities ranging from 0.01 to 0.04 T are presented. To connect these simulations to observations, we use the computed number densities and temperatures to synthesize the intensities expected in emission lines typically observed with the Extreme Ultraviolet Imaging Spectrometer on Hinode. These intensities are used to compute differential emission measure distributions using the Monte Carlo Markov Chain code, which are very similar to those derived from observations of solar active regions. We conclude that coronal heating is found to be strongly intermittent in space and time, with only small portions of the coronal loop being heated: in fact, at any given time, most of the corona is cooling down.« less

Nature and Variability of Coronal Streamers and their Relationship to the Slow Speed Wind

NASA Technical Reports Server (NTRS)

Strachan, Leonard

2005-01-01

NASA Grant NAG5-12781 is a study on the "Nature and Variability of Coronal Streamers and their Relationship to the Slow Speed Wind." The two main goals of this study are to identify: 1) Where in the streamer structure does the solar wind originate, and 2) What coronal conditions are responsible for the variability of the slow speed wind. To answer the first question, we examined the mostly closed magnetic field regions in streamer cores to search for evidence of outflow. Preliminary results from the OVI Doppler dimming ratios indicates that most of the flow originates from the edges of coronal streamers but this idea should be confirmed by a comparison of the coronal plasma properties with in situ solar wind data. To answer the second question, the work performed thus far suggests that solar minimum streamers have larger perpendicular velocity distributions than do solar maximum streamers. If it can be shown that solar minimum streamers also produce higher solar wind speeds then this would suggest that streamers and coronal holes have similar solar wind acceleration mechanisms. The key to both questions lie in the analysis of the in situ solar wind data sets. This work was not able to be completed during the period of performance and therefore the grant was formally extended for an additional year at no cost to NASA. We hope to have final results and a publication by the end of the calendar year 2004. The SAO personnel involved in the research are Leonard Strachan (PI), Mari Paz Miralles, Alexander Panasyuk, and a Southern University student Michael Baham.

THE ROLE OF THE INNER CORONAL NULL POINT IN THE FORMATION AND EVOLUTION OF SOLAR QUIESCENT PROMINENCES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Y. Z., E-mail: yzzhangmail@sohu.com

2015-02-10

Using a 2.5-dimensional MHD simulation, we investigate the role played by the inner coronal null point in the formation and evolution of solar quiescent prominences. The flux rope is characterized by its magnetic fluxes, the toroidal magnetic flux Φ {sub p} and the poloidal flux Φ{sub ψ}. It is found that for a given Φ {sub p}, the catastrophe does not occur in the flux rope system until Φ{sub ψ} increases to a critical point. Moreover, the magnetic flux of the null point is the maximum value of the magnetic flux in the quadrupole background magnetic field, and represented bymore » ψ {sub N}. The results show that the bigger ψ {sub N} usually corresponds to the smaller catastrophic point, the lower magnetic energy of the flux rope system, and the lesser magnetic energy inside the flux rope. Our results confirm that catastrophic disruption of the prominence occurs more easily when there is a bigger ψ {sub N}. However, ψ {sub N} has little influence on the maximum speed of the coronal mass ejections (CMEs) with an erupted prominence. Thus we argue that a topological configuration with the inner coronal null point is a necessary structure for the formation and evolution of solar quiescent prominences. In conclusion, it is easier for the prominences to form and to erupt as a core part of the CMEs in the magnetic structure with a greater ψ {sub N}.« less

Energy-Containing Length Scale at the Base of a Coronal Hole: New Observational Findings

NASA Astrophysics Data System (ADS)

Abramenko, V.; Dosch, A.; Zank, G. P.; Yurchyshyn, V.; Goode, P. R.

2012-12-01

Dynamics of the photospheric flux tubes is thought to be a key factor for generation and propagation of MHD waves and magnetic stress into the corona. Recently, New Solar Telescope (NST, Big Bear Solar Observatory) imaging observations in helium I 10830 Å revealed ultrafine, hot magnetic loops reaching from the photosphere to the corona and originating from intense, compact magnetic field elements. One of the essential input parameters to run the models of the fast solar wind is a characteristic energy-containing length scale, lambda, of the dynamical structures transverse to the mean magnetic field in a coronal hole (CH) in the base of the corona. We used NST time series of solar granulation motions to estimate the velocity fluctuations, as well as NST near-infrared magnetograms to derive the magnetic field fluctuations. The NST adaptive optics corrected speckle-reconstructed images of 10 seconds cadence were an input for the local correlation tracking (LCT) code to derive the squared transverse velocity patterns. We found that the characteristic length scale for the energy-carrying structures in the photosphere is about 300 km, which is two orders of magnitude lower than it was adopted in previous models. The influence of the result on the coronal heating and fast solar wind modeling will be discussed.; Correlation functions calculated from the squared velocities for the three data sets: a coronal hole, quiet sun and active region plage area.

Faraday Rotation and Models for the Plasma Structure of the Solar Corona

NASA Astrophysics Data System (ADS)

Mancuso, Salvatore; Spangler, Steven R.

2000-08-01

Faraday rotation observations of polarized radiation from natural radio sources are unique among remote diagnostics of the solar corona in that they provide information on the coronal magnetic field. Dual frequency radio polarization measurements yield the rotation measure, a quantity that is proportional to the integral along the line of sight of the product of the electron density and the line-of-sight component of the magnetic field. We made linear polarization observations with the NRAO Very Large Array of 13 polarized radio sources occulted by the solar corona. The observations were made at frequencies of 1465 and 1665 MHz on four days in 1997 May and cover a 20 day period, sampling elongations ranging from about 5 to 14 Rsolar. The magnitudes of the rotation measures observed range from about 11 to 0 rad m-2. The relatively low values for the rotation measures are due to the solar minimum configuration of the corona at the time of the observations, with the lines of sight to the sources generally not crossing sector boundaries. The largest rotation measure was observed for the extended radio source 3C 79 on 1997 May 11 and corresponds to a case in which the line of sight passed next to the streamer belt at small solar elongations. We have developed a three-dimensional model of the solar corona that is in excellent agreement with the observed rotation measures, as well as being completely consistent with other coronal diagnostics such as coronagraph images. In particular, our observations support the coronal magnetic field model of Pätzold et al. (1987) they would be inconsistent with coronal magnetic fields significantly weaker or stronger than this model. The plasma density distribution in the corona is successfully modeled by a dense streamer belt component and a more tenuous coronal hole component. Details of these models are given in § 3 of this paper. The principal disagreement between the model and observations occurs for three lines of sight for which the model predicts nearly zero rotation measure but for which we measure small but significant values of -1 to -2 rad m-2. These lines of sight passed over the solar polar regions. We discuss the possibility that these residual rotation measures are due to static coronal plasma structures, not described by global coronal models, or to very long wavelength coronal Alfvén waves. Fluctuations in the rotation measure on timescales of a few hours were observed for some sources and not others. When detected, they were of order 1-2 rad m-2 and occurred on timescales of several hours.

Slow Solar Wind: Observations and Modeling

NASA Technical Reports Server (NTRS)

Abbo, L.; Ofman, L.; Antiochos, S. K.; Hansteen, V. H.; Harra, L.; Ko, Y.-K.; Lapenta, G.; Li, B.; Riley, P.; Strachan, L.;

Coronal mass ejections and coronal structures

NASA Technical Reports Server (NTRS)

Hildner, E.; Bassi, J.; Bougeret, J. L.; Duncan, R. A.; Gary, D. E.; Gergely, T. E.; Harrison, R. A.; Howard, R. A.; Illing, R. M. E.; Jackson, B. V.

1986-01-01

Research on coronal mass ejections (CMF) took a variety of forms, both observational and theoretical. On the observational side there were: case studies of individual events, in which it was attempted to provide the most complete descriptions possible, using correlative observations in diverse wavelengths; statistical studies of the properties CMEs and their associated activity; observations which may tell us about the initiation of mass ejections; interplanetary observations of associated shocks and energetic particles even observations of CMEs traversing interplanetary space; and the beautiful synoptic charts which show to what degree mass ejections affect the background corona and how rapidly (if at all) the corona recovers its pre-disturbance form. These efforts are described in capsule form with an emphasis on presenting pictures, graphs, and tables so that the reader can form a personal appreciation of the work and its results.

Morphology Of A Hot Prominence Cavity Observed with Hinode/XRT and SDO/AIA

NASA Technical Reports Server (NTRS)

Weber, Mark A.; Reeves, K. K.; Gibson, S. E.; Kucera, T. A.

2012-01-01

Prominence cavities appear as circularly shaped voids in coronal emission over polarity inversion lines where a prominence channel is straddling the solar limb. The presence of chromospheric material suspended at coronal altitudes is a common but not necessary feature within these cavities. These voids are observed to change shape as a prominence feature rotates around the limb. We use a morphological model projected in cross-sections to fit the cavity emission in Hinode/XRT passbands, and then apply temperature diagnostics to XRT and SDO/AIA data to investigate the thermal structure. We find significant evidence that the prominence cavity is hotter than the corona immediately outside the cavity boundary. This investigation follows upon "Thermal Properties of A Solar Coronal Cavity Observed with the X-ray Telescope on Hinode" by Reeves et al., 2012, ApJ, in press.

Active Region Jets II: Triggering and Evolution of Violent Jets

NASA Astrophysics Data System (ADS)

Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David; Panesar, Navdeep K.; Martinez, Francisco

2017-08-01

We study a series of X-ray-bright, rapidly evolving active-region coronal jets outside the leading sunspot of AR 12259, using Hinode/XRT, SDO/AIA and HMI, and IRIS/SJ data. The detailed evolution of such rapidly evolving “violent” jets remained a mystery after our previous investigation of active region jets (Sterling et al. 2016, ApJ, 821, 100). The jets we investigate here erupt from three localized subregions, each containing a rapidly evolving (positive) minority-polarity magnetic-flux patch bathed in a (majority) negative-polarity magnetic-flux background. At least several of the jets begin with eruptions of what appear to be thin (thickness ˜<2‧‧) miniature-filament (minifilament) “strands” from a magnetic neutral line where magnetic flux cancelation is ongoing, consistent with the magnetic configuration presented for coronal-hole jets in Sterling et al. (2015, Nature, 523, 437). For some jets strands are difficult/ impossible to detect, perhaps due to their thinness, obscuration by surrounding bright or dark features, or the absence of erupting cool-material minifilaments in those jets. Tracing in detail the flux evolution in one of the subregions, we find bursts of strong jetting occurring only during times of strong flux cancelation. Averaged over seven jetting episodes, the cancelation rate was ~1.5×10^19 Mx/hr. An average flux of ~5×10^18 Mx canceled prior to each episode, arguably building up ~10^28—10^29 ergs of free magnetic energy per jet. From these and previous observations, we infer that flux cancelation is the fundamental process responsible for the pre-eruption buildup and triggering of at least many jets in active regions, quiet regions, and coronal holes.

LATERAL OFFSET OF THE CORONAL MASS EJECTIONS FROM THE X-FLARE OF 2006 DECEMBER 13 AND ITS TWO PRECURSOR ERUPTIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sterling, Alphonse C.; Moore, Ronald L.; Harra, Louise K., E-mail: alphonse.sterling@nasa.gov, E-mail: ron.moore@nasa.gov, E-mail: lkh@mssl.ucl.ac.uk

2011-12-10

Two GOES sub-C-class precursor eruptions occurred within {approx}10 hr prior to and from the same active region as the 2006 December 13 X4.3-class flare. Each eruption generated a coronal mass ejection (CME) with center laterally far offset ({approx}> 45 Degree-Sign ) from the co-produced bright flare. Explaining such CME-to-flare lateral offsets in terms of the standard model for solar eruptions has been controversial. Using Hinode/X-Ray Telescope (XRT) and EUV Imaging Spectrometer (EIS) data, and Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph (LASCO) and Michelson Doppler Imager (MDI) data, we find or infer the following. (1) The first precursormore » was a 'magnetic-arch-blowout' event, where an initial standard-model eruption of the active region's core field blew out a lobe on one side of the active region's field. (2) The second precursor began similarly, but the core-field eruption stalled in the side-lobe field, with the side-lobe field erupting {approx}1 hr later to make the CME either by finally being blown out or by destabilizing and undergoing a standard-model eruption. (3) The third eruption, the X-flare event, blew out side lobes on both sides of the active region and clearly displayed characteristics of the standard model. (4) The two precursors were offset due in part to the CME originating from a side-lobe coronal arcade that was offset from the active region's core. The main eruption (and to some extent probably the precursor eruptions) was offset primarily because it pushed against the field of the large sunspot as it escaped outward. (5) All three CMEs were plausibly produced by a suitable version of the standard model.« less

On the Relationship Between Solar Wind Speed, Geomagnetic Activity, and the Solar Cycle Using Annual Values

NASA Technical Reports Server (NTRS)

Wilson, Robert M.; Hathaway, David H.

2008-01-01

The aa index can be decomposed into two separate components: the leading sporadic component due to solar activity as measured by sunspot number and the residual or recurrent component due to interplanetary disturbances, such as coronal holes. For the interval 1964-2006, a highly statistically important correlation (r = 0.749) is found between annual averages of the aa index and the solar wind speed (especially between the residual component of aa and the solar wind speed, r = 0.865). Because cyclic averages of aa (and the residual component) have trended upward during cycles 11-23, cyclic averages of solar wind speed are inferred to have also trended upward.

More Macrospicule Jets in On-Disk Coronal Holes

NASA Astrophysics Data System (ADS)

Adams, Mitzi; Sterling, Alphonse; Moore, Ronald

2015-04-01

We examine the magnetic structure and dynamics of multiple jets found in coronal holes close to or at disk center. All data are from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO). We report on observations of about ten jets in an equatorial coronal hole spanning 2011 February 27 and 28. We show the evolution of these jets in AIA 193 Å, examine the magnetic field configuration and flux changes in the jet area, and discuss the probable trigger mechanism of these events. We reported on another jet in this same coronal hole on 2011 February 27, ~13:04 UT (Adams et al 2014, ApJ, 783: 11). That jet is a previously unrecognized variety of blowout jet, in which the base-edge bright point is a miniature filament-eruption flare arcade made by internal reconnection of the legs of the erupting field. In contrast, in the presently-accepted "standard" picture for blowout jets, the base-edge bright point is made by interchange reconnection of initially-closed erupting jet-base field with ambient open field. This poster presents further evidence of the production of the base-edge bright point in blowout jets by internal reconnection. Our observations suggest that most of the bigger and brighter EUV jets in coronal holes are blowout jets of the new-found variety.

More Macrospicule Jets in On-Disk Coronal Holes

NASA Technical Reports Server (NTRS)

Adams, M. L.; Sterling, A. C.; Moore, R. L.

2015-01-01

We examine the magnetic structure and dynamics of multiple jets found in coronal holes close to or on disk center. All data are from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO). We report on observations of about ten jets in an equatorial coronal hole spanning 2011 February 27 and 28. We show the evolution of these jets in AIA 193 A, examine the magnetic field configuration and flux changes in the jet area, and discuss the probable trigger mechanism of these events. We reported on another jet in this same coronal hole on 2011 February 27, (is) approximately 13:04 UT (Adams et al 2014, ApJ, 783: 11). That jet is a previously-unrecognized variety of blowout jet, in which the base-edge bright point is a miniature filament-eruption flare arcade made by internal reconnection of the legs of the erupting field. In contrast, in the presently-accepted 'standard' picture for blowout jets, the base-edge bright point is made by interchange reconnection of initially-closed erupting jet-base field with ambient open field. This poster presents further evidence of the production of the base-edge bright point in blowout jets by internal reconnection. Our observations suggest that most of the bigger and brighter EUV jets in coronal holes are blowout jets of the new-found variety.

Coronal bright points associated with minifilament eruptions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Junchao; Jiang, Yunchun; Yang, Jiayan

2014-12-01

Coronal bright points (CBPs) are small-scale, long-lived coronal brightenings that always correspond to photospheric network magnetic features of opposite polarity. In this paper, we subjectively adopt 30 CBPs in a coronal hole to study their eruptive behavior using data from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory. About one-quarter to one-third of the CBPs in the coronal hole go through one or more minifilament eruption(s) (MFE(s)) throughout their lifetimes. The MFEs occur in temporal association with the brightness maxima of CBPs and possibly result from the convergence and cancellationmore » of underlying magnetic dipoles. Two examples of CBPs with MFEs are analyzed in detail, where minifilaments appear as dark features of a cool channel that divide the CBPs along the neutral lines of the dipoles beneath. The MFEs show the typical rising movements of filaments and mass ejections with brightenings at CBPs, similar to large-scale filament eruptions. Via differential emission measure analysis, it is found that CBPs are heated dramatically by their MFEs and the ejected plasmas in the MFEs have average temperatures close to the pre-eruption BP plasmas and electron densities typically near 10{sup 9} cm{sup –3}. These new observational results indicate that CBPs are more complex in dynamical evolution and magnetic structure than previously thought.« less

SYMPATHETIC FILAMENT ERUPTIONS CONNECTED BY CORONAL DIMMINGS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang Yunchun; Yang Jiayan; Hong Junchao

2011-09-10

We present for the first time detailed observations of three successive, interdependent filament eruptions that occurred one by one within 5 hr from different locations beyond the range of a single active region. The first eruption was observed from an active region and was associated with a coronal mass ejection (CME), during which diffuse and complex coronal dimmings formed, largely extending to the two other filaments located in quiet-Sun regions. Then, both quiescent filaments consecutively underwent the second and third eruptions, while the nearby dimmings were persistent. Comparing the result of a derived coronal magnetic configuration, the magnetic connectivity betweenmore » the dimmings suggested that they were caused by the joint effect of simple expansion of overlying loop systems forced by the first eruption, as well as by its erupting field interacting or reconnecting with the surrounding magnetic structures. Note that the dimming process in the first eruption indicated a weakening and partial removal of an overlying magnetic field constraint on the two other filaments, and thus one can physically connect these eruptions as sympathetic. It appears that the peculiar magnetic field configuration in our event was largely favorable to the occurrence of sympathetic filament eruptions. Because coronal dimmings are frequent and common phenomena in solar eruptions, especially in CME events, it is very likely that they represent a universal agent that can link consecutive eruptions nearby with sympathetic eruptions.« less

The Interior Structure, Dynamics, and Heliospheric Impact of Reconnection-Driven Solar Coronal Hole Jets

NASA Astrophysics Data System (ADS)

Roberts, Merrill Alan

From bright loop structures and polar plumes to solar flares and coronal mass ejections (CMEs), our Sun has shown itself to be a highly dynamic star over a multitude of spatial and temporal scales. In fact, as the resolutions of our observations have improved, it has become clear that even coronal holes, the Sun's so called dark and quiet regions, are full of activity. Coronal hole (CH) jets are one example of this activity, a solar transient that occurs ubiquitously in coronal hole regions and which may contribute significant mass and energy to the corona and the solar wind. CH jets have been shown to share many properties with their larger and more energetic cousins, flares and CMEs, thereby providing an opportunity to understand these more complex and infrequent solar features. CH jets may also provide a source for microstreams and torsional Alfven waves found in the solar wind and interplanetary medium, as well as insight into basic processes for driving the fast solar wind and heating the corona. The purpose of this work is to deepen our understanding of CH jets by examining state-of-the-art fully 3D MHD simulations of CH jet eruptions. First, we investigate the internal structure and turbulent flows inside a model CH jet through an analysis of the simulation described by Karpen et al. (2017). An analysis of the radial variability within the simulated jet is performed, as well as a multi-scale turbulence analysis. We confirm the occurrence of multi-scale MHD turbulence within the model jet, and show that the resulting jet wake can be divided into three radially stratified regions based on its internal structure. Second, the 3D model space is extended to 60 solar radii and simulated encounters of the soon-to-be-launched Parker Solar Probe (PSP, Fox et al., 2016) mission with our model jet are produced and analyzed in order to identify signatures that may be seen in the eventual PSP observations. Our results suggest that PSP should encounter CH jets in situ, and that each of the three jet regions found have unique, identifiable signatures that could be detected by PSP. These findings suggest that CH jets are internally complex, with multi-scale, radially stratified internal structure which evolves as the jet progresses through the heliosphere. PSP will have a unique opportunity to observe this newly predicted and previously unobserved fine structure when it descends into the corona in the 2020s, and our results will serve to interpret the PSP data, as well as provide a means to test the validity of our model by comparison with them.

Thermal Properties of A Solar Coronal Cavity Observed with the X-Ray Telescope on Hinode

NASA Technical Reports Server (NTRS)

Reeves, Katherine K.; Gibson, Sarah E.; Kucera, Theresa A.; Hudson, Hugh S.; Kano, Ryouhei

2011-01-01

Coronal cavities are voids in coronal emission often observed above high latitude filament channels. Sometimes, these cavities have areas of bright X-ray emission in their centers. In this study, we use data from the X-ray Telescope (XRT) on the Hinode satellite to examine the thermal emission properties of a cavity observed during July 2008 that contains bright X-ray emission in its center. Using ratios of XRT filters, we find evidence for elevated temperatures in the cavity center. The area of elevated temperature evolves from a ring-shaped structure at the beginning of the observation, to an elongated structure two days later, finally appearing as a compact round source four days after the initial observation. We use a morphological model to fit the cavity emission, and find that a uniform structure running through the cavity does not fit the observations well. Instead, the observations are reproduced by modeling several short cylindrical cavity "cores" with different parameters on different days. These changing core parameters may be due to some observed activity heating different parts of the cavity core at different times. We find that core temperatures of 1.75 MK, 1.7 MK and 2.0 MK (for July 19, July 21 and July 23, respectively) in the model lead to structures that are consistent with the data, and that line-of-sight effects serve to lower the effective temperature derived from the filter ratio.

Coronal bright points in microwaves

NASA Technical Reports Server (NTRS)

Kundu, M. R.; Nitta, N.

1988-01-01

An excellent map of the quiet sun showing coronal bright points at 20-cm wavelength was produced using the VLA on February 13, 1987. The locations of bright points (BPs) were studied relative to features on the photospheric magnetogram and Ca K spectroheliogram. Most bright points appearing in the full 5-hour synthesized map are associated with small bipolar structures on the photospheric magnetogram; and the brightest part of a BP tends to lie on the boundary of a supergranulation network. The bright points exhibit rapid variations in intensity superposed on an apparently slow variation.

IMPULSIVE PHASE CORONAL HARD X-RAY SOURCES IN AN X3.9 CLASS SOLAR FLARE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen Qingrong; Petrosian, Vahe, E-mail: qrchen@gmail.com, E-mail: vahep@stanford.edu

2012-03-20

We present the analysis of a pair of unusually energetic coronal hard X-ray (HXR) sources detected by the Reuven Ramaty High Energy Solar Spectroscopic Imager during the impulsive phase of an X3.9 class solar flare on 2003 November 3, which simultaneously shows two intense footpoint (FP) sources. A distinct loop top (LT) coronal source is detected up to {approx}150 keV and a second (upper) coronal source up to {approx}80 keV. These photon energies, which were not fully investigated in earlier analysis of this flare, are much higher than commonly observed in coronal sources and pose grave modeling challenges. The LTmore » source in general appears higher in altitude with increasing energy and exhibits a more limited motion compared to the expansion of the thermal loop. The high-energy LT source shows an impulsive time profile and its nonthermal power-law spectrum exhibits soft-hard-soft evolution during the impulsive phase, similar to the FP sources. The upper coronal source exhibits an opposite spatial gradient and a similar spectral slope compared to the LT source. These properties are consistent with the model of stochastic acceleration of electrons by plasma waves or turbulence. However, the LT and FP spectral index difference (varying from {approx}0 to 1) is much smaller than commonly measured and than that expected from a simple stochastic acceleration model. Additional confinement or trapping mechanisms of high-energy electrons in the corona are required. Comprehensive modeling including both kinetic effects and the macroscopic flare structure may shed light on this behavior. These results highlight the importance of imaging spectroscopic observations of the LT and FP sources up to high energies in understanding electron acceleration in solar flares. Finally, we show that the electrons producing the upper coronal HXR source may very likely be responsible for the type III radio bursts at the decimetric/metric wavelength observed during the impulsive phase of this flare.« less

Brightness and magnetic evolution of solar coronal bright points

NASA Astrophysics Data System (ADS)

Ugarte Urra, Ignacio

This thesis presents a study of the brightness and magnetic evolution of several Extreme ultraviolet (EUV) coronal bright points (hereafter BPs). The study was carried out using several instruments on board the Solar and Heliospheric Observatory, supported by the high resolution imaging from the Transition Region And Coronal Explorer. The results confirm that, down to 1" resolution, BPs are made of small loops with lengths of [approximate]6 Mm and cross-sections of ≈2 Mm. The loops are very dynamic, evolving in time scales as short as 1 - 2 minutes. This is reflected in a highly variable EUV response with fluctuations highly correlated in spectral lines at transition region temperatures, but not always at coronal temperatures. A wavelet analysis of the intensity variations reveals the existence of quasi-periodic oscillations with periods ranging 400--1000s, in the range of periods characteristic of the chromospheric network. The link between BPs and network bright points is discussed, as well as the interpretation of the oscillations in terms of global acoustic modes of closed magnetic structures. A comparison of the magnetic flux evolution of the magnetic polarities to the EUV flux changes is also presented. Throughout their lifetime, the intrinsic EUV emission of BPs is found to be dependent on the total magnetic flux of the polarities. In short time scales, co-spatial and co-temporal coronal images and magnetograms, reveal the signature of heating events that produce sudden EUV brightenings simultaneous to magnetic flux cancellations. This is interpreted in terms of magnetic reconnection events. Finally, a electron density study of six coronal bright points produces values of ≈1.6×10 9 cm -3 , closer to active region plasma than to quiet Sun. The analysis of a large coronal loop (half length of 72 Mm) introduces the discussion on the prospects of future plasma diagnostics of BPs with forthcoming solar missions.

SUNSPOT ROTATION AS A DRIVER OF MAJOR SOLAR ERUPTIONS IN THE NOAA ACTIVE REGION 12158

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vemareddy, P.; Ravindra, B.; Cheng, X., E-mail: vemareddy@iiap.res.in

We studied the development conditions of sigmoid structure under the influence of the magnetic non-potential characteristics of a rotating sunspot in the active region (AR) 12158. Vector magnetic field measurements from the Helioseismic Magnetic Imager and coronal EUV observations from the Atmospheric Imaging Assembly reveal that the erupting inverse-S sigmoid had roots at the location of the rotating sunspot. The sunspot rotates at a rate of 0°–5° h{sup −1} with increasing trend in the first half followed by a decrease. The time evolution of many non-potential parameters had a good correspondence with the sunspot rotation. The evolution of the ARmore » magnetic structure is approximated by a time series of force-free equilibria. The non-linear force-free field magnetic structure around the sunspot manifests the observed sigmoid structure. Field lines from the sunspot periphery constitute the body of the sigmoid and those from the interior overlie the sigmoid, similar to a flux rope structure. While the sunspot was rotating, two major coronal mass ejection eruptions occurred in the AR. During the first (second) event, the coronal current concentrations were enhanced (degraded), consistent with the photospheric net vertical current; however, magnetic energy was released during both cases. The analysis results suggest that the magnetic connections of the sigmoid are driven by the slow motion of sunspot rotation, which transforms to a highly twisted flux rope structure in a dynamical scenario. Exceeding the critical twist in the flux rope probably leads to the loss of equilibrium, thus triggering the onset of the two eruptions.« less

Morphology of a Hot Coronal Cavity Core as Observed by Hinode/XRT

NASA Technical Reports Server (NTRS)

Reeves, K. K.; Gibson, S. E.; Kucera, T. A.; Hudson, H. S.

2010-01-01

We follow a coronal cavity that was observed by Hinode/XRT during the summer of 2008. This cavity has a persistent area of relatively bright X-ray emission in its center. We use multifilter data from XRT to study the thermal emission from this cavity, and find that the bright center is hotter than the surrounding cavity plasma with temperatures of about 1.6 MK. We follow the morphology of this hot feature as the cavity structure rotates over the limb during the several days between July 19 - 23 2008. We find that the hot structure at first looks fairly circular, then appears to expand and elongate, and then shrinks again to a compact circular shape. We interpret this apparent change in shape as being due to the morphology of the filament channel associated with the cavity, and the change in viewing angle as the structure rotates over the limb of the Sun.

FLOWS AND WAVES IN BRAIDED SOLAR CORONAL MAGNETIC STRUCTURES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pant, V.; Datta, A.; Banerjee, D., E-mail: vaibhav@iiap.res.in

We study the high frequency dynamics in the braided magnetic structure of an active region (AR 11520) moss as observed by the High-Resolution Coronal Imager (Hi-C). We detect quasi-periodic flows and waves in these structures. We search for high frequency dynamics while looking at power maps of the observed region. We find that shorter periodicities (30–60 s) are associated with small spatial scales which can be resolved by Hi-C only. We detect quasi-periodic flows with a wide range of velocities, from 13–185 km s{sup −1}, associated with braided regions. This can be interpreted as plasma outflows from reconnection sites. Wemore » also find short period and large amplitude transverse oscillations associated with the braided magnetic region. Such oscillations could be triggered by reconnection or such oscillations may trigger reconnection.« less

COMPARISON OF ADAPTIVE STATISTICAL ITERATIVE RECONSTRUCTION (ASIR™) AND MODEL-BASED ITERATIVE RECONSTRUCTION (VEO™) FOR PAEDIATRIC ABDOMINAL CT EXAMINATIONS: AN OBSERVER PERFORMANCE STUDY OF DIAGNOSTIC IMAGE QUALITY.

PubMed

Hultenmo, Maria; Caisander, Håkan; Mack, Karsten; Thilander-Klang, Anne

2016-06-01

The diagnostic image quality of 75 paediatric abdominal computed tomography (CT) examinations reconstructed with two different iterative reconstruction (IR) algorithms-adaptive statistical IR (ASiR™) and model-based IR (Veo™)-was compared. Axial and coronal images were reconstructed with 70 % ASiR with the Soft™ convolution kernel and with the Veo algorithm. The thickness of the reconstructed images was 2.5 or 5 mm depending on the scanning protocol used. Four radiologists graded the delineation of six abdominal structures and the diagnostic usefulness of the image quality. The Veo reconstruction significantly improved the visibility of most of the structures compared with ASiR in all subgroups of images. For coronal images, the Veo reconstruction resulted in significantly improved ratings of the diagnostic use of the image quality compared with the ASiR reconstruction. This was not seen for the axial images. The greatest improvement using Veo reconstruction was observed for the 2.5 mm coronal slices. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

FAST CONTRACTION OF CORONAL LOOPS AT THE FLARE PEAK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu Rui; Wang Haimin

On 2005 September 8, a coronal loop overlying the active region NOAA 10808 was observed in TRACE 171 A to contract at {approx}100 km s{sup -1} at the peak of an X5.4-2B flare at 21:05 UT. Prior to the fast contraction, the loop underwent a much slower contraction at {approx}6 km s{sup -1} for about 8 minutes, initiating during the flare preheating phase. The sudden switch to fast contraction is presumably corresponding to the onset of the impulsive phase. The contraction resulted in the oscillation of a group of loops located below, with the period of about 10 minutes. Meanwhile,more » the contracting loop exhibited a similar oscillatory pattern superimposed on the dominant downward motion. We suggest that the fast contraction reflects a suddenly reduced magnetic pressure underneath due either to (1) the eruption of magnetic structures located at lower altitudes or to (2) the rapid conversion of magnetic free energy in the flare core region. Electrons accelerated in the shrinking trap formed by the contracting loop can theoretically contribute to a late-phase hard X-ray burst, which is associated with Type IV radio emission. To complement the X5.4 flare which was probably confined, a similar event observed in SOHO/EIT 195 A on 2004 July 20 in an eruptive, M8.6 flare is briefly described, in which the contraction was followed by the expansion of the same loop leading up to a halo coronal mass ejection. These observations further substantiate the conjecture of coronal implosion and suggest coronal implosion as a new exciter mechanism for coronal loop oscillations.« less

Force-free field modeling of twist and braiding-induced magnetic energy in an active-region corona

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thalmann, J. K.; Tiwari, S. K.; Wiegelmann, T., E-mail: julia.thalmann@uni-graz.at

2014-01-01

The theoretical concept that braided magnetic field lines in the solar corona may dissipate a sufficient amount of energy to account for the brightening observed in the active-region (AR) corona has only recently been substantiated by high-resolution observations. From the analysis of coronal images obtained with the High Resolution Coronal Imager, first observational evidence of the braiding of magnetic field lines was reported by Cirtain et al. (hereafter CG13). We present nonlinear force-free reconstructions of the associated coronal magnetic field based on Solar Dynamics Observatory/Helioseismic and Magnetic Imager vector magnetograms. We deliver estimates of the free magnetic energy associated withmore » a braided coronal structure. Our model results suggest (∼100 times) more free energy at the braiding site than analytically estimated by CG13, strengthening the possibility of the AR corona being heated by field line braiding. We were able to appropriately assess the coronal free energy by using vector field measurements and we attribute the lower energy estimate of CG13 to the underestimated (by a factor of 10) azimuthal field strength. We also quantify the increase in the overall twist of a flare-related flux rope that was noted by CG13. From our models we find that the overall twist of the flux rope increased by about half a turn within 12 minutes. Unlike another method to which we compare our results, we evaluate the winding of the flux rope's constituent field lines around each other purely based on their modeled coronal three-dimensional field line geometry. To our knowledge, this is done for the first time here.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takahashi, Takuya, E-mail: takahashi@kwasan.kyoto-u.ac.jp

Flare-associated coronal shock waves sometimes interact with solar prominences, leading to large-amplitude prominence oscillations (LAPOs). Such prominence activation gives us a unique opportunity to track the time evolution of shock–cloud interaction in cosmic plasmas. Although the dynamics of interstellar shock–cloud interaction has been extensively studied, coronal shock–solar prominence interaction is rarely studied in the context of shock–cloud interaction. Associated with the X5.4 class solar flare that occurred on 2012 March 7, a globally propagated coronal shock wave interacted with a polar prominence, leading to LAPO. In this paper, we studied bulk acceleration and excitation of the internal flow of themore » shocked prominence using three-dimensional magnetohydrodynamic (MHD) simulations. We studied eight MHD simulation runs, each with different mass density structure of the prominence, and one hydrodynamic simulation run, and we compared the result. In order to compare the observed motion of activated prominence with the corresponding simulation, we also studied prominence activation by injection of a triangular-shaped coronal shock. We found that the prominence is first accelerated mainly by magnetic tension force as well as direct transmission of the shock, and later decelerated mainly by magnetic tension force. The internal flow, on the other hand, is excited during the shock front sweeps through the prominence and damps almost exponentially. We construct a phenomenological model of bulk momentum transfer from the shock to the prominence, which agreed quantitatively with all the simulation results. Based on the phenomenological prominence activation model, we diagnosed physical parameters of the coronal shock wave. The estimated energy of the coronal shock is several percent of the total energy released during the X5.4 flare.« less

RELATIVE ABUNDANCE MEASUREMENTS IN PLUMES AND INTERPLUMES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guennou, C.; Hahn, M.; Savin, D. W., E-mail: cguennou@iac.es

2015-07-10

We present measurements of relative elemental abundances in plumes and interplumes. Plumes are bright, narrow structures in coronal holes that extend along open magnetic field lines far out into the corona. Previous work has found that in some coronal structures the abundances of elements with a low first ionization potential (FIP) <10 eV are enhanced relative to their photospheric abundances. This coronal-to-photospheric abundance ratio, commonly called the FIP bias, is typically 1 for elements with a high-FIP (>10 eV). We have used Extreme Ultraviolet Imaging Spectrometer observations made on 2007 March 13 and 14 over a ≈24 hr period tomore » characterize abundance variations in plumes and interplumes. To assess their elemental composition, we used a differential emission measure analysis, which accounts for the thermal structure of the observed plasma. We used lines from ions of iron, silicon, and sulfur. From these we estimated the ratio of the iron and silicon FIP bias relative to that for sulfur. From the results, we have created FIP-bias-ratio maps. We find that the FIP-bias ratio is sometimes higher in plumes than in interplumes and that this enhancement can be time dependent. These results may help to identify whether plumes or interplumes contribute to the fast solar wind observed in situ and may also provide constraints on the formation and heating mechanisms of plumes.« less

Probing the Quiet Solar Atmosphere from the Photosphere to the Corona

NASA Astrophysics Data System (ADS)

Kontogiannis, Ioannis; Gontikakis, Costis; Tsiropoula, Georgia; Tziotziou, Kostas

2018-04-01

We investigate the morphology and temporal variability of a quiet-Sun network region in different solar layers. The emission in several extreme ultraviolet (EUV) spectral lines through both raster and slot time-series, recorded by the EUV Imaging Spectrometer (EIS) on board the Hinode spacecraft is studied along with Hα observations and high-resolution spectropolarimetric observations of the photospheric magnetic field. The photospheric magnetic field is extrapolated up to the corona, showing a multitude of large- and small-scale structures. We show for the first time that the smallest magnetic structures at both the network and internetwork contribute significantly to the emission in EUV lines, with temperatures ranging from 8× 104 K to 6× 105 K. Two components of transition region emission are present, one associated with small-scale loops that do not reach coronal temperatures, and another component that acts as an interface between coronal and chromospheric plasma. Both components are associated with persistent chromospheric structures. The temporal variability of the EUV intensity at the network region is also associated with chromospheric motions, pointing to a connection between transition region and chromospheric features. Intensity enhancements in the EUV transition region lines are preferentially produced by Hα upflows. Examination of two individual chromospheric jets shows that their evolution is associated with intensity variations in transition region and coronal temperatures.

AN IMAGING STUDY OF A COMPLEX SOLAR CORONAL RADIO ERUPTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, S. W.; Chen, Y.; Song, H. Q.

2016-08-10

Solar coronal radio bursts are enhanced radio emission excited by energetic electrons accelerated during solar eruptions. Studying these bursts is important for investigating the origin and physical mechanism of energetic particles and further diagnosing coronal parameters. Earlier studies suffered from a lack of simultaneous high-quality imaging data of the radio burst and the eruptive structure in the inner corona. Here we present a study on a complex solar radio eruption consisting of a type II burst and three reversely drifting type III bursts, using simultaneous EUV and radio imaging data. It is found that the type II burst is closelymore » associated with a propagating and evolving CME-driven EUV shock structure, originated initially at the northern shock flank and later transferred to the top part of the shock. This source transfer is coincident with the presence of shock decay and enhancing signatures observed at the corresponding side of the EUV front. The electron energy accelerated by the shock at the flank is estimated to be ∼0.3 c by examining the imaging data of the fast-drifting herringbone structure of the type II burst. The reverse-drifting type III sources are found to be within the ejecta and correlated with a likely reconnection event therein. The implications for further observational studies and relevant space weather forecasting techniques are discussed.« less

The Influence of Post System Design and Material on the Biomechanical Behavior of Teeth with Little Remaining Coronal Structure.

PubMed

Pinto, Cristiano Lazzari; Bhering, Claudia Lopes Brilhante; de Oliveira, Gabriel Rodrigues; Maroli, Angélica; Reginato, Vagner Flávio; Caldas, Ricardo Armini; Bacchi, Atais

2018-05-14

To evaluate the influence of different post systems on the biomechanical behavior of teeth with a severe loss of remaining coronal structure. Fifty standardized bovine teeth (n = 10 per group) were restored with: cast post-and-core (CPC), prefabricated metallic post (PFM), parallel glass-fiber post (P-FP), conical glass-fiber post (C-FP), or composite core (no post, CC). The survival rate during thermomechanical challenging (TC), the fracture strength (FS), and failure patterns (FP) were evaluated. Finite element models evaluated the stress distribution after the application of 100 N. All specimens survived TC. Similar FS was observed among post-containing groups. Groups P-FP and CC presented 100% repairable fractures. The von Mises analysis showed the maximum stresses into the root canal in groups restored with metallic posts. Glass-fiber posts and CC presented the maximum stresses at the load contact point. Glass-fiber groups showed lower stresses in the analysis of maximal contact pressure; CPC led to the highest values of contact pressure. The modified von Mises (mvM) stress in dentin did not show differences among groups. Moreover, mvM values did not reach the dentin fracture limit for any group. The type of intracanal post had a relevant influence on the biomechanical behavior of teeth with little remaining coronal structure. © 2018 by the American College of Prosthodontists.

VLA Measurements of Faraday Rotation through Coronal Mass Ejections

NASA Astrophysics Data System (ADS)

Kooi, Jason E.; Fischer, Patrick D.; Buffo, Jacob J.; Spangler, Steven R.

2017-04-01

Coronal mass ejections (CMEs) are large-scale eruptions of plasma from the Sun, which play an important role in space weather. Faraday rotation is the rotation of the plane of polarization that results when a linearly polarized signal passes through a magnetized plasma such as a CME. Faraday rotation is proportional to the path integral through the plasma of the electron density and the line-of-sight component of the magnetic field. Faraday-rotation observations of a source near the Sun can provide information on the plasma structure of a CME shortly after launch. We report on simultaneous white-light and radio observations made of three CMEs in August 2012. We made sensitive Very Large Array (VLA) full-polarization observations using 1 - 2 GHz frequencies of a constellation of radio sources through the solar corona at heliocentric distances that ranged from 6 - 15 R_{⊙}. Two sources (0842+1835 and 0900+1832) were occulted by a single CME, and one source (0843+1547) was occulted by two CMEs. In addition to our radioastronomical observations, which represent one of the first active hunts for CME Faraday rotation since Bird et al. ( Solar Phys., 98, 341, 1985) and the first active hunt using the VLA, we obtained white-light coronagraph images from the Large Angle and Spectrometric Coronagraph (LASCO) C3 instrument to determine the Thomson-scattering brightness [BT], providing a means to independently estimate the plasma density and determine its contribution to the observed Faraday rotation. A constant-density force-free flux rope embedded in the background corona was used to model the effects of the CMEs on BT and Faraday rotation. The plasma densities (6 - 22×103 cm^{-3}) and axial magnetic-field strengths (2 - 12 mG) inferred from our models are consistent with the modeling work of Liu et al. ( Astrophys. J., 665, 1439, 2007) and Jensen and Russell ( Geophys. Res. Lett., 35, L02103, 2008), as well as previous CME Faraday-rotation observations by Bird et al. (1985).

Observations of disconnection of open coronal magnetic structures

NASA Technical Reports Server (NTRS)

Mccomas, D. J.; Phillips, J. L.; Hundhausen, A. J.; Burkepile, J. T.

1991-01-01

The solar maximum mission coronagraph/polarimeter observations are surveyed for evidence of magnetic disconnection of previously open magnetic structures and several sequences of images consistent with this interpretation are identified. Such disconnection occurs when open field lines above helmet streamers reconnect, in contrast to previously suggested disconnections of CMEs into closed plasmoids. In this paper a clear example of open field disconnection is shown in detail. The event, on June 27, 1988, is preceded by compression of a preexisting helmet streamer and the open coronal field around it. The compressed helmet streamer and surrounding open field region detach in a large U-shaped structure which subsequently accelerates outward from the sun. The observed sequence of events is consistent with reconnection across the heliospheric current sheet and the creation of a detached U-shaped magnetic structure. Unlike CMEs, which may open new magnetic flux into interplanetary space, this process could serve to close off previously open flux, perhaps helping to maintain the roughly constant amount of open magnetic flux observed in interplanetary space.

SELF-ORGANIZED BRAIDING AND THE STRUCTURE OF CORONAL LOOPS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berger, Mitchell A.; Asgari-Targhi, Mahboubeh, E-mail: m.berger@exeter.ac.u, E-mail: m.asgari@ucl.ac.u

2009-11-01

The Parker model for heating of the solar corona involves reconnection of braided magnetic flux elements. Much of this braiding is thought to occur at as yet unresolved scales, for example, braiding of threads within an extreme-ultraviolet or X-ray loop. However, some braiding may be still visible at scales accessible to TRACE or Hinode. We suggest that attempts to estimate the amount of braiding at these scales must take into account the degree of coherence of the braid structure. In this paper, we examine the effect of reconnection on the structure of a braided magnetic field. We demonstrate that simplemore » models of braided magnetic fields which balance the input of topological structure with reconnection evolve to a self-organized critical state. An initially random braid can become highly ordered, with coherence lengths obeying power-law distributions. The energy released during reconnection also obeys a power law. Our model gives more frequent (but smaller) energy releases nearer to the ends of a coronal loop.« less

Modelling coronal electron density and temperature profiles of the Active Region NOAA 11855

NASA Astrophysics Data System (ADS)

Rodríguez Gómez, J. M.; Antunes Vieira, L. E.; Dal Lago, A.; Palacios, J.; Balmaceda, L. A.; Stekel, T.

2017-10-01

The magnetic flux emergence can help understand the physical mechanism responsible for solar atmospheric phenomena. Emerging magnetic flux is frequently related to eruptive events, because when emerging they can reconnected with the ambient field and release magnetic energy. We will use a physic-based model to reconstruct the evolution of the solar emission based on the configuration of the photospheric magnetic field. The structure of the coronal magnetic field is estimated by employing force-free extrapolation NLFFF based on vector magnetic field products (SHARPS) observed by HMI instrument aboard SDO spacecraft from Sept. 29 (2013) to Oct. 07 (2013). The coronal plasma temperature and density are described and the emission is estimated using the CHIANTI atomic database 8.0. The performance of the our model is compared to the integrated emission from the AIA instrument aboard SDO spacecraft in the specific wavelengths 171Å and 304Å.

High coronal structure of high velocity solar wind stream sources

NASA Technical Reports Server (NTRS)

Nolte, J. T.; Krieger, A. S.; Roelof, E. C.; Gold, R. E.

1977-01-01

It is shown analytically that the transition from a high-speed stream source to the ambient coronal conditions is quite rapid in longitude in the high corona. This sharp eastern coronal boundary for the solar wind stream sources is strongly suggested by the solar wind 'dwells' which appear in plots of solar wind velocity against constant-radial-velocity-approximation source longitudes. The possibility of a systematic velocity-dependent effect in the constant-radial-velocity approximation, which would cause this boundary to appear sharper than it is, is investigated. A velocity-dependent interplanetary propagation effect or a velocity-dependent 'source altitude' are two possible sources of such a systematic effect. It is shown that, for at least some dwells, significant interplanetary effects are not likely. The variation of the Alfvenic critical radius in solar wind dwells is calculated, showing that the high-velocity stream originates from a significantly lower altitude than the ambient solar wind.

Coronal and interplanetary propagation, interplanetary acceleration, cosmic-ray observations by deep space network and anomalous component

NASA Technical Reports Server (NTRS)

Ng, C. K.

1986-01-01

The purpose is to provide an overview of the contributions presented in sessions SH3, SH1.5, SH4.6 and SH4.7 of the 19th International Cosmic Ray Conference. These contributed papers indicate that steady progress continues to be made in both the observational and the theoretical aspects of the transport and acceleration of energetic charged particles in the heliosphere. Studies of solar and interplanetary particles have placed emphasis on particle directional distributions in relation to pitch-angle scattering and magnetic focusing, on the rigidity and spatial dependence of the mean free path, and on new propagation regimes in the inner and outer heliosphere. Coronal propagation appears in need of correlative multi-spacecraft studies in association with detailed observation of the flare process and coronal magnetic structures. Interplanetary acceleration has now gone into a consolidation phase, with theories being worked out in detail and checked against observation.

UNRAVELLING THE COMPONENTS OF A MULTI-THERMAL CORONAL LOOP USING MAGNETOHYDRODYNAMIC SEISMOLOGY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prasad, S. Krishna; Jess, D. B.; Klimchuk, J. A.

Coronal loops, constituting the basic building blocks of the active Sun, serve as primary targets to help understand the mechanisms responsible for maintaining multi-million Kelvin temperatures in the solar and stellar coronae. Despite significant advances in observations and theory, our knowledge on the fundamental properties of these structures is limited. Here, we present unprecedented observations of accelerating slow magnetoacoustic waves along a coronal loop that show differential propagation speeds in two distinct temperature channels, revealing the multi-stranded and multithermal nature of the loop. Utilizing the observed speeds and employing nonlinear force-free magnetic field extrapolations, we derive the actual temperature variationmore » along the loop in both channels, and thus are able to resolve two individual components of the multithermal loop for the first time. The obtained positive temperature gradients indicate uniform heating along the loop, rather than isolated footpoint heating.« less

Probe of the solar magnetic field using the "cosmic-ray shadow" of the sun.

PubMed

Amenomori, M; Bi, X J; Chen, D; Chen, T L; Chen, W Y; Cui, S W; Danzengluobu; Ding, L K; Feng, C F; Feng, Zhaoyang; Feng, Z Y; Gou, Q B; Guo, Y Q; Hakamada, K; He, H H; He, Z T; Hibino, K; Hotta, N; Hu, Haibing; Hu, H B; Huang, J; Jia, H Y; Jiang, L; Kajino, F; Kasahara, K; Katayose, Y; Kato, C; Kawata, K; Labaciren; Le, G M; Li, A F; Li, H J; Li, W J; Liu, C; Liu, J S; Liu, M Y; Lu, H; Meng, X R; Mizutani, K; Munakata, K; Nanjo, H; Nishizawa, M; Ohnishi, M; Ohta, I; Onuma, H; Ozawa, S; Qian, X L; Qu, X B; Saito, T; Saito, T Y; Sakata, M; Sako, T K; Shao, J; Shibata, M; Shiomi, A; Shirai, T; Sugimoto, H; Takita, M; Tan, Y H; Tateyama, N; Torii, S; Tsuchiya, H; Udo, S; Wang, H; Wu, H R; Xue, L; Yamamoto, Y; Yang, Z; Yasue, S; Yuan, A F; Yuda, T; Zhai, L M; Zhang, H M; Zhang, J L; Zhang, X Y; Zhang, Y; Zhang, Yi; Zhang, Ying; Zhaxisangzhu; Zhou, X X

2013-07-05

We report on a clear solar-cycle variation of the Sun’s shadow in the 10 TeV cosmic-ray flux observed by the Tibet air shower array during a full solar cycle from 1996 to 2009. In order to clarify the physical implications of the observed solar cycle variation, we develop numerical simulations of the Sun’s shadow, using the potential field source surface model and the current sheet source surface (CSSS) model for the coronal magnetic field. We find that the intensity deficit in the simulated Sun’s shadow is very sensitive to the coronal magnetic field structure, and the observed variation of the Sun’s shadow is better reproduced by the CSSS model. This is the first successful attempt to evaluate the coronal magnetic field models by using the Sun’s shadow observed in the TeV cosmic-ray flux.

Coroners' records of accidental deaths.

PubMed Central

Levene, S

1991-01-01

This study set out to provide a description of the children involved in fatal accidents and to ascertain which deaths might have been prevented and by what means. The records from a convenience sample of four coroners (jurisdictions of Inner North London, Birmingham, Bedfordshire, and Ipswich) of inquests opened in 1984-8 on children aged under 15 killed in accidents were reviewed for information on the deceased, the accident, and the injuries sustained. Altogether 225 records (150 boys, 75 girls) were examined. Accidents to pedestrians were the commonest cause of death (81 cases), and road safety engineering measures were the most likely means by which most fatalities might have been prevented. The records frequently omitted information on social circumstances, family structure, ethnic group, or the use of safety equipment. Cooperative coroners can contribute to child safety as their records are rich in information about accidents. This could be made available to parties interested in accident prevention, including community paediatricians. PMID:1953011

A lower limit to the altitude of coronal particle storage regions deduced from solar proton energy spectra

NASA Technical Reports Server (NTRS)

Krimigis, S. M.

1973-01-01

The spectrum of low energy protons observed at 1 AU following solar flares shows little or no evidence of energy degradation down to approximately 0.3 MeV. Such observations may be used to set a lower limit on the altitude of hypothetical coronal particle storage regions, ranging from 2 to 7 R sub s. It is pointed out that closed coronal magnetic loop structures are observed to extend to 2R sub s, so that long-term storage of low energy protons does not take place in the immediate vicinity of the sun. It is further suggested that in the few cases where the proton spectrum appears to be degraded at low energies, the energy loss may be due to adiabatic deceleration in the expanding solar wind. The alternative of continual acceleration is suggested as a plausible substitute for the particle storage hypothesis.

Simultaneous Solar Maximum Mission and Very Large Array (VLA) observations of solar active regions

NASA Technical Reports Server (NTRS)

Lang, K. R.

1985-01-01

Simultaneous observations of solar active regions with the Solar Maximum Mission (SMM) Satellite and the Very Large Array (VLA) have been obtained and analyzed. Combined results enhance the scientific return for beyond that expeted from using either SMM or VLA alone. A total of two weeks of simultaneous SMM/VLA data were obtained. The multiple wavelength VLA observations were used to determine the temperature and magnetic structure at different heights within coronal loops. These data are compared with simultaneous SMM observations. Several papers on the subject are in progress. They include VLA observations of compact, transient sources in the transition region; simultaneous SMM/VLA observations of the coronal loops in one active region and the evolution of another one; and sampling of the coronal plasma using thermal cyclotron lines (magnetic field - VLA) and soft X ray spectral lines (electron density and electron temperaure-SMM).

The Instruments and Capabilities of the Miniature X-Ray Solar Spectrometer (MinXSS) CubeSats

NASA Astrophysics Data System (ADS)

Moore, Christopher S.; Caspi, Amir; Woods, Thomas N.; Chamberlin, Phillip C.; Dennis, Brian R.; Jones, Andrew R.; Mason, James P.; Schwartz, Richard A.; Tolbert, Anne K.

2018-02-01

The Miniature X-ray Solar Spectrometer (MinXSS) CubeSat is the first solar science oriented CubeSat mission flown for the NASA Science Mission Directorate, with the main objective of measuring the solar soft X-ray (SXR) flux and a science goal of determining its influence on Earth's ionosphere and thermosphere. These observations can also be used to investigate solar quiescent, active region, and flare properties. The MinXSS X-ray instruments consist of a spectrometer, called X123, with a nominal 0.15 keV full-width at half-maximum (FWHM) resolution at 5.9 keV and a broadband X-ray photometer, called XP. Both instruments are designed to obtain measurements from 0.5 - 30 keV at a nominal time cadence of 10 s. A description of the MinXSS instruments, performance capabilities, and relation to the Geostationary Operational Environmental Satellite (GOES) 0.1 - 0.8 nm flux is given in this article. Early MinXSS results demonstrate the capability of measuring variations of the solar spectral soft X-ray (SXR) flux between 0.8 - 12 keV from at least GOES A5-M5 (5 × 10^{-8} - 5 ×10^{-5} W m^{-2}) levels and of inferring physical properties (temperature and emission measure) from the MinXSS data alone. Moreover, coronal elemental abundances can be inferred, specifically for Fe, Ca, Si, Mg, S, Ar, and Ni, when the count rate is sufficiently high at each elemental spectral feature. Additionally, temperature response curves and emission measure loci demonstrate the MinXSS sensitivity to plasma emission at different temperatures. MinXSS observations coupled with those from other solar observatories can help address some of the most compelling questions in solar coronal physics. Finally, simultaneous observations by MinXSS and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) can provide the most spectrally complete soft X-ray solar flare photon flux measurements to date.

The coherent relation between the solar wind proton speed and O{sup 7+}/O{sup 6+} ratio and its coronal sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, L., E-mail: lzh@umich.edu; Landi, E.; Fisk, L. A.

We analyze the two-hour resolution solar wind proton speed (V{sub p}) and charge state ratio of O{sup 7+}/O{sup 6+} measured by ACE (SWICS and SWEPAM) from 1998 to 2011 at 1 AU. By applying a two-step mapping method, we link the solar wind in-situ observations to the corona images captured by SOHO and STEREO, in which we identify the different plasma structures, such as active regions (ARs), coronal holes (CHs) and quiet Sun regions (QS), using a classification scheme based on pixel brightness. Then we determine from which region in the corona the solar wind originates. We examine the in-situmore » properties of the solar wind streams associated with CHs, ARs and QS regions. We find that more than half of CH associated wind is actually slow wind, and O{sup 7+}/O{sup 6+} ratio has a strong coherent correlation with the location of the solar wind coronal sources. Therefore, we conclude that O{sup 7+}/O{sup 6+} ratio can be used as a much more effective discriminator to identify solar wind coronal sources region than V{sub p}.« less

Ephemeral active regions and coronal bright points: A solar maximum Mission 2 guest investigator study

NASA Technical Reports Server (NTRS)

Harvey, K. L.; Tang, F. Y. C.; Gaizauskas, V.; Poland, A. I.

1986-01-01

A dominate association of coronal bright points (as seen in He wavelength 10830) was confirmed with the approach and subsequent disappearance of opposite polarity magnetic network. While coronal bright points do occur with ephemeral regions, this association is a factor of 2 to 4 less than with sites of disappearing magnetic flux. The intensity variations seen in He I wavelength 10830 are intermittent and often rapid, varying over the 3 minute time resolution of the data; their bright point counterparts in the C IV wavelength 1548 and 20 cm wavelength show similar, though not always coincident time variations. Ejecta are associated with about 1/3 of the dark points and are evident in the C IV and H alpha data. These results support the idea that the anti-correlation of X-ray bright points with the solar cycle can be explained by the correlation of these coronal emission structures with sites of cancelling flux, indicating that, in some cases, the process of magnetic flux removal results in the release of energy. That the intensity variations are rapid and variable suggests that this process works intermittently.

Simulations of Flare Reconnection in Breakout Coronal Mass Ejections

NASA Astrophysics Data System (ADS)

DeVore, C. Richard; Karpen, J. T.; Antiochos, S. K.

2009-05-01

We report 3D MHD simulations of the flare reconnection in the corona below breakout coronal mass ejections (CMEs). The initial setup is a single bipolar active region imbedded in the global-scale background dipolar field of the Sun, forming a quadrupolar magnetic configuration with a coronal null point. Rotational motions applied to the active-region polarities at the base of the atmosphere introduce shear across the polarity inversion line (PIL). Eventually, the magnetic stress and energy reach the critical threshold for runaway breakout reconnection, at which point the sheared core field erupts outward at high speed. The vertical current sheet formed by the stretching of the departing sheared field suffers reconnection that reforms the initial low-lying arcade across the PIL, i.e., creates the flare loops. Our simulation model, the Adaptively Refined MHD Solver, exploits local grid refinement to resolve the detailed structure and evolution of the highly dynamic current sheet. We are analyzing the numerical experiments to identify and interpret observable signatures of the flare reconnection associated with CMEs, e.g., the flare loops and ribbons, coronal jets and shock waves, and possible origins of solar energetic particles. This research was supported by NASA and ONR.

MAGNETIC TOPOLOGY OF BUBBLES IN QUIESCENT PROMINENCES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dudik, J.; Aulanier, G.; Schmieder, B.

We study a polar-crown prominence with a bubble and its plume observed in several coronal filters by the SDO/AIA and in H{alpha} by the MSDP spectrograph in Bialkow (Poland) to address the following questions: what is the brightness of prominence bubbles in EUV with respect to the corona outside of the prominence and the prominence coronal cavity? What is the geometry and topology of the magnetic field in the bubble? What is the nature of the vertical threads seen within prominences? We find that the brightness of the bubble and plume is lower than the brightness of the corona outsidemore » of the prominence, and is similar to that of the coronal cavity. We constructed linear force-free models of prominences with bubbles, where the flux rope is perturbed by inclusion of parasitic bipoles. The arcade field lines of the bipole create the bubble, which is thus devoid of magnetic dips. Shearing the bipole or adding a second one can lead to cusp-shaped prominences with bubbles similar to the observed ones. The bubbles have complex magnetic topology, with a pair of coronal magnetic null points linked by a separator outlining the boundary between the bubble and the prominence body. We conjecture that plume formation involves magnetic reconnection at the separator. Depending on the viewing angle, the prominence can appear either anvil-shaped with predominantly horizontal structures, or cusp-shaped with predominantly vertical structuring. The latter is an artifact of the alignment of magnetic dips with respect to the prominence axis and the line of sight.« less

Causal learning with local computations.

PubMed

Fernbach, Philip M; Sloman, Steven A

2009-05-01

The authors proposed and tested a psychological theory of causal structure learning based on local computations. Local computations simplify complex learning problems via cues available on individual trials to update a single causal structure hypothesis. Structural inferences from local computations make minimal demands on memory, require relatively small amounts of data, and need not respect normative prescriptions as inferences that are principled locally may violate those principles when combined. Over a series of 3 experiments, the authors found (a) systematic inferences from small amounts of data; (b) systematic inference of extraneous causal links; (c) influence of data presentation order on inferences; and (d) error reduction through pretraining. Without pretraining, a model based on local computations fitted data better than a Bayesian structural inference model. The data suggest that local computations serve as a heuristic for learning causal structure. Copyright 2009 APA, all rights reserved.

Electric currents and coronal heating in NOAA active region 6952

NASA Technical Reports Server (NTRS)

Metcalf, T. R.; Canfield, R. C.; Hudson, H. S.; Mickey, D. L.; Wulser, J. -P.; Martens, P. C. H.; Tsuneta, S.

1994-01-01

We examine the spatial and temporal relationship between coronal structures observed with the soft X-ray telescope (SXT) on board the Yohkoh spacecraft and the vertical electric current density derived from photospheric vector magnetograms obtained using the Stokes Polarimeter at the Mees Solar Observatory. We focus on a single active region: AR 6952 which we observed on 7 days during 1991 December. For 11 independent maps of the vertical electric current density co-aligned with non-flaring X-ray images, we search for a morphological relationship between sites of high vertical current density in the photosphere and enhanced X-ray emission in the overlying corona. We find no compelling spatial or temporal correlation between the sites of vertical current and the bright X-ray structures in this active region.

Magnetic Roots and the Driving of Extended Coronal Heating

NASA Technical Reports Server (NTRS)

Porter, Jason G.; Falconer, D. A.; Moore, Ronald L.; Harvey, Karen L.; Rabin, Douglas M.; Shimizu, T.

1998-01-01

We report results from a continuation of a previous study, in which we found large bright coronal loops within active regions and extending from active regions that have one end rooted near an island of included magnetic polarity that is a site of enhanced coronal heating and microflares. This suggested that magnetic activity such as microflaring results in enhanced heating in both the compact core field around the island and in the large loops extending from it. We might expect that the intensity variations due to enhanced heating in the compact and extended structures would be correlated. However, although some ex- tended loops do respond to the largest events taking place in the core fields near their feet, they do not show a clear response to most smaller individual events nor to the overall envelope of coronal heating activity in the core fields at their feet as determined from longer-term observations. Thus, while it is clear that the extended loops' heating is being driven from their ends at the magnetic islands, much of this heating is apparently by some form of footpoint activity that is not strongly coupled to the heating in the footpoint core fields. One possibility is that the remote heating in the extended loops is driven by reconnection at the magnetic null over the island, and that this reconnection is driven mainly by core-field activity that produces little coronal heating within the core field itself, perhaps in the manner of the numerical simulations by Karpen, Antiochos, and DeVore.

High Resolutions Studies of the Structure of the Solar Atmosphere

DTIC Science & Technology

1992-06-30

Pairs in the Solar Wind", submitted to J. Geophys. Res., July 20, 1992. M. Karovska , F. Blundell and S. R. Habbal, "Fine Scale Structure of Active...Regions", manuscript in preparation. M. Karovska , F. Blundell and S. R. Habbal, "Fine Scale Structure of the Solar Limb in a Coronal Hole", manuscript in

The study of coronal plasma structures and fluctuations with Faraday rotation measurements

NASA Technical Reports Server (NTRS)

Sakurai, Takayuki; Sprangler, Steven R.

1994-01-01

We report dual-frequency, polarimetric measurements of Faraday rotation of extragalactic radio sources viewed through the solar corona. The observations were made at the Very Large Array in 1990 during solar maximum. Of the nine observed, an excess rotation measure of -12.6 rad/sq m was detected for one source (0010+005), which was observed at an elongation of about 9 solar radii. This measurement is in fair agreement with an a priori model rotation measure of -8.6 rad/sq m estimated from coronal potential field models and the electron density model of Paetzold et al. (1992). Our measurement provides a value for the coronal magnetic field strength at 9 solar radii given a knowledge of the magnetic field sector structure, of 12.5 +/- 2.3 mG. Rotation measurements of 0010+005 were made approximately once per hour over an 11 hr period. During this interval, a slow change of about 1 rad/sq m/hr in rotation measure was detected. Although we are not absolutely certain that this drift is not unremoved ionospheric Faraday rotation, extensive analysis of data from the other sources suggests that this is not the case (Sakurai & Spangler 1994). The very long timescale for this variation argues against the agency of magnetohydrodynamics (MHD) waves, and we suggest occultation of 0010+005 by relatively static plasma structures in the corona. We filtered our rotation measure time series to search for variations on an hourly timescale, such as those reported by Hollweg et al. (1992), which could be attributed to coronal MHD waves. We were unable to detect such fluctuations and can report only an upper limit to the rms variation of 1.6 rad/sq m. This upper limit is of the same order, but slightly larger than the values typically reported by Hollweg et al. (1982). This upper limit to the rotation measure fluctuations limits the dimensionless wave amplitude (delta B)/B in the corona to be less than 0.7. Using the number, we estimate the MHD wave flux at the coronal base to be less than 1.6 x 10(exp 5) ergs/sq cm/s. This is less than the amount of wave energy flux required by wave-driven models of the solar wind. Finally, we discuss a number of ways in which such observations could be improved in the future.

Observations of X-ray flares in G-K dwarfs by XMM-Newton

NASA Astrophysics Data System (ADS)

Pandey, Jeewan Chandra

Eclipsing binary BD +5 706 is best investigated member of rare class of cool Algols, which differ from clasical Algol systems in that the mass gaining component is also a late-type star. The analysis of X-ray lightcurve of this system registered by ROSAT suggested the primary component to be the dominant source of activity in the system (Torres et al, AJ 125, 3237, 2003). We reconstruct the spatial structure of coronal emission within the system according to the method proposed by Siarkowski, and show that coronal emission is most likely attributed to both components.

Characteristics of the interplanetary shocks formed by a sudden increase in the velocity of the solar wind from a coronal hole

NASA Technical Reports Server (NTRS)

Bravo, S.

1995-01-01

Coronal holes are the sources of the solar wind and, according to recent YOKOH observations, may undergo rapid changes which are associated with manifestations of explosive solar activity. Rapid changes in a hole's structure will produce rapid changes in the characteristics of the wind emerging from it and, in the particular c se of a sudden increase in wind velocity, this may lead to the formation of an interplanetary shock. We discuss the characteristics of shocks formed in such a way and compare them with interplanetary observations.

Feature-to-Feature Inference Under Conditions of Cue Restriction and Dimensional Correlation.

PubMed

Lancaster, Matthew E; Homa, Donald

2017-01-01

The present study explored feature-to-feature and label-to-feature inference in a category task for different category structures. In the correlated condition, each of the 4 dimensions comprising the category was positively correlated to each other and to the category label. In the uncorrelated condition, no correlation existed between the 4 dimensions comprising the category, although the dimension to category label correlation matched that of the correlated condition. After learning, participants made inference judgments of a missing feature, given 1, 2, or 3 feature cues; on half the trials, the category label was also included as a cue. The results showed superior inference of features following training on the correlated structure, with accurate inference when only a single feature was presented. In contrast, a single-feature cue resulted in chance levels of inference for the uncorrelated structure. Feature inference systematically improved with number of cues after training on the correlated structure. Surprisingly, a similar outcome was obtained for the uncorrelated structure, an outcome that must have reflected mediation via the category label. A descriptive model is briefly introduced to explain the results, with a suggestion that this paradigm might be profitably extended to hierarchical structures where the levels of feature-to-feature inference might vary with the depth of the hierarchy.

A new look at sunspot formation using theory and observations

NASA Astrophysics Data System (ADS)

Losada, I. R.; Warnecke, J.; Glogowski, K.; Roth, M.; Brandenburg, A.; Kleeorin, N.; Rogachevskii, I.

2017-10-01

Sunspots are of basic interest in the study of the Sun. Their relevance ranges from them being an activity indicator of magnetic fields to being the place where coronal mass ejections and flares erupt. They are therefore also an important ingredient of space weather. Their formation, however, is still an unresolved problem in solar physics. Observations utilize just 2D surface information near the spot, but it is debatable how to infer deep structures and properties from local helioseismology. For a long time, it was believed that flux tubes rising from the bottom of the convection zone are the origin of the bipolar sunspot structure seen on the solar surface. However, this theory has been challenged, in particular recently by new surface observation, helioseismic inversions, and numerical models of convective dynamos. In this article we discuss another theoretical approach to the formation of sunspots: the negative effective magnetic pressure instability. This is a large-scale instability, in which the total (kinetic plus magnetic) turbulent pressure can be suppressed in the presence of a weak large-scale magnetic field, leading to a converging downflow, which eventually concentrates the magnetic field within it. Numerical simulations of forced stratified turbulence have been able to produce strong super-equipartition flux concentrations, similar to sunspots at the solar surface. In this framework, sunspots would only form close to the surface due to the instability constraints on stratification and rotation. Additionally, we present some ideas from local helioseismology, where we plan to use the Hankel analysis to study the pre-emergence phase of a sunspot and to constrain its deep structure and formation mechanism.

Laser experiments to simulate coronal mass ejection driven magnetospheres and astrophysical plasma winds on compact magnetized stars

NASA Astrophysics Data System (ADS)

Horton, W.; Ditmire, T.; Zakharov, Yu. P.

2010-06-01

Laboratory experiments using a plasma wind generated by laser-target interaction are proposed to investigate the creation of a shock in front of the magnetosphere and the dynamo mechanism for creating plasma currents and voltages. Preliminary experiments are shown where measurements of the electron density gradients surrounding the obstacles are recorded to infer the plasma winds. The proposed experiments are relevant to understanding the electron acceleration mechanisms taking place in shock-driven magnetic dipole confined plasmas surrounding compact magnetized stars and planets. Exploratory experiments have been published [P. Brady, T. Ditmire, W. Horton, et al., Phys. Plasmas 16, 043112 (2009)] with the one Joule Yoga laser and centimeter sized permanent magnets.

A Brief History of CME Science

NASA Technical Reports Server (NTRS)

Alexander, David; Richardson, Ian G.; Zurbuchen, Thomas H.

2006-01-01

We present here a brief summary of the rich heritage of observational and theoretical research leading to the development of our current understanding of the initiation, structure, and evolution of Coronal Mass Ejections.

Brightness and magnetic evolution of solar coronal bright points

NASA Astrophysics Data System (ADS)

Ugarte-Urra, I.

2004-12-01

This thesis presents a study of the brightness and magnetic evolution of several Extreme ultraviolet (EUV) coronal bright points (hereafter BPs). BPs are loop-like features of enhanced emission in the coronal EUV and X-ray images of the Sun, that are associated to the interaction of opposite photospheric magnetic polarities with magnetic fluxes of ≈1018 - 1019 Mx. The study was carried out using several instruments on board the Solar and Heliospheric Observatory (SOHO): the Extreme Ultraviolet Imager (EIT), the Coronal Diagnostic Spectrometer (CDS) and the Michelson Doppler Imager (MDI), supported by the high resolution imaging from the Transition Region And Coronal Explorer (TRACE). The results confirm that, down to 1'' (i.e. ~715 km) resolution, BPs are made of small loops with lengths of ~6 Mm and cross-sections of ~2 Mm. The loops are very dynamic, evolving in time scales as short as 1 - 2 minutes. This is reflected in a highly variable EUV response with fluctuations highly correlated in spectral lines at transition region temperatures (in the range 3.2x10^4 - 3.5x10^5 K), but not always at coronal temperatures. A wavelet analysis of the intensity variations reveals, for the first time, the existence of quasi-periodic oscillations with periods ranging 400 -- 1000 s, in the range of periods characteristic of the chromospheric network. The link between BPs and network bright points is discussed, as well as the interpretation of the oscillations in terms of global acoustic modes of closed magnetic structures. A comparison of the magnetic flux evolution of the magnetic polarities to the EUV flux changes is also presented. Throughout their lifetime, the intrinsic EUV emission of BPs is found to be dependent on the total magnetic flux of the polarities. In short time scales, co-spatial and co-temporal TRACE and MDI images, reveal the signature of heating events that produce sudden EUV brightenings simultaneous to magnetic flux cancellations. This is interpreted in terms of magnetic reconnection events. Finally, a electron density study of six coronal bright points produces values of ~1.6x109 cm-3, closer to active region plasma than to quiet Sun. The analysis of a large coronal loop (half length of 72 Mm) introduces the discussion on the prospects of future plasma diagnostics of BPs with forthcoming solar missions like Solar-B.

Photospheric magnetic field of an eroded-by-solar-wind coronal mass ejection

NASA Astrophysics Data System (ADS)

Palacios, J.; Cid, C.; Saiz, E.; Guerrero, A.

2017-10-01

We have investigated the case of a coronal mass ejection that was eroded by the fast wind of a coronal hole in the interplanetary medium. When a solar ejection takes place close to a coronal hole, the flux rope magnetic topology of the coronal mass ejection (CME) may become misshapen at 1 AU as a result of the interaction. Detailed analysis of this event reveals erosion of the interplanetary coronal mass ejection (ICME) magnetic field. In this communication, we study the photospheric magnetic roots of the coronal hole and the coronal mass ejection area with HMI/SDO magnetograms to define their magnetic characteristics.

Coronal Fine Structure in Dynamic Events Observed by Hi-C

NASA Technical Reports Server (NTRS)

Winebarger, Amy; Schuler, Timothy

2013-01-01

The High-Resolution Coronal Imager (Hi-C) flew aboard a NASA sounding rocket on 2012 July 11 and captured roughly 345 s of high spatial and temporal resolution images of the solar corona in a narrowband 193 Angstrom channel. We have analyzed the fluctuations in intensity of Active Region 11520. We selected events based on a lifetime greater than 11 s (two Hi-C frames) and intensities greater than a threshold determined from the photon and readout noise. We compare the Hi-C events with those determined from AIA. We find that HI-C detects shorter and smaller events than AIA. We also find that the intensity increase in the Hi-C events is approx. 3 times greater than the intensity increase in the AIA events we conclude the events are related to linear sub-structure that is unresolved by AIA

Electrons in the solar corona. III - Coronal streamers analysis from balloon-borne coronagraph

NASA Astrophysics Data System (ADS)

Dollfus, A.; Mouradian, Z.

1981-03-01

The solar corona is discussed on the basis of observations made during a 5-hour period in France in September 1971. Using a balloon at an altitude of 32,000 m, the solar corona was cinematographed from 2 to 5 solar radii with an externally occulted coronagraph. It is noted that motions in coronal features, when they occur, exhibit deformations of structures with velocities not exceeding a few tens of km/s. Several streamers were often involved simultaneously; these variations are compatible with magnetic changes or sudden reorganizations of lines of forces. Intensity and polarization measurements are shown to give the electron density with height in the quiet corona above the equator. Three-dimensional structures and localizations of the streamers are deduced from combined photometry, polarimetry, and ground-based K coronametry.

Effects of Coronal Magnetic Field Structures on the Transport of Solar Energetic Particles

NASA Astrophysics Data System (ADS)

Zhao, Lulu; Zhang, Ming

2018-06-01

This Letter presents a model calculation of solar energetic particle (SEP) transport to test the sensitivity of the distribution of escaped SEPs in interplanetary space and dependence upon the details of the magnetic field structure in the corona. It is applied to a circumsolar event on 2011 November 3, in which SEPs are observed promptly after the solar event eruption by three spacecraft (the twin Solar TErrestrial RElations Observatories (STEREO-A and STEREO-B) and ACE) separated by more than 100° in longitude from each other. The corona magnetic field reconstructed from photosphseric field measurements using the PFSS method changes substantially before and after the solar eruption, especially around the active region. The locations of open field regions, separatrix surfaces including the heliospheric current sheet, and footpoints of magnetic field lines connected to the spacecraft location have shifted substantially. We inject 100 keV energetic electrons on the open field lines at 1.5 R s within the size of observed coronal mass ejections (CMEs) and follow their propagation in the corona and the interplanetary space. We find that with a perpendicular diffusion due to field line random walk equal to 10% of the supergranular diffusion rate, the overall distribution of escaped SEPs does not change much even though the region of open field lines from SEPs has changed. The result suggests that detailed small-scale coronal magnetic field structures and the exact magnetic field connection are not crucially important for observing SEPs in the interplanetary space.

Study of a Solar X-Ray Telescope

NASA Technical Reports Server (NTRS)

Golub, Leon

1997-01-01

The highly structured nature of the outer solar atmosphere seems to be intimately linked to the presence, at the solar surface, of magnetic fields that have been generated inside the Sun and have emerged to the surface. The corona is brightest (and also hottest) at just those locations where the magnetic field has emerged from inside the Sun. Dynamo theory predicts that strong magnetic fields will be generated deep in the solar interior and that bundles or 'ropes' of magnetic flux will float to the surface. When this happens, a magnetically bipolar region will become visible, extending above the surface in a three-dimensional structure. The field lines penetrate through the surface, showing two magnetic poles, and also exhibit a three-dimensional structure above the surface. The structure created by the field emergence is rooted in the (relatively) cool photosphere and extends through the chromosphere and transition region to the corona. Thus, the magnetic field creates a region, called an active region, which contains portions at temperatures from less than 10(exp 4) K to greater than 10(exp 6) K, and is therefore visible at wavelengths from the infrared through x-rays. The locations where the magnetic field leaves and reenters the visible surface are called the 'footpoints' of the coronal structures associated with the magnetic field. The magnetic fields themselves are not directly visible. However, the hot coronal plasma is, for the most part, constrained to follow the direction of the magnetic field lines in the atmosphere. Now, 100 years after the discovery of x-rays by Wilhelm Roentgen in 1896, we can routinely make observations of the solar corona from outside the Earth's atmosphere in this region of the electromagnetic spectrum. As shown by comparing x-ray images with magnetograms, the bright corona over these bipolar magnetic regions consists of closed structures that seem to follow the orientation of the magnetic field. Although we can see down to the photosphere at x-ray wavelengths when observing the disk of the Sun, this part of the solar atmosphere emits so little that far from the peak of its Planck curve it appears dark in x-ray images. This impression of hot plasma following the magnetic field direction is further strengthened by quantitative studies that calculate coronal magnetic field strength and direction based on photospheric measurements and compare them with the observed brightness and location of the x-ray emitting structures. Such comparisons make it clear that, for the most part, the hot plasma conforms to the geometry of the magnetic field and that the coronal brightness is strongly linked to the strength of the magnetic fields which have erupted to the solar surface from the interior. It is also the case that the larger-scale, fainter corona, as well as coronal holes, are strongly influenced by the large-scale solar magnetic field. We may get a small hint of the reason that the coronal plasma outlines the direction of B by examining the thermal conductivity of a hot plasma in the presence of a magnetic field. This quantity has enormously different values in the directions parallel and perpendicular to the field for a coronal temperature of 10(exp 6) K, a particle density of 10(exp 9)/cu cm and a magnetic field strength of 100 G, the conductivity along the field is approximately 13 orders of magnitude greater than that perpendicular to the field. It is therefore not surprising that a parcel of plasma which is locally heated would conduct that heat preferentially in the direction of the field. We also note that the thermal conductivity parallel to the magnetic field increases with temperature T, while the perpendicular conductivity decreases. To the extent that the loop aspect ratio, i.e., the ratio of loop length to loop width, is determined by the thermal conductivity, we would expect that higher temperature loops are longer and thinner than cooler ones. However, if the loop width becomes smaller than the spatial resolution of the observing instrument, this effect will not be directly observable. For organizational purposes, we provide a listing of some scientific objectives for a Solar-B x-ray telescope, arranged in terms of identifiable features in the corona.

PROPERTIES AND MODELING OF UNRESOLVED FINE STRUCTURE LOOPS OBSERVED IN THE SOLAR TRANSITION REGION BY IRIS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brooks, David H.; Reep, Jeffrey W.; Warren, Harry P.

Recent observations from the Interface Region Imaging Spectrograph ( IRIS ) have discovered a new class of numerous low-lying dynamic loop structures, and it has been argued that they are the long-postulated unresolved fine structures (UFSs) that dominate the emission of the solar transition region. In this letter, we combine IRIS measurements of the properties of a sample of 108 UFSs (intensities, lengths, widths, lifetimes) with one-dimensional non-equilibrium ionization simulations, using the HYDRAD hydrodynamic model to examine whether the UFSs are now truly spatially resolved in the sense of being individual structures rather than being composed of multiple magnetic threads.more » We find that a simulation of an impulsively heated single strand can reproduce most of the observed properties, suggesting that the UFSs may be resolved, and the distribution of UFS widths implies that they are structured on a spatial scale of 133 km on average. Spatial scales of a few hundred kilometers appear to be typical for a range of chromospheric and coronal structures, and we conjecture that this could be an important clue for understanding the coronal heating process.« less

Spectroscopic diagnostics of extended corona and solar wind with UVCS/Spartan

NASA Technical Reports Server (NTRS)

Strachan, L.; Gardner, L. D.; Kohl, J. L.

1995-01-01

The primary goal of the Ultraviolet Coronal Spectrometer on Spartan 201 (UVCS/Spartan) is to make spectroscopic diagnostic measurements that can be used to derive plasma parameters in the extended solar corona where it is believed that significant heating of the corona and acceleration of the solar wind take place. Direct and indirect measurements of particle velocity distribution, thermal and non-thermal temperatures, and bulk outflow velocities are crucial to aid in the identification of physical processes that may be responsible for coronal heating and solar wind acceleration. UVCS/Spartan has made two flights in April 1993 and September 1994, the latter coinciding with the South Polar Passage of the Ulysses spacecraft. Observations were made of the large-scale structures and sub-structures of coronal holes and streamers at heliocentric heights between 1.5 solar radii and 3.5 solar radii. Measurements were made of H I Lyman-alpha intensities and profiles, and line intensities of minor ions like O(5+) and Fe(11+). We will present results from the flights and discuss how these measurements are used to constrain values for the proton thermal and non-thermal kinetic temperatures, proton bulk outflow velocities, and minor ion temperatures and bulk outflow velocities. Plans for the upcoming flight in July 1995 will also be discussed.

Tomographic Validation of the AWSoM Model of the Inner Corona During Solar Minima

NASA Astrophysics Data System (ADS)

Manchester, W.; Vásquez, A. M.; Lloveras, D. G.; Mac Cormack, C.; Nuevo, F.; Lopez-Fuentes, M.; Frazin, R. A.; van der Holst, B.; Landi, E.; Gombosi, T. I.

2017-12-01

Continuous improvement of MHD three-dimensional (3D) models of the global solar corona, such as the Alfven Wave Solar Model (AWSoM) of the Space Weather Modeling Framework (SWMF), requires testing their ability to reproduce observational constraints at a global scale. To that end, solar rotational tomography based on EUV image time-series can be used to reconstruct the 3D distribution of the electron density and temperature in the inner solar corona (r < 1.25 Rsun). The tomographic results, combined with a global coronal magnetic model, can further provide constraints on the energy input flux required at the coronal base to maintain stable structures. In this work, tomographic reconstructions are used to validate steady-state 3D MHD simulations of the inner corona using the latest version of the AWSoM model. We perform the study for selected rotations representative of solar minimum conditions, when the global structure of the corona is more axisymmetric. We analyse in particular the ability of the MHD simulation to match the tomographic results across the boundary region between the equatorial streamer belt and the surrounding coronal holes. The region is of particular interest as the plasma flow from that zone is thought to be related to the origin of the slow component of the solar wind.

On the Doppler Velocity of Emission Line Profiles Formed in the "Coronal Contraflow" that Is the Chromosphere-Corona Mass Cycle

NASA Astrophysics Data System (ADS)

McIntosh, Scott W.; Tian, Hui; Sechler, Marybeth; De Pontieu, Bart

2012-04-01

This analysis begins to explore the complex chromosphere-corona mass cycle using a blend of imaging and spectroscopic diagnostics. Single Gaussian fits (SGFs) to hot emission line profiles (formed above 1 MK) at the base of coronal loop structures indicate material blueshifts of 5-10 km s-1, while cool emission line profiles (formed below 1 MK) yield redshifts of a similar magnitude—indicating, to zeroth order, that a temperature-dependent bifurcating flow exists on coronal structures. Image sequences of the same region reveal weakly emitting upward propagating disturbances in both hot and cool emission with apparent speeds of 50-150 km s-1. Spectroscopic observations indicate that these propagating disturbances produce a weak emission component in the blue wing at commensurate speed, but that they contribute only a few percent to the (ensemble) emission line profile in a single spatio-temporal resolution element. Subsequent analysis of imaging data shows material "draining" slowly (~10 km s-1) out of the corona, but only in the cooler passbands. We interpret the draining as the return flow of coronal material at the end of the complex chromosphere-corona mass cycle. Further, we suggest that the efficient radiative cooling of the draining material produces a significant contribution to the red wing of cool emission lines that is ultimately responsible for their systematic redshift as derived from an SGF when compared to those formed in hotter (conductively dominated) domains. The presence of counterstreaming flows complicates the line profiles, their interpretation, and asymmetry diagnoses, but allows a different physical picture of the lower corona to develop.

Role of transients in the sustainability of solar coronal plumes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raouafi, N.-E.; Stenborg, G., E-mail: NourEddine.Raouafi@jhuapl.edu

2014-06-01

We report on the role of small-scale, transient magnetic activity in the formation and evolution of solar coronal plumes. Three plumes within equatorial coronal holes are analyzed over the span of several days based on the Solar Dynamic Observatory (SDO)/Atmospheric Imaging Assembly 171 Å and 193 Å images and SDO/Helioseismic and Magnetic Imager line-of-sight magnetograms. The focus is on the role of transient structures at the footpoints in sustaining coronal plumes for relatively long periods of time (i.e., several days). The appearance of plumes is a gradual and lengthy process. In some cases, the initial stages of plume formation aremore » marked by the appearance of pillar-like structures whose footpoints are the sources of transient brightenings. In addition to nominal jets occurring prior to and during the development of plumes, the data show that a large number of small jets (i.e., {sup j}etlets{sup )} and plume transient bright points (PTBPs) occur on timescales of tens of seconds to a few minutes. These features are the result of quasi-random cancellations of fragmented and diffuse minority magnetic polarity with the dominant unipolar magnetic field concentration over an extended period of time. They unambiguously reflect a highly dynamical evolution at the footpoints and are seemingly the main energy source for plumes. This suggests a tendency for plumes to be dependent on the occurrence of transients (i.e., jetlets, and PTBPs) resulting from low-rate magnetic reconnection. The decay phase of plumes is characterized by gradual fainting and multiple rejuvenations as a result of the dispersal of the unipolar magnetic concentration and its precipitation into multiple magnetic centers.« less

Simulations of fully deformed oscillating flux tubes

NASA Astrophysics Data System (ADS)

Karampelas, K.; Van Doorsselaere, T.

2018-02-01

Context. In recent years, a number of numerical studies have been focusing on the significance of the Kelvin-Helmholtz instability in the dynamics of oscillating coronal loops. This process enhances the transfer of energy into smaller scales, and has been connected with heating of coronal loops, when dissipation mechanisms, such as resistivity, are considered. However, the turbulent layer is expected near the outer regions of the loops. Therefore, the effects of wave heating are expected to be confined to the loop's external layers, leaving their denser inner parts without a heating mechanism. Aim. In the current work we aim to study the spatial evolution of wave heating effects from a footpoint driven standing kink wave in a coronal loop. Methods: Using the MPI-AMRVAC code, we performed ideal, three dimensional magnetohydrodynamic simulations of footpoint driven transverse oscillations of a cold, straight coronal flux tube, embedded in a hotter environment. We have also constructed forward models for our simulation using the FoMo code. Results: The developed transverse wave induced Kelvin-Helmholtz (TWIKH) rolls expand throughout the tube cross-section, and cover it entirely. This turbulence significantly alters the initial density profile, leading to a fully deformed cross section. As a consequence, the resistive and viscous heating rate both increase over the entire loop cross section. The resistive heating rate takes its maximum values near the footpoints, while the viscous heating rate at the apex. Conclusions: We conclude that even a monoperiodic driver can spread wave heating over the whole loop cross section, potentially providing a heating source in the inner loop region. Despite the loop's fully deformed structure, forward modelling still shows the structure appearing as a loop. A movie attached to Fig. 1 is available at http://https://www.aanda.org

Double-coronal X-Ray and Microwave Sources Associated with a Magnetic Breakout Solar Eruption

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Yao; Wu, Zhao; Zhao, Di

Double-coronal hard X-ray (HXR) sources are believed to be critical observational evidence of bi-directional energy release through magnetic reconnection in large-scale current sheets in solar flares. Here, we present a study on double-coronal sources observed in both HXR and microwave regimes, revealing new characteristics distinct from earlier reports. This event is associated with a footpoint-occulted X1.3-class flare (2014 April 25, starting at 00:17 UT) and a coronal mass ejection that were likely triggered by the magnetic breakout process, with the lower source extending upward from the top of the partially occulted flare loops and the upper source co-incident with rapidlymore » squeezing-in side lobes (at a speed of ∼250 km s{sup −1} on both sides). The upper source can be identified at energies as high as 70–100 keV. The X-ray upper source is characterized by flux curves that differ from those of the lower source, a weak energy dependence of projected centroid altitude above 20 keV, a shorter duration, and an HXR photon spectrum slightly harder than those of the lower source. In addition, the microwave emission at 34 GHz also exhibits a similar double-source structure and the microwave spectra at both sources are in line with gyrosynchrotron emission given by non-thermal energetic electrons. These observations, especially the co-incidence of the very-fast squeezing-in motion of side lobes and the upper source, indicate that the upper source is associated with (and possibly caused by) this fast motion of arcades. This sheds new light on the origin of the corona double-source structure observed in both HXRs and microwaves.« less

Magnetic topological analysis of coronal bright points

NASA Astrophysics Data System (ADS)

Galsgaard, K.; Madjarska, M. S.; Moreno-Insertis, F.; Huang, Z.; Wiegelmann, T.

2017-10-01

Context. We report on the first of a series of studies on coronal bright points which investigate the physical mechanism that generates these phenomena. Aims: The aim of this paper is to understand the magnetic-field structure that hosts the bright points. Methods: We use longitudinal magnetograms taken by the Solar Optical Telescope with the Narrowband Filter Imager. For a single case, magnetograms from the Helioseismic and Magnetic Imager were added to the analysis. The longitudinal magnetic field component is used to derive the potential magnetic fields of the large regions around the bright points. A magneto-static field extrapolation method is tested to verify the accuracy of the potential field modelling. The three dimensional magnetic fields are investigated for the presence of magnetic null points and their influence on the local magnetic domain. Results: In nine out of ten cases the bright point resides in areas where the coronal magnetic field contains an opposite polarity intrusion defining a magnetic null point above it. We find that X-ray bright points reside, in these nine cases, in a limited part of the projected fan-dome area, either fully inside the dome or expanding over a limited area below which typically a dominant flux concentration resides. The tenth bright point is located in a bipolar loop system without an overlying null point. Conclusions: All bright points in coronal holes and two out of three bright points in quiet Sun regions are seen to reside in regions containing a magnetic null point. An as yet unidentified process(es) generates the brigh points in specific regions of the fan-dome structure. The movies are available at http://www.aanda.org

Inflows in the Inner White-light Corona: The Closing-down of Flux after Coronal Mass Ejections

NASA Astrophysics Data System (ADS)

Hess, P.; Wang, Y.-M.

2017-11-01

During times of high solar activity, the Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph C2 coronagraph has recorded multitudes of small features moving inward through its 2{--}6 {R}⊙ field of view. These outer-coronal inflows, which are concentrated around the heliospheric current sheet, tend to be poorly correlated with individual coronal mass ejection (CME) events. Using running-difference movies constructed from Solar Terrestrial Relations Observatory/COR1 coronagraph images taken during 2008-2014, we have identified large numbers of inward-moving features at heliocentric distances below 2 {R}⊙ , with the rate increasing with sunspot and CME activity. Most of these inner-coronal inflows are closely associated with CMEs, being observed during and in the days immediately following the eruptions. Here, we describe several examples of the pinching-off of tapered streamer structures in the wake of CMEs. This type of inflow event is characterized by a separation of the flow into incoming and outgoing components connected by a thin spike, which is interpreted as a continually elongating current sheet viewed edge-on; by the prior convergence of narrow rays toward the current sheet; and by a succession of collapsing loops that form a cusp-shaped structure at the base of the current sheet. The re-forming streamer overlies a growing post-eruption arcade that is visible in EUV images. These observations provide support for standard reconnection models for the formation/evolution of flux ropes during solar eruptive events. We suggest that inflow streams that occur over a relatively wide range of position angles result from the pinching-off of loop arcades whose axes are oriented parallel rather than perpendicular to the sky plane.

Polarity Comparison Between the Coronal PFSS Model Field and the Heliospheric Magnetic Field at 1 AU Over Solar Cycles 21-24

NASA Astrophysics Data System (ADS)

Koskela, J. S.; Virtanen, I. I.; Mursula, K.

2015-12-01

The solar coronal magnetic field forms an important link between the underlying source in the solar photosphere and the heliospheric magnetic field (HMF). The coronal field has traditionally been calculated from the photospheric observations using various magnetic field models between the photosphere and the corona, in particular the potential field source surface (PFSS) model. Despite its simplicity, the predictions of the PFSS model generally agree quite well with the heliospheric observations and match very well with the predictions of more elaborate models. We make here a detailed comparison between the predictions of the PFSS model with the HMF field observed at 1 AU. We use the photospheric field measured at the Wilcox Solar Observatory, SDO/HMI, SOHO/MDI and SOLIS, and the heliospheric magnetic field measurements at 1 AU collected within the OMNI 2 dataset. This database covers the solar cycles 21-24. We use different source surface distances and different numbers of harmonic components for the PFSS model. We find an optimum polarity match between the coronal field and the HMF for source surface distance of 3.5 Rs. Increasing the number of harmonic components beyond the quadrupole does not essentially improve polarity agreement, indicating that the large scale structure of the HMF at 1 AU is responsible for the agreement while the small scale structure is greatly modified between corona and 1 AU. We also discuss the solar cycle evolution of polarity match and find that the PFSS model prediction is most reliable during the declining phase of the solar cycle. We also find large differences in match percentage between northern and southern hemispheres during the times of systematic southward shift of the heliospheric current sheet (the Bashful ballerina).

Explaining observed red and blue-shifts using multi-stranded coronal loops

NASA Astrophysics Data System (ADS)

Regnier, S.; Walsh, R. W.; Pearson, J.

2012-03-01

Magnetic plasma loops have been termed the building blocks of the solar atmosphere. However, it must be recognised that if the range of loop structures we can observe do consist of many ''sub-resolution'' elements, then current one-dimensional hydrodynamic models are really only applicable to an individual plasma element or strand. Thus a loop should be viewed is an amalgamation of these strands. They could operate in thermal isolation from one another with a wide range of temperatures occurring across the structural elements. This scenario could occur when the energy release mechanism consists of localised, discrete bursts of energy that are due to small scale reconnection sites within the coronal magnetic field- the nanoflare coronal heating mechanism. These energy bursts occur in a time-dependent manner, distributed along the loop/strand length, giving a heating function that depends on space and time. An important observational discovery with the Hinode/EIS spectrometer is the existence of red and blue-shifts in coronal loops depending on the location of the footpoints (inner or outer parts of the active region), and the temperature of the emission line in which the Doppler shifts are measured. Based on the multi-stranded model developed by Sarkar and Walsh (2008, ApJ, 683, 516), we show that red and blue-shifts exist in different simulated Hinode/EIS passbands: cooler lines (OV-SiVII) being dominated by red-shifts, whilst hotter lines (FeXV-CaXVII) are a combination of both. The distribution of blue-shifts depends on the energy input and not so much on the heating location. Characteristic Doppler shifts generated fit well with observed values. We also simulate the Hinode/EIS rasters to closely compare our simulation with the observations. Even if not statistically significant, loops can have footpoints with opposite Doppler shifts.

Filament Eruptions, Jets, and Space Weather

NASA Technical Reports Server (NTRS)

Moore, Ronald; Sterling, Alphonse; Robe, Nick; Falconer, David; Cirtain, Jonathan

2013-01-01

Previously, from chromospheric H alpha and coronal X-ray movies of the Sun's polar coronal holes, it was found that nearly all coronal jets (greater than 90%) are one or the other of two roughly equally common different kinds, different in how they erupt: standard jets and blowout jets (Yamauchi et al 2004, Apl, 605, 5ll: Moore et all 2010, Apj, 720, 757). Here, from inspection of SDO/AIA He II 304 A movies of 54 polar x-ray jets observed in Hinode/XRT movies, we report, as Moore et al (2010) anticipated, that (1) most standard x-ray jets (greater than 80%) show no ejected plasma that is cool enough (T is less than or approximately 10(exp 5K) to be seen in the He II 304 A movies; (2) nearly all blownout X-ray jets (greater than 90%) show obvious ejection of such cool plasma; (3) whereas when cool plasma is ejected in standard X-ray jets, it shows no lateral expansion, the cool plasma ejected in blowout X-ray jets shows strong lateral expansion; and (4) in many blowout X-ray jets, the cool plasma ejection displays the erupting-magnetic-rope form of clasic filament eruptions and is thereby seen to be a miniature filament eruption. The XRT movies also showed most blowout X-ray jets to be larger and brighter, and hence to apparently have more energy, than most standard X-ray jets. These observations (1) confirm the dichotomy of coronal jets, (2) agree with the Shibata model for standard jets, and (3) support the conclusion of Moore et al (2010) that in blowout jets the magnetic-arch base of the jet erupts in the manner of the much larger magnetic arcades in which the core field, the field rooted along the arcade's polarity inversion line, is sheared and twisted (sigmoid), often carries a cool-plasma filament, and erupts to blowout the arcade, producing a CME. From Hinode/SOT Ca II movies of the polar limb, Sterling et al (2010, ApJ, 714, L1) found that chromospheric Type-II spicules show a dichotomy of eruption dynamics similar to that found here for the cool-plasma component of coronal X-ray jets. This favors the idea that Type-II spicules are miniature counterparts of coronal X-ray jets. In Moore et al (2011, ApJ, 731, L18), we pointed out that if Type-II spicules are magnetic eruptions that work like coronal X-ray jets, they carry an area-averaged mechanical energy flux of approximately 7x10)(exp 5) erg cm(exp -2) s(exp-1) into the corona in the form of MHD waves and jet outflow, enough to power the heating of the global corona and solar wind. On this basis, from our observations of mini-filament eruptions in blowout X-ray jets, we infer that magnetic explosions of the type that have erupting filaments in them are the main engines of both (1) the steady solar wind and (2) the CMEs that produce the most severe space weather by blasting out through the corona and solar wind, making solar energetic particle storms, and bashing the Earth's magnetosphere. We conclude that in focusing on prominences and filament eruptions, Einar had his eye on the main bet for understanding what powers all space weather, both the extreme and the normal.

Analysis of an Anemone-Type Eruption in an On-Disk Coronal Hole

NASA Technical Reports Server (NTRS)

Adams, Mitzi; Tennant, Allyn; Alexander, Caroline; Sterling, Alphonse; Moore, Ronald; Woolley, Robert

2016-01-01

We report on an eruption seen in a very small coronal hole (about 120 arcseconds across), beginning at approximately 19:00 Universal Time on March 3, 2016. The event was initially observed by an amateur astronomer (RW) in an H-alpha movie from the Global Oscillation Network Group (GONG); the eruption attracted the attention of the observer because there was no nearby active region. To examine the region in detail, we use data from the Solar Dynamics Observatory (SDO), provided by the Atmospheric Imaging Assembly (AIA) in wavelengths 193 angstroms, 304 angstroms, and 94 angstroms, and the Helioseismic and Magnetic Imager (HMI). Data analysis and calibration activities such as scaling, rotation so that north is up, and removal of solar rotation are accomplished with SunPy. The eruption in low-cadence HMI data begins with the appearance of a bipole in the location of the coronal hole, followed by (apparent) expansion outwards when the intensity of the AIA wavelengths brighten; as the event proceeds, the coronal hole disappears. From high-cadence data, we will present results on the magnetic evolution of this structure, how it is related to intensity brightenings seen in the various SDO/AIA wavelengths, and how this event compares with the standard-anemone picture.

Constraining Large-Scale Solar Magnetic Field Models with Optical Coronal Observations

NASA Astrophysics Data System (ADS)

Uritsky, V. M.; Davila, J. M.; Jones, S. I.

2015-12-01

Scientific success of the Solar Probe Plus (SPP) and Solar Orbiter (SO) missions will depend to a large extent on the accuracy of the available coronal magnetic field models describing the connectivity of plasma disturbances in the inner heliosphere with their source regions. We argue that ground based and satellite coronagraph images can provide robust geometric constraints for the next generation of improved coronal magnetic field extrapolation models. In contrast to the previously proposed loop segmentation codes designed for detecting compact closed-field structures above solar active regions, we focus on the large-scale geometry of the open-field coronal regions located at significant radial distances from the solar surface. Details on the new feature detection algorithms will be presented. By applying the developed image processing methodology to high-resolution Mauna Loa Solar Observatory images, we perform an optimized 3D B-line tracing for a full Carrington rotation using the magnetic field extrapolation code presented in a companion talk by S.Jones at al. Tracing results are shown to be in a good qualitative agreement with the large-scalie configuration of the optical corona. Subsequent phases of the project and the related data products for SSP and SO missions as wwll as the supporting global heliospheric simulations will be discussed.

OUTFLOWS AND DARK BANDS AT ARCADE-LIKE ACTIVE REGION CORE BOUNDARIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scott, J. T.; Martens, P. C. H.; Tarr, L.

Observations from the EUV Imaging Spectrometer (EIS) on board Hinode have revealed outflows and non-thermal line broadening in low intensity regions at the edges of active regions (ARs). We use data from Hinode's EIS, Solar Dynamic Observatory's Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager, and the Transition Region and Coronal Explorer instrument to investigate the boundaries of arcade-like AR cores for NOAA ARs 11112, 10978, and 9077. A narrow, low intensity region that is observed at the core's periphery as a dark band shows outflows and increased spectral line broadening. This dark band is found to exist for daysmore » and appears between the bright coronal loop structures of different coronal topologies. We find a case where the dark band region is formed between the magnetic field from emerging flux and the field of the pre-existing flux. A magnetic field extrapolation indicates that this dark band is coincident with the spine lines or magnetic separatrices in the extrapolated field. This occurs over unipolar regions where the brightened coronal field is separated in connectivity and topology. This separation does not appear to be infinitesimal and an initial estimate of the minimum distance of separation is found to be Almost-Equal-To 1.5-3.5 Mm.« less

Analysis of an Anemone-Type Eruption in an On-Disk Coronal Hole

NASA Astrophysics Data System (ADS)

Adams, Mitzi; Tennant, Allyn F.; Alexander, Caroline E.; Sterling, Alphonse C.; Moore, Ronald L.; Woolley, Robert

2016-05-01

We report on an eruption seen in a very small coronal hole (about 120'' across), beginning at approximately 19:00 UT on March 3, 2016. The event was initially observed by an amateur astronomer (RW) in an H-alpha movie from the Global Oscillation Network Group (GONG); the eruption attracted the attention of the observer because there was no nearby active region. To examine the region in detail, we use data from the Solar Dynamics Observatory (SDO), provided by the Atmospheric Imaging Assembly (AIA) in wavelengths 193 Å, 304 Å, and 94 Å, and the Helioseismic and Magnetic Imager (HMI). Data analysis and calibration activities such as scaling, rotation so that north is up, and removal of solar rotation are accomplished with SunPy. The eruption in low-cadence HMI data begins with the appearance of a bipole in the location of the coronal hole, followed by (apparent) expansion outwards when the intensity of the AIA wavelengths brighten; as the event proceeds, the coronal hole disappears. From high-cadence data, we will present results on the magnetic evolution of this structure, how it is related to intensity brightenings seen in the various SDO/AIA wavelengths, and how this event compares with the standard-anemone picture.

Observable Signatures of Energy Release in Braided Coronal Loops

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pontin, D. I.; Janvier, M.; Tiwari, S. K.

We examine the turbulent relaxation of solar coronal loops containing non-trivial field line braiding. Such field line tangling in the corona has long been postulated in the context of coronal heating models. We focus on the observational signatures of energy release in such braided magnetic structures using MHD simulations and forward modeling tools. The aim is to answer the following question: if energy release occurs in a coronal loop containing braided magnetic flux, should we expect a clearly observable signature in emissions? We demonstrate that the presence of braided magnetic field lines does not guarantee a braided appearance to themore » observed intensities. Observed intensities may—but need not necessarily—reveal the underlying braided nature of the magnetic field, depending on the degree and pattern of the field line tangling within the loop. However, in all cases considered, the evolution of the braided loop is accompanied by localized heating regions as the loop relaxes. Factors that may influence the observational signatures are discussed. Recent high-resolution observations from Hi-C have claimed the first direct evidence of braided magnetic fields in the corona. Here we show that both the Hi-C data and some of our simulations give the appearance of braiding at a range of scales.« less

Fast-sausage oscillations in coronal loops with smooth boundary

NASA Astrophysics Data System (ADS)

Lopin, I.; Nagorny, I.

2014-12-01

Aims: The effect of the transition layer (shell) in nonuniform coronal loops with a continuous radial density profile on the properties of fast-sausage modes are studied analytically and numerically. Methods: We modeled the coronal waveguide as a structured tube consisting of a cord and a transition region (shell) embedded within a magnetic uniform environment. The derived general dispersion relation was investigated analytically and numerically in the context of frequency, cut-off wave number, and the damping rate of fast-sausage oscillations for various values of loop parameters. Results: The frequency of the global fast-sausage mode in the loops with a diffuse (or smooth) boundary is determined mainly by the external Alfvén speed and longitudinal wave number. The damping rate of such a mode can be relatively low. The model of coronal loop with diffuse boundary can support a comparatively low-frequency, global fast-sausage mode of detectable quality without involving extremely low values of the density contrast. The effect of thin transition layer (corresponds to the loops with steep boundary) is negligible and produces small reductions of oscillation frequency and relative damping rate in comparison with the case of step-function density profile. Seismological application of obtained results gives the estimated Alfvén speed outside the flaring loop about 3.25 Mm/s.

Relation Between the 3D-Geometry of the Coronal Wave and Associated CME During the 26 April 2008 Event

NASA Technical Reports Server (NTRS)

Temmer, M.; Veronig, A. M.; Gopalswamy, N.; Yashiro, S.

2011-01-01

We study the kinematical characteristics and 3D geometry of a large-scale coronal wave that occurred in association with the 26 April 2008 flare-CME event. The wave was observed with the EUVI instruments aboard both STEREO spacecraft (STEREO-A and STEREO-B) with a mean speed of approx 240 km/s. The wave is more pronounced in the eastern propagation direction, and is thus, better observable in STEREO-B images. From STEREO-B observations we derive two separate initiation centers for the wave, and their locations fit with the coronal dimming regions. Assuming a simple geometry of the wave we reconstruct its 3D nature from combined STEREO-A and STEREO-B observations. We find that the wave structure is asymmetric with an inclination toward East. The associated CME has a deprojected speed of approx 750 +/- 50 km/s, and it shows a non-radial outward motion toward the East with respect to the underlying source region location. Applying the forward fitting model developed by Thernisien, Howard, and Vourlidas we derive the CME flux rope position on the solar surface to be close to the dimming regions. We conclude that the expanding flanks of the CME most likely drive and shape the coronal wave.

Bashful ballerina unveiled: Multipole analysis of the coronal magnetic field

NASA Astrophysics Data System (ADS)

Virtanen, I.; Mursula, K.

2012-12-01

Heliospheric current sheet (HCS) is the continuum of the coronal magnetic equator, dividing the heliospheric magnetic field (HMF) into two sectors (polarities). Because of its wavy structure, the HCS is often called the ballerina skirt. Several studies have proven that the HCS is southward shifted during about three years in the solar declining phase. This persistent phenomenon, called the bashful ballerina, has been verified by geomagnetic indices since 1930s, by OMNI data base since 1960s, by the WSO PFSS model since mid-1970s and by the Ulysses probe measurements during the fast latitude scans in 1994-1995 and 2007. We study here the Wilcox Solar Observatory measurements of the photospheric magnetic field and the PFSS extrapolation of the coronal magnetic field. We show that the quadrupole moment of the photospheric magnetic field, which is important for the HCS asymmetry (bashful ballerina), mainly arises from the difference between northern and southern polar field strengths. According to the WSO data the minimum time quadrupole is mainly due to the difference between the highest northern and southern latitude bins. Related studies imply that the southward shift of the HCS is related to the delayed development of southern coronal holes. We also discuss the suggested connection of the HCS asymmetry to sunspot hemispheric asymmetry.

Learning about the internal structure of categories through classification and feature inference.

PubMed

Jee, Benjamin D; Wiley, Jennifer

2014-01-01

Previous research on category learning has found that classification tasks produce representations that are skewed toward diagnostic feature dimensions, whereas feature inference tasks lead to richer representations of within-category structure. Yet, prior studies often measure category knowledge through tasks that involve identifying only the typical features of a category. This neglects an important aspect of a category's internal structure: how typical and atypical features are distributed within a category. The present experiments tested the hypothesis that inference learning results in richer knowledge of internal category structure than classification learning. We introduced several new measures to probe learners' representations of within-category structure. Experiment 1 found that participants in the inference condition learned and used a wider range of feature dimensions than classification learners. Classification learners, however, were more sensitive to the presence of atypical features within categories. Experiment 2 provided converging evidence that classification learners were more likely to incorporate atypical features into their representations. Inference learners were less likely to encode atypical category features, even in a "partial inference" condition that focused learners' attention on the feature dimensions relevant to classification. Overall, these results are contrary to the hypothesis that inference learning produces superior knowledge of within-category structure. Although inference learning promoted representations that included a broad range of category-typical features, classification learning promoted greater sensitivity to the distribution of typical and atypical features within categories.

THE EFFECTS OF LINE-OF-SIGHT INTEGRATION ON MULTISTRAND CORONAL LOOP OSCILLATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Moortel, I.; Pascoe, D. J., E-mail: ineke@mcs.st-and.ac.uk

2012-02-10

Observations have shown that transverse oscillations are present in a multitude of coronal structures. It is generally assumed that these oscillations are driven by (sub)surface footpoint motions. Using fully three-dimensional MHD simulations, we show that these footpoint perturbations generate propagating kink (Alfvenic) modes which couple very efficiently into (azimuthal) Alfven waves. Using an ensemble of randomly distributed loops, driven by footpoint motions with random periods and directions, we compare the absolute energy in the numerical domain with the energy that is 'visible' when integrating along the line of sight (LOS). We show that the kinetic energy derived from the LOSmore » Doppler velocities is only a small fraction of the actual energy provided by the footpoint motions. Additionally, the superposition of loop structures along the LOS makes it nearly impossible to identify which structure the observed oscillations are actually associated with and could impact the identification of the mode of oscillation.« less

THE KELVIN-HELMHOLTZ INSTABILITY AT CORONAL MASS EJECTION BOUNDARIES IN THE SOLAR CORONA: OBSERVATIONS AND 2.5D MHD SIMULATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moestl, U. V.; Temmer, M.; Veronig, A. M., E-mail: ute.moestl@uni-graz.at

2013-03-20

The Atmospheric Imaging Assembly on board the Solar Dynamics Observatory observed a coronal mass ejection with an embedded filament on 2011 February 24, revealing quasi-periodic vortex-like structures at the northern side of the filament boundary with a wavelength of approximately 14.4 Mm and a propagation speed of about 310 {+-} 20 km s{sup -1}. These structures could result from the Kelvin-Helmholtz instability occurring on the boundary. We perform 2.5D numerical simulations of the Kelvin-Helmholtz instability and compare the simulated characteristic properties of the instability with the observations, where we obtain qualitative as well as quantitative accordance. We study the absencemore » of Kelvin-Helmholtz vortex-like structures on the southern side of the filament boundary and find that a magnetic field component parallel to the boundary with a strength of about 20% of the total magnetic field has stabilizing effects resulting in an asymmetric development of the instability.« less

Origin and structures of solar eruptions II: Magnetic modeling

NASA Astrophysics Data System (ADS)

Guo, Yang; Cheng, Xin; Ding, MingDe

2017-07-01

The topology and dynamics of the three-dimensional magnetic field in the solar atmosphere govern various solar eruptive phenomena and activities, such as flares, coronal mass ejections, and filaments/prominences. We have to observe and model the vector magnetic field to understand the structures and physical mechanisms of these solar activities. Vector magnetic fields on the photosphere are routinely observed via the polarized light, and inferred with the inversion of Stokes profiles. To analyze these vector magnetic fields, we need first to remove the 180° ambiguity of the transverse components and correct the projection effect. Then, the vector magnetic field can be served as the boundary conditions for a force-free field modeling after a proper preprocessing. The photospheric velocity field can also be derived from a time sequence of vector magnetic fields. Three-dimensional magnetic field could be derived and studied with theoretical force-free field models, numerical nonlinear force-free field models, magnetohydrostatic models, and magnetohydrodynamic models. Magnetic energy can be computed with three-dimensional magnetic field models or a time series of vector magnetic field. The magnetic topology is analyzed by pinpointing the positions of magnetic null points, bald patches, and quasi-separatrix layers. As a well conserved physical quantity, magnetic helicity can be computed with various methods, such as the finite volume method, discrete flux tube method, and helicity flux integration method. This quantity serves as a promising parameter characterizing the activity level of solar active regions.

Forward Modeling of Coronal Mass Ejection Flux Ropes in the Inner Heliosphere with 3DCORE.

PubMed

Möstl, C; Amerstorfer, T; Palmerio, E; Isavnin, A; Farrugia, C J; Lowder, C; Winslow, R M; Donnerer, J M; Kilpua, E K J; Boakes, P D

2018-03-01

Forecasting the geomagnetic effects of solar storms, known as coronal mass ejections (CMEs), is currently severely limited by our inability to predict the magnetic field configuration in the CME magnetic core and by observational effects of a single spacecraft trajectory through its 3-D structure. CME magnetic flux ropes can lead to continuous forcing of the energy input to the Earth's magnetosphere by strong and steady southward-pointing magnetic fields. Here we demonstrate in a proof-of-concept way a new approach to predict the southward field B z in a CME flux rope. It combines a novel semiempirical model of CME flux rope magnetic fields (Three-Dimensional Coronal ROpe Ejection) with solar observations and in situ magnetic field data from along the Sun-Earth line. These are provided here by the MESSENGER spacecraft for a CME event on 9-13 July 2013. Three-Dimensional Coronal ROpe Ejection is the first such model that contains the interplanetary propagation and evolution of a 3-D flux rope magnetic field, the observation by a synthetic spacecraft, and the prediction of an index of geomagnetic activity. A counterclockwise rotation of the left-handed erupting CME flux rope in the corona of 30° and a deflection angle of 20° is evident from comparison of solar and coronal observations. The calculated Dst matches reasonably the observed Dst minimum and its time evolution, but the results are highly sensitive to the CME axis orientation. We discuss assumptions and limitations of the method prototype and its potential for real time space weather forecasting and heliospheric data interpretation.

Hanle-Zeeman Scattering Matrix for Magnetic Dipole Transitions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Megha, A.; Sampoorna, M.; Nagendra, K. N.

2017-06-01

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 ( M 1) 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 M 1 transitions usingmore » the classical magnetic dipole model of Casini and 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 M 1 transitions and compare it with that for the electric dipole ( E 1) transitions.« less

Precipitation and Release of Solar Energetic Particles from the Solar Coronal Magnetic Field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Ming; Zhao, Lulu, E-mail: mzhang@fit.edu

Most solar energetic particles (SEPs) are produced in the corona. They propagate through complex coronal magnetic fields subject to scattering and diffusion across the averaged field lines by turbulence. We examine the behaviors of particle transport using a stochastic 3D focused transport simulation in a potential field source surface model of coronal magnetic field. The model is applied to an SEP event on 2010 February 7. We study three scenarios of particle injection at (i) the compact solar flare site, (ii) the coronal mass ejection (CME) shock, and (iii) the EUV wave near the surface. The majority of particles injectedmore » on open field lines are able to escape the corona. We found that none of our models can explain the observations of wide longitudinal SEP spread without perpendicular diffusion. If the perpendicular diffusion is about 10% of what is derived from the random walk of field lines at the rate of supergranular diffusion, particles injected at the compact solar flare site can spread to a wide range of longitude and latitude, very similar to the behavior of particles injected at a large CME shock. Stronger pitch-angle scattering results in a little more lateral spread by holding the particles in the corona for longer periods of time. Some injected particles eventually end up precipitating onto the solar surface. Even with a very small perpendicular diffusion, the pattern of the particle precipitation can be quite complicated depending on the detailed small-scale coronal magnetic field structures, which could be seen with future sensitive gamma-ray telescopes.« less

Precipitation and Release of Solar Energetic Particles from the Solar Coronal Magnetic Field

NASA Astrophysics Data System (ADS)

Zhang, Ming; Zhao, Lulu

2017-09-01

Most solar energetic particles (SEPs) are produced in the corona. They propagate through complex coronal magnetic fields subject to scattering and diffusion across the averaged field lines by turbulence. We examine the behaviors of particle transport using a stochastic 3D focused transport simulation in a potential field source surface model of coronal magnetic field. The model is applied to an SEP event on 2010 February 7. We study three scenarios of particle injection at (I) the compact solar flare site, (II) the coronal mass ejection (CME) shock, and (III) the EUV wave near the surface. The majority of particles injected on open field lines are able to escape the corona. We found that none of our models can explain the observations of wide longitudinal SEP spread without perpendicular diffusion. If the perpendicular diffusion is about 10% of what is derived from the random walk of field lines at the rate of supergranular diffusion, particles injected at the compact solar flare site can spread to a wide range of longitude and latitude, very similar to the behavior of particles injected at a large CME shock. Stronger pitch-angle scattering results in a little more lateral spread by holding the particles in the corona for longer periods of time. Some injected particles eventually end up precipitating onto the solar surface. Even with a very small perpendicular diffusion, the pattern of the particle precipitation can be quite complicated depending on the detailed small-scale coronal magnetic field structures, which could be seen with future sensitive gamma-ray telescopes.

Forward Modeling of Coronal Mass Ejection Flux Ropes in the Inner Heliosphere with 3DCORE

NASA Astrophysics Data System (ADS)

Möstl, C.; Amerstorfer, T.; Palmerio, E.; Isavnin, A.; Farrugia, C. J.; Lowder, C.; Winslow, R. M.; Donnerer, J. M.; Kilpua, E. K. J.; Boakes, P. D.

2018-03-01

Forecasting the geomagnetic effects of solar storms, known as coronal mass ejections (CMEs), is currently severely limited by our inability to predict the magnetic field configuration in the CME magnetic core and by observational effects of a single spacecraft trajectory through its 3-D structure. CME magnetic flux ropes can lead to continuous forcing of the energy input to the Earth's magnetosphere by strong and steady southward-pointing magnetic fields. Here we demonstrate in a proof-of-concept way a new approach to predict the southward field Bz in a CME flux rope. It combines a novel semiempirical model of CME flux rope magnetic fields (Three-Dimensional Coronal ROpe Ejection) with solar observations and in situ magnetic field data from along the Sun-Earth line. These are provided here by the MESSENGER spacecraft for a CME event on 9-13 July 2013. Three-Dimensional Coronal ROpe Ejection is the first such model that contains the interplanetary propagation and evolution of a 3-D flux rope magnetic field, the observation by a synthetic spacecraft, and the prediction of an index of geomagnetic activity. A counterclockwise rotation of the left-handed erupting CME flux rope in the corona of 30° and a deflection angle of 20° is evident from comparison of solar and coronal observations. The calculated Dst matches reasonably the observed Dst minimum and its time evolution, but the results are highly sensitive to the CME axis orientation. We discuss assumptions and limitations of the method prototype and its potential for real time space weather forecasting and heliospheric data interpretation.

Direct Observations of Magnetic Flux Rope Formation during a Solar Coronal Mass Ejection

NASA Astrophysics Data System (ADS)

Song, H. Q.; Zhang, J.; Chen, Y.; Cheng, X.

2014-09-01

Coronal mass ejections (CMEs) are the most spectacular eruptive phenomena in the solar atmosphere. It is generally accepted that CMEs are the results of eruptions of magnetic flux ropes (MFRs). However, there is heated debate on whether MFRs exist prior to the eruptions or if they are formed during the eruptions. Several coronal signatures, e.g., filaments, coronal cavities, sigmoid structures, and hot channels (or hot blobs), are proposed as MFRs and observed before the eruption, which support the pre-existing MFR scenario. There is almost no reported observation of MFR formation during the eruption. In this Letter, we present an intriguing observation of a solar eruptive event that occurred on 2013 November 21 with the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory, which shows the formation process of the MFR during the eruption in detail. The process began with the expansion of a low-lying coronal arcade, possibly caused by the flare magnetic reconnection underneath. The newly formed ascending loops from below further pushed the arcade upward, stretching the surrounding magnetic field. The arcade and stretched magnetic field lines then curved in just below the arcade vertex, forming an X-point. The field lines near the X-point continued to approach each other and a second magnetic reconnection was induced. It is this high-lying magnetic reconnection that led to the formation and eruption of a hot blob (~10 MK), presumably an MFR, producing a CME. We suggest that two spatially separated magnetic reconnections occurred in this event, which were responsible for producing the flare and the hot blob (CME).

Direct Observations of Magnetic Flux Rope Formation during a Solar Coronal Mass Ejection

NASA Astrophysics Data System (ADS)

Song, H.; Zhang, J.; Chen, Y.; Cheng, X.

2014-12-01

Coronal mass ejections (CMEs) are the most spectacular eruptive phenomena in the solar atmosphere. It is generally accepted that CMEs are results of eruptions of magnetic flux ropes (MFRs). However, a heated debate is on whether MFRs pre-exist before the eruptions or they are formed during the eruptions. Several coronal signatures, e.g., filaments, coronal cavities, sigmoid structures and hot channels (or hot blobs), are proposed as MFRs and observed before the eruption, which support the pre existing MFR scenario. There is almost no reported observation about MFR formation during the eruption. In this presentation, we present an intriguing observation of a solar eruptive event with the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory, which shows a detailed formation process of the MFR during the eruption. The process started with the expansion of a low lying coronal arcade, possibly caused by the flare magnetic reconnection underneath. The newly-formed ascending loops from below further pushed the arcade upward, stretching the surrounding magnetic field. The arcade and stretched magnetic field lines then curved-in just below the arcade vertex, forming an X-point. The field lines near the X-point continued to approach each other and a second magnetic reconnection was induced. It is this high-lying magnetic reconnection that led to the formation and eruption of a hot blob (~ 10 MK), presumably a MFR, producing a CME. We suggest that two spatially-separated magnetic reconnections occurred in this event, responsible for producing the flare and the hot blob (CME), respectively.

SLIPPING MAGNETIC RECONNECTION, CHROMOSPHERIC EVAPORATION, IMPLOSION, AND PRECURSORS IN THE 2014 SEPTEMBER 10 X1.6-CLASS SOLAR FLARE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dudík, Jaroslav; Karlický, Marian; Dzifčáková, Elena

2016-05-20

We investigate the occurrence of slipping magnetic reconnection, chromospheric evaporation, and coronal loop dynamics in the 2014 September 10 X-class flare. Slipping reconnection is found to be present throughout the flare from its early phase. Flare loops are seen to slip in opposite directions toward both ends of the ribbons. Velocities of 20–40 km s{sup −1} are found within time windows where the slipping is well resolved. The warm coronal loops exhibit expanding and contracting motions that are interpreted as displacements due to the growing flux rope that subsequently erupts. This flux rope existed and erupted before the onset ofmore » apparent coronal implosion. This indicates that the energy release proceeds by slipping reconnection and not via coronal implosion. The slipping reconnection leads to changes in the geometry of the observed structures at the Interface Region Imaging Spectrograph slit position, from flare loop top to the footpoints in the ribbons. This results in variations of the observed velocities of chromospheric evaporation in the early flare phase. Finally, it is found that the precursor signatures, including localized EUV brightenings as well as nonthermal X-ray emission, are signatures of the flare itself, progressing from the early phase toward the impulsive phase, with the tether-cutting being provided by the slipping reconnection. The dynamics of both the flare and outlying coronal loops is found to be consistent with the predictions of the standard solar flare model in three dimensions.« less

Large-scale properties of the interplanetary magnetic field

NASA Technical Reports Server (NTRS)

Schatten, K. H.

1972-01-01

Early theoretical work of Parker is presented along with the observational evidence supporting his Archimedes spiral model. Variations present in the interplanetary magnetic field from the spiral angle are related to structures in the solar wind. The causes of these structures are found to be either nonuniform radial solar wind flow or the time evolution of the photospheric field. Coronal magnetic models are related to the connection between the solar magnetic field and the interplanetary magnetic field. Direct extension of the solar field-magnetic nozzle controversy is discussed along with the coronal magnetic models. Effects of active regions on the interplanetary magnetic field is discussed with particular reference to the evolution of interplanetary sectors. Interplanetary magnetic field magnitude variations are shown throughout the solar cycle. The percentage of time the field magnitude is greater than 10 gamma is shown to closely parallel sunspot number. The sun's polar field influence on the interplanetary field and alternative views of the magnetic field structure out of the ecliptic plane are presented. In addition, a variety of significantly different interplanetary field structures are discussed.

Two Coronal Mass Ejections Events Close to the Total Solar Eclipse Aug. 11, 1999

NASA Astrophysics Data System (ADS)

Churyumov, K. I.; Ivanchuk, V. I.

We present some results of exploration of the solar corona on the basis of analysis of its images obtained in Romania by K.I.Churyumov and in Bulgaria by V.Mormyl' and S.Kharchuk Aug. 11 1999. Structure of the corona is characterized by the presence of numerous power and thin rays which have mainly radial orientation in regard to the Sun. The high-latitude rays of the north hemisphere (especially in the NE sector) are inclined in the direction of the N-pole. The interesting peculiarity of the solar corona Aug. 11 1999 is the existence of the sabre-like thin double ray on the NE-limb, which goes from the solar limb region at p ~ 50o. It is close to the peculiar center of ``repulsion'', which is observed for the fan of rays of the E-limb. We proposed that the similar rays and the observed center of ``repulsion'' were an indicator (postcursor) which shows that in this place of the corona the phenomena of the coronal mass ejections (CME) of the coronal plasma occurred. This views was confirmed by observations of the solar corona with the help of the Lasco C2 coronograph of SOHO Aug. 10/11 1999. In the region of the NW-quadrant and near the W-equator the enough sharp transequatorial arc by height ~ 0.7Rsolar with the center at ϕo = +10 deg is detected. It is nonfull arcs which intersects set of rays structures and near its foundation on the altitude /~ 0.3Rsolar there is a coronal condensation with characteristic sizes Δ l ~ 0.1Rsolar. We think that it is tied with development of a coronal mass ejection (CME) detected by the coronograph Lasco C2 of SOHO Aug. 11/12, 1999. On the best pictures it is seen that CME had the angle sizes ~ 90 deg and filled in nearly the all NW quadrant as a not uniform buble. On the basis of the published data we determined several

Solar coronal loop heating by cross-field wave transport

NASA Technical Reports Server (NTRS)

Amendt, Peter; Benford, Gregory

1989-01-01

Solar coronal arches heated by turbulent ion-cyclotron waves may suffer significant cross-field transport by these waves. Nonlinear processes fix the wave-propagation speed at about a tenth of the ion thermal velocity, which seems sufficient to spread heat from a central core into a large cool surrounding cocoon. Waves heat cocoon ions both through classical ion-electron collisions and by turbulent stochastic ion motions. Plausible cocoon sizes set by wave damping are in roughly kilometers, although the wave-emitting core may be only 100 m wide. Detailed study of nonlinear stabilization and energy-deposition rates predicts that nearby regions can heat to values intermediate between the roughly electron volt foot-point temperatures and the about 100 eV core, which is heated by anomalous Ohmic losses. A volume of 100 times the core volume may be affected. This qualitative result may solve a persistent problem with current-driven coronal heating; that it affects only small volumes and provides no way to produce the extended warm structures perceptible to existing instruments.

Geomagnetic response of interplanetary coronal mass ejections in the Earth's magnetosphere

NASA Astrophysics Data System (ADS)

Badruddin; Mustajab, F.; Derouich, M.

2018-05-01

A coronal mass ejections (CME) is the huge mass of plasma with embedded magnetic field ejected abruptly from the Sun. These CMEs propagate into interplanetary space with different speed. Some of them hit the Earth's magnetosphere and create many types of disturbances; one of them is the disturbance in the geomagnetic field. Individual geomagnetic disturbances differ not only in their magnitudes, but the nature of disturbance is also different. It is, therefore, desirable to understand these differences not only to understand the physics of geomagnetic disturbances but also to understand the properties of solar/interplanetary structures producing these disturbances of different magnitude and nature. In this work, we use the spacecraft measurements of CMEs with distinct magnetic properties propagating in the interplanetary space and generating disturbances of different levels and nature. We utilize their distinct plasma and field properties to search for the interplanetary parameter(s) playing important role in influencing the geomagnetic response of different coronal mass ejections.

Coronal Structure of a Flaring Region and Associated Coronal Mass Ejection

NASA Technical Reports Server (NTRS)

Kundu, Mukul R.; Manoharan, P. K.

2003-01-01

We report the multiwavelength investigations of an eruptive flare event that occurred on 2001 April 2 at about 11 UT. The manifestations associated with this flare event have been studied from the near-Sun region to about 0.5 AU. The H-alpha images from the Meudon Spectroheliograph reveal a fast spectacular eruption of plasmoids from the flare site to the west and a Moreton wave disturbance propagating toward the south, A bright, fast, wide coronal mass ejection (CME) associated with this eruptive event was imaged by SOHO/LASCO and the remote-sensing interplanetary scintillation technique. The timings and positions of the Type II radio bursts, H-alpha eruption, and CME onset as well as the magnetic field configuration suggest a release of energy at the null point. The results seem to support the "breakout" scenario proposed by Antiochos and coworkers, and they are also suggestive that the energy release is followed by magnetic reconnection between the low-lying loops near the separatrix and the loop system above them.

Solar Coronal Jets Extending to High Altitudes Observed during the 2017 August 21 Total Eclipse

NASA Astrophysics Data System (ADS)

Hanaoka, Yoichiro; Hasuo, Ryuichi; Hirose, Tsukasa; Ikeda, Akiko C.; Ishibashi, Tsutomu; Manago, Norihiro; Masuda, Yukio; Morita, Sakuhiro; Nakazawa, Jun; Ohgoe, Osamu; Sakai, Yoshiaki; Sasaki, Kazuhiro; Takahashi, Koichi; Toi, Toshiyuki

2018-06-01

Coronal jets, which extend from the solar surface to beyond 2 R ⊙, were observed in the polar coronal hole regions during the total solar eclipse on 2017 August 21. In a time-series of white-light images of the corona spanning 70 minutes taken with our multi-site observations of this eclipse, six jets were found as narrow structures upwardly ejected with an apparent speed of about 450 km s‑1 in polar plumes. On the other hand, extreme-ultraviolet (EUV) images taken with the Atmospheric Image Assembly of the Solar Dynamics Observatory show that all of the eclipse jets were preceded by EUV jets. Conversely, all the EUV jets whose brightnesses are comparable to ordinary soft X-ray jets and that occurred in the polar regions near the eclipse period, were observed as eclipse jets. These results suggest that ordinary polar jets generally reach high altitudes and escape from the Sun as part of the solar wind.

Tracking of an electron beam through the solar corona with LOFAR

NASA Astrophysics Data System (ADS)

Mann, G.; Breitling, F.; Vocks, C.; Aurass, H.; Steinmetz, M.; Strassmeier, K. G.; Bisi, M. M.; Fallows, R. A.; Gallagher, P.; Kerdraon, A.; Mackinnon, A.; Magdalenic, J.; Rucker, H.; Anderson, J.; Asgekar, A.; Avruch, I. M.; Bell, M. E.; Bentum, M. J.; Bernardi, G.; Best, P.; Bîrzan, L.; Bonafede, A.; Broderick, J. W.; Brüggen, M.; Butcher, H. R.; Ciardi, B.; Corstanje, A.; Gasperin, F. de; Geus, E. de; Deller, A.; Duscha, S.; Eislöffel, J.; Engels, D.; Falcke, H.; Fender, R.; Ferrari, C.; Frieswijk, W.; Garrett, M. A.; Grießmeier, J.; Gunst, A. W.; van Haarlem, M.; Hassall, T. E.; Heald, G.; Hessels, J. W. T.; Hoeft, M.; Hörandel, J.; Horneffer, A.; Juette, E.; Karastergiou, A.; Klijn, W. F. A.; Kondratiev, V. I.; Kramer, M.; Kuniyoshi, M.; Kuper, G.; Maat, P.; Markoff, S.; McFadden, R.; McKay-Bukowski, D.; McKean, J. P.; Mulcahy, D. D.; Munk, H.; Nelles, A.; Norden, M. J.; Orru, E.; Paas, H.; Pandey-Pommier, M.; Pandey, V. N.; Pizzo, R.; Polatidis, A. G.; Rafferty, D.; Reich, W.; Röttgering, H.; Scaife, A. M. M.; Schwarz, D. J.; Serylak, M.; Sluman, J.; Smirnov, O.; Stappers, B. W.; Tagger, M.; Tang, Y.; Tasse, C.; ter Veen, S.; Thoudam, S.; Toribio, M. C.; Vermeulen, R.; van Weeren, R. J.; Wise, M. W.; Wucknitz, O.; Yatawatta, S.; Zarka, P.; Zensus, J. A.

2018-03-01

The Sun's activity leads to bursts of radio emission, among other phenomena. An example is type-III radio bursts. They occur frequently and appear as short-lived structures rapidly drifting from high to low frequencies in dynamic radio spectra. They are usually interpreted as signatures of beams of energetic electrons propagating along coronal magnetic field lines. Here we present novel interferometric LOFAR (LOw Frequency ARray) observations of three solar type-III radio bursts and their reverse bursts with high spectral, spatial, and temporal resolution. They are consistent with a propagation of the radio sources along the coronal magnetic field lines with nonuniform speed. Hence, the type-III radio bursts cannot be generated by a monoenergetic electron beam, but by an ensemble of energetic electrons with a spread distribution in velocity and energy. Additionally, the density profile along the propagation path is derived in the corona. It agrees well with three-fold coronal density model by (1961, ApJ, 133, 983).

Does TRACE Resolve Isothermal Coronal Loops?

NASA Astrophysics Data System (ADS)

Weber, Mark A.; Schmelz, J.; Kashyap, V.; Roames, J.

2006-06-01

Historically, increasing resolution of solar data has revealed ever smaller length scales for both the thermodynamics and the magnetic structure of the corona. Furthermore, the dynamics there are governed by magnetohydrodynamic processes which are difficult to observe or model. Recent results in the literature suggest that some coronal loops with cross-sections near the resolution limits of the Transition Region and Coronal Explorer (pixel size = 0.5 arc-seconds, or approx. 360 km) are, in fact, isothermally homogeneous and thus may be identified as elementary loop strands. This poster presents some ongoing work that applies state-of-the-art estimation of differential emission measures in order to evaluate these claims for a sample of loops. We find that the data give no evidence to prefer the "isothermal" hypothesis over the "multithermal" hypothesis. The authors are supported by the following funds: contract SP02H820IR to the Lockheed-Martin Corp.; NSF grant ATM-0402729; NASA grant NNG05GE68G; and NASA contracts NAS8-39073 and NAS8-03060.

Triennial Report 2006-2009. Commission 10: Solar Activity

NASA Technical Reports Server (NTRS)

Klimchuk, James A.

2008-01-01

Commission 10 deals with solar activity in all of its forms, ranging from the smallest nanoflares to the largest coronal mass ejections. This report reviews scientific progress over the roughly two-year period ending in the middle of 2008. This has been an exciting time in solar physics, highlighted by the launches of the Hinode and STEREO missions late in 2006. The report is reasonably comprehensive, though it is far from exhaustive. Limited space prevents the inclusion of many significant results. The report is divided into following sections: Photosphere and Chromosphere; Transition Region; Corona and Coronal Heating; Coronal Jets; Flares; Coronal Mass Ejection Initiation; Global Coronal Waves and Shocks; Coronal Dimming; The Link Between Low Coronal CME signatures and Magnetic Clouds; Coronal Mass Ejections in the Heliosphere; and Coronal Mass Ejections and Space Weather. Primary authorship is indicated at the beginning of each section.

To BG or not to BG: Background Subtraction for EIT Coronal Loops

NASA Astrophysics Data System (ADS)

Beene, J. E.; Schmelz, J. T.

2003-05-01

One of the few observational tests for various coronal heating models is to determine the temperature profile along coronal loops. Since loops are such an abundant coronal feature, this method originally seemed quite promising - that the coronal heating problem might actually be solved by determining the temperature as a function of arc length and comparing these observations with predictions made by different models. But there are many instruments currently available to study loops, as well as various techniques used to determine their temperature characteristics. Consequently, there are many different, mostly conflicting temperature results. We chose data for ten coronal loops observed with the Extreme ultraviolet Imaging Telescope (EIT), and chose specific pixels along each loop, as well as corresponding nearby background pixels where the loop emission was not present. Temperature analysis from the 171-to-195 and 195-to-284 angstrom image ratios was then performed on three forms of the data: the original data alone, the original data with a uniform background subtraction, and the original data with a pixel-by-pixel background subtraction. The original results show loops of constant temperature, as other authors have found before us, but the 171-to-195 and 195-to-284 results are significantly different. Background subtraction does not change the constant-temperature result or the value of the temperature itself. This does not mean that loops are isothermal, however, because the background pixels, which are not part of any contiguous structure, also produce a constant-temperature result with the same value as the loop pixels. These results indicate that EIT temperature analysis should not be trusted, and the isothermal loops that result from EIT (and TRACE) analysis may be an artifact of the analysis process. Solar physics research at the University of Memphis is supported by NASA grants NAG5-9783 and NAG5-12096.

Deriving the Coronal Magnetic Field Using Parametric Transformation Analysis

NASA Technical Reports Server (NTRS)

Gary, G. Allen; Rose, M. Franklin (Technical Monitor)

2001-01-01

When plasma-beta greater than 1 then the gas pressure dominates over the magnetic pressure. This ratio as a function along the coronal magnetic field lines varies from beta greater than 1 in the photosphere at the base of the field lines, to beta much less than 1 in the mid-corona, to beta greater than 1 in the upper corona. Almost all magnetic field extrapolations do not or cannot take into account the full range of beta. They essentially assume beta much less than 1, since the full boundary conditions do not exist in the beta greater than 1 regions. We use a basic parametric representation of the magnetic field lines such that the field lines can be manipulated to match linear features in the EUV and SXR coronal images in a least squares sense. This research employs free-form deformation mathematics to generate the associated coronal magnetic field. In our research program, the complex magnetic field topology uses Parametric Transformation Analysis (PTA) which is a new and innovative method to describe the coronal fields that we are developing. In this technique the field lines can be viewed as being embedded in a plastic medium, the frozen-in-field-line concept. As the medium is deformed the field lines are similarly deformed. However the advantage of the PTA method is that the field line movement represents a transformation of one magnetic field solution into another magnetic field solution. When fully implemented, this method will allow the resulting magnetic field solution to fully match the magnetic field lines with EUV/SXR coronal loops by minimizing the differences in direction and dispersion of a collection of PTA magnetic field lines and observed field lines. The derived magnetic field will then allow beta greater than 1 regions to be included, the electric currents to be calculated, and the Lorentz force to be determined. The advantage of this technique is that the solution is: (1) independent of the upper and side boundary conditions, (2) allows non-vanishing magnetic forces, and (3) provides a global magnetic field solution, which contains high- and low-beta regimes and maximizes the similarity between the field lines structure and all the coronal images of the region. The coronal image analysis is crucial to the investigation and for the first time these images can be exploited to derive the coronal magnetic field in a well-posed mathematical formulation. This program is an outgrowth of an investigation in which an extrapolated potential field was required to be "inflated" in order to have the field lines match the Yohkoh/SXT images. The field lines were radially stretched resulting in a better match to the coronal loops of an active region. The PTA method of radial and non-radial deformations of field lines to provide a match to the EUV/SXR images will be presented.

The solar XUV He I and He II emission lines. I - Intensities and gross center-to-limb behavior

NASA Technical Reports Server (NTRS)

Mango, S. A.; Bohlin, J. D.; Glackin, D. L.; Linsky, J. L.

1978-01-01

The center-to-limb variation of the He II 304- and 256-A lines and He I 584- and 537-A lines is derived for different solar features, but averaged over the chromospheric supergranulation structure. The general trend is for limb brightening in quiet-sun regions, limb neutrality in unipolar magnetic regions (UMR), and limb darkening in polar coronal holes. The center-to-limb behavior in these optically thick emission lines indicates collisional excitation and decreasing transition-region temperature gradients with respect to optical depth in the sequence quiet sun to UMR to coronal hole.

Sprawling Coronal Hole

NASA Image and Video Library

2017-10-16

A large coronal hole stands out as the most obvious feature on the sun this week (Oct. 12-13, 2017). The dark structure, shaped kind of like the Pi symbol, spreads across much of the top of the sun. Though one cannot tell from this image and video clip in false-color extreme ultraviolet light, it is spewing high-speed solar wind particles into space and has been doing this all week. It is likely that these charged particles have been interacting with Earth's atmosphere and generating many aurora displays in regions near the poles the past several days. Animations are available at https://photojournal.jpl.nasa.gov/catalog/PIA22047

Determination of Differential Emission Measure Distribution of Coronal Structures Observed by SphinX During Recent Minimum of Solar Activity

NASA Astrophysics Data System (ADS)

Kepa, Anna; Gburek, Szymon; Siarkowski, Marek; Sylwester, Barbara; Sylwester, Janusz; Kowalinski, Miroslaw

SphinX is a high-sensitivity soft X-ray spectrophotometer which measures soft X-ray spectra in the energy range between 0.8 keV and 15 keV. From February to November 2009 the instrument has observed unusually quiet solar coronal emission as well as a number of weak solar flares. Based on SphinX spectra it is possible to study the differential emission measure distributions (DEM) in the temperature range roughly between 1 MK and 10 MK. The aim of the present study is to unveil DEM plasma distributions for selected activity conditions and analyze their variability.

A study of coronal bright points at 20 cm wavelength

NASA Technical Reports Server (NTRS)

Nitta, N.; Kundu, M. R.

1988-01-01

The paper presents the results of a study of coronal bright points observed at 20 cm with the VLA on a day when the sun was exceptionally quiet. Microwave maps of bright points were obtained using data for the entire observing period of 5 hours, as well as for shorter periods of a few minutes. Most bright points, especially those appearing in the full-period maps, appear to be associated with small bipolar structures on the photospheric magnetogram. Overlays of bright point (BP) maps on the Ca(+) K picture, show that the brightest part of BP tends to lie on the boundary of a supergranulation network.

A Normal Incidence X-ray Telescope (NIXT) Sounding Rocket Payload

NASA Technical Reports Server (NTRS)

Golub, Leon

1998-01-01

The solar corona, and the coronae of solar-type stars, consist of a low-density magnetized plasma at temperatures exceeding 10(exp 6) K. The primary coronal emission is therefore in the UV and soft X-ray range. The observed close connection between solar magnetic fields and the physical parameters of the corona implies a fundamental role for the magnetic field in coronal structuring and dynamics. Variability of the corona occurs on all temporal and spatial scales - at one extreme, as the result of plasma instabilities, and at the other extreme driven by the global magnetic flux emergence patterns of the solar cycle.

Quasi-periodic Counter-propagating Fast Magnetosonic Wave Trains from Neighboring Flares: SDO/AIA Observations and 3D MHD Modeling

NASA Astrophysics Data System (ADS)

Ofman, Leon; Liu, Wei

2018-06-01

Since their discovery by the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) in the extreme ultraviolet, rapid (phase speeds of ∼1000 km s‑1), quasi-periodic, fast-mode propagating (QFP) wave trains have been observed accompanying many solar flares. They typically propagate in funnel-like structures associated with the expanding magnetic field topology of the active regions (ARs). The waves provide information on the associated flare pulsations and the magnetic structure through coronal seismology (CS). The reported waves usually originate from a single localized source associated with the flare. Here we report the first detection of counter-propagating QFPs associated with two neighboring flares on 2013 May 22, apparently connected by large-scale, trans-equatorial coronal loops. We present the first results of a 3D MHD model of counter-propagating QFPs in an idealized bipolar AR. We investigate the excitation, propagation, nonlinearity, and interaction of the counter-propagating waves for a range of key model parameters, such as the properties of the sources and the background magnetic structure. In addition to QFPs, we also find evidence of trapped fast- (kink) and slow-mode waves associated with the event. We apply CS to determine the magnetic field strength in an oscillating loop during the event. Our model results are in qualitative agreement with the AIA-observed counter-propagating waves and used to identify the various MHD wave modes associated with the observed event, providing insights into their linear and nonlinear interactions. Our observations provide the first direct evidence of counter-propagating fast magnetosonic waves that can potentially lead to turbulent cascade and carry significant energy flux for coronal heating in low-corona magnetic structures.

The effect of dentinal fluid flow during loading in various directions--simulation of fluid-structure interaction.

PubMed

Su, Kuo-Chih; Chang, Chih-Han; Chuang, Shu-Fen; Ng, Eddie Yin-Kwee

2013-06-01

This study uses a fluid-structure interaction (FSI) simulation to evaluate the fluid flow in a dental intrapulpal chamber induced by the deformation of the tooth structure during loading in various directions. The FSI is used for the biomechanics simulation of dental intrapulpal responses with the force loading gradually increasing from 0 to 100N at 0°, 30°, 45°, 60°, and 90° on the tooth surface in 1s, respectively. The effect of stress or deformation on tooth and fluid flow changes in the pulp chamber are evaluated. A horizontal loading force on a tooth may induce tooth structure deformation, which increases fluid flow velocity in the coronal pulp. Thus, horizontal loading on a tooth may easily induce tooth pain. This study suggests that experiments to investigate the relationship between loading in various directions and dental pain should avoid measuring the bulk pulpal fluid flow from radicular pulp, but rather should measure the dentinal fluid flow in the dentinal tubules or coronal pulp. The FSI analysis used here could provide a powerful tool for investigating problems with coupled solid and fluid structures in dental biomechanics. Copyright © 2012 Elsevier Ltd. All rights reserved.

Small-Scale Activity Above the Penumbra of a Fast-Rotating Sunspot

NASA Astrophysics Data System (ADS)

Bharti, L.; Quintero Noda, C.; Rakesh, S.; Sobha, B.; Pandya, A.; Joshi, C.

2018-03-01

High-resolution observations of small-scale activity above the filamentary structure of a fast-rotating sunspot of NOAA Active Region 10930 are presented. The penumbral filament that intrudes into the umbra shows a central dark core and substructures. It almost approached another end of the umbra, like a light bridge. The chromospheric Ca ii H images show many jet-like structures with a bright leading edge above it. These bright jets move across the filament tips and show coordinated up and down motions. Transition region images also show brightening at the same location above the intrusion. Coronal 195 Å images suggest that one end of the bright coronal loop footpoints resides in this structure. The intrusion has opposite polarity with respect to the umbra. Strong downflows are observed at the edges along the length of the intrusion where the opposite-polarity field is enhanced. We also observe a counter-Evershed flow in the filamentary structure that also displays brightening and energy dissipation in the upper atmosphere. This scenario suggests that the jets and brightenings are caused by low-altitude reconnection driven by opposite-polarity fields and convective downflows above such structures.

The green corona database and the coronal index of solar activity

NASA Astrophysics Data System (ADS)

Minarovjech, M.; Rušin, V.; Saniga, M.

2011-10-01

The green coronal line Fe XIV 530.3 nm ranks amongst the most pronounced emission lines in the visible part of the solar spectrum. Its observations outside solar eclipses started sporadically in 1939 (the Arosa coronal station), being extended, in 1946, to more coronal stations. It was found that the green corona intensities vary with solar cycle, so they are a good candidate to express solar activity in the corona. Several attempts have been made to create a single homogeneous coronal data set from different coronal stations. We will present our homogeneous coronal data set, based on the Lomnický Štít photometric scale. Also, the coronal index of solar activity as created from this database in the period 1939—2010 will be discussed.

On the derivation of empirical limits on the helium abundance in coronal holes below 1.5 solar radius

NASA Technical Reports Server (NTRS)

Habbal, Shadia Rifai; Esser, Ruth

1994-01-01

We present a simple technique describing how limits on the helium abundance, alpha, defined as the ratio of helium to proton number density, can be inferred from measurements of the electron density and temperature below 1.5 solar radius. As an illustration, we apply this technique to two different data sets: emission-line intensities in the extreme ultraviolet (EUV) and white-light observations, both measured in polar coronal holes. For the EUV data, the temperature gradient is derived from line intensity ratios, and the density gradient is replaced by the gradient of the line intensity. The lower limit on alpha derived from these data is 0.2-0.3 at 1 solar radius and drops very sharply to interplanetary values of a few percent below 1.06 solar radius. The white-light observations yield density gradients in the inner corona beyond 1.25 solar radius but do not have corresponding temperature gradients. In this case we consider an isothermal atmosphere, and derive an upper limit of 0.2 for alpha. These examples are used to illustrate how this technique could be applicable to the more extensive data to be obtained with the upcoming SOHO mission. Although only ranges on alpha can be derived, the application of the technique to data currently available merely points to the fact that alpha can be significantly large in the inner corona.

Properties and Radial Trends of Coronal Mass Ejecta and Their Associated Shocks Observed by Ulysses in the Ecliptic Plane. Appendix 2; Repr. from Journal of Geophysical Research, v. 105, 2000 p 12,617-12,626

NASA Technical Reports Server (NTRS)

Riley, Pete; Gosling, J. T.; McComas, D. J.; Forsyth, R. J.

2001-01-01

In this paper, magnetic and plasma measurements are used to analyze 17 interplanetary coronal mass ejections (CMEs) identified by Ulysses during its in-ecliptic passage to Jupiter. We focus on the expansion characteristics of these CMEs (as inferred from the time rate of change of the velocity profiles through the CMEs) and the properties of 14 forward shocks unambiguously associated with these CMEs. We highlight radial trends from 1 to 5.4 AU. Our results indicate that the CMEs are generally expanding at all heliocentric distances. With regard to the shocks preceding these ejecta, we note the following: (1) There is a clear tendency for the shock speed (in the upstream frame of reference) to decrease with increasing heliocentric distance as the CMEs transfer momentum to the ambient solar wind and slow down; (2) 86% of the shock fronts are oriented in the ecliptic plane such that their normals point westward (i.e., in the direction of planetary motion about the Sun), (3) 86% of the shocks are propagating toward the heliographic equator; and (4) no clear trend was found in the strength of the shocks versus heliocentric distance. These results are interpreted using simple dynamical arguments and are supported by fluid and magnetohydrodynamic (MHD) simulations.

Theoretical quantification of shock-timing sensitivities for direct-drive inertial confinement fusion implosions on OMEGA

DOE PAGES

Cao, D.; Boehly, T. R.; Gregor, M. C.; ...

2018-05-16

Using temporally shaped laser pulses, multiple shocks can be launched in direct-drive inertial confinement fusion implosion experiments to set the shell on a desired isentrope or adiabat. The velocity of the first shock and the times at which subsequent shocks catch up to it are measured through the VISAR diagnostic on OMEGA. Simulations reproduce these velocity and shock-merger time measurements when using laser pulses designed for setting mid-adiabat (α ~ 3) implosions, but agreement degrades for lower-adiabat (α ~ 1) designs. Several possibilities for this difference are studied: errors in placing the target at the center of irradiation (target offset),more » variations in energy between the different incident beams (power imbalance), and errors in modeling the laser energy coupled into the capsule. Simulation results indicate that shock timing is most sensitive to details of the density and temperature profiles in the coronal plasma, which influences the laser energy coupled into the target, and only marginally sensitive to target offset and beam power imbalance. A new technique under development to infer coronal profiles using x-ray self-emission imaging can be applied to the pulse shapes used in shock-timing experiments. In conclusion, this will help identify improved physics models to implement in codes and consequently enhance shock-timing predictive capability for low-adiabat pulses.« less

Current Sheet Evolution in the Aftermath of a CME Event

NASA Technical Reports Server (NTRS)

Bemporad, A.; Poletto, G.; Suess, S. T.; Ko, Y.-K.; Schwadron, N. A.; Elliott, H. A.; Raymond, J. C.

2005-01-01

We report on SOHO-UVCS observations of the coronal restructuring following a Coronal Mass Ejection (CME) on November 26,2002, at the time of a SOHO-Ulysses quadrature campaign. Starting about 3 hours after a CME in the NW quadrant, UVCS began taking spectra at 1.7 solar radius, covering emission from both cool and hot plasma. Observations continued, with occasional gaps, for more than 2 days. Emission in the 974.8 Angstrom line of [Fe XVIII], indicating temperatures above 6 x 10(exp 6) K, was observed throughout the campaign in a spatially limited location. Comparison with EIT images shows the Fe XVIII emission to overlie a growing post-flare loop system formed in the aftermath of the CME. The emission most likely originates in a current sheet overlying the arcade. Analysis of the [Fe XVIII] emission allows us to infer the evolution of physical parameters in the current sheet over the entire span of our observations: in particular, we give the temperature vs. time in the current sheet and estimate the density. At the time of the quadrature, Ulysses was directly above the location of the CME and intercepted the ejecta. High ionization state Fe was detected by Ulysses-SWICS throughout the magnetic cloud associated with the CME. Both the remote and in situ observations are compared with predictions of theoretical CME models.

PHYSICAL PARAMETERS OF STANDARD AND BLOWOUT JETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pucci, Stefano; Romoli, Marco; Poletto, Giannina

2013-10-10

The X-ray Telescope on board the Hinode mission revealed the occurrence, in polar coronal holes, of much more numerous jets than previously indicated by the Yohkoh/Soft X-ray Telescope. These plasma ejections can be of two types, depending on whether they fit the standard reconnection scenario for coronal jets or if they include a blowout-like eruption. In this work, we analyze two jets, one standard and one blowout, that have been observed by the Hinode and STEREO experiments. We aim to infer differences in the physical parameters that correspond to the different morphologies of the events. To this end, we adoptmore » spectroscopic techniques and determine the profiles of the plasma temperature, density, and outflow speed versus time and position along the jets. The blowout jet has a higher outflow speed, a marginally higher temperature, and is rooted in a stronger magnetic field region than the standard event. Our data provide evidence for recursively occurring reconnection episodes within both the standard and the blowout jet, pointing either to bursty reconnection or to reconnection occurring at different locations over the jet lifetimes. We make a crude estimate of the energy budget of the two jets and show how energy is partitioned among different forms. Also, we show that the magnetic energy that feeds the blowout jet is a factor of 10 higher than the magnetic energy that fuels the standard event.« less

Origin of Pre-Coronal-Jet Minifilaments: Flux Cancellation

NASA Astrophysics Data System (ADS)

Panesar, N. K.; Sterling, A. C.; Moore, R. L.

2017-12-01

We recently investigated the triggering mechanism of ten quiet-region coronal jet eruptions and found that magnetic flux cancellation at the neutral line of minifilaments is the main cause of quiet-region jet eruptions (Panesar et al 2016). However, what leads to the formation of the pre-jet minifilaments remained unknown. In the present work, we study the longer-term evolution of the magnetic field that leads to the formation of pre-jet minifilaments by using SDO/AIA intensity images and concurrent line of sight SDO/HMI magnetograms. We find that each of the ten pre-jet minifilaments formed due to progressive flux cancellation between the minority-polarity and majority-polarity flux patches (with a minority-polarity flux loss of 10% - 40% prior to minifilament birth). Apparently, the flux cancellation between the opposite polarity flux patches builds a highly-sheared field at the magnetic neutral line, and that field holds the cool transition region minifilament plasma. Even after the formation of minifilaments, the flux continues to cancel, making the minifilament body more thick and prominent. Further flux cancellation between the opposite-flux patches leads to the minifilament eruption and a resulting jet. From these observations, we infer that flux cancellation is usually the process that builds up the sheared and twisted field in pre-jet minifilaments, and that triggers it to erupt and drive a jet.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fujiki, K.; Tokumaru, M.; Hayashi, K.

We developed an automated prediction technique for coronal holes using potential magnetic field extrapolation in the solar corona to construct a database of coronal holes appearing from 1975 February to 2015 July (Carrington rotations from 1625 to 2165). Coronal holes are labeled with the location, size, and average magnetic field of each coronal hole on the photosphere and source surface. As a result, we identified 3335 coronal holes and found that the long-term distribution of coronal holes shows a similar pattern known as the magnetic butterfly diagram, and polar/low-latitude coronal holes tend to decrease/increase in the last solar minimum relativemore » to the previous two minima.« less

Efficient Exact Inference With Loss Augmented Objective in Structured Learning.

PubMed

Bauer, Alexander; Nakajima, Shinichi; Muller, Klaus-Robert

2016-08-19

Structural support vector machine (SVM) is an elegant approach for building complex and accurate models with structured outputs. However, its applicability relies on the availability of efficient inference algorithms--the state-of-the-art training algorithms repeatedly perform inference to compute a subgradient or to find the most violating configuration. In this paper, we propose an exact inference algorithm for maximizing nondecomposable objectives due to special type of a high-order potential having a decomposable internal structure. As an important application, our method covers the loss augmented inference, which enables the slack and margin scaling formulations of structural SVM with a variety of dissimilarity measures, e.g., Hamming loss, precision and recall, Fβ-loss, intersection over union, and many other functions that can be efficiently computed from the contingency table. We demonstrate the advantages of our approach in natural language parsing and sequence segmentation applications.

An equatorial coronal hole at solar minimum

NASA Technical Reports Server (NTRS)

Bromage, B. J. I.; DelZanna, G.; DeForest, C.; Thompson, B.; Clegg, J. R.

1997-01-01

The large transequatorial coronal hole that was observed in the solar corona at the end of August 1996 is presented. It consists of a north polar coronal hole called the 'elephant's trunk or tusk'. The observations of this coronal hole were carried out with the coronal diagnostic spectrometer onboard the Solar and Heliospheric Observatory (SOHO). The magnetic field associated with the equatorial coronal hole is strongly connected to that of the active region at its base, resulting in the two features rotating at almost the same rate.

SLOW MAGNETOACOUSTIC WAVES OBSERVED ABOVE A QUIET-SUN REGION IN A DARK CAVITY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu Jiajia; Zhou Zhenjun; Wang Yuming

Waves play a crucial role in diagnosing the plasma properties of various structures in the solar corona and coronal heating. Slow magnetoacoustic (MA) waves are one of the important types of magnetohydrodynamic waves. In past decades, numerous slow MA waves were detected above active regions and coronal holes, but were rarely found elsewhere. Here, we investigate a 'tornado'-like structure consisting of quasi-periodic streaks within a dark cavity at about 40-110 Mm above a quiet-Sun region on 2011 September 25. Our analysis reveals that these streaks are actually slow MA wave trains. The properties of these wave trains, including phase speed,more » compression ratio, and kinetic energy density, are similar to those of the reported slow MA waves, except that the period of these waves is about 50 s, much shorter than the typical reported values (3-5 minutes).« less

Introduction of the ASGARD code (Automated Selection and Grouping of events in AIA Regional Data)

NASA Astrophysics Data System (ADS)

Bethge, Christian; Winebarger, Amy; Tiwari, Sanjiv K.; Fayock, Brian

2017-08-01

We have developed the ASGARD code to automatically detect and group brightenings ("events") in AIA data. The event selection and grouping can be optimized to the respective dataset with a multitude of control parameters. The code was initially written for IRIS data, but has since been optimized for AIA. However, the underlying algorithm is not limited to either and could be used for other data as well.Results from datasets in various AIA channels show that brightenings are reliably detected and that coherent coronal structures can be isolated by using the obtained information about the start, peak, and end times of events. We are presently working on a follow-up algorithm to automatically determine the heating and cooling timescales of coronal structures. This will be done by correlating the information from different AIA channels with different temperature responses. We will present the code and preliminary results.

Prediction of solar energetic particle event histories using real-time particle and solar wind measurements

NASA Technical Reports Server (NTRS)

Roelof, E. C.; Gold, R. E.

1978-01-01

The comparatively well-ordered magnetic structure in the solar corona during the decline of Solar Cycle 20 revealed a characteristic dependence of solar energetic particle injection upon heliographic longitude. When analyzed using solar wind mapping of the large scale interplanetary magnetic field line connection from the corona to the Earth, particle fluxes display an approximately exponential dependence on heliographic longitude. Since variations in the solar wind velocity (and hence the coronal connection longitude) can severely distort the simple coronal injection profile, the use of real-time solar wind velocity measurements can be of great aid in predicting the decay of solar particle events. Although such exponential injection profiles are commonplace during 1973-1975, they have also been identified earlier in Solar Cycle 20, and hence this structure may be present during the rise and maximum of the cycle, but somewhat obscured by greater temporal variations in particle injection.

What Preparatory Science is Needed in Coronal Structure and Activity

NASA Technical Reports Server (NTRS)

Antiochos, S. K.

2011-01-01

Solar Orbiter and Solar Probe Plus will launch in six short years! Before then, we need to accomplish a great deal of science in order to be able to maximize the return of these missions. Preparatory science is especially important for exploratory missions such as SO and SPP, because they truly will be going "where no mission has gone before". Such preparatory science may include all types of research: theory, modeling, data exploitation, and supporting observations. This meeting provides an opportunity for the community to define and begin this critical preparatory work. In this talk I will provide an overview of our state of knowledge in coronal structure and activity, describe what I believe are the most promising opportunities for advances by SO and SPP, and lead a discussion on what programs need to be implemented now in order to achieve these science advances by the time SO and SPP launch.

Coronal Polarization of Pseudostreamers and the Solar Polar Field Reversal

NASA Technical Reports Server (NTRS)

Rachmeler, L. A.; Guennou, C.; Seaton, D. B.; Gibson, S. E.; Auchere, F.

2016-01-01

The reversal of the solar polar magnetic field is notoriously hard to pin down due to the extreme viewing angle of the pole. In Cycle 24, the southern polar field reversal can be pinpointed with high accuracy due to a large-scale pseudostreamer that formed over the pole and persisted for approximately a year. We tracked the size and shape of this structure with multiple observations and analysis techniques including PROBA2/SWAP EUV images, AIA EUV images, CoMP polarization data, and 3D tomographic reconstructions. We find that the heliospheric field reversed polarity in February 2014, whereas in the photosphere, the last vestiges of the previous polar field polarity remained until March 2015. We present here the evolution of the structure and describe its identification in the Fe XII 1074nm coronal emission line, sensitive to the Hanle effect in the corona.