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.

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.

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.

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.

Large-Scale Coronal Heating, Clustering of Coronal Bright Points, and Concentration of Magnetic Flux

NASA Technical Reports Server (NTRS)

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

1998-01-01

By combining quiet-region Fe XII coronal images from SOHO/EIT with magnetograms from NSO/Kitt Peak and from SOHO/MDI, we show that on scales larger than a supergranule the population of network coronal bright points and the magnetic flux content of the network are both markedly greater under the bright half of the quiet corona than under the dim half. These results (1) support the view that the heating of the entire corona in quiet regions and coronal holes is driven by fine-scale magnetic activity (microflares, explosive events, spicules) seated low in the magnetic network, and (2) suggest that this large-scale modulation of the magnetic flux and coronal heating is a signature of giant convection cells.

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.

An Assessment of Magnetic Conditions for Strong Coronal Heating in Solar Active Regions by Comparing Observed Loops with Computed Potential Field Lines

NASA Technical Reports Server (NTRS)

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

1999-01-01

We report further results on the magnetic origins of coronal heating found from registering coronal images with photospheric vector magnetograms. For two complementary active regions, we use computed potential field lines to examine the global non-potentiality of bright extended coronal loops and the three-dimensional structure of the magnetic field at their feet, and assess the role of these magnetic conditions in the strong coronal heating in these loops. The two active regions are complementary, in that one is globally potential and the other is globally nonpotential, while each is predominantly bipolar, and each has an island of included polarity in its trailing polarity domain. We find the following: (1) The brightest main-arch loops of the globally potential active region are brighter than the brightest main- arch loops of the globally strongly nonpotential active region. (2) In each active region, only a few of the mainarch magnetic loops are strongly heated, and these are all rooted near the island. (3) The end of each main-arch bright loop apparently bifurcates above the island, so that it embraces the island and the magnetic null above the island. (4) At any one time, there are other main-arch magnetic loops that embrace the island in the same manner as do the bright loops but that are not selected for strong coronal heating. (5) There is continual microflaring in sheared core fields around the island, but the main-arch bright loops show little response to these microflares. From these observational and modeling results we draw the following conclusions: (1) The heating of the main-arch bright loops arises mainly from conditions at the island end of these loops and not from their global non-potentiality. (2) There is, at most, only a loose coupling between the coronal heating in the bright loops of the main arch and the coronal heating in the sheared core fields at their feet, although in both the heating is driven by conditions/events in and around the island. (3) The main-arch bright loops are likely to be heated via reconnection driven at the magnetic null over the island. The details of how and where (along the null line) the reconnection is driven determine which of the split-end loops are selected for strong heating. (4) The null does not appear to be directly involved in the heating of the sheared core fields or in the heating of an extended loop rooted in the island. Rather, these all appear to be heated by microflares in the sheared core field.

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

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.

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.

Flux Cancelation as the Trigger of Quiet-Region Coronal Jet Eruptions

NASA Technical Reports Server (NTRS)

Panesar, Navdeep K.; Sterling, Alphonse; Moore, Ronald L.

2017-01-01

Coronal jets are frequent magnetically channeled narrow eruptions. They occur in various solar environments: quiet regions, coronal holes and active regions. All coronal jets observed in EUV (Extreme UltraViolet) and X-ray images show a bright spire with a base brightening, also known as jet bright point (JBP). Recent studies show that coronal jets are driven by small-scale filament eruptions. Sterling et al. 2015 did extensive study of 20 polar coronal hole jets and found that X-ray jets are mainly driven by the eruption of minifilaments. What leads to these minifilament eruptions?

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.

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.

Micro Coronal Bright Points Observed in the Quiet Magnetic Network by SOHO/EIT

NASA Technical Reports Server (NTRS)

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

1997-01-01

When one looks at SOHO/EIT Fe XII images of quiet regions, one can see the conventional coronal bright points (> 10 arcsec in diameter), but one will also notice many smaller faint enhancements in brightness (Figure 1). Do these micro coronal bright points belong to the same family as the conventional bright points? To investigate this question we compared SOHO/EIT Fe XII images with Kitt Peak magnetograms to determine whether the micro bright points are in the magnetic network and mark magnetic bipoles within the network. To identify the coronal bright points, we applied a picture frame filter to the Fe XII images; this brings out the Fe XII network and bright points (Figure 2) and allows us to study the bright points down to the resolution limit of the SOHO/EIT instrument. This picture frame filter is a square smoothing function (hlargelyalf a network cell wide) with a central square (quarter of a network cell wide) removed so that a bright point's intensity does not effect its own background. This smoothing function is applied to the full disk image. Then we divide the original image by the smoothed image to obtain our filtered image. A bright point is defined as any contiguous set of pixels (including diagonally) which have enhancements of 30% or more above the background; a micro bright point is any bright point 16 pixels or smaller in size. We then analyzed the bright points that were fully within quiet regions (0.6 x 0.6 solar radius) centered on disk center on six different days.

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.

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.

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

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.

The Magnetic Evolution of Coronal Hole Bright Points

NASA Astrophysics Data System (ADS)

He, Y.; Muglach, K.

2017-12-01

Space weather refers to the state of the heliosphere and the geospace environment that are caused primarily by solar activity. Coronal mass ejections and flares originate in active regions and filaments close to the solar surface and can cause geomagnetic storms and solar energetic particles events, which can damage both spacecraft and ground-based systems that are critical for society's well-being. Coronal bright points are small-scale magnetic regions on the sun that seem to be similar to active regions, but are about an order of magnitude smaller. Due to their shorter lifetime, the complete evolutionary cycle of these mini active regions can be studied, from the time they appear in extreme-ultraviolet (EUV) images to the time they fade. We are using data from the Solar Dynamics Observatory (SDO) to study both the coronal EUV flux and the photospheric magnetic field and compare them to activities of the coronal bright point.

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.

Origin of Pre-Coronal-Jet Minifilaments: Flux Cancellation

NASA Technical Reports Server (NTRS)

Panesar, Navdeep K.; Sterling, Alphonse; Moore, Ronald L.

2017-01-01

Coronal jets are frequent magnetically channeled narrow eruptions. All coronal jets observed in EUV and X-ray images show a bright spire with a base brightening, also known as jet bright point (JBP). Recent studies of jets show that coronal jets are driven by small-scale filament eruptions (e.g. Hong et al. 2011, Shen et al. 2012, Adams et al. 2014, Sterling et al. 2015). We recently investigated the triggering mechanism of ten on-disk 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).

Coronal loops and active region structure

NASA Technical Reports Server (NTRS)

Webb, D. F.; Zirin, H.

1981-01-01

Synoptic H-alpha Ca K, magnetograph and Skylab soft X-ray and EUV data were compared for the purpose of identifying the basic coronal magnetic structure of loops in a 'typical' active region and studying its evolution. A complex of activity in July 1973, especially McMath 12417, was emphasized. The principal results are: (1) most of the brightest loops connected the bright f plage to either the sunspot penumbra or to p satellite spots; no non-flaring X-ray loops end in umbrae; (2) short, bright loops had one or both ends in regions of emergent flux, strong field or high field gradients; (3) stable, strongly sheared loop arcades formed over filaments; (4) EFRs were always associated with compact X-ray arcades; and (5) loops connecting to other active regions had their bases in outlying plage of weak field strength in McM 417 where H-alpha fibrils marked the direction of the loops

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.

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.

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).

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.

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 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.

On Heating Large Bright Coronal Loops by Magnetic Microexplosions at their Feet

NASA Technical Reports Server (NTRS)

Moore, Ronald L; Falconer, D. A.; Porter, Jason G.

1999-01-01

In previous work, by registering Yohkoh SXT coronal X-ray images with MSFC vector magnetograms, we found that: (1) many of the larger bright coronal loops rooted at one or both ends in an active region are rooted around magnetic islands of included polarity, (2) the core field encasing the neutral line encircling the island is strongly sheared, and (3) this sheared core field is the seat of frequent microflares. This suggests that the coronal heating in these extended bright loops is driven by many small explosive releases of stored magnetic energy from the sheared core field at their feet, some of which magnetic microexplosions also produce the microflare heating in the core fields. In this paper, we show that this scenario is feasible in terms of the energy Abstract: required for the observed coronal heating and the magnetic energy available in the observed sheared core fields. In a representative active region, from the X-ray and vector field data, we estimate the coronal heating consumption by a selected typical large bright loop, the coronal heating consumption by a typical microflare at the foot of this loop, the frequency of microflares at the foot, and the available magnetic energy in the microflaring core field. We find that: (1) the rate of magnetic energy release to power the microflares at the foot (approx. 6 x 10(ext 25)erg/s) is enough to also power the coronal heating in the body of the extended loop (approx. 2 x l0(exp 25 erg/s), and (2) there is enough stored magnetic energy in the sheared core field to sustain the microflaring and extended loop heating for about a day, which is a typical time for buildup of neutral-line magnetic shear in an active region. 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.

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

NASA Astrophysics Data System (ADS)

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

2017-08-01

We have analyzed an equatorial coronal-hole jet observed by SDO/AIA on 09 January 2014. The source-region magnetic field structure is consistent with the embedded-bipole topology that we identified and modeled previously as a source of coronal jets (Pariat et al. 2009, 2010, 2015, 2016; Karpen et al. 2017; Wyper et al. 2016). Initial brightenings were observed below a small but distinct “mini-filament” about 25 min before jet onset. A bright circular structure, interpreted as magnetic flux rope (MFR), surrounded the mini-filament. The MFR and filament rose together slowly at first, with a speed of ˜15 km s-1. When bright footpoints and loops appeared below, analogous to flare ribbons and arcade, the MFR/mini-filament rose rapidly (˜126 km s-1), and a bright elongated feature interpreted as a current sheet appeared between the MFR and the growing arcade. Multiple plasmoids propagating upward (˜135 km s-1) and downward (˜55 km s-1) were detected in this sheet. The jet was triggered when the rising MFR interacted with the overlying magnetic structure, most likely at a stressed magnetic null distorted into a current sheet. This event thus exhibits clear evidence of “flare” reconnection below the MFR as well as breakout reconnection above it, consistent with the breakout model for a wide range of solar eruptions (Antiochos et al. 1999; Devore & Antiochos 2008; Karpen et al. 2012; Wyper et al. 2017). Breakout reconnection destroyed the MFR and enabled the entrained coronal plasma and mini-filament to escape onto open field lines, producing an untwisting jet. SDO/HMI magnetograms reveal small footpoint motions at the eruption site and its surroundings, but do not show significant flux emergence or cancellation during or 1-2 hours before the eruption. Therefore, the free energy powering this jet most likely originated in magnetic shear concentrated at the polarity inversion line within the embedded bipole - a mini-filament channel - possibly created by helicity condensation (Antiochos 2013; Knizhnik et al. 2015, 2017).This work was supported in part by a grant from the NASA H-SR program and the NASA Postdoctoral Program.

The decay of coronal loops brightened by flares and transients

NASA Technical Reports Server (NTRS)

Krieger, A. S.

1978-01-01

Observations of X-ray emitting loops derived from Skylab S-054 photographs, and combined with temperature and brightness estimates from Solrad data, are used to determine brightness decay times resulting from various coronal energy loss mechanisms. Conductive losses are found to be more rapid than radiative losses. Attention is given to the role of geometrical inhibition of conduction as a possible mechanism of brightness decay. Soft X-ray observations are consistent with the continuation of the 'evaporation' driven by thermal conduction late into the decay phase of the event.

Substituting the polarizer mechanism with a polarization camera - an experiment to confirm its capability

NASA Astrophysics Data System (ADS)

Reginald, Nelson Leslie; Gopalswamy, Natchimuthuk; Guhathakurta, Madhulika; Yashiro, Seiji

2016-05-01

Experiments that require polarized brightness measurements, traditionally have done so by taking three successive images through a polarizer that is rotated through three well-defined angles. With the advent of the polarization camera, the polarized brightness can be measured from a single image. This also eliminates the need for a polarizer and the associated rotator mechanisms and can contribute towards less weight, size, less power requirements, and importantly higher temporal resolution. We intend to demonstrate the capabilities of the polarization camera by conducting a field experiment in conjunction with the total solar eclipse of 21 August 2017 using the Imaging Spectrograph of Coronal Electrons (ISCORE) instrument (Reginald et. al., solar physics, 2009, 260, 347-361). In this instrumental concept four K-coronal images of the corona through four filters centered at 385.0, 398.7, 410.0, 423.3 nm with a bandpass of 4 nm are expected to allow us to determine the coronal electron temperature and electron speed all around the corona. In order to determine the K-coronal brightness through each filter, we would have to take three images by rotating a polarizer through three angles for each of the filters, and it is not feasible owing to the short durations of total solar eclipses. Therefore, in the past we have assumed the total brightness (F + K) measured by each of the four filters to represent K-coronal brightness, which is true in low solar corona. However, with the advent of the polarization camera we can now measure the Stokes Polarization Parameters on a pixel by pixel basis for every image taken by the polarization camera. This allows us to independently quantify the total brightness (K+F) and polarized brightness (K). Also in addition to the four filter images that allow us to measure the electron temperature and electron speed, taking an additional image without a filter will give us enough information to determine the electron density. This instrumental concept was first tried in conjunction with the total solar eclipse of 9 March 2016 in Maba, Indonesia, but was unfortunately clouded out.

Coronal "wave": Magnetic Footprint Of A Cme?

NASA Astrophysics Data System (ADS)

Attrill, Gemma; Harra, L. K.; van Driel-Gesztelyi, L.; Demoulin, P.; Wuelser, J.

2007-05-01

We propose a new mechanism for the generation of "EUV coronal waves". This work is based on new analysis of data from SOHO/EIT, SOHO/MDI & STEREO/EUVI. Although first observed in 1997, the interpretation of coronal waves as flare-induced or CME-driven remains a debated topic. We investigate the properties of two "classical" SOHO/EIT coronal waves in detail. The source regions of the associated CMEs possess opposite helicities & the coronal waves display rotations in opposite senses. We observe deep dimmings near the flare site & also widespread diffuse dimming, accompanying the expansion of the EIT wave. We report a new property of these EIT waves, namely, that they display dual brightenings: persistent ones at the outermost edge of the core dimming regions & simultaneously diffuse brightenings constituting the leading edge of the coronal wave, surrounding the expanding diffuse dimmings. We show that such behaviour is consistent with a diffuse EIT wave being the magnetic footprint of a CME. We propose a new mechanism where driven magnetic reconnections between the skirt of the expanding CME & quiet-Sun magnetic loops generate the observed bright diffuse front. The dual brightenings & widespread diffuse dimming are identified as innate characteristics of this process. In addition we present some of the first analysis of a STEREO/EUVI limb coronal wave. We show how the evolution of the diffuse bright front & dimmings can be understood in terms of the model described above. We show that an apparently stationary part of the bright front can be understood in terms of magnetic interchange reconnections between the expanding CME & the "open" magnetic field of a low-latitude coronal hole. We use both the SOHO/EIT & STEREO/EUVI events to demonstrate that through successive reconnections, this new model provides a natural mechanism via which CMEs can become large-scale in the lower corona.

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.

Simultaneous observations of changes in coronal bright point emission at the 20 cm radio and He Lambda 10830 wavelengths

NASA Technical Reports Server (NTRS)

Habbal, Shadia R.; Harvey, Karen L.

1986-01-01

Preliminary results of observations of solar coronal bright points acquired simultaneously from ground based observatories at the radio wavelength of 20 cm and in the He I wavelength 10830 line on September 8, 1985, are reported. The impetus for obtaining simultaneous radio and optical data is to identify correlations, if any, in changes of the low transition-coronal signatures of bright points with the evolution of the magnetic field, and to distinguish between intermittent heating and changes in the magnetic field topology. Although simultaneous observations of H alpha emission and the photospheric magnetic field at Big Bear were also made, as well as radio observations from Owen Valley Radio Interferometer and Solar Maximum Mission (SSM) (O VIII line), only the comparison between He 10830 and the Very Large Array (VLA) radio data are presented.

The relationship between solar activity and coronal hole evolution

NASA Technical Reports Server (NTRS)

Nolte, J. T.; Davis, J. M.; Gerassimenko, M.; Krieger, A. S.; Solodyna, C. V.; Golub, L.

1978-01-01

The relationship between coronal hole evolution and solar active regions during the Skylab period is examined. A tendency is found for holes to grow or remain stable when the activity nearby, seen as calcium plages and bright regions in X-rays, is predominantly large, long-lived regions. It is also found that there is a significantly higher number of small, short-lived active regions, as indicated by X-ray bright points, in the vicinity of decaying holes than there is near other holes. This is interpreted to mean that holes disappear at least in part because they become filled with many small scale, magnetically closed, X-ray emitting features. This interpretation, together with the observation that the number of X-ray bright points was much larger near solar minimum than it was during the Skylab period, provides a possible explanation for the disappearance of the large, near-equatorial coronal holes at the time of solar minimum.

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.

Solar corona during the 1994 and 1999 eclipses

NASA Astrophysics Data System (ADS)

Badalyan, O. G.; Sýkora, J.

2008-06-01

The lower and middle layers of the corona are studied analyzing the ground-based observations carried out during the November 3, 1994 and August 11, 1999 total solar eclipses. While the 1994 eclipse took place nearby the solar activity minimum, the 1999 eclipse occurred closer to the solar cycle maximum. Structures, isolines of brightness and polarization, and topology of the magnetic field lines of force (calculated under a potential approximation) of these two coronae are mutually compared. It is confirmed that the brightness distribution in the corona corresponds to the hydrostatic distribution of density at the distances 1.2-1.8R⊙. Temperature 1.4 MK and density n0 = 3.3 × 108cm-3 are found for the equatorial coronal regions of the 1999 corona. Physical conditions in the polar coronal regions are investigated analyzing the brightness and polarization of the 1994 eclipse. We have found that the degree of polarization in polar plumes is about 10% higher than that in the inter-plumes space. Consideration of the brightness in plumes and in the adjacent background space allowed us to conclude that the temperatures there are close to 1 MK. The density in the individual plumes is near n0 = 2.7 × 108cm-3, while it decreases to about n0 = 2.0 × 108cm-3 in the inter-plumes space. It is pointed out that the simultaneous interpretation of the measured brightness and polarization struggles with some difficulties.

Observing Flux Rope Formation During the Impulsive Phase of a Solar Eruption

NASA Astrophysics Data System (ADS)

Cheng, X.; Zhang, J.; Liu, Y.; Ding, M. D.

2011-05-01

Magnetic flux ropes are believed to be an important structural component of coronal mass ejections (CMEs). While there exists much observational evidence of flux ropes after the eruption, e.g., as seen in remote-sensing coronagraph images or in situ solar wind data, the direct observation of flux ropes during CME impulsive phase has been rare. In this Letter, we present an unambiguous observation of a flux rope still in the formation phase in the low corona. The CME of interest occurred above the east limb on 2010 November 3 with footpoints partially blocked. The flux rope was seen as a bright blob of hot plasma in the Atmospheric Imaging Assembly (AIA) 131 Å passband (peak temperature ~11 MK) rising from the core of the source active region, rapidly moving outward and stretching the surrounding background magnetic field upward. The stretched magnetic field seemed to curve-in behind the core, similar to the classical magnetic reconnection scenario in eruptive flares. On the other hand, the flux rope appeared as a dark cavity in the AIA 211 Å passband (2.0 MK) and 171 Å passband (0.6 MK) in these relatively cool temperature bands, a bright rim clearly enclosed the dark cavity. The bright rim likely represents the pileup of the surrounding coronal plasma compressed by the expanding flux rope. The composite structure seen in AIA multiple temperature bands is very similar to that in the corresponding coronagraph images, which consists of a bright leading edge and a dark cavity, commonly believed to be a flux rope.

Latitudinal variability of large-scale coronal temperature and its association with the density and the global magnetic field

NASA Technical Reports Server (NTRS)

Guhathakurta, M.; Fisher, R. R.

1994-01-01

In this paper we utilize the latitiude distribution of the coronal temperature during the period 1984-1992 that was derived in a paper by Guhathakurta et al, 1993, utilizing ground-based intensity observations of the green (5303 A Fe XIV) and red (6374 A Fe X) coronal forbidden lines from the National Solar Observatory at Sacramento Peak, and establish it association with the global magnetic field and the density distributions in the corona. A determination of plasma temperature, T, was estimated from the intensity ratio Fe X/Fe XIV (where T is inversely proportional to the ratio), since both emission lines come from ionized states of Fe, and the ratio is only weakly dependent on density. We observe that there is a large-scale organization of the inferred coronal temperature distribution that is associated with the large-scale, weak magnetic field structures and bright coronal features; this organization tends to persist through most of the magnetic activity cycle. These high-temperature structures exhibit time-space characteristics which are similar to those of the polar crown filaments. This distribution differs in spatial and temporal characterization from the traditional picture of sunspot and active region evolution over the range of the sunspot cycle, which are manifestations of the small-scale, strong magnetic field regions.

The observation of possible reconnection events in the boundary changes of solar coronal holes

NASA Technical Reports Server (NTRS)

Kahler, S. W.; Moses, J. Daniel

1989-01-01

Coronal holes are large scale regions of magnetically open fields which are easily observed in solar soft X-ray images. The boundaries of coronal holes are separatrices between large scale regions of open and closed magnetic fields where one might expect to observe evidence of solar magnetic reconnection. Previous studies by Nolte and colleagues using Skylab X-ray images established that large scale (greater than or equal to 9 x 10(4) km) changes in coronal hole boundaries were due to coronal processes, i.e., magnetic reconnection, rather than to photospheric motions. Those studies were limited to time scales of about one day, and no conclusion could be drawn about the size and time scales of the reconnection process at hole boundaries. Sequences of appropriate Skylab X-ray images were used with a time resolution of about 90 min during times of the central meridian passages of the coronal hole labelled Coronal Hole 1 to search for hole boundary changes which can yield the spatial and temporal scales of coronal magnetic reconnection. It was found that 29 of 32 observed boundary changes could be associated with bright points. The appearance of the bright point may be the signature of reconnection between small scale and large scale magnetic fields. The observed boundary changes contributed to the quasi-rigid rotation of Coronal Hole 1.

The Coronal Analysis of SHocks and Waves (CASHeW) framework

NASA Astrophysics Data System (ADS)

Kozarev, Kamen A.; Davey, Alisdair; Kendrick, Alexander; Hammer, Michael; Keith, Celeste

2017-11-01

Coronal bright fronts (CBF) are large-scale wavelike disturbances in the solar corona, related to solar eruptions. They are observed (mostly in extreme ultraviolet (EUV) light) as transient bright fronts of finite width, propagating away from the eruption source location. Recent studies of individual solar eruptive events have used EUV observations of CBFs and metric radio type II burst observations to show the intimate connection between waves in the low corona and coronal mass ejection (CME)-driven shocks. EUV imaging with the atmospheric imaging assembly instrument on the solar dynamics observatory has proven particularly useful for detecting large-scale short-lived CBFs, which, combined with radio and in situ observations, holds great promise for early CME-driven shock characterization capability. This characterization can further be automated, and related to models of particle acceleration to produce estimates of particle fluxes in the corona and in the near Earth environment early in events. We present a framework for the coronal analysis of shocks and waves (CASHeW). It combines analysis of NASA Heliophysics System Observatory data products and relevant data-driven models, into an automated system for the characterization of off-limb coronal waves and shocks and the evaluation of their capability to accelerate solar energetic particles (SEPs). The system utilizes EUV observations and models written in the interactive data language. In addition, it leverages analysis tools from the SolarSoft package of libraries, as well as third party libraries. We have tested the CASHeW framework on a representative list of coronal bright front events. Here we present its features, as well as initial results. With this framework, we hope to contribute to the overall understanding of coronal shock waves, their importance for energetic particle acceleration, as well as to the better ability to forecast SEP events fluxes.

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.

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.

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

Observing Flux Rope Formation During the Impulsive Phase of a Solar Eruption

NASA Astrophysics Data System (ADS)

Cheng, Xin; Zhang, J.; Yang, L.; Ding, M.

2011-05-01

Magnetic flux rope is believed to be an important structural component of coronal mass ejections (CMEs). While there exist much observational evidence of the flux rope post the eruption, e.g., as seen in remote-sensing coronagraph images or in-situ solar wind data, the direct observation of flux ropes during CME impulsive phase has been rare or non-exist. In this Letter, we present an unambiguous observation of a flux rope still in the formation phase in the low corona. The CME of interest occurred above the east limb on 2010 November 03 with footpoints partially blocked. The flux rope was seen as a blob of hot plasma in AIA 131 A passband (peak temperature 11 MK) rising from the core of the source active region, rapidly moving outward and stretching upward the surrounding background magnetic field. The stretched magnetic field seemed to curve-in, similar to the classical magnetic reconnection scenario in eruptive flares. The flux rope was also seen as a dark cavity in AIA 211 A passpand (2.0 MK) and 171 A passband (0.6 MK); in these relatively cool temperature bands, a bright rim clearly enclosed the dark cavity. The bright rim likely represents the pile-up of the surrounding coronal plasma compressed by the expanding flux rope. The composite structure seen in AIA multiple temperature bands is very similar to that in the corresponding coronagraph images, which consists of a bright leading edge and a dark cavity, commonly believed to be a flux rope.

A search for outflows from X-ray bright points in coronal holes

NASA Technical Reports Server (NTRS)

Mullan, D. J.; Waldron, W. L.

1986-01-01

Properties of X-ray bright points using two of the instruments on Solar Maximum Mission were investigated. The mass outflows from magnetic regions were modeled using a two dimensional MHD code. It was concluded that mass can be detected from X-ray bright points provided that the magnetic topology is favorable.

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

NASA Technical Reports Server (NTRS)

Avallone, Ellis; Tiwari, Sanjiv K.; Panesar, Navdeep K.; Moore, Ronald L.; Winebarger, Amy

2017-01-01

Coronal plumes are bright magnetic funnels that are found in quiet regions and coronal holes that extend high into the solar corona whose lifetimes can last from hours to days. The heating processes that make plumes bright involve the magnetic field at the base of the plume, but their intricacies remain mysterious. Raouafi et al. (2014) infer from observation that plume heating is a consequence of magnetic reconnection at the base, whereas Wang et al. (2016) infer that plume heating is a result of convergence of the magnetic flux at the plume's base, or base flux. Both papers suggest that the base flux in their plumes is of mixed polarity, but do not quantitatively measure the base flux or consider whether a critical magnetic field strength is required for plume production. To investigate the magnetic origins of plume heating, we track plume luminosity in the 171 Å wavelength as well as the abundance and strength of the base flux over the lifetimes of six unipolar coronal plumes. Of these, three are in coronal holes and three are in quiet regions. For this sample, we find that plume heating is triggered when convergence of the base flux surpasses a field strength of approximately 300 - 500 Gauss, and that the luminosity of both quiet region and coronal hole plumes respond similarly to the strength of the magnetic field in the base.

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

A NuSTAR census of coronal parameters in Seyfert galaxies

NASA Astrophysics Data System (ADS)

Tortosa, A.; Bianchi, S.; Marinucci, A.; Matt, G.; Petrucci, P. O.

2018-06-01

Context. We discuss the results of the hot corona parameters of active galactic nuclei (AGN) that have been recently measured with NuSTAR. The values taken from the literature of a sample of 19 bright Seyfert galaxies are analysed. Aims: The aim of this work is to look for correlations between coronal parameters, such as the photon index and cut-off energy (when a phenomenological model is adopted) or the optical depth and temperature (when a Comptonization model is used), and other parameters of the systems, such as the black hole mass or the Eddington ratio. Methods: We analysed the coronal parameters of the 19 unobscured, bright Seyfert galaxies that are present in the Swift/BAT 70-month catalogue and that have been observed by NuSTAR, alone or simultaneously with others X-ray observatories, such as Swift, Suzaku, or XMM-Newton. Results: We found an anti-correlation with a significance level >98% between the coronal optical depth and the coronal temperature of our sample. On the other hand, no correlation between the above parameters and the black hole mass, the accretion rate, and the intrinsic spectral slope of the sources is found.

THE UBIQUITOUS PRESENCE OF LOOPLIKE FINE STRUCTURE INSIDE SOLAR ACTIVE REGIONS

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

Wang, Y.-M., E-mail: yi.wang@nrl.navy.mil

Although most of the solar surface outside active regions (ARs) is pervaded by small-scale fields of mixed polarity, this magnetic “carpet” or “junkyard” is thought to be largely absent inside AR plages and strong network. However, using extreme-ultraviolet images and line-of-sight magnetograms from the Solar Dynamics Observatory, we find that unipolar flux concentrations, both inside and outside ARs, often have small, loop-shaped Fe ix 17.1 and Fe xii 19.3 nm features embedded within them, even though no minority-polarity flux is visible in the corresponding magnetograms. Such looplike structures, characterized by horizontal sizes of ∼3–5 Mm and varying on timescales ofmore » minutes or less, are seen inside bright 17.1 nm moss, as well as in fainter moss-like regions associated with weaker network outside ARs. We also note a tendency for bright coronal loops to show compact, looplike features at their footpoints. Based on these observations, we suggest that present-day magnetograms may be substantially underrepresenting the amount of minority-polarity flux inside plages and strong network, and that reconnection between small bipoles and the overlying large-scale field could be a major source of coronal heating both in ARs and in the quiet Sun.« less

A Coronal Hole Jet Observed with Hinode and the Solar Dynamics Observatory

NASA Technical Reports Server (NTRS)

Young, Peter H.; Muglach, Karin

2014-01-01

A small blowout jet was observed at the boundary of the south coronal hole on 2011 February 8 at around 21:00 UT. Images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) revealed an expanding loop rising from one footpoint of a compact, bipolar bright point. Magnetograms from the Helioseismic Magnetic Imager (HMI) on board SDO showed that the jet was triggered by the cancelation of a parasitic positive polarity feature near the negative pole of the bright point. The jet emission was present for 25 mins and it extended 30 Mm from the bright point. Spectra from the EUV Imaging Spectrometer on board Hinode yielded a temperature and density of 1.6 MK and 0.9-1.7 × 10( exp 8) cu cm for the ejected plasma. Line-of-sight velocities reached up to 250 km/s. The density of the bright point was 7.6 × 10(exp 8) cu cm, and the peak of the bright point's emission measure occurred at 1.3 MK, with no plasma above 3 MK.

Polarization Observations of the Total Solar Eclipse of August 21, 2017

NASA Astrophysics Data System (ADS)

Burkepile, J.; Boll, A.; Casini, R.; de Toma, G.; Elmore, D. F.; Gibson, K. L.; Judge, P. G.; Mitchell, A. M.; Penn, M.; Sewell, S. D.; Tomczyk, S.; Yanamandra-Fisher, P. A.

2017-12-01

A total solar eclipse offers ideal sky conditions for viewing the solar corona. Light from the corona is composed of three components: the E-corona, made up of spectral emission lines produced by ionized elements in the corona; the K-corona, produced by photospheric light that is Thomson scattered by coronal electrons; and the F-corona, produced by sunlight scattered from dust particles in the near Sun environment and in interplanetary space. Polarized white light observations of the corona provide a way of isolating the K-corona to determine its structure, brightness, and density. This work focuses on broadband white light polarization observations of the corona during the upcoming solar eclipse from three different instruments. We compare coronal polarization brightness observations of the August 21, 2017 total solar eclipse from the NCAR/High Altitude Observatory (HAO) Rosetta Stone experiment using the 4-D Technology PolarCam camera with the two Citizen PACA_CATE17Pol telescopes that will acquire linear polarization observations of the eclipse and the NCAR/HAO K-Cor white light coronagraph observations from the Mauna Loa Solar Observatory in Hawaii. This comparison includes a discussion of the cross-calibration of the different instruments and reports the results of the coronal polarization brightness and electron density of the corona. These observations will be compared with results from previous coronal measurements taken at different phases of the solar cycle. In addition, we report on the performance of the three different polarimeters. The 4-D PolarCam uses a linear polarizer array, PACA_CATE17Pol uses a nematic liquid crystal retarder in a single beam configuration and K-Cor uses a pair of ferroelectric liquid crystal retarders in a dual-beam configuration. The use of the 4-D PolarCam camera in the Rosetta Stone experiment is to demonstrate the technology for acquiring high cadence polarization measurements. The Rosetta Stone experiment is funded through the NASA award NNH16ZDA001N-ISE. The Citizen Science approach to measuring the polarized solar corona during the eclipse is funded through NASA award NNX17AH76G. The NCAR Mauna Loa Solar Observatory is funded by the National Science Foundation.

Coronal bright points at 6cm wavelength

NASA Technical Reports Server (NTRS)

Fu, Qijun; Kundu, M. R.; Schmahl, E. J.

1988-01-01

Results are presented from observations of bright points at a wavelength of 6-cm using the VLA with a spatial resolution of 1.2 arcsec. During two hours of observations, 44 sources were detected with brightness temperatures between 2000 and 30,000 K. Of these sources, 27 are associated with weak dark He 10830 A features at distances less than 40 arcsecs. Consideration is given to variations in the source parameters and the relationship between ephemeral regions and bright points.

Structure and Evoluton of the Large Scale Solar and Heliospheric Magnetic Fields.

DTIC Science & Technology

1984-04-01

symmetric about the equator and therefore reinforces the dipole field. This has the effect of pushing the current sheet toward the equator as shown in Figure...drift only slightly in longitude. The postive sector near 90’ remains strong through the year too. The positive sector near 2700 appears to grow in...sheet position determined from coronal polarization brightness measurements from the Mauna Loa coronameter. An immediate problem with using the

Polar Coronal Hole Ephemeral Regions, the Fast Solar Wind and the Global Magnetic Dynamo

NASA Technical Reports Server (NTRS)

Cirtain, Jonathan W.

2010-01-01

The X-Ray Telescope aboard Hinode has been regularly observing both the north and south solar polar coronal holes from November 2006 through March 2009. We use the observations of emerged flux regions within the coronal hole as evidenced by small x-ray bright points to study the physical properties of these regions. The width of the emerged flux region loop footpoints, the duration of the x-ray emission lifetime for the emerged flux region, the latitude of formation and whether an x-ray or EUV jet was observed were all recorded. In the present work we detail these observations and show a dependence on the width of the emerged flux region (bright point) to the number of x-ray jets observed. The distribution of base width is then related to a power law for number of emerged flux regions as a function of base width.

The Multi-Spectral Solar Telescope Array (MSSTA)

NASA Technical Reports Server (NTRS)

Walker, A. B. C., Jr.; Barbee, Troy W., Jr.; Hoover, Richard B.

1997-01-01

In 1987, our consortium pioneered the application of normal incidence multilayer X-ray optics to solar physics by obtaining the first high resolution narrow band, "thermally differentiated" images of the corona', using the emissions of the Fe IX/Fe X complex at ((lambda)lambda) approx. 171 A to 175 A, and He II Lyman (beta) at 256 A. Subsequently, we developed a rocket borne solar observatory, the Multi Spectral Solar Telescope Array (MSSTA) that pioneered multi-thermal imaging of the solar atmosphere, using high resolution narrow band X-ray, EUV and FUV optical systems. Analysis of MSSTA observations has resulted in four significant insights into the structure of the solar atmosphere: (1) the diameter of coronal loops is essentially constant along their length; (2) models of the thermal and density structure of polar plumes based on MSSTA observations have been shown to be consistent with the thesis that they are the source of high speed solar wind streams; (3) the magnetic structure of the footpoints of polar plumes is monopolar, and their thermal structure is consistent with the thesis that the chromosphere at their footpoints is heated by conduction from above; (4) coronal bright points are small loops, typically 3,500 - 20,000 km long (5 sec - 30 sec); their footpoints are located at the poles of bipolar magnetic structures that are are distinguished from other network elements by having a brighter Lyman a signature. Loop models derived for 26 bright points are consistent with the thesis that the chromosphere at their footpoints is heated by conduction from the corona.

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.

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.

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

Three-Dimensional Structure and Energy Balance of a Coronal Mass Ejection

NASA Technical Reports Server (NTRS)

Lee, J.-Y.; Raymond, J. C.; Ko, Y.-K.; Kim, K.-S.

2009-01-01

UVCS observed Doppler-shifted material of a partial halo coronal mass ejection (CME) on 2001 December 13. The observed ratio of [O VJ/O V] is a reliable density diagnostic important for assessing the state of the plasma. Earlier UVCS observations of CMEs found evidence that the ejected plasma is heated long after the eruption. This paper investigated the heating rates, which represent a significant fraction of the CME energy budget. The parameterized heating and radiative and adiabatic cooling have been used to evaluate the temperature evolution of the CME material with a time-dependent ionization state model. Continuous heating is required to match the UVCS observations. To match the O VI bright knots, a higher heating rate is required such that the heating energy is greater than the kinetic energy.

The Magnetic Free Energy in Active Regions

NASA Technical Reports Server (NTRS)

Metcalf, Thomas R.; Mickey, Donald L.; LaBonte, Barry J.

2001-01-01

The magnetic field permeating the solar atmosphere governs much of the structure, morphology, brightness, and dynamics observed on the Sun. The magnetic field, especially in active regions, is thought to provide the power for energetic events in the solar corona, such as solar flares and Coronal Mass Ejections (CME) and is believed to energize the hot coronal plasma seen in extreme ultraviolet or X-rays. The question remains what specific aspect of the magnetic flux governs the observed variability. To directly understand the role of the magnetic field in energizing the solar corona, it is necessary to measure the free magnetic energy available in active regions. The grant now expiring has demonstrated a new and valuable technique for observing the magnetic free energy in active regions as a function of time.

The Peculiar Solar Minimum 23/24 Revealed by the Microwave Butterfly Diagram

NASA Technical Reports Server (NTRS)

Gopalswamy, Natchimuthuk; Yashiro, Seiji; Makela, Pertti; Shibasaki, Kiyoto; Hathaway, David

2010-01-01

The diminished polar magnetic field strength during the minimum between cycles 23 and 24 is also reflected in the thermal radio emission originating from the polar chromosphere. During solar minima, the polar corona has extended coronal holes containing intense unipolar flux. In microwave images, the coronal holes appear bright, with a brightness enhancement of 500 to 2000 K with respect to the quiet Sun. The brightness enhancement corresponds to the upper chromosphere, where the plasma temperature is approx.10000 K. We constructed a microwave butterfly diagram using the synoptic images obtained by the Nobeyama radioheliograph (NoRH) showing the evolution of the polar and low latitude brightness temperature. While the polar brightness reveals the chromospheric conditions, the low latitude brightness is attributed to active regions in the corona. When we compared the microwave butterfly diagram with the magnetic butterfly diagram, we found a good correlation between the microwave brightness enhancement and the polar field strength. The microwave butterfly diagram covers part of solar cycle 22, whole of cycle 23, and part of cycle 24, thus enabling comparison between the cycle 23/24 and cycle 22/23 minima. The microwave brightness during the cycle 23/24 minimum was found to be lower than that during the cycle 22/23 minimum by approx.250 K. The reduced brightness temperature is consistent with the reduced polar field strength during the cycle 23/24 minimum seen in the magnetic butterfly diagram. We suggest that the microwave brightness at the solar poles is a good indicator of the speed of the solar wind sampled by Ulysses at high latitudes..

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

Brightness Variations in the Solar Atmosphere as Seen by SOHO

NASA Astrophysics Data System (ADS)

Brkovic, A.; Rüedi, I.; Solanki, S. K.; Huber, M. C. E.; Stenflo, J. O.; Stucki, K.; Harrison, R.; Fludra, A.

We present preliminary results of a statistical analysis of the brightness variations of solar features at different levels in the solar atmosphere. We observed quiet Sun regions at disc centre using the Coronal Diagnostic Spectrometer (CDS) onboard the Solar and Heliospheric Observatory (SOHO). We find significant variability at all time scales in all parts of the quiet Sun, from darkest intranetwork to brightest network. Such variations are observed simultaneously in the chromospheric He I 584.33 Angstroms (2 \\cdot 10^4 K) line, the transition region O V 629.74 Angstroms (2.5 \\cdot 10^5 K) and coronal Mg IX 368.06 Angstroms (10^6 K) line. The relative variability is independent of brightness and most of the variability appears to take place on time scales longer than 5 minutes for all 3 spectral lines. No significant differences are observed between the different data sets.

THE BLOB CONNECTION: SEARCHING FOR LOW CORONAL SIGNATURES OF SOLAR POST-CME BLOBS

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

Schanche, Nicole E; Reeves, Katharine K; Webb, David F., E-mail: nschanche@cfa.harvard.edu

2016-11-01

Bright linear structures, thought to be indicators of a current sheet (CS), are often seen in Large Angle and Spectrometric Coronagraph (LASCO) on the Solar and Heliospheric Observatory (SOHO) white-light data in the wake of coronal mass ejections (CMEs). In a subset of these post-CME structures, relatively bright blobs are seen moving outward along the rays. These blobs have been interpreted as consequences of the plasmoid instability in the CS, and can help us to understand the dynamics of the reconnection. We examine several instances, taken largely from the SOHO /LASCO CME-rays Catalog, where these blobs are clearly visible inmore » white-light data. Using radially filtered, difference, wavelet enhanced, and multiscale Gaussian normalized images to visually inspect Solar Dynamics Observatory /Atmospheric Imaging Assembly (AIA) data in multiple wavelengths, we look for signatures of material that correspond both temporally and spatially to the later appearance of the blobs in LASCO/C2. Constraints from measurements of the blobs allow us to predict the expected count rates in DN pixel{sup −1} s{sup −1} for each AIA channel. The resulting values would make the blobs bright enough to be detectable at 1.2 R {sub ⊙}. However, we do not see conclusive evidence for corresponding blobs in the AIA data in any of the events. We do the same calculation for the “cartwheel CME,” an event in which blobs were seen in X-rays, and find that our estimated count rates are close to those observed. We suggest several possibilities for the absence of the EUV blobs including the formation of the blob higher than the AIA field of view, blob coalescence, and overestimation of blob densities.« less

Small-scale swirl events in the quiet Sun chromosphere

NASA Astrophysics Data System (ADS)

Wedemeyer-Böhm, S.; Rouppe van der Voort, L.

2009-11-01

Context: Recent progress in instrumentation enables solar observations with high resolution simultaneously in the spatial, temporal, and spectral domains. Aims: We use such high-resolution observations to study small-scale structures and dynamics in the chromosphere of the quiet Sun. Methods: We analyse time series of spectral scans through the Ca ii 854.2 nm spectral line obtained with the CRISP instrument at the Swedish 1-m Solar Telescope. The targets are quiet Sun regions inside coronal holes close to disc-centre. Results: The line core maps exhibit relatively few fibrils compared to what is normally observed in quiet Sun regions outside coronal holes. The time series show a chaotic and dynamic scene that includes spatially confined “swirl” events. These events feature dark and bright rotating patches, which can consist of arcs, spiral arms, rings or ring fragments. The width of the fragments typically appears to be of the order of only 0.2 arcsec, which is close to the effective spatial resolution. They exhibit Doppler shifts of -2 to -4 km s-1 but sometimes up to -7 km s-1, indicating fast upflows. The diameter of a swirl is usually of the order of 2´´. At the location of these swirls, the line wing and wide-band maps show close groups of photospheric bright points that move with respect to each other. Conclusions: A likely explanation is that the relative motion of the bright points twists the associated magnetic field in the chromosphere above. Plasma or propagating waves may then spiral upwards guided by the magnetic flux structure, thereby producing the observed intensity signature of Doppler-shifted ring fragments. The movie is only available in electronic form at http://www.aanda.org Marie Curie Intra-European Fellow of the European Commission.

Development of a current sheet in the wake of a fast coronal mass ejection

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

Ling, A. G.; Webb, D. F.; Burkepile, J. T.

2014-04-01

A bright ray that developed in the wake of a fast coronal mass ejection (CME) on 2005 September 7 presents a unique opportunity to study the early development and physical characteristics of a reconnecting current sheet (CS). Polarization brightness images from the Mk4 K-Coronameter at the Mauna Loa Solar Observatory are used to determine the structure of the ray along its axis low in the corona as it progressed outward. Coverage of the early development of the ray out to ∼1.3 R {sub ☉} for a period of ∼27 hr after the start of the event enables for the firstmore » time in white light a measurement of a CME CS from the top of the arcade to the base of the flux rope. Measured widths of the ray are combined to obtain the kinematics of the upper and lower {sup Y-}points described in reconnection flux-rope models such as that of Lin and Forbes. The time dependence of these points are used to derive values for the speed and acceleration of the growth of the CS. We note the appearance of a large structure which increases in size as it expands outward in the early development of the ray and an apparent oscillation with a period of ∼0.5 hr in the position angle of the ray.« 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.

The Spinning Corona of FK Comae

NASA Astrophysics Data System (ADS)

Kashyap, Vinay

2010-09-01

FK Comae is an ultra-fast rotating, single yellow giant, product of a recent W UMa merger. Extraordinary levels of FUV and X-ray emission rate FK Comae a coronal powerhouse on par with the most extreme of the better known activity heavyweights: short-period RS CVn binaries. As a single star, FK Comae has clear advantages as a laboratory for exploring the outer limits of magnetospheric activity among the coronal cool stars. FK Comae has a long history of attention at optical and X-ray wavelengths, thanks to its generously spotted surface, and proclivity to flare regularly at high energies. FUSE discovered ultra-broad, redshifted profiles of OVI and CIII, but unfortunately the singular observation could not be repeated, thanks to the satellite's flaky attitude system. The remarkable FUV spectrum was taken just a few months before STIS failed in 2004, so there was no opportunity to turn the more powerful gaze of Hubble to the task. Now, finally, the amazing sensitivity of Cosmic Origins Spectrograph can be brought to bear: a single orbit can capture an FUV spectrum of FK Comae with S/N at instrumental limits for bright lines, and digging down to faint FeXXI 1354 {bridge to the coordinated Chandra HETGS pointing we are carrying out}.We will trace how the bright FUV regions relate spatially to the photospheric dark spots, to inform ideas of coronal structure and heating in these advanced objects. We will probe whether a global magnetosphere exists, and whether the field lines are loaded with hot coronal gas {>10 MK}, as well as the cooler 0.3 MK material already suggested by highly broadened FUSE OVI. Further, we will test whether the striking 100 km/s redshifts of the FUV lines, and similar shifts seen in NeX by Chandra HETGS, are caused by persistent coronal flows {outflows, perhaps implicated in magnetic braking; or inflows, like "coronal rain" on the Sun}. Our method is to exploit, on the one hand, emission-line "Doppler imaging," whereby bright surface regions are mapped onto specific locations in the global profile, according to the line-of-sight rotational velocity. On the other hand, we compare features of different opacity and excitation {e.g., SiIII 1206, SiIII 1892, and SiIV 1393} to deduce whether, say, a red asymmetry is caused by blueshifted absorption, or alternatively by infall of the entire feature. Multiple epochs spaced over two rotation periods break the degeneracy between profile distortions caused by disk passage of hot patches {Doppler imaging part}, and those caused by large-scale gas kinematics. Contemporaneous starspot maps from the ground will provide a fundamental magnetic context for the coordinated FUV and X-ray campaigns.

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.

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

Evaluation of the Minifilament-Eruption Scenario for Solar Coronal Jets in Polar Coronal Holes

NASA Technical Reports Server (NTRS)

Baikie, Tomi K.; Sterling, Alphonse C.; Falconer, David; Moore, Ronald L.; Savage, Sabrina L.

2016-01-01

Solar coronal jets are suspected to result from magnetic reconnection low in the Sun's atmosphere. Sterling et al. (2015) looked as 20 jets in polar coronal holes, using X-ray images from the Hinode/X-Ray Telescope (XRT) and EUV images from the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA). They suggested that each jet was driven by the eruption of twisted closed magnetic field carrying a small-scale filament, which they call a 'minifilament', and that the jet was produced by reconnection of the erupting field with surrounding open field. In this study, we carry out a more extensive examination of polar coronal jets. From 180 hours of XRT polar coronal hole observations spread over two years (2014-2016), we identified 130 clearly-identifiable X-ray jet events and thus determined an event rate of over 17 jets per day per in the Hinode/XRT field of view. From the broader set, we selected 25 of the largest and brightest events for further study in AIA 171, 193, 211, and 304 Angstrom images. We find that at least the majority of the jets follow the minifilament-eruption scenario, although for some cases the evolution of the minifilament in the onset of its eruption is more complex than presented in the simplified schematic of Sterling et al. (2015). For all cases in which we could make a clear determination, the spire of the X-ray jet drifted laterally away from the jet-base-edge bright point; this spire drift away from the bright point is consistent with expectations of the minifilament-eruption scenario for coronal-jet production. This work was supported with funding from the NASA/MSFC Hinode Project Office, and from the NASA HGI program.

Density and white light brightness in looplike coronal mass ejections - Temporal evolution

NASA Technical Reports Server (NTRS)

Steinolfson, R. S.; Hundhausen, A. J.

1988-01-01

Three ambient coronal models suitable for studies of time-dependent phenomena were used to investigate the propagation of coronal mass ejections initiated in each atmosphere by an identical energy source. These models included those of a static corona with a dipole magnetic field, developed by Dryer et al. (1979); a steady polytropic corona with an equatorial coronal streamer, developed by Steinolfson et al. (1982); and Steinolfson's (1988) model of heated corona with an equatorial coronal streamer. The results indicated that the first model does not adequately represent the general characteristics of observed looplike mass ejections, and the second model simulated only some of the observed features. Only the third model, which included a heating term and a streamer, was found to yield accurate simulation of the mess ejection observations.

Flares observed by the normal incidence X-ray telescope on 1989 September 11

NASA Technical Reports Server (NTRS)

Herant, M.; Pardo, F.; Spiller, E.; Golub, L.

1991-01-01

Two solar flare events have been observed in soft X-rays during a sounding-rocket flight of the Normal-Incidence X-ray Telescope payload on September 11, 1989. The flare in X-rays involves a single bright loop crossing the neutral line, and having its footpoints at the southern ends of the ribbons; this loop accounts for more than 66 percent of the emission. Within the remainder of each of the flare ribbons, a complex coronal structure is also observed to be interacting with the main flare loop. A second event, in an active region at the limb, has a strong correlation with H-alpha images obtained at the same time. This indicates the coexistence, and indeed the close proximity, of coronal and chromospheric temperature material. Interpretations of this phenomenon are discussed.

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

The Foggy EUV Corona and Coronal Heating by MHD Waves from Explosive Reconnection Events

NASA Technical Reports Server (NTRS)

Moore, Ron L.; Cirtain, Jonathan W.; Falconer, David A.

2008-01-01

In 0.5 arcsec/pixel TRACE coronal EUV images, the corona rooted in active regions that are at the limb and are not flaring is seen to consist of (1) a complex array of discrete loops and plumes embedded in (2) a diffuse ambient component that shows no fine structure and gradually fades with height. For each of two not-flaring active regions, found that the diffuse component is (1) approximately isothermal and hydrostatic and (2) emits well over half of the total EUV luminosity of the active-region corona. Here, from a TRACE Fe XII coronal image of another not-flaring active region, the large sunspot active region AR 10652 when it was at the west limb on 30 July 2004, we separate the diffuse component from the discrete loop component by spatial filtering, and find that the diffuse component has about 60% of the total luminosity. If under much higher spatial resolution than that of TRACE (e. g., the 0.1 arcsec/pixel resolution of the Hi-C sounding-rocket experiment proposed by J. W. Cirtain et al), most of the diffuse component remains diffuse rather being resolved into very narrow loops and plumes, this will raise the possibility that the EUV corona in active regions consists of two basically different but comparably luminous components: one being the set of discrete bright loops and plumes and the other being a truly diffuse component filling the space between the discrete loops and plumes. This dichotomy would imply that there are two different but comparably powerful coronal heating mechanisms operating in active regions, one for the distinct loops and plumes and another for the diffuse component. We present a scenario in which (1) each discrete bright loop or plume is a flux tube that was recently reconnected in a burst of reconnection, and (2) the diffuse component is heated by MHD waves that are generated by these reconnection events and by other fine-scale explosive reconnection events, most of which occur in and below the base of the corona where they are seen as UV explosive events, EUV blinkers, and type II spicules. These MHD waves propagate across field lines and dissipate, heating the plasma in the field between the bright loops and plumes.

ALMA Discovery of Solar Umbral Brightness Enhancement at λ = 3 mm

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

Iwai, Kazumasa; Loukitcheva, Maria; Shimojo, Masumi

We report the discovery of a brightness enhancement in the center of a large sunspot umbra at a wavelength of 3 mm using the Atacama Large Millimeter/sub-millimeter Array (ALMA). Sunspots are among the most prominent features on the solar surface, but many of their aspects are surprisingly poorly understood. We analyzed a λ = 3 mm (100 GHz) mosaic image obtained by ALMA that includes a large sunspot within the active region AR12470, on 2015 December 16. The 3 mm map has a 300″ × 300″ field of view and 4.″9 × 2.″2 spatial resolution, which is the highest spatialmore » resolution map of an entire sunspot in this frequency range. We find a gradient of 3 mm brightness from a high value in the outer penumbra to a low value in the inner penumbra/outer umbra. Within the inner umbra, there is a marked increase in 3 mm brightness temperature, which we call an umbral brightness enhancement. This enhanced emission corresponds to a temperature excess of 800 K relative to the surrounding inner penumbral region and coincides with excess brightness in the 1330 and 1400 Å slit-jaw images of the Interface Region Imaging Spectrograph ( IRIS ), adjacent to a partial lightbridge. This λ = 3 mm brightness enhancement may be an intrinsic feature of the sunspot umbra at chromospheric heights, such as a manifestation of umbral flashes, or it could be related to a coronal plume, since the brightness enhancement was coincident with the footpoint of a coronal loop observed at 171 Å.« less

ALMA Discovery of Solar Umbral Brightness Enhancement at λ = 3 mm

NASA Astrophysics Data System (ADS)

Iwai, K.; Loukitcheva, M.; Shimojo, M.; Solanki, S. K.; White, S. M.

2017-12-01

We report the discovery of a brightness enhancement in the center of a large sunspot umbra at a wavelength of 3 mm using the Atacama Large Millimeter/sub-millimeter Array (ALMA). Sunspots are among the most prominent features on the solar surface, but many of their aspects are surprisingly poorly understood. We analyzed a λ = 3 mm (100 GHz) mosaic image obtained by ALMA that includes a large sunspot within the active region AR12470, on 2015 December 16. The 3 mm map has a 300''×300'' field of view and 4.9''×2.2'' spatial resolution, which is the highest spatial resolution map of an entire sunspot in this frequency range. We find a gradient of 3 mm brightness from a high value in the outer penumbra to a low value in the inner penumbra/outer umbra. Within the inner umbra, there is a marked increase in 3 mm brightness temperature, which we call an umbral brightness enhancement. This enhanced emission corresponds to a temperature excess of 800 K relative to the surrounding inner penumbral region and coincides with excess brightness in the 1330 and 1400 Å slit-jaw images of the Interface Region Imaging Spectrograph (IRIS), adjacent to a partial lightbridge. This λ = 3 mm brightness enhancement may be an intrinsic feature of the sunspot umbra at chromospheric heights, such as a manifestation of umbral flashes, or it could be related to a coronal plume, since the brightness enhancement was coincident with the footpoint of a coronal loop observed at 171 Å.

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

Coronal Hole All Spread Out

NASA Image and Video Library

2017-11-16

This image from NASA's Solar Dynamics Observatory shows a broad coronal hole was the dominant feature this week on the sun (Nov. 7-9, 2017). It was easily recognizable as the dark expanse across the top of the sun and extending down in each side. Coronal holes are magnetically open areas on the sun that allow high-speed solar wind to gush out into space. They always appear darker in extreme ultraviolet. This one was likely the source of bright aurora that shimmered for numerous observers, with some reaching down even to Nebraska. Movies are available at https://photojournal.jpl.nasa.gov/catalog/PIA22113

Relationship between extreme ultraviolet microflares and small-scale magnetic fields in the quiet Sun

NASA Astrophysics Data System (ADS)

Jiang, Fayu; Zhang, Jun; Yang, Shuhong

2016-04-01

Microflares are small dynamic signatures observed in X-ray and extreme-ultraviolet channels. Because of their impulsive emission enhancements and wide distribution, they are thought to be closely related to coronal heating. By using the high resolution 171 Å images from the Atmospheric Imaging Assembly and the lines-of-sight magnetograms obtained by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, we trace 10794 microflares in a quiet region near the disk center with a field of view of 960''× 1068'' during 24 hr. The microflares have an occurrence rate of 4.4 × 103 hr-1 extrapolated over the whole Sun. Their average brightness, size, and lifetime are 1.7 I0 (of the quiet Sun), 9.6 Mm2, and 3.6 min, respectively. There exists a mutual positive correlation between the microflares' brightness, area and lifetime. In general, the microflares distribute uniformly across the solar disk, but form network patterns locally, which are similar to and matched with the magnetic network structures. Typical cases show that the microflares prefer to occur in magnetic cancellation regions of network boundaries. We roughly calculate the upper limit of energy flux supplied by the microflares and find that the result is still a factor of ˜15 below the coronal heating requirement.

Relationship between extreme ultraviolet microflares and small-scale magnetic fields in the quiet Sun

NASA Astrophysics Data System (ADS)

Jiang, Fayu; Zhang, Jun; Yang, Shuhong

2015-06-01

Microflares are small dynamic signatures observed in X-ray and extreme-ultraviolet channels. Because of their impulsive emission enhancements and wide distribution, they are thought to be closely related to coronal heating. By using the high-resolution 171 Å images from the Atmospheric Imaging Assembly and the lines-of-sight magnetograms obtained by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, we trace 10794 microflares in a quiet region near the disk center with a field of view of 960″ × 1068″ during 24 hr. The microflares have an occurrence rate of 4.4 × 103 hr-1 extrapolated over the whole Sun. Their average brightness, size, and lifetime are 1.7I0 (of the quiet Sun), 9.6 Mm2, and 3.6 min, respectively. There exists a mutual positive correlation between the microflares' brightness, area, and lifetime. In general, the microflares distribute uniformly across the solar disk, but form network patterns locally, which are similar to and matched with the magnetic network structures. Typical cases show that the microflares prefer to occur in magnetic cancellation regions of network boundaries. We roughly calculate the upper limit of energy flux supplied by the microflares and find that the result is still a factor of ˜ 15 below the coronal heating requirement.

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.

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.

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.

Correspondence between solar fine-scale structures in the corona, transition region, and lower atmosphere from collaborative observations

NASA Technical Reports Server (NTRS)

Moses, J. Daniel; Cook, J. W.; Bartoe, J.-D. F.; Brueckner, G. E.; Dere, K. P.; Webb, D. F.; Davis, John M.; Recely, F.; Martin, S. F.; Zirin, H.

1989-01-01

The Soft X-Ray Imaging Payload and the High Resolution Telescope and Spectrograph (HRTS) instrument were launched from White Sands on 11 December 1987 in coordinated sounding rocket flights to investigate the correspondence of coronal and transition region structures, especially the relationship between X-ray bright points (XBPs) and transition region small spatial scale energetic events. The coaligned data from X-ray images are presented along with maps of sites of transition region energetic events observed in C IV (100,000 K), HRTS 1600 A spectroheliograms of the T sub min region and ground based magnetogram and He I 10830 A images.

Solar x ray astronomy rocket program

NASA Technical Reports Server (NTRS)

1990-01-01

The dynamics were studied of the solar corona through the imaging of large scale coronal structures with AS&E High Resolution Soft X ray Imaging Solar Sounding Rocket Payload. The proposal for this program outlined a plan of research based on the construction of a high sensitivity X ray telescope from the optical and electronic components of the previous flight of this payload (36.038CS). Specifically, the X ray sensitive CCD camera was to be placed in the prime focus of the grazing incidence X ray mirror. The improved quantum efficiency of the CCD detector (over the film which had previously been used) allows quantitative measurements of temperature and emission measure in regions of low x ray emission such as helmet streamers beyond 1.2 solar radii or coronal holes. Furthermore, the improved sensitivity of the CCD allows short exposures of bright objects to study unexplored temporal regimes of active region loop evolution.

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.

FK Comae, King of Spin: the Movie

NASA Astrophysics Data System (ADS)

Ayres, Thomas

2010-09-01

FK Comae is an ultra-fast rotating, single yellow giant, product of a recent W UMa merger. Extraordinary levels of FUV and X-ray emission rate FK Comae a coronal powerhouse on par with the most extreme of the better known activity heavyweights: short-period RS CVn binaries. As a single star, FK Comae has clear advantages as a laboratory for exploring the outer limits of magnetospheric activity among the coronal cool stars. FK Comae has a long history of attention at optical and X-ray wavelengths, thanks to its generously spotted surface, and proclivity to flare regularly at high energies. FUSE discovered ultra-broad, redshifted profiles of O VI and C III, but unfortunately the singular observation could not be repeated, thanks to the satellite's flaky attitude system. The remarkable FUV spectrum was taken just a few months before STIS failed in 2004, so there was no opportunity to turn the more powerful gaze of Hubble to the task. Now, finally, the amazing sensitivity of Cosmic Origins Spectrograph can be brought to bear: a single orbit can capture an FUV spectrum of FK Comae with S/N at instrumental limits for bright lines, and digging down to faint Fe XXI 1354 {bridge to the coordinated Chandra HETGS pointing we also are proposing}.We will trace how the bright FUV regions relate spatially to the photospheric dark spots, to inform ideas of coronal structure and heating in these advanced objects. We will probe whether a global magnetosphere exists, and whether the field lines are loaded with hot coronal gas {>10 MK}, as well as the cooler 0.3 MK material already suggested by highly broadened FUSE O VI. Further, we will test whether the striking 100 km/s redshifts of the FUV lines, and similar shifts seen in Ne X by Chandra HETGS, are caused by a massive coronal outflow {perhaps implicated in magnetic braking}. Our method is to exploit, on the one hand, emission-line "Doppler imaging," whereby bright surface regions are mapped onto specific locations in the global profile, according to the line-of-sight rotational velocity. On the other hand, we compare features of different opacity and excitation {e.g., Si III 1206 and Si IV 1393} to deduce whether, say, a red asymmetry is caused by blueshifted absorption, or alternatively by infall of the entire feature. Multiple epochs spaced over two rotation periods break the degeneracy between profile distortions caused by disk passage of hot patches {Doppler imaging part}, and those caused by large-scale flows. Contemporaneous spot maps from the ground will provide a fundamental magnetic context for the coordinated FUV and X-ray "movies."

Solar burst precursors and energy build-up at microwave wavelengths

NASA Technical Reports Server (NTRS)

Lang, Kenneth R.; Wilson, Robert F.

1986-01-01

We summarize high-resolution microwave observations (VLA) of heating and magnetic triggering in coronal loops. Magnetic changes that precede solar eruptions on time scales of tens of minutes involve primarily emerging coronal loops and the interaction of two or more loops. Thermal cyclotron lines have been detected in coronal loops, suggesting the presence of hot current sheets that enhance emission from relatively thin layers of enhanced temperature and constant magnetic field. These current sheets may play a role in the excitation of solar bursts. A filament-associated source with a high brightness temperature and steep radiation spectrum occurs above a region of apparently weak photospheric field. This source might be attributed to currents that enhance coronal magnetic fields. Compact (phi=5 sec) transient sources with lifetimes of 30 to 60 minutes have also been detected in regions of apparently weak photospheric field. We conclude by comparing VLA observations of coronal loops with simultaneous SMM-XRP observations.

Solar burst precursors and energy build-up at microwave wavelengths

NASA Astrophysics Data System (ADS)

Lang, Kenneth R.; Wilson, Robert F.

We summarize high-resolution microwave observations (VLA) of heating and magnetic triggering in coronal loops. Magnetic changes that precede solar eruptions on time scales of tens of minutes involve primarily emerging coronal loops and the interaction of two or more loops. Thermal cyclotron lines have been detected in coronal loops, suggesting the presence of hot current sheets that enhance emission from relatively thin layers of enhanced temperature and constant magnetic field. These current sheets may play a role in the excitation of solar bursts. A filament-associated source with a high brightness temperature and steep radiation spectrum occurs above a region of apparently weak photospheric field. This source might be attributed to currents that enhance coronal magnetic fields. Compact (phi=5 sec) transient sources with lifetimes of 30 to 60 minutes have also been detected in regions of apparently weak photospheric field. We conclude by comparing VLA observations of coronal loops with simultaneous SMM-XRP observations.

Coronal ``Wave'': Magnetic Footprint of a Coronal Mass Ejection?

NASA Astrophysics Data System (ADS)

Attrill, Gemma D. R.; Harra, Louise K.; van Driel-Gesztelyi, Lidia; Démoulin, Pascal

2007-02-01

We investigate the properties of two ``classical'' EUV Imaging Telescope (EIT) coronal waves. The two source regions of the associated coronal mass ejections (CMEs) possess opposite helicities, and the coronal waves display rotations in opposite senses. We observe deep core dimmings near the flare site and also widespread diffuse dimming, accompanying the expansion of the EIT wave. We also report a new property of these EIT waves, namely, that they display dual brightenings: persistent ones at the outermost edge of the core dimming regions and simultaneously diffuse brightenings constituting the leading edge of the coronal wave, surrounding the expanding diffuse dimmings. We show that such behavior is consistent with a diffuse EIT wave being the magnetic footprint of a CME. We propose a new mechanism where driven magnetic reconnections between the skirt of the expanding CME magnetic field and quiet-Sun magnetic loops generate the observed bright diffuse front. The dual brightenings and the widespread diffuse dimming are identified as innate characteristics of this process.

Towards a Data-Optimized Coronal Magnetic Field Model (DOC-FM): Synthetic Test Beds and Multiwavelength Forward Modeling

NASA Astrophysics Data System (ADS)

Gibson, S. E.; Dalmasse, K.; Fan, Y.; Fineschi, S.; MacKay, D.; Rempel, M.; White, S. M.

2015-12-01

Understanding the physical state of the solar corona is key to deciphering the origins of space weather as well as to realistically representing the environment to be navigated by missions such as Solar Orbiter and Solar Probe Plus. However, inverting solar coronal observations to reconstruct this physical state -- and in particular the three-dimensional coronal magnetic field - is complicated by limited lines of sight and by projection effects. On the other hand, the sensitivity of multiwavelength observations to different physical mechanisms implies a potential for simultaneous probing of different parts of the coronal plasma. In order to study this complementarity, and to ultimately establish an optimal set of observations for constraining the three-dimensional coronal magnetic field, we are developing a suite of representative simulations to act as diagnostic test beds. We will present three such test beds: a coronal active region, a quiescent prominence, and a global corona. Each fully define the physical state of density, temperature, and vector magnetic field in three dimensions throughout the simulation domain. From these test beds, and using the FORWARD SolarSoft IDL codes, we will create a broad range of synthetic data. Radio observables will include intensity and circular polarization (including gyroresonance effects) and Faraday rotation for a range of frequencies. Infrared and visible forbidden line diagnostics of Zeeman and saturated Hanle effects will yield full Stokes vector (I, Q, U, V) synthetic data, and UV permitted line Hanle diagnostics will yield intensity and linear polarization. In addition, we will synthesize UV and SXR imager data, UV/EUV spectrometric data, and white light brightness and polarized brightness. All of these synthetic data, along with the "ground truth" physical state of the simulations from which they are derived, will be made available to the community for the purpose of testing coronal inversion techniques.

Studies of coronal lines with electronic cameras during the eclipse of 7 march 1970.

PubMed

Fort, B

1970-12-01

The experimental design described here allows us to study with 2-A. bandpass filters the brightness distribution of the green coronal line, the two infrared lines of Fe XIII, and the neighboring coronal continuum. For the first time, in an eclipse expedition, electrostatic cameras derived from the Lallemand type are used; full advantage was taken of their speed, especially in the near infrared spectral range, and their good photometric qualities. They permit the measurement of intensity and polarization of the lines in the corona to a height of 1.25 solar radii above the limb of the sun, with a spatial resolution >/= (10")(2).

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.

Intercomparison of the LASCO-C2, SECCHI-COR1, SECCHI-COR2, and Mk4 Coronagraphs

NASA Technical Reports Server (NTRS)

Frazin, Richard A.; Vasquez, Alberto M.; Thompson, William T.; Hewett, Russell J.; Lamy, Philippe; Llebaria, Antoine; Vourlidas, Angelos; Burkepile, Joan

2012-01-01

In order to assess the reliability and consistency of white-light coronagraph measurements, we report on quantitative comparisons between polarized brightness [pB] and total brightness [B] images taken by the following white-light coronagraphs: LASCO-C2 on SOHO, SECCHI-COR1 and -COR2 on STEREO, and the ground-based MLSO-Mk4. The data for this comparison were taken on 16 April 2007, when both STEREO spacecraft were within 3.1 deg. of Earth’s heliographic longitude, affording essentially the same view of the Sun for all of the instruments. Due to the difficulties of estimating stray-light backgrounds in COR1 and COR2, only Mk4 and C2 produce reliable coronal-hole values (but not at overlapping heights), and these cannot be validated without rocket flights or ground-based eclipse measurements. Generally, the agreement between all of the instruments’ pB values is within the uncertainties in bright streamer structures, implying that measurements of bright CMEs also should be trustworthy. Dominant sources of uncertainty and stray light are discussed, as is the design of future coronagraphs from the perspective of the experiences with these instruments.

Relationship between coronal holes and high speed streams at L1: arrival times, durations, and intensities

NASA Astrophysics Data System (ADS)

Luo, B.; Bu, X.; Liu, S.; Gong, J.

2017-12-01

Coronal holes are sources of high-speed steams (HSS) of solar wind. When coronal holes appear at mid/low latitudes on the Sun, consequential HSSs may impact Earth and cause recurrent geospace environment disturbances, such as geomagnetic storms, relativistic electron enhancements at the geosynchronous orbit, and thermosphere density enhancements. Thus, it is of interests for space weather forecasters to predict when (arrival times), how long (time durations), and how severe (intensities) HSSs may impact Earth when they notice coronal holes on the sun and are anticipating their geoeffectiveness. In this study, relationship between coronal holes and high speed streams will be statistically investigated. Several coronal hole parameters, including passage times of solar central meridian, coronal hole longitudinal widths, intensities reflected by mean brightness, are derived using Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) images for years 2011 to 2016. These parameters will be correlated with in-situ solar wind measurements measured at the L1 point by the ACE spacecraft, which can give some results that are useful for space weather forecaster in predicting the arrival times, durations, and intensities of coronal hole high-speed streams in about 3 days advance.

The evolution of a coronal streamer and the photospheric magnetic field

NASA Technical Reports Server (NTRS)

Poland, A. I.; Macqueen, R. M.

1981-01-01

A large equatorial coronal streamer observed in the outer corona grew in brightness and size during successive limb passages between October 6, 1973 and January 10, 1974 (solar rotations 1606-1611). Unlike previous studies of streamers and their photospheric associations, no definite surface feature could be identified in the present case. This suggests that the streamer is associated with the large scale photospheric magnetic field. Comparison of the streamer growth with observed underlying photospheric magnetic flux changes indicated that as the streamer increased in brightness, areal extent, and density, the photospheric magnetic flux decreased. Three possible explanations for the streamer's growth are presented, the conceptually simplest being that the decrease in photospheric field results in an opening of the flux tubes under the streamer, which permits an increase mass flux through the streamer.

Challenging Some Contemporary Views of Coronal Mass Ejections. II. The Case for Absent Filaments

NASA Astrophysics Data System (ADS)

Howard, T. A.; DeForest, C. E.; Schneck, U. G.; Alden, C. R.

2017-01-01

When a coronal mass ejection (CME) appears in a coronagraph it often exhibits three parts. This “classic” three-part configuration consists of a bright leading edge, a dark circular- or teardrop-shaped cavity, and a bright core within the cavity. It is generally accepted that these are manifestations of coronal plasma pileup, the driving magnetic flux rope, and the associated eruptive filament, respectively. The latter has become accepted by the community since coronagraph CMEs have been commonly associated with eruptive filaments for over 40 years. In this second part of our series challenging views on CMEs, we present the case that the inner core of the three-part coronagraph CME may not be, and in the most common cases is not, a filament. We present our case in the form of four exhibits showing that most of the CMEs in a broad survey are not associated with an eruptive filament at the Sun, and that the cores of those CMEs that are filament-associated do not geometrically resemble or consist of material from the associated filament. We conclude with a discussion on the possible causes of the bright CME core and what happens to the filament material postlaunch. We discuss how the CME core could arise spontaneously from the eruption of a flux rope from the Sun, or could be the result of a mathematical caustic produced by the geometric projection of a twisted flux rope.

CHALLENGING SOME CONTEMPORARY VIEWS OF CORONAL MASS EJECTIONS. II. THE CASE FOR ABSENT FILAMENTS

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

Howard, T. A.; DeForest, C. E.; Schneck, U. G.

2017-01-01

When a coronal mass ejection (CME) appears in a coronagraph it often exhibits three parts. This “classic” three-part configuration consists of a bright leading edge, a dark circular- or teardrop-shaped cavity, and a bright core within the cavity. It is generally accepted that these are manifestations of coronal plasma pileup, the driving magnetic flux rope, and the associated eruptive filament, respectively. The latter has become accepted by the community since coronagraph CMEs have been commonly associated with eruptive filaments for over 40 years. In this second part of our series challenging views on CMEs, we present the case that themore » inner core of the three-part coronagraph CME may not be, and in the most common cases is not, a filament. We present our case in the form of four exhibits showing that most of the CMEs in a broad survey are not associated with an eruptive filament at the Sun, and that the cores of those CMEs that are filament-associated do not geometrically resemble or consist of material from the associated filament. We conclude with a discussion on the possible causes of the bright CME core and what happens to the filament material postlaunch. We discuss how the CME core could arise spontaneously from the eruption of a flux rope from the Sun, or could be the result of a mathematical caustic produced by the geometric projection of a twisted flux rope.« less

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.

Ballet of Loops

NASA Image and Video Library

2018-06-11

Giant, bright coronal loops trace out the magnetic field lines above an active region from June 4-6, 2018. The wavelength of extreme ultraviolet light shown here is emitted by ionized iron travelling along the field lines, super-heated to approximately 1 million degrees K. Coronal loops were not seen in this level of detail until the Solar Dynamics Observatory was launched in 2010 and came online, giving solar scientists new data with which to study the Sun and its processes. https://photojournal.jpl.nasa.gov/catalog/PIA22508

RS CVn binaries: Testing the solar-stellar dynamo connection

NASA Technical Reports Server (NTRS)

Dempsey, R.

1995-01-01

We have used the Extreme Ultraviolet Explorer satellite to study the coronal emission from the EUV-bright RS CVn binaries Sigma2 CrB, observed February 10-21, 1994, and II Peg, observed October 1-5, 1993. We present time-resolved and integrated EUV short-, medium-, and long-wavelength spectra for these binaries. Sigma2 CrB shows significant first-order emission features in the long-wavelength region. The coronal emission distributions and electron densities are estimated for those active coronae dominated by high temperature plasma.

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

Solar-burst precursors and energy buildup at microwave wavelengths

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

Lang, K.R.; Willson, R.F.

High-resolution microwave observations (VLA) of heating and magnetic triggering in coronal loops are summarized. Magnetic changes that precede solar eruptions on time scales of tens of minutes involve primarily emerging coronal loops and the interaction of two or more loops. Thermal cyclotron lines were detected in coronal loops, suggesting the presence of hot current sheets that enhance emission from relatively thin layers of enhanced temperature and constant magnetic field. These current sheets may play a role in the excitation of solar bursts. A filament-associated source with a high brightness temperature and steep radiation spectrum occurs above a region of apparentlymore » weak photospheric field. This source might be attributed to currents that enhance coronal magnetic fields. Compact (phi=5 sec) transient sources with lifetimes of 30 to 60 minutes were also detected in regions of apparently weak photospheric field. VLA observations of coronal loops are compared with simultaneous SMM-XRP observations in conclusion.« less

Radio observations of a coronal mass ejection induced depletion in the outer solar corona

NASA Astrophysics Data System (ADS)

Ramesh, R.; Sastry, Ch. V.

2000-06-01

We report the first low frequency radio observations of a depletion that occurred in the outer solar corona in the aftermath of the CME event of 1986 June 5, with the large E-W one dimensional grating interferometer at the Gauribidanur radio observatory. We estimated the mass loss associated with the depletion and found that it agrees well with the value obtained through white light observations of the event. The radio brightness temperature at the location of the depletion was less by a factor of ~ 7 compared to the ambient. The angular extent over which the decrease in brightness took place was <= 3'. The electron density variation was found to be proportional to r-10. Since observations at different wavelength bands have different physical origins, the radio method might be useful in independently estimating the characteristics of CME induced coronal depletions.

Temperature and EUV Intensity in a Coronal Prominence Cavity and Streamer

NASA Technical Reports Server (NTRS)

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

2012-01-01

We analyze the temperature and EUV line emission of a coronal cavity and surrounding streamer in terms of a morphological forward model. We use a series of iron line ratios observed with the Hinode Extreme-ultraviolet Imaging Spectrograph (EIS) on 2007 Aug. 9 to constrain temperature as a function of altitude in a morphological forward model of the streamer and cavity. We also compare model prediction of the EIS EUV line intensities and polarized brightness (pB) data from the Mauna Loa Solar Observatory (MLSO) MK4. This work builds on earlier analysis using the same model to determine geometry of and density in the same cavity and streamer. The fit to the data with altitude dependent temperature profiles indicates that both the streamer and cavity have temperatures in the range 1.4-1.7 MK. However, the cavity exhibits substantial substructure such that the altitude dependent temperature profile is not sufficient to completely model conditions in the cavity. Coronal prominence cavities are structured by magnetism so clues to this structure are to be found in their plasma properties. These temperature substructures are likely related to structures in the cavity magnetic field. Furthermore, we find that the model overestimates the line intensities by a factor of 4-10, while overestimating pB data by no more than a factor of 1.4. One possible explanation for this is that there may be a significant amount of material at temperatures outside of the range log T(K) approximately equals 5.8 - 6.7 in both the cavity and the streamer.

MHD Modelling of Coronal Loops: Injection of High-Speed Chromospheric Flows

NASA Technical Reports Server (NTRS)

Petralia, A.; Reale, F.; Orlando, S.; Klimchuk, J. A.

2014-01-01

Context. Observations reveal a correspondence between chromospheric type II spicules and bright upward-moving fronts in the corona observed in the extreme-ultraviolet (EUV) band. However, theoretical considerations suggest that these flows are probably not the main source of heating in coronal magnetic loops. Aims. We investigate the propagation of high-speed chromospheric flows into coronal magnetic flux tubes and the possible production of emission in the EUV band. Methods. We simulated the propagation of a dense 104 K chromospheric jet upward along a coronal loop by means of a 2D cylindrical MHD model that includes gravity, radiative losses, thermal conduction, and magnetic induction. The jet propagates in a complete atmosphere including the chromosphere and a tenuous cool (approximately 0.8 MK) corona, linked through a steep transition region. In our reference model, the jet initial speed is 70 km per second, its initial density is 10(exp 11) per cubic centimeter, and the ambient uniform magnetic field is 10 G. We also explored other values of jet speed and density in 1D and different magnetic field values in 2D, as well as the jet propagation in a hotter (approximately 1.5 MK) background loop. Results. While the initial speed of the jet does not allow it to reach the loop apex, a hot shock-front develops ahead of it and travels to the other extreme of the loop. The shock front compresses the coronal plasma and heats it to about 10(exp 6) K. As a result, a bright moving front becomes visible in the 171 Angstrom channel of the SDO/AIA mission. This result generally applies to all the other explored cases, except for the propagation in the hotter loop. Conclusions. For a cool, low-density initial coronal loop, the post-shock plasma ahead of upward chromospheric flows might explain at least part of the observed correspondence between type II spicules and EUV emission excess.

The Strength and Radial Profile of the Coronal Magnetic Field from the Standoff Distance of a Coronal Mass Ejection-Driven Shock

NASA Technical Reports Server (NTRS)

Gopalswamy, Nat; Yashiro, Seiji

2011-01-01

We determine the coronal magnetic field strength in the heliocentric distance range 6-23 solar radii (Rs) by measuring the shock standoff distance and the radius of curvature of the flux rope during the 2008 March 25 coronal mass ejection imaged by white-light coronagraphs. Assuming the adiabatic index, we determine the Alfven Mach number, and hence the Alfven speed in the ambient medium using the measured shock speed. By measuring the upstream plasma density using polarization brightness images, we finally get the magnetic field strength upstream of the shock. The estimated magnetic field decreases from approximately 48 mG around 6 Rs to 8 mG at 23 Rs. The radial profile of the magnetic field can be described by a power law in agreement with other estimates at similar heliocentric distances.

Low coronal signatures of coronal mass ejections

NASA Astrophysics Data System (ADS)

Attrill, Gemma Diana Ruth

Coronal mass ejections (CMEs) are vast eruptions of magnetised plasma that explode from the solar atmosphere. This thesis focuses on understanding the nascent stages of CMEs, and their magnetic development as they expand into the interplanetary space of our solar system. This is an important part of our effort to understand the space weather environment that we live in, and increasingly interact with through satellite communications technologies. Predominantly through combining extreme ultra-violet imaging and magnetogram data, two low coronal signatures of CMEs, namely coronal waves and dimmings, are studied. A comprehensive list of observational properties of EIT coronal waves is compiled and potential counterparts in radio, Ha, soft X-rays and He n wavelengths are also discussed. New observational constraints on EIT coronal waves are presented, most notably diffuse coronal waves are shown to have a magnetic nature. Finding that many observational constraints are not satisfactorily explained by current theories, a new model for understanding the physical nature of diffuse coronal waves is developed. The new model interprets diffuse coronal "wave" bright fronts to be the low coronal magnetic footprint of CMEs. Implications for developing our understanding of how CMEs become large-scale in the low corona are discussed. Application of the model demonstrates how an understanding of the formation of complex global-scale coronal dimmings can be derived. For the first time it is shown that study of the evolution and magnetic nature of coronal dimming regions can be used to probe the post-eruptive evolution of the CME. Finally, a study is presented regarding why and how CME-related dimmings recover, despite the "open" magnetic connectivity of the ejecta to the Sun being maintained as indicated by electron heat flux measurements at 1 AU.

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

STRUCTURE AND DYNAMICS OF THE 2012 NOVEMBER 13/14 ECLIPSE WHITE-LIGHT CORONA

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

Pasachoff, J. M.; Rušin, V.; Saniga, M.

2015-02-20

Continuing our series of observations of coronal motion and dynamics over the solar-activity cycle, we observed from sites in Queensland, Australia, during the 2012 November 13 (UT)/14 (local time) total solar eclipse. The corona took the low-ellipticity shape typical of solar maximum (flattening index ε = 0.01), a change from the composite coronal images we observed and analyzed in this journal and elsewhere for the 2006 and 2008-2010 eclipses. After crossing the northeast Australian coast, the path of totality was over the ocean, so further totality was seen only by shipborne observers. Our results include velocities of a coronal massmore » ejection (CME; during the 36 minutes of passage from the Queensland coast to a ship north of New Zealand, we measured 413 km s{sup –1}) and we analyze its dynamics. We discuss the shapes and positions of several types of coronal features seen on our higher-resolution composite Queensland coronal images, including many helmet streamers, very faint bright and dark loops at the bases of helmet streamers, voids, and radially oriented thin streamers. We compare our eclipse observations with models of the magnetic field, confirming the validity of the predictions, and relate the eclipse phenomenology seen with the near-simultaneous images from NASA's Solar Dynamics Observatory (SDO/AIA), NASA's Extreme Ultraviolet Imager on Solar Terrestrial Relations Observatory, ESA/Royal Observatory of Belgium's Sun Watcher with Active Pixels and Image Processing (SWAP) on PROBA2, and Naval Research Laboratory's Large Angle and Spectrometric Coronagraph Experiment on ESA's Solar and Heliospheric Observatory. For example, the southeastern CME is related to the solar flare whose origin we trace with a SWAP series of images.« less

Which Bow Shock Theory, Gasdynamic or Magnetohydrodynamic, Better Explains CME Stand-off Distance Ratios from LASCO-C2 Observations ?

NASA Astrophysics Data System (ADS)

Lee, Jae-Ok; Moon, Y.-J.; Lee, Jin-Yi; Kim, R.-S.; Cho, K.-S.

2017-03-01

It is generally believed that fast coronal mass ejections (CMEs) can generate their associated shocks, which are characterized by faint structures ahead of CMEs in white-light coronagraph images. In this study, we examine whether the observational stand-off distance ratio, defined as the CME stand-off distance divided by its radius, can be explained by bow shock theories. Of 535 SOHO/LASCO CMEs (from 1996 to 2015) with speeds greater than 1000 km s-1 and angular widths wider than 60°, we select 18 limb CMEs with the following conditions: (1) their Alfvénic Mach numbers are greater than one under Mann’s magnetic field and Saito’s density distributions; and (2) the shock structures ahead of the CMEs are well identified. We determine observational CME stand-off distance ratios by using brightness profiles from LASCO-C2 observations. We compare our estimates with theoretical stand-off distance ratios from gasdynamic (GD) and magnetohydrodynamic (MHD) theories. The main results are as follows. Under the GD theory, 39% (7/18) of the CMEs are explained in the acceptable ranges of adiabatic gamma (γ) and CME geometry. Under the MHD theory, all the events are well explained when we consider quasi-parallel MHD shocks with γ = 5/3. When we use polarized brightness (pB) measurements for coronal density distributions, we also find similar results: 8% (1/12) under GD theory and 100% (12/12) under MHD theory. Our results demonstrate that the bow shock relationships based on MHD theory are more suitable than those based on GD theory for analyzing CME-driven shock signatures.

Which Bow Shock Theory, Gasdynamic or Magnetohydrodynamic, Better Explains CME Stand-off Distance Ratios from LASCO-C2 Observations ?

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

Lee, Jae-Ok; Moon, Y.-J.; Lee, Jin-Yi

It is generally believed that fast coronal mass ejections (CMEs) can generate their associated shocks, which are characterized by faint structures ahead of CMEs in white-light coronagraph images. In this study, we examine whether the observational stand-off distance ratio, defined as the CME stand-off distance divided by its radius, can be explained by bow shock theories. Of 535 SOHO /LASCO CMEs (from 1996 to 2015) with speeds greater than 1000 km s{sup −1} and angular widths wider than 60°, we select 18 limb CMEs with the following conditions: (1) their Alfvénic Mach numbers are greater than one under Mann’s magneticmore » field and Saito’s density distributions; and (2) the shock structures ahead of the CMEs are well identified. We determine observational CME stand-off distance ratios by using brightness profiles from LASCO-C2 observations. We compare our estimates with theoretical stand-off distance ratios from gasdynamic (GD) and magnetohydrodynamic (MHD) theories. The main results are as follows. Under the GD theory, 39% (7/18) of the CMEs are explained in the acceptable ranges of adiabatic gamma ( γ ) and CME geometry. Under the MHD theory, all the events are well explained when we consider quasi-parallel MHD shocks with γ = 5/3. When we use polarized brightness (pB) measurements for coronal density distributions, we also find similar results: 8% (1/12) under GD theory and 100% (12/12) under MHD theory. Our results demonstrate that the bow shock relationships based on MHD theory are more suitable than those based on GD theory for analyzing CME-driven shock signatures.« less

CONVERGING SUPERGRANULAR FLOWS AND THE FORMATION OF CORONAL PLUMES

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

Wang, Y.-M.; Warren, H. P.; Muglach, K., E-mail: yi.wang@nrl.navy.mil, E-mail: harry.warren@nrl.navy.mil, E-mail: karin.muglach@nasa.gov

Earlier studies have suggested that coronal plumes are energized by magnetic reconnection between unipolar flux concentrations and nearby bipoles, even though magnetograms sometimes show very little minority-polarity flux near the footpoints of plumes. Here we use high-resolution extreme-ultraviolet (EUV) images and magnetograms from the Solar Dynamics Observatory (SDO) to clarify the relationship between plume emission and the underlying photospheric field. We find that plumes form where unipolar network elements inside coronal holes converge to form dense clumps, and fade as the clumps disperse again. The converging flows also carry internetwork fields of both polarities. Although the minority-polarity flux is sometimesmore » barely visible in the magnetograms, the corresponding EUV images almost invariably show loop-like features in the core of the plumes, with the fine structure changing on timescales of minutes or less. We conclude that the SDO observations are consistent with a model in which plume emission originates from interchange reconnection in converging flows, with the plume lifetime being determined by the ∼1 day evolutionary timescale of the supergranular network. Furthermore, the presence of large EUV bright points and/or ephemeral regions is not a necessary precondition for the formation of plumes, which can be energized even by the weak, mixed-polarity internetwork fields swept up by converging flows.« less

Synchronized observations of bright points from the solar photosphere to the corona

NASA Astrophysics Data System (ADS)

Tavabi, Ehsan

2018-05-01

One of the most important features in the solar atmosphere is the magnetic network and its relationship to the transition region (TR) and coronal brightness. It is important to understand how energy is transported into the corona and how it travels along the magnetic field lines between the deep photosphere and chromosphere through the TR and corona. An excellent proxy for transportation is the Interface Region Imaging Spectrograph (IRIS) raster scans and imaging observations in near-ultraviolet (NUV) and far-ultraviolet (FUV) emission channels, which have high time, spectral and spatial resolutions. In this study, we focus on the quiet Sun as observed with IRIS. The data with a high signal-to-noise ratio in the Si IV, C II and Mg II k lines and with strong emission intensities show a high correlation with TR bright network points. The results of the IRIS intensity maps and dopplergrams are compared with those of the Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) instruments onboard the Solar Dynamical Observatory (SDO). The average network intensity profiles show a strong correlation with AIA coronal channels. Furthermore, we applied simultaneous observations of the magnetic network from HMI and found a strong relationship between the network bright points in all levels of the solar atmosphere. These features in the network elements exhibited regions of high Doppler velocity and strong magnetic signatures. Plenty of corona bright points emission, accompanied by the magnetic origins in the photosphere, suggest that magnetic field concentrations in the network rosettes could help to couple the inner and outer solar atmosphere.

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.

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.

On the Detection of Coronal Dimmings and the Extraction of Their Characteristic Properties

NASA Astrophysics Data System (ADS)

Dissauer, K.; Veronig, A. M.; Temmer, M.; Podladchikova, T.; Vanninathan, K.

2018-03-01

Coronal dimmings are distinct phenomena associated with coronal mass ejections (CMEs). The study of coronal dimmings and the extraction of their characteristic parameters help us to obtain additional information regarding CMEs, especially on the initiation and early evolution of Earth-directed CMEs. We present a new approach to detect coronal dimming regions based on a thresholding technique applied on logarithmic base-ratio images. Characteristic dimming parameters describing the dynamics, morphology, magnetic properties, and the brightness of coronal dimming regions are extracted by cumulatively summing newly dimmed pixels over time. It is also demonstrated how core dimming regions are identified as a subset of the overall identified dimming region. We successfully apply our method to two well-observed coronal dimming events. For both events, the core dimming regions are identified and the spatial evolution of the dimming area reveals the expansion of the dimming region around these footpoints. We also show that in the early impulsive phase of the dimming expansion the total unsigned magnetic flux involved in the dimming regions is balanced and that up to 30% of this flux results from the localized core dimming regions. Furthermore, the onset in the profile of the area growth rate is cotemporal with the start of the associated flares and in one case also with the fast rise of the CME, indicating a strong relationship of coronal dimmings with both flares and CMEs.

Dynamic Moss Observed with Hi-C

NASA Technical Reports Server (NTRS)

Alexander, Caroline; Winebarger, Amy; Morton, Richard; Savage, Sabrina

2014-01-01

The High-resolution Coronal Imager (Hi-C), flown on 11 July 2012, has revealed an unprecedented level of detail and substructure within the solar corona. Hi-­-C imaged a large active region (AR11520) with 0.2-0.3'' spatial resolution and 5.5s cadence over a 5 minute period. An additional dataset with a smaller FOV, the same resolution, but with a higher temporal cadence (1s) was also taken during the rocket flight. This dataset was centered on a large patch of 'moss' emission that initially seemed to show very little variability. Image processing revealed this region to be much more dynamic than first thought with numerous bright and dark features observed to appear, move and disappear over the 5 minute observation. Moss is thought to be emission from the upper transition region component of hot loops so studying its dynamics and the relation between the bright/dark features and underlying magnetic features is important to tie the interaction of the different atmospheric layers together. Hi-C allows us to study the coronal emission of the moss at the smallest scales while data from SDO/AIA and HMI is used to give information on these structures at different heights/temperatures. Using the high temporal and spatial resolution of Hi-C the observed moss features were tracked and the distribution of displacements, speeds, and sizes were measured. This allows us to comment on both the physical processes occurring within the dynamic moss and the scales at which these changes are occurring.

Dynamic Moss Observed with Hi-C

NASA Technical Reports Server (NTRS)

Alexander, Caroline; Winebarger, Amy; Morton, Richard; Savage, Sabrina

2014-01-01

The High-resolution Coronal Imager (Hi-C), flown on 11 July 2012, has revealed an unprecedented level of detail and substructure within the solar corona. Hi-C imaged a large active region (AR11520) with 0.2-0.3'' spatial resolution and 5.5s cadence over a 5 minute period. An additional dataset with a smaller FOV, the same resolution, but with a higher temporal cadence (1s) was also taken during the rocket flight. This dataset was centered on a large patch of 'moss' emission that initially seemed to show very little variability. Image processing revealed this region to be much more dynamic than first thought with numerous bright and dark features observed to appear, move and disappear over the 5 minute observation. Moss is thought to be emission from the upper transition region component of hot loops so studying its dynamics and the relation between the bright/dark features and underlying magnetic features is important to tie the interaction of the different atmospheric layers together. Hi-C allows us to study the coronal emission of the moss at the smallest scales while data from SDO/AIA and HMI is used to give information on these structures at different heights/temperatures. Using the high temporal and spatial resolution of Hi-C the observed moss features were tracked and the distribution of displacements, speeds, and sizes were measured. This allows us to comment on both the physical processes occurring within the dynamic moss and the scales at which these changes are occurring.

Empirical studies of solar flares: Comparison of X-ray and H alpha filtergrams and analysis of the energy balance of the X-ray plasma

NASA Technical Reports Server (NTRS)

Moore, R. L.

1979-01-01

The physics of solar flares was investigated through a combined analysis of X-ray filtergrams of the high temperature coronal component of flares and H alpha filtergrams of the low temperature chromospheric component. The data were used to study the magnetic field configuration and its changes in solar flares, and to examine the chromospheric location and structure of X-ray bright points (XPB) and XPB flares. Each topic and the germane data are discussed. The energy balance of the thermal X-ray plasma in flares, while not studied, is addressed.

Sparkling extreme-ultraviolet bright dots observed with Hi-C

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

Régnier, S.; Alexander, C. E.; Walsh, R. W.

Observing the Sun at high time and spatial scales is a step toward understanding the finest and fundamental scales of heating events in the solar corona. The high-resolution coronal (Hi-C) instrument has provided the highest spatial and temporal resolution images of the solar corona in the EUV wavelength range to date. Hi-C observed an active region on 2012 July 11 that exhibits several interesting features in the EUV line at 193 Å. One of them is the existence of short, small brightenings 'sparkling' at the edge of the active region; we call these EUV bright dots (EBDs). Individual EBDs havemore » a characteristic duration of 25 s with a characteristic length of 680 km. These brightenings are not fully resolved by the SDO/AIA instrument at the same wavelength; however, they can be identified with respect to the Hi-C location of the EBDs. In addition, EBDs are seen in other chromospheric/coronal channels of SDO/AIA, which suggests a temperature between 0.5 and 1.5 MK. Based on their frequency in the Hi-C time series, we define four different categories of EBDs: single peak, double peak, long duration, and bursty. Based on a potential field extrapolation from an SDO/HMI magnetogram, the EBDs appear at the footpoints of large-scale, trans-equatorial coronal loops. The Hi-C observations provide the first evidence of small-scale EUV heating events at the base of these coronal loops, which have a free magnetic energy of the order of 10{sup 26} erg.« less

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

Orange, N. Brice; Chesny, David L.; Oluseyi, Hakeem M.

Increasing evidence for coronal heating contributions from cooler solar atmospheric layers, notably quiet Sun (QS) conditions, challenges standard solar atmospheric descriptions of bright transition region (TR) emission. As such, questions about the role of dynamic QS transients in contributing to the total coronal energy budget are raised. Using observations from the Atmospheric Imaging Assembly and Heliosemic Magnetic Imager on board the Solar Dynamics Observatory, and numerical model extrapolations of coronal magnetic fields, we investigate a dynamic QS transient that is energetically isolated to the TR and extrudes from a common footpoint shared with two heated loop arcades. A non-causal relationshipmore » is established between episodic heating of the QS transient and widespread magnetic field re-organization events, while evidence is found favoring a magnetic topology that is typical of eruptive processes. Quasi-steady interchange reconnection events are implicated as a source of the transient’s visibly bright radiative signature. We consider the QS transient’s temporally stable (≈35 minutes) radiative nature to occur as a result of the large-scale magnetic field geometries of the QS and/or relatively quiet nature of the magnetic photosphere, which possibly act to inhibit energetic build-up processes that are required to initiate a catastrophic eruption phase. This work provides insight into the QS’s thermodynamic and magnetic relation to eruptive processes that quasi-steadily heat a small-scale dynamic and TR transient. This work explores arguments of non-negligible coronal heating contributions from cool atmospheric layers in QS conditions and contributes evidence to the notion that  solar wind mass feeds off of dynamic transients therein.« less

Signatures of Nonlinear Waves in Coronal Plumes and Holes

NASA Technical Reports Server (NTRS)

Ofman, Leon

1999-01-01

In recent Ultraviolet Coronagraph Spectrometer/Solar and Heliospheric Observatory (UVCS/SOHO) White Light Channel (WLC) observations we found quasi-periodic variations in the polarized brightness (pB) in the polar coronal holes at heliocentric distances of 1.9-2.45 solar radii. The motivation for the observation is the 2.5D Magnetohydrodynamics (MHD) model of solar wind acceleration by nonlinear waves, that predicts compressive fluctuations in coronal holes. To help identify the waves observed with the UVCS/WLC we model the propagation and dissipation of slow magnetosonic waves in polar plumes using 1D MHD code in spherical geometry, We find that the slow waves nonlinearly steepen in the gravitationally stratified plumes. The nonlinear steepening of the waves leads to enhanced dissipation due to compressive viscosity at the wave-fronts.

Characteristics of polar coronal hole jets

NASA Astrophysics Data System (ADS)

Chandrashekhar, K.; Bemporad, A.; Banerjee, D.; Gupta, G. R.; Teriaca, L.

2014-01-01

Context. High spatial- and temporal-resolution images of coronal hole regions show a dynamical environment where mass flows and jets are frequently observed. These jets are believed to be important for the coronal heating and the acceleration of the fast solar wind. Aims: We studied the dynamics of two jets seen in a polar coronal hole with a combination of imaging from EIS and XRT onboard Hinode. We observed drift motions related to the evolution and formation of these small-scale jets, which we tried to model as well. Methods: Stack plots were used to find the drift and flow speeds of the jets. A toymodel was developed by assuming that the observed jet is generated by a sequence of single reconnection events where single unresolved blobs of plasma are ejected along open field lines, then expand and fall back along the same path, following a simple ballistic motion. Results: We found observational evidence that supports the idea that polar jets are very likely produced by multiple small-scale reconnections occurring at different times in different locations. These eject plasma blobs that flow up and down with a motion very similar to a simple ballistic motion. The associated drift speed of the first jet is estimated to be ≈27 km s-1. The average outward speed of the first jet is ≈171 km s-1, well below the escape speed, hence if simple ballistic motion is considered, the plasma will not escape the Sun. The second jet was observed in the south polar coronal hole with three XRT filters, namely, C-poly, Al-poly, and Al-mesh filters. Many small-scale (≈3″-5″) fast (≈200-300 km s-1) ejections of plasma were observed on the same day; they propagated outwards. We observed that the stronger jet drifted at all altitudes along the jet with the same drift speed of ≃7 km s-1. We also observed that the bright point associated with the first jet is a part of sigmoid structure. The time of appearance of the sigmoid and that of the ejection of plasma from the bright point suggest that the sigmoid is the progenitor of the jet. Conclusions: The enhancement in the light curves of low-temperature EIS lines in the later phase of the jet lifetime and the shape of the jet's stack plots suggests that the jet material falls back, and most likely cools down. To further support this conclusion, the observed drifts were interpreted within a scenario where reconnection progressively shifts along a magnetic structure, leading to the sequential appearance of jets of about the same size and physical characteristics. On this basis, we also propose a simple qualitative model that mimics the observations. Movies 1-3 are available in electronic form at http://www.aanda.org Warning, no authors found for 2014A&A...561A..97.

Evolution of 3D electron density of the solar corona from the minimum to maximum of Solar Cycle 24

NASA Astrophysics Data System (ADS)

Wang, Tongjiang; Reginald, Nelson L.; Davila, Joseph M.; St Cyr, O. C.

2016-10-01

The variability of the solar white-light corona and its connection to the solar activity has been studied for more than a half century. It is widely accepted that the temporal variation of the total radiance of the K-corona follows the solar cycle pattern (e.g., correlated with sunspot number). However, the origin of this variation and its relationships with regard to coronal mass ejections and the solar wind are yet to be clearly understood. COR1-A and -B instruments onboard the STEREO spacecraft have continued to perform high-cadence (5 min) polarized brightness (pB) measurements from two different vantage points from the solar minimum to the solar maximum of Solar Cycle 24. With these pB observations we have reconstructed the 3D coronal density between 1.5-4.0 solar radii for 100 Carrington rotations (CRs) from 2007 to 2014 using the spherically symmetric inversion (SSI) method. We validate these 3D density reconstructions by other means such as tomography, MHD modeling, and pB inversion of LASCO/C2 data. We analyze the solar cycle variations of total coronal mass (or average density) over the global Sun and in two hemispheres, as well as the variations of the streamer area and mean density. We find the short-term oscillations of 8-9 CRs during the ascending and maximum phases through wavelet analysis. We explore the origin of these oscillations based on evolution of the photospheric magnetic flux and coronal structures.

Digging in the coronal graveyard - A Rosat observation of the red giant Arcturus

NASA Technical Reports Server (NTRS)

Ayres, Thomas R.; Fleming, Thomas A.; Schmitt, Juergen H. M. M.

1991-01-01

A deep exposure of the bright star Arcturus (Alpha Bootis: K1 III) with the Roentgensatellit (Rosat) failed to detect soft X-ray emission from the archetype 'noncoronal' red giant. The 3-sigma upper limit in the energy band 0.1-2.4 keV corresponds to an X-ray luminosity of less than 3 x 10 to the 25th erg/s, equivalent to a coronal surface flux density of less than 0.0001 solar. The nondetection safely eliminates coronal irradiation as a possible mechanism to produce the highly variable He I 10830 feature and emphasizes the sharp decline in solarlike coronal activity that accompanies the evolution of low-mass single stars away from the main sequence. While the most conspicuous object in the Rosat field of view was not visible in X-rays, at least one fainter star is among the about 60 sources recorded: the Sigma Sct variable CN Boo, an A8 giant in the UMa Stream.

Digital Compositing Techniques for Coronal Imaging (Invited review)

NASA Astrophysics Data System (ADS)

Espenak, F.

2000-04-01

The solar corona exhibits a huge range in brightness which cannot be captured in any single photographic exposure. Short exposures show the bright inner corona and prominences, while long exposures reveal faint details in equatorial streamers and polar brushes. For many years, radial gradient filters and other analog techniques have been used to compress the corona's dynamic range in order to study its morphology. Such techniques demand perfect pointing and tracking during the eclipse, and can be difficult to calibrate. In the past decade, the speed, memory and hard disk capacity of personal computers have rapidly increased as prices continue to drop. It is now possible to perform sophisticated image processing of eclipse photographs on commercially available CPU's. Software programs such as Adobe Photoshop permit combining multiple eclipse photographs into a composite image which compresses the corona's dynamic range and can reveal subtle features and structures. Algorithms and digital techniques used for processing 1998 eclipse photographs will be discussed which are equally applicable to the recent eclipse of 1999 August 11.

A white-light /Fe X/H-alpha coronal transient observation to 10 solar radii

NASA Technical Reports Server (NTRS)

Wagner, W. J.; Illing, R. M. E.; Sawyer, C. B.; House, L. L.; Sheeley, N. R., Jr.; Howard, R. A.; Koomen, M. J.; Michels, D. J.; Smartt, R. N.; Dryer, M.

1983-01-01

Multitelescope observations of the coronal transient of April 15-16, 1980 provide simultaneous data from the Solar Maximum Mission Coronagraph/Polarimeter, the Solwind Coronagraph, and the new Emission line Coronagraph of the Sacramento Peak Observatory. An eruptive prominence-associated white light transient is for the first time seen as an unusual wave or brightening in Fe X 6374 A (but not in Fe XIV 5303 A). Several interpretations of this fleeting enhancement are offered. The prominence shows a slowly increasing acceleration which peaks at the time of the Fe event. The white light loop transient surrounding the prominence expands at a well-documented constant speed to solar radii, with an extrapolated start time at zero height coincident with the surface activity. This loop transient exemplifies those seen above 1.7 solar radii, in that leading the disturbance is a bright N(e)-enhanced) loop rather than a dark one. This is consistent with a report of the behavior of another eruptive event observed by Fisher and Poland (1981) which began as a density depletion in the lower corona, with a bright loop forming at greater altitudes. The top of the bright loop ultimately fades in the outer corona while slow radial growth continues in the legs.

The structure of the white-light corona and the large-scale solar magnetic field

NASA Technical Reports Server (NTRS)

Sime, D. G.; Mccabe, M. K.

1990-01-01

The large-scale density structure of the white-light solar corona is compared to the organization of the solar magnetic field as identified by the appearance of neutral lines in the photosphere to examine whether any consistent relationship exists between the two. During the period covering Carrington rotations 1717 to 1736 brightness enhancements in the low corona tend to lie over the global neutral sheet identified in the photospheric magnetic field. The brightest of these enhancements are associated with neutral lines throguh active regions. These associations are not 1-1, but do hold both in stable and evolving conditions of the corona. A significant number of long-lived neutral lines is found, including filaments seen in H-alpha, for which there are not coronal enhancements.

Bright Loops at 171

NASA Technical Reports Server (NTRS)

2007-01-01

STEREO was able to capture bright loops in exquisite detail as they were arcing above an active region (May 26, 2007) over an 18 hour period. What we are actually seeing are charged particles spinning along magnetic field lines that extend above the Sun's surface. Active regions are areas of intense magnetic activity and often the source of solar storms. In fact, the clip ends with a flourish in which a small coronal mass ejection (CME) blows out into space. This is from the STEREO Ahead spacecraft at the 171 Angstroms wavelength in extreme ultraviolet light.

NuSTAR spectral analysis of two bright Seyfert 1 galaxies: MCG +8-11-11 and NGC 6814

NASA Astrophysics Data System (ADS)

Tortosa, A.; Bianchi, S.; Marinucci, A.; Matt, G.; Middei, R.; Piconcelli, E.; Brenneman, L. W.; Cappi, M.; Dadina, M.; De Rosa, A.; Petrucci, P. O.; Ursini, F.; Walton, D. J.

2018-01-01

We report on the NuSTAR observations of two bright Seyfert 1 galaxies, namely MCG +8-11-11 (100 ks) and NGC 6814 (150 ks). The main goal of these observations was to investigate the Comptonization mechanisms acting in the innermost regions of an active galactic nucleus (AGN) which are believed to be responsible for the UV/X-ray emission. The spectroscopic analysis of the NuSTAR spectra of these two sources revealed that although they had different properties overall (black hole masses, luminosity and Eddington ratios), they had very similar coronal properties. Both presented a power-law spectrum with a high-energy cut-off at ∼150-200 keV, a relativistically broadened Fe K α line and the associated disc reflection component, plus a narrow iron line likely emitted in Compton thin and distant matter. The intrinsic continuum was well described by Comptonization models that show for MCG +8-11-11 a temperature of the coronal plasma of kTe ∼ 60 keV and an extrapolated optical depth τ = 1.8; for NGC 6814, the coronal temperature was kTe ∼ 45 keV with an extrapolated optical depth of τ = 2.5. We compare and discuss these values to some most common Comptonization models that aim at explaining the energy production and stability of coronae in AGNs.

Quasi-periodic Oscillation of a Coronal Bright Point

NASA Astrophysics Data System (ADS)

Samanta, Tanmoy; Banerjee, Dipankar; Tian, Hui

2015-06-01

Coronal bright points (BPs) are small-scale luminous features seen in the solar corona. Quasi-periodic brightenings are frequently observed in the BPs and are generally linked with underlying magnetic flux changes. We study the dynamics of a BP seen in the coronal hole using the Atmospheric Imaging Assembly images, the Helioseismic and Magnetic Imager magnetogram on board the Solar Dynamics Observatory, and spectroscopic data from the newly launched Interface Region Imaging Spectrograph (IRIS). The detailed analysis shows that the BP evolves throughout our observing period along with changes in underlying photospheric magnetic flux and shows periodic brightenings in different EUV and far-UV images. With the highest possible spectral and spatial resolution of IRIS, we attempted to identify the sources of these oscillations. IRIS sit-and-stare observation provided a unique opportunity to study the time evolution of one footpoint of the BP as the slit position crossed it. We noticed enhanced line profile asymmetry, enhanced line width, intensity enhancements, and large deviation from the average Doppler shift in the line profiles at specific instances, which indicate the presence of sudden flows along the line-of-sight direction. We propose that transition region explosive events originating from small-scale reconnections and the reconnection outflows are affecting the line profiles. The correlation between all these parameters is consistent with the repetitive reconnection scenario and could explain the quasi-periodic nature of the brightening.

Source of Quasi-Periodic Brightenings of Solar Coronal Bright Points: Waves or Repeated Reconnections

NASA Astrophysics Data System (ADS)

Samanta, Tanmoy; Tian, Hui; Banerjee, Dipankar

2016-07-01

Coronal bright points (BPs) are small-scale luminous features seen in the solar corona. Quasi-periodic brightenings are frequently observed in the BPs and are generally linked with underlying magnetic flux changes. We study the dynamics of a BP seen in the coronal hole using the Atmospheric Imaging Assembly images, the Helioseismic and Magnetic Imager magnetogram on board the Solar Dynamics Observatory, and spectroscopic data from the newly launched Interface Region Imaging Spectrograph (IRIS). The detailed analysis shows that the BP evolves throughout our observing period along with changes in underlying photospheric magnetic flux and shows periodic brightenings in different EUV and far-UV images. With the highest possible spectral and spatial resolution of IRIS, we attempted to identify the sources of these oscillations. IRIS sit-and-stare observation provided a unique opportunity to study the time evolution of one footpoint of the BP as the slit position crossed it. We noticed enhanced line profile asymmetry, enhanced line width, intensity enhancements, and large deviation from the average Doppler shift in the line profiles at specific instances, which indicate the presence of sudden flows along the line-of-sight direction. We propose that transition region explosive events originating from small-scale reconnections and the reconnection outflows are affecting the line profiles. The correlation between all these parameters is consistent with the repetitive reconnection scenario and could explain the quasi-periodic nature of the brightening.

Imaging Prominence Eruptions out to 1 AU

NASA Astrophysics Data System (ADS)

Wood, Brian E.; Howard, Russell A.; Linton, Mark G.

2016-01-01

Views of two bright prominence eruptions trackable all the way to 1 AU are here presented, using the heliospheric imagers on the Solar TErrestrial RElations Observatory (STEREO) spacecraft. The two events first erupted from the Sun on 2011 June 7 and 2012 August 31, respectively. Only these two examples of clear prominence eruptions observable this far from the Sun could be found in the STEREO image database, emphasizing the rarity of prominence eruptions this persistently bright. For the 2011 June event, a time-dependent 3D reconstruction of the prominence structure is made using point-by-point triangulation. This is not possible for the August event due to a poor viewing geometry. Unlike the coronal mass ejection (CME) that accompanies it, the 2011 June prominence exhibits little deceleration from the Sun to 1 AU, as a consequence moving upwards within the CME. This demonstrates that prominences are not necessarily tied to the CME's magnetic structure far from the Sun. A mathematical framework is developed for describing the degree of self-similarity for the prominence's expansion away from the Sun. This analysis suggests only modest deviations from self-similar expansion, but close to the Sun the prominence expands radially somewhat more rapidly than self-similarity would predict.

Coronal Structures in Cool Stars

NASA Technical Reports Server (NTRS)

Oliversen, Ronald (Technical Monitor); Dupree, Andrea K.

2004-01-01

Many papers have been published that further elucidate the structure of coronas in cool stars as determined from EUVE, HST, FUSE, Chandra, and XMM-Newton observations. In addition we are exploring the effects of coronas on the He I 1083081 transition that is observed in the infrared. Highlights of these are summarized below including publications during this reporting period and presentations. Ground-based magnetic Doppler imaging of cool stars suggests that active stars have active regions located at high latitudes on their surface. We have performed similar imaging in X-ray to locate the sites of enhanced activity using Chandra spectra. Chandra HETG observations of the bright eclipsing contact binary 44i Boo and Chandra LETG observations for the eclipsing binary VW Cep show X-ray line profiles that are Doppler-shifted by orbital motion. After careful analysis of the spectrum of each binary, a composite line-profile is constructed by adding the individual spectral lines. This high signal-to-noise ratio composite line-profile yields orbital velocities for these binaries that are accurate to 30 km/sec and allows their orbital motion to be studied at higher time resolutions. In conjunction with X-ray lightcurves, the phase-binned composite line-profiles constrain coronal structures to be small and located at high latitudes. These observations and techniques show the power of the Doppler Imaging Technique applied to X-ray line emission.

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.

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.

Magnetic loops, downflows, and convection in the solar corona

NASA Technical Reports Server (NTRS)

Foukal, P.

1978-01-01

Optical and extreme-ultraviolet observations of solar loop structures show that flows of cool plasma from condensations near the loop apex are a common property of loops associated with radiations whose maximum temperature is greater than approximately 7000 K and less than approximately 3,000,000 K. It is suggested that the mass balance of these structures indicates reconnection by means of plasma motion across field lines under rather general circumstances (not only after flares). It is shown that the cool material has lower gas pressure than the surrounding coronal medium. The density structure of the bright extreme ultraviolet loops suggests that downflows of cool gas result from isobaric condensation of plasma that is either out of thermal equilibrium with the local energy deposition rate into the corona, or is thermally unstable. The evidence is thought to indicate that magnetic fields act to induce a pattern of forced convection.

NEW VACUUM SOLAR TELESCOPE OBSERVATIONS OF A FLUX ROPE TRACKED BY A FILAMENT ACTIVATION

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

Yang, Shuhong; Zhang, Jun; Liu, Zhong

2014-04-01

One main goal of the New Vacuum Solar Telescope (NVST) which is located at the Fuxian Solar Observatory is to image the Sun at high resolution. Based on the high spatial and temporal resolution NVST Hα data and combined with the simultaneous observations from the Solar Dynamics Observatory for the first time, we investigate a flux rope tracked by filament activation. The filament material is initially located at one end of the flux rope and fills in a section of the rope; the filament is then activated by magnetic field cancellation. The activated filament rises and flows along helical threads,more » tracking the twisted flux rope structure. The length of the flux rope is about 75 Mm, the average width of its individual threads is 1.11 Mm, and the estimated twist is 1π. The flux rope appears as a dark structure in Hα images, a partial dark and partial bright structure in 304 Å, and as a bright structure in 171 Å and 131 Å images. During this process, the overlying coronal loops are quite steady since the filament is confined within the flux rope and does not erupt successfully. It seems that, for the event in this study, the filament is located and confined within the flux rope threads, instead of being suspended in the dips of twisted magnetic flux.« less

Coronal hole boundaries evolution at small scales. I. EIT 195 Å  and TRACE 171 Å view

NASA Astrophysics Data System (ADS)

Madjarska, M. S.; Wiegelmann, T.

2009-09-01

Aims: We aim to study the small-scale evolution at the boundaries of an equatorial coronal hole connected with a channel of open magnetic flux to the polar region and an “isolated” one in the extreme-ultraviolet spectral range. We determine the spatial and temporal scale of these changes. Methods: Imager data from TRACE in the Fe ix/x 171 Å passband and EIT on-board Solar and Heliospheric Observatory in the Fe xii 195 Å passband were analysed. Results: We found that small-scale loops known as bright points play an essential role in coronal hole boundary evolution at small scales. Their emergence and disappearance continuously expand or contract coronal holes. The changes appear to be random on a time scale comparable to the lifetime of the loops seen at these temperatures. No signature was found for a major energy release during the evolution of the loops. Conclusions: Although coronal holes seem to maintain their general shape during a few solar rotations, a closer look at their day-by-day and even hour-by-hour evolution demonstrates significant dynamics. The small-scale loops (10´´-40´´ and smaller) which are abundant along coronal hole boundaries contribute to the small-scale evolution of coronal holes. Continuous magnetic reconnection of the open magnetic field lines of the coronal hole and the closed field lines of the loops in the quiet Sun is more likely to take place. Movies are only available in electronic form at http://www.aanda.org

Coronal rain in magnetic bipolar weak fields

NASA Astrophysics Data System (ADS)

Xia, C.; Keppens, R.; Fang, X.

2017-07-01

Aims: We intend to investigate the underlying physics for the coronal rain phenomenon in a representative bipolar magnetic field, including the formation and the dynamics of coronal rain blobs. Methods: With the MPI-AMRVAC code, we performed three dimensional radiative magnetohydrodynamic (MHD) simulation with strong heating localized on footpoints of magnetic loops after a relaxation to quiet solar atmosphere. Results: Progressive cooling and in-situ condensation starts at the loop top due to radiative thermal instability. The first large-scale condensation on the loop top suffers Rayleigh-Taylor instability and becomes fragmented into smaller blobs. The blobs fall vertically dragging magnetic loops until they reach low-β regions and start to fall along the loops from loop top to loop footpoints. A statistic study of the coronal rain blobs finds that small blobs with masses of less than 1010 g dominate the population. When blobs fall to lower regions along the magnetic loops, they are stretched and develop a non-uniform velocity pattern with an anti-parallel shearing pattern seen to develop along the central axis of the blobs. Synthetic images of simulated coronal rain with Solar Dynamics Observatory Atmospheric Imaging Assembly well resemble real observations presenting dark falling clumps in hot channels and bright rain blobs in a cool channel. We also find density inhomogeneities during a coronal rain "shower", which reflects the observed multi-stranded nature of coronal rain. Movies associated to Figs. 3 and 7 are available at http://www.aanda.org

Reconnection-Driven Coronal-Hole Jets with Gravity and Solar Wind

NASA Technical Reports Server (NTRS)

Karpen, J. T.; Devore, C. R.; Antiochos, S. K.; Pariat, E.

2017-01-01

Coronal-hole jets occur ubiquitously in the Sun's coronal holes, at EUV and X-ray bright points associated with intrusions of minority magnetic polarity. The embedded-bipole model for these jets posits that they are driven by explosive, fast reconnection between the stressed closed field of the embedded bipole and the open field of the surrounding coronal hole. Previous numerical studies in Cartesian geometry, assuming uniform ambient magnetic field and plasma while neglecting gravity and solar wind, demonstrated that the model is robust and can produce jet-like events in simple configurations. We have extended these investigations by including spherical geometry,gravity, and solar wind in a nonuniform, coronal hole-like ambient atmosphere. Our simulations confirm that the jet is initiated by the onset of a kink-like instability of the internal closed field, which induces a burst of reconnection between the closed and external open field, launching a helical jet. Our new results demonstrate that the jet propagation is sustained through the outer corona, in the form of a traveling nonlinear Alfven wave front trailed by slower-moving plasma density enhancements that are compressed and accelerated by the wave. This finding agrees well with observations of white-light coronal-hole jets, and can explain microstreams and torsional Alfven waves detected in situ in the solar wind. We also use our numerical results to deduce scaling relationships between properties of the coronal source region and the characteristics of the resulting jet, which can be tested against observations.

Polar Chromospheric Signatures of the Subdued Cycle 23/24 Solar Minimum

NASA Technical Reports Server (NTRS)

Gopalswamy, N.; Yashiro, S.; Makela, P.; Shibasaki, K.; Hathaway, D.

2010-01-01

Coronal holes appear brighter than the quiet Sun in microwave images, with a brightness enhancement of 500 to 2000 K. The brightness enhancement corresponds to the upper chromosphere, where the plasma temperature is about 10000 K. We constructed a microwave butterfly diagram using the synoptic images obtained by the Nobeyama radioheliograph (NoRH) showing the evolution of the polar and low latitude brightness temperature. While the polar brightness reveals the chromospheric conditions, the low latitude brightness is attributed to active regions in the corona. When we compared the microwave butterfly diagram with the magnetic butterfly diagram, we found a good correlation between the microwave brightness enhancement and the polar field strength. The microwave butterfly diagram covers part of solar cycle 22, whole of cycle 23, and part of cycle 24, thus enabling comparison between the cycle 23/24 and cycle 22/23 minima. The microwave brightness during the cycle 23/24 minimum was found to be lower than that during the cycle 22/23 minimum by approximately 250 K. The reduced brightness temperature is consistent with the reduced polar field strength during the cycle 23/24 minimum seen in the magnetic butterfly diagram. We suggest that the microwave brightness at the solar poles is a good indicator of the speed of the solar wind sampled by Ulysses at high latitudes.

The velocity field of a coronal mass ejection - The event of September 1, 1980

NASA Technical Reports Server (NTRS)

Low, B. C.; Hundhausen, A. J.

1987-01-01

The velocity field of a mass ejection that was observed by the coronagraph of the SMM satellite over the northwest limb of the sun at about 0600 UT on September 1, 1980 is studied in detail. A descriptive account of the event is given, concentrating on qualitative features of the mass motion and suggesting a possible origin of the unusual two-loop structure. The velocity field is analyzed quantitatively, and the implications of the results for the mass ejection theory are considered. It is concluded that a self-similar description of the velocity field is a gross oversimplification and that although some evidence of wave propagation can be found, the bright features in the mass ejection are plasma structures moving with frozen-in magnetic fields, rather than waves propagating through plasmas and magnetic fields.

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.

Physical Conditions in the Solar Corona Derived from the Total Solar Eclipse Observations obtained on 2017 August 21 Using a Polarization Camera

NASA Astrophysics Data System (ADS)

Gopalswamy, N.; Yashiro, Seiji; Reginald, Nelson; Thakur, Neeharika; Thompson, Barbara J.; Gong, Qian

2018-01-01

We present preliminary results obtained by observing the solar corona during the 2017 August 21 total solar eclipse using a polarization camera mounted on an eight-inch Schmidt-Cassegrain telescope. The observations were made from Madras Oregon during 17:19 to 17:21 UT. Total and polarized brightness images were obtained at four wavelengths (385, 398.5, 410, and 423 nm). The polarization camera had a polarization mask mounted on a 2048x2048 pixel CCD with a pixel size of 7.4 microns. The resulting images had a size of 975x975 pixels because four neighboring pixels were summed to yield the polarization and total brightness images. The ratio of 410 and 385 nm images is a measure of the coronal temperature, while that at 423 and 398.5 nm images is a measure of the coronal flow speed. We compared the temperature map from the eclipse observations with that obtained from the Solar Dynamics Observatory’s Atmospheric Imaging Assembly images at six EUV wavelengths, yielding consistent temperature information of the corona.

Observations of the variability of coronal bright points by the Soft X-ray Telescope on Yohkoh

NASA Technical Reports Server (NTRS)

Strong, Keith T.; Harvey, Karen; Hirayama, Tadashi; Nitta, Nariaki; Shimizu, Toshifumi; Tsuneta, Saku

1992-01-01

We present the initial results of a study of X-ray bright points (XBPs) made with data from the Yohkoh Soft X-ray Telescope. High temporal and spatial resolution observations of several XBPs illustrate their intensity variability over a wide variety of time scales from a few minutes to hours, as well as rapid changes in their morphology. Several XBPs produced flares during their lifetime. These XBP flares often involve magnetic loops, which are considerably larger than the XBP itself, and which brighten along their lengths at speeds of up to 1100 km/s.

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

Howard, T. A.; DeForest, C. E., E-mail: howard@boulder.swri.edu

We present a data-driven narrative of the launch and early evolution of the magnetic structure that gave rise to the coronal mass ejection (CME) on 2008 December 12. The structure formed on December 7 and launched early on December 12. We interpret this structure as a flux rope based on prelaunch morphology, postlaunch magnetic measurements, and the lack of large-scale magnetic reconnection signatures at launch. We ascribe three separate onset mechanisms to the complete disconnection of the flux rope from the Sun. It took 19 hr for the flux rope to be fully removed from the Sun, by which timemore » the segment that first disconnected was around 40 R {sub ☉} away. This implies that the original flux rope was stretched or broken; we provide evidence for a possible bisection. A transient dark arcade was observed on the Sun that was later obscured by a bright arcade, which we interpret as the strapping field stretching and magnetically reconnecting as it disconnected from the coronal field. We identify three separate structures in coronagraph images to be manifestations of the same original flux rope, and we describe the implications for CME interpretation. We cite the rotation in the central flux rope vector of the magnetic clouds observed in situ by ACE/Wind and STEREO-B as evidence of the kink instability of the eastern segment of the flux rope. Finally, we discuss possible alternative narratives, including multiple prelaunch magnetic structures and the nonflux rope scenario. Our results support the view that, in at least some CMEs, flux rope formation occurs before launch.« less

The Driving Magnetic Field and Reconnection in CME/Flare Eruptions and Coronal Jets

NASA Technical Reports Server (NTRS)

Moore, Ronald L.

2010-01-01

Signatures of reconnection in major CME (coronal mass ejection)/flare eruptions and in coronal X-ray jets are illustrated and interpreted. The signatures are magnetic field lines and their feet that brighten in flare emission. CME/flare eruptions are magnetic explosions in which: 1. The field that erupts is initially a closed arcade. 2. At eruption onset, most of the free magnetic energy to be released is not stored in field bracketing a current sheet, but in sheared field in the core of the arcade. 3. The sheared core field erupts by a process that from its start or soon after involves fast "tether-cutting" reconnection at an initially small current sheet low in the sheared core field. If the arcade has oppositely-directed field over it, the eruption process from its start or soon after also involves fast "breakout" reconnection at an initially small current sheet between the arcade and the overarching field. These aspects are shown by the small area of the bright field lines and foot-point flare ribbons in the onset of the eruption. 4. At either small current sheet, the fast reconnection progressively unleashes the erupting core field to erupt with progressively greater force. In turn, the erupting core field drives the current sheet to become progressively larger and to undergo progressively greater fast reconnection in the explosive phase of the eruption, and the flare arcade and ribbons grow to become comparable to the pre-eruption arcade in lateral extent. In coronal X-ray jets: 1. The magnetic energy released in the jet is built up by the emergence of a magnetic arcade into surrounding unipolar "open" field. 2. A simple jet is produced when a burst of reconnection occurs at the current sheet between the arcade and the open field. This produces a bright reconnection jet and a bright reconnection arcade that are both much smaller in diameter that the driving arcade. 3. A more complex jet is produced when the arcade has a sheared core field and undergoes an ejective eruption in the manner of a miniature CME/flare eruption. The jet is then a combination of a miniature CME and the products of more widely distributed reconnection of the erupting arcade with the open field than in simple jets.

The Image-Optimized Corona; Progress on Using Coronagraph Images to Constrain Coronal Magnetic Field Models

NASA Astrophysics Data System (ADS)

Jones, S. I.; Uritsky, V. M.; Davila, J. M.

2017-12-01

In absence of reliable coronal magnetic field measurements, solar physicists have worked for several decades to develop techniques for extrapolating photospheric magnetic field measurements into the solar corona and/or heliosphere. The products of these efforts tend to be very sensitive to variation in the photospheric measurements, such that the uncertainty in the photospheric measurements introduces significant uncertainty into the coronal and heliospheric models needed to predict such things as solar wind speed, IMF polarity at Earth, and CME propagation. Ultimately, the reason for the sensitivity of the model to the boundary conditions is that the model is trying to extact a great deal of information from a relatively small amout of data. We have published in recent years about a new method we are developing to use morphological information gleaned from coronagraph images to constrain models of the global coronal magnetic field. In our approach, we treat the photospheric measurements as approximations and use an optimization algorithm to iteratively find a global coronal model that best matches both the photospheric measurements and quasi-linear features observed in polarization brightness coronagraph images. Here we will summarize the approach we have developed and present recent progress in optimizing PFSS models based on GONG magnetograms and MLSO K-Cor images.

OBSERVING CORONAL NANOFLARES IN ACTIVE REGION MOSS

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

Testa, Paola; DeLuca, Ed; Golub, Leon

2013-06-10

The High-resolution Coronal Imager (Hi-C) has provided Fe XII 193A images of the upper transition region moss at an unprecedented spatial ({approx}0.''3-0.''4) and temporal (5.5 s) resolution. The Hi-C observations show in some moss regions variability on timescales down to {approx}15 s, significantly shorter than the minute-scale variability typically found in previous observations of moss, therefore challenging the conclusion of moss being heated in a mostly steady manner. These rapid variability moss regions are located at the footpoints of bright hot coronal loops observed by the Solar Dynamics Observatory/Atmospheric Imaging Assembly in the 94 A channel, and by the Hinode/X-Raymore » Telescope. The configuration of these loops is highly dynamic, and suggestive of slipping reconnection. We interpret these events as signatures of heating events associated with reconnection occurring in the overlying hot coronal loops, i.e., coronal nanoflares. We estimate the order of magnitude of the energy in these events to be of at least a few 10{sup 23} erg, also supporting the nanoflare scenario. These Hi-C observations suggest that future observations at comparable high spatial and temporal resolution, with more extensive temperature coverage, are required to determine the exact characteristics of the heating mechanism(s).« less

A small-scale eruption leading to a blowout macrospicule jet in an on-disk coronal hole

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

Adams, Mitzi; Sterling, Alphonse C.; Moore, Ronald L.

2014-03-01

We examine the three-dimensional magnetic structure and dynamics of a solar EUV-macrospicule jet that occurred on 2011 February 27 in an on-disk coronal hole. The observations are from the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) and the SDO Helioseismic and Magnetic Imager (HMI). The observations reveal that in this event, closed-field-carrying cool absorbing plasma, as in an erupting mini-filament, erupted and opened, forming a blowout jet. Contrary to some jet models, there was no substantial recently emerged, closed, bipolar-magnetic field in the base of the jet. Instead, over several hours, flux convergence and cancellation at the polarity inversionmore » line inside an evolved arcade in the base apparently destabilized the entire arcade, including its cool-plasma-carrying core field, to undergo a blowout eruption in the manner of many standard-sized, arcade-blowout eruptions that produce a flare and coronal mass ejection. Internal reconnection made bright 'flare' loops over the polarity inversion line inside the blowing-out arcade field, and external reconnection of the blowing-out arcade field with an ambient open field made longer and dimmer EUV loops on the outside of the blowing-out arcade. That the loops made by the external reconnection were much larger than the loops made by the internal reconnection makes this event a new variety of blowout jet, a variety not recognized in previous observations and models of blowout jets.« less

The association of chromospheric and coronal phenomena with the evolution of the quiet sun magnetic fields

NASA Technical Reports Server (NTRS)

Harvey, Karen L.; Tang, Frances; Gaizauskas, Victor

1986-01-01

Using daily full-disk magnetograms and He I 10830 spectroheliograms to study the count and surface distribution of ephemeral regions over the solar cycle, Harvey (1985) concluded that the small dark structures seen in 10830, thought to correspond to X-ray bright points, were more often associated with magnetic bipoles that appeared to result from an encounter of already existing opposite polarity magentic flux than with emerging small magnetic bipoles (ephemeral regions). Such encounters would be more likely to occur in areas of mixed polarity. The fractional area of the sun covered by mixed polarity fields varies anti-correlated with the solar cycle leading to a possible explanation for the 180 degrees out of phase solar cycle variation of X-ray bright points. To establish the validity of this suggestion, a detailed study of time-sequence magnetic field, He I wavelength 10830, Ha, C IV, and Si II observations of selected areas of the quiet sun was initiated about 2 years ago. The preliminary results of this study are reported.

RECONNECTION-DRIVEN CORONAL-HOLE JETS WITH GRAVITY AND SOLAR WIND

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

Karpen, J. T.; DeVore, C. R.; Antiochos, S. K.

Coronal-hole jets occur ubiquitously in the Sun's coronal holes, at EUV and X-ray bright points associated with intrusions of minority magnetic polarity. The embedded-bipole model for these jets posits that they are driven by explosive, fast reconnection between the stressed closed field of the embedded bipole and the open field of the surrounding coronal hole. Previous numerical studies in Cartesian geometry, assuming uniform ambient magnetic field and plasma while neglecting gravity and solar wind, demonstrated that the model is robust and can produce jet-like events in simple configurations. We have extended these investigations by including spherical geometry, gravity, and solarmore » wind in a nonuniform, coronal hole-like ambient atmosphere. Our simulations confirm that the jet is initiated by the onset of a kink-like instability of the internal closed field, which induces a burst of reconnection between the closed and external open field, launching a helical jet. Our new results demonstrate that the jet propagation is sustained through the outer corona, in the form of a traveling nonlinear Alfvén wave front trailed by slower-moving plasma density enhancements that are compressed and accelerated by the wave. This finding agrees well with observations of white-light coronal-hole jets, and can explain microstreams and torsional Alfvén waves detected in situ in the solar wind. We also use our numerical results to deduce scaling relationships between properties of the coronal source region and the characteristics of the resulting jet, which can be tested against observations.« less

Two Coronal Holes on the Sun Viewed by SDO

NASA Image and Video Library

2015-03-17

NASA’s Solar Dynamics Observatory, or SDO, captured this solar image on March 16, 2015, which clearly shows two dark patches, known as coronal holes. The larger coronal hole of the two, near the southern pole, covers an estimated 6- to 8-percent of the total solar surface. While that may not sound significant, it is one of the largest polar holes scientists have observed in decades. The smaller coronal hole, towards the opposite pole, is long and narrow. It covers about 3.8 billion square miles on the sun - only about 0.16-percent of the solar surface. Coronal holes are lower density and temperature regions of the sun’s outer atmosphere, known as the corona. Coronal holes can be a source of fast solar wind of solar particles that envelop the Earth. The magnetic field in these regions extends far out into space rather than quickly looping back into the sun’s surface. Magnetic fields that loop up and back down to the surface can be seen as arcs in non-coronal hole regions of the image, including over the lower right horizon. The bright active region on the lower right quadrant is the same region that produced solar flares last week. Credit: NASA/Goddard/SDO NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Height Dependence of Plasma Properties of a Dark Lane and a Cool Loop in a Solar Limb Active Region Observed by Hinode/EIS

NASA Astrophysics Data System (ADS)

Lee, K.; Imada, S.; Moon, Y.; Lee, J.

2013-12-01

We investigate spectral properties of a cool loop and a dark lane over a limb active region on 2007 March 14 by the Hinode/EUV Imaging Spectrometer. The cool loop is clearly seen in the spectral lines formed at the transition region temperature. The dark lane is characterized by an elongated faint structure in coronal spectral lines and rooted on a bright point. We determine their electron densities, Doppler velocities, and non-thermal velocities with height over the limb. We derived electron densities using the density sensitive line pairs of Mg VII, Si X, Fe XII, Fe XIII and Fe XIV spectra. Under the hydrostatic equilibrium and isothermal assumption, we determine their temperatures from the density scale height. Comparing the scale height temperatures to the peak formation temperatures of the spectral lines, we note that the scale height temperature of the cool loop is consistent with a peak formation temperature of the Fe XII and the scale height temperatures of the dark lane from each spectral lines are much lower than their peak formation temperatures. The non-thermal velocity in the cool loop slightly decreases along the loop while that in the dark lane sharply falls off with height. The variation of non-thermal velocity with height in the cool loop and the dark lane is contrast to that in off-limb polar coronal holes which are considered as source of the solar wind. Such a decrease in the non-thermal velocity may be explained by wave damping near the solar surface or turbulence due to magnetic reconnection near the bright point.

Anti­-parallel Filament Flows and Bright Dots Observed in the EUV with Hi-­C

NASA Technical Reports Server (NTRS)

Alexander, Caroline E.; Regnier, Stephane; Walsh, Robert; Winebarger, Amy

2013-01-01

Hi-C obtained the highest spatial and temporal resolution observations ever taken in the solar EUV corona. Hi-C reveals dynamics and structure at the limit of its temporal and spatial resolution. Hi-C observed various fine-scale features that SDO/AIA could not pick out. For the first time in the corona, Hi-C revealed magnetic braiding and component reconnection consistent with coronal heating. Hi-C shows evidence of reconnection and heating in several different regions and magnetic configurations with plasma being heated to 0.3 - 8 x 10(exp 6) K temperatures. Surprisingly, many of the first results highlight plasma at temperatures that are not at the peak of the response functions.

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.

Breakout Reconnection Observed by the TESIS EUV Telescope

NASA Astrophysics Data System (ADS)

Reva, A. A.; Ulyanov, A. S.; Shestov, S. V.; Kuzin, S. V.

2016-01-01

We present experimental evidence of the coronal mass ejection (CME) breakout reconnection, observed by the TESIS EUV telescope. The telescope could observe solar corona up to 2 R⊙ from the Sun center in the Fe 171 Å line. Starting from 2009 April 8, TESIS observed an active region (AR) that had a quadrupolar structure with an X-point 0.5 R⊙ above photosphere. A magnetic field reconstructed from the Michelson Doppler Imager data also has a multipolar structure with an X-point above the AR. At 21:45 UT on April 9, the loops near the X-point started to move away from each other with a velocity of ≈7 km s-1. At 01:15 UT on April 10, a bright stripe appeared between the loops, and the flux in the GOES 0.5-4 Å channel increased. We interpret the loops’ sideways motion and the bright stripe as evidence of the breakout reconnection. At 01:45 UT, the loops below the X-point started to slowly move up. At 15:10 UT, the CME started to accelerate impulsively, while at the same time a flare arcade formed below the CME. After 15:50 UT, the CME moved with constant velocity. The CME evolution precisely followed the breakout model scenario.

IMAGING PROMINENCE ERUPTIONS OUT TO 1 AU

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

Wood, Brian E.; Howard, Russell A.; Linton, Mark G., E-mail: brian.wood@nrl.navy.mil

2016-01-10

Views of two bright prominence eruptions trackable all the way to 1 AU are here presented, using the heliospheric imagers on the Solar TErrestrial RElations Observatory (STEREO) spacecraft. The two events first erupted from the Sun on 2011 June 7 and 2012 August 31, respectively. Only these two examples of clear prominence eruptions observable this far from the Sun could be found in the STEREO image database, emphasizing the rarity of prominence eruptions this persistently bright. For the 2011 June event, a time-dependent 3D reconstruction of the prominence structure is made using point-by-point triangulation. This is not possible for the August event due to amore » poor viewing geometry. Unlike the coronal mass ejection (CME) that accompanies it, the 2011 June prominence exhibits little deceleration from the Sun to 1 AU, as a consequence moving upwards within the CME. This demonstrates that prominences are not necessarily tied to the CME's magnetic structure far from the Sun. A mathematical framework is developed for describing the degree of self-similarity for the prominence's expansion away from the Sun. This analysis suggests only modest deviations from self-similar expansion, but close to the Sun the prominence expands radially somewhat more rapidly than self-similarity would predict.« less

3D MHD MODELING OF TWISTED CORONAL LOOPS

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

Reale, F.; Peres, G.; Orlando, S.

We perform MHD modeling of a single bright coronal loop to include the interaction with a non-uniform magnetic field. The field is stressed by random footpoint rotation in the central region and its energy is dissipated into heating by growing currents through anomalous magnetic diffusivity that switches on in the corona above a current density threshold. We model an entire single magnetic flux tube in the solar atmosphere extending from the high- β chromosphere to the low- β corona through the steep transition region. The magnetic field expands from the chromosphere to the corona. The maximum resolution is ∼30 km.more » We obtain an overall evolution typical of loop models and realistic loop emission in the EUV and X-ray bands. The plasma confined in the flux tube is heated to active region temperatures (∼3 MK) after ∼2/3 hr. Upflows from the chromosphere up to ∼100 km s{sup −1} fill the core of the flux tube to densities above 10{sup 9} cm{sup −3}. More heating is released in the low corona than the high corona and is finely structured both in space and time.« less

Three-Dimensional Simulations of Tearing and Intermittency in Coronal Jets

NASA Technical Reports Server (NTRS)

Wyper, P. F.; DeVore, C. R.; Karpen, J. T.; Lynch, B. J.

2016-01-01

Observations of coronal jets increasingly suggest that local fragmentation and intermittency play an important role in the dynamics of these events. In this work we investigate this fragmentation in high-resolution simulations of jets in the closed-field corona. We study two realizations of the embedded-bipole model, whereby impulsive helical out flows are driven by reconnection between twisted and untwisted field across the domed fan plane of a magnetic null. We find that the reconnection region fragments following the onset of a tearing-like instability, producing multiple magnetic null points and flux-rope structures within the current layer. The flux ropes formed within the weak- field region in the center of the current layer are associated with \\blobs" of density enhancement that become filamentary threads as the flux ropes are ejected from the layer, whereupon new flux ropes form behind them. This repeated formation and ejection of flux ropes provides a natural explanation for the intermittent out flows, bright blobs of emission, and filamentary structure observed in some jets. Additional observational signatures of this process are discussed. Essentially all jet models invoke reconnection between regions of locally closed and locally open field as the jet-generation mechanism. Therefore, we suggest that this repeated tearing process should occur at the separatrix surface between the two flux systems in all jets. A schematic picture of tearing-mediated jet reconnection in three dimensions is outlined.

Plasma Brightenings in a Failed Solar Filament Eruption

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

Li, Y.; Ding, M. D., E-mail: yingli@nju.edu.cn

Failed filament eruptions are solar eruptions that are not associated with coronal mass ejections. In a failed filament eruption, the filament materials usually show some ascending and falling motions as well as generating bright EUV emissions. Here we report a failed filament eruption (SOL2016-07-22) that occurred in a quiet-Sun region observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory . In this event, the filament spreads out but gets confined by the surrounding magnetic field. When interacting with the ambient magnetic field, the filament material brightens up and flows along the magnetic field lines through the coronamore » to the chromosphere. We find that some materials slide down along the lifting magnetic structure containing the filament and impact the chromosphere, and through kinetic energy dissipation, cause two ribbon-like brightenings in a wide temperature range. There is evidence suggesting that magnetic reconnection occurs between the filament magnetic structure and the surrounding magnetic fields where filament plasma is heated to coronal temperatures. In addition, thread-like brightenings show up on top of the erupting magnetic fields at low temperatures, which might be produced by an energy imbalance from a fast drop of radiative cooling due to plasma rarefaction. Thus, this single event of a failed filament eruption shows the existence of a variety of plasma brightenings that may be caused by completely different heating mechanisms.« less

THREE-DIMENSIONAL SIMULATIONS OF TEARING AND INTERMITTENCY IN CORONAL JETS

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

Wyper, P. F.; DeVore, C. R.; Karpen, J. T.

Observations of coronal jets increasingly suggest that local fragmentation and intermittency play an important role in the dynamics of these events. In this work, we investigate this fragmentation in high-resolution simulations of jets in the closed-field corona. We study two realizations of the embedded-bipole model, whereby impulsive helical outflows are driven by reconnection between twisted and untwisted field across the domed fan plane of a magnetic null. We find that the reconnection region fragments following the onset of a tearing-like instability, producing multiple magnetic null points and flux-rope structures within the current layer. The flux ropes formed within the weak-fieldmore » region in the center of the current layer are associated with “blobs” of density enhancement that become filamentary threads as the flux ropes are ejected from the layer, whereupon new flux ropes form behind them. This repeated formation and ejection of flux ropes provides a natural explanation for the intermittent outflows, bright blobs of emission, and filamentary structure observed in some jets. Additional observational signatures of this process are discussed. Essentially all jet models invoke reconnection between regions of locally closed and locally open field as the jet-generation mechanism. Therefore, we suggest that this repeated tearing process should occur at the separatrix surface between the two flux systems in all jets. A schematic picture of tearing-mediated jet reconnection in three dimensions is outlined.« less

Chromospheric Signatures of the Subdued Cycle 23/24 Solar Minimum in Microwaves

NASA Technical Reports Server (NTRS)

Yashiro, S.; Makela, P.; Shibasaki, K.; Hathaway, D.

2011-01-01

Coronal holes appear brighter than the quiet Sun in microwave images, with a brightness enhancement of 500 to 2000 K. The brightness enhancement corresponds to the upper chromosphere, where the plasma temperature is about 10000 K. We constructed a microwave butterfly diagram using the synoptic images obtained by the Nobeyama radio-heliograph (NoRH) showing the evolution of the polar and low latitude brightness temperature. While the polar brightness reveals the chromospheric conditions, the low latitude brightness is attributed to active regions in the corona. When we compared the microwave butterfly diagram with the magnetic butterfly diagram, we found a good correlation between the microwave brightness enhancement and the polar field strength. The microwave butterfly diagram covers part of solar cycle 22, whole of cycle 23, and part of cycle 24, thus enabling comparison between the cycle 23/24 and cycle 22/23 minima. The microwave brightness during the cycle 23/24 minimum was found to be lower than that during the cycle 22/23 minimum by approx.250 K. The reduced brightness temperature is consistent with the reduced polar field strength during the cycle 23/24 minimum seen in the magnetic butterfly diagram. We suggest that the microwave brightness at the solar poles is a good indicator of the speed of the solar wind sampled by Ulysses at high latitudes.

Solar Magnetic Carpet III: Coronal Modelling of Synthetic Magnetograms

NASA Astrophysics Data System (ADS)

Meyer, K. A.; Mackay, D. H.; van Ballegooijen, A. A.; Parnell, C. E.

2013-09-01

This article is the third in a series working towards the construction of a realistic, evolving, non-linear force-free coronal-field model for the solar magnetic carpet. Here, we present preliminary results of 3D time-dependent simulations of the small-scale coronal field of the magnetic carpet. Four simulations are considered, each with the same evolving photospheric boundary condition: a 48-hour time series of synthetic magnetograms produced from the model of Meyer et al. ( Solar Phys. 272, 29, 2011). Three simulations include a uniform, overlying coronal magnetic field of differing strength, the fourth simulation includes no overlying field. The build-up, storage, and dissipation of magnetic energy within the simulations is studied. In particular, we study their dependence upon the evolution of the photospheric magnetic field and the strength of the overlying coronal field. We also consider where energy is stored and dissipated within the coronal field. The free magnetic energy built up is found to be more than sufficient to power small-scale, transient phenomena such as nanoflares and X-ray bright points, with the bulk of the free energy found to be stored low down, between 0.5 - 0.8 Mm. The energy dissipated is currently found to be too small to account for the heating of the entire quiet-Sun corona. However, the form and location of energy-dissipation regions qualitatively agree with what is observed on small scales on the Sun. Future MHD modelling using the same synthetic magnetograms may lead to a higher energy release.

Observations of Upward Propagating Waves in the Transition Region and Corona above Sunspots

NASA Astrophysics Data System (ADS)

Hou, Zhenyong; Huang, Zhenghua; Xia, Lidong; Li, Bo; Fu, Hui

2018-03-01

We present observations of persistent oscillations of some bright features in the upper-chromosphere/transition region above sunspots taken by IRIS SJ 1400 Å and upward propagating quasi-periodic disturbances along coronal loops rooted in the same region taken by the AIA 171 Å passband. The oscillations of the features are cyclic oscillatory motions without any obvious damping. The amplitudes of the spatial displacements of the oscillations are about 1″. The apparent velocities of the oscillations are comparable to the sound speed in the chromosphere, but the upward motions are slightly larger than that of the downward. The intensity variations can take 24%–53% of the background, suggesting nonlinearity of the oscillations. The FFT power spectra of the oscillations show a dominant peak at a period of about 3 minutes, which is consistent with the omnipresent 3 minute oscillations in sunspots. The amplitudes of the intensity variations of the upward propagating coronal disturbances are 10%–15% of the background. The coronal disturbances have a period of about 3 minutes, and propagate upward along the coronal loops with apparent velocities in a range of 30 ∼ 80 km s‑1. We propose a scenario in which the observed transition region oscillations are powered continuously by upward propagating shocks, and the upward propagating coronal disturbances can be the recurrent plasma flows driven by shocks or responses of degenerated shocks that become slow magnetic-acoustic waves after heating the plasma in the coronal loops at their transition-region bases.

Imaging spectroscopy of solar radio burst fine structures.

PubMed

Kontar, E P; Yu, S; Kuznetsov, A A; Emslie, A G; Alcock, B; Jeffrey, N L S; Melnik, V N; Bian, N H; Subramanian, P

2017-11-15

Solar radio observations provide a unique diagnostic of the outer solar atmosphere. However, the inhomogeneous turbulent corona strongly affects the propagation of the emitted radio waves, so decoupling the intrinsic properties of the emitting source from the effects of radio wave propagation has long been a major challenge in solar physics. Here we report quantitative spatial and frequency characterization of solar radio burst fine structures observed with the Low Frequency Array, an instrument with high-time resolution that also permits imaging at scales much shorter than those corresponding to radio wave propagation in the corona. The observations demonstrate that radio wave propagation effects, and not the properties of the intrinsic emission source, dominate the observed spatial characteristics of radio burst images. These results permit more accurate estimates of source brightness temperatures, and open opportunities for quantitative study of the mechanisms that create the turbulent coronal medium through which the emitted radiation propagates.

Coronal X-ray enhancements associated with H-alpha filament disappearances

NASA Technical Reports Server (NTRS)

Webb, D. F.; Krieger, A. S.; Rust, D. M.

1976-01-01

The X-ray telescope experiment aboard the Skylab/ATM mission provided high-resolution soft X-ray images of the lower corona away from active regions, revealing frequent large-scale transient X-ray enhancements which could often be associated with the disappearance of H-alpha filaments. The X-ray emitting structures featured peak brightnesses similar to those of nonflaring active region structures, durations from 3 to 40 hours, shapes that in general outlined the preexisting H-alpha filaments to as large as 400,000 km, apparent expansion velocities of the order of tens of km/sec, and observed peak temperatures of the order of a few million degrees. One such event is described and analyzed in detail. Two explanations of the events are discussed: (1) excess cool material is present in the filament cavity, contributing to the X-ray enhancement, and (2) the enhancement is due to the compression of preexisting material by a changing magnetic field.

THE MAGELLANIC STREAM: BREAK-UP AND ACCRETION ONTO THE HOT GALACTIC CORONA

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

Tepper-García, Thor; Bland-Hawthorn, Joss; Sutherland, Ralph S.

The Magellanic H i Stream (≈2 × 10{sup 9} M{sub ⊙} [d/55 kpc]{sup 2}) encircling the Galaxy at a distance d is arguably the most important tracer of what happens to gas accreting onto a disk galaxy. Recent observations reveal that the Stream’s mass is in fact dominated (3:1) by its ionized component. Here we revisit the origin of the mysterious Hα recombination emission observed along much of its length that is overly bright (∼150–200 mR) for the known Galactic ultraviolet (UV) background (≈20–40 mR [d/55 kpc]{sup −2}). In an earlier model, we proposed that a slow shock cascade wasmore » operating along the Stream due to its interaction with the extended Galactic hot corona. We find that for a smooth coronal density profile, this model can explain the bright Hα emission if the coronal density satisfies 2 × 10{sup −4} < (n/cm{sup −3}) < 4 × 10{sup −4} at d = 55 kpc. But in view of updated parameters for the Galactic halo and mounting evidence that most of the Stream must lie far beyond the Magellanic Clouds (d > 55 kpc), we revisit the shock cascade model in detail. At lower densities, the H i gas is broken down by the shock cascade but mostly mixes with the hot corona without significant recombination. At higher densities, the hot coronal mass (including the other baryonic components) exceeds the baryon budget of the Galaxy. If the Hα emission arises from the shock cascade, the upper limit on the smooth coronal density constrains the Stream’s mean distance to ≲75 kpc. If, as some models indicate, the Stream is even further out, either the shock cascade is operating in a regime where the corona is substantially mass-loaded with recent gas debris, or an entirely different ionization mechanism is responsible.« less

Understanding Coronal Dimming and its Relation to Coronal Mass Ejections

NASA Astrophysics Data System (ADS)

Mason, J. P.; Woods, T. N.; Caspi, A.; Hock, R. A.

2013-12-01

When extreme ultraviolet (EUV) emitting material in the corona is lost during a coronal mass ejection (CME), the solar spectral irradiance is impacted and these effects are observed in data from the Solar Dynamics Observatory (SDO) EUV Variability Experiment (EVE) and Atmospheric Imaging Assembly (AIA). This process is one of the physical mechanisms that can lead to the observation of 'coronal dimming,' a phenomenon lasting eight hours on average and rarely persisting longer than one day. Other mechanisms that can cause observed dimming include obscuration of bright material (e.g., flare arcade) by dark material (e.g., filament), temperature evolution (e.g., cool plasma being heated causing transient decreases in characteristic emission lines), and propagation of global waves. Each of these processes has a unique spectral signature, which will be explained and exemplified. In particular, the 7 August 2010 M1.0 flare with associated ~870 km/s CME will be analyzed in detail using both AIA and EVE to demonstrate new techniques for isolating dimming due to the CME ('core dimming'). Further analysis will estimate CME mass and velocity using only parameterization of core dimming and compare these estimates to traditionally calculated CME kinetics.

Imaging Coronal Mass Ejections and Large-Scale Solar Wind Structure Using IPS and Thomson-Scattered Sunlight (Invited)

NASA Astrophysics Data System (ADS)

Clover, J. M.; Jackson, B. V.; Buffington, A.; Hick, P. P.; Bisi, M. M.; Tokumaru, M.; Fujiki, K.

2010-12-01

The Solar Mass Ejection Imager (SMEI) observes Thomson-scattered white light from heliospheric electrons across almost all of the sky nearly all of the time since early 2003. Interplanetary scintillation (IPS) observations of velocity and g-level provide similar structure information but with a less-complete sky-and-time coverage. The Solar TErrestrial RElations Observatory (STEREO) twin spacecraft outer Heliospheric Imagers (HI-2) currently image the heliosphere in Thomson-scattered light near the ecliptic plane far from Earth. The Solar-Terrestrial Environment Laboratory (STELab) IPS observations provide IPS velocity and g-level values, which in conjunction with our tomographic reconstruction program, yield velocities and densities of the inner heliosphere in three dimensions. The same tomographic program substitutes SMEI Thomson-scattering brightness information for the g-level values to derive heliospheric densities from these data alone. We look at the global structure of the heliosphere concentrating mainly on three events from 2007 through the rise phase of Solar Cycle 24. The first event, observed in both the IPS and SMEI defines the three-dimensional velocity and density structure around the time of the shock observed at Earth on 02:02 UT 17 December 2007. The second event, seen only by SMEI, is that of the 23-26 April 2008 coronal mass ejection (CME) and its interplanetary counterpart. The third event is the CME (and its interplanetary counterpart) that took place 17 January 2010 and arrived at STEREO-B about four days later. For each event, we isolate the particular portion of the heliosphere attributed to the transient density structure using our tomographic technique, and then estimate its extent.

Coronal Rain, Solar Storm

NASA Image and Video Library

2010-03-19

Explanation: In this picture, the Sun's surface is quite dark. A frame from a movie recorded on November 9th by the orbiting TRACE telescope, it shows coronal loops lofted over a solar active region. Glowing brightly in extreme ultraviolet light, the hot plasma entrained above the Sun along arching magnetic fields is cooling and raining back down on the solar surface. Hours earlier, on November 8th, astronomers had watched this particular active region produce a not so spectacular solar flare. Still, the M-class flare spewed forth an intense storm of particles, suddenly showering satellites near the Earth with high energy protons. The flare event was also associated with a large coronal mass ejection, a massive cloud of material which impacted our fair planet's magnetic field about 31 hours later. The result ... a strong geomagnetic storm. Credit: NASA/GSFC/TRACE To learn more go to: nasascience.nasa.gov/missions/trace To learn more about NASA's Sun Earth Day go here: sunearthday.nasa.gov/2010/index.php

Eruptions that Drive Coronal Jets in a Solar Active Region

NASA Technical Reports Server (NTRS)

Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David A.; Panesar, Navdeep K.; Akiyama, Sachiko; Yashiro, Seiji; Gopalswamy, Nat

2016-01-01

Solar coronal jets are common in both coronal holes and in active regions (e.g., Shibata et al. 1992, Shimojo et al. 1996, Cirtain et al. 2007. Savcheva et al. 2007). Recently, Sterling et al. (2015), using data from Hinode/XRT and SDO/AIA, found that coronal jets originating in polar coronal holes result from the eruption of small-scale filaments (minifilaments). The jet bright point (JBP) seen in X-rays and hotter EUV channels off to one side of the base of the jet's spire develops at the location where the minifilament erupts, consistent with the JBPs being miniature versions of typical solar flares that occur in the wake of large-scale filament eruptions. Here we consider whether active region coronal jets also result from the same minifilament-eruption mechanism, or whether they instead result from a different mechanism (e.g. Yokoyama & Shibata 1995). We present observations of an on-disk active region (NOAA AR 11513) that produced numerous jets on 2012 June 30, using data from SDO/AIA and HMI, and from GOES/SXI. We find that several of these active region jets also originate with eruptions of miniature filaments (size scale 20'') emanating from small-scale magnetic neutral lines of the region. This demonstrates that active region coronal jets are indeed frequently driven by minifilament eruptions. Other jets from the active region were also consistent with their drivers being minifilament eruptions, but we could not confirm this because the onsets of those jets were hidden from our view. This work was supported by funding from NASA/LWS, NASA/HGI, and Hinode. A full report of this study appears in Sterling et al. (2016).

CORONAL AND CHROMOSPHERIC SIGNATURES OF LARGE-SCALE DISTURBANCES ASSOCIATED WITH A MAJOR SOLAR ERUPTION

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

Zong, Weiguo; Dai, Yu, E-mail: ydai@nju.edu.cn

We present both coronal and chromospheric observations of large-scale disturbances associated with a major solar eruption on 2005 September 7. In the Geostationary Operational Environmental Satellites/Solar X-ray Imager (SXI), arclike coronal brightenings are recorded propagating in the southern hemisphere. The SXI front shows an initially constant speed of 730 km s{sup −1} and decelerates later on, and its center is near the central position angle of the associated coronal mass ejection (CME) but away from the flare site. Chromospheric signatures of the disturbances are observed in both Mauna Loa Solar Observatory (MLSO)/Polarimeter for Inner Coronal Studies Hα and MLSO/Chromospheric Helium Imore » Imaging Photometer He i λ10830 and can be divided into two parts. The southern signatures occur in regions where the SXI front sweeps over, with the Hα bright front coincident with the SXI front, while the He i dark front lags the SXI front but shows a similar kinematics. Ahead of the path of the southern signatures, oscillations of a filament are observed. The northern signatures occur near the equator, with the Hα and He i fronts coincident with each other. They first propagate westward and then deflect to the north at the boundary of an equatorial coronal hole. Based on these observational facts, we suggest that the global disturbances are associated with the CME lift-off and show a hybrid nature: a mainly non-wave CME flank nature for the SXI signatures and the corresponding southern chromospheric signatures, and a shocked fast-mode coronal MHD wave nature for the northern chromospheric signatures.« less

Impulsively Generated Wave Trains in Coronal Structures. II. Effects of Transverse Structuring on Sausage Waves in Pressurelesss Slabs

NASA Astrophysics Data System (ADS)

Li, Bo; Guo, Ming-Zhe; Yu, Hui; Chen, Shao-Xia

2018-03-01

Impulsively generated sausage wave trains in coronal structures are important for interpreting a substantial number of observations of quasi-periodic signals with quasi-periods of order seconds. We have previously shown that the Morlet spectra of these wave trains in coronal tubes depend crucially on the dispersive properties of trapped sausage waves, the existence of cutoff axial wavenumbers, and the monotonicity of the dependence of the axial group speed on the axial wavenumber in particular. This study examines the difference a slab geometry may introduce, for which purpose we conduct a comprehensive eigenmode analysis, both analytically and numerically, on trapped sausage modes in coronal slabs with a considerable number of density profiles. For the profile descriptions examined, coronal slabs can trap sausage waves with longer axial wavelengths, and the group speed approaches the internal Alfvén speed more rapidly at large wavenumbers in the cylindrical case. However, common to both geometries, cutoff wavenumbers exist only when the density profile falls sufficiently rapidly at distances far from coronal structures. Likewise, the monotonicity of the group speed curves depends critically on the profile steepness right at the structure axis. Furthermore, the Morlet spectra of the wave trains are shaped by the group speed curves for coronal slabs and tubes alike. Consequently, we conclude that these spectra have the potential for inferring the subresolution density structuring inside coronal structures, although their detection requires an instrumental cadence of better than ∼1 s.

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.

Suppression of heating of coronal loops rooted in opposite polarity sunspot umbrae

NASA Astrophysics Data System (ADS)

Tiwari, Sanjiv K.; Thalmann, Julia K.; Moore, Ronald L.; Panesar, Navdeep; Winebarger, Amy R.

2016-05-01

EUV observations of active region (AR) coronae reveal the presence of loops at different temperatures. To understand the mechanisms that result in hotter or cooler loops, we study a typical bipolar AR, near solar disk center, which has moderate overall magnetic twist and at least one fully developed sunspot of each polarity. From AIA 193 and 94 A images we identify many clearly discernible coronal loops that connect plage or a sunspot of one polarity to an opposite-polarity plage region. The AIA 94 A images show dim regions in the umbrae of the spots. To see which coronal loops are rooted in a dim umbral area, we performed a non-linear force-free field (NLFFF) modeling using photospheric vector magnetic field measurements obtained with the HMI onboard SDO. After validation of the NLFFF model by comparison of calculated model field lines and observed loops in AIA 193 and 94, we specify the photospheric roots of the model field lines. The model field then shows the coronal magnetic loops that arch from the dim umbral areas of the opposite polarity sunspots. Because these coronal loops are not visible in any of the coronal EUV and X-ray images of the AR, we conclude they are the coolest loops in the AR. This result suggests that the loops connecting opposite polarity umbrae are the least heated because the field in umbrae is so strong that the convective braiding of the field is strongly suppressed.We hypothesize that the convective freedom at the feet of a coronal loop, together with the strength of the field in the body of the loop, determines the strength of the heating. In particular, we expect the hottest coronal loops to have one foot in an umbra and the other foot in opposite-polarity penumbra or plage (coronal moss), the areas of strong field in which convection is not as strongly suppressed as in umbra. Many transient, outstandingly bright, loops in the AIA 94 movie of the AR do have this expected rooting pattern. We will also present another example of AR in which we find a similar rooting pattern of coronal loops.

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.

Solar Hard X-ray Observations with NuSTAR

NASA Astrophysics Data System (ADS)

Marsh, Andrew; Smith, D. M.; Krucker, S.; Hudson, H. S.; Hurford, G. J.; White, S. M.; Mewaldt, R. A.; Harrison, F. A.; Grefenstette, B. W.; Stern, D.

2012-05-01

High-sensitivity imaging of coronal hard X-rays allows detection of freshly accelerated nonthermal electrons at the acceleration site. A few such observations have been made with Yohkoh and RHESSI, but a leap in sensitivity could help pin down the time, place, and manner of reconnection. Around the time of this meeting, the Nuclear Spectroscopic Telescope ARray (NuSTAR), a NASA Small Explorer for high energy astrophysics that uses grazing-incidence optics to focus X-rays up to 80 keV, will be launched. Three weeks will be dedicated to solar observing during the baseline two-year mission. NuSTAR will be 200 times more sensitive than RHESSI in the hard X-ray band. This will allow the following new observations, among others: 1) Extrapolation of the micro/nanoflare distribution by two orders of magnitude down in flux; 2) Search for hard X-rays from network nanoflares (soft X-ray bright points) and evaluation of their role in coronal heating; 3) Discovery of hard X-ray bremsstrahlung from the electron beams driving type III radio bursts, and measurement of their electron spectrum; 4) Hard X-ray studies of polar soft X-ray jets and impulsive solar energetic particle events at the edge of coronal holes; 5) Study of coronal bremsstrahlung from particles accelerated by coronal mass ejections as they are first launched; 6) Study of particles at the coronal reconnection site when flare footpoints and loops are occulted; 7) Search for weak high-temperature coronal plasmas in active regions that are not flaring; and 8) Search for hypothetical axion particles created in the solar core via the hard X-ray signal from their conversion to X-rays in the coronal magnetic field. NuSTAR will also serve as a pathfinder for a future dedicated space mission with enhanced capabilities, such as a satellite version of the FOXSI sounding rocket.

Major Solar Flare

NASA Image and Video Library

2017-09-11

A large sunspot was the source of a powerful solar flare (an X 9.3) and a coronal mass ejection (Sept. 6, 2017). The flare was the largest solar flare of the last decade. For one thing, it created a strong shortwave radio blackout over Europe, Africa and the Atlantic Ocean. Sunspot 2673 has been also the source of several other smaller to medium-sized solar flares over the past few days. Data from the SOHO spacecraft shows the large cloud of particles blasting into space just after the flare. Note: the bright vertical line and the other rays with barred lines are aberrations in our instruments caused by the bright flash of the flare. https://photojournal.jpl.nasa.gov/catalog/PIA21949

Differential Rotation via Tracking of Coronal Bright Points.

NASA Astrophysics Data System (ADS)

McAteer, James; Boucheron, Laura E.; Osorno, Marcy

2016-05-01

The accurate computation of solar differential rotation is important both as a constraint for, and evidence towards, support of models of the solar dynamo. As such, the use of Xray and Extreme Ultraviolet bright points to elucidate differential rotation has been studied in recent years. In this work, we propose the automated detection and tracking of coronal bright points (CBPs) in a large set of SDO data for re-evaluation of solar differential rotation and comparison to other results. The big data aspects, and high cadence, of SDO data mitigate a few issues common to detection and tracking of objects in image sequences and allow us to focus on the use of CBPs to determine differential rotation. The high cadence of the data allows to disambiguate individual CBPs between subsequent images by allowing for significant spatial overlap, i.e., by the fact that the CBPs will rotate a short distance relative to their size. The significant spatial overlap minimizes the effects of incorrectly detected CBPs by reducing the occurrence of outlier values of differential rotation. The big data aspects of the data allows to be more conservative in our detection of CBPs (i.e., to err on the side of missing CBPs rather than detecting extraneous CBPs) while still maintaining statistically larger populations over which to study characteristics. The ability to compute solar differential rotation through the automated detection and tracking of a large population of CBPs will allow for further analyses such as the N-S asymmetry of differential rotation, variation of differential rotation over the solar cycle, and a detailed study of the magnetic flux underlying the CBPs.

Spectroscopic Study of a Dark Lane and a Cool Loop in a Solar Limb Active Region by Hinode/EIS

NASA Astrophysics Data System (ADS)

Lee, K.; Imada, S.; Moon, Y.; Lee, J.

2012-12-01

We investigate a cool loop and a dark lane over a limb active region on 2007 March 14 by the Hinode/EUV Imaging Spectrometer (EIS). The cool loop is clearly seen in the EIS spectral lines formed at the transition region temperature (log T = 5.8). The dark lane is characterized by an elongated faint structure in coronal spectral lines (log T = 5.8 - 6.1) and rooted on a bright point. We examine their electron densities, Doppler velocities, and non-thermal velocities as a function of distance from the limb using the spectral lines formed at different temperatures (log T = 5.4 - 6.4). The electron densities of the cool loop and the dark lane are derived from the density sensitive line pairs of Mg VII, Fe XII, and Fe XIV spectra. Under the hydrostatic equilibrium and isothermal assumption, we determine their temperatures from the density scale height. Comparing the scale height temperatures to the peak formation temperatures of the spectral lines, we note that the scale height temperature of the cool loop is consistent with a peak formation temperature of the Mg VII (log T = 5.8) and the scale height temperature of the dark lane is close to a peak formation temperature of the Fe XII and Fe XIII (log T = 6.1 - 6.2). It is interesting to note that the structures of the cool loop and the dark lane are most visible in these temperature lines. While the non-thermal velocity in the cool loop slightly decreases (less than 7 km {s-1}) along the loop, that in the dark lane sharply falls off with height. The variation of non-thermal velocity with height in the cool loop and the dark lane is contrast to that in off-limb polar coronal holes which are considered as source of the fast solar wind. Such a decrease in the non-thermal velocity may be explained by wave damping near the solar surface or turbulence due to magnetic reconnection near the bright point.

Interactions of Dust Grains with Coronal Mass Ejections and Solar Cycle Variations of the F-Coronal Brightness

NASA Technical Reports Server (NTRS)

Ragot, B. R.; Kahler, S. W.

2003-01-01

The density of interplanetary dust increases sunward to reach its maximum in the F corona, where its scattered white-light emission dominates that of the electron K corona above about 3 Solar Radius. The dust will interact with both the particles and fields of antisunward propagating coronal mass ejections (CMEs). To understand the effects of the CME/dust interactions we consider the dominant forces, with and without CMEs. acting on the dust in the 3-5 Solar Radius region. Dust grain orbits are then computed to compare the drift rates from 5 to 3 Solar Radius. for periods of minimum and maximum solar activity, where a simple CME model is adopted to distinguish between the two periods. The ion-drag force, even in the quiet solar wind, reduces the drift time by a significant factor from its value estimated with the Poynting-Robertson drag force alone. The ion-drag effects of CMEs result in even shorter drift times of the large (greater than or approx. 3 microns) dust grains. hence faster depletion rates and lower dust-pain densities, at solar maxima. If dominated by thermal emission, the near-infrared brightness will thus display solar cycle variations close to the dust plane of symmetry. While trapping the smallest of the grains, the CME magnetic fields also scatter the grains of intermediate size (0.1-3 microns) in latitude. If light scattering by small grains close to the Sun dominates the optical brightness. the scattering by the CME magnetic fields will result in a solar cycle variation of the optical brightness distribution not exceeding 100% at high latitudes, with a higher isotropy reached at solar maxima. A good degree of latitudinal isotropy is already reached at low solar activity since the magnetic fields of the quiet solar wind so close to the Sun are able to scatter the small (less than or approx. 3 microns) grains up to the polar regions in only a few days or less, producing strong perturbations of their trajectories in less than half their orbital periods. Finally, we consider possible observable consequences of individual CME/dust interactions. We show that the dust grains very likely have no observable effect on the dynamics of CMEs. The effect of an individual CME on the dust grains, however, might serve as a forecasting tool for the directions and amplitudes of the magnetic fields within the CME.

THE WAVE PROPERTIES OF CORONAL BRIGHT FRONTS OBSERVED USING SDO/AIA

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

Long, David M.; DeLuca, Edward E.; Gallagher, Peter T., E-mail: longda@tcd.ie

2011-11-15

Coronal bright fronts (CBFs) are large-scale wavefronts that propagate through the solar corona at hundreds of kilometers per second. While their kinematics have been studied in detail, many questions remain regarding the temporal evolution of their amplitude and pulse width. Here, contemporaneous high cadence, multi-thermal observations of the solar corona from the Solar Dynamic Observatory (SDO) and Solar TErrestrial RElations Observatory (STEREO) spacecraft are used to determine the kinematics and expansion rate of a CBF wavefront observed on 2010 August 14. The CBF was found to have a lower initial velocity with weaker deceleration in STEREO observations compared to SDOmore » observations ({approx}340 km s{sup -1} and -72 m s{sup -2} as opposed to {approx}410 km s{sup -1} and -279 m s{sup -2}). The CBF kinematics from SDO were found to be highly passband-dependent, with an initial velocity ranging from 379 {+-} 12 km s{sup -1} to 460 {+-} 28 km s{sup -1} and acceleration ranging from -128 {+-} 28 m s{sup -2} to -431 {+-} 86 m s{sup -2} in the 335 A and 304 A passbands, respectively. These kinematics were used to estimate a quiet coronal magnetic field strength range of {approx}1-2 G. Significant pulse broadening was also observed, with expansion rates of {approx}130 km s{sup -1} (STEREO) and {approx}220 km s{sup -1} (SDO). By treating the CBF as a linear superposition of sinusoidal waves within a Gaussian envelope, the resulting dispersion rate of the pulse was found to be {approx}8-13 Mm{sup 2} s{sup -1}. These results are indicative of a fast-mode magnetoacoustic wave pulse propagating through an inhomogeneous medium.« less

Revealing the Nature of Extreme Coronal-line Emitter SDSS J095209.56+214313.3

NASA Astrophysics Data System (ADS)

Palaversa, Lovro; Gezari, Suvi; Sesar, Branimir; Stuart, J. Scott; Wozniak, Przemyslaw; Holl, Berry; Ivezić, Željko

2016-03-01

Extreme coronal-line emitter (ECLE) SDSS J095209.56+214313.3, known by its strong, fading, high-ionization lines, has been a long-standing candidate for a tidal disruption event however, a supernova (SN) origin has not yet been ruled out. Here we add several new pieces of information to the puzzle of the nature of the transient that powered its variable coronal lines: (1) an optical light curve from the Lincoln Near Earth Asteroid Research (LINEAR) survey that serendipitously catches the optical flare, and (2) late-time observations of the host galaxy with the Swift Ultraviolet and Optical Telescope (UVOT) and X-ray telescope (XRT) and the ground-based Mercator telescope. The well-sampled, ˜10 yr long, unfiltered LINEAR light curve constrains the onset of the flare to a precision of ±5 days and enables us to place a lower limit on the peak optical magnitude. Difference imaging allows us to estimate the location of the flare in proximity of the host galaxy core. Comparison of the GALEX data (early 2006) with the recently acquired Swift UVOT (2015 June) and Mercator observations (2015 April) demonstrates a decrease in the UV flux over a ˜10 yr period, confirming that the flare was UV-bright. The long-lived UV-bright emission, detected 1.8 rest-frame years after the start of the flare, strongly disfavors an SN origin. These new data allow us to conclude that the flare was indeed powered by the tidal disruption of a star by a supermassive black hole and that tidal disruption events are in fact capable of powering the enigmatic class of ECLEs.

Revealing the nature of extreme coronal-line emitter SDSS J095209.56+214313.3

DOE PAGES

Palaversa, Lovro; Gezari, Suvi; Sesar, Branimir; ...

2016-03-08

Extreme coronal-line emitter (ECLE) SDSS J095209.56+214313.3, known by its strong, fading, high-ionization lines, has been a long-standing candidate for a tidal disruption event; however, a supernova (SN) origin has not yet been ruled out. Here we add several new pieces of information to the puzzle of the nature of the transient that powered its variable coronal lines: (1) an optical light curve from the Lincoln Near Earth Asteroid Research (LINEAR) survey that serendipitously catches the optical flare, and (2) late-time observations of the host galaxy with the Swift Ultraviolet and Optical Telescope (UVOT) and X-ray telescope (XRT) and the ground-basedmore » Mercator telescope. The well-sampled, ~10 yr long, unfiltered LINEAR light curve constrains the onset of the flare to a precision of ±5 days and enables us to place a lower limit on the peak optical magnitude. Difference imaging allows us to estimate the location of the flare in proximity of the host galaxy core. Comparison of the GALEX data (early 2006) with the recently acquired Swift UVOT (2015 June) and Mercator observations (2015 April) demonstrates a decrease in the UV flux over a ~10 yr period, confirming that the flare was UV-bright. The long-lived UV-bright emission, detected 1.8 rest-frame years after the start of the flare, strongly disfavors an SN origin. In conclusion, these new data allow us to conclude that the flare was indeed powered by the tidal disruption of a star by a supermassive black hole and that tidal disruption events are in fact capable of powering the enigmatic class of ECLEs.« less

REVEALING THE NATURE OF EXTREME CORONAL-LINE EMITTER SDSS J095209.56+214313.3

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

Palaversa, Lovro; Holl, Berry; Gezari, Suvi

Extreme coronal-line emitter (ECLE) SDSS J095209.56+214313.3, known by its strong, fading, high-ionization lines, has been a long-standing candidate for a tidal disruption event; however, a supernova (SN) origin has not yet been ruled out. Here we add several new pieces of information to the puzzle of the nature of the transient that powered its variable coronal lines: (1) an optical light curve from the Lincoln Near Earth Asteroid Research (LINEAR) survey that serendipitously catches the optical flare, and (2) late-time observations of the host galaxy with the Swift Ultraviolet and Optical Telescope (UVOT) and X-ray telescope (XRT) and the ground-based Mercator telescope.more » The well-sampled, ∼10 yr long, unfiltered LINEAR light curve constrains the onset of the flare to a precision of ±5 days and enables us to place a lower limit on the peak optical magnitude. Difference imaging allows us to estimate the location of the flare in proximity of the host galaxy core. Comparison of the GALEX data (early 2006) with the recently acquired Swift UVOT (2015 June) and Mercator observations (2015 April) demonstrates a decrease in the UV flux over a ∼10 yr period, confirming that the flare was UV-bright. The long-lived UV-bright emission, detected 1.8 rest-frame years after the start of the flare, strongly disfavors an SN origin. These new data allow us to conclude that the flare was indeed powered by the tidal disruption of a star by a supermassive black hole and that tidal disruption events are in fact capable of powering the enigmatic class of ECLEs.« less

Revealing the nature of extreme coronal-line emitter SDSS J095209.56+214313.3

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

Palaversa, Lovro; Gezari, Suvi; Sesar, Branimir

Extreme coronal-line emitter (ECLE) SDSS J095209.56+214313.3, known by its strong, fading, high-ionization lines, has been a long-standing candidate for a tidal disruption event; however, a supernova (SN) origin has not yet been ruled out. Here we add several new pieces of information to the puzzle of the nature of the transient that powered its variable coronal lines: (1) an optical light curve from the Lincoln Near Earth Asteroid Research (LINEAR) survey that serendipitously catches the optical flare, and (2) late-time observations of the host galaxy with the Swift Ultraviolet and Optical Telescope (UVOT) and X-ray telescope (XRT) and the ground-basedmore » Mercator telescope. The well-sampled, ~10 yr long, unfiltered LINEAR light curve constrains the onset of the flare to a precision of ±5 days and enables us to place a lower limit on the peak optical magnitude. Difference imaging allows us to estimate the location of the flare in proximity of the host galaxy core. Comparison of the GALEX data (early 2006) with the recently acquired Swift UVOT (2015 June) and Mercator observations (2015 April) demonstrates a decrease in the UV flux over a ~10 yr period, confirming that the flare was UV-bright. The long-lived UV-bright emission, detected 1.8 rest-frame years after the start of the flare, strongly disfavors an SN origin. In conclusion, these new data allow us to conclude that the flare was indeed powered by the tidal disruption of a star by a supermassive black hole and that tidal disruption events are in fact capable of powering the enigmatic class of ECLEs.« less

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.

CONSTRAINING A MODEL OF TURBULENT CORONAL HEATING FOR AU MICROSCOPII WITH X-RAY, RADIO, AND MILLIMETER OBSERVATIONS

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

Cranmer, Steven R.; Wilner, David J.; MacGregor, Meredith A.

2013-08-01

Many low-mass pre-main-sequence stars exhibit strong magnetic activity and coronal X-ray emission. Even after the primordial accretion disk has been cleared out, the star's high-energy radiation continues to affect the formation and evolution of dust, planetesimals, and large planets. Young stars with debris disks are thus ideal environments for studying the earliest stages of non-accretion-driven coronae. In this paper we simulate the corona of AU Mic, a nearby active M dwarf with an edge-on debris disk. We apply a self-consistent model of coronal loop heating that was derived from numerical simulations of solar field-line tangling and magnetohydrodynamic turbulence. We alsomore » synthesize the modeled star's X-ray luminosity and thermal radio/millimeter continuum emission. A realistic set of parameter choices for AU Mic produces simulated observations that agree with all existing measurements and upper limits. This coronal model thus represents an alternative explanation for a recently discovered ALMA central emission peak that was suggested to be the result of an inner 'asteroid belt' within 3 AU of the star. However, it is also possible that the central 1.3 mm peak is caused by a combination of active coronal emission and a bright inner source of dusty debris. Additional observations of this source's spatial extent and spectral energy distribution at millimeter and radio wavelengths will better constrain the relative contributions of the proposed mechanisms.« less

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.

OSO 8 observational limits to the acoustic coronal heating mechanism

NASA Technical Reports Server (NTRS)

Bruner, E. C., Jr.

1981-01-01

An improved analysis of time-resolved line profiles of the C IV resonance line at 1548 A has been used to test the acoustic wave hypothesis of solar coronal heating. It is shown that the observed motions and brightness fluctuations are consistent with the existence of acoustic waves. Specific account is taken of the effect of photon statistics on the observed velocities, and a test is devised to determine whether the motions represent propagating or evanescent waves. It is found that on the average about as much energy is carried upward as downward such that the net acoustic flux density is statistically consistent with zero. The statistical uncertainty in this null result is three orders of magnitue lower than the flux level needed to heat the corona.

Evidence of suppressed heating of coronal loops rooted in opposite polarity sunspot umbrae

NASA Astrophysics Data System (ADS)

Tiwari, Sanjiv K.; Thalmann, Julia K.; Winebarger, Amy R.; Panesar, Navdeep K.; Moore, Ronald

2015-04-01

Observations of active region (AR) coronae in different EUV wavelengths reveal the presence of various loops at different temperatures. To understand the mechanisms that result in hotter or cooler loops, we study a typical bipolar AR, near solar disk center, which has moderate overall magnetic twist and at least one fully developed sunspot of each polarity. From AIA 193 and 94 A images we identify many clearly discernible coronal loops that connect opposite-polarity plage or a sunspot to a opposite-polarity plage region. The AIA 94 A images show dim regions in the umbrae of the spots. To see which coronal loops are rooted in a dim umbral area, we performed a non-linear force-free field (NLFFF) modeling using photospheric vector magnetic field measurements obtained with the Heliosesmic Magnetic Imager (HMI) onboard SDO. After validation of the NLFFF model by comparison of calculated model field lines and observed loops in AIA 193 and 94 A, we specify the photospheric roots of the model field lines. The model field then shows the coronal magnetic loops that arch from the dim umbral area of the positive-polarity sunspot to the dim umbral area of a negative-polarity sunspot. Because these coronal loops are not visible in any of the coronal EUV and X-ray images of the AR, we conclude they are the coolest loops in the AR. This result suggests that the loops connecting opposite polarity umbrae are the least heated because the field in umbrae is so strong that the convective braiding of the field is strongly suppressed.From this result, we further hypothesize that the convective freedom at the feet of a coronal loop, together with the strength of the field in the body of the loop, determines the strength of the heating. In particular, we expect the hottest coronal loops to have one foot in an umbra and the other foot in opposite-polarity penumbra or plage (coronal moss), the areas of strong field in which convection is not as strongly suppressed as in umbrae. Many transient, outstandingly bright, loops in the AIA 94 A movie of the AR do have this expected rooting pattern.

Dextroposition of the Heart

DTIC Science & Technology

2007-10-01

The atrial chamber that is connected to the inferior vena cava is typically the right atrium . The pulmonary veins typically empty into the left ...only “a left chest wall 6 cm scar consistent with surgical history.” The screening chest x-ray is presented below (Fig 1A). Technical limitations...Cardiac MRI images further define the internal cardiac anatomy. On a coronal bright blood MRI image (Fig. 1B; LA = left atrium ; LPA = left

The Triggering Mechanism of Quiet-Region Coronal Jet Eruptions: Flux Cancelation

NASA Technical Reports Server (NTRS)

Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.

2017-01-01

Coronal jets are frequent transient features on the Sun, observed in EUV and X-ray emissions. They occur in active regions, quiet Sun and coronal holes, and appear as a bright spire with base brightenings. Recent studies show that many coronal jets are driven by the eruption of a minifilament. Here we investigate the magnetic cause of jet-driving minifilament eruptions. We study ten randomly-found on-disk quiet-region coronal jets using SDO/AIA intensity images and SDO/HMI magnetograms. For all ten events, we track the evolution of photospheric magnetic flux in the jet-base region in EUV images and find that (a) a cool (transition-region temperature) minifilament is present prior to each jet eruption; (b) the pre-eruption minifilament resides above the polarity-inversion line between majority-polarity and minority-polarity magnetic flux patches; (c) the opposite-polarity flux patches converge and cancel with each other; (d) the cancelation between the majority-polarity and minority-polarity flux patches eventually destabilizes the field holding the minifilament to erupt outwards; (e) the envelope of the erupting field barges into ambient oppositely-directed far-reaching field and undergoes external reconnection (interchange reconnection); (f) the external reconnection opens the envelope field and the minifilament field inside, allowing reconnected-heated hot material and cool minifilament material to escape along the far-reaching field, producing the jet spire. In summary, we found that each of our ten jets resulted from a minifilament eruption following flux cancelation at the magnetic neutral line under the pre-eruption minifilament. These observations show that flux cancelation is usually the trigger of quiet-region coronal jet eruptions.

Measuring the Coronal Properties of IC 4329A with NuSTAR

NASA Technical Reports Server (NTRS)

Brenneman, L. W.; Madejski, G.; Fuerst, F.; Matt, G.; Elvis, M.; Harrison, F. A.; Ballantyne, D. R.; Boggs, S. E.; Christensen, F. E.; Craig, W. W.;

Coronal plasma development in wire-array z-pinches made of twisted-pairs

NASA Astrophysics Data System (ADS)

Hoyt, C. L.; Greenly, J. B.; Gourdain, P. A.; Knapp, P. F.; Pikuz, S. A.; Shelkovenko, T. A.; Hammer, D. A.; Kusse, B. R.

2009-11-01

We have investigated coronal and core plasma development in wire array z-pinches in which single fine wires are replaced by twisted-pairs (``cable'') on the 1 MA, 100 ns rise time COBRA pulsed power generator. X-ray radiography, employed to investigate dense wire core expansion, showed periodic axial nonuniformity and evidence for shock waves developing where the individual wire plasmas collide. Laser shadowgraphy images indicated that the axial instability properties of the coronal plasma are substantially modified from ordinary wire arrays. Cable mass per unit length, material and the twist wavelength were varied in order to study their effects upon the instability wavelength. Implosion uniformity and bright-spot formation, as well as magnetic topology evolution, have also been investigated using self-emission imaging, x-ray diagnostics and small B-dot probes, respectively. Results from the cable-array z-pinches will be compared with results from ordinary wire-array z-pinches. This research was supported by the SSAA program of the National Nuclear Security Administration under DOE Cooperative agreement DE-FC03-02NA00057.

Explosive plasma flows in a solar flare

NASA Technical Reports Server (NTRS)

Zarro, Dominic M.; Canfield, Richard C.; Metcalf, Thomas R.; Strong, Keith T.

1988-01-01

Solar Maximum Mission soft X-ray data and Sacramento Peak Observatory H-alpha observations are combined in a study of the impulsive phase of a solar flare. A blue asymmetry, indicative of upflows, was observed in the coronal Ca XIX line during the soft X-ray rise phase. A red asymmetry, indicative of downflows, was observed simultaneously in chromospheric H-alpha emitted from bright flare kernels during the period of hard X-ray emission. Combining the velocity data with a measurement of coronal electron density, it is shown that the impulsive phase momentum of upflowing soft X-ray-emitting plasma equalled that of the downflowing H-alpha-emitting plasma to within one order of magnitude. In particular, the momentum of the upflowing plasma was 2 x 10 to the 21st g cm/s while that of the downflowing plasma was 7 x 10 to the 21st g cm/s, with a factor of 2 uncertainty on each value. This equality supports the explosive chromospheric evaporation model of solar flares, in which a sudden pressure increase at the footprint of a coronal loop produces oppositely directed flows in the heated plasma.

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.

Dynamical and Physical Properties of a Post-Coronal Mass Ejection Current Sheet

NASA Technical Reports Server (NTRS)

Ko, Yuan-Kuen; Raymond, John C.; Lin, Jun; Lawrence, Gareth; Li, Jing; Fludra, Andrzej

2003-01-01

In the eruptive process of the Kopp-Pneuman type, the closed magnetic field is stretched by the eruption so much that it is usually believed to be " open " to infinity. Formation of the current sheet in such a configuration makes it possible for the energy in the coronal magnetic field to quickly convert into thermal and kinetic energies and cause significant observational consequences, such as growing postflare/CME loop system in the corona, separating bright flare ribbons in the chromosphere, and fast ejections of the plasma and the magnetic flux. An eruption on 2002 January 8 provides us a good opportunity to look into these observational signatures of and place constraints on the theories of eruptions. The event started with the expansion of a magnetic arcade over an active region, developed into a coronal mass ejection (CME), and left some thin streamer-like structures with successively growing loop systems beneath them. The plasma outflow and the highly ionized states of the plasma inside these streamer-like structures, as well as the growing loops beneath them, lead us to conclude that these structures are associated with a magnetic reconnection site, namely, the current sheet, of this eruptive process. We combine the data from the Ultraviolet Coronagraph Spectrometer, Large Angle and Spectrometric Coronagraph Experiment, EUV Imaging Telescope, and Coronal Diagnostic Spectrometer on board the Solar and Heliospheric Observatory, as well is from the Mauna Loa Solar Observatory Mark IV K-coronameter, to investigate the morphological and dynamical properties of this event, as well as the physical properties of the current sheet. The velocity and acceleration of the CME reached up to 1800 km/s and 1 km/sq s, respectively. The acceleration is found to occur mainly at the lower corona (<2.76 Solar Radius). The post-CME loop systems showed behaviors of both postflare loops (upward motion with decreasing speed) and soft X-ray giant arches (upward motion with constant speed, or acceleration) according to the definition of Svestka. In the current sheet, the presence of highly ionized ions, such as Fe(+17) and Ca(+13), suggests temperature as high as (3-4) x 10(exp 6) K, and the plasma outflows have speeds ranging from 300 to 650 km/s. Absolute elemental abundances in the current sheet show a strong first ionization potential effect and have values similar to those found in the active region streamers. The magnetic field strength in the vicinity of the current sheet is found to be of the order of 1 G.

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.

Multi-wavelength observations of the solar atmosphere from the August 21, 2017 total solar eclipse

NASA Astrophysics Data System (ADS)

Tomczyk, S.; Boll, A.; Bryans, P.; Burkepile, J.; Casini, R.; DeLuca, E.; Gibson, K. L.; Judge, P. G.; McIntosh, S. W.; Samra, J.; Sewell, S. D.

2017-12-01

We will conduct three experiments at the August 21, 2017 total solar eclipse that we call the Rosetta Stone experiments. First, we will obtain narrow-bandpass images at infrared wavelengths of the magnetically sensitive coronal emission lines of Fe IX 2855 nm, Mg VIII 3028 nm and Si IX 3935 nm with a FLIR thermal imager. Information on the brightness of these lines is important for identifying the optimal lines for coronal magnetometry. These images will also serve as context images for the airborne AirSpec IR coronal spectroscopy experiment (Samra et al). Second, we will obtain linear polarization images of the visible emission lines of Fe X 637 nm and Fe XI 789 nm as well as the continuum polarization near 735 nm. These will be obtained with a novel detector with an integral array of linear micro-polarizers oriented at four different angles that enable polarization images without the need for liquid crystals or rotating elements. These measurements will provide information on the orientation of magnetic fields in the corona and serve to demonstrate the new detector technology. Lastly, we will obtain high cadence spectra as the moon covers and uncovers the chromosphere immediately after 2nd contact and before third contact. This so-called flash spectrum will be used to obtain information about chromospheric structure at a spatial resolution higher than is possible by other means. In this talk, we will describe the instrumentation used in these experiments and present initial results obtained with them. This work is supported by a grant from NASA, through NSF base funding of HAO/NCAR and by generous loans of equipment from our corporate partners, FLIR, 4D Technologies and Avantes.

Microfilament-Eruption Mechanism for Solar Spicules

NASA Technical Reports Server (NTRS)

Sterling, Alphonse C.; Moore, Ronald L.

2017-01-01

Recent studies indicate that solar coronal jets result from eruption of small-scale filaments, or "minifilaments" (Sterling et al. 2015, Nature, 523, 437; Panesar et al. ApJL, 832L, 7). In many aspects, these coronal jets appear to be small-scale versions of long-recognized large-scale solar eruptions that are often accompanied by eruption of a large-scale filament and that produce solar flares and coronal mass ejections (CMEs). In coronal jets, a jet-base bright point (JBP) that is often observed to accompany the jet and that sits on the magnetic neutral line from which the minifilament erupts, corresponds to the solar flare of larger-scale eruptions that occurs at the neutral line from which the large-scale filament erupts. Large-scale eruptions are relatively uncommon (approximately 1 per day) and occur with relatively large-scale erupting filaments (approximately 10 (sup 5) kilometers long). Coronal jets are more common (approximately 100s per day), but occur from erupting minifilaments of smaller size (approximately 10 (sup 4) kilometers long). It is known that solar spicules are much more frequent (many millions per day) than coronal jets. Just as coronal jets are small-scale versions of large-scale eruptions, here we suggest that solar spicules might in turn be small-scale versions of coronal jets; we postulate that the spicules are produced by eruptions of "microfilaments" of length comparable to the width of observed spicules (approximately 300 kilometers). A plot of the estimated number of the three respective phenomena (flares/CMEs, coronal jets, and spicules) occurring on the Sun at a given time, against the average sizes of erupting filaments, minifilaments, and the putative microfilaments, results in a size distribution that can be fitted with a power-law within the estimated uncertainties. The counterparts of the flares of large-scale eruptions and the JBPs of jets might be weak, pervasive, transient brightenings observed in Hinode/CaII images, and the production of spicules by microfilament eruptions might explain why spicules spin, as do coronal jets. The expected small-scale neutral lines from which the microfilaments would be expected to erupt would be difficult to detect reliably with current instrumentation, but might be apparent with instrumentation of the near future. A full report on this work appears in Sterling and Moore 2016, ApJL, 829, L9.

EUV Waves Driven by the Sudden Expansion of Transequatorial Loops Caused by Coronal Jets

NASA Astrophysics Data System (ADS)

Shen, Yuandeng; Tang, Zehao; Miao, Yuhu; Su, Jiangtao; Liu, Yu

2018-06-01

We present two events to study the driving mechanism of extreme-ultraviolet (EUV) waves that are not associated with coronal mass ejections (CMEs), by using high-resolution observations taken by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. Observational results indicate that the observed EUV waves were accompanied by flares and coronal jets, but not the CMEs that were regarded as drivers of most EUV waves in previous studies. In the first case, it is observed that a coronal jet is ejected along a transequatorial loop system at a plane-of-the-sky (POS) speed of 335 ± 22 km s{}-1; in the meantime, an arc-shaped EUV wave appeared on the eastern side of the loop system. In addition, the EUV wave further interacted with another interconnecting loop system and launched a fast propagating (QFP) magnetosonic wave along the loop system, which had a period of 200 s and a speed of 388 ± 65 km s{}-1, respectively. In the second case, we observed a coronal jet that ejected at a POS speed of 282 ± 44 km s{}-1 along a transequatorial loop system as well as the generation of bright EUV waves on the eastern side of the loop system. Based on the observational results, we propose that the observed EUV waves on the eastern side of the transequatorial loop systems are fast-mode magnetosonic waves and that they are driven by the sudden lateral expansion of the transequatorial loop systems due to the direct impingement of the associated coronal jets, while the QFP wave in the fist case formed due to the dispersive evolution of the disturbance caused by the interaction between the EUV wave and the interconnecting coronal loops. It is noted that EUV waves driven by sudden loop expansions have shorter lifetimes than those driven by CMEs.

Solar Hard X-ray Observations with NuSTAR

NASA Astrophysics Data System (ADS)

Smith, David M.; Krucker, S.; Hudson, H. S.; Hurford, G. J.; White, S. M.; Mewaldt, R. A.; Stern, D.; Grefenstette, B. W.; Harrison, F. A.

2011-05-01

High-sensitivity imaging of coronal hard X-rays allows detection of freshly accelerated nonthermal electrons at the acceleration site. A few such observations have been made with Yohkoh and RHESSI, but a leap in sensitivity could help pin down the time, place, and manner of reconnection. In 2012, the Nuclear Spectroscopic Telescope Array (NuSTAR), a NASA Small Explorer for high energy astrophysics that uses grazing-incidence optics to focus X-rays up to 80 keV, will be launched. NuSTAR is capable of solar pointing, and three weeks will be dedicated to solar observing during the baseline two-year mission. NuSTAR will be 200 times more sensitive than RHESSI in the hard X-ray band. This will allow the following new observations, among others: 1) Extrapolation of the micro/nanoflare distribution by two orders of magnitude down in flux 2) Search for hard X-rays from network nanoflares (soft X-ray bright points) and evaluation of their role in coronal heating 3) Discovery of hard X-ray bremsstrahlung from the electron beams driving type III radio bursts, and measurement of their electron spectrum 4) Hard X-ray studies of polar soft X-ray jets and impulsive solar energetic particle events at the edge of coronal holes, and comparison of these events with observations of 3He and other particles in interplanetary space 5) Study of coronal bremsstrahlung from particles accelerated by coronal mass ejections as they are first launched 6) Study of particles at the coronal reconnection site when flare footpoints are occulted; and 7) Search for hypothetical axion particles created in the solar core via the hard X-ray signal from their conversion to X-rays in the coronal magnetic field. NuSTAR will also serve as a pathfinder for a future dedicated space mission with enhanced capabilities, such as a satellite version of the FOXSI sounding rocket.

The Large-scale Coronal Structure of the 2017 August 21 Great American Eclipse: An Assessment of Solar Surface Flux Transport Model Enabled Predictions and Observations

NASA Astrophysics Data System (ADS)

Nandy, Dibyendu; Bhowmik, Prantika; Yeates, Anthony R.; Panda, Suman; Tarafder, Rajashik; Dash, Soumyaranjan

2018-01-01

On 2017 August 21, a total solar eclipse swept across the contiguous United States, providing excellent opportunities for diagnostics of the Sun’s corona. The Sun’s coronal structure is notoriously difficult to observe except during solar eclipses; thus, theoretical models must be relied upon for inferring the underlying magnetic structure of the Sun’s outer atmosphere. These models are necessary for understanding the role of magnetic fields in the heating of the corona to a million degrees and the generation of severe space weather. Here we present a methodology for predicting the structure of the coronal field based on model forward runs of a solar surface flux transport model, whose predicted surface field is utilized to extrapolate future coronal magnetic field structures. This prescription was applied to the 2017 August 21 solar eclipse. A post-eclipse analysis shows good agreement between model simulated and observed coronal structures and their locations on the limb. We demonstrate that slow changes in the Sun’s surface magnetic field distribution driven by long-term flux emergence and its evolution governs large-scale coronal structures with a (plausibly cycle-phase dependent) dynamical memory timescale on the order of a few solar rotations, opening up the possibility for large-scale, global corona predictions at least a month in advance.

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.

EUV brightness variations in the quiet Sun

NASA Astrophysics Data System (ADS)

Brković, A.; Rüedi, I.; Solanki, S. K.; Fludra, A.; Harrison, R. A.; Huber, M. C. E.; Stenflo, J. O.; Stucki, K.

2000-01-01

The Coronal Diagnostic Spectrometer (CDS) onboard the SOHO satellite has been used to obtain movies of quiet Sun regions at disc centre. These movies were used to study brightness variations of solar features at three different temperatures sampled simultaneously in the chromospheric He I 584.3 Ä (2 * 104 K), the transition region O V 629.7 Ä (2.5 * 105 K) and coronal Mg IX 368.1 Ä (106 K) lines. In all parts of the quiet Sun, from darkest intranetwork to brightest network, we find significant variability in the He I and O V line, while the variability in the Mg IX line is more marginal. The relative variability, defined by rms of intensity normalised to the local intensity, is independent of brightness and strongest in the transition region line. Thus the relative variability is the same in the network and the intranetwork. More than half of the points on the solar surface show a relative variability, determined over a period of 4 hours, greater than 15.5% for the O V line, but only 5% of the points exhibit a variability above 25%. Most of the variability appears to take place on time-scales between 5 and 80 minutes for the He I and O V lines. Clear signs of ``high variability'' events are found. For these events the variability as a function of time seen in the different lines shows a good correlation. The correlation is higher for more variable events. These events coincide with the (time averaged) brightest points on the solar surface, i.e. they occur in the network. The spatial positions of the most variable points are identical in all the lines.

A magnetohydrodynamic theory of coronal loop transients

NASA Technical Reports Server (NTRS)

Yeh, T.

1982-01-01

The physical and geometrical characteristics of solar coronal loop transients are described in an MHD model based on Archimedes' MHD buoyancy force. The theory was developed from interpretation of coronagraphic data, particularly from Skylab. The brightness of a loop is taken to indicate the electron density, and successive pictures reveal the electron enhancement in different columns. The forces which lift the loop off the sun surface are analyzed as an MHD buoyancy force affecting every mass element by imparting an inertial force necessary for heliocentrifugal motion. Thermal forces are responsible for transferring the ambient stress to the interior of the loop to begin the process. The kinematic and hydrostatic buoyancy overcome the gravitational force, and a flux rope can then curve upward, spiralling like a corkscrew with varying cross section around the unwinding solar magnetic field lines.

Relations Between FUV Excess and Coronal Soft X-Ray Emission Among Dwarf Stars

NASA Astrophysics Data System (ADS)

Smith, Graeme H.; Hargrave, Mason; Eckholm, Elliot

2017-11-01

The far-ultraviolet magnitudes of late-F, G and early-K dwarfs with (B - V) ⩾ 0.50 as measured by the GALEX satellite are shown to correlate with soft X-ray luminosity. This result indicates that line and continuum emission from stellar active regions make significant contributions to the flux in the GALEX FUV band for late-F, G and K dwarfs. By contrast, detection of a correlation between FUV brightness and soft X-ray luminosity among early-F dwarfs requires subtraction of the photospheric component from the FUV flux. The range in (B - V) among F and G dwarfs over which a correlation between uncorrected FUV magnitude and X-ray luminosity is detected coincides with the range in colour over which coronal and chromospheric emission correlates with stellar rotation.

A Closer Look at the Alpha Persei Coronal Conundrum

NASA Astrophysics Data System (ADS)

Ayres, Thomas R.

2017-03-01

A ROSAT survey of the Alpha Per open cluster in 1993 detected its brightest star, the mid-F supergiant α Persei: the X-ray luminosity and spectral hardness were similar to coronally active late-type dwarf members. Later, in 2010, a Hubble Cosmic Origins Spectrograph SNAPshot of α Per found the far-ultraviolet (FUV) coronal-proxy Si IV unexpectedly weak. This, and a suspicious offset of the ROSAT source, suggested that a late-type companion might be responsible for the X-rays. Recently, a multifaceted program tested that premise. Ground-based optical coronography and near-UV imaging with Hubble Space Telescope (HST) Wide-Field Camera 3 searched for any close-in faint candidate coronal objects, but without success. Then, a Chandra pointing found the X-ray source single and coincident with the bright star. Significantly, the Si IV emissions of α Per, in a deeper FUV spectrum collected by the HST Cosmic Origin Spectrograph as part of the joint program, are aligned well with chromospheric atomic oxygen (which must be intrinsic to the luminous star), within the context of cooler late-F and early-G supergiants, including Cepheid variables. This pointed to the X-rays as the fundamental anomaly. The overluminous X-rays still support the case for a hyperactive dwarf secondary, albeit now spatially unresolved. However, an alternative is that α Per represents a novel class of coronal source. Resolving the first possibility now has become more difficult, because the easy solution—a well-separated companion—has been eliminated. Testing the other possibility will require a broader high-energy census of the early-F supergiants.

Numerical modeling of coronal mass ejections based on various pre-event model atmospheres

NASA Technical Reports Server (NTRS)

Suess, S. T.; Wang, A. H.; Wu, S. T.; Poletto, G.

1994-01-01

We examine how the initial state (pre-event corona) affects the numerical MHD simulation for a coronal mass ejection (CME). Earlier simulations based on a pre-event corona with a homogeneous density and temperature distribution at lower boundary (i.e. solar surface) have been used to analyze the role of streamer properties in determining the characteristics of loop-like transients. The present paper extends these studies to show how a broader class of global coronal properties leads not only to different types of CME's, but also modifies the adjacent quiet corona and/or coronal holes. We consider four pre-event coronal cases: (1) Constant boundary conditions and a polytropic gas with gamma = 1.05; (2) Non-constant (latitude dependent) boundary conditions and a polytropic gas with gamma = 1.05; (3) Constant boundary conditions with a volumetric energy source and gamma = 1.67; (4) Non-constant (latitude dependent) boundary conditions with a volumetric energy source and gamma = 1.67. In all models, the pre-event magnetic fields separate the corona into closed field regions (streamers) and open field regions. The CME's initiation is simulated by introducing at the base of the corona, within the streamer region, a standard pressure pulse and velocity change. Boundary values are determined using MHD characteristic theory. The simulations show how different CME's, including loop-like transients, clouds, and bright rays, might occur. There are significant new features in comparison to published results. We conclude that the pre-event corona is a crucial factor in dictating CME's properties.

Numerical Modeling of Coronal Mass Ejections Based on Various Pre-event Model Atmospheres

NASA Technical Reports Server (NTRS)

Wang, A. H.; Wu, S. T.; Suess, S. T.; Poletto, G.

1995-01-01

We examine how the initial state (pre-event corona) affects the numerical MHD simulation for a coronal mass ejection (CME). Earlier simulations based on a pre-event corona with a homogeneous density and temperature distribution, at the lower boundary (i.e., solar surface) have been used to analyze the role of streamer properties in determining the characteristics of loop-like transients. The present paper extends these studies to show how a broader class of global coronal properties leads not only to different types of CME's, but also modifies the adjacent quiet corona and/or coronal holes. We consider four pre-event coronal cases: (1) constant boundary conditions and a polytropic gas with gamma = 1.05; (2) non-constant (latitude dependent) boundary conditions and a polytropic gas with gamma = 1.05; (3) constant boundary conditions with a volumetric energy source and gamma = 1.67; (4) non-constant (latitude dependent) boundary conditions with a volumetric energy source and gamma = 1.67. In all models, the pre-event magnetic fields separate the corona into closed field regions (streamers) and open field regions. The CME's initiation is simulated by introducing at the base of the corona, within the streamer region, a standard pressure pulse and velocity change. Boundary values are determined using magnetohydrodynamic (MHD) characteristic theory. The simulations show how different CME's, including loop-like transients, clouds and bright rays, might occur. There are significant new features in comparison to published results. We conclude that the pre-event corona is a crucial factor in dictating CME's properties.

Chasing the Great American 2017 Total Solar Eclipse: Coronal Results from NASA's WB-57F High-Altitude Research Aircraft

NASA Astrophysics Data System (ADS)

Caspi, A.; Tsang, C.; DeForest, C. E.; Seaton, D. B.; Bryans, P.; Burkepile, J.; Casey, T. A.; Collier, J.; Darrow, D.; DeLuca, E.; Durda, D. D.; Gallagher, P.; Golub, L.; Judge, P. G.; Laurent, G. T.; Lewis, J.; Mallini, C.; Parent, T.; Propp, T.; Steffl, A.; Tomczyk, S.; Warner, J.; West, M. J.; Wiseman, J.; Zhukov, A.

2017-12-01

Total solar eclipses present rare opportunities to study the complex solar corona, down to altitudes of just a few percent of a solar radius above the surface, using ground-based and airborne observatories that would otherwise be dominated by the intense solar disk and high sky brightness. Studying the corona is critical to gaining a better understanding of physical processes that occur on other stars and astrophysical objects, as well as understanding the dominant driver of space weather that affects human assets at Earth and elsewhere. For example, it is still poorly understood how the corona is heated to temperatures of 1-2 MK globally and up to 5-10 MK above active regions, while the underlying chromosphere is 100 times cooler; numerous theories abound, but are difficult to constrain due to the limited sensitivities and cadences of prior measurements. The origins and stability of coronal fans, and the extent of their reach to the middle and outer corona, are also not well known, limited in large part by sensitivities and fields of view of existing observations. Airborne observations during the eclipse provide unique advantages; by flying in the stratosphere at altitudes of 50 kft or higher, they avoid all weather, the seeing quality is enormously improved, and additional wavelengths such as near- IR also become available due to significantly reduced water absorption. For an eclipse, an airborne observatory can also follow the shadow, increasing the total observing time by 50% or more. We present results of solar coronal measurements from airborne observations of the 2017 Great American Total Solar Eclipse using two of NASA's WB-57 high-altitude research aircraft, each equipped with two 8.7" telescopes feeding high-sensitivity visible (green-line) and medium-wave IR (3-5 μm) cameras operating at high cadence (30 Hz) with 3 arcsec/pixel platescale and ±3 R_sun fields of view. The aircraft flew along the eclipse path, separated by 110 km, to observe a summed 7.5 minutes of totality in both visible and NIR, enabling groundbreaking studies of high-speed wave motions and nanojets in the lower corona, the structure and extent of coronal fans, and constraints on a potential primordial dust ring around the Sun. We review the mission, and the results of analysis on the visible and IR coronal measurements.

Detection of 17 GHz radio emission from X-ray-bright points

NASA Technical Reports Server (NTRS)

Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N.

1994-01-01

Using observations made with the Nobeyama radio heliograph (NRH) at 17 GHz and the Yohkoh/SXT experiment, we report the first detection of 17 GHz signatures of coronal X-ray-bright points (XBPs). This is also the first reported detection of flaring bright points in microwaves. We have detected four BPs at 17 GHz out of eight identified in SXT data on 1992 July 31, for which we looked for 17 GHz emission. For one XBP located in a quiet mixed-polarity region, the peak times at 17 GHz and X-rays are very similar, and both are long-lasting-about 2 hr in duration. There is a second BP (located near an active region) which is most likely flaring also, but the time profiles in the two spectral domains are not similar. The other two 17 GHz BPs are quiescent with fluctuations superposed upon them. For the quiet region XBP, the gradual, long-lasting, and unpolarized emission suggests that the 17 GHz emission is thermal.

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.

A Magnetic Reconnection Event in the Solar Atmosphere Driven by Relaxation of a Twisted Arch Filament System

NASA Astrophysics Data System (ADS)

Huang, Zhenghua; Mou, Chaozhou; Fu, Hui; Deng, Linhua; Li, Bo; Xia, Lidong

2018-02-01

We present high-resolution observations of a magnetic reconnection event in the solar atmosphere taken with the New Vacuum Solar Telescope, Atmospheric Imaging Assembly (AIA), and Helioseismic and Magnetic Imager (HMI). The reconnection event occurred between the threads of a twisted arch filament system (AFS) and coronal loops. Our observations reveal that the relaxation of the twisted AFS drives some of its threads to encounter the coronal loops, providing inflows of the reconnection. The reconnection is evidenced by flared X-shape features in the AIA images, a current-sheet-like feature apparently connecting post-reconnection loops in the Hα + 1 Å images, small-scale magnetic cancelation in the HMI magnetograms and flows with speeds of 40–80 km s‑1 along the coronal loops. The post-reconnection coronal loops seen in the AIA 94 Å passband appear to remain bright for a relatively long time, suggesting that they have been heated and/or filled up by dense plasmas previously stored in the AFS threads. Our observations suggest that the twisted magnetic system could release its free magnetic energy into the upper solar atmosphere through reconnection processes. While the plasma pressure in the reconnecting flux tubes are significantly different, the reconfiguration of field lines could result in transferring of mass among them and induce heating therein.

Coronal structures deduced from photospheric magnetic field and He I lambda 10830 observations

NASA Technical Reports Server (NTRS)

Harvey, Karen L.

1995-01-01

The National Solar Observatory synoptic program provides an extensive and unique data base of high-resolution full-disk observations of the line-of-sight photospheric magnetic fields and of the He I lambda 10830 equivalent width. These data have been taken nearly daily for more than 21 years since 1974 and provide the opportunity to investigate the behavior of the magnetic fields in the photosphere and those inferred for the corona spanning on the time scales of a day to that of a solar cycle. The intensity of structures observed in He I lambda 10830 are strongly modulated by overlying coronal radiation; areas with low coronal emission are generally brighter in He I lambda 10830, while areas with high coronal emission are darker. For this reason, He I lambda 10830 was selected in the mid-1970's as way to identify and monitor coronal holes, magnetic fields with an open configuration, and the sources of high-speed solar wind streams. The He I lambda 10830 spectroheliograms also show a wide variety of other structures from small-scale, short-lived dark points (less than 30 arc-sec, hours) to the large-scale, long-lived two 'ribbon' flare events that follow the filament eruptions (1000 arc-sec, days). Such structures provide clues about the connections and changes in the large-scale coronal magnetic fields that are rooted in concentrations of magnetic network and active regions in the photosphere. In this paper, what observations of the photospheric magnetic field and He I lambda 10830 can tell us about the short- and long-term evolution of the coronal magnetic fields will be discussed, focussing on the quiet Sun and coronal holes. These data and what we infer from them will be compared with direct observations of the coronal structure from the Yohkoh Soft X-ray Telescope.

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.

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

Howard, T. A., E-mail: howard@boulder.swri.edu

The physical properties of eruptive prominences are unknown at large distances from the Sun. They are rarely, if ever, measured by in situ spacecraft and until recently our ability to measure them beyond the fields of view of solar imagers has been severely limited. The data quality of heliospheric imaging has reached a point where some quantitative measurements of prominences are now possible. I present the first such measurements of a bright prominence continually out to distances of around 1 AU from the Sun. This work follows on from the preparatory work presented in an accompanying paper, which showed thatmore » that the brightness of a prominence can be safely assumed to arise entirely from Thomson scattering in the STEREO/HI fields of view. Measurements of distance, speed, and mass are provided along with those from its accompanying coronal mass ejection (CME) to demonstrate their geometric, kinematic, and mass relationships. I find that the prominence travels with a slower speed than that of the CME, but its location relative to the CME structure does not conform to the expected location for basic geometric expansion. Further, the mass of the prominence was found to decrease by around an order of magnitude while that of the CME increased by an order of magnitude across the same distance.« less

Ion Traps at the Sun: Implications for Elemental Fractionation

NASA Astrophysics Data System (ADS)

Fleishman, Gregory D.; Musset, Sophie; Bommier, Véronique; Glesener, Lindsay

2018-04-01

Why the tenuous solar outer atmosphere, or corona, is much hotter than the underlying layers remains one of the greatest challenges for solar modeling. Detailed diagnostics of the coronal thermal structure come from extreme ultraviolet (EUV) emission. The EUV emission is produced by heavy ions in various ionization states and depends on the amount of these ions and on plasma temperature and density. Any nonuniformity of the elemental distribution in space or variability in time affects thermal diagnostics of the corona. Here we theoretically predict ionized chemical element concentrations in some areas of the solar atmosphere, where the electric current is directed upward. We then detect these areas observationally, by comparing the electric current density with the EUV brightness in an active region. We found a significant excess in EUV brightness in the areas with positive current density rather than negative. Therefore, we report the observational discovery of substantial concentrations of heavy ions in current-carrying magnetic flux tubes, which might have important implications for the elemental fractionation in the solar corona known as the first ionization potential effect. We call such areas of heavy ion concentration the “ion traps.” These traps hold enhanced ion levels until they are disrupted by a flare, whether large or small.

Infrared coronal emission lines and the possibility of their maser emission in Seyfert nuclei

NASA Technical Reports Server (NTRS)

Greenhouse, Matthew A.; Feldman, Uri; Smith, Howard A.; Klapisch, Marcel; Bhatia, Anand K.; Bar-Shalom, Abi

1993-01-01

Energetic emitting regions have traditionally been studied via x-ray, UV and optical emission lines of highly ionized intermediate mass elements. Such lines are often referred to as 'coronal lines' since the ions, when produced by collisional ionization, reach maximum abundance at electron temperatures of approx. 10(exp 5) - 10(exp 6) K typical of the sun's upper atmosphere. However, optical and UV coronal lines are also observed in a wide variety of Galactic and extragalactic sources including the Galactic interstellar medium, nova shells, supernova remnants, galaxies and QSOs. Infrared coronal lines are providing a new window for observation of energetic emitting regions in heavily dust obscured sources such as infrared bright merging galaxies and Seyfert nuclei and new opportunities for model constraints on physical conditions in these sources. Unlike their UV and optical counterparts, infrared coronal lines can be primary coolants of collisionally ionized plasmas with 10(exp 4) less than T(sub e)(K) less than 10(exp 6) which produce little or no optical or shorter wavelength coronal line emission. In addition, they provide a means to probe heavily dust obscured emitting regions which are often inaccessible to optical or UV line studies. In this poster, we provide results from new model calculations to support upcoming Infrared Space Observatory (ISO) and current ground-based observing programs involving infrared coronal emission lines in AGN. We present a complete list of infrared (lambda greater than 1 micron) lines due to transitions within the ground configurations 2s(2)2p(k) and 3s(2)3p(k) (k = 1 to 5) or the first excited configurations 2s2p and 3s3p of highly ionized (x greater than or equal to 100 eV) astrophysically abundant (n(X)/n(H) greater than or equal to 10(exp -6)) elements. Included are approximately 74 lines in ions of O, Ne, Na, Mg, Al, Si, S, Ar, Ca, Fe, and Ni spanning a wavelength range of approximately 1 - 280 microns. We present new results from detailed balance calculations, new critical densities for collisional de-excitation, intrinsic photon rates, branching ratios, and excitation temperatures for the majority of the compiled transitions. The temperature and density parameter space for dominant cooling via infrared coronal lines is presented, and the relationship of infrared to optical coronal lines is discussed.

AN ERUPTIVE HOT-CHANNEL STRUCTURE OBSERVED AT METRIC WAVELENGTH AS A MOVING TYPE-IV SOLAR RADIO BURST

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

Vasanth, V.; Chen, Yao; Feng, Shiwei

2016-10-10

Hot-channel (HC) structure, observed in the high-temperature passbands of the Atmospheric Imaging Assembly/ Solar Dynamic Observatory , is regarded as one candidate of coronal flux rope that is an essential element of solar eruptions. Here, we present the first radio imaging study of an HC structure in the metric wavelength. The associated radio emission manifests as a moving type-IV (t-IVm) burst. We show that the radio sources co-move outward with the HC, indicating that the t-IV emitting energetic electrons are efficiently trapped within the structure. The t-IV sources at different frequencies present no considerable spatial dispersion during the early stagemore » of the event, while the sources spread gradually along the eruptive HC structure at later stage with significant spatial dispersion. The t-IV bursts are characterized by a relatively high brightness temperature (∼10{sup 7}–10{sup 9} K), a moderate polarization, and a spectral shape that evolves considerably with time. This study demonstrates the possibility of imaging the eruptive HC structure at the metric wavelength and provides strong constraints on the t-IV emission mechanism, which, if understood, can be used to diagnose the essential parameters of the eruptive structure.« less

Oscillations in the wake of a flare blast wave

NASA Astrophysics Data System (ADS)

Tothova, D.; Innes, D. E.; Stenborg, G.

2011-04-01

Context. Oscillations of coronal loops in the Sun have been reported in both imaging and spectral observations at the onset of flares. Images reveal transverse oscillations, whereas spectra detect line-of-sight velocity or Doppler-shift oscillations. The Doppler-shift oscillations are commonly interpreted as longitudinal modes. Aims: Our aim is to investigate the relationship between loop dynamics and flows seen in TRACE 195 Å images and Doppler shifts observed by SUMER in Si iii 1113.2 Å and FeXIX 1118.1 Å at the time of a C.8-class limb flare and an associated CME. Methods: We carefully co-aligned the sequence of TRACE 195 Å images to structures seen in the SUMER Si iii, CaX, and FeXIX emission lines. Additionally, Hα observations of a lifting prominence associated with the flare and the coronal mass ejection (CME) are available in three bands around 6563.3 Å. They give constraints on the timing and geometry. Results: Large-scale Doppler-shift oscillations in FeXIX and transverse oscillations in intensity images were observed over a large region of the corona after the passage of a wide bright extreme-ultraviolet (EUV) disturbance, which suggests ionization, heating, and acceleration of hot plasma in the wake of a blast wave. The online movie associated to Fig. 2 is available at http://www.aanda.org and at http://www.mps.mpg.de/data/outgoing/tothova/movie.gif

Far-Side Halo Outburst

NASA Image and Video Library

2017-12-08

The Sun blew out a powerful coronal mass ejection (CME) from just around the edge of the Sun (Oct. 14, 2014). The particle cloud expanded around all the Sun in a rough circle, hence the name 'halo' CME. This event was also associated with a fairly strong flare. The active region that was the source of these events is just rotating into view. Then, we can better observe its size and structure. The bright object to the right and just above the Sun is Venus now on the far side of the Sun. Credit: NASA/ESA/SOHO NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Buildup of a highly twisted magnetic flux rope during a solar eruption.

PubMed

Wang, Wensi; Liu, Rui; Wang, Yuming; Hu, Qiang; Shen, Chenglong; Jiang, Chaowei; Zhu, Chunming

2017-11-06

The magnetic flux rope is among the most fundamental magnetic configurations in plasma. Although its presence after solar eruptions has been verified by spacecraft measurements near Earth, its formation on the Sun remains elusive, yet is critical to understanding a broad spectrum of phenomena. Here we study the dynamic formation of a magnetic flux rope during a classic two-ribbon flare. Its feet are identified unambiguously with conjugate coronal dimmings completely enclosed by irregular bright rings, which originate and expand outward from the far ends of flare ribbons. The expansion is associated with the rapid ribbon separation during the flare main phase. Counting magnetic flux through the feet and the ribbon-swept area reveals that the rope's core is more twisted than its average of four turns. It propagates to the Earth as a typical magnetic cloud possessing a similar twist profile obtained by the Grad-Shafranov reconstruction of its three dimensional structure.

Buildup of a highly twisted magnetic flux rope during a solar eruption

NASA Astrophysics Data System (ADS)

Wang, Wensi; Liu, Rui; Wang, Yuming; Hu, Qiang; Shen, Chenglong; Jiang, Chaowei; Zhu, Chunming

2017-11-01

The magnetic flux rope is among the most fundamental magnetic configurations in plasma. Although its presence after solar eruptions has been verified by spacecraft measurements near Earth, its formation on the Sun remains elusive, yet is critical to understanding a broad spectrum of phenomena. Here we study the dynamic formation of a magnetic flux rope during a classic two-ribbon flare. Its feet are identified unambiguously with conjugate coronal dimmings completely enclosed by irregular bright rings, which originate and expand outward from the far ends of flare ribbons. The expansion is associated with the rapid ribbon separation during the flare main phase. Counting magnetic flux through the feet and the ribbon-swept area reveals that the rope's core is more twisted than its average of four turns. It propagates to the Earth as a typical magnetic cloud possessing a similar twist profile obtained by the Grad-Shafranov reconstruction of its three dimensional structure.

Unique Blasting

NASA Image and Video Library

2017-12-08

The Sun blasted out five coronal mass ejections (CMEs) over about two days (Feb. 26-28, 2013) and each one had quite a different shape and structure, seen here in a video bit.ly/Za8Aso. The most interesting one (seen above) blew out to the right with a bright, elongated center, likely part of a solar filament, that maintained its curly-Q shape as it expanded out of view. The images were taken by SOHO LASCO C2 coronagraph. The Sun is represented by the white circle and the red disk blocks out the Sun and part of the corona. Credit: NASA/Goddard/SOHO NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

ESCAPE : a first step to high resolution solar coronagraphy in Antarctica

NASA Astrophysics Data System (ADS)

Damé, L.; Abe, L.; Faurobert, M.; Fineschi, S.; Kuzin, S.; Lamy, P.; Meftah, M.; Vives, S.

2012-06-01

The Dome C high plateau is unique for coronagraphic observations: sky brightness is reduced, water vapour is low, seeing is excellent and continuity of observations on several weeks is possible. ESCAPE (the Extreme Solar Coronagraphy Antarctic Program Experiment) will perform 2-dimensional spectroscopy of the forbidden line of FeXIV at 530.285 nm: precise line profile analysis will allow the diagnostic of the nature of waves by simultaneous measurements of velocities and intensities in the corona. ESCAPE is proposed to Institut Paul-Emile Victor (IPEV) for a campaign in 2012-2013 at Dome C/Concordia since all subsystems are available in particular thanks to an ESA STARTIGER 2010 R&D "Toward a New Generation of Formation Flying Coronagraph". Using state-of-the-art technologies developed for Space missions (a Three Mirrors Anastigmat telescope, the TMA, a 4 stages Liquid Crystal Tunable-filter Polarimeter, the LCTP) allows us to propose an automated Coronal Green Line full-field Polarimeter for unique observations (waves nature and intensity to address coronal heating) with the best possible performances on Earth and for preparing and testing the technologies for the next steps in Space. No other site would allow such coronagraphic performances (the sky brightness is a factor 2 to 4 better than in Hawaï) and with high spatial resolution (better than an arcsec is possible).

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.

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.

Examining the Properties of Jets in Coronal Holes

NASA Technical Reports Server (NTRS)

Gaulle, Owen; Adams, Mitzi L.; Tennant, A. F.

2012-01-01

Data from the Solar Dynamics Observatory (SDO) were used to look for triggers of jets in a coronal hole. It has been proposed that bright points affiliated with the jets are caused by either random collisions between magnetic elements or by magnetic flux emerging from the photosphere; either of which can give rise to magnetic reconnection. Images from the 193AA filter of the Atmospheric Imaging Assembly (AIA) were searched to identify and locate jets. Changes in the line-of-sight magnetic field prior to the time of the jet were sought in data from the Helioseismic Magnetic Imager (HMI). In total we studied 15 different jets that occurred over a two day period starting 2011-02-27 00:00:00 UTC and ending 2011-02-28 23:59:55 UTC. All of the jets were contained within a coronal hole that was close to disk center. Of the 15 that we studied 6 were shown to have an increase of the parameter B2 (where B is the line-of-sight component of the magnetic field), within one hour prior to the creation of the jet and 10 were within 3 hours before the event.

Blowout Surge due to Interaction between a Solar Filament and Coronal Loops

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

Li, Haidong; Jiang, Yunchun; Yang, Jiayan

2017-06-20

We present an observation of the interaction between a filament and the outer spine-like loops that produces a blowout surge within one footpoint of large-scale coronal loops on 2015 February 6. Based the observation of the AIA 304 and 94 Å, the activated filament is initially embedded below a dome of a fan-spine configuration. Due to the ascending motion, the erupting filament reconnects with the outer spine-like field. We note that the material in the filament blows out along the outer spine-like field to form the surge with a wider spire, and a two-ribbon flare appears at the site ofmore » the filament eruption. In this process, small bright blobs appear at the interaction region and stream up along the outer spine-like field and down along the eastern fan-like field. As a result, a leg of the filament becomes radial and the material in it erupts, while another leg forms the new closed loops. Our results confirm that the successive reconnection occurring between the erupting filament and the coronal loops may lead to a strong thermal/magnetic pressure imbalance, resulting in a blowout surge.« less

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.

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.

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.

A Closer Look at the Alpha Persei Coronal Conundrum

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

Ayres, Thomas R., E-mail: Thomas.Ayres@Colorado.edu

2017-03-01

A ROSAT survey of the Alpha Per open cluster in 1993 detected its brightest star, the mid-F supergiant α Persei: the X-ray luminosity and spectral hardness were similar to coronally active late-type dwarf members. Later, in 2010, a Hubble Cosmic Origins Spectrograph SNAPshot of α Per found the far-ultraviolet (FUV) coronal-proxy Si iv unexpectedly weak. This, and a suspicious offset of the ROSAT source, suggested that a late-type companion might be responsible for the X-rays. Recently, a multifaceted program tested that premise. Ground-based optical coronography and near-UV imaging with Hubble Space Telescope ( HST ) Wide-Field Camera 3 searched formore » any close-in faint candidate coronal objects, but without success. Then, a Chandra pointing found the X-ray source single and coincident with the bright star. Significantly, the Si iv emissions of α Per, in a deeper FUV spectrum collected by the HST Cosmic Origin Spectrograph as part of the joint program, are aligned well with chromospheric atomic oxygen (which must be intrinsic to the luminous star), within the context of cooler late-F and early-G supergiants, including Cepheid variables. This pointed to the X-rays as the fundamental anomaly. The overluminous X-rays still support the case for a hyperactive dwarf secondary, albeit now spatially unresolved. However, an alternative is that α Per represents a novel class of coronal source. Resolving the first possibility now has become more difficult, because the easy solution—a well-separated companion—has been eliminated. Testing the other possibility will require a broader high-energy census of the early-F supergiants.« less

X-Ray Properties of Low-mass Pre-main Sequence Stars in the Orion Trapezium Cluster

NASA Astrophysics Data System (ADS)

Schulz, Norbert S.; Huenemoerder, David P.; Günther, Moritz; Testa, Paola; Canizares, Claude R.

2015-09-01

The Chandra HETG Orion Legacy Project (HOLP) is the first comprehensive set of observations of a very young massive stellar cluster that provides high-resolution X-ray spectra of very young stars over a wide mass range (0.7-2.3 {M}⊙ ). In this paper, we focus on the six brightest X-ray sources with T Tauri stellar counterparts that are well-characterized at optical and infrared wavelengths. All stars show column densities which are substantially smaller than expected from optical extinction, indicating that the sources are located on the near side of the cluster with respect to the observer as well as that these stars are embedded in more dusty environments. Stellar X-ray luminosities are well above 1031 erg s-1, in some cases exceeding 1032 erg s-1 for a substantial amount of time. The stars during these observations show no flares but are persistently bright. The spectra can be well fit with two temperature plasma components of 10 MK and 40 MK, of which the latter dominates the flux by a ratio 6:1 on average. The total emission measures range between 3-8 × 1054 cm-3 and are comparable to active coronal sources. The fits to the Ne ix He-Like K-shell lines indicate forbidden to inter-combination line ratios consistent with the low-density limit. Observed abundances compare well with active coronal sources underlying the coronal nature of these sources. The surface flux in this sample of 0.6-2.3 {M}⊙ classical T Tauri stars shows that coronal activity increases significantly between ages 0.1 and 10 Myr. The results demonstrate the power of X-ray line diagnostics to study coronal properties of T Tauri stars in young stellar clusters.

Constraining Line-of-sight Confusion in the Corona Using Linearly Polarized Observations of the Infrared FeXIII 1075nm and SiX 1430nm Emission Lines

NASA Astrophysics Data System (ADS)

Dima, G. I.; Kuhn, J. R.; Berdyugina, S.

2017-12-01

Measurements of the coronal magnetic field are difficult because of the intrinsically faint emission of coronal plasma and the large spurious background due to the bright solar disk. This work addresses the problem of resolving the confusion of the line-of-sight (LOS) integration through the optically-thin corona being observed. Work on developing new measuring techniques based on single-point inversions using the Hanle effect has already been described (Dima et al. 2016). It is important to develop a technique to assess when the LOS confusion makes comparing models and observations problematic. Using forward integration of synthetic emission through magnetohydrodynamic (MHD) models together with simultaneous linearly polarized observations of the FeXIII 1075nm and SiX 1430nm emission lines allows us to assess LOS confusion. Since the lines are both in the Hanle saturated regime their polarization angles are expected to be aligned as long as the gas is sampling the same magnetic field. If significant contributions to the emission is taking place from different regions along the LOS due to the additive nature of the polarized brightness the measured linear polarization between the two lines will be offset. The size of the resolution element is important for this determination since observing larger coronal regions will confuse the variation along the LOS with that in the plane-of-sky. We also present comparisons between synthetic linearly polarized emission through a global MHD model and observations of the same regions obtained using the 0.5m Scatter-free Observatory for Limb Active Regions and Coronae (SOLARC) telescope located on Haleakala, Maui. This work is being done in preparation for the type of observations that will become possible when the next generation 4m DKIST telescope comes online in 2020.

Brief Outburst

NASA Image and Video Library

2015-03-11

The Sun blew out a coronal mass ejection along with part of a solar filament over a three-hour period (Feb. 24, 2015). While some of the strands fell back into the Sun, a substantial part raced into space in a bright cloud of particles (as observed by the SOHO spacecraft). The activity was captured in a wavelength of extreme ultraviolet light. Because this occurred way over near the edge of the Sun, it was unlikely to have any effect on Earth. Credit: NASA/Solar Dynamics Observatory

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

Interaction of Two Filaments in a Long Filament Channel Associated with Twin Coronal Mass Ejections

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

Zheng, Ruisheng; Chen, Yao; Wang, Bing

Using the high-quality observations of the Solar Dynamics Observatory , we present the interaction of two filaments (F1 and F2) in a long filament channel associated with twin coronal mass ejections (CMEs) on 2016 January 26. Before the eruption, a sequence of rapid cancellation and emergence of the magnetic flux has been observed, which likely triggered the ascending of the west filament (F1). The east footpoints of rising F1 moved toward the east far end of the filament channel, accompanied by post-eruption loops and flare ribbons. This likely indicated a large-scale eruption involving the long filament channel, which resulted frommore » the interaction between F1 and the east filament (F2). Some bright plasma flew over F2, and F2 stayed at rest during the eruption, likely due to the confinement of its overlying lower magnetic field. Interestingly, the impulsive F1 pushed its overlying magnetic arcades to form the first CME, and F1 finally evolved into the second CME after the collision with the nearby coronal hole. We suggest that the interaction of F1 and the overlying magnetic field of F2 led to the merging reconnection that forms a longer eruptive filament loop. Our results also provide a possible picture of the origin of twin CMEs and show that the large-scale magnetic topology of the coronal hole is important for the eventual propagation direction of CMEs.« less

Computer Vision for the Solar Dynamics Observatory (SDO)

NASA Astrophysics Data System (ADS)

Martens, P. C. H.; Attrill, G. D. R.; Davey, A. R.; Engell, A.; Farid, S.; Grigis, P. C.; Kasper, J.; Korreck, K.; Saar, S. H.; Savcheva, A.; Su, Y.; Testa, P.; Wills-Davey, M.; Bernasconi, P. N.; Raouafi, N.-E.; Delouille, V. A.; Hochedez, J. F.; Cirtain, J. W.; Deforest, C. E.; Angryk, R. A.; de Moortel, I.; Wiegelmann, T.; Georgoulis, M. K.; McAteer, R. T. J.; Timmons, R. P.

2012-01-01

In Fall 2008 NASA selected a large international consortium to produce a comprehensive automated feature-recognition system for the Solar Dynamics Observatory (SDO). The SDO data that we consider are all of the Atmospheric Imaging Assembly (AIA) images plus surface magnetic-field images from the Helioseismic and Magnetic Imager (HMI). We produce robust, very efficient, professionally coded software modules that can keep up with the SDO data stream and detect, trace, and analyze numerous phenomena, including flares, sigmoids, filaments, coronal dimmings, polarity inversion lines, sunspots, X-ray bright points, active regions, coronal holes, EIT waves, coronal mass ejections (CMEs), coronal oscillations, and jets. We also track the emergence and evolution of magnetic elements down to the smallest detectable features and will provide at least four full-disk, nonlinear, force-free magnetic field extrapolations per day. The detection of CMEs and filaments is accomplished with Solar and Heliospheric Observatory (SOHO)/ Large Angle and Spectrometric Coronagraph (LASCO) and ground-based Hα data, respectively. A completely new software element is a trainable feature-detection module based on a generalized image-classification algorithm. Such a trainable module can be used to find features that have not yet been discovered (as, for example, sigmoids were in the pre- Yohkoh era). Our codes will produce entries in the Heliophysics Events Knowledgebase (HEK) as well as produce complete catalogs for results that are too numerous for inclusion in the HEK, such as the X-ray bright-point metadata. This will permit users to locate data on individual events as well as carry out statistical studies on large numbers of events, using the interface provided by the Virtual Solar Observatory. The operations concept for our computer vision system is that the data will be analyzed in near real time as soon as they arrive at the SDO Joint Science Operations Center and have undergone basic processing. This will allow the system to produce timely space-weather alerts and to guide the selection and production of quicklook images and movies, in addition to its prime mission of enabling solar science. We briefly describe the complex and unique data-processing pipeline, consisting of the hardware and control software required to handle the SDO data stream and accommodate the computer-vision modules, which has been set up at the Lockheed-Martin Space Astrophysics Laboratory (LMSAL), with an identical copy at the Smithsonian Astrophysical Observatory (SAO).

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.

Why a geoeffective CME was missed by SOHO LASCO?

NASA Astrophysics Data System (ADS)

Chi, Y.; Zhang, J.; Shen, C.; Hess, P.; Feng, L.; Wang, Y.; Mishra, W.

2017-12-01

During 2011 May 25, two Earth directed coronal mass ejections (CMEs) were recorded by STEREO COR2 as limb CMEs, when the separation between twin STEREO spacecraft and Earth was approximately 90°. At the same time, SOHO LASCO did not record corresponding halo or partial halo CME. These CMEs provided an opportunity to study why SOHO LASCO may miss Earth direction CME. According to GCS model, we find the two CMEs both have small half angle and aspect ratio. Most part of CMEs are behind the occulter of SOHO LASCO C2. We also estimated the two CMEs' mass and find the both CMEs' mass is small. The expected CME brightness according to the CME's mass is in the same order of the noise of SOHO LASCO. In the HI1 Fov, We have found evidence of interaction between the two CMEs. Combining with the WIND in situ observations, we find the CMEs are adjacent to each other. The duration of the two flux rope structure are 7 and 6.6 hours, respectively. This may provide an evidence that small flux structure without corresponding CME is also the solar erupted structure.

Bright point study. [of solar corona

NASA Technical Reports Server (NTRS)

Tang, F.; Harvey, K.; Bruner, M.; Kent, B.; Antonucci, E.

1982-01-01

Transition region and coronal observations of bright points by instruments aboard the Solar Maximum Mission and high resolution photospheric magnetograph observations on September 11, 1980 are presented. A total of 31 bipolar ephemeral regions were found in the photosphere from birth in 9.3 hours of combined magnetograph observations from three observatories. Two of the three ephemeral regions present in the field of view of the Ultraviolet Spectrometer-Polarimeter were observed in the C IV 1548 line. The unobserved ephemeral region was determined to be the shortest-lived (2.5 hr) and lowest in magnetic flux density (13G) of the three regions. The Flat Crystal Spectrometer observed only low level signals in the O VIII 18.969 A line, which were not statistically significant to be positively identified with any of the 16 ephemeral regions detected in the photosphere. In addition, the data indicate that at any given time there lacked a one-to-one correspondence between observable bright points and photospheric ephemeral regions, while more ephemeral regions were observed than their counterparts in the transition region and the corona.

Evolution of Fine-scale Penumbral Magnetic Structure and Formation of Penumbral Jets

NASA Astrophysics Data System (ADS)

Tiwari, S. K.; Moore, R. L.; Rempel, M.; Winebarger, A. R.

2015-12-01

Sunspot penumbra consists of spines (more vertical field) and penumbral filaments (interspines). Spines are outward extension of umbra. Penumbral filaments are recently found, both in observations and magnetohydrodynamic (MHD) simulations, to be magnetized stretched granule-like convective cells, with strong upflows near the head that continues along the central axis with weakening strength of the flow. Strong downflows are found at the tails of filaments and weak downflows along the sides of it. These lateral downflows often contain opposite polarity magnetic field to that of spines; most strongly near the heads of filaments. In spite of this advancement in understanding of small-scale structure of sunspot penumbra, how the filaments and spines evolve and interact remains uncertain. Penumbral jets, bright, transient features, seen in the chromosphere, are one of several dynamic events in sunspot penumbra. It has been proposed that these penumbral microjets result from component (acute angle) reconnection of the magnetic field in spines with that in interspines and could contribute to transition-region and coronal heating above sunspots. In a recent investigation, it was proposed that the jets form as a result of reconnection between the opposite polarity field at edges of filaments with spine field, and it was found that these jets do not significantly directly heat the corona above sunspots. We discuss how the proposed formation of penumbral jets is integral to the formation mechanism of penumbral filaments and spines, and may explain why penumbral jets are few and far between. We also point out that the generation of the penumbral jets could indirectly drive coronal heating via generation of MHD waves or braiding of the magnetic field.

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.

The Fundamental Structure of Coronal Loops

NASA Technical Reports Server (NTRS)

Winebarger, Amy; Warren, Harry; Cirtain, Jonathan; Kobayashi, Ken; Korreck, Kelly; Golub, Leon; Kuzin, Sergey; Walsh, Robert; DePontieu, Bart; Title, Alan;

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.

Behavior of Solar Cycles 23 and 24 Revealed by Microwave Observations

NASA Technical Reports Server (NTRS)

Gopalswamy, N.; Yashiro, S.; Maekelae, P.; Michalek, G.; Shibasaki, K.; Hathaway, D. H.

2012-01-01

Using magnetic and microwave butterfly diagrams, we compare the behavior of solar polar regions to show that (1) the polar magnetic field and the microwave brightness temperature during solar minimum substantially diminished during the cycle 23/24 minimum compared to the 22/23 minimum. (2) The polar microwave brightness temperature (Tb) seems to be a good proxy for the underlying magnetic field strength (B). The analysis indicates a relationship, B = 0.0067Tb - 70, where B is in G and Tb in K. (3) Both the brightness temperature and the magnetic field strength show north-south asymmetry most of the time except for a short period during the maximum phase. (4) The rush-to-the-pole phenomenon observed in the prominence eruption (PE) activity seems to be complete in the northern hemisphere as of 2012 March. (5) The decline of the microwave brightness temperature in the north polar region to the quiet-Sun levels and the sustained PE activity poleward of 60degN suggest that solar maximum conditions have arrived at the northern hemisphere. The southern hemisphere continues to exhibit conditions corresponding to the rise phase of solar cycle 24. Key words: Sun: chromosphere Sun: coronal mass ejections (CMEs) Sun: filaments, prominences Sun: photosphere Sun: radio radiation Sun: surface magnetism

On Heating the Sun's Corona by Magnetic Explosions: Feasibility in Active Regions and prospects for Quiet Regions and Coronal Holes

NASA Technical Reports Server (NTRS)

Moore, Ronald L.; Falconer, D. A.; Porter, Jason G.; Suess, Steven T.

1999-01-01

We build a case for the persistent strong coronal heating in active regions and the pervasive quasi-steady heating of the corona in quiet regions and coronal holes being driven in basically the same way as the intense transient heating in solar flares: by explosions of sheared magnetic fields in the cores of initially closed bipoles. We begin by summarizing the observational case for exploding sheared core fields being the drivers of a wide variety of flare events, with and without coronal mass ejections. We conclude that the arrangement of an event's flare heating, whether there is a coronal mass ejection, and the time and place of the ejection relative to the flare heating are all largely determined by four elements of the form and action of the magnetic field: (1) the arrangement of the impacted, interacting bipoles participating in the event, (2) which of these bipoles are active (have sheared core fields that explode) and which are passive (are heated by injection from impacted active bipoles), (3) which core field explodes first, and (4) which core-field explosions are confined within the closed field of their bipoles and which ejectively open their bipoles. We then apply this magnetic-configuration framework for flare heating to the strong coronal heating observed by the Yohkoh Soft X-ray Telescope in an active region with strongly sheared core fields observed by the MSFC vector magnetograph. All of the strong coronal heating is in continually microflaring sheared core fields or in extended loops rooted against the active core fields. Thus, the strong heating occurs in field configurations consistent with the heating being driven by frequent core-field explosions that are smaller but similar to those in confined flares and flaring arches. From analysis of the thermal and magnetic energetics of two selected core-field microflares and a bright extended loop, we find that (1) it is energetically feasible for the sheared core fields to drive all of the coronal heating in the active region via a staccato of magnetic microexplosions, (2) the microflares at the feet of the extended loop behave as the flares at the feet of flaring arches in that more coronal heating is driven within the active bipole than in the extended loop, (3) the filling factor of the X-ray plasma in the core field microflares and in the extended loop is approximately 0.1, and (4) to release enough magnetic energy for a typical microflare (10^27 - 10^28 erg), a microflaring strand of sheared core field need expand and/or untwist by only a few percent at most. Finally, we point out that (1) the field configurations for strong coronal heating in our example active region (i.e., neutral-line core fields, many embedded in the feet of extended loops) are present in abundance in the magnetic network in quiet regions and coronal holes, and (2) it is known that many network bipoles do microflare and that many produce detectable coronal heating. We therefore propose that exploding sheared core fields are the drivers of most of the heating and dynamics of the solar atmosphere, ranging from the largest and most powerful coronal mass ejections and flares, to the vigorous microflaring and coronal heating in active regions, to the multitude of fine-scale explosive events in the magnetic network. The low-lysing exploding core fields in the network drive microflares, spicules, global coronal heating, and ,consequently, the solar wind.

First detection of thermal radio emission from solar-type stars with the Karl G. Jansky very large array

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

Villadsen, Jackie; Hallinan, Gregg; Bourke, Stephen

2014-06-20

We present the first detections of thermal radio emission from the atmospheres of solar-type stars τ Cet, η Cas A, and 40 Eri A. These stars all resemble the Sun in age and level of magnetic activity, as indicated by X-ray luminosity and chromospheric emission in Ca II H and K lines. We observed these stars with the Karl G. Jansky Very Large Array with sensitivities of a few μJy at combinations of 10.0, 15.0, and 34.5 GHz. τ Cet, η Cas A, and 40 Eri A are all detected at 34.5 GHz with signal-to-noise ratios of 6.5, 5.2, andmore » 4.5, respectively. 15.0 GHz upper limits imply a rising spectral index greater than 1.0 for τ Cet and 1.6 for η Cas A, at the 95% confidence level. The measured 34.5 GHz flux densities correspond to stellar disk-averaged brightness temperatures of roughly 10,000 K, similar to the solar brightness temperature at the same frequency. We explain this emission as optically thick thermal free-free emission from the chromosphere, with possible contributions from coronal gyroresonance emission above active regions and coronal free-free emission. These and similar quality data on other nearby solar-type stars, when combined with Atacama Large Millimeter/Submillimeter Array observations, will enable the construction of temperature profiles of their chromospheres and lower transition regions.« less

Investigating the ability of solar coronal shocks to accelerate solar energetic particles

NASA Astrophysics Data System (ADS)

Kwon, R. Y.; Vourlidas, A.

2017-12-01

We estimate the density compression ratio of shocks associated with coronal mass ejections (CMEs) and investigate whether they can accelerate solar energetic particles (SEPs). Using remote-sensing, multi-viewpoint coronagraphic observations, we have developed a method to extract the sheath electron density profiles along the shock normal and estimate the density compression ratio. Our method uses the ellipsoid model to derive the 3D geometry of the sheaths, including the line-of-sight (LOS) depth. The sheath density profiles along the shock normal are modeled with double-Gaussian functions, and the modeled densities are integrated along the LOSs to be compared with the observed brightness in STEREO COR2-Ahead. The upstream densities are derived from either the pB-inversion of the brightness in a pre-event image or an empirical model. We analyze two fast halo CMEs observed on 2011 March 7 and 2014 February 25 that are associated with SEP events detected by multiple spacecraft located over a broad range of heliolongitudes. We find that the density compression peaks around the CME nose and decreases at larger position angles. Interestingly, we find that the supercritical region extends over a large area of the shock and lasts longer (several tens of minutes) than past reports. This finding implies that CME shocks may be capable of accelerating energetic particles in the corona over extended spatial and temporal scales and may, therefore, be responsible for the wide longitudinal distribution of these particles in the inner heliosphere.

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.

Spectroscopic Study of a Dark Lane and a Cool Loop in a Solar Limb Active Region by Hinode/EIS

NASA Astrophysics Data System (ADS)

Lee, Kyoung-Sun; Imada, S.; Moon, Y.-J.; Lee, Jin-Yi

2014-01-01

We investigated a cool loop and a dark lane over a limb active region on 2007 March 14 using the Hinode/EUV Imaging Spectrometer. The cool loop is clearly seen in the spectral lines formed at the transition region temperature. The dark lane is characterized by an elongated faint structure in the coronal spectral lines and is rooted on a bright point. We examined their electron densities, Doppler velocities, and nonthermal velocities as a function of distance from the limb. We derived electron densities using the density sensitive line pairs of Mg VII, Si X, Fe XII, Fe XIII, and Fe XIV spectra. We also compared the observed density scale heights with the calculated scale heights from each peak formation temperatures of the spectral lines under the hydrostatic equilibrium. We noted that the observed density scale heights of the cool loop are consistent with the calculated heights, with the exception of one observed cooler temperature; we also found that the observed scale heights of the dark lane are much lower than their calculated scale heights. The nonthermal velocity in the cool loop slightly decreases along the loop, while nonthermal velocity in the dark lane sharply falls off with height. Such a decrease in the nonthermal velocity may be explained by wave damping near the solar surface or by turbulence due to magnetic reconnection near the bright point.

The Triggering Mechanism of coronal jets and CMEs: Flux Cancelation

NASA Technical Reports Server (NTRS)

Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.

2017-01-01

Recent investigations show that coronal jets are driven by the eruption of a small-scale filament (10,000 - 20,000 km long, called a minifilament) following magnetic flux cancelation at the neutral line underneath the minifilament. Minifilament eruptions appear to be analogous to larger-scale solar filament eruptions: they both reside, before the eruption, in the highly sheared field between the adjacent opposite-polarity magnetic flux patches (neutral line); jet-producing minifilament and larger-scale solar filament first show a slow-rise, followed by a fast-rise as they erupt; during the jet-producing minifilament eruption a jet bright point (JBP) appears at the location where the minifilament was rooted before the eruption, analogous to the situation with CME-producing larger-scale filament eruptions where a solar flare arcade forms during the filament eruption along the neutral line along which the filament resided prior to its eruption. In the present study we investigate the triggering mechanism of CME-producing large solar filament eruptions, and find that enduring flux cancelation at the neutral line of the filaments often triggers their eruptions. This corresponds to the finding that persistent flux cancelation at the neutral is the cause of jet-producing minifilament eruptions. Thus our observations support coronal jets being miniature version of CMEs.

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.

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.

Determination of the coronal magnetic field from vector magnetograph data

NASA Technical Reports Server (NTRS)

Mikic, Zoran

1991-01-01

A new algorithm was developed, tested, and applied to determine coronal magnetic fields above solar active regions. The coronal field above NOAA active region AR5747 was successfully estimated on 20 Oct. 1989 from data taken at the Mees Solar Observatory of the Univ. of Hawaii. It was shown that observational data can be used to obtain realistic estimates of coronal magnetic fields. The model has significantly extended the realism with which the coronal magnetic field can be inferred from observations. The understanding of coronal phenomena will be greatly advanced by a reliable technique, such as the one presented, for deducing the detailed spatial structure of the coronal field. The payoff from major current and proposed NASA observational efforts is heavily dependent on the success with which the coronal field can be inferred from vector magnetograms. In particular, the present inability to reliably obtain the coronal field has been a major obstacle to the theoretical advancement of solar flare theory and prediction. The results have shown that the evolutional algorithm can be used to estimate coronal magnetic fields.

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.

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.

Impulsive EUV bursts observed in C IV with OSO-8. [UV solar spectra

NASA Technical Reports Server (NTRS)

Athay, R. G.; White, O. R.; Lites, B. W.; Bruner, E. C., Jr.

1980-01-01

Time sequences of profiles of the 1548 A line of C IV containing 51 EUV bursts observed in or near active regions are analyzed to determine the brightness, Doppler shift and line broadening characteristics of the bursts. The bursts have mean lifetimes of approximately 150 s, and mean increases in brightness at burst maximum of four-fold as observed with a field of view of 2 x 20 arc sec. Mean burst diameters are estimated to be 3 arc sec, or smaller. All but three of the bursts show Doppler shifts with velocities sometimes exceeding 75 km/s; 31 are dominated by red shifts and 17 are dominated by blue shifts. Approximately half of the latter group have red-shifted precursors. The bursts are interpreted as prominence material, such as surges and coronal rain, moving through the field of view of the spectrometer.

Solar Radio Burst Associated with the Falling Bright EUV Blob

NASA Astrophysics Data System (ADS)

Karlický, Marian; Zemanová, Alena; Dudík, Jaroslav; Radziszewski, Krzysztof

2018-02-01

At the beginning of the 2015 November 4 flare, in the 1300–2000 MHz frequency range, we observed a very rare slow positively drifting burst. We searched for associated phenomena in simultaneous EUV observations made by IRIS, SDO/AIA, and Hinode/XRT, as well as in H α observations. We found that this radio burst was accompanied with the bright blob, visible at transition region, coronal, and flare temperatures, falling down to the chromosphere along the dark loop with a velocity of about 280 km s‑1. The dark loop was visible in H α but disappeared afterward. Furthermore, we found that the falling blob interacted with the chromosphere as expressed by a sudden change of the H α spectra at the location of this interaction. Considering different possibilities, we propose that the observed slow positively drifting burst is generated by the thermal conduction front formed in front of the falling hot EUV blob.

Chandra's Darkest Bright Star: not so Dark after All?

NASA Astrophysics Data System (ADS)

Ayres, Thomas R.

2008-11-01

The Chandra High Resolution camera (HRC) has obtained numerous short exposures of the ultraviolet (UV)-bright star Vega (α Lyrae; HD 172167: A0 V), to calibrate the response of the detector to out-of-band (non-X-ray) radiation. A new analysis uncovered a stronger "blue leak" in the imaging section (HRC-I) than reported in an earlier study of Vega based on a subset of the pointings. The higher count rate—a factor of nearly 2 above prelaunch estimates—raised the possibility that genuine coronal X-rays might lurk among the out-of-band events. Exploiting the broader point-spread function of the UV leak compared with soft X-rays identified an excess of counts centered on the target, technically at 3σ significance. A number of uncertainties, however, prevent a clear declaration of a Vegan corona. A more secure result would be within reach of a deep uninterrupted HRC-I pointing.

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

Transition-Region/Coronal Signatures of Penumbral Microjets: Hi-C, SDO/AIA and Hinode (SOT/FG) Observations

NASA Technical Reports Server (NTRS)

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

2014-01-01

Penumbral microjets are bright, transient features seen in the chromosphere of sunspot penumbrae. Katsuaka et al. (2007) noted their ubiquity and characterized them using the Ca II H-line filter on Hinode's Solar Optical Telescope (SOT). The jets are 1000{4000 km in length, 300{400 km in width, and last less than one minute. It was proposed that these penumbral microjets could contribute to the transition-region and coronal heating above sunspots. We examine whether these microjets appear in the transition-region (TR) and/or corona or are related{ temporally and spatially{ to similar brightenings in the TR and/or corona. First, we identify penumbral microjets with the SOT's Ca II H-line filter. The chosen sunspot is observed on July 11, 2012 from 18:50:00 UT to 20:00:00 UT at approx. 14 inches, -30 inches. We then examine the sunspot in the same field of view and at the same time in other wavelengths. We use the High Resolution Coronal Imager Telescope (Hi-C) at 193A and the 1600A, 304A, 171A, 193A, and 94A passbands of the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamic Observatory. We include examples of these jets and where they should appear in the other passbands, but find no signifcant association, except for a few jets with longer lifetimes and bigger sizes seen at locations in the penumbra with repeated stronger brightenings. We conclude that the normal microjets are not heated to transition-region/coronal temperatures, but the larger jets are.

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.

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).

3D Modeling of CMEs observed with STEREO

NASA Astrophysics Data System (ADS)

Bosman, E.; Bothmer, V.

2012-04-01

From January 2007 until end of 2010, 565 typical large-scale coronal mass ejections (CMEs) have been identified in the SECCHI/COR2 synoptic movies of the STEREO Mission. A subset comprising 114 CME events, selected based on the CME's brightness appearance in the SECCHI/COR2 images, has been modeled through the Graduated Cylindrical Shell (GCS) Model developed by Thernisien et al. (2006). This study presents an overview of the GCS forward-modeling results and an interpretation of the CME characteristics in relationship to their solar source region properties and solar cycle appearances.

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.

Multi-wave band SMM-VLA observations of an M2 flare and an associated coronal mass ejection

NASA Technical Reports Server (NTRS)

Willson, Robert F.; Lang, Kenneth R.; Schmelz, Joan T.; Gonzalez, Raymond D.; Smith, Kermit L.

1991-01-01

Results are presented of observations of an M2 flare and an associated coronal mass ejection CME by instruments on the SMM as well as by the VLA and other ground-based observatories on September 30, 1988. The multiwave band data show a gradual slowly changing event which lasted several hours. The microwave burst emission was found to originate in compact moderately circularly polarized sources located near the sites of bright H-alpha and soft X-ray emission. These data are combined with estimates of an electron temperature of 1.5 x 10 to the 7th K and an emission measure of about 2.0 x 10 to the 49th/cu cm obtained from Ca XIX and Fe XXV spectra to show that the microwave emission can be attributed to thermal gyrosynchrotron radiation in regions where the magnetic field strength is 425-650 G. The CME acceleration at low altitudes is measured on the basis of ground- and space-based coronagraphs.

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.

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.

SphinX Measurements of the 2009 Solar Minimum X-Ray Emission

NASA Astrophysics Data System (ADS)

Sylwester, J.; Kowalinski, M.; Gburek, S.; Siarkowski, M.; Kuzin, S.; Farnik, F.; Reale, F.; Phillips, K. J. H.; Bakała, J.; Gryciuk, M.; Podgorski, P.; Sylwester, B.

2012-06-01

The SphinX X-ray spectrophotometer on the CORONAS-PHOTON spacecraft measured soft X-ray emission in the 1-15 keV energy range during the deep solar minimum of 2009 with a sensitivity much greater than GOES. Several intervals are identified when the X-ray flux was exceptionally low, and the flux and solar X-ray luminosity are estimated. Spectral fits to the emission at these times give temperatures of 1.7-1.9 MK and emission measures between 4 × 1047 cm-3 and 1.1 × 1048 cm-3. Comparing SphinX emission with that from the Hinode X-ray Telescope, we deduce that most of the emission is from general coronal structures rather than confined features like bright points. For one of 27 intervals of exceptionally low activity identified in the SphinX data, the Sun's X-ray luminosity in an energy range roughly extrapolated to that of ROSAT (0.1-2.4 keV) was less than most nearby K and M dwarfs.

North-south asymmetry of Ca II K regions determined from OAUC spectroheliograms: 1996 - 2006

NASA Astrophysics Data System (ADS)

Dorotovič, I.; Rybák, J.; Garcia, A.; Journoud, P.

2010-12-01

The solar activity (SA) evolution levels are not identical in the northern and southern Sun's hemispheres. This fact was repeatedly confirmed in the past by the analysis of a number of long-term observations of various SA indices in individual atmospheric layers of the Sun and in different bandwidths. The north-south asymmetry (NSA) is thus a significant tool in investigation of long-term SA variations. This paper presents a software tool to determine the NSA of the area of bright chromospheric plages, as measured in the Ca II K3 spectroheliograms registered since 1926 in the Observatário Astronómico da Universidade de Coimbra, Portugal, as well as evolution of sizes of these areas in the period 1996 - 2006. The algorithm of the program is limited to determining the total area of bright features in the Ca II K3 emission line based on the definition of the threshold value for relative brightness and, therefore, it does not resolve brightness of individual chromospheric features. A comparison and cross-correlation of this NSA with the NSAs found for the sunspots and coronal green line brightness have been added. In the near future we intend to 1) determine the NSA of the area of bright chromospheric Ca II K3 regions back to the year 1926, and 2) compare the evolution of the surface area of these regions in the period 1970-2006 with the evolution of the magnetic index obtained at Mt. Wilson Observatory, which would also help in setting up a proxy reconstruction of the magnetic index back to 1926. Since 2007 new spectroheliograms have been recorded using a CCD camera and, therefore, in the future we will also address this issue for the period 2007 - present.

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.

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

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.

Suicide Comet HD Video

NASA Image and Video Library

2010-03-16

Captured March 12, 2010 The SOHO spacecraft captured a very bright, sungrazing comet as it rocketed towards the Sun (Mar. 12, 2010) and was vaporized. This comet is arguably the brightest comet that SOHO has observed since Comet McNaught in early 2007. The comet is believed to belong to the Kreutz family of comets that broke up from a much larger comet many hundreds of years ago. They are known to orbit close to the Sun. A coronal mass ejection (CME) burst away from the Sun during the bright comet’s approach. Interestingly, a much smaller comet that preceded this one can be seen about half a day earlier on just about the identical route. And another pair of small comets followed the same track into the Sun after the bright one. Such a string of comets has never been witnessed before by SOHO. SOHO's C3 coronagraph instrument blocks out the Sun with an occulting disk; the white circle represents the size of the Sun. The planet Mercury can also be seen moving from left to right just beneath the Sun. To learn more and to download the video and still images go here: sohowww.nascom.nasa.gov/pickoftheweek/old/15mar2010/ Credit: NASA/GSFC/SOHO

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

An evolutionary computation based algorithm for calculating solar differential rotation by automatic tracking of coronal bright points

NASA Astrophysics Data System (ADS)

Shahamatnia, Ehsan; Dorotovič, Ivan; Fonseca, Jose M.; Ribeiro, Rita A.

2016-03-01

Developing specialized software tools is essential to support studies of solar activity evolution. With new space missions such as Solar Dynamics Observatory (SDO), solar images are being produced in unprecedented volumes. To capitalize on that huge data availability, the scientific community needs a new generation of software tools for automatic and efficient data processing. In this paper a prototype of a modular framework for solar feature detection, characterization, and tracking is presented. To develop an efficient system capable of automatic solar feature tracking and measuring, a hybrid approach combining specialized image processing, evolutionary optimization, and soft computing algorithms is being followed. The specialized hybrid algorithm for tracking solar features allows automatic feature tracking while gathering characterization details about the tracked features. The hybrid algorithm takes advantages of the snake model, a specialized image processing algorithm widely used in applications such as boundary delineation, image segmentation, and object tracking. Further, it exploits the flexibility and efficiency of Particle Swarm Optimization (PSO), a stochastic population based optimization algorithm. PSO has been used successfully in a wide range of applications including combinatorial optimization, control, clustering, robotics, scheduling, and image processing and video analysis applications. The proposed tool, denoted PSO-Snake model, was already successfully tested in other works for tracking sunspots and coronal bright points. In this work, we discuss the application of the PSO-Snake algorithm for calculating the sidereal rotational angular velocity of the solar corona. To validate the results we compare them with published manual results performed by an expert.

Deceleration and dispersion of large-scale coronal bright fronts

NASA Astrophysics Data System (ADS)

Long, D. M.; Gallagher, P. T.; McAteer, R. T. J.; Bloomfield, D. S.

2011-07-01

Context. One of the most dramatic manifestations of solar activity are large-scale coronal bright fronts (CBFs) observed in extreme ultraviolet (EUV) images of the solar atmosphere. To date, the energetics and kinematics of CBFs remain poorly understood, due to the low image cadence and sensitivity of previous EUV imagers and the limited methods used to extract the features. Aims: In this paper, the trajectory and morphology of CBFs was determined in order to investigate the varying properties of a sample of CBFs, including their kinematics and pulse shape, dispersion, and dissipation. Methods: We have developed a semi-automatic intensity profiling technique to extract the morphology and accurate positions of CBFs in 2.5-10 min cadence images from STEREO/EUVI. The technique was applied to sequences of 171 Å and 195 Å images from STEREO/EUVI in order to measure the wave properties of four separate CBF events. Results: Following launch at velocities of ~240-450 km s-1 each of the four events studied showed significant negative acceleration ranging from ~-290 to -60 m s-2. The CBF spatial and temporal widths were found to increase from ~50 Mm to ~200 Mm and ~100 s to ~1500 s respectively, suggesting that they are dispersive in nature. The variation in position-angle averaged pulse-integrated intensity with propagation shows no clear trend across the four events studied. These results are most consistent with CBFs being dispersive magnetoacoustic waves. Figures 3-8, 10, 11, 13-15, 17, 18 and the movie are 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.

New techniques for the characterisation of dynamical phenomena in solar coronal images

NASA Astrophysics Data System (ADS)

Robbrecht, E.

2007-02-01

During a total solar eclipse, a narrow strip of the Earth's surface is shielded completely by the Moon from the disk of the Sun. In this strip, the corona appears crown-like around the shade of the Moon. It was uncertain until the middle of the 20th century whether the corona was a solar phenomenon or if it was related to the Moon or whether it represented an artifact produced by the Earth's atmosphere. The answer to this question was provided by Grotrian (1939) and Edlèn (1942). Based on studies of iron emission lines, they suggested that the surface of the Sun is surrounded by a hot tenuous gas having a temperature of million degrees Kelvin and thus in a state of high ionization. This discovery was a result from spectroscopy, a field of research which started in 1666 with Sir Isaac Newton's observations of sunlight, dispersed by a prism. It is now clear that the hot solar corona is made of a low density plasma, highly structured by the magnetic field on length scales ranging from the Sun's diameter to the limit of angular resolution (e.g. Démoulin and Klein 2000). The need to resolve and study the corona down to such scales has determined a vigorous scientific and technological impulse toward the development of solar Ultraviolet (UV) and X-ray telescopes with high spatial and temporal resolution. With the advent of the satellite SOHO (Solar and Heliospheric Observatory, see chapter 1), the picture of a quiet corona was definitely sent to the past. EUV (Extreme UV) image sequences of the lower solar corona revealed a finely structured medium constantly agitated by a wide variety of transients (e.g. Harrison 1998). Active regions consisting of large magnetic loops with enhanced temperature and density are observed, as well as "quiet" areas, coronal holes and numerous structures of different scales such as plumes, jets, spicules, X-ray bright points, blinkers, all structured by magnetic fields. Launched in 1998, the Transition Region And Coronal Explorer (TRACE) was an important step on the way to subarcsecond telescopes. It allows a spatial resolution of 1" in the EUV and UV bands and, simultaneously, a temporal resolution of the order of a few seconds. Coronal physics studies are dominated by two major and interlinked problems: coronal heating and solar wind acceleration. Above the chromosphere there is a thin transition layer in which the temperature suddenly increases and density drops. How can the temperature of the solar corona be three orders of magnitude higher than the temperature of the photosphere? In order for this huge temperature gradient to be stationary, non-thermal energy must be transported from below the photosphere towards the chromosphere and corona and converted into heat to balance the radiative and conductive losses. This puzzle of origin, transport and conversion of energy is referred to as the "coronal heating problem". Due to its fundamental role in the structuring of the corona, the magnetic field is supposed to play an important role in the heating. In this dissertation we describe two aspects of solar coronal dynamics: waves in coronal loops (Part I) and coronal mass ejections (Part II). We investigate the influence of (semi-) automated techniques on solar coronal research. This is a timely discussion since the observation of solar phenomena is transitioning from manual detection to "Solar Image Processing". Our results are mainly based on images from the Extreme UV Imaging Telescope (EIT) and the Large Angle and Spectrometric Coronagraph (LASCO), two instruments onboard the satellite SOHO (Solar and Heliospheric Observatory) of which we recently celebrated its 11th anniversary. The high quality of the images together with the long timespan created a valuable database for solar physics research. Part I reports on the first detection of slow magnetoacoustic waves in transequatorial coronal loops observed in high cadence image sequences simultaneously produced by EIT and TRACE (Transition Region And Coronal Explorer). Ten years of EUV observations made it clear that these disturbances are a widespread phenomenon in active region loops. The existence of these waves in the corona had been predicted by the theory of magnetohydrodynamics (MHD), which we revise briefly. Just like in helioseismology, coronal seismology uses observations of oscillations to derive physical parameters which are not directly measurable, such as the Alfvén speed or the magnetic field strength. The comparison with helioseismology does not fully hold in the sense that the dense photosphere does not allow any seeing inside. Instead, for the corona we do have direct observations, but because of its optical thinness these observations leave space for many interpretations. At the end of the forties, it was suggested that the corona could be heated by the dissipation of acoustic waves (sound waves) driven by the p-mode oscillations, generated by turbulence in the convection zone. While they travel upwards, these waves form shocks and heat the plasma by viscous dissipation. Nowadays, they are believed to be only important for lower chromospheric heating. By the time the upper chromosphere is reached, the acoustic waves are heavily damped and what rests is reflected by the steep temperature and density gradients in the transition zone. As such, they cannot deposit enough energy in the corona to sufficiently heat it to the observed temperatures. Dissipation of magnetic energy by Alfvén waves or directly by the reconnection process in current sheets are considered to be more likely to heat the corona. Part II addresses the question of detecting coronal mass ejections (CMEs) in coronagraphic white light data. The study of CMEs is a rather young (≲ 30 years) field of research. Coronal mass ejections are sudden expulsions of mass and magnetic field from the solar corona into the interplanetary medium. A classical CME carries away some 10^15 g of coronal mass and can liberate energies of 10^23-10^25 J. They are often observed n association with low coronal activity, such as flares and filament eruptions. During the first years of CME observation, it was believed that a flare was a necessary condition for CME occurrence. The widely accepted picture today is that flares and CMEs are both different manifestations of magnetic field restructuring through reconnection (flare) and the expulsion of mass (CME). Up till now, the SOHO mission has been the best mission for CME studies because of the increased resolution, cadence, sensitivity and dynamic range of the LASCO instruments, but also because of the large array of ground-based instruments (Howard 2006). The complexity of the CME-picture grew likewise. The next mission with a coronagraph is the NASA STEREO mission (Solar Terrestrial Relations Observatory), launched on 26 Oct. 2006. In chapter 4 we test the possibility of automatically detecting CMEs in LASCO data. We describe the algorithm CACTus (Computer Aided CME Tracking) and test its validity on a short period of 6 days. In chapter 5 we present our newly constructed CME catalog based on our automated detection scheme. It is the first automatically generated catalog which runs over a complete solar cycle (cycle 23). It required no human interaction, which implies it is totally objective. It includes all transients obeying the observational definition of CME as a "new, discrete, bright, white-light feature in the coronagraph field-of-view moving radially outward" (Hundhausen et al. 1984). As a result, our catalog contains much more events, mostly narrow, than are included in the classical CDAW CME catalog (Yashiro et al. 2004) which is assembled manually. We discuss the CME rate over the solar cycle and present important new statistics on the CACTus CME parameters (size, latitude, speed). CME research has gained an increased interest due to their strong space weather impact. Space weather is defined by the European Space Agency (ESA) 1 as the "conditions on the Sun and in the solar wind, magnetosphere, ionosphere and thermosphere that can influence the performance and reliability of space-borne and ground-based technological systems and can endanger human life or health." The significance of space weather lies in its potential impact on man-made technologies on Earth and in space, for example, on satellites and spacecraft, electricity power grids, pipelines, radio and telephone communications and on geophysical exploration. Space weather also has implications for manned space flight, both in Earth orbit and further out into space. Solar activity is the main source of space weather. It is now well established that CMEs are the primary cause of geomagnetic storms and that their associated shocks accelerate high energetic particles. These particles can directly and indirectly influence the operation of spacecraft and affect communication and navigation. In order to protect systems and people that might be at risk from space weather effects, we need to understand the causes of space weather and try to predict its impact on the heliosphere as soon as possible. A growing field in this respect is Solar mage Processing (SIP). It allows continuous monitoring and interpretation of new incoming data. This is not only interesting for space weather forecasting, but it is also needed to be able to handle efficiently the large data flow which is expected from recently launched and future missions. In chapter 6 we revise the current capabilities for automated detection of CMEs and related phenomena.

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

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

Toward a Next Generation Solar Coronagraph: Development of a Compact Diagnostic Coronagraph on the ISS

NASA Astrophysics Data System (ADS)

Cho, K.-S.; Bong, S.-C.; Choi, S.; Yang, H.; Kim, J.; Baek, J.-H.; Park, J.; Lim, E.-K.; Kim, R.-S.; Kim, S.; Kim, Y.-H.; Park, Y.-D.; Clarke, S. W.; Davila, J. M.; Gopalswamy, N.; Nakariakov, V. M.; Li, B.; Pinto, R. F.

2017-10-01

The Korea Astronomy and Space Science Institute plans to develop a coronagraph in collaboration with National Aeronautics and Space Administration (NASA) and to install it on the International Space Station (ISS). The coronagraph is an externally occulted one-stage coronagraph with a field of view from 3 to 15 solar radii. The observation wavelength is approximately 400 nm, where strong Fraunhofer absorption lines from the photosphere experience thermal broadening and Doppler shift through scattering by coronal electrons. Photometric filter observations around this band enable the estimation of 2D electron temperature and electron velocity distribution in the corona. Together with a high time cadence (<12 min) of corona images used to determine the geometric and kinematic parameters of coronal mass ejections, the coronagraph will yield the spatial distribution of electron density by measuring the polarized brightness. For the purpose of technical demonstration, we intend to observe the total solar eclipse in August 2017 with the filter system and to perform a stratospheric balloon experiment in 2019 with the engineering model of the coronagraph. The coronagraph is planned to be installed on the ISS in 2021 for addressing a number of questions (e.g., coronal heating and solar wind acceleration) that are both fundamental and practically important in the physics of the solar corona and of the heliosphere.

HINODE/EIS SPECTROSCOPIC VALIDATION OF VERY HOT PLASMA IMAGED WITH THE SOLAR DYNAMICS OBSERVATORY IN NON-FLARING ACTIVE REGION CORES

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

Testa, Paola; Reale, Fabio, E-mail: ptesta@cfa.harvard.edu

2012-05-01

We use coronal imaging observations with the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA), and Hinode/Extreme-ultraviolet Imaging Spectrometer (EIS) spectral data to explore the potential of narrowband EUV imaging data for diagnosing the presence of hot (T {approx}> 5 MK) coronal plasma in active regions. We analyze observations of two active regions (AR 11281, AR 11289) with simultaneous AIA imaging and EIS spectral data, including the Ca XVII line (at 192.8 A), which is one of the few lines in the EIS spectral bands sensitive to hot coronal plasma even outside flares. After careful co-alignment of the imaging and spectral data,more » we compare the morphology in a three-color image combining the 171, 335, and 94 A AIA spectral bands, with the image obtained for Ca XVII emission from the analysis of EIS spectra. We find that in the selected active regions the Ca XVII emission is strong only in very limited areas, showing striking similarities with the features bright in the 94 A (and 335 A) AIA channels and weak in the 171 A band. We conclude that AIA imaging observations of the solar corona can be used to track hot plasma (6-8 MK), and so to study its spatial variability and temporal evolution at high spatial and temporal resolution.« less

The quiescent and flaring EUV spectrum of Algol and its relationship to other active coronae. EUV spectroscopy of bright hyades coronae: 71 Tauri and Theta 1 Tauri

NASA Technical Reports Server (NTRS)

Stern, Robert A.

1994-01-01

This program involves analysis and interpretation of EUVE spectrometer observations of the active stars Algol (beta Per) and 71 Tauri. The EUVE satellite spectrometers observed the prototype eclipsing binary Algol over nearly 1.5 orbital periods. Effective exposure times were 100 ksec and 89 ksec in the short wave (70-180 A) and medium wave (140-370 A) channels. High temperature (up to 20 MK) Fe XVI-XXIV emission lines are clearly detected in the overall spectrum. In addition, a quiescent continuum is present which increases towards shorter wavelengths. Using synthesized spectra of optically thin line and continuum emission folded through the instrumental response, we have examined constraints on the (Fe/H) coronal abundance in Algol. We find that the coronal Fe is underabundant by factors that approximately equal 2-4 relative to solar photospheric values, unless an unreasonably large quantity of coronal plasma at T greater than 30 MK is present in the quiescent spectrum. The latter possibility is, however, inconsistent with available X-ray data. Lightcurves of the high temperature EUV lines compared to line emission at He II 304 A show considerable differences, with much deeper minima present in the He II line during both primary and secondary eclipses. Toward the end of the observation a moderate flare lasting approximately 6 hours was detected in the high temperature Fe emission lines. The 71 Tau observation, for about the same exposure time, revealed only a handful of weak emission lines; however, the strongest lines were also those of Fe XXIII/XX, suggesting a hot coronal plasma. No obvious flaring or other variation was present in the 71 Tau Deep Survey lightcurve.

TETHER-CUTTING RECONNECTION BETWEEN TWO SOLAR FILAMENTS TRIGGERING OUTFLOWS AND A CORONAL MASS EJECTION

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

Chen, Huadong; Zhang, Jun; Li, Leping

Triggering mechanisms of solar eruptions have long been a challenge. A few previous case studies have indicated that preceding gentle filament merging via magnetic reconnection may launch following intense eruption, according to the tether-cutting (TC) model. However, the detailed process of TC reconnection between filaments has not been exhibited yet. In this work, we report the high-resolution observations from the Interface Region Imaging Spectrometer (IRIS) of TC reconnection between two sheared filaments in NOAA active region 12146. The TC reconnection commenced on ∼15:35 UT on 2014 August 29 and triggered an eruptive GOES C4.3-class flare ∼8 minutes later. An associatedmore » coronal mass ejection appeared in the field of view of the Solar and Heliospheric Observatory/LASCO C2 about 40 minutes later. Thanks to the high spatial resolution of IRIS data, bright plasma outflows generated by the TC reconnection are clearly observed, which moved along the subarcsecond fine-scale flux tube structures in the erupting filament. Based on the imaging and spectral observations, the mean plane-of-sky and line-of-sight velocities of the TC reconnection outflows are separately measured to be ∼79 and 86 km s{sup −1}, which derives an average real speed of ∼120 km s{sup −1}. In addition, it is found that spectral features, such as peak intensities, Doppler shifts, and line widths in the TC reconnection region are evidently enhanced compared to those in the nearby region just before the flare.« less

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.

Spectroscopic study of a dark lane and a cool loop in a solar limb active region by Hinode/EIS

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

Lee, Kyoung-Sun; Imada, S.; Moon, Y.-J.

2014-01-10

We investigated a cool loop and a dark lane over a limb active region on 2007 March 14 using the Hinode/EUV Imaging Spectrometer. The cool loop is clearly seen in the spectral lines formed at the transition region temperature. The dark lane is characterized by an elongated faint structure in the coronal spectral lines and is rooted on a bright point. We examined their electron densities, Doppler velocities, and nonthermal velocities as a function of distance from the limb. We derived electron densities using the density sensitive line pairs of Mg VII, Si X, Fe XII, Fe XIII, and Femore » XIV spectra. We also compared the observed density scale heights with the calculated scale heights from each peak formation temperatures of the spectral lines under the hydrostatic equilibrium. We noted that the observed density scale heights of the cool loop are consistent with the calculated heights, with the exception of one observed cooler temperature; we also found that the observed scale heights of the dark lane are much lower than their calculated scale heights. The nonthermal velocity in the cool loop slightly decreases along the loop, while nonthermal velocity in the dark lane sharply falls off with height. Such a decrease in the nonthermal velocity may be explained by wave damping near the solar surface or by turbulence due to magnetic reconnection near the bright point.« less

TRACE Images of the Solar Chromosphere, Transition Region, and Low Corona at High Cadence and High Spatial Resolution

NASA Astrophysics Data System (ADS)

Tarbell, T. D.; Handy, B. N.; Judge, P. G.

1999-05-01

We present TRACE images and movies showing C IV emission (transition region at 80,000 degrees) and UV continuum (temperature minimum region) of quiet and active regions. TRACE images using the 1550, 1600, and 1700 Angstroms filters can be combined to estimate the total emission in the C IV 1548 and 1550 lines and the UV continuum. These are supplemented in different observations with MDI magnetograms, TRACE 171 Angstroms images (Fe IX/X and perhaps O VI), and SUMER spectra of chromospheric and transition region lines from SOHO JOP 72. In quiet sun, bright C IV transients are seen in the vicinity of flux emergence, flux cancellation, and less dramatic interactions of small magnetic structures. Some of these are accompanied by high-velocity explosive events seen in SUMER spectra. The C IV emission can be well-separated from the photospheric magnetic footpoints, suggesting that it takes place on current sheets higher in the atmosphere separating different flux systems. In active regions, both bright and dark fibrils or loops are seen in C IV. Many nano/micro/sub flares are seen, some but not all of which are associated with emerging flux. The C IV emission of "moss" regions, footpoints of hot coronal loops, is contrasted with that of similar plage which does not have hot loops above it. This work was supported by the NASA contracts and grants for TRACE, MDI, and SOHO.

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

Evidence for explosive chromospheric evaporation in a solar flare observed with SMM

NASA Technical Reports Server (NTRS)

Zarro, D. M.; Saba, J. L. R.; Strong, K. T.; Canfield, R. C.; Metcalf, T.

1986-01-01

SMM soft X-ray data and Sacramento Peak Observatory H-alpha observations are combined in a study of the impulsive phase of a solar flare. A blue asymmetry, indicative of upflow motions, was observed in the coronal Ca XIX line during the soft X-ray rise phase. H-alpha redshifts, indicative of downward motions, were observed simultaneously in bright flare kernels during the period of hard X-ray emission. It is shown that, to within observational errors, the impulsive phase momentum transported by the upflowing soft X-ray plasma is equivalent to that of the downward moving chromospheric material.

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.

Subarcsecond bright points and quasi-periodic upflows below a quiescent filament observed by IRIS

NASA Astrophysics Data System (ADS)

Li, T.; Zhang, J.

2016-05-01

Context. The new Interface Region Imaging Spectrograph (IRIS) mission provides high-resolution observations of UV spectra and slit-jaw images (SJIs). These data have become available for investigating the dynamic features in the transition region (TR) below the on-disk filaments. Aims: The driver of "counter-streaming" flows along the filament spine is still unknown yet. The magnetic structures and the upflows at the footpoints of the filaments and their relations with the filament mainbody have not been well understood. We study the dynamic evolution at the footpoints of filaments in order to find some clues for solving these questions. Methods: Using UV spectra and SJIs from the IRIS, along with coronal images and magnetograms from the Solar Dynamics Observatory (SDO), we present the new features in a quiescent filament channel: subarcsecond bright points (BPs) and quasi-periodic upflows. Results: The BPs in the TR have a spatial scale of about 350-580 km and lifetimes of more than several tens of minutes. They are located at stronger magnetic structures in the filament channel with a magnetic flux of about 1017-1018 Mx. Quasi-periodic brightenings and upflows are observed in the BPs, and the period is about 4-5 min. The BP and the associated jet-like upflow comprise a "tadpole-shaped" structure. The upflows move along bright filament threads, and their directions are almost parallel to the spine of the filament. The upflows initiated from the BPs with opposite polarity magnetic fields have opposite directions. The velocity of the upflows in the plane of sky is about 5-50 km s-1. The emission line of Si IV 1402.77 Å at the locations of upflows exhibits obvious blueshifts of about 5-30 km s-1, and the line profile is broadened with the width of more than 20 km s-1. Conclusions: The BPs seem to be the bases of filament threads, and the upflows are able to convey mass for the dynamic balance of the filament. The "counter-streaming" flows in previous observations may be caused by the propagation of bi-directional upflows initiated from opposite polarity magnetic fields. We suggest that quasi-periodic brightenings of BPs and quasi-periodic upflows result from small-scale oscillatory magnetic reconnections, which are modulated by solar p-mode waves.

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 Three-dimensional Magnetic Structure and the Successive Eruptive Nature of Active Region 12371

NASA Astrophysics Data System (ADS)

Vemareddy, P.; Demóulin, P.

2018-04-01

We study the magnetic structure of a successively erupting sigmoid in active region 12371 by modeling the quasi-static coronal field evolution with nonlinear force-free field (NLFFF) equilibria. Helioseismic and Magnetic Imager/Solar Dynamic Observatory vector magnetograms are used as input to the NLFFF model. In all eruption events, the modeled structure resembles the observed pre-eruptive coronal sigmoid and the NLFFF core field is a combination of double inverse-J-shaped and inverse-S field lines with dips touching the photosphere. Such field lines are formed by the flux cancellation reconnection of opposite-J field lines at bald-patch locations, which in turn implies the formation of a weakly twisted flux-rope (FR) from large-scale sheared arcade field lines. Later on, this FR undergoes coronal tether-cutting reconnection until a coronal mass ejection is triggered. The modeled structure captured these major features of sigmoid-to-arcade-to-sigmoid transformation, which is reoccuring under continuous photospheric flux motions. Calculations of the field line twist reveal a fractional increase followed by a decrease of the number of pixels having a range of twist. This traces the buildup process of a twisted core field by slow photospheric motions and the relaxation after eruption, respectively. Our study infers that the large eruptivity of this AR is due to a steep decrease of the background coronal field meeting the torus instability criteria at a low height (≈40 Mm) in contrast to noneruptive ARs.

INFERRING THE CORONAL DENSITY IRREGULARITY FROM EUV SPECTRA

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

Hahn, M.; Savin, D. W., E-mail: mhahn@astro.columbia.edu

2016-09-20

Understanding the density structure of the solar corona is important for modeling both coronal heating and the solar wind. Direct measurements are difficult because of line-of-sight integration and possible unresolved structures. We present a new method for quantifying such structures using density-sensitive extreme ultraviolet line intensities to derive a density irregularity parameter, a relative measure of the amount of structure along the line of sight. We also present a simple model to relate the inferred irregularities to physical quantities, such as the filling factor and density contrast. For quiet-Sun regions and interplume regions of coronal holes, we find a densitymore » contrast of at least a factor of 3–10 and corresponding filling factors of about 10%–20%. Our results are in rough agreement with other estimates of the density structures in these regions. The irregularity diagnostic provides a useful relative measure of unresolved structure in various regions of the corona.« less

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.

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.

Distribution of lifetimes for coronal soft X-ray bright points

NASA Technical Reports Server (NTRS)

Golub, L.; Krieger, A. S.; Vaiana, G. S.

1976-01-01

The lifetime 'spectrum' of X-ray bright points (XBPs) is measured for a sample of 300 such features using soft X-ray images obtained with the S-054 X-ray spectrographic telescope aboard Skylab. 'Spectrum' here is defined as a function which gives the relative number of XBPs having a specific lifetime as a function of lifetime. The results indicate that a two-lifetime exponential can be fit to the decay curves of XBPs, that the spectrum is heavily weighted toward short lifetimes, and that the number of features lasting 20 to 30 hr or more is greater than expected. A short-lived component with an average lifetime of about 8 hr and a long-lived 1.5-day component are consistently found along with a few features lasting 50 hr or more. An examination of differences among the components shows that features lasting 2 days or less have a broad heliocentric-latitude distribution while nearly all the longer-lived features are observed within 30 deg of the solar equator.

ULTRA-NARROW NEGATIVE FLARE FRONT OBSERVED IN HELIUM-10830 Å USING THE 1.6 m NEW SOLAR TELESCOPE

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

Xu, Yan; Liu, Chang; Jing, Ju

2016-03-10

Solar flares are sudden flashes of brightness on the Sun and are often associated with coronal mass ejections and solar energetic particles that have adverse effects on the near-Earth environment. By definition, flares are usually referred to as bright features resulting from excess emission. Using the newly commissioned 1.6 m New Solar Telescope at Big Bear Solar Observatory, we show a striking “negative” flare with a narrow but unambiguous “dark” moving front observed in He i 10830 Å, which is as narrow as 340 km and is associated with distinct spectral characteristics in Hα and Mg ii lines. Theoretically, such negativemore » contrast in He i 10830 Å can be produced under special circumstances by nonthermal electron collisions or photoionization followed by recombination. Our discovery, made possible due to unprecedented spatial resolution, confirms the presence of the required plasma conditions and provides unique information in understanding the energy release and radiative transfer in astronomical objects.« less

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.

Is there a UV/X-ray connection in IRAS 13224-3809?

NASA Astrophysics Data System (ADS)

Buisson, D. J. K.; Lohfink, A. M.; Alston, W. N.; Cackett, E. M.; Chiang, C.-Y.; Dauser, T.; De Marco, B.; Fabian, A. C.; Gallo, L. C.; García, J. A.; Jiang, J.; Kara, E.; Middleton, M. J.; Miniutti, G.; Parker, M. L.; Pinto, C.; Uttley, P.; Walton, D. J.; Wilkins, D. R.

2018-04-01

We present results from the optical, ultraviolet, and X-ray monitoring of the NLS1 galaxy IRAS 13224-3809 taken with Swift and XMM-Newton during 2016. IRAS 13224-3809 is the most variable bright AGN in the X-ray sky and shows strong X-ray reflection, implying that the X-rays strongly illuminate the inner disc. Therefore, it is a good candidate to study the relationship between coronal X-ray and disc UV emission. However, we find no correlation between the X-ray and UV flux over the available ˜40 d monitoring, despite the presence of strong X-ray variability and the variable part of the UV spectrum being consistent with irradiation of a standard thin disc. This means either that the X-ray flux which irradiates the UV emitting outer disc does not correlate with the X-ray flux in our line of sight and/or that another process drives the majority of the UV variability. The former case may be due to changes in coronal geometry, absorption or scattering between the corona and the disc.

Debunking the Myth of Two-Temperature Coronae for RS CVn Systems Using Contemporaneous

NASA Astrophysics Data System (ADS)

Linsky, Jeffrey L.

For many years the standard analysis of low energy resolution x-ray observations of active late-type stars with the IPC, PSPC, TGS, and SSS has been to assume that the stellar coronae have plasma at only two temperatures. This type of analysis is constrained by the small information content and limited bandpass of the data but has NO PHYSICAL BASIS WHATSOEVER. We propose to test this hypothesis and to go beyond it to derive continuous emission measure distributions for the coronae of three very bright RS CVn systems (sigma-2 Cor Bor, UX Ari and VY Ari) using CONTEMPORANEOUS high resolution EUVE spectra and the improved x-ray energy resolution of ASCA. EUVE provides Fe lines with a broad range of ionization to derive the emission measure EM(T) independent of any uncertainties in the coronal abundances, while ASCA provides information on the hot plasma as seen in blended features of Mg, Si, S, and Fe and can test for coronal abundances different from the photosphere. We will model the quiescent and flare emission with magnetic loops.

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.

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.

Coronal magnetic structures observing campaign. I - Simultaneous microwave and soft X-ray observations of active regions at the solar limb

NASA Astrophysics Data System (ADS)

Nitta, N.; White, S. M.; Kundu, M. R.; Gopalswamy, N.; Holman, G. D.; Brosius, J. W.; Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.

1991-06-01

Using simultaneous microwave and soft X-ray measurements made with the Very Large Array (VLA) at 6 and 20 cm and the X-ray Polychromator (XRP) aboard the Solar Maximum Mission (SMM), we have studied two active regions near the solar limb. These observations were taken as part of the Coronal Magnetic Structures Observing Campaign (CoMStOC), a collaboration designed to study the magnetic field in the solar corona. The images in soft X-rays and at 20 cm wavelength are similar: both show peaks above the active regions and extended bridge of emission 200,000 km long connecting the two regions. The brightness temperature of the 20 cm emission is lower than that predicted from the X-ray emitting material, however; it can be attributed to free-free emission in cooler (<106 K) plasma not visible to XRP, with an optical depth ˜1. The 6 cm emission is concentrated at lower altitudes and in a ˜160,000 km long bundle of loops in the northern active region. Comparison of the 6 cm map with the potential magnetic field lines computed from photospheric magnetic fields (measured 2 days earlier) indicates that the 6 cm emission is associated with fields of less than ˜200 G. Such fields would be too weak to attribute the observed 6 cm emission to gyroresonance radiation. Analysis of the 6 cm loop bundle indicates that it is strongly asymmetric, with the magnetic field in the northern leg ˜2 times stronger than in the southern leg; the 6 cm emission most likely arises from a combination of hot ( ≥ 2 × 106 K) and cool plasmas, while the 20 cm emission becomes optically thick in the cooler (˜9 × 103 K) plasma. We estimate an Alfvén speed ˜7000 km s-1 and ratio of electron gyrofrequency to plasma frequency ˜1.0 in the northern leg of the 6 cm loop.

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.

MAGNETIC FLUX SUPPLEMENT TO CORONAL BRIGHT POINTS

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

Mou, Chaozhou; Huang, Zhenghua; Xia, Lidong

Coronal bright points (BPs) are associated with magnetic bipolar features (MBFs) and magnetic cancellation. Here we investigate how BP-associated MBFs form and how the consequent magnetic cancellation occurs. We analyze longitudinal magnetograms from the Helioseismic and Magnetic Imager to investigate the photospheric magnetic flux evolution of 70 BPs. From images taken in the 193 Å passband of the Atmospheric Imaging Assembly (AIA) we dermine that the BPs’ lifetimes vary from 2.7 to 58.8 hr. The formation of the BP MBFs is found to involve three processes, namely, emergence, convergence, and local coalescence of the magnetic fluxes. The formation of anmore » MBF can involve more than one of these processes. Out of the 70 cases, flux emergence is the main process of an MBF buildup of 52 BPs, mainly convergence is seen in 28, and 14 cases are associated with local coalescence. For MBFs formed by bipolar emergence, the time difference between the flux emergence and the BP appearance in the AIA 193 Å passband varies from 0.1 to 3.2 hr with an average of 1.3 hr. While magnetic cancellation is found in all 70 BPs, it can occur in three different ways: (I) between an MBF and small weak magnetic features (in 33 BPs); (II) within an MBF with the two polarities moving toward each other from a large distance (34 BPs); (III) within an MBF whose two main polarities emerge in the same place simultaneously (3 BPs). While an MBF builds up the skeleton of a BP, we find that the magnetic activities responsible for the BP heating may involve small weak fields.« less

PROBING THE SOLAR WIND ACCELERATION REGION WITH THE SUN-GRAZING COMET C/2002 S2

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

Giordano, S.; Raymond, J. C.; Lamy, P.

Comet C/2002 S2, a member of the Kreutz family of sungrazing comets, was discovered in white-light images of the Large Angle and Spectromeric Coronagraph Experiment coronagraph on the Solar and Heliospheric Observatory (SOHO) on 2002 September 18 and observed in H I Lyα emission by the SOHO Ultraviolet Coronagraph Spectrometer (UVCS) instrument at four different heights as it approached the Sun. The H I Lyα line profiles detected by UVCS are analyzed to determine the spectral parameters: line intensity, width, and Doppler shift with respect to the coronal background. Two-dimensional comet images of these parameters are reconstructed at the differentmore » heights. A novel aspect of the observations of this sungrazing comet data is that, whereas the emission from most of the tail is blueshifted, that along one edge of the tail is redshifted. We attribute these shifts to a combination of solar wind speed and interaction with the magnetic field. In order to use the comet to probe the density, temperature, and speed of the corona and solar wind through which it passes, as well as to determine the outgassing rate of the comet, we develop a Monte Carlo simulation of the H I Lyα emission of a comet moving through a coronal plasma. From the outgassing rate, we estimate a nucleus diameter of about 9 m. This rate steadily increases as the comet approaches the Sun, while the optical brightness decreases by more than a factor of 10 and suddenly recovers. This indicates that the optical brightness is determined by the lifetimes of the grains, sodium atoms, and molecules produced by the comet.« less

The density compression ratio of shock fronts associated with coronal mass ejections

NASA Astrophysics Data System (ADS)

Kwon, Ryun-Young; Vourlidas, Angelos

2018-02-01

We present a new method to extract the three-dimensional electron density profile and density compression ratio of shock fronts associated with coronal mass ejections (CMEs) observed in white light coronagraph images. We demonstrate the method with two examples of fast halo CMEs (˜2000 km s-1) observed on 2011 March 7 and 2014 February 25. Our method uses the ellipsoid model to derive the three-dimensional geometry and kinematics of the fronts. The density profiles of the sheaths are modeled with double-Gaussian functions with four free parameters, and the electrons are distributed within thin shells behind the front. The modeled densities are integrated along the lines of sight to be compared with the observed brightness in COR2-A, and a χ2 approach is used to obtain the optimal parameters for the Gaussian profiles. The upstream densities are obtained from both the inversion of the brightness in a pre-event image and an empirical model. Then the density ratio and Alfvénic Mach number are derived. We find that the density compression peaks around the CME nose, and decreases at larger position angles. The behavior is consistent with a driven shock at the nose and a freely propagating shock wave at the CME flanks. Interestingly, we find that the supercritical region extends over a large area of the shock and lasts longer (several tens of minutes) than past reports. It follows that CME shocks are capable of accelerating energetic particles in the corona over extended spatial and temporal scales and are likely responsible for the wide longitudinal distribution of these particles in the inner heliosphere. Our results also demonstrate the power of multi-viewpoint coronagraphic observations and forward modeling in remotely deriving key shock properties in an otherwise inaccessible regime.

Statistical study of coronal mass ejection source locations: Understanding CMEs viewed in coronagraphs

NASA Astrophysics Data System (ADS)

Wang, Yuming; Chen, Caixia; Gui, Bin; Shen, Chenglong; Ye, Pinzhong; Wang, S.

2011-04-01

How to properly understand coronal mass ejections (CMEs) viewed in white light coronagraphs is crucial to many relative researches in solar and space physics. The issue is now particularly addressed in this paper through studying the source locations of all the 1078 Large Angle and Spectrometric Coronagraph (LASCO) CMEs listed in Coordinated Data Analysis Workshop (CDAW) CME catalog during 1997-1998 and their correlation with CMEs' apparent parameters. By manually checking LASCO and Extreme Ultraviolet Imaging Telescope (EIT) movies of these CMEs, we find that, except 231 CMEs whose source locations cannot be identified due to poor data, there are 288 CMEs with location identified on the frontside solar disk, 234 CMEs appearing above solar limb, and 325 CMEs without evident eruptive signatures in the field of view of EIT. On the basis of the statistical results of CMEs' source locations, there are four physical issues: (1) the missing rate of CMEs by SOHO LASCO and EIT, (2) the mass of CMEs, (3) the causes of halo CMEs, and (4) the deflections of CMEs in the corona, are exhaustively analyzed. It is found that (1) about 32% frontside CMEs cannot be recognized by SOHO, (2) the brightness of a CME at any heliocentric distance is roughly positively correlated with its speed, and the CME mass derived from the brightness is probably overestimated, (3) both projection effect and violent eruption are the major causes of halo CMEs, and especially for limb halo CMEs the latter is the primary one, and (4) most CMEs deflected toward equator near the solar minimum; these deflections can be classified into three types: the asymmetrical expansion, the nonradial ejection, and the deflected propagation.

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.

Validation of Spherically Symmetric Inversion by Use of a Tomographically Reconstructed Three-Dimensional Electron Density of the Solar Corona

NASA Technical Reports Server (NTRS)

Wang, Tongjiang; Davila, Joseph M.

2014-01-01

Determining the coronal electron density by the inversion of white-light polarized brightness (pB) measurements by coronagraphs is a classic problem in solar physics. An inversion technique based on the spherically symmetric geometry (spherically symmetric inversion, SSI) was developed in the 1950s and has been widely applied to interpret various observations. However, to date there is no study of the uncertainty estimation of this method. We here present the detailed assessment of this method using a three-dimensional (3D) electron density in the corona from 1.5 to 4 solar radius as a model, which is reconstructed by a tomography method from STEREO/COR1 observations during the solar minimum in February 2008 (Carrington Rotation, CR 2066).We first show in theory and observation that the spherically symmetric polynomial approximation (SSPA) method and the Van de Hulst inversion technique are equivalent. Then we assess the SSPA method using synthesized pB images from the 3D density model, and find that the SSPA density values are close to the model inputs for the streamer core near the plane of the sky (POS) with differences generally smaller than about a factor of two; the former has the lower peak but extends more in both longitudinal and latitudinal directions than the latter. We estimate that the SSPA method may resolve the coronal density structure near the POS with angular resolution in longitude of about 50 deg. Our results confirm the suggestion that the SSI method is applicable to the solar minimum streamer (belt), as stated in some previous studies. In addition, we demonstrate that the SSPA method can be used to reconstruct the 3D coronal density, roughly in agreement with the reconstruction by tomography for a period of low solar activity (CR 2066). We suggest that the SSI method is complementary to the 3D tomographic technique in some cases, given that the development of the latter is still an ongoing research effort.

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.

The SOHO-Stellar Connection

NASA Technical Reports Server (NTRS)

Ayres, Thomas R.

1999-01-01

I discusses practical aspects of the so-called "solar-stellar" connection; namely, the fundamental principles, the tools at the disposal of the stellar astronomer, and a few recent examples of the connection in action. I provide an overall evolutionary context for coronal activity, calling attention to the very different circumstances of low mass main sequence stars like the Sun, which are active mainly early in their lives; compared with more massive stars, whose coronally active phase occurs near the end of their lives, during their brief incursion into the cool half of the Hertzsprung-Russell diagram as yellow and then red giants. On the instrumental slide, I concentrate primarily on spectroscopy, in the ultraviolet and X-ray bands where coronae leave their most obvious signatures. I present an early glimpse of the type of moderate resolution spectra we can expect from the recently launched Chandra observatory, and contemporaneous HST STIS high-resolution UV measurements of the CXO calibration star Capella (alpha Aur; G8 III + G1 III). I compare STIS spectra of solar-type dwarfs-zeta Dor (F7 V), an active coronal source; and alpha Cen A (G2 V), a near twin of the Sun-to a trace obtained with the SOHO SUMER imaging UV spectrometer. I also compare STIS line profiles of the active coronal dwarf to the corresponding features in the mixed-activity "hybrid-chromosphere" bright giant alpha TrA (K2 II) and the archetype "noncoronal" red giant Arcturus (alpha Boo; K2 III). The latter shows dramatic evidence for a "cool absorber" in its outer atmosphere that is extinguishing the "hot lines" (like Si IV lambda1393 and N V lambda1238) below about 1500 A, probably through absorption in the Si I lambda1525 and C I lambda1240 photoionization continua. The disappearance of coronae across the "Linsky-Haisch" dividing line near K1 III thus apparently is promoted by a dramatic overturning in the outer atmospheric structure, namely the coronae of the red giants seem to lie beneath their extended chromospheres, rather than outside as in the Sun. I then discuss an intriguing long-slit STIS low-resolution observation of an X-ray active late-A dwarf in the nearby Hyades cluster: the spatially resolved UV spectroscopy clearly shows that a previously unseen close companion (a dKe or dMe) likely is responsible for the coronal activity, rather than some unexplained departure of the A dwarf from its expected state of X-ray dormancy. Finally, I describe early results from a joint observing campaign involving SOHO SUMER, TRACE, and the Kitt Peak Infrared Imaging Spectrometer, conducted May 1999, to explore the dynamics of the quiet solar atmosphere through the key "magnetic transition zone" that separates the kinetically dominated deep photosphere from the magnetically dominated coronal regime. Linking spatially and temporally resolved solar properties to aspects of the averaged lineshapes (for example: widths, asymmetries, intensity ratios, and Doppler shifts) is a crucial step in carrying any physical wisdom we develop in the solar setting to the distant stars.

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.

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.

Evaluating the Uncertainties in the Electron Temperature and Radial Speed Measurements Using White Light Corona Eclipse Observations

NASA Technical Reports Server (NTRS)

Reginald, Nelson L.; Davilla, Joseph M.; St. Cyr, O. C.; Rastaetter, Lutz

2014-01-01

We examine the uncertainties in two plasma parameters from their true values in a simulated asymmetric corona. We use the Corona Heliosphere (CORHEL) and Magnetohydrodynamics Around the Sphere (MAS) models in the Community Coordinated Modeling Center (CCMC) to investigate the differences between an assumed symmetric corona and a more realistic, asymmetric one. We were able to predict the electron temperatures and electron bulk flow speeds to within +/-0.5 MK and +/-100 km s(exp-1), respectively, over coronal heights up to 5.0 R from Sun center.We believe that this technique could be incorporated in next-generation white-light coronagraphs to determine these electron plasma parameters in the low solar corona. We have conducted experiments in the past during total solar eclipses to measure the thermal electron temperature and the electron bulk flow speed in the radial direction in the low solar corona. These measurements were made at different altitudes and latitudes in the low solar corona by measuring the shape of the K-coronal spectra between 350 nm and 450 nm and two brightness ratios through filters centered at 385.0 nm/410.0 nm and 398.7 nm/423.3 nm with a bandwidth of is approximately equal to 4 nm. Based on symmetric coronal models used for these measurements, the two measured plasma parameters were expected to represent those values at the points where the lines of sight intersected the plane of the solar limb.

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

An Explanation of Remarkable Emission-line Profiles in Post-flare Coronal Rain

NASA Astrophysics Data System (ADS)

Lacatus, Daniela A.; Judge, Philip G.; Donea, Alina

2017-06-01

We study broad redshifted emission in chromospheric and transition region lines that appears to correspond to a form of post-flare coronal rain. Profiles of Mg II, C II, and Si IV lines were obtained using IRIS before, during, and after the X2.1 flare of 2015 March 11 (SOL2015-03-11T16:22). We analyze the profiles of the five transitions of Mg II (the 3p-3s h and k transitions, and three lines belonging to the 3d-3p transitions). We use analytical methods to understand the unusual profiles, together with higher-resolution observational data of similar phenomena observed by Jing et al. The peculiar line ratios indicate anisotropic emission from the strands that have cross-strand line center optical depths (k line) of between 1 and 10. The lines are broadened by unresolved Alfvénic motions whose energy exceeds the radiation losses in the Mg II lines by an order of magnitude. The decay of the line widths is accompanied by a decay in the brightness, suggesting a causal connection. If the plasma is ≲99% ionized, ion-neutral collisions can account for the dissipation; otherwise, a dynamical process seems necessary. Our work implies that the motions are initiated during the impulsive phase, to be dissipated as radiation over a period of an hour, predominantly by strong chromospheric lines. The coronal “rain” we observe is far more turbulent than most earlier reports have indicated, with implications for plasma heating mechanisms.

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.

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 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.

Solar Coronal Structure Study

NASA Technical Reports Server (NTRS)

Nitta, Nariaki; Bruner, Marilyn E.; Saba, Julia; Strong, Keith; Harvey, Karen

2000-01-01

The subject of this investigation is to study the physics of the solar corona through the analysis of the EUV and UV data produced by two flights (12 May 1992 and 25 April 1994) of the Lockheed Solar Plasma Diagnostics Experiment (SPDE) sounding rocket payload, in combination with Yohkoh and ground-based data. Each rocket flight produced both spectral and imaging data. These joint datasets are useful for understanding the physical state of various features in the solar atmosphere at different heights ranging from the photosphere to the corona at the time of the, rocket flights, which took place during the declining phase of a solar cycle, 2-4 years before the minimum. The investigation is narrowly focused on comparing the physics of small- and medium-scale strong-field structures with that of large-scale, weak fields. As we close th is investigation, we have to recall that our present position in the understanding of basic solar physics problems (such as coronal heating) is much different from that in 1995 (when we proposed this investigation), due largely to the great success of SOHO and TRACE. In other words, several topics and techniques we proposed can now be better realized with data from these missions. For this reason, at some point of our work, we started concentrating on the 1992 data, which are more unique and have more supporting data. As a result, we discontinued the investigation on small-scale structures, i.e., bright points, since high-resolution TRACE images have addressed more important physics than SPDE EUV images could do. In the final year, we still spent long time calibrating the 1992 data. The work was complicated because of the old-fashioned film, which had problems not encountered with more modern CCD detectors. After our considerable effort on calibration, we were able to focus on several scientific topics, relying heavily on the SPDE UV images. They include the relation between filaments and filament channels, the identification of hot loops, and the physical conditions of such loops especially at their foot-points. A total of four papers were completed from this contract which are listed in the last section.

Dynamical Thermal Structure of Super-arcade Downflows in Solar Flares

NASA Astrophysics Data System (ADS)

Chen, Xin; Liu, Rui; Deng, Na; Wang, Haimin

2015-04-01

Super­-arcade downflows (SADs) have been frequently observed during the gradual phase of flares near the limb. In coronal emission lines sensitive to flaring plasmas, they appear as tadpole-like dark voids against the bright fan-shape “haze” above the well-defined flare arcade and flow toward the arcade. We carefully studied several selected SADs from two flare events using data observed by Solar Dynamic Observatory / Atmospheric Imaging Assembly and calculated their differential emission measures (DEMs) as well as the DEM-weighted temperature. Our analysis shows that SADs are associated with a substantially decreased DEMs, by 1~3 order of magnitude, compared with the surrounding plasma. None of the SADs indicate DEM solutions above 20 MK, which implies that SADs are indeed density depletion rather than very hot plasma. This depression in DEMs rapidly recovers as SADs pass through, generally in a few minutes. In addition, we found that SADs in one event appear spatio-temporally associated with the formation of postflare loops. These results are examined against models and numerical simulations.

A Different Way to Visualize Solar Changes

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-07-01

This time series of SDO images of an active region shows coronal dimming as well as flares. These images can be combined into a minimum-value persistence map (bottom panel) that better reveals the entire dimming region. [Adapted from Thompson Young 2016]What if there were a better way to analyze a comets tail, the dimming of the Suns surface, or the path of material in a bright solar eruption? A recent study examines a new technique for looking at these evolving features.Mapping Evolving FeaturesSometimes interesting advances in astronomy come from simple, creative new approaches to analyzing old data. Such is the case in a new study by Barbara Thompson and Alex Young (NASA Goddard Space Flight Center), which introduces a technique called persistence mapping to better examine solar phenomena whose dynamic natures make them difficult to analyze.What is a persistence map? Suppose you have a set of N images of the same spatial region, with each image taken at a different time. To create a persistence map of these images, you would combine this set of images by retaining only the most extreme (for example, the maximum) value for each pixel, throwing away the remaining N-1 values for each pixel.Persistence mapping is especially useful for bringing out rare or intermittent phenomena features that would often be washed out if the images were combined in a sum or average instead. Thompson and Young describe three example cases where persistence mapping brings something new to the table.Top: Single SDO image of Comet Lovejoy. Center: 17 minutes of SDO images, combined in a persistence map. The structure of the tail is now clearly visible. Bottom: For comparison, the average pixel value for this sequence of images. Click for a closer look![Thompson Young 2016]A Comets TailAs Comet Lovejoy passed through the solar corona in 2011, solar physicists analyzed extreme ultraviolet images of its tail because the motion of the tail particles reveals information about the local coronal magnetic field.Past analyses have averaged or summed images of the comet in orbit to examine its tail. But a persistence map of the maximum pixel values far more clearly shows the striations within the tail that reveal the directions of the local magnetic field lines.Dimming of the SunDimming of the Suns corona near active regions tells us about the material thats evacuated during coronal mass ejections. This process can be complex: regions dim at different times, and flares sometimes hide the dimming, making it difficult to observe. But understanding the entire dimming region is necessary to infer the total mass loss and complete magnetic footprint of a gradual eruption from the Suns surface.SDO and STEREO-A images of a prominence eruption. Tracking the falling material is difficult due to the complex background. [Thompson Young 2016]Creating a persistence map of minimum pixel values achieves this and also neatly sidesteps the problem of flares hiding the dimming regions, since the bright pixels are discarded. In the authors example, a persistence map estimates 50% more mass loss for a coronal dimming event than the traditional image analysis method, and it reveals connections between dimming regions that were previously missed.An Erupting ProminenceThe authors final example is of falling prominence material after a solar eruption, seen in absorption against the bright corona. They show that you can construct a persistence map of minimum pixel values over the time the material falls (see the cover image), allowing the materials paths to be tracked despite the evolving background behind it. Tracing these trajectories provides information about the local magnetic field.Thompson and Youngs examples indicate that persistence mapping clearly provides new information in some cases of intermittent or slowly evolving solar phenomena. It will be interesting to see where else this technique can be applied!CitationB. J. Thompson and C. A. Young 2016 ApJ 825 27. doi:10.3847/0004-637X/825/1/27

Management of an uncomplicated crown fracture by reattaching the fractured fragment-Case report.

PubMed

Martos, Josué; Pinto, Karoline V A; Miguelis, Tiago M F; Xavier, Cristina B

2017-12-01

Coronal fractures of the anterior teeth are common sequelae of traumatic dental injuries. Reattachment of fractured tooth fragments using dental adhesive techniques offers some advantages, including restoration of the function, esthetics, shape, texture, and brightness of the surface. The present report describes a clinical case of reattachment with a 4-year clinical and radiographic follow up in a permanent maxillary central incisor with an uncomplicated crown fracture. Fragment reattachment is a conservative procedure, preserving esthetics and functionality, and it can provide an immediate positive emotional response from the patient. © 2017 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Hinode Takes an X-Ray of a Powerful Solar Flare

NASA Image and Video Library

2017-09-10

On Sept. 10, 2017, the Hinode satellite observed an enormous X-class flare burst from an active region on the western edge of the Sun. The video shows the high-energy flare as seen by Hinode's X-Ray Telescope. The emission was so bright that the initial blast caused the detector to saturate. The giant explosion sent a huge cloud of superhot plasma zooming into interplanetary space -- a phenomenon known as a coronal mass ejection. Studying large flares like this one with a variety of instruments is key to understanding exactly what causes these dramatic eruptions, and one day predicting them before they occur.

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.

FK COMAE BERENICES, KING OF SPIN: THE COCOA-PUFS PROJECT

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

Ayres, Thomas R.; Kashyap, V.; Saar, S.

COCOA-PUFS is an energy-diverse, time-domain study of the ultra-fast spinning, heavily spotted, yellow giant FK Comae Berenices (FK Com: HD117555; G4 III). This single star is thought to be a recent binary merger, and is exceptionally active by measure of its intense ultraviolet (UV) and X-ray emissions, and proclivity to flare. COCOA-PUFS was carried out with the Hubble Space Telescope in the UV (1200–3000 Å), using mainly its high-performance Cosmic Origins Spectrograph, but also high precision Space Telescope Imaging Spectrograph; Chandra X-ray Observatory in the soft X-rays (0.5–10 keV), utilizing its High-Energy Transmission Grating Spectrometer; together with supporting photometry andmore » spectropolarimetry in the visible from the ground. This is an introductory report on the project. FK Com displayed variability on a wide range of timescales over all wavelengths during the week-long main campaign, including a large X-ray flare; “super-rotational broadening” of the far-ultraviolet “hot lines” (e.g., Si iv 1393 Å; 8 × 10{sup 4} K) together with chromospheric Mg ii 2800 Å and C ii 1335 Å (1–3 × 10{sup 4} K); large Doppler swings suggestive of bright regions alternately on advancing and retreating limbs of the star; and substantial redshifts of the epoch-average emission profiles. These behaviors paint a picture of a highly extended, dynamic, hot (∼10 MK) coronal magnetosphere around the star, threaded by cooler structures perhaps analogous to solar prominences and replenished continually by surface activity and flares. Suppression of angular momentum loss by the confining magnetosphere could temporarily postpone the inevitable stellar spindown, thereby lengthening this highly volatile stage of coronal evolution.« less

Type III Solar Radio Burst Source Region Splitting due to a Quasi-separatrix Layer

NASA Astrophysics Data System (ADS)

McCauley, Patrick I.; Cairns, Iver H.; Morgan, John; Gibson, Sarah E.; Harding, James C.; Lonsdale, Colin; Oberoi, Divya

2017-12-01

We present low-frequency (80–240 MHz) radio imaging of type III solar radio bursts observed by the Murchison Widefield Array on 2015 September 21. The source region for each burst splits from one dominant component at higher frequencies into two increasingly separated components at lower frequencies. For channels below ∼132 MHz, the two components repetitively diverge at high speeds (0.1c–0.4c) along directions tangent to the limb, with each episode lasting just ∼2 s. We argue that both effects result from the strong magnetic field connectivity gradient that the burst-driving electron beams move into. Persistence mapping of extreme-ultraviolet jets observed by the Solar Dynamics Observatory reveals quasi-separatrix layers (QSLs) associated with coronal null points, including separatrix dome, spine, and curtain structures. Electrons are accelerated at the flare site toward an open QSL, where the beams follow diverging field lines to produce the source splitting, with larger separations at larger heights (lower frequencies). The splitting motion within individual frequency bands is interpreted as a projected time-of-flight effect, whereby electrons traveling along the outer field lines take slightly longer to excite emission at adjacent positions. Given this interpretation, we estimate an average beam speed of 0.2c. We also qualitatively describe the quiescent corona, noting in particular that a disk-center coronal hole transitions from being dark at higher frequencies to bright at lower frequencies, turning over around 120 MHz. These observations are compared to synthetic images based on the MHD algorithm outside a sphere (MAS) model, which we use to flux-calibrate the burst data.

FK Comae Berenices, King of Spin: The COCOA-PUFS Project

NASA Astrophysics Data System (ADS)

Ayres, Thomas R.; Kashyap, V.; Saar, S.; Huenemoerder, D.; Korhonen, H.; Drake, J. J.; Testa, P.; Cohen, O.; Garraffo, C.; Granzer, T.; Strassmeier, K.

2016-03-01

COCOA-PUFS is an energy-diverse, time-domain study of the ultra-fast spinning, heavily spotted, yellow giant FK Comae Berenices (FK Com: HD117555; G4 III). This single star is thought to be a recent binary merger, and is exceptionally active by measure of its intense ultraviolet (UV) and X-ray emissions, and proclivity to flare. COCOA-PUFS was carried out with the Hubble Space Telescope in the UV (1200-3000 Å), using mainly its high-performance Cosmic Origins Spectrograph, but also high precision Space Telescope Imaging Spectrograph; Chandra X-ray Observatory in the soft X-rays (0.5-10 keV), utilizing its High-Energy Transmission Grating Spectrometer; together with supporting photometry and spectropolarimetry in the visible from the ground. This is an introductory report on the project. FK Com displayed variability on a wide range of timescales over all wavelengths during the week-long main campaign, including a large X-ray flare; “super-rotational broadening” of the far-ultraviolet “hot lines” (e.g., Si IV 1393 Å 8 × 104 K) together with chromospheric Mg II 2800 Å and C II 1335 Å (1-3 × 104 K); large Doppler swings suggestive of bright regions alternately on advancing and retreating limbs of the star; and substantial redshifts of the epoch-average emission profiles. These behaviors paint a picture of a highly extended, dynamic, hot (˜10 MK) coronal magnetosphere around the star, threaded by cooler structures perhaps analogous to solar prominences and replenished continually by surface activity and flares. Suppression of angular momentum loss by the confining magnetosphere could temporarily postpone the inevitable stellar spindown, thereby lengthening this highly volatile stage of coronal evolution. COordinated Campaign of Observations and Analysis, Photosphere to Upper Atmosphere, of a Fast-rotating Star.

Flow Sources of The Solar Wind Stream Structieres

NASA Astrophysics Data System (ADS)

Lotova, N. A.; Obridko, V. N.; Vladimirskii, K. V.

The large-scale stream structure of the solar wind flow was studied at the main acceler- ation area of 10 to 40 solar radii from the Sun. Three independent sets of experimental data were used: radio astronomy observations of radio wave scattering on near-solar plasmas (large radio telescopes of the P.N.Lebedev Physical Institute were used); mor- phology of the WLC as revealed by the SOHO optical solar corona observations; solar magnetic field strength and configuration computed using the Wilcox Solar Observa- tory data. Experimental data of 1997-1998 years on the position of the transition, tran- sonic region of the solar wind flow were used as a parameter reflecting the intensity of the solar plasmas acceleration process. Correlation studies of these data combined with the magnetic field strength at the solar corona level revealed several types of the solar wind streams differing in the final result, the velocity at large distances from the Sun. Besides of the well-known flows stemming from the polar coronal holes, high-speed streams were observed arising in lateral areas of the streamer structures in contrast to the main body of the streamers, being a known source of the slow solar wind. The slowest streams arise at areas of mixed magnetic field structure compris- ing both open and closed (loop-like) filed lines. In the white-light corona images this shows extensive areas of bright amorphous luminosity.

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.

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

Can Polar Fields Explain Missing Open Flux?

NASA Astrophysics Data System (ADS)

Linker, J.; Downs, C.; Caplan, R. M.; Riley, P.; Mikic, Z.; Lionello, R.

2017-12-01

The "open" magnetic field is the portion of the Sun's magnetic field that extends out into the heliosphere and becomes the interplanetary magnetic field (IMF). Both the IMF and the Sun's magnetic field in the photosphere have been measured for many years. In the standard paradigm of coronal structure, the open magnetic field originates primarily in coronal holes. The regions that are magnetically closed trap the coronal plasma and give rise to the streamer belt. This basic picture is qualitatively reproduced by models of coronal structure using photospheric magnetic fields as input. If this paradigm is correct, there are two primary observational constraints on the models: (1) The open field regions in the model should approximately correspond to coronal holes observed in emission, and (2) the magnitude of the open magnetic flux in the model should match that inferred from in situ spacecraft measurements. Linker et al. (2017, ApJ, submitted) investigated the July 2010 time period for a range of observatory maps and both PFSS and MHD models. We found that all of the model/map combinations underestimated the interplanetary magnetic flux, unless the modeled open field regions were larger than observed coronal holes. An estimate of the open magnetic flux made entirely from solar observations (combining detected coronal hole boundaries with observatory synoptic magnetic maps) also underestimated the interplanetary magnetic flux. The magnetic field near the Sun's poles is poorly observed and may not be well represented in observatory maps. In this paper, we explore whether an underestimate of the polar magnetic flux during this time period could account for the overall underestimate of open magnetic flux. Research supported by NASA, AFOSR, and NSF.

EIGENMODES OF THREE-DIMENSIONAL MAGNETIC ARCADES IN THE SUN’S CORONA

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

Hindman, Bradley W.; Jain, Rekha, E-mail: hindman@solarz.colorado.edu

We develop a model of coronal-loop oscillations that treats the observed bright loops as an integral part of a larger three-dimensional (3D) magnetic structure comprised of the entire magnetic arcade. We demonstrate that magnetic arcades within the solar corona can trap MHD fast waves in a 3D waveguide. This is accomplished through the construction of a cylindrically symmetric model of a magnetic arcade with a potential magnetic field. For a magnetically dominated plasma, we derive a governing equation for MHD fast waves and from this equation we show that the magnetic arcade forms a 3D waveguide if the Alfvén speedmore » increases monotonically beyond a fiducial radius. Both magnetic pressure and tension act as restoring forces, instead of just tension as is generally assumed in 1D models. Since magnetic pressure plays an important role, the eigenmodes involve propagation both parallel and transverse to the magnetic field. Using an analytic solution, we derive the specific eigenfrequencies and eigenfunctions for an arcade possessing a discontinuous density profile. The discontinuity separates a diffuse cylindrical cavity and an overlying shell of denser plasma that corresponds to the bright loops. We emphasize that all of the eigenfunctions have a discontinuous axial velocity at the density interface; hence, the interface can give rise to the Kelvin–Helmholtz instability. Further, we find that all modes have elliptical polarization with the degree of polarization changing with height. However, depending on the line of sight, only one polarization may be clearly visible.« 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.

Solar cycle evolution of solar wind speed structure between 1973 and 1985 observed with the interplanetary scintillation method

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

Kojima, M.; Kakinuma, T.

1987-07-01

The solar cycle evolution of solar wind speed structure was studied for the years from 1973 to 1985 on a basis of interplanetary scintillation observations using a new method for mapping solar wind speed to the source surface. The major minimum-speed regions are distributed along a neutral line through the whole period of a solar cycle: when solar activity is low, they are distributed on the wavy neutral line along the solar equator; in the active phase they also tend to be distributed along the neutral line, which has a large latitudinal amplitude. The minimum-speed regions tend to be distributedmore » not only along the neutral line but also at low magnetic intensity regions and/or coronal bright regions which do not correspond to the neutral line. As the polar high-speed regions extend equatorward around the minimum phase, the latitudinal gradient of speed increases at the boundaries of the low-speed region, and the width of the low-speed region decreases. One or two years before the minimum of solar activity, two localized minimum-speed regions appear on the neutral line, and their locations are longitudinally separated by 180. copyright American Geophysical Union 1987« less

An analysis of source structure effects in radio interferometry measurements

NASA Technical Reports Server (NTRS)

Thomas, J. B.

1980-01-01

To begin a study of structure effects, this report presents a theoretical framework, proposes an effective position approach to structure corrections based on brightness distribution measurements, and analyzes examples of analytical and measured brightness distributions. Other topics include the effect of the frequency dependence of a brightness distribution on bandwidth synthesis (BWS) delay, the determination of the absolute location of a measured brightness distribution, and structure effects in dual frequency calibration of charged particle delays. For the 10 measured distributions analyzed, it was found that the structure effect in BWS delay at X-band (3.6 cm) can reach 30 cm, but typically falls in the range of 0 to 5 cm. A trial limit equation that is dependent on visibility was successfully tested against the 10 measured brightness distributions (seven sources). If the validity of this particular equation for an upper limit can be established for nearly all sources, the structure effect in BWS delay could be greatly reduced without supplementary measurements of brightness distributions.

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.

Hot coronal plasma phenomena disclosed, classified and studied in the SPIRIT experiment on CORONAS-F mission

NASA Astrophysics Data System (ADS)

Urnov, Alexander; Kuzin, Sergey; Bogachev, Sergey; Goryaev, Farid; Dennis, Brian; Reva, Anton; Shestov, Sergey; Soloviev, Alexander; Zhitnik, Igor

The advent of XUV full-Sun monochromatic imaging spectroscopy in the SPIRIT experiment on CORONAS-F (2001-2005) helped to reveal highly dynamic 4 -20 MK coronal plasma structures characterized by various sizes from 6" through 0.3 solar radius and lifetimes from several minutes to several days. Due to the high dynamic range (more than four orders of magnitude) of the X-Ray detector, the monochromatic images in the Mg XII ion line at 8.42 ˚ allowed the A whole Sun light curves of the GOES 1-8˚ channel to be decomposed over the temporal flux A profiles of individual X-Ray sources. Thus, the GOES background emission was shown to be the result of a superposition of a series of low intensity "elemental bursts" each lasting for 10-20 min and recurring at different locations on the solar disk. A new phenomenon of small size, short-lived X-ray "hot spots" (hot X-ray bright points, HXBP) has been disclosed in addition to the previously reported giant post-eruptive sources ("spiders"). The classification has been proposed of hot plasma phenomena by their spatial and temporal properties being the "markers" of energy storage and release sites for all observable X-ray sources. It was also shown that these sources are characterized by complex topology rather than by the strength of the magnetic field since they associated only with active region loop systems comprising of more than two spots. Diagnostic techniques developed on the basis of monochromatic and broad band data simultaneously measured on CORONAS-F, GOES, and RHESSI were used to obtain space-time dynamics of the temperature and density content for hot coronal plasma structures in the range logT=6.0 -7.2. A theoretical description of the spider phenomena based on long-duration recurrently flaring giant magneto-plasma formations, is given using the Chandrasekhar-Prendergast model of a spherical magnetic vortex, generalized to account for density perturbations. This model presents a sequence of magnetic toroidal configurations stabilized within a spherical cover by an external potential magnetic field. It reveals remarkable properties that help to explain, by simple physical considerations, how the conditions sufficient for fast and efficient energy release, specific for a weak flare, may take place sporadically without disrupting the whole system. The generalized solution gives a realistic picture of observable phenomena allowing new possibilities for the generation of dissipative flare-like processes in the spherical magnetic vortex, and, thus, providing a natural description of their specific features.

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

Zeng, Zhicheng; Chen, Bin; Goode, Philip R.

Jets are ubiquitously present in both quiet and active regions on the Sun. They are widely believed to be driven by magnetic reconnection. A fan-spine structure has been frequently reported in some coronal jets and flares, and has been regarded as a signature of ongoing magnetic reconnection in a topology consisting of a magnetic null connected by a fan-like separatrix surface and a spine. However, for small-scale chromospheric jets, clear evidence of such structures is rather rare, although it has been implied in earlier works that showed an inverted-Y-shaped feature. Here we report high-resolution (0.″16) observations of a small-scale chromosphericmore » jet obtained by the New Solar Telescope (NST) using 10830 Å filtergrams. Bi-directional flows were observed across the separatrix regions in the 10830 Å images, suggesting that the jet was produced due to magnetic reconnection. At the base of the jet, a fan-spine structure was clearly resolved by the NST, including the spine and the fan-like surface, as well as the loops before and after the reconnection. A major part of this fan-spine structure, with the exception of its bright footpoints and part of the base arc, was invisible in the extreme ultraviolet and soft X-ray images (observed by the Atmosphere Imaging Assembly and the X-Ray Telescope, respectively), indicating that the reconnection occurred in the upper chromosphere. Our observations suggest that the evolution of this chromospheric jet is consistent with a two-step reconnection scenario proposed by Török et al.« less

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

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.

The bright-bright and bright-dark mode coupling-based planar metamaterial for plasmonic EIT-like effect

NASA Astrophysics Data System (ADS)

Yu, Wei; Meng, Hongyun; Chen, Zhangjie; Li, Xianping; Zhang, Xing; Wang, Faqiang; Wei, Zhongchao; Tan, Chunhua; Huang, Xuguang; Li, Shuti

2018-05-01

In this paper, we propose a novel planar metamaterial structure for the electromagnetically induced transparency (EIT)-like effect, which consists of a split-ring resonator (SRR) and a pair of metal strips. The simulated results indicate that a single transparency window can be realized in the symmetry situation, which originates from the bright-bright mode coupling. Further, a dual-band EIT-like effect can be achieved in the asymmetry situation, which is due to the bright-bright mode coupling and bright-dark mode coupling, respectively. Different EIT-like effect can be simultaneously achieved in the proposed structure with the different situations. It is of certain significance for the study of EIT-like effect.

Solar corona photographed from Apollo 15 one minute prior to sunrise

NASA Image and Video Library

1971-07-31

AS15-98-13311 (31 July 1971) --- The solar corona, as photographed from the Apollo 15 spacecraft about one minute prior to sunrise on July 31, 1971, is seen just beyond the lunar horizon. The bright object on the opposite of the frame is the planet Mercury. The bright star near the frame center is Regulus, and the lesser stars form the head of the constellation Leo. Mercury is approximately 28 degrees from the center of the sun. The solar coronal streamers, therefore, appear to extend about eight degrees from the sun's center. This solar corona photograph was the second in a series of seven. Three such series were obtained by astronaut Alfred M. Worden, command module pilot, during the solo part of his lunar orbital flight. They represent man's first view of this part of the sun's light. While astronauts David R. Scott, commander, and James B. Irwin, lunar module pilot, descended in the Lunar Module (LM) "Falcon" to explore the Hadley-Apennine area of the moon, astronaut Worden remained with the Command and Service Modules (CSM) in lunar orbit.

Science Objectives of the FOXSI Small Explorer Mission Concept

NASA Astrophysics Data System (ADS)

Shih, Albert Y.; Christe, Steven; Alaoui, Meriem; Allred, Joel C.; Antiochos, Spiro K.; Battaglia, Marina; Buitrago-Casas, Juan Camilo; Caspi, Amir; Dennis, Brian R.; Drake, James; Fleishman, Gregory D.; Gary, Dale E.; Glesener, Lindsay; Grefenstette, Brian; Hannah, Iain; Holman, Gordon D.; Hudson, Hugh S.; Inglis, Andrew R.; Ireland, Jack; Ishikawa, Shin-Nosuke; Jeffrey, Natasha; Klimchuk, James A.; Kontar, Eduard; Krucker, Sam; Longcope, Dana; Musset, Sophie; Nita, Gelu M.; Ramsey, Brian; Ryan, Daniel; Saint-Hilaire, Pascal; Schwartz, Richard A.; Vilmer, Nicole; White, Stephen M.; Wilson-Hodge, Colleen

2016-05-01

Impulsive particle acceleration and plasma heating at the Sun, from the largest solar eruptive events to the smallest flares, are related to fundamental processes throughout the Universe. While there have been significant advances in our understanding of impulsive energy release since the advent of RHESSI observations, there is a clear need for new X-ray observations that can capture the full range of emission in flares (e.g., faint coronal sources near bright chromospheric sources), follow the intricate evolution of energy release and changes in morphology, and search for the signatures of impulsive energy release in even the quiescent Sun. The FOXSI Small Explorer (SMEX) mission concept combines state-of-the-art grazing-incidence focusing optics with pixelated solid-state detectors to provide direct imaging of hard X-rays for the first time on a solar observatory. We present the science objectives of FOXSI and how its capabilities will address and resolve open questions regarding impulsive energy release at the Sun. These questions include: What are the time scales of the processes that accelerate electrons? How do flare-accelerated electrons escape into the heliosphere? What is the energy input of accelerated electrons into the chromosphere, and how is super-heated coronal plasma produced?

Alpha Centauri at a Crossroads

NASA Astrophysics Data System (ADS)

Ayres, Thomas

2015-10-01

Nearby Alpha Centauri AB (G2V+K1V) contains the two best characterized solar-like dwarf stars, which also have the best studied multi-MK coronal X-ray activity cycles, extending back to the 1970's. Objective is to continue tracking the evolving multi-decadal high-energy narrative of Alpha Cen with semiannual X-ray pointings in Chandra Cycles 16-18, as the system reaches a coronal crossroads: solar twin A rising toward starspot cycle maximum, K-type companion B sinking into a minimum. HST/STIS UV spectra will support and leverage the X-ray measurements by probing chromospheric and subcoronal dynamics, with connection to the corona through the FUV Fe XII 1242 forbidden line. Only Chandra can resolve the AB X-ray pair as the Alpha Cen orbit also reaches a crossroads in 2016 (only 4 separation), and only HST/STIS can measure the bright Alpha Cen stars with sufficient UV spectral resultion and wavelength coherence. What's more, the recent validation of the STIS NDA,B,C long slits for echelle use now make feasible NUV E230H measurements (e.g., of key chromospheric tracers Mg II 2800 and Mg I 2852) which heretofore were not practical in a long-term program of this nature.

Alpha Centauri at a Crossroads

NASA Astrophysics Data System (ADS)

Ayres, Thomas

2016-10-01

Nearby Alpha Centauri AB (G2V+K1V) contains the two best characterized solar-like dwarf stars, which also have the best studied multi-MK coronal X-ray activity cycles, extending back to the 1970's. Objective is to continue tracking the evolving multi-decadal high-energy narrative of Alpha Cen with semiannual X-ray pointings in Chandra Cycles 16-18, as the system reaches a coronal crossroads: solar twin A rising toward starspot cycle maximum, K-type companion B sinking into a minimum. HST/STIS UV spectra will support and leverage the X-ray measurements by probing chromospheric and subcoronal dynamics, with connection to the corona through the FUV Fe XII 1242 forbidden line. Only Chandra can resolve the AB X-ray pair as the Alpha Cen orbit also reaches a crossroads in 2016 (only 4 separation), and only HST/STIS can measure the bright Alpha Cen stars with sufficient UV spectral resolution and wavelength coherence. What's more, the recent validation of the STIS NDA,B,C long slits for echelle use now make feasible NUV E230H measurements (e.g., of key chromospheric tracers Mg II 2800 and Mg I 2852) which heretofore were not practical in a long-term program of this nature.

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.

Combining Linear Polarization Measurements of both Forbidden/Permitted Coronal Emission Lines for measuring the Vector Magnetic Field in the Solar Corona

NASA Astrophysics Data System (ADS)

Dima, G. I.; Kuhn, J. R.; Mickey, D.

2014-12-01

Measuring the coronal vector magnetic field is still a major challenge in solar physics. This is due to the intrinsic weakness of the field (~4 G at a height of 0.1 Rsun above an active region) and the large thermal broadening of coronal emission lines. Current methods deduce either the direction of the magnetic field or the magnetic flux density. We propose using concurrent linear polarization measurements in the near IR of forbidden and permitted lines to calculate the coronal vector magnetic field. The effect of the magnetic field on the polarization properties of emitted light is encapsulated in the Hanle effect. In the unsaturated Hanle regime both the direction and strength of the magnetic field affect the linear polarization, while for saturated Hanle the polarization is insensitive to the strength of the field. Coronal forbidden lines are always in the saturated Hanle regime so the linear polarization holds no information on the strength of the field. By pairing measurements of both forbidden and permitted lines we would be able to obtain both the direction and strength of the field. The near-IR region of the spectrum offers the opportunity to study this problem from the ground. The FeXIII 1.075 um and SiX 1.431 um forbidden lines are strongly polarizable and are sufficiently bright over a large field of view (out to 1.5 Rsun). Measurements of both these lines can be paired up with the recently observed coronal HeI 1.083 um permitted line. The first data set used to test this technique was taken during the March 29, 2006 total solar eclipse and consisted of near-IR spectra covering the spectral region 0.9-1.8 um, with a field of view of 3 x 3 Rsun. The data revealed unexpectedly strong SiX emission compared to FeXIII. Using the HAO FORWARD suite of codes we produced simulated emission maps from a global HMD model for the day of the eclipse. Comparing the intensity variation of the measurements and the model we predict that SiX emission is more extended for this day that the model would suggest, further supporting the possible usefulness of SiX polarimetry. The development of this method and associated tools will be critical in interpreting the high spectral, spatial and temporal IR measurements that will be possible when the Daniel K. Inouye Solar Telescope (DKIST) is completed in a few years time.

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

Observations of Fe XIV Line Intensity Variations in the Solar Corona During the 21 August 2017 Solar Eclipse

NASA Astrophysics Data System (ADS)

Johnson, Payton; Ladd, Edwin

2018-01-01

We present time- and spatially-resolved observations of the inner solar corona in the 5303 Å line of Fe XIV, taken during the 21 August 2017 solar eclipse from a field observing site in Crossville, TN. These observations are used to characterize the intensity variations in this coronal emission line, and to compare with oscillation predictions from models for heating the corona by magnetic wave dissipation.The observations were taken with two Explore Scientific ED 102CF 102 mm aperture triplet apochromatic refractors. One system used a DayStar custom-built 5 Å FWHM filter centered on the Fe XIV coronal spectral line and an Atik Titan camera for image collection. The setup produced images with a pixel size of 2.15 arcseconds (~1.5 Mm at the distance to the Sun), and a field of view of 1420 x 1060 arcseconds, covering approximately 20% of the entire solar limb centered near the emerging sunspot complex AR 2672. We obtained images with an exposure time of 0.22 seconds and a frame rate of 2.36 Hz, for a total of 361 images during totality.An identical, co-aligned telescope/camera system observed the same portion of the solar corona, but with a 100 Å FWHM Baader Planetarium solar continuum filter centered on a wavelength of 5400 Å. Images with an exposure time of 0.01 seconds were obtained with a frame rate of 4.05 Hz. These simultaneous observations are used as a control to monitor brightness variations not related to coronal line oscillations.

THE CURIOUS CASE OF THE ALPHA PERSEI CORONA: A DWARF IN SUPERGIANT'S CLOTHING?

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

Ayres, Thomas R., E-mail: Thomas.Ayres@Colorado.edu

2011-09-10

Alpha Persei (HD 20902: F5 Iab) is a luminous, nonvariable supergiant located at the blue edge of the Cepheid instability strip. It is one of the brightest coronal X-ray sources in the young open cluster bearing its name, yet warm supergiants as a class generally avoid conspicuous high-energy activity. The Cosmic Origins Spectrograph on the Hubble Space Telescope has recently uncovered additional oddities. The 1290-1430 A far-ultraviolet (FUV) spectrum of {alpha} Per is dominated by photospheric continuum emission, with numerous superposed absorption features, mainly stellar. However, the normal proxies of coronal activity, such as the Si IV 1400 A doubletmore » (T {approx} 8 x 10{sup 4} K), are very weak, as are the chromospheric C II 1335 A multiplet (T {approx} 3 x 10{sup 4} K) and O I 1305 A triplet. In fact, the Si IV features of {alpha} Per are not only narrower than those of later, G-type supergiants of similar L{sub X}/L{sub bol}, but are also fainter (in L{sub SiIV}/L{sub bol}) by two orders of magnitude. Further, a reanalysis of the ROSAT pointing on {alpha} Per finds the X-ray centroid offset from the stellar position by 9'', at a moderate level of significance. The FUV and X-ray discrepancies raise the possibility that the coronal source might be unrelated to the supergiant, perhaps an accidentally close dwarf cluster member; heretofore unrecognized in the optical, lost in the glare of the bright star.« less

Constraining Stellar Coronal Mass Ejections through Multi-wavelength Analysis of the Active M Dwarf EQ Peg

NASA Astrophysics Data System (ADS)

Crosley, M. K.; Osten, R. A.

2018-03-01

Stellar coronal mass ejections remain experimentally unconstrained, unlike their stellar flare counterparts, which are observed ubiquitously across the electromagnetic spectrum. Low-frequency radio bursts in the form of a type II burst offer the best means of identifying and constraining the rate and properties of stellar CMEs. CME properties can be further improved through the use of proposed solar-stellar scaling relations and multi-wavelength observations of CMEs through the use of type II bursts and the associated flares expected to occur alongside them. We report on 20 hr of observation of the nearby, magnetically active, and well-characterized M dwarf star EQ Peg. The observations are simultaneously observed with the Jansky Very Large Array at their P-band (230–470 MHz) and at the Apache Point observatory in the SDSS u‧ filter (λ = 3557 Å). Dynamic spectra of the P-band data, constructed to search for signals in the frequency-time domains, did not reveal evidence of drifting radio bursts that could be ascribed to type II bursts. Given the sensitivity of our observations, we are able to place limits on the brightness temperature and source size of any bursts that may have occurred. Using solar scaling rations on four observed stellar flares, we predict CME parameters. Given the constraints on coronal density and photospheric field strength, our models suggest that the observed flares would have been insufficient to produce detectable type II bursts at our observed frequencies. We consider the implications of these results, and other recent findings, on stellar mass loss.

Cracking the Conundrum of F-supergiant Coronae

NASA Astrophysics Data System (ADS)

Ayres, Thomas R.

2018-02-01

Chandra X-ray and HST far-ultraviolet (FUV) observations of three early-F supergiants have shed new light on a previous puzzle involving a prominent member of the class: α Persei (HD 20902: F5 Ib). The warm supergiant is a moderately strong, hard coronal (T∼ {10}7 K) X-ray source, but has 10 times weaker “subcoronal” Si IV 1393 Å (T∼ 8× {10}4 K) emissions than early-G supergiants of similar high-energy properties. The α Per X-ray excess was speculatively ascribed to a close-in hyperactive G-dwarf companion, which could have escaped previous notice, lost in the glare of the bright star. However, a subsequent dedicated multi-wavelength imaging campaign failed to find any evidence for a resolved secondary. The origin of the α Per high-energy dichotomy then devolved to (1) an unresolved companion or (2) intrinsic coronal behavior. Exploring the second possibility, the present program has found that early-F supergiants do appear to belong to a distinct coronal class, characterized by elevated X-ray/FUV ratios, although sharing some similarities with Cepheid variables in their transitory X-ray “high states.” Remarkably, the early-F supergiants now are seen to align with the low-activity end of the X-ray/FUV sequence defined by late-type dwarfs, suggesting that the disjoint behavior relative to the G supergiants might be attributed to thinner outer atmospheres on the F types, as in dwarfs, but in this case perhaps caused by a weakened “ionization valve” effect due to overly warm photospheres.

Coronal Loop Evolution Observed with AIA and Hi-C

NASA Technical Reports Server (NTRS)

Mulu-Moore, Fana; Winebarger, A.; Cirtain, J.; Kobayashi, K.; Korreck, K.; Golub, L.; Kuzin. S.; Walsh, R.; DeForest, C.; DePontieu, B.;

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.

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.

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.

EUV observations of the active sun from the Harvard experiment on ATM. [Apollo Telescope Mount

NASA Technical Reports Server (NTRS)

Noyes, R. W.; Foukal, P. V.; Reeves, E. M.; Schmahl, E. J.; Timothy, J. G.; Vernazza, J. E.; Withbroe, G. L.; Huber, M. C. E.

1975-01-01

Some extreme UV observations of solar active regions made with a scanning spectroheliometer are described. Spectroheliograms constructed from digital data using a computer-driven cathode-ray tube display show clearly how the appearance of an active region changes as a function of temperature. Flare studies indicate that the impulsive rise in EUV emission occurs essentially simultaneously at all levels from the transition zone to the corona. Observations of sunspots reveal a very intense emission in transition zone lines. A matrix of Mg x rasters covering the entire sun reveals several hundred bright points having dimensions of 30 arc seconds or less. Other observations include coronal holes and prominences.

A study of excess H-alpha emission in chromospherically active M dwarf

NASA Technical Reports Server (NTRS)

Young, Arthur; Skumanich, Andrew; Stauffer, John R.; Harlan, Eugene; Bopp, Bernard W.

1989-01-01

Spectroscopic observations from three observatories are combined to study the properties of the excess H-alpha emission which characterizes the most chromospherically active subset of the M dwarf stars, known as the dMe stars. It is demonstrated that the excess H-alpha luminosity from these stars is a monotonically decreasing function of their (R-I) color, and evidence is presented which suggests that the product of the mean surface brightness and the mean filling factor of the emissive regions is essentially constant with color. Another significant result of the study is a linear correlation between the excess luminosity in H-alpha and the coronal X-ray luminosity.

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.

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.

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.

Coronal Properties of X-ray bright stars in young associations: abundances, temperatures and variability

NASA Astrophysics Data System (ADS)

Argiroffi, Costanza

2006-03-01

In this work I have investigated open issues related to the X-ray radiation from young stars, including heating mechanisms of the emitting plasma, its chemical composition, and possible effects due to circumstellar accretion disks. To this aim, I have analyzed observations of young nearby stars taken with the X-ray observatories XMM-Newton and Chandra. For a detailed study of the characteristics of the X-ray emitting plasma, I have selected two X-ray bright young stars, TWA 5 and PZ Tel, for which high-resolution X-ray spectroscopy was achievable, and two regions of the young stellar association Upper Scorpius (USco), for which X-ray images and medium-resolution spectra of individual sources were obtained. TWA 5 is a 10 Myr old star in the TW Hydrae association, which is still accreting material from its circumstellar envelope, while PZ Tel is a ? 12 Myr star in the beta Pictoris moving group, which already dissipated its circumstellar disk. The different evolutionary stages of these two stars allow to probe whether X-ray emission is produced, or affected, by accretion processes. High-resolution X-ray spectra of TWA 5 and PZ Tel were gathered with the grating spectrometers on board XMM-Newton and Chandra, respectively. From the measurements of individual emission line fluxes in their X-ray spectra, I have derived emission measure distributions vs. temperature, abundances, and electron densities of the X-ray emitting plasma. I have found that, in spite of their different evolutionary status, hot (T ? 10 MK) plasma is the main responsible for the observed X-ray emission of both stars. The hot plasma on TWA 5 displays peculiar element abundances with respect to the solar photospheric composition with Ne/Fe ? 10(Ne/Fe), while the coronal plasma on PZ Tel shows Ne/Fe ? 3(Ne/Fe). To explain the strong Fe underabundance (? 0.1 Fe) and the extremely high Ne/Fe ratio of TWA 5 I have considered three different scenarios: (1) coronal plasma may be affected by selective element depletion dependent on the first ionization potential (FIP), similar to the inverse FIP effect usually observed in the coronae of very active stars; (2) the X-ray emitting plasma on TWA 5 may be partially heated by the shock produced by the infall accretion streams onto the stellar photosphere, and hence it may originate from the circumstellar disk, where grain depletion is a possible cause of the metal deficiency; (3) the peculiar abundances on TWA 5 are due to the local chemical composition of the original cloud from which the star formed, and this explains why TWA 5 shares the same abundances with TW Hydrae, another young star located in the same stellar association. The 5 Myr old USco association, due to its vicinity (145 pc) and low circumstellar extinction, is a good laboratory to perform a detailed study of PMS stars of this age. Here I present the results of the analysis of deep XMM-Newton observations of two USco regions covering an area of ?0.4 deg^2 . I have detected 224 X-ray sources among which 22 have been identified with probable USco members on the basis of near infrared and optical photometry. Among these 22 sources, I have recognized 13 sources as USco members for the first time. Except for the intermediate mass star HD 142578, all the detected USco sources are low mass stars of spectral type ranging from G to late M, and including at least one brown dwarf. The X-ray spectral analysis of the most intense USco sources indicates metal depleted plasma with temperature of ? 10 MK, resembling the typical case of active main sequence stars, as already found for TWA 5 and PZ Tel. Strong flares detected from 4 USco members have allowed me to derive coronal lengths of the flaring structures by performing time resolved spectroscopy during the flare decay phases. In all cases the flaring loops have sizes of 10^10 - 10^11 cm, hence smaller than the corresponding stellar radii. These results suggest that, in these very young stars coronal plasma is confined in compact loops. The coronal properties of PZ Tel, TWA 5, and of the USco members indicate that the coronae of pre-main sequence stars become similar to those of older active main-sequence stars on short time scales (? 5 Myr), in terms of average temperature, density, elemental abundances, and loop lengths, even if accretion processes from circumstellar disks are still at work.

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.

ON THE ACTIVE REGION BRIGHT GRAINS OBSERVED IN THE TRANSITION REGION IMAGING CHANNELS OF IRIS

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

Skogsrud, H.; Voort, L. Rouppe van der; Pontieu, B. De

The Interface Region Imaging Spectrograph (IRIS) provides spectroscopy and narrow band slit-jaw (SJI) imaging of the solar chromosphere and transition region at unprecedented spatial and temporal resolutions. Combined with high-resolution context spectral imaging of the photosphere and chromosphere as provided by the Swedish 1 m Solar Telescope (SST), we can now effectively trace dynamic phenomena through large parts of the solar atmosphere in both space and time. IRIS SJI 1400 images from active regions, which primarily sample the transition region with the Si iv 1394 and 1403 Å lines, reveal ubiquitous bright “grains” which are short-lived (two to five minute)more » bright roundish small patches of sizes 0.″5–1.″7 that generally move limbward with velocities up to about 30 km s{sup −1}. In this paper, we show that many bright grains are the result of chromospheric shocks impacting the transition region. These shocks are associated with dynamic fibrils (DFs), most commonly observed in Hα. We find that the grains show the strongest emission in the ascending phase of the DF, that the emission is strongest toward the top of the DF, and that the grains correspond to a blueshift and broadening of the Si iv lines. We note that the SJI 1400 grains can also be observed in the SJI 1330 channel which is dominated by C ii lines. Our observations show that a significant part of the active region transition region dynamics is driven from the chromosphere below rather than from coronal activity above. We conclude that the shocks that drive DFs also play an important role in the heating of the upper chromosphere and lower transition region.« less

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 TWO-RIBBON WHITE-LIGHT FLARE ASSOCIATED WITH A FAILED SOLAR ERUPTION OBSERVED BY ONSET, SDO, AND IRIS

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

Cheng, X.; Hao, Q.; Ding, M. D.

Two-ribbon brightenings are one of the most remarkable characteristics of an eruptive solar flare and are often used to predict the occurrence of coronal mass ejections (CMEs). Nevertheless, it was recently called into question whether all two-ribbon flares are eruptive. In this paper, we investigate a two-ribbon-like white-light (WL) flare that is associated with a failed magnetic flux rope (MFR) eruption on 2015 January 13, which has no accompanying CME in the WL coronagraph. Observations by the Optical and Near-infrared Solar Eruption Tracer and the Solar Dynamics Observatory reveal that with the increase of the flare emission and the acceleration ofmore » the unsuccessfully erupting MFR, two isolated kernels appear at the WL 3600 Å passband and quickly develop into two elongated ribbon-like structures. The evolution of the WL continuum enhancement is completely coincident in time with the variation of Fermi hard X-ray 26–50 keV flux. An increase of continuum emission is also clearly visible at the whole FUV and NUV passbands observed by the Interface Region Imaging Spectrograph. Moreover, in one WL kernel, the Si iv, C ii, and Mg ii h/k lines display significant enhancement and non-thermal broadening. However, their Doppler velocity pattern is location-dependent. At the strongly bright pixels, these lines exhibit a blueshift, while at moderately bright ones, the lines are generally redshifted. These results show that the failed MFR eruption is also able to produce a two-ribbon flare and high-energy electrons that heat the lower atmosphere, causing the enhancement of the WL and FUV/NUV continuum emissions and chromospheric evaporation.« less

Understanding the Impact of Return-Current Losses on the X-Ray Emission from Solar Flares

NASA Technical Reports Server (NTRS)

Holman, Gordon D.

2012-01-01

I obtain and examine the implications of one-dimensional analytic solutions for return-current losses on an initially power-law distribution of energetic electrons with a sharp low-energy cutoff in flare plasma with classical (collisional) resistivity. These solutions show, for example, that return-current losses are not sensitive to plasma density, but are sensitive to plasma temperature and the low energy cutoff of the injected nonthermal electron distribution. A characteristic distance from the electron injection site, x(sub rc), is derived. At distances less than x(sub rc) the electron flux density is not reduced by return-current losses, but plasma heating can be substantial in this region, in the upper, coronal part of the flare loop. Before the electrons reach the collisional thick-target region of the flare loop, an injected power-law electron distribution with a low-energy cutoff maintains that structure, but with a flat energy distribution below the cutoff energy, which is now determined by the total potential drop experienced by the electrons. Modifications due to the presence of collisional losses are discussed. I compare these results with earlier analytical results and with more recent numerical simulations. Emslie's 1980 conjecture that there is a maximum integrated X-ray source brightness on the order of 10(exp -15) photons per square centimeter per second per square centimeter is examined. I find that this is not actually a maximum brightness and its value is parameter dependent, but it is nevertheless a valuable benchmark for identifying return-current losses in hard X-ray spectra. I discuss an observational approach to identifying return-current losses in flare data, including identification of a return-current "bump" in X-ray light curves at low photon energies.

A Forecast of Reduced Solar Activity and Its Implications for NASA

NASA Technical Reports Server (NTRS)

Schatten, Kenneth; Franz, Heather

2005-01-01

The "Solar Dynamo" method of solar activity forecasting is reviewed. Known generically as a 'precursor" method, insofar as it uses observations which precede solar activity generation, this method now uses the Solar Dynamo Amplitude (SODA) Index to estimate future long-term solar activity. The peak amplitude of the next solar cycle (#24), is estimated at roughly 124 in terms of smoothed F10.7 Radio Flux and 74 in terms of the older, more traditional smoothed international or Zurich Sunspot number (Ri or Rz). These values are significantly smaller than the amplitudes of recent solar cycles. Levels of activity stay large for about four years near the peak in smoothed activity, which is estimated to occur near the 2012 timeflame. Confidence is added to the prediction of low activity by numerous examinations of the Sun s weakened polar field. Direct measurements are obtained by the Mount Wilson Solar Observatory and the Wilcox Solar Observatory. Further support is obtained by examining the Sun s polar faculae (bright features), the shape of coronal soft X-ray "holes," and the shape of the "source surface" - a calculated coronal feature which maps the large scale structure of the Sun s field. These features do not show the characteristics of well-formed polar coronal holes associated with typical solar minima. They show stunted polar field levels, which are thought to result in stunted levels of solar activity during solar cycle #24. The reduced levels of solar activity would have concomitant effects upon the space environment in which satellites orbit. In particular, the largest influences would affect orbit determination of satellites in LEO (Low Earth Orbit), based upon the altered thermospheric and exospheric densities. A decrease in solar activity would result in smaller satellite decay rates, as well as fewer large solar events that can destroy satellite electronic functions. Other effects of reduced solar activity upon the space environment include enhanced galactic cosmic rays and more space debris at low altitudes (from the decay of old satellite parts, etc.). The reasons are well known: namely, solar activity serves to sweep the inner heliosphere of galactic cosmic rays, and lower exospheric densities result in decreased drag on LEO debris, allowing longer lifetimes.

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.

Visual evidence of the Sterno-Etrussia geomagnetic excursion (~2700 BP)?

NASA Astrophysics Data System (ADS)

Raspopov, O. M.; Dergachev, V. A.; Goos'kova, E. G.; Morner, N.-A.

2003-04-01

In the Bible's Old Testament Book of Ezekiel there is a description of the Ezekiel's vision of "a great cloud with brightness round about it" to the north of the observation site. The event described in the Bible occurred in 593 BC, i.e., approximately 2600 years ago. Ezekiel was at that time approximately 100 km south of Babylon (latitude ~ 32 N, longitude ~ 45 E). Auroral specialists interpret the Ezekiel's vision as observation of coronal auroral displays at low latitudes. However, to support this hypothesis, it is necessary to understand the physical mechanism responsible for generation of these forms of auroras at low latitudes. Analysis of palaeo- and archaeomagnetic data, including our data on magnetic properties of sediments of the Barents and White Seas and the literature data, has shown that about 2700 BP, i.e., in Ezekiel's time, development of a geomagnetic "Sterno-Etrussia" excursion took place. The duration of the excursion during which the northern geomagnetic pole wandered to the Southern Hemisphere was no more than 200-300 years. Manifestations of this excursion were found in 16 regions of the Eurasian continent and adjacent seas and also in the North and South America. By plotting the path along which the northern geomagnetic pole wandered to the southern latitudes during this excursion on the basis of palaeomagnetic data, we have found that it wandered in the longitude sector plus or minus 30 degrees, and about 2700 BP the northern geomagnetic pole was at the longitude close to the Babylon longitude, where Ezekiel had his vision. Thus, at that time Babylon was at high geomagnetic latitudes where regular coronal auroral displays occur. Records of observation of the unusual brightness of the sky in the V-VI centuries BC can also be found in Greek chronicles. This indicates that the Ezekiel's vision was not the only observation of auroras at low latitudes during the period considered here. This work was supported by INTAS, Grant 97-31008 and PFBR, Grant 00-05-64921.

On the Relation Between Facular Bright Points and the Magnetic Field

NASA Astrophysics Data System (ADS)

Berger, Thomas; Shine, Richard; Tarbell, Theodore; Title, Alan; Scharmer, Goran

1994-12-01

Multi-spectral images of magnetic structures in the solar photosphere are presented. The images were obtained in the summers of 1993 and 1994 at the Swedish Solar Telescope on La Palma using the tunable birefringent Solar Optical Universal Polarimeter (SOUP filter), a 10 Angstroms wide interference filter tuned to 4304 Angstroms in the band head of the CH radical (the Fraunhofer G-band), and a 3 Angstroms wide interference filter centered on the Ca II--K absorption line. Three large format CCD cameras with shuttered exposures on the order of 10 msec and frame rates of up to 7 frames per second were used to create time series of both quiet and active region evolution. The full field--of--view is 60times 80 arcseconds (44times 58 Mm). With the best seeing, structures as small as 0.22 arcseconds (160 km) in diameter are clearly resolved. Post--processing of the images results in rigid coalignment of the image sets to an accuracy comparable to the spatial resolution. Facular bright points with mean diameters of 0.35 arcseconds (250 km) and elongated filaments with lengths on the order of arcseconds (10(3) km) are imaged with contrast values of up to 60 % by the G--band filter. Overlay of these images on contemporal Fe I 6302 Angstroms magnetograms and Ca II K images reveals that the bright points occur, without exception, on sites of magnetic flux through the photosphere. However, instances of concentrated and diffuse magnetic flux and Ca II K emission without associated bright points are common, leading to the conclusion that the presence of magnetic flux is a necessary but not sufficient condition for the occurence of resolvable facular bright points. Comparison of the G--band and continuum images shows a complex relation between structures in the two bandwidths: bright points exceeding 350 km in extent correspond to distinct bright structures in the continuum; smaller bright points show no clear relation to continuum structures. Size and contrast statistical cross--comparisons compiled from measurements of over two-thousand bright point structures are presented. Preliminary analysis of the time evolution of bright points in the G--band reveals that the dominant mode of bright point evolution is fission of larger structures into smaller ones and fusion of small structures into conglomerate structures. The characteristic time scale for the fission/fusion process is on the order of minutes.

Advancing Heliophysics and Space Weather Research with Student Internships and Faculty Development

NASA Astrophysics Data System (ADS)

Johnson, L. P.; Ng, C.; Marchese, P.; Austin, S. A.; Frost, J.; Cheung, T. K.; Tremberger, G.; Robbins, I.; Carlson, B. E.; Paglione, T.; Damas, C.; Steiner, J. C.; Rudolph, E.; Lewis, E.; Ford, K. S.; Cline, T.

2011-12-01

Expanding research capability in Heliophysics and Space Weather is the major focus of a collaboration between the City University of New York (CUNY) and NASA Goddard Space Fight Center (GSFC). The Heliophysics Education Consortium has a two-pronged approach centered on undergraduate research and faculty development. Summer 2011 student research projects include: Comparison of Fast Propagating Solar Waves and Slow Kelvin-Helmholtz Waves captured by SDO; Brightness Fluctuation of March 8, 2011 Eruption with Magnetic Rope Structure Measured by SDO; Investigation of Sunspot Regions, Coronal Mass Ejections and Solar Flares; An Integration and Testing Methodology for a Microsatellite; Comparative Analysis of Attitude Control Systems for Microsatellites; Spectral Analysis of Aerosols in Jupiter's Atmosphere Using HST Data; Alternative Sources of 5 GHz and 15 GHz Emissions in Active Galactic Nuclei; Probing Starburst-Driven Superwinds; Asteroid Astrometry; and Optimize an Electrostatic Deflection Element on PIXIES (Plasma Ion Experiment - Ion and Electron Sensor) for a CUNY student at GSFC. Faculty development workshops were conducted by Space Weather Action Center scientists. These workshops included a faculty development session at the CUNY Graduate Center and high school teachers professional development series at Queensborough Community College. The project is supported by NASA award NNX10AE72G.

Solar Scientist Confirm Existence of Flux Ropes on the Sun

NASA Image and Video Library

2013-02-14

Caption: This is an image of magnetic loops on the sun, captured by NASA's Solar Dynamics Observatory (SDO). It has been processed to highlight the edges of each loop to make the structure more clear. A series of loops such as this is known as a flux rope, and these lie at the heart of eruptions on the sun known as coronal mass ejections (CMEs.) This is the first time scientists were able to discern the timing of a flux rope's formation. (SDO AIA 131 and 171 difference blended image of flux ropes during CME.) Credit: NASA/Goddard Space Flight Center/SDO ---- On July 18, 2012, a fairly small explosion of light burst off the lower right limb of the sun. Such flares often come with an associated eruption of solar material, known as a coronal mass ejection or CME – but this one did not. Something interesting did happen, however. Magnetic field lines in this area of the sun's atmosphere, the corona, began to twist and kink, generating the hottest solar material – a charged gas called plasma – to trace out the newly-formed slinky shape. The plasma glowed brightly in extreme ultraviolet images from the Atmospheric Imaging Assembly (AIA) aboard NASA’s Solar Dynamics Observatory (SDO) and scientists were able to watch for the first time the very formation of something they had long theorized was at the heart of many eruptive events on the sun: a flux rope. Eight hours later, on July 19, the same region flared again. This time the flux rope's connection to the sun was severed, and the magnetic fields escaped into space, dragging billions of tons of solar material along for the ride -- a classic CME. "Seeing this structure was amazing," says Angelos Vourlidas, a solar scientist at the Naval Research Laboratory in Washington, D.C. "It looks exactly like the cartoon sketches theorists have been drawing of flux ropes since the 1970s. It was a series of figure eights lined up to look like a giant slinky on the sun." To read more about this new discovery go to: 1.usa.gov/14UHsTt

Solar Scientist Confirm Existence of Flux Ropes on the Sun

NASA Image and Video Library

2017-12-08

Caption: This is an image of magnetic loops on the sun, captured by NASA's Solar Dynamics Observatory (SDO). It has been processed to highlight the edges of each loop to make the structure more clear. A series of loops such as this is known as a flux rope, and these lie at the heart of eruptions on the sun known as coronal mass ejections (CMEs.) This is the first time scientists were able to discern the timing of a flux rope's formation. (SDO AIA 131 and 171 difference blended image of flux ropes during CME.) Credit: NASA/Goddard Space Flight Center/SDO ---- On July 18, 2012, a fairly small explosion of light burst off the lower right limb of the sun. Such flares often come with an associated eruption of solar material, known as a coronal mass ejection or CME – but this one did not. Something interesting did happen, however. Magnetic field lines in this area of the sun's atmosphere, the corona, began to twist and kink, generating the hottest solar material – a charged gas called plasma – to trace out the newly-formed slinky shape. The plasma glowed brightly in extreme ultraviolet images from the Atmospheric Imaging Assembly (AIA) aboard NASA’s Solar Dynamics Observatory (SDO) and scientists were able to watch for the first time the very formation of something they had long theorized was at the heart of many eruptive events on the sun: a flux rope. Eight hours later, on July 19, the same region flared again. This time the flux rope's connection to the sun was severed, and the magnetic fields escaped into space, dragging billions of tons of solar material along for the ride -- a classic CME. "Seeing this structure was amazing," says Angelos Vourlidas, a solar scientist at the Naval Research Laboratory in Washington, D.C. "It looks exactly like the cartoon sketches theorists have been drawing of flux ropes since the 1970s. It was a series of figure eights lined up to look like a giant slinky on the sun." To read more about this new discovery go to: 1.usa.gov/14UHsTt

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).

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.

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.

Fibrillar Chromospheric Spicule-Like Counterparts to an EUV and Soft X-Ray Blowout Coronal Jet

NASA Technical Reports Server (NTRS)

Sterling, Alphonse C.; Harra, Louise K.; Moore, Ronald L.

2010-01-01

We observe an erupting jet feature in a solar polar coronal hole, using data from Hinode/SOT, EIS, and XRT, with supplemental data from STEREO/EUVI. From EUV and soft X-ray (SXR) images we identify the erupting feature as a blowout coronal jet: in SXRs it is a jet with bright base, and in EUV it appears as an eruption of relatively cool (approximately 50,000 K) material of horizontal size scale approximately 30" originating from the base of the SXR jet. In SOT Ca II H images the most pronounced analog is a pair of thin (approximately 1") ejections, at the locations of either of the two legs of the erupting EUV jet. These Ca II features eventually rise beyond 45", leaving the SOT field of view, and have an appearance similar to standard spicules except that they are much taller. They have velocities similar to that of "type II" spicules, approximately 100 kilometers per second, and they appear to have spicule-like substructures splitting off from them with horizontal velocity approximately 50 kilometers per second, similar to the velocities of splitting spicules measured by Sterling et al. (2010). Motions of splitting features and of other substructures suggest that the macroscopic EUV jet is spinning or unwinding as it is ejected. This and earlier work suggests that a sub-population of Ca II type II spicules are the Ca II manifestation of portions of larger-scale erupting magnetic jets. A different sub-population of type II spicules could be blowout jets occurring on a much smaller horizontal size scale than the event we observe here.

Decayless low-amplitude kink oscillations: a common phenomenon in the solar corona?

NASA Astrophysics Data System (ADS)

Anfinogentov, S. A.; Nakariakov, V. M.; Nisticò, G.

2015-11-01

Context. We investigate the decayless regime of coronal kink oscillations recently discovered in the Solar Dynamics Observatory (SDO)/AIA data. In contrast to decaying kink oscillations that are excited by impulsive dynamical processes, this type of transverse oscillations is not connected to any external impulsive impact, such as a flare or coronal mass ejection, and does not show any significant decay. Moreover the amplitude of these decayless oscillations is typically lower than that of decaying oscillations. Aims: The aim of this research is to estimate the prevalence of this phenomenon and its characteristic signatures. Methods: We analysed 21 active regions (NOAA 11637-11657) observed in January 2013 in the 171 Å channel of SDO/AIA. For each active region we inspected six hours of observations, constructing time-distance plots for the slits positioned across pronounced bright loops. The oscillatory patterns in time-distance plots were visually identified and the oscillation periods and amplitudes were measured. We also estimated the length of each oscillating loop. Results: Low-amplitude decayless kink oscillations are found to be present in the majority of the analysed active regions. The oscillation periods lie in the range from 1.5 to 10 min. In two active regions with insufficient observation conditions we did not identify any oscillation patterns. The oscillation periods are found to increase with the length of the oscillating loop. Conclusions: The considered type of coronal oscillations is a common phenomenon in the corona. The established dependence of the oscillation period on the loop length is consistent with their interpretation in terms of standing kink waves. Appendix A is available in electronic form at http://www.aanda.org

EXPLAINING INVERTED-TEMPERATURE LOOPS IN THE QUIET SOLAR CORONA WITH MAGNETOHYDRODYNAMIC WAVE-MODE CONVERSION

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

Schiff, Avery J.; Cranmer, Steven R.

Coronal loops trace out bipolar, arch-like magnetic fields above the Sun’s surface. Recent measurements that combine rotational tomography, extreme-ultraviolet imaging, and potential-field extrapolation have shown the existence of large loops with inverted-temperature profiles, i.e., loops for which the apex temperature is a local minimum, not a maximum. These “down loops” appear to exist primarily in equatorial quiet regions near solar minimum. We simulate both these and the more prevalent large-scale “up loops” by modeling coronal heating as a time-steady superposition of (1) dissipation of incompressible Alfvén wave turbulence and (2) dissipation of compressive waves formed by mode conversion from themore » initial population of Alfvén waves. We found that when a large percentage (>99%) of the Alfvén waves undergo this conversion, heating is greatly concentrated at the footpoints and stable “down loops” are created. In some cases we found loops with three maxima that are also gravitationally stable. Models that agree with the tomographic temperature data exhibit higher gas pressures for “down loops” than for “up loops,” which is consistent with observations. These models also show a narrow range of Alfvén wave amplitudes: 3 to 6 km s{sup -1} at the coronal base. This is low in comparison to typical observed amplitudes of 20–30 km s{sup -1} in bright X-ray loops. However, the large-scale loops we model are believed to compose a weaker diffuse background that fills much of the volume of the corona. By constraining the physics of loops that underlie quiescent streamers, we hope to better understand the formation of the slow solar wind.« less

Waves and Turbulence in the Solar Corona: A Surplus of Sources and Sinks

NASA Astrophysics Data System (ADS)

Cranmer, Steven R.

2018-06-01

The Sun's corona is a hot, dynamic, and highly stochastic plasma environment, and we still do not yet understand how it is heated. Both the loop-filled coronal base and the extended acceleration region of the solar wind appear to be filled with waves and turbulent eddies. Models that invoke the dissipation of these magnetohydrodynamic (MHD) fluctuations have had some success in explaining the heating. In this presentation I will review some new insights about the different ways these waves are thought to be created and destroyed. For example: (1) Intergranular bright points in the photosphere are believed to extend upwards as coronal flux tubes, and their transverse oscillations are driven by the underlying convection. New high-resolution MHD simulations predict the kinetic energy spectra of the resulting coronal waves and serve as predictions for upcoming DKIST observations. (2) Magnetic reconnection in the supergranular network of the low corona can also generate MHD waves, and new Monte Carlo models of the resulting power spectra will be presented. The total integrated power in these waves is typically small in comparison to that of photosphere-driven waves, but they dominate the total spectrum at periods longer than about 30 minutes. (3) Because each magnetic field line in the corona is tied to at least one specific chromospheric footpoint (each with its own base pressure), the corona also plays host to field-aligned "density striations." These fluctuations vary with the supergranular network on timescales of roughly a day, but they also act as a spatially varying background through which the higher-frequency waves propagate. These multiple sources of space/time variability must be taken into account to properly understand off-limb measurements from CoMP and EIS/Hinode, as well as in-situ measurements from Parker Solar Probe.

MINIFILAMENT ERUPTIONS THAT DRIVE CORONAL JETS IN A SOLAR ACTIVE REGION

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

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

We present observations of eruptive events in an active region adjacent to an on-disk coronal hole on 2012 June 30, primarily using data from the Solar Dynamics Observatory ( SDO )/Atmospheric Imaging Assembly (AIA), SDO /Helioseismic and Magnetic Imager (HMI), and STEREO - B . One eruption is of a large-scale (∼100″) filament that is typical of other eruptions, showing slow-rise onset followed by a faster-rise motion starting as flare emissions begin. It also shows an “EUV crinkle” emission pattern, resulting from magnetic reconnections between the exploding filament-carrying field and surrounding field. Many EUV jets, some of which are surges,more » sprays and/or X-ray jets, also occur in localized areas of the active region. We examine in detail two relatively energetic ones, accompanied by GOES M1 and C1 flares, and a weaker one without a GOES signature. All three jets resulted from small-scale (∼20″) filament eruptions consistent with a slow rise followed by a fast rise occurring with flare-like jet-bright-point brightenings. The two more-energetic jets showed crinkle patters, but the third jet did not, perhaps due to its weakness. Thus all three jets were consistent with formation via erupting minifilaments, analogous to large-scale filament eruptions and to X-ray jets in polar coronal holes. Several other energetic jets occurred in a nearby portion of the active region; while their behavior was also consistent with their source being minifilament eruptions, we could not confirm this because their onsets were hidden from our view. Magnetic flux cancelation and emergence are candidates for having triggered the minifilament eruptions.« less

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

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

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.

The formation process of the He I lambda 10830 line in cool giant stars

NASA Technical Reports Server (NTRS)

Luttermoser, Donald G.

1993-01-01

The Final Report on the formation process of the He I lambda 10830 line in cool giant stars is presented. The research involves observing a sample of cool giant stars with ROSAT. These stars were selected from the list of bright stars which display He I lambda 10830 in absorption or emission and lie on the cool side of the coronal dividing line. With measured x ray fluxes or upper limits measured by the Position Sensitive Proportional Counter (PSPC), the role x rays play in the formation of this important line was investigated using the non-LTE radiative transfer code PANDORA. Hydrodynamic calculations were performed to investigate the contributions of acoustic wave heating in the formation of this line as well.

The Extreme Ultraviolet Flux of Very Low Mass Stars

NASA Astrophysics Data System (ADS)

Drake, Jeremy

2017-09-01

The X-ray and EUV emission of stars is vital for understanding the atmospheres and evolution of their planets. The coronae of dwarf stars later than M6 behave differently to those of earlier spectral types and are more X-ray dim and radio bright. Too faint to have been observed by EUVE, their EUV behavior is currently highly uncertain. We propose to observe a small sample of late M dwarfs using the off-axis HRC-S thin Al" filter that is sensitive to EUV emission in the 50-200 A range. The measured fluxes will be used to understand the amount of cooler coronal plasma present, and extend X-ray-EUV flux relations to the latest stellar types.

Observations of the Ca II K line in Hel0830A dark points on August 3, 1985

NASA Technical Reports Server (NTRS)

Holt, Rush D.; Park, Albert H.; Thompson, Joseph C.; Mullan, D. M.

1986-01-01

Spectroheliograms taken in the light of He I 10830 A at the National Solar Observatory Vacuum Telescope on Kitt Peak were used to identify coronal holes and bright points (BPs). Target points were identified, coordinates calculated, and spectra recorded. For each spectrum, the difference in wavelength between the Ca II K minimum and the FeI reference line was calculated. It was noteworthy that the overall effect is a blueshift. It should be noted that if material of chromospheric density moves outward at this velocity, it could supply the mass flux of the solar wind if this chromospheric flow was concentrated in a few dozen sources, each of a diameter of a few arc seconds.

Twisted Fields

NASA Image and Video Library

2017-12-08

OHO captured this image of a CME from the side – but the structure looks much different from the classic light bulb CME. The filament of material bursting off the sun has a helical magnetic structure, which is unraveling like a piece of yarn during the eruption. Credit: ESA/NASA/SOHO..---..CME WEEK: What To See in CME Images Two main types of explosions occur on the sun: solar flares and coronal mass ejections. Unlike the energy and x-rays produced in a solar flare – which can reach Earth at the speed of light in eight minutes – coronal mass ejections are giant, expanding clouds of solar material that take one to three days to reach Earth. Once at Earth, these ejections, also called CMEs, can impact satellites in space or interfere with radio communications. During CME WEEK from Sept. 22 to 26, 2014, we explore different aspects of these giant eruptions that surge out from the star we live with. When a coronal mass ejection blasts off the sun, scientists rely on instruments called coronagraphs to track their progress. Coronagraphs block out the bright light of the sun, so that the much fainter material in the solar atmosphere -- including CMEs -- can be seen in the surrounding space. CMEs appear in these images as expanding shells of material from the sun's atmosphere -- sometimes a core of colder, solar material (called a filament) from near the sun's surface moves in the center. But mapping out such three-dimensional components from a two-dimensional image isn't easy. Watch the slideshow to find out how scientists interpret what they see in CME pictures. The images in the slideshow are from the three sets of coronagraphs NASA currently has in space. One is on the joint European Space Agency and NASA Solar and Heliospheric Observatory, or SOHO. SOHO launched in 1995, and sits between Earth and the sun about a million miles away from Earth. The other two coronagraphs are on the two spacecraft of the NASA Solar Terrestrial Relations Observatory, or STEREO, mission, which launched in 2006. The two STEREO spacecraft are both currently viewing the far side of the sun. Together these instruments help scientists create a three-dimensional model of any CME as its journey unfolds through interplanetary space. Such information can show why a given characteristic of a CME close to the sun might lead to a given effect near Earth, or any other planet in the solar system...NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

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.

Thermal energy creation and transport and X-ray/EUV emission in a thermodynamic MHD CME simulation

NASA Astrophysics Data System (ADS)

Reeves, K.; Mikic, Z.; Torok, T.; Linker, J.; Murphy, N. A.

2017-12-01

We model a CME using the PSI 3D numerical MHD code that includes coronal heating, thermal conduction and radiative cooling in the energy equation. The magnetic flux distribution at 1 Rs is produced by a localized subsurface dipole superimposed on a global dipole field, mimicking the presence of an active region within the global corona. We introduce transverse electric fields near the neutral line in the active region to form a flux rope, then a converging flow is imposed that causes the eruption. We follow the formation and evolution of the current sheet and find that instabilities set in soon after the reconnection commences. We simulate XRT and AIA EUV emission and find that the instabilities manifest as bright features emanating from the reconnection region. We examine the quantities responsible for plasma heating and cooling during the eruption, including thermal conduction, radiation, adiabatic compression and expansion, coronal heating and ohmic heating due to dissipation of currents. We find that the adiabatic compression plays an important role in heating the plasma around the current sheet, especially in the later stages of the eruption when the instabilities are present. Thermal conduction also plays an important role in the transport of thermal energy away from the current sheet region throughout the reconnection process.

Plasma upflows and microwave emission in hot supra-arcade structure associated with AN M1.6 limb flare

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

Kim, S.; Shibasaki, K.; Bain, H.-M.

2014-04-20

We have investigated a supra-arcade structure associated with an M1.6 flare, which occurred on the south-east limb on 2010 November 4. It is observed in EUV with the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, microwaves at 17 and 34 GHz with the Nobeyama Radioheliograph (NoRH), and soft X-rays of 8-20 keV with RHESSI. Interestingly, we found exceptional properties of the supra-arcade thermal plasma from the AIA 131 Å and the NoRH: (1) plasma upflows along large coronal loops and (2) enhancing microwave emission. RHESSI detected two soft X-ray sources, a broad one in the middle ofmore » the supra-arcade structure and a bright one just above the flare-arcade. We estimated the number density and thermal energy for these two source regions during the decay phase of the flare. In the supra-arcade source, we found that there were increases of the thermal energy and the density at the early and last stages, respectively. On the contrary, the density and thermal energy of the source on the top of the flare-arcade decreases throughout. The observed upflows imply that there is continuous energy supply into the supra-arcade structure from below during the decay phase of the flare. It is hard to explain by the standard flare model in which the energy release site is located high in the corona. Thus, we suggest that a potential candidate of the energy source for the hot supra-arcade structure is the flare-arcade, which has exhibited a predominant emission throughout.« less

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.

Influence of Forest-Canopy Morphology and Relief on Spectral Characteristics of Taiga Forests

NASA Astrophysics Data System (ADS)

Zhirin, V. M.; Knyazeva, S. V.; Eydlina, S. P.

2017-12-01

The article deals with the results of a statistical analysis reflecting tendencies (trends) of the relationship between spectral characteristics of taiga forests, indicators of the morphological structure of forest canopy and illumination of the territory. The study was carried out on the example of the model forest territory of the Priangarskiy taiga region of Eastern Siberia (Krasnoyarsk krai) using historical data (forest inventory 1992, Landsat 5 TM 16.06.1989) and the digital elevation model. This article describes a method for determining the quantitative indicator of morphological structure of forest canopy based on taxation data, and the authors propose to subdivide the morphological structure into high complexity, medium complexity, and relatively simple. As a result of the research, dependences of average values of spectral brightness in near and short-wave infrared channels of a Landsat 5 TM image for dark-coniferous, light-coniferous and deciduous forests from the degree of complexity of the forest-canopy structure are received. A high level of variance and maximum brightness average values are marked in green moss (hilocominosa) dark-coniferous and various-grass (larioherbosa) dark-coniferous forests and light-coniferous forests with a complex structure of canopy. The parvifoliate forests are characterized by high values of brightness in stands with a relatively simple structure of the canopy and by a small variance in brightness of any degree of the structure of the canopy complexity. The increase in brightness for the lit slopes in comparison with shaded ones in all stands with a difficult morphological canopy structure is revealed. However, the brightness values of the lit and shaded slopes do not differ for stands with a medium complexity of the structure. It is noted that, in addition to the indicator of the forest-canopy structure, the possible impact on increasing the variance of spectral brightness for the taxation plot has a variability of the slope ratio of "microslopes" inside the forest plot if it exceeds 60%.

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.

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.

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).

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.