On the Structure and Evolution of a Polar Crown Prominence/Filament System

Polar crown prominences, that partially circle the Sun’s poles between 60° and 70° latitude, are made of chromospheric plasma. We aim to diagnose the 3D dynamics of a polar crown prominence using high-cadence EUV images from the Solar Dynamics Observatory (SDO)/AIA at 304, 171, and 193 Å and the Ahead spacecraft of the Solar Terrestrial Relations Observatory (STEREO-A)/EUVI at 195 Å. Using time series across specific structures, we compare flows across the disk in 195 Å with the prominence dynamics seen on the limb. The densest prominence material forms vertical columns that are separated by many tens of Mm and connected by dynamic bridges of plasma that are clearly visible in 304/171 Å two-colour images. We also observe intermittent but repetitious flows with velocity 15 km?s^?1 in the prominence that appear to be associated with EUV bright points on the solar disk. The boundary between the prominence and the overlying cavity appears as a sharp edge. We discuss the structure of the coronal cavity seen both above and around the prominence. SDO/HMI and GONG magnetograms are used to infer the underlying magnetic topology. The evolution and structure of the prominence with respect to the magnetic field seems to agree with the filament-linkage model.     

A blowout surge from the eruption of a miniature filament confined by large coronal loops

By means of Hα, EUV, soft X-ray, hard X-ray, and photospheric magnetic field observations, we report the surge-like eruption of a small-scale filament, called “blowout surge” according to recent observations, occurring on a plage region around AR 10876 on 1 May 2006. Along magnetic polarity reversal boundaries with obvious magnetic cancelations, the filament was located underneath a compact coronal arcade and close to one end of large coronal loops around the AR’s periphery. The filament started to erupt about 8 min before the main impulsive phase of a small two-ribbon flare, which had two Hα blue-wing kernels connected by hard X-ray loop-top sources on the both sides of the filament. After the flare end, the filament further underwent a distant eruption following a path nearly along the preexisting large loops, and thus looked like an Hα surge and an EUV jet. During the eruption, a small coronal dimming was formed near the flare, while weak brightenings appeared around the remote end of the large loops. We interpret these joint observations as the filament eruption being confined and guided by the large loops. The filament eruption, initially embedded in one footpoint region of the large loops, can break away from the magnetic restraint of the overlying compact arcade, but might be still limited inside the large loops. As a result, the eruption took a surge form that can only expand laterally along the large loops rather than erupt radially.     

Downflow-induced brightening following a filament eruption

The plasma from solar filament eruptions sometimes falls down to the lower solar atmosphere. These interesting events can help us to understand the properties of downflows, such as the temperature and the conversion between kinetic energy and thermal energy. We analyze the case of a filament eruption in active region NOAA 11283 and brightening caused by the return of filament material on September 7 and 8, 2011, observed by the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) aboard the Solar Dynamics Observatory (SDO). Magnetic flux cancellation was observed as a result of the eruption after the eruptive filament started to ascend. Another filament near the eruptive filament was disturbed by an extreme ultraviolet (EUV) wave that was triggered by the eruptive filament, causing it to oscillate. Based on coronal seismology, the mean magnetic field strength in the oscillatory filament was estimated to be approximately 18 ± 2 G. Some plasma separated from the filament and fell down to the solar northwest surface after the filament eruption. The velocities of the downflows increased at accelerations lower than the gravitational acceleration. The main characteristic temperature of the downflows was about 5 × 10⁴ K. When the plasma blobs fell down to lower atmospheric heights, the high-speed downward-travelling plasma collided with plasma at lower atmospheric heights, causing the plasma to brighten. The brightening was observed in all 8 AIA channels, demonstrating that the temperature of the plasma in the brightening covered a wide range of values, from 10⁵ K to 10⁷ K. This brightening indicates the conversion between kinetic energy and thermal energy.     

A Technique for Removing Background Features in SECCHI – EUVI He ii 304 Å Filtergrams: Application to the Filament Eruption of 22 May 2008

The STEREO mission has been providing a stereoscopic view of filament eruptions in the EUV. The clearest view during a filament eruption is seen in He ii 304 Å observations. One of the main problems in visualizing filament dynamics in He ii 304 Å is the strong background contrast due to surface features. We present a technique that removes background features and leaves behind only the filamentary structure, as seen by STEREO-A and -B. The technique uses a pair of STEREO He ii 304 Å images observed simultaneously. The STEREO-B image is geometrically transformed to a STEREO-A view so that the background images appear similar. Filaments, being elevated structures, i.e., not lying on the same spherical surface as background features, do not appear similar in the transformed view. Thus, subtracting the two images cancels the background but leaves behind the filament structure. We apply this technique to study the dynamics of the filament-eruption event of 22 May 2008, which was observed by STEREO and followed by several ground-based observatories participating in the Joint Observing Programme (JOP 178).     

Stereoscopic Analysis of the 19 May 2007 Erupting Filament

A filament eruption, accompanied by a B9.5 flare, coronal dimming, and an EUV wave, was observed by the Solar TERrestrial Relations Observatory (STEREO) on 19 May 2007, beginning at about 13:00 UT. Here, we use observations from the SECCHI/EUVI telescopes and other solar observations to analyze the behavior and geometry of the filament before and during the eruption. At this time, STEREO A and B were separated by about 8.5°, sufficient to determine the three-dimensional structure of the filament using stereoscopy. The filament could be followed in SECCHI/EUVI 304 Å stereoscopic data from about 12 hours before to about 2 hours after the eruption, allowing us to determine the 3D trajectory of the erupting filament. From the 3D reconstructions of the filament and the chromospheric ribbons in the early stage of the eruption, simultaneous heating of both the rising filamentary material and the chromosphere directly below is observed, consistent with an eruption resulting from magnetic reconnection below the filament. Comparisons of the filament during eruption in 304 Å and Hα? show that when it becomes emissive in He II, it tends to disappear in Hα?, indicating that the disappearance probably results from heating or motion, not loss, of filamentary material.     

Nonlinear calibration of vector magnetograms by the video vector magnetograph at Huairou

We compare the results of two calibration methods for deriving a photospheric vector magnetogram, as applied to the Fei 5324.19 Å line. The first method ignores the dependence of its calibration coefficients on the inclination angle. The second method is a multi-iteration, nonlinear calibration technique developed by [M.J. Hagyard, J.I. Kineke, Solar Phys. 158 (1995) 11], which allows the polarization signals to depend on both field strength and inclination angle. We compare the relationship between the derived solar magnetic field and the Stokes parameters under both methods. We find that the circular polarization signal of the Fei 5324.19 Å line is linearly proportional to the longitudinal strength, B_L, when the field strength ranges from 0 to 1000 Gauss. For B_L > 1000 G and inclination angles ranging from 30° to 90°, deviation from linearity is significant. For the transverse field, B_T, the assumption of linearity only holds for 0 < B_T < 300 G. In contrast to the former method of calibration, the improved calibration method accounts for the nonlinear relationship between polarization signals and the magnetic field strength. Using [A. Skumanich, in: J.H. Thomas and N.O. Weiss (Eds.), Sunspots: Theory and Observations. Kluwer, Dordrecht, 1992, p. 121] dipole field model, we show that the Fei 5324.19 Å line has more linear property than the Fei 6302.5 Å line.     

3D Evolution of a Filament Disappearance Event Observed by STEREO

A filament disappearance event was observed on 22 May 2008 during our recent campaign JOP 178. The filament, situated in the Southern Hemisphere, showed sinistral chirality consistent with the hemispheric rule. The event was well observed by several observatories, in particular by THEMIS. One day, before the disappearance, Hα observations showed up- and down-flows in adjacent locations along the filament, which suggest plasma motions along twisted flux rope. THEMIS and GONG observations show shearing photospheric motions leading to magnetic flux canceling around barbs. STEREO A, B spacecraft with separation angle 52.4°, showed quite different views of this untwisting flux rope in He ii 304 Å images. Here, we reconstruct the three-dimensional geometry of the filament during its eruption phase using STEREO EUV He ii 304 Å images and find that the filament was highly inclined to the solar normal. The He ii 304 Å movies show individual threads, which oscillate and rise to an altitude of about 120 Mm with apparent velocities of about 100 km?s^?1 during the rapid evolution phase. Finally, as the flux rope expands into the corona, the filament disappears by becoming optically thin to undetectable levels. No CME was detected by STEREO, only a faint CME was recorded by LASCO at the beginning of the disappearance phase at 02:00 UT, which could be due to partial filament eruption. Further, STEREO Fe xii 195 Å images showed bright loops beneath the filament prior to the disappearance phase, suggesting magnetic reconnection below the flux rope.     

Alternating Twist Along an Erupting Prominence

Triangulation measurements using observations from the two Solar Terrestrial Relations Observatory (STEREO) spacecraft, combined with observations from the Solar Dynamics Observatory (SDO), are used to characterize the behavior of a prominence involved in two successive coronal mass ejections 6?–?7 December 2010. The STEREO separation at the time was 171.6^°, which was functionally equivalent to a separation of 8.4^°, and thus very favorable for feature co-identification above the limb. The first eruption at ≈?14:16 UT on 6 December of the middle branch of the prominence starts off a series of magnetic reconfigurations in the right branch, which itself erupts at ≈?2:06 UT the next day, about 12 hours after the first eruption. The cool prominence material seen at 304?Å drains back down to the surface, but a flux-rope-like magnetic structure is seen to erupt in both 195?Å by the STEREO/Extreme Ultraviolet Imager (EUVI), and in white light by the STEREO/COR1 inner coronagraph. In between the two eruptions, two different signs of helicity are seen in the measured twist of the right branch. This is interpreted to be caused by the overall prominence channel being composed of different segments with alternating helicity signs. The erupting parts on 6 and 7 December both show positive twist, but negative twist is seen in between these positive sections. Negative twist is consistent with the dextral chirality signs seen in the He ii line at 304?Å prior to both eruptions. However, during the period between the eruptions, a region of positive twist grows and replaces the region of negative twist, and finally erupts. We interpret these observations in the light of models that predict that helicity cancellation can be an important factor in the triggering of flares and coronal mass ejections.     

Failed Eruption of a Filament as a Driver for Vertical Oscillations of Coronal Loops

We present observations of a failed eruption of a magnetic flux rope recorded during the M6.2 flare of 14 July 2004. The observations were mainly made with TRACE 171 Å and 1600 Å filters. The flare was accompanied by a destabilization of a magnetic structure observed as a filament eruption. After an initial acceleration, the eruption slowed down and finally was stopped by the overlying coronal loops. The observations suggest that the whole event is well described by the quadrupole model of a solar flare. The failed eruption stretched the overlying loops, and they were then observed to be oscillating. We were able to observe clear vertical polarization of the oscillatory motion in the TRACE images. The derived parameters of the oscillatory motion are an initial amplitude of 9520 km, a period of 377 s, and an exponential damping time of 500 s. Differences between the existing models and the observations have been found. The analyzed event is the second sample for global vertical kink waves found besides the first by Wang and Solanki (Astrophys. J. Lett. 421, 33, 2004).     

Soft X-ray emissions of Si IX in Procyon

A detailed analysis of emission lines of carbon-like silicon reveals that some ratios of n = 3 → 2 line intensities are sensitive to the electron density, n_e. The ratio between two groups of 3d → 2p transition lines of 55.246 Å and 55.346 Å provides a good diagnostic of n_e because of the combined characteristic of sensitivity to electron density and relative insensitivity to temperature. From this ratio, a lower limit of the electron density of 0.6 × 10⁸ cm⁻³ was set for Procyon, which is consistent with the values constrained by C V and Si X emission lines. Significant discrepancies were found between theoretical predictions and observations for the 3s → 2p lines relative to 3d → 2p lines in Procyon, recently measured using the Chandra high-resolution transmission grating instrument. The difference of more than a factor of 3, cannot be explained by uncertainties of atomic data. Ness and co-workers also suggested that the effect of opacity appeared not to be a major factor for the discrepancy. For the 3s → 2p line at 61.611 Å, present work indicates that the large discrepancy may be from the contamination of a S VIII line at 61.645 Å. For lines at 61.702 and 61.846 Å, we suggest that the discrepancies may be attributed to contaminations by currently yet-unknown spectral lines.     

Ultraviolet spectral variations of FK Comae and V 1794 Cygni

Ultraviolet spectra of FK Comae and V1794 Cygni observed with the Hubble Space Telescope Cosmic Origins Spectrograph (HST COS) and the International Ultraviolet Explorer (IUE) satellites were analyzed for the period 1981–2011. Temporal variations of line fluxes of the O I 1306 Å, C II 1336 Å, C IV 1550 Å, He II 1640 Å and Mg II k & h 2800 Å, produced in the transition regions and chromospheres of these stars, imply variations in density and temperature changes in the line emitting regions as a result of the rapid rotation and magnetic fields responsible for stellar activity. Results are consistent with the models of Ramsey et al. (1981), Oliveira and Foing (1999), and Korhonen et al. (2000).     

A multiwavelength study of an M-class flare and the origin of an associated eruption from NOAA AR 11045

In this paper, we study multiwavelength observations of an M6.4 flare in Active Region NOAA 11045 on 7 February 2010. The space- and ground-based observations from STEREO, SoHO/MDI, EIT, and Nobeyama Radioheliograph were used for the study. This active region rapidly appeared at the north-eastern limb with an unusual emergence of a magnetic field. We find a unique observational signature of the magnetic field configuration at the flare site. Our observations show a change from dipolar to quadrapolar topology. This change in the magnetic field configuration results in its complexity and a build-up of the flare energy. We did not find any signature of magnetic flux cancellation during this process. We interpret the change in the magnetic field configuration as a consequence of the flux emergence and photospheric flows that have opposite vortices around the pair of opposite polarity spots. The negative-polarity spot rotating counterclockwise breaks the positive-polarity spot into two parts. The STEREO-A 195 Å and STEREO-B 171 Å coronal images during the flare reveal that a twisted flux tube expands and erupts resulting in a coronal mass ejection (CME). The formation of co-spatial bipolar radio contours at the same location also reveals the ongoing reconnection process above the flare site and thus the acceleration of non-thermal particles. The reconnection may also be responsible for the detachment of a ring-shaped twisted flux tube that further causes a CME eruption with a maximum speed of 446 km/s in the outer corona.     

The association between sunspot magnetic fields and superpenumbral fibrils

Spectropolarimetric observations of a sunspot were carried out with the Tenerife Infrared Polarimeter at Observatorio del Teide, Tenerife, Spain. Maps of the physical parameters were obtained from an inversion of the Stokes profiles observed in the infrared Fe I line at 15648 Å The regular sunspot consisted of a light bridge which separated the two umbral cores of the same polarity. One of the arms of the light bridge formed an extension of a penumbral filament which comprised weak and highly inclined magnetic fields. In addition, the Stokes V profiles in this filament had an opposite sign as the sunspot and some resembled Stokes Q or U. This penumbral filament terminated abruptly into another at the edge of the sunspot, where the latter was relatively vertical by about 30°. Chromospheric Hα and He II 304 Å filtergrams revealed three superpenumbral fibrils on the limb‐side of the sunspot, in which one fibril extended into the sunspot and was oriented along the highly inclined penumbral counterpart of the light bridge. An intense, elongated brightening was observed along this fibril that was co‐spatial with the intersecting penumbral filaments in the photosphere. Our results suggest that the disruption in the sunspot magnetic field at the location of the light bridge could be the source of reconnection that led to the intense chromospheric brightening and facilitated the supply of cool material in maintaining the overlying superpenumbral fibrils. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Contamination of the 5394 Å spectral region by telluric lines

The spectral region in the vicinity of 5394 Å contains three prominent photospheric spectral lines, which can be used as a solar plasma diagnostic tool. The occurrence of telluric lines in this region is a potential source of systematic and random errors in these solar spectral lines. The goal of our investigation was to determine the telluric line contamination of this interesting spectral region. Several series of high-resolution solar spectra within an interval of about 4 Å around the 5394 Å wavelength were observed at different zenith distances of the Sun. Comparison of these spectra has permitted identification of telluric lines in this spectral interval. The observations were carried out with the horizontal solar spectrograph of the Heliophysical Observatory in Debrecen. Telluric feature blending was identified in the blue and red wings of the Fe I 5393.2 Å line, and in the local continuum of the Mn I 5394.7 Å line. The blue wing of the Fe I 5395.2 Å line is contaminated by a weak telluric feature too. The red continuum of this line has a more prominent telluric contamination. A dozen of water vapor telluric lines that determined the observed telluric features were identified in this spectral interval. The profiles of three telluric lines that have a significant influence on both the profiles of solar spectral lines and the level of local continuum were derived, and the variation of their parameters (equivalent width and central depth) with air mass were analyzed.     

Spectral behavior of the symbiotic nova AG Pegasi observed with IUE and HST

Ultraviolet spectra from the International Ultraviolet Explorer (IUE) and from the Hubble Space Telescope (HST) of the symbiotic novae AG Peg during the period 1978–1996 are analyzed. Some spectra showing the modulations of spectral lines at different times are presented. We determined the reddening from the 2200 Å feature, finding that E(B−V) = 0.10 ± 0.02. We studied N IV] at 1486 Å, C IV 1550 Å, and O III] at 1660 Å, produced in the fast wind from the hot white dwarf. The mean wind velocity of the three emission lines is 1300 km s⁻¹ (FWHM). The mean wind mass loss rate is ∼6 × 10⁻⁷ M_⊙ yr⁻¹. The mean temperature is ∼6.5 × 10⁵ K. The mean ultraviolet luminosity is ∼5 × 10³³ erg s⁻¹. The modulations of line fluxes in the emitting region at different times are attributed to the variations of density and temperature of the ejected matter as a result of variations in the rate of mass loss.     

The Thickness and Scale of Late-stage Basalts in Oceanus Procellarumtwo

Oceanus Procellarum, the largest lunar mare, is distributed with a large area of the late-stage (Eratosthenian) basalts. Research on the thickness, volume, and eruption flux of the late-stage basalts is essential for understanding the late thermal evolution of Oceanus Procellarum, even the Moon. The Eratosthenian basalts are rich in olivine and ilmenite, while the underlying Imbrian basalts are rich in pyroxene. Their significant spectral differences are easy to be distinguished using the hyperspectral data. We determine whether a crater has penetrated the overlying basalt layer by the data of Moon Mineralogy Mapper (M³), and estimate the thickness of Eratosthenian basalts in the Oceanus Procellarum region by using a crater excavation technique. A high-resolution thickness distribution map of the last-stage basalts within the Oceanus Procellarum has been acquired. The results show that the averaged thickness of Eratosthenian basalts in the Oceanus Procellarum region varies from (24 ± 2) m to (88 ± 2) m. Among them, the thickness of Eratosthenian basalts in the western Aristarchus is the greatest (>60 m), whereas the southernmost area of the study has a minimum thickness of about 28–31 m. The basalt thickness at the Chang’e-5 potential landing site Mons Rümker is about 31–38 m. The thickness of Eratosthenian basalts in the east of Marius is about 35–45 m, which is much smaller than the value of 100 ～ 300 m estimated by Weider et al. The total volume of Eratosthenian basalts is estimated to be ～1.39 × 10⁴ km³, which is only about 1.6% of total basalts in Oceanus Procellarum. This indicates that the magmatism in the Eratosthenian period has been greatly weakened compared to the Imbrian period.     

Magnetic Causes of the Eruption of a Quiescent Filament

During the JOP178 campaign in August 2006, we observed the disappearance of our target, a large quiescent filament located at S25°, after an observation time of three days (24 August to 26 August). Multi-wavelength instruments were operating: THEMIS/MTR (“MulTi-Raies”) vector magnetograph, TRACE (“Transition Region and Coronal Explorer”) at 171 Å and 1600 Å and Hida Domeless Solar telescope. Counter-streaming flows (+/?10 km?s^?1) in the filament were detected more than 24 hours before its eruption. A slow rise of the global structure started during this time period with a velocity estimated to be of the order of 1 km?s^?1. During the hour before the eruption (26 August around 09:00 UT) the velocity reached 5 km?s^?1. The filament eruption is suspected to be responsible for a slow CME observed by LASCO around 21:00 UT on 26 August. No brightening in Hα or in coronal lines, no new emerging polarities in the filament channel, even with the high polarimetry sensitivity of THEMIS, were detected. We measured a relatively large decrease of the photospheric magnetic field strength of the network (from 400 G to 100 G), whose downward magnetic tension provides stability to the underlying stressed filament magnetic fields. According to some MHD models based on turbulent photospheric diffusion, this gentle decrease of magnetic strength (the tension) could act as the destabilizing mechanism which first leads to the slow filament rise and its fast eruption.     

Initiation of Coronal Mass Ejections by Sunspot Rotation

We study a filament eruption, two-ribbon flare, and coronal mass ejection (CME) that occurred in NOAA Active Region 10898 on 6 July 2006. The filament was located South of a strong sunspot that dominated the region. In the evolution leading up to the eruption, and for some time after it, a counter-clockwise rotation of the sunspot of about 30 degrees was observed. We suggest that the rotation triggered the eruption by progressively expanding the magnetic field above the filament. To test this scenario, we study the effect of twisting the initially potential field overlying a pre-existing flux-rope, using three-dimensional zero-β MHD simulations. We first consider a relatively simple and symmetric system, and then study a more complex and asymmetric magnetic configuration, whose photospheric-flux distribution and coronal structure are guided by the observations and a potential field extrapolation. In both cases, we find that the twisting leads to the expansion of the overlying field. As a consequence of the progressively reduced magnetic tension, the flux-rope quasi-statically adapts to the changed environmental field, rising slowly. Once the tension is sufficiently reduced, a distinct second phase of evolution occurs where the flux-rope enters an unstable regime characterised by a strong acceleration. Our simulations thus suggest a new mechanism for the triggering of eruptions in the vicinity of rotating sunspots.     

Manifestations of Coronal Mass Ejections in the EUV Range from Data of the <Emphasis Type="Italic">CORONAS-F</Emphasis>/SPIRIT Telescope

We briefly overview results of our study of the large-scale solar activity associated with coronal mass ejections (CMEs). The observational material is constituted with data of the SPIRIT telescope aboard the CORONAS-F satellite in the three EUV channels 175, 284, and 304 Å. In particular, we consider a powerful geoeffective event of November 4, 2003, which was not observed by the SOHO/EIT telescope, a series of extremely powerful events of October 2003, and an event of November 18, 2003, with filament eruption. The efficiency of combined analysis of the SPIRIT and EIT data is demonstrated. The analysis confirms the coincidence of many dimmings in different spectral channels, including coronal lines with different excitation temperatures and the transition-region line, as well as the global character and homology of dimmings in recurrent events. The higher cadence SPIRIT observations at 304 Å reveal a slowly propagating large-scale darkening probably caused by absorption of emission in the dense, cold plasma of an eruptive filament.     

Estimation of spicule magnetic field using observed kink waves

We apply the method of MHD seismology to estimate the magnetic field in spicules using observed kink waves. We include the effects of gravitational stratification, the neglect of which leads to an error of around 30% in the estimation of the magnetic field. With stratification included, we find the magnetic field in spicules in the range of 8–16 G. We also estimate a density of 7.4 × 10⁻¹⁰ kg m⁻³ in spicules. The estimated values of magnetic field and density are in agreement with the available observations. Improved measurement of height, oscillation period, and plasma density in spicules will further enhance the precision of this method.