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

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NASA NTRS2016

Solar Activity Studies using Microwave Imaging Observations

We report on the status of solar cycle 24 based on polar prominence eruptions (PEs) and microwave brightness enhancement (MBE) information obtained by the Nobeyama radioheliograph. The north polar region of the Sun had near-zero field strength for more than three years (2012-2015) and ended only in September 2015 as indicated by the presence of polar PEs and the lack of MBE. The zero-polar-field condition in the south started only around 2013, but it ended by June 2014. Thus the asymmetry in the times of polarity reversal switched between cycle 23 and 24. The polar MBE is a good proxy for the polar magnetic field strength as indicated by the high degree of correlation between the two. The cross-correlation between the high- and low-latitude MBEs is significant for a lag of approximately 5.5 to 7.3 years, suggesting that the polar field of one cycle indicates the sunspot number of the next cycle in agreement with the Babcock-Leighton mechanism of solar cycles. The extended period of near-zero field in the north-polar region should result in a weak and delayed sunspot activity in the northern hemisphere in cycle 25.

microwave radio emission↗
NASA NTRS1992

Prediction of magnetic orientation in driver gas associated -Bz events

The source regions of five strong -Bz events detected at 1 AU for which solar sources were identified by Tang et al. (1989) and Tsurutani et al. (1992) are investigated in order to determine whether the magnetic orientation of driver gas in the interplanetary medium observed at the earth can be predicted when its solar source is identified. Three -Bz events were traced to flare-associated coronal mass ejections (CMEs), one to an eruptive prominence associated CME, and one to three possible solar sources. The computed magnetic orientations at the candidate 'release height' (the height where the front of a CME ceases to accelerate) above the flare sites associated with CMEs show the existence of the expected southward field component. It is concluded that the magnetic orientation in flare-associated CME generated driver gas may be predictable.

Hoeksema, J. T.↗
NASA NTRS1976

Interpretation of broad-band polarimetry of solar coronal transients - Importance of H-alpha emission

An eruptive prominence and coronal transient was observed in H-alpha, He II 304-A, and coronal white light (3700-7000 A). This event was generically similar to many other coronal transients associated with eruptive prominences in that loops of material propagated outward through the corona. It differed in that some of the prominence material was observed above 1.75 solar radii in both coronal white light and He II. Polarization analysis of the white-light data shows that the observed radiance from the loop-like transient was entirely due to free electron or Thomson scattering, whereas the white-light radiance from the prominence material was dominated by H-alpha emission. By comparing the white-light observations with model calculations, the densities along the loop and limits on the temperature and density of the prominence are obtained. Material observed in both white light and He II is shown to be cool prominence material, whereas analysis indicates that the transient-loop material is hot and coronal in origin. The time sequence of observations leads to the hypothesis that the prominence material is heated as it is ejected from the sun.

Poland, A. I.↗
NASA NTRS2010

Strong Rotation of an Erupting Quiescent Polar Crown Prominence

On 5-6 June 2007, a large quiescent polar crown prominence was observed to erupt by the two Solar Terrestrial Relations Observatory (STEREO) spacecraft. This eruption was particularly visible in the 304 A channel of the Extreme Ultraviolet Imager (EUVI) telescopes. A detailed analysis of the fine structures in the images allows the three-dimensional structure of the erupting prominence to be derived. The prominence is seen to undergo substantial rotation of at least 90 along the radial axis as it rises, with indications that additional rotation occurred before the prominence rose into the STEREO fields of view. Two temporary structures ("spurs") are seen to form at an angle to the main spine of the prominence, and are interpreted as signs of reconnection. These reconnection events contribute to the overall rotation of the prominence. A significant fraction of the prominence material is drained through new field lines caused by one of the reconnection events, resulting in only a weak coronal mass ejection event observed by the STEREO and SOHO coronagraphs. The eruption is interpreted as being initiated by the helical kink instability, with subsequent modification by the reconnection events.

Source record↗
NASA NTRS1995

Abundance ratios of oxygen, neon, and magnesium in solar active regions and flares: The FIP effect

Relative abundances of oxygen, neon, and magnesium have been derived for a sample of nine solar active regions, flares, and an erupting prominance by combining plots of the ion differential emission measures. The observations were photographed in the 300-600 A range by the Naval Research Laboratory (NRL) spectroheliograph on Skylab. Methods for deriving the Mg/Ne abundance ratio-which measures the separation between the low- first ionization potential (FIP) and high-FIP abundnace plateaus-have been described in previous papers. In this paper we describe the spectroscopic methods for deriving the O/Ne abundance ratio, which gives the ratio between two high-FIP elements. The plot of the O/Ne ratio versus the Mg/Ne ratio in the sample of nine Skylab events is shown. The variation in the Mg/Ne ratio by a factor of 6 is associated with a much smaller range in the O/Ne ratio. This is broadly consistent with the presence of the standard FIP pattern of abundances in the outer atmosphere of the Sun. However, a real change in the relative abundances of oxygen and neon by a factor of 1.5 cannot be excluded.

Widing, K. G.↗
NASA NTRS2011

3D Reconstruction of a Rotating Erupting Prominence

A bright prominence associated with a coronal mass ejection (CME) was seen erupting from the Sun on 9 April 2008. This prominence was tracked by both the Solar Terrestrial Relations Observatory (STEREO) EUVI and COR1 telescopes, and was seen to rotate about the line of sight as it erupted; therefore, the event has been nicknamed the "Cartwheel CME." The threads of the prominence in the core of the CME quite clearly indicate the structure of a weakly to moderately twisted flux rope throughout the field of view, up to heliocentric heights of 4 solar radii. Although the STEREO separation was 48 deg, it was possible to match some sharp features in the later part of the eruption as seen in the 304 Angstrom line in EUVI and in the H alpha-sensitive bandpass of COR1 by both STEREO Ahead and Behind. These features could then be traced out in three dimensional space, and reprojected into a view in which the eruption is directed towards the observer. The reconstructed view shows that the alignment of the prominence to the vertical axis rotates as it rises up to a leading-edge height of approximately equals 2.5 solar radii, and then remains approximately constant. The alignment at 2.5 solar radii differs by about 115 deg. from the original filament orientation inferred from H alpha and EUV data, and the height profile of the rotation, obtained here for the first time, shows that two thirds of the total rotation is reached within approximately equals 0.5 solar radii above the photosphere. These features are well reproduced by numerical simulations of an unstable moderately twisted flux rope embedded in external flux with a relatively strong shear field component.

Thompson, W. T.↗
NASA NTRS2011

3D Reconstruction of a Rotating Erupting Prominence

A bright prominence associated with a coronal mass ejection (CME) was seen erupting from the Sun on 9 April 2008. This prominence was tracked by both the Solar Terrestrial Relations Observatory (STEREO) EUVI and COR1 telescopes, and was seen to rotate about the line of sight a it erupted; therefore, the event has been nicknamed the "Cartwheel CME." The threads of the prominence in the core of the CME quite clearly indicate the structure of a weakly to moderately twisted flux rope throughout the field of view, up to heliocentric heights of 4 solar radii. Although the STEREO separation was 48 deg, it was possible to match some sharp features in the later part of the eruption as seen in the 304 A line in EUVI and in the H-alpha-sensitive bandpass of COR I by both STEREO Ahead and Behind. These features could then be traced out in three-dimensional space, and reprojected into a view in which the eruption is directed toward the observer. The reconstructed view shows that the alignment of the prominence to the vertical axis rotates as it rises up to a leading-edge height of approximately equal to 2.5 solar radii, and then remains approximately constant. The alignment at 2.5 solar radii differs by about 115 deg from the original filament orientation inferred from H-alpha and EUV data, and the height profile of the rotation, obtained here for the first time, shows that two thirds of the total rotation are reached within approximately equal to 0.5 solar radii above the photosphere. These features are well reproduced by numerical simulations of an unstable moderately twisted flux rope embedded in external flux with a relatively strong shear field component.

Thompson, W. T.↗
NASA NTRS1990

Numerical simulations of solar disturbances and their interplanetary consequences

Time-dependent MHD numerical simulations are used to study responses of the solar atmosphere and interplanetary medium to simulated solar disturbances. A number of 2D and 3D examples of coronal mass ejection (CME) simulations and some current controversies concerning the basic processes of CME initiation are discussed. Footpoint shearing motion is tested to determine whether it can provide a reasonable mechanism for CME development from arch filament configurations. Possible interplanetary consequences to CME-like disturbances are demonstrated by using 3D simulations to determine the dynamic response of the solar wind to a plasmoid injection from an eruptive filament or prominence. The possibility that a plasmoid may be generated in the interplanetary medium by a solar-generated shock that propagates through a heliospheric current sheet is discussed. Application of the 3D model for the interpretation of interplanetary scintillation observations is addressed.

Dryer, M.↗
NASA NTRS1983

Observations of interplanetary shocks - Recent progress

Attention is given to interplanetary shock observations conducted since 1978, with emphasis on shocks associated with such solar transient phenomena as coronal transients and eruptive prominences, as well as with flares. A correlation between shocks and Storm Sudden Commencements is found to persist into the recent maximum, and shocks associated with disappearing filaments and coronal transients rather than with flares have been identified. Preliminary results on the thickness of interplanetary shocks have been obtained, and several quasi-parallel shocks have been identified which propagate along, rather than across, the magnetic field. The plasma drivers that accompany interplanetary shocks exhibit distinctive features in electric, ion and magnetic field data.

Smith, E. J.↗
NASA NTRS1977

Coronal mass-ejections-kinematics of the 19 December 1973 event

A detailed description of the observed kinematics of the coronal disturbance of December 19, 1973, is presented along with inferences about the temperatures, densities, magnetic fields, and electric currents within the event. This disturbance consisted of the eruption of a previously quiescent prominence, an associated ejection of coronal material, and the destruction of a large coronal streamer. Observations of the prominence and the corona with a scanning spectroheliometer and a white-light coronagraph aboard Skylab before, during, and after the prominence eruption are discussed, and the temperature and density in the eruptive prominence are traced as the prominence rose to a height of 3 solar radii over 7 hr. The results obtained are shown to reinforce previous arguments that the material comprising the bulk of the mass ejected from the corona in transient events arises from the low corona rather than from the eruptive prominence, which may accompany the coronal mass ejection.

Schmahl, E.↗
NASA NTRS1986

Magnetic field re-arrangement after prominence eruption

It has long been known that magnetic reconnection plays a fundamental role in a variety of solar events. Although mainly invoked in flare problems, large scale loops interconnecting active regions, evolving coronal hole boundaries, the solar magnetic cycle itself, provide different evidence of phenomena which involve magnetic reconnection. A further example might be given by the magnetic field rearrangement which occurs after the eruption of a prominence. Since most often a prominence reforms after its disappearance and may be observed at about the same position it occupied before erupting, the magnetic field has to undergo a temporary disruption of relax back, via reconnection, to a configuration similar to the previous one. The above sequence of events is best observable in the case of two ribbon (2-R) flares but most probably is associated with all filament eruptions. Even if the explanation of the magnetic field rearrangement after 2-R flares in terms of reconnection is generally accepted, the lack of a 3-dimensional model capable of describing the field reconfiguration, has prevented, up to now, a thorough analysis of its topology as traced by H alpha/x ray loops. A numerical technique is presented which enables oneto predict and visualize the reconnected configuration, at any time, and therefore allows one to make a significant comparison of observations and model predictions throughout the whole process.

Kopp, R. A.↗
NASA NTRS2017

Prominence Eruption Initiated by Helical Kink Instability of an Embedded Flux Rope

We study the triggering mechanism of a limb-prominence eruption and the associated coronal mass ejection (CME) near AR 12342 using Solar Dynamics Observatory and Large Angle and Spectrometric Coronagraph/Solar Heliospheric Observatory observations. The prominence is seen with an embedded flux thread (FT) at one end and bifurcates from the middle to a different footpoint location. The morphological evolution of the FT is similar to that of an unstable flux rope (FR), which we regard as a prominence-embedded FR. The FR twist exceeds the critical value. In addition, the morphology of the prominence plasma in 304 Å images marks the helical nature of the magnetic skeleton, with a total of 2.96 turns along arc length. The potential field extrapolation model indicates that the critical height of the background magnetic field gradient falls within the inner corona (105 Mm), which is consistent with the extent of coronal plasma loops. These results suggest that the helical kink instability in the embedded FR caused the slow rise of the prominence to the height of the torus instability domain. Moreover, the differential emission measure analysis unveils heating of the prominence plasma to coronal temperatures during an eruption, suggesting reconnection-related heating underneath the upward rising embedded FR. The prominence starts with a slow rise motion of 10 km s(exp. -1), which is followed by fast and slow acceleration phases that have an average acceleration of 28.9 m s(exp. -2) and 2.4 m s(exp. -2) in C2 and C3 field of view, respectively. As predicted by previous numerical simulations, the observed synchronous kinematic profiles of the CME leading edge and the core support the involved FR instability in the prominence initiation.

Vemareddy, P.↗
NASA NTRS1981

Studies of the corona with the Solar Maximum Mission coronagraph/polarimeter

The visible wavelength coronagraph/polarimeter on the Solar Maximum Mission (SMM) spacecraft is providing data on the flare processes manifested by coronal transients and on the degree of disruption of the evolutionary corona at the present epoch of the solar activity cycle. Among the first results are the discovery of frequent H-alpha emission from remnants of eruptive prominences in the outer corona and first observations of Fe XIV line emission to 3.2 solar radii. In the early stages of transients, cavities less dense than the ambient corona are occasionally found trailing the transient loops, with the loops being relatively thick and structureless. Some 22 transients have been identified in the initial survey of 52 days of observations; from this sample the preliminary conclusion is that transients during the SMM era (near solar maximum) occur over a wider range of latitude than, but with about the same range of speeds as, transients during the Skylab era (near solar minimum).

House, L. L.↗
NASA NTRS1997

A multi-wavelength analysis of the February 6/7, 1997 coronal mass ejection

The coronal mass ejection (CME) event on 6 to 7 February 1997 that originate from the southwest quadrant of the sun are analyzed. The CME is accelerated from a projected speed of 170 km/s to about 650 km/s at 25 solar radii. The CME is an arcade eruption followed by bright prominence core structures. The CME was accompanied by an arcade formation. The X-ray and extreme ultraviolet observations suggest that the reconnection proceeded from the northwest and the southeast end of a filament channel. The CME event caused interplanetary effects that produced a medium size geomagnetic storm on earth. Issues relating to the origin and propagation of geo-effective solar disturbances are addressed.

Plunkett, S. P.↗
NASA NTRS1983

Coronal transients in FE XIV 5303A: First two-dimensional photoelectric ground-based observations

An observational program was undertaken at Sacramento Peak Observatory to photoelectrically detect coronal transients. Continuous observations are made in the Fe XIV 5303A green line, utilizing the 40 cm coronagraph and the Photoelectric Coronal Photometer. Scans at three heights above the limb are combined to form a low resolution picture of the greenline corona every 20 to 30 minutes. Difference pictures, relative to an initial scan, are generated to search for sudden changes in the corona. The first few days of operation of this program have yielded three low-lying events ( 1.55 solar radii) following minor chromospheric activity (a surge and eruptive prominences), which propagated up through the corona with velocities on the order of 100 km/s.

Altrock, R. C.↗
NASA NTRS2016

Unusual Polar Conditions in Solar Cycle 24 and Their Implications for Cycle 25

We report on the prolonged solar-maximum conditions until late 2015 at the north-polar region of the Sun indicated by the occurrence of high-latitude prominence eruptions (PEs) and microwave brightness temperature close to the quiet-Sun level. These two aspects of solar activity indicate that the polarity reversal was completed by mid-2014 in the south and late 2015 in the north. The microwave brightness in the south-polar region has increased to a level exceeding the level of the Cycle 23/24 minimum, but just started to increase in the north. The northsouth asymmetry in the polarity reversal has switched from that in Cycle 23. These observations lead us to the hypothesis that the onset of Cycle 25 in the northern hemisphere is likely to be delayed with respect to that in the southern hemisphere. We find that the unusual condition in the north is a direct consequence of the arrival of poleward surges of opposite polarity from the active region belt. We also find that multiple rush-to-the-pole episodes were indicated by the PE locations that lined up at the boundary between opposite-polarity surges. The high-latitude PEs occurred in the boundary between the incumbent polar flux and the insurgent flux of opposite polarity.

Gopalswamy, Nat↗
NASA NTRS2012

An Analysis of the Origin and Propagation of the Multiple Coronal Mass Ejections of 2010 August 1

On 2010 August 1, the northern solar hemisphere underwent significant activity that involved a complex set of active regions near central meridian with, nearby, two large prominences and other more distant active regions. This activity culminated in the eruption of four major coronal mass ejections (CMEs), effects of which were detected at Earth and other solar system bodies. Recognizing the unprecedented wealth of data from the wide range of spacecraft that were available-providing the potential for us to explore methods for CME identification and tracking, and to assess issues regarding onset and planetary impact-we present a comprehensive analysis of this sequence of CMEs.We show that, for three of the four major CMEs, onset is associated with prominence eruption, while the remaining CME appears to be closely associated with a flare. Using instrumentation on board the Solar Terrestrial Relations Observatory spacecraft, three of the CMEs could be tracked out to elongations beyond 50◦; their directions and speeds have been determined by various methods, not least to assess their potential for Earth impact. The analysis techniques that can be applied to the other CME, the first to erupt, are more limited since that CME was obscured by the subsequent, much faster event before it had propagated far from the Sun; we discuss the speculation that these two CMEs interact. The consistency of the results, derived from the wide variety of methods applied to such an extraordinarily complete data set, has allowed us to converge on robust interpretations of the CME onsets and their arrivals at 1 AU.

Harrison, R. A.↗
NASA NTRS1986

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

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

Illing, R. M. E.↗