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NASA NTRS1986

Analysis of the prominence associated with the coronal mass ejection of August 18, 1980

This paper develops a diagnostic method based on the observed H-alpha and continuum brightness to derive the electron density, line of sight thickness, and degree of ionization of hydrogen as functions of the temperature of the prominence filaments. Analysis of data from the event of August 18, 1980, illustrates that the rising prominence material has decreased density, increased temperature, and increased ionization of hydrogen relative to quiescent prominences in the lower corona. Hydrogen is found to be 90-99 percent ionized, electron densities are near 10 to the 8th/cu cm, and the temperature is near 20,000 K. The increased ionization is due mainly to the decreased density.

Athay, R. Grant↗
NASA NTRS1987

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

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.

Low, B. C.↗
NASA NTRS1993

Comment on 'Geomagnetic activity associated with earth passage of interplanetary shock disturbances and coronal mass ejections' by J. T. Gosling, D. J. McComas, J. L. Philips, and S. J. Bame

It is contended that statistical data do not support the claim of Gosling et al. (1991) to the effect that the initial speed of a solar wind driver gas close to the sun appears to be the most crucial factor in determining if an earthward direct event will be effective in exciting a large geomagnetic disturbance. It is argued that the time intervals are much too large to observe the storm-time B sub Z dependence. Gosling et al. reply that this comment is based on a serious misunderstanding of their conclusions.

Tsurutani, Bruce T.↗
NASA NTRS2000

Onset of the Magnetic Explosion in Solar Flares and Coronal Mass Ejections

We present observations of the magnetic field configuration and its transformation in six solar eruptive events that show good agreement with the Hirayama-Shibata model for eruptive flares. The observations arc X-ray images from the Yohkoh Soft X-ray Telescope (SXT) and magnetograms from Kitt Peak National Solar Observatory, interpreted together with the 1-8 Angstrom X-ray flux observed by GOES. The observations show: 1. Each event is a magnetic explosion that occurs in an initially closed magnetic bipole in which the core field is sheared and twisted in the shape of a sigmoid, having an oppositely curved elbow on each end. The arms of the opposite elbows are sheared past each other so that they overlap and are crossed low above the neutral line in the middle of the bipole. 2. Although four of the explosions arc ejective (blow open the bipole) and two are confined (arc arrested within the closed bipole), all six begin the same way. In the SXT iniages, the explosion begins with brightening and expansion of the two elbows together with the appearance of short bright sheared loops low over the neutral line under the crossed arms and, rising up from the crossed arms, long strands connecting the far ends of the elbows. 3. All six events arc single-bipole events in that during the onset and early development of the explosion they show no evidence for reconnection between the exploding bipole and any surrounding magnetic fields. We conclude that in each of our events the magnetic explosion was unleashed by runaway tether-cutting via implosive/explosive rcconnection in the middle of the sigmoid, as in the Hirayama-Shibata model. The similarity of the onsets of the two confined explosions to the onsets of the four ejective explosions and their agreement with the model indicate that runaway reconnection inside a sheared core field can begin whether or not the overlying fields (the envelope field and contiguous fields that press down on the envelope) allow the explosion to be ejective. We consider the implications ofthis for the unleashing of magnetic explosions in field configurations composed of to or more impacted bipoles.

Moore, R. L.↗
NASA NTRS2001

Reply to "Comment on the Paper ''On the Determination of Electron Polytrope Indices Within Coronal Mass Ejections in the Solar Wind'"'

We strongly disagree with the essence of the Osherovich (hereafter Osherovich) comment on one of our papers. The following paragraphs provide the basis of our disagreement and elaborate on why we believe that none of the concluding statements in his Comment are true. Our most important point is that one can apply the model developed by Osherovich and colleagues to real data obtained at a single point in space to determine the polytropic index within magnetic clouds if and only if the highly idealized assumptions of that model conform to physical reality. There is good reason to believe that those assumptions do not provide an accurate physical description of real magnetic clouds in the spherically expanding solar wind.

Gosling, J. T.↗
NASA NTRS2001

Prediction of Coronal Mass Ejections From Vector Magnetograms: Quantitative Measures as Predictors

We derived two quantitative measures of an active region's global nonpotentiality from the region's vector magnetogram, 1) the net current (I(sub N)), and 2) the length of strong-shear, strong-field main neutral line (Lss), and used these two measures in a pilot study of the CME productivity of 4 active regions. We compared the global nonpotentiality measures to the active regions' CME productivity determined from GOES and Yohkoh/SXT observations. We found that two of the active regions were highly globally nonpotential and were CME productive, while the other two active regions had little global nonpotentiality and produced no CMEs. At the Fall 2000 AGU, we reported on an expanded study (12 active regions and 17 magnetograms) in which we evaluated four quantitative global measures of an active region's magnetic field and compared these measures with the CME productivity. The four global measures (all derived from MSFC vector magnetograms) included our two previous measures (I(sub N) and L(sub ss)) as well as two new ones, the total magnetic flux (PHI) (a measure of an active region's size), and the normalized twist (alpha (bar)= muIN/PHI). We found that the three quantitative measures of global nonpotentiality (I(sub N), L(sub ss), alpha (bar)) were all well correlated (greater than 99% confidence level) with an active region's CME productivity within plus or minus 2 days of the day of the magnetogram. We will now report on our findings of how good our quantitative measures are as predictors of active-region CME productivity, using only CMEs that occurred after the magnetogram. We report the preliminary skill test of these quantitative measures as predictors. We compare the CME prediction success of our quantitative measures to the CME prediction success based on an active region's past CME productivity. We examine the cases of the handful of false positive and false negatives to look for improvements to our predictors. This work is funded by NSF through the Space Weather Program and by NASA through the Solar Physics Supporting Research and Technology Program.

Falconer, D. A.↗
NASA NTRS2001

The Role of Magnetograms in Testing Models of Coronal Mass Ejections

A general review of current and future magnetographic capabilities is presented with emphasis on how they address observational predictions of CME models (e.g., the model/observation matrix developed in the SHINE 2000 workshop). Existing line-of-sight magnetographs can observe certain structural and kinematic properties of CME source regions when they are on the visible disk. These include polarity configuration, location and structure of the magnetic inversion line, proper motions of magnetic elements, and time variation of flux. Additional chromospheric magnetograms provide information on how the field spreads with height and, if properly sequenced with photospheric magnetograms, can determine whether flux is emerging or submerging. Vector magnetographs can provide information about currents and magnetic shear but will only begin to attain the spatial and temporal coverage appropriate to CMEs with the advent of the SOLIS vector spectromagnetograph and, hopefully, its copies at several widely spaced longitudes. Important additions to the SHINE 2000 matrix are required to define an observational program. These include spatial and temporal resolutions and extents as well as needed sensitivity.

Jones, Harrison P.↗
NASA NTRS2003

A Measure from Line-of-Sight Magnetograms for Prediction of Coronal Mass Ejections

From a sample of 17 vector magnetograms of 12 bipolar active regions, we have recently found (1) that a measure of the overall nonpotentiality (the overall twist and shear in the magnetic field) of an active region is given by the strong-shear length L(sub SS), the length of the portion of the main neutral line on which the observed transverse fields is strong (greater than 150 G) and strongly sheared (shear angle greater than 45 deg), and (2) that L(sub SS) is well correlated with the CME productivity of the active regions during the +/- 2-day time window centered on the day of the magnetogram. In the present paper, from the same sample of 17 vector magnetograms, we show that there is a viable proxy for L(sub SS) that can be measured from a line-of-sight magnetogram. This proxy is the strong-gradient length L(sub SG), the length of the portion of the main neutral line on which the potential transverse field is strong (greater than 150 G) and the gradient of the line-of-sight field is sufficiently steep (greater than or approximately 50 G/Mm). In our sample of active regions, L(sub SG) is statistically significantly correlated with L(sub SS) (correlation confidence level greater than 95%), and L(sub SG) is as strongly correlated with active-region CME productivity as is L(sub SS)(correlation confidence level approximately 99.7%). Because L(sub SG) can be measured from line-of-sight magnetograms obtained from conventional magnetographs, such as the magnetograph mode of the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO), it is a dependable substitute for L(sub SS) for use in operational CME forecasting. In addition, via measurement of L(sub SG), the years-long, nearly continuous sequence of 1.5-hour-cadence full-disk line-of-sight magnetograms from MDI can be used to track the growth and decay of the large-scale nonpotentiality in active regions and to examine the role of this evolution in active-region CME productivity.

Falconer, D. A.↗
NASA NTRS2006

Origin of the Sheared Magnetic Fields that Erupt in Flares and Coronal Mass Ejections

From a search of the Yohkoh/SXT whole-Sun movie in the years 2000 and 2001, we found 37 flare-arcade events for which there were full-disk magnetograms from SOHO/MDI, coronagraph movies from SOHO/LASCO, and before and after full-disk chromospheric images from SOHOBIT and/or from ground-based observatories. For each event, the observations show or strongly imply that the flare arcade was produced in the usual way by the eruption of sheared core field (as a flux rope) from along the neutral line inside a mature bipolar magnetic arcade. Two-thirds (25) of these arcades had the normal leading-trailing magnetic polarity arrangement of the active regions in the hemisphere of the arcade, but the other third (12) had reversed polarity, their leading flux being the trailing-polarity remnant of one or more old active regions and their trailing flux being the leading-polarity remnant of one or more other old active regions. From these observations, we conclude: (1) The sheared core field in a reversed-polarity arcade must be formed by processes in and above the photosphere, not by the emergence of a twisted flux rope bodily from below the photosphere. (2) The sheared core fields in the normal-polarity arcades were basically the same as those in the reversed-polarity arcades: both showed similar sigmoidal form and produced similar explosions (similar flares and CMEs). (3) Hence, the sheared core fields in normal-polarity mature arcades are likely formed mainly by the same processes as in reversed-polarity arcades. (4) These processes should be discernible in high-resolution magnetogram sequences and movies of the photosphere, chromosphere, and corona such those to come from Solar-B

Moore, Ronald L.↗
NASA NTRS2006

Forecasting Coronal Mass Ejections from Line-of-Sight Magnetograms

We show that the length of strong-gradient, strong-field main neutral line, L(sub SGM), which can be measured from line-of-sight magnetograms such as from SOHO/MDI, is both a measure of active-region nonpotentiality and a useful predictor of an active region's future CME productivity. To demonstrate that L(sub SGM) is a nonpotentiality measure, we show that it is strongly correlated with a direct measure of nonpotentiality. For an appropriate choice of a threshold value, an active region s measured LsGM can be used as a predictor of whether the active region will produce a CME within a few days after the magnetogram. For our set of 36 MSFC vector magnetograms of bipolar active regions, L(sub SGM) is found to have a success rate of 80% for prediction of CME productivity in the 0-2 day window. The development of L(sub SGM) as a method of measuring nonpotentiality for forecasting large, fast CMEs from present space based assets is of value to NASA's Space Exploration Initiative (manned missions to the Moon and Mars)

Falconer, D. A.↗
NASA NTRS2007

The Width of a Solar Coronal Mass Ejection and the Source of the Driving Magnetic Explosion

We show that the strength of the magnetic field in the area covered by the flare arcade following a CME-producing ejective solar eruption can be estimated from the final angular width of the CME in the outer corona and the final angular width of the flare arcade. We assume (1) the flux-rope plasmoid ejected from the flare site becomes the interior of the CME plasmoid, (2) in the outer corona (R greater than 2R(sub Sun)) the CME is roughly a spherical plasmoid with legs shaped like a light bulb, and (3) beyond some height in or below the outer corona the CME plasmoid is in lateral pressure balance with the surrounding magnetic field. The strength of the nearly radial magnetic field in the outer corona is estimated from the radial component of the interplanetary magnetic field measured by Ulysses. We apply this model to three well-observed CMEs that exploded from flare regions of extremely different size and magnetic setting. One of these CMEs is an over-and-out CME that exploded from a laterally far offset compact ejective flare. In each event, the estimated source-region field strength is appropriate for the magnetic setting of the flare. This agreement (1) indicates that CMEs are propelled by the magnetic field of the CME plasmoid pushing against the surrounding magnetic field, (2) supports the magnetic-arch-blowout scenario for over-and-out CMEs, and (3) shows that a CME s final angular width in the outer corona can be estimated from the amount of magnetic flux covered by the source-region flare arcade.

Moore, Ronald L.↗
NASA NTRS2007

The Coronal-Dimming Footprint of a Streamer-Puff Coronal Mass Ejection: Confirmation of the Magnetic-Arch-Blowout Scenario

In this paper, for a CME of the particular variety recently identified by Bemporad et al (2005), we present new evidence that strengthens the conclusion of Bemporad et al that for these CMEs the pre-eruption magnetic field that explodes to drive the CME is laterally far offset from the radial path of the full-blown CME in the outer corona. In CMEs of the particular variety of those found by Bemporad et al, the flare-site field that explodes is much more compact than the flare-site fields that explode in most major flares and large CMEs, and is located in a flank of the base of a streamer. After presenting our new evidence for how CMEs of this variety are produced, we cite and discuss examples of larger flare-producing magnetic explosions that are not necessarily in a flank of a streamer but occur together with a large CME that in the outer corona is laterally far offset from the flare. We conclude that there is a broad class of CMEs that come from flare-producing magnetic explosions of various sizes and that are laterally far offset from the flare. We propose that all CMEs of this broad class are produced in basically the same way as those of the particular variety of the one that we present in this paper. In this paper, it is therefore convenient and useful to refer to this broad class of CMEs (regardless of the pre-eruption size of the offset field that explodes and whether or not this field is in the flank of a streamer), as "over-and-out" CMEs. Because the lack of recognition of this class of CMEs has contributed to the confusion and controversy regarding the relation between flares and CMEs (e.g., Kahler 1992; Gosling 1993; Hudson et al 1995), it is important that this class of CME have an explicit name. We adopt the name over-and-out CME because it is a needed descriptive term, especially for the purpose of this paper.

Moore, Ronald L.↗
NASA NTRS2007

The Width of a Solar Coronal Mass Ejection and the Source of the Driving Magnetic Explosion: A Test of the Standard Scenario for CME Production

We show that the strength (B(sub F1are)) of the magnetic field in the area covered by the flare arcade following a CME-producing ejective solar eruption can be estimated from the final angular width (Final Theta(sub CME)) of the CME in the outer corona and the final angular width (Theta(sub Flare)) of the flare arcade: B(sub Flare) approx. equals 1.4[(Final Theta(sub CME)/Theta(sub Flare)] (exp 2)G. We assume (1) the flux-rope plasmoid ejected from the flare site becomes the interior of the CME plasmoid; (2) in the outer corona (R > 2 (solar radius)) the CME is roughly a "spherical plasmoid with legs" shaped like a lightbulb; and (3) beyond some height in or below the outer corona the CME plasmoid is in lateral pressure balance with the surrounding magnetic field. The strength of the nearly radial magnetic field in the outer corona is estimated from the radial component of the interplanetary magnetic field measured by Ulysses. We apply this model to three well-observed CMEs that exploded from flare regions of extremely different size and magnetic setting. One of these CMEs was an over-and-out CME, that is, in the outer corona the CME was laterally far offset from the flare-marked source of the driving magnetic explosion. In each event, the estimated source-region field strength is appropriate for the magnetic setting of the flare. This agreement (1) indicates that CMEs are propelled by the magnetic field of the CME plasmoid pushing against the surrounding magnetic field; (2) supports the magnetic-arch-blowout scenario for over-and-out CMEs; and (3) shows that a CME's final angular width in the outer corona can be estimated from the amount of magnetic flux covered by the source-region flare arcade.

Moore, Ronald L.↗
NASA NTRS2008

Recent STEREO Observations of Coronal Mass Ejections

Over 400 CMEs have been observed by STEREO SECCHI COR1 during the mission's three year duration (2006-2009). Many of the solar activity indicators have been at minimal values over this period, and the Carrington rotation-averaged CME rate has been comparable to that measured during the minima between Cycle 21-22 (SMM C/P) and Cycle 22-23 (SOHO LASCO). That rate is about 0.5 CMEs/day. During the current solar minimum (leading to Cycle 24), there have been entire Carrington rotations where no sunspots were detected and the daily values of the 2800 MHz solar flux remained below 70 sfu. CMEs continued to be detected during these exceptionally quiet periods, indicating that active regions are not necessary to the generation of at least a portion of the CME population. In the past, researchers were limited to a single view of the Sun and could conclude that activity on the unseen portion of the disk might be associated with CMEs. But as the STEREO mission has progressed we have been able to observe an increasing fraction of the Sun's corona with STEREO SECCHI EUVI and were able to eliminate this possibility. Here we report on the nature of CMEs detected during these exceptionally quiet periods, and we speculate on how the corona remains dynamic during such conditions.

SaintCyr, Chris Orville↗
NASA NTRS2010

A Historic View of Solar Coronal Mass Ejections (CMEs)

We present a historic overview of CME observations, ending with concepts for future measurement capabilities. One of the first detections of what we now call a CME was provided by instrumentation on OSO-7 and reported by Tousey (1973); but the phrase "corona) mass ejection" was coined after the Skylab/ATM coronagraph detected dozens of the transients over its nine month observing run (e.g., Munro et al., 1979). Pre-discovery identification of likely CMEs were then reported in historic eclipse photographs and drawings (e.g., Eddy, 1974; Cliver, 1989). Multi-year observations followed with groundbased MLSO MK3/4 coronagraph (1980-present), and spacebased missions: Solwind (1979-1985), SMM (1980-1989), SOHO LASCO/EIT (1996-present), SMEI (2003-present), and STEREO SECCHI (2006-present). The Spartan 201 coronagraph flew in space multiple times. The influential Gosling (1993) "solar flare myth" manuscript identified CMEs as the cause of the most severe geomagnetic storms, thus cementing their importance in Sun-Earth connection studies. A new window into CMEs was opened with the launch of SOHO in 1995 when the UVCS spectrometer began returning plasma diagnostics of a significant number of events (e.g., Ciaravella et al., 2006). What about the future for CME research? Statistical properties of the UVCS CME observations are forthcoming; the STEREO mission should continue to return views of CMEs from unique vantage points; and the recent launch of SDO should provide new insights into the small spatial scale dynamics of activity associated with CMEs. Several new observing techniques have been demonstrated at total eclipses, and inclusion on spacebased platforms in the future could also prove valuable for understanding CMEs. A common element of several recent proposals is to image the white-light corona with extremely high spatial resolution. The momentary glimpses of the corona during total solar eclipses have shown fine structure that is not captured by global models, and dynamics of these structured elements may be important to resolve the question of CME initiation.

SaintCyr, Orville C.↗
NASA NTRS2010

Radio-Loud Coronal Mass Ejections Without Shocks Near Earth

Type II radio bursts are produced by low energy electrons accelerated in shocks driven by corona) mass ejections (CMEs). One can infer shocks near the Sun, in the Interplanetary medium, and near Earth depending on the wavelength range in which the type II bursts are produced. In fact, type II bursts are good indicators of CMEs that produce solar energetic particles. If the type 11 burst occurs from a source on the Earth-facing side of the solar disk, it is highly likely that a shock arrives at Earth in 2-3 days and hence can be used to predict shock arrival at Earth. However, a significant fraction of CMEs producing type II bursts were not associated shocks at Earth, even though the CMEs originated close to the disk center. There are several reasons for the lack of shock at 1 AU. CMEs originating at large central meridian distances (CMDs) may be driving a shock, but the shock may not be extended sufficiently to reach to the Sun-Earth line. Another possibility is CME cannibalism because of which shocks merge and one observes a single shock at Earth. Finally, the CME-driven shock may become weak and dissipate before reaching 1 AU. We examined a set of 30 type II bursts observed by the Wind/WAVES experiment that had the solar sources very close to the disk center (within a CMD of 15 degrees), but did not have shock at Earth. We find that the near-Sun speeds of the associated CMEs average to approx.600 km/s, only slightly higher than the average speed of CMEs associated with radio-quiet shocks. However, the fraction of halo CMEs is only approx.28%, compared to 40% for radio-quiet shocks and 72% for all radio-loud shocks. We conclude that the disk-center radio loud CMEs with no shocks at 1 AU are generally of lower energy and they drive shocks only close to the Sun.

Gopalswamy, N.↗
NASA NTRS2010

Aspects of Coronal Mass Ejections Related to Space Weather

Solar cycle 23 witnessed an unprecedented array of space- and ground-based instruments observing the violent eruptions from the Sun that had huge impact on the heliosphere. It was possible to characterize corona) mass ejections (CMEs) that cause extreme solar energetic particle events and geomagnetic storms, the two aspects that concern the space weather community. In this paper I discuss the special populations of CMEs that have significant interplanetary consequences: shock-driving CMEs identified based on their association with type 11 radio bursts and in-situ shocks, SEP-producing CMEs, and geoeffective CMEs (those that produce geomagnetic storms). I discuss the kinematic and solar-source properties of these populations and how they vary with the solar activity cycle. I also compare their properties with the general population of CMEs, so one can recognize when and where these events occur on the Sun.

Gopalswamy, Nat↗