Joan T. Burkepile

Active and Eruptive Prominences and Their Relationship to Coronal Mass Ejections

In order to understand better the dynamical processes in the solar atmosphere that are associated with coronal mass ejections (CMEs), we have carried out a study of prominence activity using Hα observations obtained at the Mauna Loa Solar Observatory (MLSO). After developing clear definitions of active prominences (APs) and eruptive prominences (EPs), we examined 54 Hα events to identify distinguishing characteristics of APs and EPs and to study the relationship between prominence activity and CMEs. The principal characteristics we found to distinguish clearly between APs and EPs are maximum projected radial height, projected radial velocity, and projected radial acceleration. We determined CME associations with Hα events by using white-light data from the Mk III K-Coronameter at MLSO and the LASCO C2 Coronagraph on SOHO. We found that EPs are more strongly associated with CMEs than are APs and that the CMEs associated with EPs generally have cores, while those associated with APs do not. A majority of the EPs in the study exhibit separation of escaping material from the bulk of the prominence—the latter initially lifting away from and then returning toward the solar surface. This separation tends to occur in the height range from 1.20 to 1.35 R0, and we infer that it involves the formation of an X-type neutral line in this region, which allows disconnection of part of the prominence material. This disconnection view of prominence eruption seems most consistent with flux rope models of prominence support.

A comparison of ground-based and spacecraft observations of coronal mass ejections from 1980–1989

We report here an analysis of observations of solar coronal mass ejections (CMEs) acquired in white light by the Mark III (MK3) K coronameter at Mauna Loa Solar Observatory between 1980 and 1989. Statistical properties of the locations, sizes, and speeds of these events are described. These properties are compared to those in the two other white light CME catalogs from the 1980s, the CMEs observed by the Solwind and SMM spaceborne coronagraphs, and relatively good statistical agreement is found between the three data sets taken over the entire period of observation. A detailed examination was performed for the 141 MK3 CMEs that were also observed by SMM. Virtually all (93%) of the CMEs detected low in the corona by the MK3 instrument were observed to travel out of the SMM field of view, into interplanetary space. The average width of CMEs in the MK3 field of view was 12° smaller than that measured in SMM, and we interpret this statistic as an indication of some increase in size as CMEs move outward through the corona. For a subset of 55 of those mass ejections we were able to combine detailed observations from both MK3 and SMM. Using the combined measurements, we were able to detect and to quantify the initial period of acceleration in a much larger fraction (61%) of the features than was possible from either MK3 alone (9%) or SMM alone (21%). The acceleration was positive for 87% of those features, with an average (median) value of +0.264 km s−2 (+0.044 km s−2). A distinction in terms of association with other forms of solar activity was also evident in this analysis: 55% of the CMEs associated with active regions moved with constant speed, but 82% of the features associated with the eruption of solitary prominences moved with constant acceleration. Also, the average speed for CMEs associated with active regions was significantly faster than those with prominence association (955 versus 411 km s−1). The detection of positive acceleration demonstrates that the forces propelling the CME continue to dominate these events, at least through the altitudes covered by the MK3 and SMM fields of view.

Speeds of coronal mass ejections: SMM observations from 1980 and 1984-1989

The speeds of 936 features in 673 coronal mass ejections have been determined from trajectories observed with the Solar Maximum Mission (SMM) coronagraph in 1980 and 1984-1989. The distribution of observed speeds has a range (from 5th to 95th percentile) of 35 to 911 km s−1; the average and median speeds are 349 and 285 km s−1. The speed distributions of some selected classes of mass ejections are significantly different. For example, the speeds of 331 “outer loops” range from 80 to 1042 km s−1; the average and median speeds for this class of ejections are 445 and 372 km s−1. The speed distributions from each year of SMM observations show significant changes, with the annual average speeds varying from 157 (1984) to 458 km s−1 (1985). These variations are not simply related to the solar activity cycle; the annual averages from years near the sunspot maxima and minimum are not significantly different. The widths, latitudes, and speeds of mass ejections determined from the SMM observations are only weakly correlated. In particular, mass ejection speeds vary only slightly with the heliographic latitudes of the ejection. High-latitude ejections, which occur well poleward of the active latitudes, have speeds similar to active latitude ejections.

THE CALM BEFORE THE STORM: THE LINK BETWEEN QUIESCENT CAVITIES AND CORONAL MASS EJECTIONS

Determining the state of the corona prior to CMEs is crucial to understanding and ultimately predicting solar eruptions. A common and compelling feature of CMEs is their three-part morphology, as seen in white-light observations of a bright expanding loop, followed by a relatively dark cavity, and finally a bright core associated with an erupting prominence/filament. This morphology is an important constraint on CME models. It is also quite common for a three-part structure of loop, cavity, and prominence core to exist quiescently in the corona, and this is equivalently an important constraint on models of CME-precursor magnetic structure. These quiescent structures exist in the low corona, primarily below approximately 1.6R� , and so are currently observable in white light duringsolar eclipses, or else by the Mauna Loa Solar Observatory Mk4 coronameter. We present the first comprehensive, quantitative analysis of white-light quiescent cavities as observed by the Mk4 coronameter. We find that such cavities are ubiquitous, as they are the coronal limb counterparts to filament channels observed on the solar disk. We consider examples that range from extremely long-lived, longitudinally extended polar-crown-filament-related cavities to smallercavitiesassociated withfilamentsnearorwithinactiveregions.Theformerareoftenvisiblefordaysandeven weeks at a time and can be identified as long-lived cavities that survive for months. We quantify cavity morphology and intensity contrast properties and consider correlations between these properties. We find multiple cases in which quiescentcavitiesdirectlyeruptintoCMEsandconsiderhowmorphologicalandintensitycontrastpropertiesofthese cases differ from the general population of cavities. Finally, we discuss the implications that these observations may have for the state of the corona just prior to a CME, and more generally for the nature of coronal MHD equilibria.

The Structure and Evolution of a Sigmoidal Active Region

Solar coronal sigmoidal active regions have been shown to be precursors to some coronal mass ejections. Sigmoids, or S-shaped structures, may be indicators of twisted or helical magnetic structures, having an increased likelihood of eruption. We present here an analysis of a sigmoidal regions three-dimensional structure and how it evolves in relation to its eruptive dynamics. We use data taken during a recent study of a sigmoidal active region passing across the solar disk (an element of the third Whole Sun Month campaign). While S-shaped structures are generally observed in soft X-ray (SXR) emission, the observations that we present demonstrate their visibility at a range of wavelengths including those showing an associated sigmoidal filament. We examine the relationship between the S-shaped structures seen in SXR and those seen in cooler lines in order to probe the sigmoidal regions three-dimensional density and temperature structure. We also consider magnetic field observations and extrapolations in relation to these coronal structures. We present an interpretation of the disk passage of the sigmoidal region, in terms of a twisted magnetic flux rope that emerges into and equilibrates with overlying coronal magnetic field structures, which explains many of the key observed aspects of the regions structure and evolution. In particular, the evolving flux rope interpretation provides insight into why and how the region moves between active and quiescent phases, how the regions sigmoidicity is maintained during its evolution, and under what circumstances sigmoidal structures are apparent at a range of wavelengths.

Magnetic Geometry and Dynamics of the Fast Coronal Mass Ejection of 1997 September 9

A coronal mass ejection (CME) was observed on 1997 September 9 by the Mauna Loa Solar Observatory Mark III K-coronameter (MK3) and by the LASCO C2/C3 and EIT instruments on board the SOHO spacecraft. Magnetograms and EIT images obtained on days leading up to the eruption show a neutral line that appears to correspond to the site of the eruption. Taken together, the data from these instruments provide a comprehensive, beginning-to-end record of the event within the 32 R☉ field of view. The motion of several features are tracked through the fields of view of MK3, C2, and C3. The CME exhibits the previously identified morphological features and dynamical properties consistent with those of an erupting magnetic flux rope with its legs connected to the Sun. The LASCO images and magnetograms indicate that the flux rope axis was aligned with the neutral line approximately 2 days behind the west limb. Its apparent orientation provides an oblique view of an erupting flux rope, a view that has not been discussed previously. A theoretical flux rope model is used to understand the forces responsible for the observed CME dynamics. Synthetic coronagraph images based on the model flux rope are constructed.

Constraints on Coronal Mass Ejection Dynamics from Simultaneous Radio and White-Light Observations

Simultaneous radio and white-light observations are used to deduce information on the dynamics of two coronal mass ejection (CME) events that occurred about 2 hr apart on 2001 January 20 and that were associated with eruptions from the same active region on the Sun. The analysis combines both space-based and ground-based data. The radio data were obtained from the WAVES experiment on the Wind spacecraft and from the Culgoora radiospectrograph in Australia. The white-light data were from the LASCO experiment on SOHO and from the Mk4 coronameter at the Mauna Loa Solar Observatory. For these CME events we demonstrate that the frequency drift rate of the type II radio emissions, generated by the shocks driven by the white-light CMEs, are consistent with the plane-of-sky height-time measurements, provided that the propagation direction of the CMEs and their associated radio sources was along a radial line from the Sun at a solar longitude of ~E50°. These results imply that the true CME speeds were estimated to be ~1.4 times higher than the measured plane-of-sky speeds and that the CMEs originated from solar eruptions centered near E50°. This CME origin is consistent with the known active region and flare site associated with these two CME events. Furthermore, we argue that the type II radio emissions generated by these CMEs must have originated in enhanced density regions of the corona. We investigate whether the type II radiation could have originated in one or more dense coronal streamers, whose densities were estimated from the polarization brightness measurements made by LASCO at that time. Finally, we use these radio and white-light observations to speculate about the dynamics and scales involved in the interaction between these two CMEs.

Observational Interpretation of an Active Prominence on 1999 May 1

This paper presents an observational study of an active prominence observed in He I 1083 nm intensity and velocity data obtained at the Mauna Loa Solar Observatory, which provide physical insight into dynamical processes associated with prominences. We compare these observations with existing theoretical prominence models, which fall into two main classes: dip models and flux rope models. Dip models use sagging magnetic arches to explain prominence support, while flux rope models are characterized by helical magnetic field lines that trap prominence material at the bottom of the rope. The prominence on which we focus in the present paper has four interesting components of activity, all of which we attempt to explain using each of three different prominence models: the normal and inverse polarity flux rope models and the dip model. Our objective is to test the viability of each of these models in describing this type of activity. The model that appears consistent with the observed activity in this particular prominence is the inverse polarity flux rope model. We suggest that the process of vertical reconnection between an inverse polarity flux rope and an underlying magnetic arcade may best describe the observed prominence activity.

Multialtitude Observations of a Coronal Jet during the Third Whole Sun Month Campaign

On 1999 August 26, a coronal jet occurred at the northwest limb near a sigmoid active region (AR 8668) that was the target for a joint observation plan (SOHO joint observing program 106) during the third Whole Sun Month Campaign. This jet was observed by several instruments at the limb (SOHO/CDS, SOHO/EIT, TRACE, and Mauna Loa Solar Observatory CHIP and PICS) and at 1.64 R☉ (SOHO/UVCS). At the limb, this jet event displayed both low- and high-temperature components. Both high- and low-temperature components were evident during the early phase (first 20 minutes) of the event. However, the low-temperature component is maintained for ~1 hr after the higher temperature component is gone. There is a second brightening (a possible second jet) seen by EIT and TRACE about 50 minutes after the onset of the first jet. The line-of-sight motion at the limb began with a 300 km s-1 redshift and evolved to a 200 km s-1 blueshift. At 1.64 R☉, the intensities of Lyα and Lyβ in the jet increased by a factor of several hundred compared with the background corona. The C III λ977 line also brightened significantly. This indicates low-temperature [~(1-2) × 105 K] emission in the jet, while the intensities of O VI λ1032 and O VI λ1037 increased by as much as a factor of 8. The UVCS data show evidence of heating at the early phase of the event. The Doppler shift in the lines indicates that the line-of-sight (LOS) velocity in the jet started from ~150 km s-1 in blueshift and ended at ~100 km s-1 in redshift. This LOS motion seen at 1.64 R☉ was apparently opposite to what was observed when the jet emerged from the limb. The Doppler dimming analysis indicates that the radial outflow speed correlates with the magnitude of the LOS speed. Interestingly, UVCS observations at 2.33 and 2.66 R☉ show no trace of the jet and SOHO/LASCO observations also yield no firm detection. We find that a simple ballistic model can explain most of the dynamical properties of this jet, while the morphology and the thermal properties agree well with reconnection-driven X-ray jet models.

Transient Coronal Holes as Seen in the He I 1083 nm MLSO Observations

Observations from Yohkoh SXT and SOHO EIT have shown that dimming regions often appear on the solar disk near the location of a coronal mass ejection (CME). We now can see brightenings in He I 1083 nm observations made at the Mauna Loa Solar Observatory (MLSO) that form at the same time and are cospatial with the EUV intensity dimmings observed from space. The He I 1083 nm brightenings are induced by a decrease of the overlying coronal radiation. The EUV and X-ray dimmings and He I 1083 nm brightenings can thus be interpreted as different manifestations of the decreased coronal density caused by the ejection of coronal material during the eruption, i.e., as transient coronal holes. In this paper we present examples of transient coronal holes that form during the CME onset as seen in He I 1083 nm data and compare them with simultaneous observations in the Fe XII 19.5 nm line. We find that there is good agreement in both shape and size of the transient coronal holes at these two wavelengths. The 3 minute cadence of the He I 1083 nm observations taken at MLSO is used to determine the appearance and evolution of transient coronal holes with high temporal accuracy. Additional data in the H? line and in broadband visible light are used to investigate the relation of transient coronal holes to the flare, filament eruption, and CME. The cases presented here illustrate how the higher time cadence of the MLSO observations can complement space data to establish the chronology of the various manifestations of solar activity associated with a CME.