Coronal Mass Ejections III
Presiding: D A Biesecker, NOAA Space Environment Center; B Welsch, Space Sciences Laboratory, University of California, Berkeley
SP44A-01 15:30h
Roll Effect in Prominence Eruption Explained by Anisotropic Electrical Conductivity
When a prominence erupts, it generally rises non-radially and the top part of the prominence ribbon bends in one direction to make the ribbon horizontally flat. Also the legs of the prominence undergo twisting motions of opposite senses. This phenomenon was discovered and named as "role effect" by S. F. Martin. This effect can hardly be understood in the framework of ideal MHD or MHD with isotropic conductivity. Such breaking of a geometrical symmetry in the evolution of an initially symmetric system can take place when the electrical conductivity is anisotropic. We perform simulations of a solar plasma evolution with anisotropic electrical conductivity. Now the magnetic field does not only move together with plasma bulk flows, but also against electric currents. Thus the rising motion of the field is skewed to one direction. When magnetic reconnection takes place in a magnetic loop or arcade, the direction of the current in the current sheet region and in the region connected to this current sheet by field lines is opposite to that in the underlying reconnected loops. This explains why the Doppler shift at the top and outer parts of the erupting prominence is opposite to that in the bottom part between the prominence legs. Furthermore, this reasoning can account for how the sign of the roll effect depends on the chirality of the prominence as observed.
SP44A-02 15:45h
Flare Emission Onset in the Slow-Rise and Fast-Rise Phases of an Erupting Solar Filament Observed with TRACE
We observe the eruption of an active-region solar filament of 1998 July~11 using high time cadence and high spatial resolution EUV observations from the TRACE satellite, along with soft X-ray images from the soft X-ray telescope (SXT) on the Yohkoh satellite, hard X-ray fluxes from the BATSE instrument on the ( CGRO) satellite and from the hard X-ray telescope (HXT) on Yohkoh, and ground-based magnetograms. We concentrate on the initiation of the eruption in an effort to understand the eruption mechanism. First the filament undergoes slow upward movement in a "slow rise" phase with an approximately constant velocity of ≈ 15~km~s-1 that lasts about 10~min, and then it erupts in a "fast-rise" phase, reaching a velocity of ≈ 200~km~s-1 in about 5~min, followed by a period of deceleration. EUV brightenings begin just before the start of the filament's slow rise, and remain immediately beneath the rising filament during the slow rise; initial soft X-ray brightenings occur at about the same time and location. Strong hard X-ray emission begins after the onset of the fast rise, and does not peak until the filament has traveled a substantial altitude (to a height about equal to the initial length of the erupting filament) beyond its initial location. Our observations are consistent with the slow-rise phase of the eruption resulting from the onset of "tether cutting" reconnection between magnetic fields beneath the filament, and the fast rise resulting from an explosive increase in the reconnection rate or by catastrophic destabilization of the overlying filament-carrying fields. About two days prior to the event new flux emerged near the location of the initial brightenings, and this recently-emerged flux could have been a catalyst for initiating the tether-cutting reconnection. With the exception of the initial slow rise, our findings qualitatively agree with the prediction for erupting-flux-rope height as a function of time in a model discussed by Chen & Shibata~(2000) based on reconnection between emerging flux and a flux rope. NASA supported this work through NASA SR&T and SEC GI grants.
SP44A-03 16:00h
On the Relationship Among Magnetic Twist, Reconnection Rate and Acceleation in Solar Eruptions
We investigate the statistical correlation between the magnetic twist and properties of solar eruptions such as acceleration of eruptive filaments and magnetic reconnection rate of corresponding two-ribbon flares. We anticipate to provide observational evidence for, or against, the speculation that increasing magnetic twist is more likely giving rise to the violent solar eruptions. The magnetic twist is characterized by the linear force-free (LFFF) magnetic field constant α. We adopt a method for the reconstruction of the LFFF magnetic field in a bounded domain that was described in Abramenko and Yurchishin (1996). The best-fit value of α is selected so that the extrapolated field gives the closest match to the coronal observations. The magnetic reconnection rate of two-ribbon flares, in terms of electric field inside the reconnecting current sheet(RCS) and flux change rate involved in magnetic reconnection in the low corona, is derived by measuring the expansion of flare ribbons across the the magnetic field. Based our limited events studied so far, there appears to be a tendency that the magnetic field with higher α shows higher filament acceleration and magnetic reconnection rate.
SP44A-04 16:15h
The Mass Properties of Coronal Mass Ejections: Evolution & Statistics
A defining property of a Coronal Mass Ejection (CME) is naturally its mass. The LASCO observations of 1000s of CMEs over the last 8 years allow us to constrain statistically the "typical" CME mass but also to examine its evolution as a function of time during each event. Such work could not be done in the past due to the lower cadence and instrument sensitivity. Our analysis of the CME mass properties has revealed some interesting and maybe unexpected results. For example, close to half of the observed CMEs seem to blend into the background before reaching 30 Rs. In this paper, we will discuss our findings for the LASCO CME sample from 1996 to 2004.
SP44A-05 16:30h
Preliminary Three Dimensional CME Mass and Energy Using Solar Mass Ejection Imager (SMEI) Data
White-light Thomson scattering observations from the Solar Mass Ejection Imager (SMEI) have recorded the inner heliospheric response to several hundred CMEs including the May 28, 2003 halo CME, the October 28, 2003 halo CME, and numerous other heliospheric structures. Here we show the extent of several well-observed CMEs in SMEI observations, and show how we are able to track events from their first measurements in SMEI approximately 20° from the solar disk until they vanish from the SMEI 180° field of view. Several portions of large CMEs observed by the LASCO coronagraphs can be tracked into the interplanetary medium associated with the initial CME response and the underlying erupting prominence structure. We use a 3D reconstruction technique that obtains perspective views from outward-flowing solar wind as observed from Earth, iteratively fitting a kinematic solar wind density model using the SMEI white light observations and, when available, the Solar-Terrestrial Environment Laboratory (STELab), Japan interplanetary scintillation (IPS) velocity data. This 3D modeling technique allows us to separate the heliospheric response in SMEI from background noise, and to estimate the 3D structure of the CME and its mass. For instance, the analysis shows and tracks outward the northward portion of the loop structure of the October 28, 2003 CME observed as a halo in LASCO images that passes Earth on October 29. We determine an excess mass for this structure of 6.7×1016g and a total mass including an ambient background of 8.3×1016g. The very fast structure compared in a 3D pixel to pixel comparison with the IPS velocity data gives a kinetic energy for the northward portion of this event of 2.0×1034erg as it passes Earth.
http://cass185.ucsd.edu/smei/smei.html
SP44A-06 16:45h
Relating heliospheric CME composition and associated flare magnitude
We present results from a continuing effort to study heliospheric CME ejecta within the context of solar CME observations. Previously we reported that in situ charge state ratios are positively correlated with associated flare magnitude for events occurring in central longitudes. We now present further correlations with elemental abundances of helium, neon and magnesium. We use partial correlation analysis to isolate the individual contributions from each signature. These correlations between in situ quantities and flare magnitudes indicate that flare eruptions have a stronger influence on CME material than previously thought.