Solar Wind/SOHO 16

Session: Session 8: CMEs and ICMEs (08)
Type: Oral presentation
Date: Friday, June 17, 2005
Time: 08:30 - 12:55

Seq   Time   Title   Abs No
1   08:30   From CMEs to ICMEs: Problems, progress and prospects
Peter , Cargill
Imperial College, UNITED KINGDOM

The connection between CMEs seen at the Sun and their interplanetary couterparts, notably magnetic flux ropes and other manifestations, has been clear in generic terms for a decade. However, the availability of continual solar and interplanetary data from SOHO, WIND and ACE in the past decade has made real progress possible in understanding cause and effect. This talk will examine the current standing of the field, and address future prospects. Particular emphasis will be placed on the potential capabilities of multi-spacecraft observations and large-scale computational models.

2   09:30   ICME-CME Connections: Outstanding Questions
Crooker, Nancy
Boston University, UNITED STATES

Although material from coronal mass ejections (CMEs) observed in the interplanetary medium (ICMEs) is usually easy to recognize, a number of basic questions remain concerning the linked issues of its relationship to what is observed on the Sun and its evolution as it propagates through the heliosphere. These include questions about structure, dynamics, magnetic connections, filament material, composition and charge-state patterns, and the imprint of the solar dipolar field component. Progress gained through both modeling and observational studies is reviewed, with particular attention to a new technique for identifying sites of interchange reconnection at the footpoints of ICMEs using suprathermal electron measurements.

3   09:55   The Breakout Model for CME Initiation in 3-Dimensions
Lynch, Benjamin1; Antiochos, S. K.2; DeVore, C. R.3; Zurbuchen, T. H.4
1Univ. of Michigan / Naval Research Lab, UNITED STATES; 2Naval Research Laboratory / Univ. of Michigan, UNITED STATES; 3Naval Research Laboratory, UNITED STATES; 4Univ. of Michigan, UNITED STATES

We present numerical MHD simulations that demonstrate, for the first time, the breakout model for the initiation of coronal mass ejections in the most general 3D magnetic topology. An elongated bipolar active region configuration with a spine and 3D separator fan surface is shown to build up sufficient magnetic free energy and have the necessary complexity to produce a fast eruption of low-lying sheared flux over part of the active region neutral line. We concentrate on the details of the overlying breakout magnetic reconnection that triggers the unstable, rapid expansion of sheared flux and the classic eruptive flare reconnection which produces a twisted flux rope structure and a >1000 km/s eruption.

4   10:10   Quantitative Study of Initiation and Evolution of CMEs in Different Solar Wind Models
Poedts, Stefaan; Jacobs, C.; Chane, E.; van der Holst, B.; Dubey, G.; Kimpe, D.

The shocks and magnetic clouds related to fast Coronal Mass Ejections (CMEs) in the solar corona and interplanetary space play a crucial role in the study of space weather. Better predictions of space weather events require a deeper insight in the physics behind them. Therefore, numerical simulations of some simplified CME models were performed by means of a finite volume, explicit solver to advance the equations of magnetohydrodynamics (MHD).

In our CME initiation studies we compare two different kinds of initiation models, viz. foot point shearing and magnetic flux emergence. The effect of the initiation parameters, like the shear velocity, the extend of the shear region, the emergence rate of the magnetic flux, etc., on the evolution parameters of the CMEs (velocity, acceleration rate, instability threshold, etc.) is studied. Another important aspect of our study is the fact that we do the same CME simulations superposed on different models for the background solar wind. This enables us to quantify the effects of both the CME parameters (e.g. the initiation mechanism, the presence and polarity of magnetic flux rope, etc.) and the background solar wind model on the CME evolution parameters. The use of the same numerical code/technique for all simulations is essential for this quantification.

5   10:25   Evolution of the Three-dimensional Structure of a Halo Coronal Mass Ejection from Polarimetric analysis
Moran, Thomas1; Moran, TGM2
1Catholic University of America, NASA/GSFC, UNITED STATES; 2Catholic University of America and NASA/GSFC, UNITED STATES

We present the evolution of the three-dimensional structure of a halo coronal mass ejection determined from polarimetric analysis of SOHO/LASCO coronagraphic observations. Polarimetric three-dimensional reconstruction shows that the CME base approximates a distorted cone, with angular spreads of 80 to 110 degrees. This structure changed little over the 16 hours of observations, fading slowly with time. Waves were detected propagating outward on the base structure, which were manifested as expanding, concentric wavefronts comprising many narrow radially aligned structures moving at 150 km/sec to 390 km/sec with periods and wavelengths of 130 minutes and 1 to 2 solar radii, respectively. The modes reveal the base to be filamentary, consistent with a magnetic flux loop arcade structure.

6   11:25   Dimensions of structured coronal mass ejections
Cremades, Hebe1; Bothmer, V.2
1Max-Planck-Institut für Sonnensystemforschung, GERMANY; 2Universitäts-Sternwarte Göttingen, GERMANY

The collection of coronal mass ejections (CMEs) analyzed here comprises CMEs which exhibit white-light fine structures (structured CMEs), likely indicative of their possible 3D topology. These CME events have been selected from the SOHO/LASCO dataset within the period 1996-2002. Results based on the investigation of the low coronal and photospheric source regions associated with the structured CMEs, indicated that these CMEs are essentially organized along a symmetry axis, in a cylindrical manner. The cylindrical configuration of these CMEs seems to agree with that of a large-scale helical magnetic flux rope.
Depending on the orientation of the structured CMEs with respect to the observer, it was possible to measure the cylinders cross-section D and length L for a number of cases. The ratio between the average values of D and L of 1.6 was remarkably identical when measured in both instruments, EIT and LASCO/C2. The extrapolation of D and L to 1 AU shows agreement with the radial diameter and azimuthal broadness of magnetic clouds a special subset of interplanetary CMEs. Furthermore, the findings related to CME deflection explain the detection in the ecliptic of interplanetary CMEs that originated at high altitudes.

7   11:40   The Coronal and Interplanetary Transport of CMEs determined from White-Light, Radio and In-situ Shock Measurements
Reiner, Michael1; Reiner, Michael J1; Kaiser, Michael L2

The accurate characterization of the coronal and interplanetary transport of CMEs is crucial for predicting the potential onset of space weather events. It has proven difficult to determine the CME kinematics from the LASCO coronagraph observations alone because these measurements give only plane-of-sky speeds and accelerations and extend to plane-of-sky distances of only 0.15 AU (32 Rs); CME kinematics can change significantly beyond that distance. To accurately track the corresponding ICME, additional observations are required. Recently, the all-sky (SMEI) images, which extend the white-light observations from 0.33 AU (70 Rs), have become available. Nevertheless, the majority of CMEs observed during solar cycle 23 have available only the LASCO white-light observations. Some CMEs, especially the fast and energetic ones, drive strong interplanetary shocks. Although the driven shock is the most conspicuous identifying in-situ feature of the ICME, the corresponding shock feature in the white-light images is still not obvious. On the other hand, these CME-driven shocks can generate radio emissions at decreasing frequencies as the CME/shock propagates through the decreasing interplanetary density. Thus remote radio sensing can also be used to investigate the evolution and propagation of ICMEs throughout the inner heliosphere. These radio observations have the distinct advantage, in principle, of measuring the true radial speeds and accelerations of the CME, which can differ significantly from the plane-of-sky values. We have previously developed techniques for using the LASCO white-light observations, the measured in-situ shock speeds, and the constraints provided by the radio data from the WAVES experiment on the WIND spacecraft to reconstruct the complete speed/acceleration profiles of CME-shocks from the solar corona to 1 AU. We use this technique to derive the true speed/acceleration profile for a large number of CME events observed during solar cycle 23. Insights into the coronal and interplanetary propagation of CME/ICMEs provided by the statistical analyses of these data will be presented and discussed.

8   11:55   Propagation Characteristics of Geo-Effective CMEs
SRIVASTAVA, NANDITA; Srivastava, N.; Mathew, S.K.
Udaipur Solar Observatory, PRL, INDIA

The expansion speeds of several halo coronal mass ejections observed by LASCO aboard SoHO during 1996-2003 which produced strong geomagnetic storms (DST < - 100 nT) have been measured. The radial propagation profiles of these CMEs have been inferred from the measured expansion speeds. We also investigate if the propagation profiles of these geo-effective CMEs are of blast wave nature. A comparison of observed propagation profiles with the Sedov-type power-law blast waves shows that the profiles are distinctly different for the geo-effective CMEs associated with the flares than those associated with eruptive prominences. This difference in behaviour of propagation profiles may provide a clue to the initial trigger mechanism of geo-effective halo CMEs and their nature of propagation in the ambient solar wind.

9   12:10   Severe Solar Storms in the Declining Phase of Solar Cycle 23
Zhukov, Andrei1; Bothmer, V.2; Veselovsky, I. S.3; Dmitriev, A. V.3; Van der Linden, R.1; Romashets, E. P.4; Vandas, M.5
1Royal Observatory of Belgium, BELGIUM; 2Astrophysical Institute, University Goettingen, GERMANY; 3Skobeltsyn Institute of Nuclear Physics, Moscow State University, RUSSIAN FEDERATION; 4IZMIRAN, RUSSIAN FEDERATION; 5Astronomical Institute, Praha, CZECH REPUBLIC

The severe solar storm that occurred on July 14, 2000 around times of the Sun's global magnetic field polarity reversal was at that time the most intense one of cycle 23 in terms of its geo-effectiveness. Since then, many more severe storms have occurred in the declining phase of cycle 23: in March and November 2001, in October and November 2003, in July and November 2004 and in January 2005. Some of them have even exceeded the July 2000 storm in terms of their geo-effectiveness. All events were accompanied by strong flares and Coronal Mass Ejections (CMEs). We identified the CMEs responsible for ensuing geomagnetic storms and the CME source regions using the observations of the corona in white light and EUV by LASCO and EIT instruments onboard SOHO. The measurements of the photospheric magnetic field taken by SOHO/MDI were used to investigate the evolution of the photospheric flux in the identified CME source regions. The magnetic field evolution responsible for the intense solar storms is discussed with respect to the structure and response of the global solar corona and the characteristics of ICMEs observed at 1 AU. The importance of ICME interaction and some implications for the operational space weather forecast are discussed. The study is supported through the European Union as project INTAS 03-51-6206.

10   12:25   The Pertinence of Three Dimensional Solar Mass Ejection Imager (SMEI) Solar Wind Analysis to Ulysses Observations
Jackson, B.1; Buffington, A.1; Hick, P.1; Yu, Y.1; Webb, D.2

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 and heliospheric structures in SMEI observations, and show how we are able to track their outward motion from their first measurements in SMEI approximately 20° from the solar disk until they vanish in the distant SMEI 180° field of view. 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, Japan interplanetary scintillation (IPS) velocity data. This 3D modeling technique permits us to separate the heliospheric response in SMEI from background noise, and to estimate the 3D structure of the transient heliospheric features and their mass. The Ulysses spacecraft is nearly always within the SMEI field of view, and the closer Ulysses is to the Earth the more accurate the measured brightness signal at the Ulysses location. The SMEI 3D reconstructions can show heliospheric density structures along the line of sight in which Ulysses is immersed, adding context information for the instruments on the spacecraft, and these analyses also become more accurate as the spacecraft approaches the Sun.

11   12:40   Composition of Interplanetary Coronal Mass Ejections at All Latitudes
von Steiger, Rudolf1; Zurbuchen, T. H.2; Kilchenmann, A.3
1International Space Science Institute, SWITZERLAND; 2Department of AOSS, Univ. of Michigan, Ann Arbor, MI, UNITED STATES; 3International Space Science Institute, Bern, SWITZERLAND

The Ulysses mission has now completed two full revolutions on its unique, high inclination orbit. The second of these orbits occurred around the solar activity maximum of cycle 23, and consequently numerous interplanetary coronal mass ejections (ICMEs) were encountered. These ICMEs were identified both by their kinetic and magnetic signatures as well as by their composition signatures such as high average charge states or high helium abundance. The latter are particularly attractive because they remain virtually unchanged as the ICME travels through the heliosphere. ICMEs were observed at all heliographic latitudes all the way up to 80 degrees, the highest latitude reached by Ulysses. It seems, though, that at high latitudes the ICME rate was lower than what could be expected from the rate of solar activity, and the rate of ICMEs with high charge states appears to be lower still. We present and discuss an overview of ICMEs observed at Ulysses at all latitudes, with an attempt to identify possible systematic trends of ICME signatures with heliographic latitude.