SH23B-1633
Modeling of CME propagation to the L1 point: comparison to the observations and error bars due to the uncertainty of the cone model parameters.
We studied the performance of the combined WSA (corona) and ENLIL (heliosphere) models by analyzing different halo CME propagation and evolution to the L1 point and compared the results to ACE observations. We simulated CMEs related to a number of geomagnetic storms and events and used CME arrival time, magnitude of impact, magnetopause standoff distance, and duration of the event to characterize the model performance. A cone model-based halo CME representation is inserted into the combined models. Cone model parameters (initial CME radial velocity and 3 angles defining cone geometry) are used as input to the ENLIL model. We analyze the dependence of the modeling results to the uncertainty in this parameters and establish error bars for the model estimates.
SH23B-1634
Multi-spacecraft Recovery of a Magnetic Cloud and its Origin From Magnetic Reconnection on the Sun
Multi-point spacecraft observations of a magnetic cloud on May 22, 2007 has given us the opportunity to apply a multi-spacecraft technique to infer the structure of this large-scale magnetic flux rope in the solar wind. Combining WIND and STEREO-B magnetic field and plasma measurements, since these spacecraft entered the ejecta, we construct a combined magnetic field map by integrating the Grad-Shafranov equation, this being one of the very first applications of this technique in the interplanetary context. From this we obtain robust results on the shape of the cross-section, the orientation and magnetic fluxes of the cloud. The only slightly "flattened" shape is discussed with respect to its heliospheric environment and theoretical expectations. We also relate these results to observations of the Solar source region and its associated two- ribbon flare on May 19, 2007 using Hα images from the Kanzelhöhe observatory, SOHO/MDI magnetograms and SECCHI/EUVI 171~Å~images. We find a close correspondence between the magnetic flux reconnected in the flare and the poloidal flux of the magnetic cloud. The axial flux of the cloud agrees with the prediction of a recent 3D finite sheared arcade model to within a factor of 2, which is evidence for formation of at least half of the magnetic flux of the ejected flux rope during the eruption. We outline the relevance of this result to models of coronal mass ejection initiation, and find that to explain the solar and interplanetary observations elements from sheared-arcade as well as erupting-flux-rope models are needed.
SH23B-1635
Inverting Geometrical and Kinematical Properties of 3-D Rope-like CMEs From 2-D Frontside Halo CMEs
90 percentage of intense geomagnetic storms are generated by Earth-directed halo CMEs. Such geometrical and kinematial properties as the radial CME propagation direction, speed and acceleration are the must for forecasting the arrival time and speed of the associated ICME at the Earth's orbit. By using the elliptic cone model to mimic the 3-D rope-like CME structure, we have developed inversion equations to invert the geometrical [Zhao, 2008] and kinematical properties [Zhao et al, 2008] of the 3-D rope-like CMEs for frontside halo CMEs. This work further improves the inversion equations so that the geometrical and kinematical properties of 3-D rope-like CMEs can be more accurately inverted for most frontside halo CMEs. The dependence of the error in the inversion solution on the error in measured halo parameters is discussed.
SH23B-1636
Signatures of Two Distinct Initiation Mechanisms in the Evolution of CMEs in the Lower Corona.
We present a comparison of a three-dimensional (3D) simulation of coronal mass ejections (CMEs), in the lower corona, generated with two different initiation mechanisms presented in the literature: Gibson & Low (1998) (as GL98 hereafter) and Titov & Démoulin (1999) (as TD99 hereafter). The simulations are performed using the Space Weather Modeling Framework (SWMF) during the solar minimum (CR1922). Our goal is to understand how the initial magnetic configuration of a CME affects its evolution through the lower corona, until 6R☉. We found that both CME-driven shocks are quasi-parallel at the nose and that GL98 presents a higher shock acceleration (~150 m/ s2 versus ~100 m/ s2) and a higher Mach number, indicating it would accelerate particles more efficiently. Both CMEs also presented a post-shock compression for R>3R☉, being slightly larger in the case of TD99. They presented also a similar sheath width that increases while propagating away from the Sun (larger in GL98 case). We also found that in GL98 case the CME is driven by a combination of magnetic and thermal pressure, while in TD99 case the thermal pressure dominates its evolution. One of the reasons why GL98 presents higher force values, is probably related to the fact that its sheath mass is ~20% larger than for TD99. This paper intends to serve as a prototype for future comparisons of CME evolution, in the lower corona.
SH23B-1637
Compositional signatures in magnetic-cloud ICMEs
Approximately one third of all ICMEs (Interplanetary Coronal Mass Ejections) detected at one AU distance from the Sun show a smooth rotation in their magnetic field vector (often accompanied by an enhanced magnetic field strength). Theses structures are called MCs (Magnetic Clouds). Their well ordered magnetic field makes them accessible to magnetic field modelling. Assuming a specific field topology and fitting the model to the observed magnetic field data allows reconstruction of the spacecraft trajectory inside a MC. Some differences in elemental and charge-state composition between MCs and ambient solar wind are well known (Examples are: Enhanced iron charge states, enhanced O7+ to O6+ ratios, and enhanced Alpha to proton ratios). The question addressed here is whether these differences result from spacecraft trajectories through different parts of the individual MC or from a different origin of MCs as compared to the majority of ICMEs. We fitted the magnetic-field data of approximately 60 MCs observed from 2001 to 2007 by ACE (Advanced Composition Explorer) near Earth and compared the thus derived position information with solar wind composition data as measured by SWICS (Solar Wind Ion Composition Spectrometer).
SH23B-1638
Flux Rope Eruption From the Sun to the Earth: What do Reversals in the Azimuthal Magnetic Field Gradient Tell us About the Evolution of the Magnetic Structure?
Using ACE in situ data we identify and describe an interplanetary magnetic cloud (MC) observed near Earth on 13 April 2006. We also use multi-instrument and multi-wavelength observations from SOHO, TRACE and ground-based solar observatories to determine the solar source of this magnetic cloud. A launch window for the MC between 9 and 11 April 2006 was estimated from the propagation time of the ejecta observed near Earth. A number of large active regions were present on the Sun during this period, which were initially considered to be the most likely candidate source regions of the MC. However, it was determined that the solar source of the MC was a small, spotless active region observed in the Northern Hemisphere. Following an eruption from this region on 11 April 2006, the ACE spacecraft detected, 59 h later, the passage of the MC, preceded by the arrival of a weak, forward fast shock. The link between the eruption in this active region and the interplanetary MC is supported by several pieces of evidence, including the location of the solar source near to the disk centre and to the east of the central meridian (in agreement with the spacecraft trajectory through the western leg of the magnetic cloud), the propagation time of the ejecta, the agreement between the amount of flux in the magnetic cloud and in the active region, and the agreement between the signs of helicity of the magnetic cloud and the active region (which differs from the sign of helicity of each of the other active regions on the Sun at this time). In addition, the active region is located on the boundary of a coronal hole, and a high speed solar wind stream originating from this region is observed near Earth shortly after the passage of the magnetic cloud. This event highlights the complexities associated with locating the solar source of an ICME observed near Earth, and serves to emphasise that it is the combination of a number of physical characteristics and signatures that is important for successfully tying together the Earth-end and the Sun-end of an event. Further investigation of this MC has revealed some sub-structure towards its centre, observed as a small scale reversal of the azimuthal magnetic field of the MC, similar to that reported by Dasso et al., 2007. We explore several possible explanations for this signature, including the occurrence of multiple flux ropes and/or warping of the magnetic cloud. We also consider whether magnetic reconnection plays a role in creating the geometry that would explain these observations.
SH23B-1639
High-Latitude Active Region Associations of CMEs During the Cycle 23 Rise Phase
We do active-region associations of CMEs observed with the SoHO/LASCO during a 1-year rise period of solar cycle 23 (1997-1998) to determine some global magnetic properties of the CME-associated new cycle regions. This is a repetition of a similar study done with CMEs observed by the SMM coronagraph in 1986- 1987, a time when the numbers of active regions on the disk were small and associations most easily made. At that time it was found that the CME association was low for isolated regions, defined as those with no other active regions located within a 30° range of longitude. The coupled high-latitude regions, those accompanied by high or low-latitude regions within 30° of longitude, were accompanied by many more CMEs. We look for this effect in the LASCO CME data for all CMEs and for fast (> 900 km/s) and wide (> 60 °) CMEs. Both the 1986-87 and 1997-98 rise phases were periods with large fractions of MCs among all ICMEs, so confirmation of the SMM results could yield clues to the possible role of active region interactions in the origins of MCs.
SH23B-1640
Breakout coronal mass ejection or streamer blowout: the bugle effect
We present three-dimensional numerical magnetohydrodynamic simulations of coronal mass ejections (CMEs) initiated by the breakout mechanism. The initial steady state consists of a bipolar active region embedded in the solar wind. The field orientation of the active region is opposite to that of the overarching helmet streamer, so that this pre-eruptive region consists of three arcades with a magnetic null line on the leading edge of the central arcade. By applying footpoint motion near the polarity inversion line of the central arcade, the breakout reconnection is turned on. During the eruption, the plasma in front of the breakout arcade gets swept up. The latter effect causes a pre-event swelling of the streamer. The width of the helmet streamer increases in time and follows a "bugle" pattern. In this paper, we will demonstrate that if this pre- event streamer swelling is insufficient, reconnection on the sides of the erupting breakout arcade/flux rope sets in. This will ultimately disconnect the helmet top, resulting in a streamer blowout CME. On the other hand, if this pre-event swelling is effective enough, the breakout reconnection will continue all the way to the top of the helmet streamer. The breakout mechanisms will then succeed in creating a breakout CME.
SH23B-1641
The Ambient Solar Wind's Effect on Coronal Mass Ejection Transit Time
Most empirical and numerical models of Interplanetary Coronal Mass Ejection (ICME) propagation use the initial CME velocity as their primary, if not only, observational input. These models generally predict a wide spread of 1 AU transit times for ICMEs with the same initial velocity. We use a 3D coupled MHD model of the corona and heliosphere to determine the ambient solar wind's effect on the propagation of ICMEs from 30 solar radii to 1AU. We quantitatively characterize this deceleration by the velocity of the upstream ambient solar wind. The effects of varying solar wind parameters on the ICME transit time are quantified and can explain the observed spread in transit times for ICMEs of the same initial velocity. We develop an adjustment formula that can be used in conjunction with other models to reduce the spread in predicted transit times of Earth-directed ICMEs, and discuss possible practical applications of this formula.
SH23B-1642
Evolution of two Flaring Active Regions With CME Association
We study the coronal magnetic field structure of two active regions, one during solar activity minimum (June 2007) and another one during a more active time (January 2004). The temporal evolution was explored with the help of nonlinear force-free coronal magnetic field extrapolations of SOLIS/VSM and NAOJ/SFT photospheric vector magnetograms. We study the active region NOAA 10960 observed on 2007 June 7 with three SOLIS/VSM snapshots taken during a small C1.0 flare of time cadence 10 minutes and six snapshots during a quiet period. The total magnetic energy in the active region was approximately 3 × 1025 J. Before the flare the free magnetic energy was about 5~% of the potential field energy. A part of this excess energy was released during the flare, producing almost a potential configuration at the beginning of the quiet period. The return to an almost potential structure can be assigned to a CME as recorded by the SoHO/LASCO instrument on 2007 June 07 around 10 minutes after the flare peaked, so that whatever magnetic helicity was bodily removed from the structure. This was compared with active region 10540 observed on 2004 January 18 -- 21, which was analyzed with the help of vector magnetograph data from the Solar Flare Telescope in Japan of time cadence of about 1 day. The free energy was Efree≈ 66~% of the total energy which was sufficiently high to power a M6.1 flare on January 20, which was associated with a CME 20 minutes later. The activity of AR 10540 was significantly higher than for AR 10960, as was the total magnetic energy. Furthermore, we found the common feature that magnetic energy accumulates before the flare/CME and a significant part of the excess energy is released during the eruption.
SH23B-1643
Relating Solar Energetic Proton Populations Observed Within the Terrestrial Magnetosphere to Coronal Mass Ejections, Magnetic Flux Ropes observations at 1 AU
We report the results of a correlative study of interplanetary characteristics of Coronal Mass Ejections (CME) , Magnetic Flux Ropes and Solar Energetic Protons (SEP) observed within the terrestrial magnetosphere. SEPs access not only the polar regions via open field lines but also reach lower latitudes depending upon their rigidities and the time-variable cutoff during active periods. These penetrating SEPs may get trapped and form new radiation belts which have widely varying lifetimes. We will investigate the relationship between the terrestrial SEPs and interplenatary CMEs and shock parameters using data from multiple spacecraft. SEP observations will use measurements by instruments onboard the SAMPEX and Polar spacecraft. Interplanetary CMEs and shock parameters will be characterized by measurements from the ACE, WIND, and SOHO spacecraft. The findings of such correlative studies may help to understand the processes responsible for stable trapping of SEPs and the subsequent formation of new radiation belts.
SH23B-1644
Interplanetary shock shapes: comparison of local and global parameters
We are presenting a study of the shapes of interplanetary shocks observed by multiple spacecraft. The shock normal orientation and propagation speed are calculated locally from the magnetic field and plasma measurements of the Wind spacecraft by applying the Koval and Szabo [2008] technique which uses the isotropic Rankine-Hugoniot (RH) conservation equations. We have modified the technique by applying the anisotropic and multi-ion RH conservation equations in order to improve the accuracy of the calculated parameters. These local parameters are consequently used to predict the times of the shock arrival to the locations of the other spacecraft available in the solar wind assuming shock planarity and constant propagation speed. We compare the predicted times with those observed as well as compare the Wind local shock normal orientation and propagation speed with the corresponding global parameters determined from the four-spacecraft locations and times of the shock passages (when available). The agreement of the shock shapes with the planar assumption is discussed based on the shock drivers. We also discuss the influence of temperature anisotropy and alpha-particle parameters on the accuracy of the locally calculated shock parameters. Determining the true orientation of CME-driven shocks is important for a better understanding of particle acceleration processes.
SH23B-1645
Reconstruction of three-dimensional structure of coronal mass ejections using SOHO and STEREO polarimetric observations
We present reconstructions of coronal mass ejections (CMEs) from SOHO and STEREO polarimetric observations. Polarimetry of CME scattered white light provides information on the density distribution along the line of sight. Reconstructions of the three-dimensional (3D) structure of several halo CMEs observed with SOHO show a bilateral symmetry, which we interpret as an expanding magnetic flux loop arcade. We combine measurements from the STEREO A and B spacecraft spacecraft to determine the three-dimensional positions of several points in the eruptions using both parallax and polarimetric techniques. In addition, we determine the gross 3D density distribution and direction of several CMEs.
SH23B-1646
Relationship of Interplanetary Shock Micro and Macro Characteristics: A Wind Study
The non-linear least squared MHD fitting technique of Szabo [1994] has been recently further refined to provide realistic confidence regions for interplanetary shock normal directions and speeds. Analyzing Wind observed interplanetary shocks from 1995 to 2001, macro characteristics such as shock strength, Theta Bn and Mach numbers can be compared to the details of shock micro or kinetic structures. The now commonly available very high time resolution (11 or 22 vectors/sec) Wind magnetic field data allows the precise characterization of shock kinetic structures, such as the size of the foot, ramp, overshoot and the duration of damped oscillations on either side of the shock. Detailed comparison of the shock micro and macro characteristics will be given. This enables the elucidation of shock kinetic features, relevant for particle energization processes, for observations where high time resolution data is not available. Moreover, establishing a quantitative relationship between the shock micro and macro structures will improve the confidence level of shock fitting techniques during disturbed solar wind conditions.
SH23B-1647
Hemispheric and longitudinal asymmetries in CME occurrence according to the corrected SOHO/LASCO CME catalog
The coronal mass ejections (CME) have been observed by the SOHO/LASCO coronagraphs nearly continuously since 1996. These observations have been collected in a database which contains thousands of CMEs whose detailed properties have been studied and discussed in a large number of papers. Here we study the spatial distribution of CMEs in the solar atmosphere. We note on a serious, systematic error in the hemispheric and longitudinal location of the CMEs included in the latter half of the SOHO/LASCO catalog. This error greatly distorts previous results on the spatial location of CMEs at that time. Here we correct the SOHO/LASCO CME catalog for this error and analyze the hemispheric and longitudinal asymmetries in CME occurrence according to the corrected CME database. We show that these results are essentially different from those obtained from the uncorrected catalog. E.g., in the corrected CME catalog the northern hemisphere produces more CMEs than the south in most years in 1997-2007 while the south is clearly more active according to the original catalog. We note on signatures of similar mid-term quasi-periodicities (quasi- biannual oscillations) in CME occurrence that are seen in several other solar and heliospheric parameters. We also find evidence for active longitudes in the CME data, which persist for the entire SOHO interval (solar cycle 23).
SH23B-1648
Simulations of the CME-Flare Relationship
Observations of coronal mass ejections (CMEs) and solar flares have revealed a high correlation between the acceleration of the ejecta and the plasma heating and particle acceleration signified by the soft and hard X-ray emissions of the associated flare. The latter are generally thought to result from magnetic reconnection. This finding has stimulated the discussion of the CME-flare relationship, but at the same time it has made it difficult to find a conclusive answer as to whether magnetic reconnection or an ideal MHD instability is the prime cause of the eruptions. Numerical simulations of unstable flux ropes will be presented that are in very satisfactory quantitative agreement with erupting filaments, both, confined to the corona and ejective (i.e., developing into a CME). Some of these simulations indeed show a high degree of synchronization between the initial exponential acceleration of the flux rope, due to the ideal MHD instability, and the development of reconnection flows. However, others show a very delayed onset of reconnection, even after the flux rope's acceleration peak. In addition, the reconnection flows generally lag behind the motions driven by the ideal instability as the flux rope rise velocity nears the saturation phase. Comparison of the simulation results with observations suggests that the ideal MHD process is the primary driver of the coupled CME-flare phenomenon. The strong differences in the degree of synchronization, which the simulated systems show in the main rise phase of the eruption, are related to the magnetic topology prior to the eruption. Given the observational result of a high correlation between CME and flare development (Zhang & Dere 2006), these simulations yield constraints on the topology and lead us to conclude that a seed for a reconnecting current sheet must typically be present already at the onset of the eruption.
SH23B-1649
MHD Modeling of Coronal Inquietude Related to CME Lift-off
Different kinds of transient phenomena are common in the solar corona during the lift-off of coronal mass ejections (CMEs), such as EIT waves, metric type II bursts and solar energetic particle (SEP) events. While the exact nature and genesis of these disturbances is under debate, it is clear that erupting CMEs induce large-amplitude waves in the solar corona during the lift-off process that influence the coronal environment. Therefore, knowledge of the waves produced by evolving CMEs is essential for gaining insight into the interrelationship of the various solar transient phenomena. In this study, we employ magnetohydrodynamic (MHD) simulations of CME lift-off to study the mass motions, shocks and other large-amplitude waves induced by the CME. We pay special attention to the first few minutes of the eruption. The relation to observed wave phenomena on the solar disk, and formation times of the CME-driven shocks and their possibility to produce energetic particles are addressed. In addition, we discuss the radio emissions produced by the shocks under different conditions in the ambient corona.
SH23B-1650
On the Characteristics of Shocks driven by limb CMEs
We investigate the characteristics of bow shocks driven by limb CMEs near the Sun, including speed, width, compression ratio, and the relationshipof the standoff distance with CME size (the radius of curvature of a CME) and shock Mach number. We choose a subset of limb CMEs with distinct association of the decameter- hectometric (DH) type II burst, which is a good evidence of the existence CME-driven shock. The DH spectral domain corresponds to plasma frequencies within the field view of the SOHO/LASCO coronagraphs. Choosing limb events has several advantages: 1) there is no projection effects for CME speed measurements, 2) it is easier to determine the width of a CME and the front bow shock, 3) there is high confidence level for the plasma density determination from the white-light CME brightness. By studying the shock stand off distance and compression ratio, we obtain the shock Mach number and the Alfven speed profile in the corona.