SH32A-0768
Early Evolution of CMEs as Observed by SECCHI EUVI on STEREO
We report on two eruptions associated with small (C1 and B8) flares that occurred in AR 956 on 2007 May 19 and 20, as observed stereoscopically by EUVI. The separation of the two spacecraft was approximately 9 degrees. Pairs of images in 171~Å\ and 304~Å\ from two view angles are used to constrain the trajectories of the ejecta or filaments that appear to be responsible for the associated CMEs; they were not homologous. We study how the 3D motions of the ejecta in the low corona correspond to the CMEs at higher altitudes. We also discuss the possible relation between the early CME propagation and the coronal magnetic field topology inferred from EUV loops in EUVI and TRACE 171~Å\ images.
SH32A-0769
Multi-spacecraft Observations of 3He-rich Solar Energetic Particle Events
Solar energetic particle events with large abundance enhancements of 3He relative to 4He have been extensively studied since the 1970s using in situ observations from near-Earth spacecraft. These events, in which the compositional fractionation is believed to be the result of resonant wave-particle interactions, are thought to occur at the site of a solar flare when magnetic reconnection leads to the dissipation of a large amount of energy in plasma waves and the release of some previously-trapped particles onto open field lines. The very localized acceleration implied in such a model should result in energetic particle events that extend over relatively narrow range of heliolongitudes when observed near 1 AU. Several studies supporting this view have reported longitude distributions covering several tens of degrees for solar flares associated with 3He-rich events observed with a single, near-Earth spacecraft. The twin STEREO spacecraft, launched in October 2006 and moving away from Earth at 22.5 degrees per year, allow observations of individual 3He-rich events from two separated vantage points. We report observations of He isotopes in the MeV energy range from the first year of operation of the Low Energy Telescope (LET) instruments on STEREO-A and -B and compare with data from the ACE/SIS instrument, situated midway between the two STEREO spacecraft. This work was supported by NASA under grants NAS5-12929 and NAS5-03131.
SH32A-0770
3D Magnetic Modeling of Active Regions Using STEREO/EUVI
With the recent availability of stereoscopic data from the Extreme Ultraviolet Imager (EUVI) on the Solar Terrestrial Relations Observatory (STEREO) we have an unprecedented opportunity to investigate the accuracy of 3D magnetic field models. These data will be put to best use by modeling techniques that make no assumptions about the nature of the field (that it is potential, force-free, etc.). The Gary-Alexander radial stretching method use a series of transformations to map a simple potential field to a more complicated target field, and compare the transformed field lines with observed coronal structures in the EUV. Unlike many other simulation techniques, this approach requires only that the field remain divergence-free and continuous at the photosphere. Here we apply this transformation method to STEREO/EUVI data. We obtain a 3D potential field extrapolation using an MDI magnetogram, and utilize stereoscopy to derive the 3D field line coordinates from pairs of EUV images at 171Å. By comparing the 3D coordinates of the transformed model field lines with those of the real field lines as seen by EUVI, we can place constraints on the distribution of magnetic field and current in an active region.
SH32A-0771
3D Topology of Prominences Measured with STEREO/EUVI
Using images from the STEREO/EUVI A and B spacecraft and stereoscopic triangulation methods developed by Aschwanden et al for the reconstruction of the 3D geometry of curvi-linear structures in the solar corona, we determine three dimensional model reconstructions of several long-lived prominences as well as their topology - in particular the twist and number of helical turns. The derived geometries are analyzed together with photospheric magnetograms and potential field extrapolations (PFFS) and compared to various models for the magnetic confinement and support of prominence plasmas.
SH32A-0772
3-D reconstruction of CME related transient coronal phenomena observed with the STEREO/SECCHI Extreme Ultraviolet Imager
One of the primary objectives of the SECCHI investigation on STEREO is to study the initiation of CMEs in the low corona, and to better understand CME related changes of the three-dimensional coronal structure. The SECCHI Extreme Ultraviolet Imagers (EUVI) have been observing the solar corona from two significantly different vantage points since about March 2007. They have since captured several CMEs, including a few during the SECCHI campaign in May 2007, at an observatory separation angle of about 7-8 degrees. Observations at relatively small separation angles allow for easier identification of features in two views, which is critical for visually aided tie- point tools, as well as for more automated 3-D reconstruction methods. EUVI movies taken during the early onset of a CME show a range of transient phenomena, including coronal ejecta that can be tracked into the coronagraph fields of view, erupting filaments that trail the coronal ejecta, displacement of active region loops, coronal dimming, and "EIT" waves. We present preliminary results of our first 3-D reconstruction attempts on a selection of such CME related phenomena, with emphasis on coronal ejecta and active region loop displacements.
SH32A-0773
The source region magnetic conditions of solar eruption events observed by multi spacecraft
The magnetic connectivity, topology and properties including magnetic flux changes, magnetic gradient and flow field from LCT of three active regions will be derived from photospheric magnetograms and synoptic maps to understand the initiation condition of eruptions/flares originated from the regions and the potential impact on the heliosphere and magnetosphere. The three active regions are AR10930 in December 2006 and AR10953 and AR10956 in May 2007. AR10930 and AR10956 are responsible for the two Magnetic Clouds observed by IMPACT on STEREO A/B during the first half year of the mission. The associated coronal CME/flare/filament activities will be studied using solar imaging data from SOHO, STEREO, BBSO and HINODE. We will analyze photospheric magnetograms and synoptic maps from MDI and GONG. Vector magnetic field observations from HINODE and SOLIS are currently being sought and if available will be value added information for initiation of the eruptions. PFSS model field line tracing based on the synoptic maps gives the magnetic topology and connectivity in the active region and the global large scale field. The large scale field results including regions with closed arcades and fields open to the interplanetary space give the context and relative location of the source region of the eruptions.
SH32A-0774
Stereoscopic Results from NASA's STEREO Mission
Coronal mass ejections (CMEs) play a major role in the dynamics of Earth's geospace. However, the origin, magnetic configuration, and evolution of these solar manifestations are not well understood. The current twin- spacecraft mission, Solar Terrestrial Relations Observatory (STEREO), has provided images for stereoscopic analysis of coronal features. A catalog of CME events and associated low coronal (EUVI) activity that occurred in May 2007 was created to help understand the origin of CMEs. Three CME events, May 15th, 20th, 22nd, were selected for further investigation using the Sunloop software tool. This tool uses a "tiepointing" method and triangulation to do 3D reconstruction of coronal loops and prominences from simultaneous stereoscopic images from the SECCHI image suite on STEREO. The catalog and the results of the software tool analysis on the three events will be presented. Qualitative analysis of SECCHI/EUVI data using anaglyphs will also be presented.
SH32A-0775
Stereoscopic Observations of Low Coronal Ejections With and Without CMEs
Yohkoh soft X-ray images of solar flares have frequently shown characteristic ejections during the impulsive phase. They are thought to be plasmoids that hold important information on magnetic reconnection. These ejections are intimately associated with coronal mass ejections (e.g., Nitta & Akiyama 1999; Kim et al. 2005). They probably represent internal structures of CMEs, i.e., high-temperature counterparts of filament eruptions. However, their relation with ejections seen at low temperatures has not been studied systematically, although TRACE has revealed many beautiful examples. In this work we study ejections observed by the SECCHI EUVI on STEREO. Some of them are associated with CMEs, and others are not. Using pairs of EUVI images from spacecraft A and B, the trajectories of ejecta in individual channels (with representative temperatures 0.1-2 MK) are reconstructed in 3D. We discuss these ejections at different temperatures in the context of CMEs. Specifically, we ask what kinetic properties are correlated with CMEs and how they are related with CME manifestations in the low corona such as dimming and waves.
SH32A-0776
Extraction of Faint Features From STEREO COR1 Data
In white light coronagraph data, many kinematic properties of coronal features are measured by eye. These kinds of measurements can be difficult or impossible for features whose brightness is comparable to the noise level of the images. This could present a particular problem for those attempting to study future events coincident in the two STEREO COR1 coronagraphs. As their angular separation increases it will be increasingly difficult to see events in both instruments, since brightness falls off quickly with distance from the plane of the sky. In this work we seek to extend the intensity range of features that can be studied in COR1 data to previously intractable signal levels, using an unusual image differencing method and an angular integration technique presented by Dal Lago et al (2004). Challenges inherent to using this scheme with COR1 data will be discussed and examples of such faint features in original and enhanced versions will be presented.
SH32A-0777
A simulation of a CME propagation and shock evolution in the lower solar corona
We present a simulation of the evolution of a CME (~800km/s at 5 solar radii) in the lower solar corona (until 5 solar radii) using Space Weather Modeling Framework (SWMF). The configuration of the sun's magnetic field is based on the MDI data on the solar surface during Carrington Rotation 1922. The pre-CME background solar wind is generated under this boundary condition and Wang-Sheeley-Arge (WSA) model. To initiate a CME, we inserted a Titov-Demoulin flux rope in an active region near the solar equator. The zone along nose of the CME is refined to resolve the CME-driven-shock. Our results show that a higher density region is followed by a dark cavity behind the shock and the higher density region is expanding while propagating away from the sun. These features are consistent with the CME observations which shows that a bright front followed by a dark area after the shock. After the initiation stage, in which the CME has a large acceleration followed by a deceleration, the CME demonstrates a nearly constant and slow acceleration of the order of 100m/s 2. At 5 solar radii, the CME has a speed of 800km/s. Although CME is accelerating, the Mach number of the shock is decreasing because the Alfven speed upstream of the shock is increasing. Detailed analysis of the pressures on the CME shows that the thermal pressure account for most of the acceleration of the CME and the magnetic pressure contribute to the acceleration at an early time but it becomes negligible when the CME moves further away from the sun. We also present the evolution of shock geometry near the nose of the CME and find that the shock is nearly perpendicular. Further investigation of the dependency in latitude of the shock and their effects on particle acceleration are required in a future work.
SH32A-0778
Forward modeling reconstruction techniques applied to STEREO-SECCHI data
In past works, forward modeling techniques have been successfully used to study the morphology and the electron density of streamers and flux rope coronal mass ejections. Nevertheless, these studies have been done using SOHO-LASCO data. The STEREO mission, launched in October 2007, provide now 2 new points of view in addition to the one provided by SOHO. Besides the Lyot coronagraphs aboard the STEREO-SECCHI instrument package, the Heliospheric Imagers, also part of the SECCHI package, provide now a new and extended view of the corona, from 7 degrees elongation to almost 90 degrees. In this study, we will make use of the 3 points of view provided by these two missions to constrain better the three-dimensional reconstruction of CMEs, from few solar radii, up to Earth orbit. We will present the results concerning the morphology, dynamics and electron density obtained for different recent CME events.
SH32A-0779
Towards a Better Understanding of CME Onsets with SECCHI on STEREO
Observations of the first minutes in the life of Coronal Mass Ejections (CMEs) represent the main key into identifying the physical mechanism(s) behind them. Previous observations of CME onsets were limited by factors such as low cadence, small field of view, single-temperature coverage, and lack of 3D information. These limitations are significantly mitigated by the availability of SECCHI observations onboard the STEREO mission. We analyze a series of high-cadence, multi-temperature observations of CME onsets taken with the EUVI/SECCHI imagers tied with high-cadence coronagraphic COR1/SECCHI observations. We discuss how our perception of well-known features pertinent to CME onsets such as dimmings, EIT waves and cavities is shaped by the unique characteristics of SECCHI observations, and of the 3D information available in STEREO obervations in particular. We finally discuss how the generic elements of our observations compare with the expectations of CME models in an attempt to place some constraints on them.
SH32A-0780
Three-dimensional Coronal Mass Ejection Structure and Dynamics from Stereoscopic Polarimetric Observations
We present a study of the three-dimensional structure of coronal mass ejections (CMEs) from polarimetric observations made by the SOHO/LASCO and STEREO/SECCHI coronagraphs. The polarimetric reconstruction technique alone can provide mean line-of-sight distance from the plane of the sky at multiple positions in CMEs. In the case of filamentary structures this provides accurate three-dimensional positions. We argue that in the later stage of halo CMEs this technique provides accurate reconstruction of the lower portion of the eruption. We also use the polarimetric technique to test the results provided by purely stereoscopic analysis, and use both types of information in combination to infer the maximum structural detail possible, without assuming a CME model. We compare our results with a dynamical, magnetohydrodynamic CME model based on the eruption of a magnetic flux loop arcade. This model solves the equations of motion of multiple high-aspect ratio twisted flux loops, which are driven by diamagnetic, gravitational and drag forces. Forces from adjacent loops result in collective effects which partially determine the CME shape. The model can reproduce total brightness and polarimetric observations of both limb and halo CMEs.
SH32A-0781
Two-spacecraft Reconstruction of a Magnetic Cloud and Comparison to its Solar Source
Relating observations of coronal mass ejections (CMEs) and their interplanetary counterpart (ICMEs) is a centerpoint of Sun-Earth connection studies and our ability to forecast space weather. Here we focus on the ICME containing a magnetic cloud which reached Earth on November 20, 2003 and gave rise to the strongest storm of solar cycle 23, with a minimum Dst of -472 nT. Its strong geoeffective impact came about two weeks after the massive eruptions known as "Halloween" events resulted in comparable geo-effects. The aims of this study are threefold. We first apply an advanced methodology to analyze with diverse observations the event on the solar disk, which occurred on Nov 18, 2003, and was associated with an M4 flare and a halo CME. We then employ a Grad-Shafranov reconstruction technique to model the magnetic field geometry at 1 AU. To this end, we use measurements acquired by spacecraft WIND and ACE, ~400 RE apart. We show how these twin-spacecraft observations allow us to optimize the reconstructed map. Finally, we relate the solar to the interplanetary observations, paying special attention to the orientations and the magnetic fluxes involved at the two locales. By comparing the flare with the original cloud fluxes we infer a possible in-situ flux rope formation during the eruption, though uncertainties are still significant. The error margins in the comparisons are also carefully assessed.
SH32A-0782
Waves near interplanetary shocks observed by STEREO
We investigate the properties of interplanetary shocks that form ahead of virtually all fast propagating coronal mass ejections (CMEs). Understanding the characteristics of these shocks and their surrounding regions is of great interest as they play a major role in the acceleration of solar energetic particles (SEPs). In this work we study low frequency waves upstream and downstream of interplanetary shocks (IP) observed by the twin spacecraft mission STEREO. In the upstream region waves can be generated by ion beams reflected or otherwise energized at the shock. Downstream the wave spectrum may be formed by both, waves generated locally and waves transmitted through the shock.The efficiency of wave generation and wave convection to the shock depends on the shock Mach number, and the angle between the IMF and the shock normal. Waves can disturb the shock and participate in ion acceleration processes. Multi-point STEREO measurements will allow us to study wave characteristics in different regions near IP shocks and determine the effects that these fluctuations have on particle energization.
SH32A-0783
Numerical Simulation of a Coronal Mass Ejection in the Lower Corona: Comparison of Two Initiation Models
Coronal mass ejections (CME), eruptions of plasma and embedded magnetic field from the Sun's corona into interplanetary space, are the most energetic events on the Sun. The exact processes involved in the release of CMEs are not known. In order to understand them and how they affect the environment around Earth we need to comprehend their eruption, development and propagation through the interplanetary space. In this work, we present a simulation of a CME event occurred during the solar minimum. This simulation was performed using the Space Weather Modeling Framework (SWMF). Within this model, after generating a global steady state of the solar corona, for CR1922, we drive a CME to erupt using two different initiation models presented in the literature; Gibson and Low (1998) and Titov and Démoulin (1999). The ejections, that were followed up to distances of 10 R\sun, reached maximum speeds of 800-1000 km s-1. We discuss these two CME initiation models establishing a comparative analysis of their characteristics and how the initiation process changes the evolution of a simulated CME.
SH32A-0784
Wind-Ulysses Simultaneous Observations of Interplanetary Radio and Plasma Waves : a Pot- pourri
The radio receivers on the Wind spacecraft (4-13825 kHz) and Ulysses spacecraft (1.25-940 kHz) have continuously observed radio and plasma waves in the interplanetary medium. In the present paper, we shall focus on the solar radio emissions that are generated by flare suprathermal electrons (type III bursts) and by Interplanetary Coronal Mass Ejection (ICME) related shocks (type II bursts), and on the plasma quasi-thermal noise which constitutes the limit background of all radio observations in space. We shall present some examples of simultaneous observations by Ulysses and Wind of type II emissions (radio tracking of ICME driven shocks), of type III bursts (emission mode, localization, directivity), and of plasma thermal noise (solar wind diagnostics).
SH32A-0785
Modeling STEREO White-Light Observations of CMEs with 3D MHD Simulations
We model the Thomson-scattered white-light appearance of a variety of 3D MHD models of CMEs during solar minimum to reproduce large-scale features of SECCHI observations. We create a gallery of expected CME shapes at large elongations as seen by SECCHI. We examine evidence of shock propagation, magnetic clouds, CME pancaking, and complex time evolution as CMEs propagate at large elongation past the Thomson sphere. A key point is to determine how the structure of CMEs and CME-driven shocks are affected by interaction with the ambient solar wind. MHD models are performed with BATSRUS and SWMF, and formulated by first arriving at a steady state corona and solar wind employing synoptic magnetograms. We initiate CMEs from active regions low in the corona with magnetic flux ropes.
SH32A-0786
Kinematics of CMEs observed by LASCO and SECCHI
By analyzing CMEs observed by LASCO and SECCHI we can examine differences in propagation and mass that result from difference views of the same event. Observed variations in properties provide insight into several issues including the pileup of coronal mass ahead of expanding CMEs and the impact of drag between CMEs and the solar wind. In this presentation we will examine these properties for several CMEs. At lower heights, these events are observed by the coronagraphs in all three satellites (SOHO, STEREO-A, and STEREO-B). When possible, these events are traced to larger heights with the STEREO Heliographic Imagers (HI-1 and HI-2) on STEREO-A and -B.
SH32A-0787
Dynamics of CMEs in the STEREO Field of View: Theory and Observation
The initial acceleration and the subsequent dynamics of coronal mass ejections (CMEs) are investigated using the new SECCHI data. Specifically, the erupting flux-rope model of CMEs is used to model observed CME trajectories beyond the 30 Rs LASCO field of view. The forces acting on CMEs in the inner corona and the heliosphere are explicitly calculated. In this work, we address two limitations imposed by the previous observations: (1) direct comparison of theory and data was limited to the LASCO field of view and (2) the 3D morphology and the direction of propagation were uncertain. The new SECCHI data allow one, for the first time, to extend model comparison/validation beyond the 30 Rs field of view, and the two-spacecraft view of the sun makes it possible to determine the 3D geometry of CMEs significantly better. We will theoretically model the dynamics of CMEs observed by STEREO A and B, from the low corona (EUVI) to the heliosphere (Heliospheric Imagers HI-1 and HI-2). Synthetic coronagraph images for the STEREO A and B observing positions will be used to constrain the 3D geometry of observed CMEs. In the lower corona, LASCO data will be compared with the SECCHI data. \medskip Work supported by ONR and NASA.
SH32A-0788
Using Global MHD Models to Interpret STEREO Observations
The STEREO mission presents a unique opportunity to combine both remote and in situ observations from multiple vantage points, and, in particular, to provide simultaneous limb and disk-centered observations. In spite of this wealth of data, the system remains remarkably under-sampled, and reconstructing 3-D structure from the observations remains a formidable task. In this presentation we use global MHD models, which reproduce the eruption and evolution of specific CME events through the corona and past the orbit of Earth, to explore the relationship between the various remote sensing and in situ observations that would be seen at the two STEREO spacecraft. These simulations were developed as part of our contribution to NASA's Living With a Star TR&T focused science topic on the relationship between ICMEs and their solar sources. Our model, which incorporates coronal heating, thermal conduction, and radiation, is capable of reproducing a wide variety of measurements, ranging from (polarized) brightness and emission images to in situ time series of magnetic and plasma parameters. Moreover, we can construct quantities that are either not directly observable, or can only be inferred locally, such as the Alfven speed, the location of the heliospheric current sheet, and the three-dimensional topology of the magnetic field. We believe that the combination of sophisticated modeling results and the exciting new measurements from the STEREO mission will allow us to address fundamental questions concerning the origin and evolution of CMEs, ultimately allowing us to develop predictive capabilities related to their potential to generate space weather effects.
SH32A-0789
CME Evolution Characteristics in the Inner Heliosphere Observed Using SMEI and STEREO/SECCHI/HI Data
Geometric and propagation characteristics of interplanetary coronal mass ejections (ICMEs) are investigated using data obtained by the Large Angle Spectroscopic Coronagraph (LASCO), the Solar Mass Ejection Imager (SMEI) and the SECCHI imaging experiments on each STEREO spacecraft. The early evolution of CMEs can be tracked by the LASCO C2 &\ C3 and SECCHI COR1 &\ COR2 coronagraphs and the HI instruments can view them further into the heliosphere. SMEI is an all-sky imager that has tracked ICMEs from elongations >20° to beyond 100°. Both HI and SMEI hence have the ability to observe the same transient at the same time. We present results for ICMEs observed on 24--29 January and February through May 2007. This includes measurements of the structural and kinematic evolution of ICMEs and comparison with an appropriate drive/drag model. Crucial to the analysis procedure is an understanding of the effects of projection across large distances, which are not generally required with coronagraph data. Also discussed is the physics behind the evolution of ICMEs at large distances from the Sun, including the required inclusion of an internal driving force for some ICMEs, which sustains the transient's high speed well into the interplanetary medium.
SH32A-0790
Validation of Far-side Imaging of Solar Active Regions through Numerical Simulations
Helioseismology provides important tools for understanding the solar interior as well as for space weather forecast. Using observation data from instruments such as MDI (Michelson Doppler Imager) aboard the SOHO (Solar and Heliospheric Observatory) spacecraft, helioseismic inferences have tremendously advanced our knowledge and understanding of the interior structure and dynamics of the Sun. In general, the methods used for analyzing observations are based on simplified models of wave propagation such as ray or Born approximation, but have not been validated by more sophisticated models or numerical simulations. Here, we evaluate one technique, far-side imaging of solar active region by time-distance helioseismology, by using artificial oscillation data derived from numerical simulations of wave propagation in the Sun. The simulations are performed for the full spherical Sun. Active regions are modeled by locally modifying the speed of sound. We evaluate the performance of the far-side imaging technique by varying the size and location of the artificial active region, and analyse the appearance of ghost images and artifacts. This research is supported by NASA's Living with a Star program. The support ot the NASA Postdoctoral Program administered by Oak Ridge Associated Universities is gratefully acknowledged. Simulations have been performed on the Columbia Supercomputer at NASA Ames Research Center.
SH32A-0791
Imaging Solar Farside and Tachocline Using SOHO/MDI Data and Numerical Simulations
To be able to see large solar active regions when they are located on the farside of the Sun before rotating into the earth side is of great importance for space weather forecast. By analyzing acoustic wave signals that are reflected back to the near-side from the farside after four and five skips, we are able to map the real-time farside active regions with good signal to noise ratio by use of SOHO/MDI medium-l observations. This technique is validated by employing numerical data that simulate the solar global acoustic wavefields. Solar tachocline is generally believed as the location where solar dynamo operates. We have developed a time-distance helioseismology code to measure and invert sound speed perturbations at the tachocline area, and also tested the code by use of numerical simulation data. The technique is then used on SOHO/MDI medium-l observations to map the evolution of the tachocline from 1996 through 2007.
SH32A-0792
Synoptic Views of the Solar Limb: RHESSI Radius and SOHO Images
The RHESSI mission includes precise astrometric measurements of the solar limb shape at optical wavelengths as a part of its aspect-determination system. These data have precisions below 1 mas and extend over the full lifetime of the mission (from February, 2002). Synoptic maps of the limb shape reveal facular regions as increases, and sunspots as decreases, in the apparent radius. We compare these signatures with synoptic SOHO images for a 3-month period in 2004. The patterns are strongly similar, but the EUV synoptic maps have contributions from features not at the exact limb, which dominates the RHESSI data. This study anticipates making use of such high-contrast coronal or chromospheric measurements to provide a masking function to screen against these features in determinations of the true solar oblateness and higher-order permanent shape features. We also explore the possibility of cross-correlating RHESSI sunspot images against those of other optical telescopes, such as MDI, as a means of calibrating the roll coordinate of the telescope pointing.