SH13B-1520
3D Reconstruction of an Erupting Prominence
A bright prominence associated with a CME was seen erupting from the Sun on April 9, 2008. This prominence was tracked in both the STEREO EUVI and COR1 telescopes, and was seen to undergo complex churning motions as it erupted. Although the STEREO separation was 48 degrees, it was possible to match some sharp features in the later part of the eruption as seen in the 304 A line in EUVI by both STEREO Ahead and Behind. These features could then be traced out in three-dimensional space, and reprojected into a view in which the eruption is directed towards the observer. The reconstructed view shows that the alignment of the prominence rotates as it rises through the EUVI field-of-view out to 1.4 solar radii, and then remains constant as seen by COR1. The final alignment differed by about 140 degrees from the original filament orientation.
SH13B-1521
A MHS model in the solar corona
Since direct measurements of the solar coronal magnetic field and plasma are extremely difficult and inaccurate, we use a modeling approach based on observational quantities, e.g. the measured photospheric magnetic field, to reconstruct the structure of the global solar corona.An analytic magnetohydrostatic (MHS) model (Neukirch 95) was taken to extrapolate the magnetic field in the corona from photospheric magnetic field measurement from the Wilcox Solar Observatory. The boundary conditions are given by a synoptic magnetogram on the photosphere and by a source surface at the outer boundary. In the model, the electric current density was decomposed into two components: one component is aligned with the magnetic field lines, whereas the other component flows in spherical shells. The second component of the current generates finite Lorentz forces, which are balanced by the plasma pressure gradient and the gravity force. So the 3D distribution of the magnetic field and plasma can be derived self-consistently in one model. The magnetic field distribution of our model differs noticeably from both potential and force-free field models for the same boundary conditions. The plasma density in the MHS model is higher in the equatorial plane than in the polar region, which gives a reasonable result.
SH13B-1522
Solar EUV Spectral Irradiance Throughout The 3-Dimensional Heliosphere
When Ulysses moved from 30 to 80 degrees in solar latitude (July 2001), the Ulysses GAS instrument measured an apparent increase in the neutral He density. This is more naturally interpreted as a latitudinal dependence (decrease) of the loss rate due to solar photoionization rather than a true increase of the neutral He density. This concept has been tested through the development of a 3-Dimensional solar EUV model for the Heliosphere. The model concept has been presented earlier, and we are now presenting results and applications of the new model. Using daily SOHO EIT observations, over successive Carrington rotations, we have developed a three- dimensional model for solar EUV fluxes observed at any heliospheric position, projected to any heliospheric position. The combined effects of solar rotational and latitude-dependent flux variability are explicitly treated in this model. The flux model will be compared with other direct spectral irradiance observations in the ecliptic plane, such as those available from the TIMED SEE instrument as well as broadband measurements available from the SOHO/SEM irradiance time series. These comparisons will be used in part to validate the current results. We then use this flux to compute the photoionization rate of the in-flowing neutral Helium, and compare the modeled change with that observed along the spacecraft trajectory with the direct measurements from the out-of-ecliptic Ulysses GAS observations. The unique GAS comparisons will provide validation of the original hypothesis as to the latitudinal dependence (decrease) of the loss rate due to solar photoionization rather than an increase of the neutral He density.
SH13B-1523
Using STEREO/EUVI to Study Active Region Magnetic Fields
We examine the effect of linear transformations on the misalignment between model magnetic fields and coronal loops in active regions, as observed with STEREO/EUVI on three separate occasions between April 30 and May 19, 2007. We perform stereoscopic triangulation of some 100 EUVI loops in each active region, and identify the tangent vectors along every loop. Using magnetogram information from SOHO/MDI we compute a 3D potential field and interpolate the magnetic field vector at every position along the EUVI loops. The angle between the loop tangent vector and the magnetic field vector provides a measure of the misalignment angle between the observed field configuration and the model. We then transform the field in a way that preserves the divergence-free condition while injecting electric currents into the system. With this modified field we repeat our calculation of the misalignment angles between the magnetic field vectors and the EUV loop tangent vectors, quantifying the improvement of the transformed magnetic field model. Results of this type of magnetic modeling are presented for three active regions.
SH13B-1524
Comparing Eclipse Observations of the August 1, 2008 Solar Corona with an MHD Model Prediction
Total solar eclipses offer a unique opportunity to study the white light and emission coronae at high resolution. Newly developed image-processing techniques allow us to combine many individual coronal images with different exposures to produce coronal images during an eclipse that resemble those taken with radially graded filters, but with a higher quality. In a separate effort, magnetohydrodynamic (MHD) models have been used to predict the structure of the corona prior to eclipses, using measurements of photospheric magnetic fields on the Sun. In particular, such an MHD model was used to predict the structure of the corona for the August 1, 2008 total solar eclipse. The eclipse was observed from Altaj village, Mongolia, under perfect seeing conditions. The white-light corona was observed with 6 telescopes, with a focal lenses ranging from 200 mm to 1250 mm. The emission corona at 530.3 nm (Fe XIV) was imaged thorough a narrow passband filter with a transmission width of 0.03 nm. To separate out the 530.3 nm corona, the scattered background was substracted from a white-light coronal image taken at 529.1 nm, taken simultaneously with another narrow passband filter with a transmission width of 0.03 nm. This was the first time that the green emission corona was observed during an eclipse. We will compare the observed images with features from the predicted MHD model, including magnetic field line traces and simulated polarization brightness images. Research partially supported by NASA and NSF.
SH13B-1525
EUV Microwaves in the Solar Corona
The high temporal and spatial resolution of the SECCHI/STEREO EUV telescopes allowed us to uncover and study small scale events with a morphology identical to large-scale coronal mass ejections observed as coronal waves and dimmings on the solar disk. They are seen to develop from microflaring sites in a wide angular sector of the quiet Sun. The events observed differ from those on large scale by smaller geometrical sizes, shorter lifetime, and the reduced intensity of flare and dimmings. The area and total intensity of the small scale dimmings are 2 orders of magnitude smaller than for large scale events. The maximum front speed of SECCHI microwaves is 18.5 km/s, which is 1 order of magnitude smaller than slow magnetosonic wave speed in correspondent layers of solar corona.
SH13B-1526
Modeling of Solar Radiation Belts
Stable particle trapping in the complicated magnetic field of the solar corona -- "solar radiation belts" -- at first seems unlikely in the face of the Sun's complex, variable magnetic field. By integrating particle orbit equations in the guiding-center approximation, we investigate the fates of energetic ions in model coronal magnetic fields. We use both PFSS (Potential Field Source Surface) and simple analytic field models. Contrary to naive expectation, we find that significant numbers of particles remain trapped more than long enough to circumnavigate the Sun, neither precipitating to the surface nor attaining open field lines. The drift "shells" corresponding to conservation of the third adiabatic invariant may be complicated in form. A close look at the dependence of the cross-field drift speed on magnetic field strength and topology accounts for this finding.
SH13B-1527
Understanding the FIP Effect in Coronal Mass Ejections
The abundance patterns in coronal mass ejections (CMEs) are broadly similar to those in the slow speed solar wind and solar corona, but exhibit some subtle differences. The FIP effect, the enhancement in abundance of elements with first ionization potential (FIP) below about 10eV, is very similar, but in some cases can be a significantly stronger enhancement than the usual factor of about 3. The abundance ratio He/H is usually depleted in the solar wind, but less so in CMEs. We explore a model of element abundance fractionation originally proposed by Laming (2004), where chromospheric ions, but not neutrals, are subject to the ponderomotive force arising from Alfven wave propagation in the non uniform chromosphere. In solar conditions, this force is generally directed upwards, enhancing the coronal abundance of elements which are ionized in the chromosphere. By varying the model chromosphere and the spectrum of ionizing radiation, we investigate to what degree these abundance variations may be explained within the Alfven wave model. Work supported by NASA Grants NNG05HL39I (SOHO GI) and NNG08EK62I (STEREO GI), and by basic research funds of the Office of Naval Research.
SH13B-1528
2006 LWS TR&T Solar Wind Focused Science Topic Team: Overview of Current Results
We present a summary of the research conducted by the members of the 2006 LWS TR&T Solar Wind Focused Science Topic (FST) Team on the physical processes that heat and accelerate the solar wind. The Team applied a combination of theoretical studies, numerical simulations, and observations for their investigation of the role of energy sources and kinetic mechanisms responsible for the heating and acceleration of the solar wind. In particular, the FST Team examined magnetic reconnection, waves, and turbulence as possible heating mechanisms. Plasma properties and their evolution over the solar cycle, determined from the analysis of remote and in situ measurements of solar wind source regions and streams, are being used to constrain the models. The consistency of candidate theoretical models with existing observational data for the solar wind will be discussed.
SH13B-1529
Kinematics of concurrent metric and kilometric type II bursts observed by Wind/WAVES and groundbased radio telescopes
We present the kinematics of the kilometric type II bursts which are concurrent with metric type II that are rarely studied. We investigate whether kilometric and metric type II has the same driver or not. We utilize the data taken from Wind/WAVES experiment observed from 1996 to 2006. For the same period, metric data collected from various ground based telescopes like GRASS, HiRAISO, and Culgoora. We use new software tool to extract the parameters from the dynamic spectrum. We compare the kinematics of the above events assuming various density models
SH13B-1530
SECCHI View of CME Dynamics: Observation and Theory
The SECCHI observations provide an unprecedented view of the acceleration and propagation of CMEs in the corona and the heliosphere. The LASCO observations of the past 10 years have established that most, if not all, CMEs can be understood as expanding magnetic flux ropes. It has been shown that the observed dynamics in this regime can be correctly replicated by the erupting flux-rope model. We extend the application of this theoretical model to the new SECCHI EUVI, COR-1, COR-2, and HI-1 observations of CMEs and their dynamics, which can be measured out to about 100 Rs projected. Four observed flux-rope CMEs are discussed. We calculate the forces from various contributions acting on these CMEs. It is shown that the erupting flux-rope model is able to fit the observed CME trajectories throughout the EUVI-COR1-COR2-HI1 field of view. This indicates that the model correctly captures the basic physics, i.e., forces and magnetic geometry, of acceleration and propagation of CMEs. It is found that significantly larger values of the drag coefficient in the model than previously used are required to fit both the COR-1/COR-2 data and HI-1 data. The new expanded field of view of SECCHI imposes stronger constraints on model parameters than does the previous LASCO data set. Work supported by ONR and NASA
SH13B-1531
Recreating the Three Dimensional Structure of Interplanetary Coronal Mass Ejections
With the abundance of heliospheric image data in recent years from the Solar Mass Ejection Imager (SMEI) aboard Coriolis and the Heliospheric Imagers (HIs) aboard STEREO it is of critical importance that the appearance of Interplanetary Coronal Mass Ejections (ICMEs) in these images be thoroughly understood. At large distances from the Sun, many of the standard assumptions required for producing measurements from images of Coronal Mass Ejections (CMEs) in coronagraphs do not apply. To extract meaningful physical parameters from ICME images it is necessary to consider the physics responsible for their appearance. We have developed a model based on a theory that builds up a picture of the observed ICME from the Thomson physics of a single electron, to an integrated line of sight, to a complete ICME including the consequences of its geometry relative to the observer. This has allowed us to extract the physical parameters responsible for the ICME appearance (kinematic properties and geometry) for any ICME from which reliable leading edge measurements can be made. We present the theoretical framework for the model and demonstrate its utility by discussing a single example ICME that was observed by SMEI and the HIs in November 2007. Our results indicate the model has produced a reliable convergence for this event and the extracted parameters corresponding to the structure and timing of the event observed with the heliospheric imagers and the available in-situ measurements from the STEREO and ACE spacecraft. We conclude with a discussion of the physics responsible for the evolution of this ICME.
SH13B-1532
Calibration Results for the COR2 Instrument Aboard the STEREO Satellite
We report on the calibration status of the COR2 internally occulting coronagraphs aboard the Solar Terrestrial Relations Observatory (STEREO) satellites. The COR2 instruments are part of the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) instrument package aboard STEREO. The field of view of the COR2 instruments extends from 2.5 to 15 solar radii and its linear spectral filter transmits from 650nm to 750nm. All pre-flight optical calibration efforts were preformed at the Naval Research Laboratory's Solar Coronagraph Optical Test Chamber (SCOTCH), including: a vignetting function, calculation of stray light effects and image quality. To verify the instrument performance in flight we have developed a star fitting routine to extract the intensity of various stars as they transverse the telescope's field of view. Using the pre- flight and in-flight results in combination with star positions and star counts, we derived calibration factors for the external/internal geometric and photometric calibration. Specifically, calibration efforts include pointing corrections, distortion and vignetting. Calibrations will be implemented to improve the accuracy of scientific calculations performed using the COR2 data set.
SH13B-1533
Eigenmodes of Langmuir waves trapped into the density holes
Recently Ergun with co-authors [1] have published an interesting observation by WAVES experiment onboard STEREO (S/WAVES) satellite: Langmuir wave eigenmodes trapped into the density holes in the solar wind. We present the theoretical study of such eigenmodes trapped into the density holes in the framework of the first Zakharov equation, where the prescribed density profile is supposed to be moving but static. We assign different 2 and 3 dimensional density holes, in the last case we consider the profiles having cylindrical symmetry and we analyze the eigenmode type solutions. We compare electric field envelope profiles with the observations of the S/WAVES experiment. We obtain the condition that relates the density hole depth with its characteristic spatial scales for the trapped wave mode to exist. It is similar to the Zakharov's condition that defines the threshold for nonlinearity to dominate over dispersion. The major consequence of this study consists in the conclusion that the role these wave modes can play in the process of the beam-plasma interaction is determined by the characteristics of the density fluctuations in the solar wind. They can be important if the probability of the occurrence of density fluctuations satisfying the condition for the wave trapping is large enough. [1] Ergun, R., et al., Eigenmode Structure in Solar-Wind Langmuir Waves, PRL 101, 051101 (2008)
SH13B-1534
Reconstruction of the solar corona from STEREO COR1 observations
The COR1 instruments provide white light observations of the solar corona from 1.5 to 4 Rsun where the transition from closed to open coronal structures takes a place. The reconstruction is performed by the regularized tomography inversion method and gives a 3D distribution of the electron density in the corona from 1.5 to 4 Rsun. The method allows to reconstruct only structures which are stationary during an observation period, i.e. from quarter to half a solar rotation.
SH13B-1535
Electron temperatures and its bulk flow speeds in the low solar corona measured during the total solar eclipse on 29 March 2006 in Libya
We conducted an experiment that measured the K-coronal spectra in the visible wavelength region, simultaneously at multiple locations in the low solar corona in conjunction with the total solar eclipse on 29 March 2006 in Libya. The shapes of these measured K-coronal spectra were then matched with K-coronal models with different combinations of electron temperatures and electron bulk flow speeds to obtain the best fit. Results show electron temperatures and bulk flow speeds of 1.10 ± 0.05 MK, 103.0 ± 92.0 kms-1; 0.98 ± 0.12 MK, 0.0 + 10.0 kms-1; 0.70 ± 0.08 MK, 0.0 + 10.0 kms-1 at 1.1 R☉ in the solar north, east and west, respectively, and 0.93 ± 0.12 MK, 0.0 + 10.0 kms-1 at 1.2R☉ in the solar east, in agreement with expectations. The instrument used in this experiment, (MACS)for Multi Aperture Coronal Spectrograph, used fiber optics in the focal plane of a 12 inch Schmidt Cassegrain telescope that were positioned at the locations where the above results were obtained. The light from these fibers were then simulteously fed in to a spectrograph that contained only reflective optics for the purpose of enhancing the transmission of light in the blue end of the spectrum. This was important because steep intensity gradients occurred in this region, which distinguished between different K-coronal models.
SH13B-1536
Observational and Theoretical Challenges to Wave or Turbuelence Acceleration of the Fast Solar Wind
We use both observations and theoretical considerations to show that hydromagnetic waves or turbulence cannot produce the acceleration of the fast solar wind and the related heating of the open solar corona. Waves do exist as shown by Hinode and other observations, and can play a role in the differential heating and acceleration of minor ions, but their amplitudes are not sufficient to power the wind, as demonstrated by extrapolation of magnetic spectra from Helios and Ulysses observations. Dissipation mechanisms invoked to circumvent this conclusion cannot be effective for a variety of reasons. In particular, turbulence does not play a strong role in the corona as shown by both eclipse observations of coronal striations and theoretical considerations of line-tying to a nonturbulent photosphere, nonlocality of interactions, and the nature of the kinetic dissipation. In the absence of wave heating and acceleration, the chromosphere and transition region become the natural source of open coronal energization. We suggest a variant of the "velocity filtration" approach in which the emergence and complex churning of the magnetic flux in the chromosphere and transition region continuously and ubiquitously produces the nonthermal distributions required. These particles are then released by magnetic carpet reconnection at a wide range of scales and produce the wind as described in kinetic approaches. Since the carpet reconnection is not the main source of the energization of the plasma, there is no expectation of an observable release of energy in nanoflares.
SH13B-1537
Development of Solar Wind Model Driven by Empirical Heat Flux and Pressure Terms
We are developing a time stationary self-consistent 2D MHD model of the solar corona and solar wind as suggested by Sittler et al. (2003). Sittler & Guhathakurta (1999) developed a semi-empirical steady state model (SG model) of the solar wind in a multipole 3-streamer structure, with the model constrained by Skylab observations. Guhathakurta et al. (2006) presented a more recent version of their initial work. Sittler et al. (2003) modified the SG model by investigating time dependent MHD, ad hoc heating term with heat conduction and empirical heating solutions. Next step of development of 2D MHD models was performed by Sittler & Ofman (2006). They derived effective temperature and effective heat flux from the data-driven SG model and fit smooth analytical functions to be used in MHD calculations. Improvements of the Sittler & Ofman (2006) results now show a convergence of the 3-streamer topology into a single equatorial streamer at altitudes > 2 RS. This is a new result and shows we are now able to reproduce observations of an equatorially confined streamer belt. In order to allow our solutions to be applied to more general applications, we extend that model by using magnetogram data and PFSS model as a boundary condition. Initial results were presented by Selwa et al. [2008]. We choose solar minimum magnetogram data since during solar maximum the boundary conditions are more complex and the coronal magnetic field may not be described correctly by PFSS model. As the first step we studied the simplest 2D MHD case with variable heat conduction, and with empirical heat input combined with empirical momentum addition for the fast solar wind. We use realistic magnetic field data based on NSO/GONG data, and plan to extend the study to 3D. This study represents the first attempt of fully self-consistent realistic model based on real data and including semi-empirical heat flux and semi-empirical effective pressure terms. References: Sittler E. C. Jr. and Guhathakurta M., 1999, ApJ, 523, 812-826 Sittler E. C. Jr., Ofman L., Gibson S., Guhathakurta M., Davila J., Skoug R., Fludra A., Holzer T., 2003, Solar Wind 10, 113 Sittler, E. C. Jr. and Ofman L., 2006, ILWS, GOA, India Guhathakurta, M., E. C. Sittler Jr. and L. Ofman, JGR, Vol 111, A11215, 2006. Selwa, M., L. Ofman, E. C. Sittler Jr. and M. Kramar, Development of solar wind model driven by empirical heat flux, SHINE Meeting, 2008.
SH13B-1538
Coronal Mass Ejections Associated With Impulsive Solar Flares - Observations With SECCHI EUVI On STEREO
Long-duration flares, sometimes referred to as Long Decay Events (LDEs), are known to be unmistakable signatures of coronal mass ejections (CMEs), and often of fast and large ones. Short-duration or impulsive flares, on the other hand, do not as frequently accompany CMEs, even though X-ray plasmoid ejections seen in some of these flares may suggest that all flares are eruptive irrespective of durations. Some of these ejections in X-ray or EUV images could be failed ejections, however, meaning that they do not move into interplanetary medium. A complementary, and perhaps more reliable signature of a CME in the low corona may be large-scale dimming typically observed at 1-2 MK. We report on high cadence observations of SECCHI EUVI on STEREO that show this phenomenon in weak impulsive flares more frequently than expected. We systematically study flare periods with good data coverage. In order to avoid false dimming, we use both base and running difference images after carefully co-aligning the image pairs. Some of the dimming events were observed in more than one channel and at two widely separated view angles, letting us better understand the nature of dimming especially in terms of the associated CME. We discuss how the properties of dimming are reflected in CME parameters, how to distinguish the impulsive flares with large- scale effects from those that are confined, and whether similar events could account for orphan ICMEs without a clearly associated CME near the Sun.
SH13B-1539
Temporal and Physical Relationships Between CME Acceleration and Flare Energy Release
The physical relationship between CMEs and flares is re-examined from both observational and theoretical points of view, utilizing the new SECCHI as well as LASCO observations. For the theoretical model, we use the erupting flux-rope model that has been shown to replicate observed CME trajectories. Mathematically, this model starts with an equilibrium flux rope and drives it with a specified function dΦp(t)/dt increasing the poloidal flux Φp. Physically, the injected flux may be of coronal or subphotospheric origin. The function dΦp/dt is parameterized by the ramp-up and ramp-down time scales, the peak duration, and the peak value. For each event, we obtain the "best fit" solution to fit the entire trajectory (out to HI1 if available) by adjusting these parameters. It is found that the duration of required poloidal flux injection is closely correlated with the duration of associated GOES X-ray profile. This correlation holds for short- duration as well as long-duration flares. This suggests that the poloidal flux injection has a physical connection to observed CME dynamics and flare energy release. Injection of poloidal flux produces an electromotive force (EMF) around the flux rope that has the same functional form and duration as dΦp/dt. The EMF is sufficient to accelerate particles to several tens of keV and higher in one collisional mean free path. In the model, the main acceleration phase is governed by the intrinsic time scale (Alfvenic time in the flux rope) and the geometry (footpoint separation distance) of the flux rope, insensitive to the form of dΦp/dt. The duration of the flux injection, however, is sensitive to the long-time propagation properties of the CME in HI1 field of view. The model results are compared with published results of arcade models. Work supported by ONR and NASA
SH13B-1540
Hard X-ray Emission From Partially Occulted Solar Flares
The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) is optimized for fine energy and spatial resolution of hard X-ray (HXR) emission from solar flares. Most RHESSI flares exhibit strong HXR emission from bright flare loop footpoints, drowning out faint emission from higher in the corona. Partial occultation of flares by the solar disk obscures these bright footpoints, allowing for detailed observations of faint coronal HXR sources. It is therefore necessary to identify and characterize flares with high occultation heights. Here we present a technique for determining flare occultation heights by extrapolating the paths of active flare regions across the solar disk. A statistical study of 55 flares compares occultation heights to nonthermal X-ray emission. Compared with statistical results of on-disk flares, it is estimated that this coronal emission is at least 20 times fainter than the expected footpoint emission, confirming that partial occultation is crucial for the study of faint coronal sources. HXR images made by RHESSI are also compared with images at longer wavelengths from the TRACE, EIT, and STEREO instruments.
SH13B-1541
Numerical Simulations of Heliospheric Events and Comparison with Multi-Point In-Situ and Remote Observations
Modeling the origin of coronal mass ejections (CMEs) is still in the research phase and it is not expected that real events can be routinely simulated in near future. Therefore, we have developed an intermediate modeling system which uses fitted coronagraph observations and launches 3D ejecta into background solar wind. This modeling system is fast and robust, and it enables simulation of virtually any observed heliospheric event. Multi-point in-situ and remote observations are crucial to estimating accuracy of numerical simulations. We present 3D numerical magnetohydrodynamic simulations of selected heliospheric events observed by ACE, STEREO, MESSENGER, and SMEI spacecraft. We assumed different initial spherical or flux-rope geometric CME-like structures, simulated their interactions with the structured background solar wind, and present comparison with resent observations.
SH13B-1542
The CME-ICME Connection and Interplanetary Structure During Solar Minimum
When an interplanetary transient (ICME) exhibits a large angle and smooth rotation in the IMF vector, it is classified as a magnetic cloud (MC) and commonly interpreted as the signature of a magnetic flux rope. On the average bout a third of ICME ejecta are MCs, although the fraction seems to be larger during the quiet phase of the solar cycle. Non-flux rope ICMEs are likely (1) distorted during the transit through heliosphere, (2) observed at an unfavorable crossing angle if the ICME structure has spatial variation, (3) or are simply have a more complex internal structure. Five Magnetic Clouds (MC) have been found from a total of nine ICMEs observed during 2007 January 01 to 2008 August 31, when the separation of STEREO A (STA) and B (STB) spacecraft varied between 0.05 to 70.35 degrees heliolongitude. We investigate the four best MCs using observations from three spacecraft (STA, STB and ACE). The first MC seems to have been detected by all three spacecraft (STA and STB 40.4 degrees apart), while the latter three were detected by only one of the STEREO spacecraft and sometimes by ACE. From the inferred flux rope orientation at each crossing and the spatial variation of the ICME properties, we interpret how each MC flux rope was situated relative to the spacecraft, and its connection to the Sun from corresponding coronal and heliospheric modeling results. Each of the MCs can be associated at low confidence (in contrary to expectations for solar minimum time) with a CME observed by coronagraphs on board STEREO and/or SOHO. All potential parent CMEs were very slow in the 200 km/s range (plane-of-sky), but the speeds of the MCs were between ~390 and ~480 km/s, indicating acceleration in the heliosphere. Solar disk activities are minor around the four CMEs, with no GOES x-ray flares, and two possibly associated filament eruptions. Some CME structures appear to form in the coronagraph field of view rather than rising from below. Several low/mid- latitude coronal holes and a highly warped coronal streamer arcade and source surface neutral line dominate the coronal structure during the period of the study. Previous studies have shown that the MC fluxrope orientation may be aligned with the large-scale coronal streamer arcades. Estimated MC orientations are discussed and compared with events during the previous solar minimum, which exhibited a more dipolar coronal structure. This work was supported, in part, by NASA NNG06GE51G, NNX08AJ04G, and NAS5-03131.
SH13B-1543
Modeling the 31 December 2007 Coronal Mass Ejection and Its Impact at Messenger
The three-dimensional numerical hydrodynamic model, ENLIL, is used to investigate the evolution of a coronal mass ejection (CME) observed on 31 December 2007. The CME is launched into a tilted-dipole ambient solar wind flow that is appropriate around solar activity minimum. Accurate computation of the background solar wind parameters, provided by the empirical WSA model, is crucial for modeling transient disturbances as they propagate and interact with magnetic structures in the inner heliosphere, such as the heliospheric current sheet. The CME was launched using the angular width, speed, and direction of propagation determined by the geometric localization technique. This technique utilizes a series of lines of sight from two space-based coronagraphs to determine gross propagation characteristics of CMEs in three- dimensional space. We compare the results of our model analysis to observations from Messenger. We also discuss the interaction of the CME with the heliospheric current sheet.
SH13B-1544
Comparison of Large-Scale Density Fluctuations in the Outer Corona and in the Inner Heliosphere for Both Fast and Slow Solar Wind
The low frequency spectra of the proton density of fast and slow solar wind streams, measured in the inner heliosphere with the HELIOS 2 in-situ instrumentation, are compared with those due to the large-scale density fluctuations observed with the Ultraviolet Coronagraph Spectrometer, UVCS/SOHO, in the outer corona where the streams are accelerated. The interplanetary and coronal data have been detected during solar minimum of different activity cycles. The density fluctuations exhibit the same low-frequency spectral dependence, 1/f2, both in the corona and in the inner heliosphere, thus suggesting that the discontinuities resulting in the 1/f2 noise, observed in the interplanetary space, are likely to have a coronal origin. The present study shows that in the outer corona the fast wind plasma is mainly consisting of Alfvén fluctuations as in the inner heliosphere. Coherent structures, on the other hand, are mainly found in the slow coronal wind. In addition, a high degree of phase synchronization is observed in the slow solar wind fluctuations both at coronal and heliospheric levels. This is an indication that the phase coherent structures observed in the interplanetary medium in the low-speed streams are likely to be advected directly from the acceleration regions of the slow solar wind, rather than resulting as a product of stream-stream dynamic interactions in the heliosphere.
SH13B-1545
Voltage Pulses on STEREO/WAVES: Nanoparticles Picked-up by the Solar Wind?
We suggest that the very large number of intense voltage pulses detected by the STEREO/WAVES instrument are produced by impact ionisation of nanoparticles striking the spacecraft at a velocity of several hundreds of km/s. Nanoparticles have such a large charge-to-mass ratio that the electric field induced by the solar wind magnetic field accelerates them very efficiently. Since the voltage produced by dust impacts increases very fast with speed, such nanoparticles produce voltage pulses as high as do larger grains of smaller speeds. The flux of nanoparticles inferred in this way is similar to that recently detected on the International Space Station, and it is greater by one order of magnitude than the interplanetary dust flux model but the uncertainties make it marginally compatible. The present results may represent the first detection of fast nanoparticles in interplanetary space near 1 AU.
SH13B-1546
Presence Of A Reverse Shock In The Evolution Of A CME In The Lower Solar Corona
We study the birth and the evolution of a reverse shock in the evolution of a CME in the lower solar corona. We study the evolution of the CME with Space Weather Modeling Framework (SWMF). To initiate the CME, we inserted a Titov-Demoulin (TD) flux rope in an active region of the Sun with magnetic field based on the MDI data for the solar surface during Carrington rotation 1922. The CME advances on the top of a background solar wind created with the help of Wang-Sheeley-Arge (WSA) model. We'd explore the signature and characteristics of the reverse shock as the CME evolves through the lower corona. We also discuss it's implications on the acceleration of particles.
SH13B-1547
Image Representation of Sunspot Magnetic Fields in Source-Surface Models of Corona and Heliosphere
Source-surface models of the solar corona and heliosphere typically entail spherical-harmonic expansions of scalar magnetic potentials that extend to rather high degree and order so as to accommodate localized magnetic fields associated with sunspots. Here it is proposed to approximate sunspot magnetic fields in the corona by placing a few magnetic monopoles beneath the Sun's surface (i.e., inside the Sun), so as to reduce the number of internal spherical harmonics required for a good fit. (Magnetic monopoles are permitted in such a construction if they add-up to zero magnetic charge and reside outside the region of physical interest.) Magnetic image charges placed outside the source surface can serve to nullify the tangential component of the resulting magnetic field on a sphere of any desired radius (e.g., rs = 2.5rsun). More generally, however, the source surface should be non-spherical (typically prolate) in a way that reflects the underlying structure of the Sun's main B field. A source surface that seems to work well in this respect [Schulz, Ann. Geophysicae, 15, 1379-1387, 1997] is a surface of constant F = r- kB, where B is the scalar strength of the Sun's main magnetic field (including any sunspot fields thus modeled) and k (~ 1.4) is a shape parameter. If the region surrounded by the source surface is regarded as current-free, then the source surface itself should be made (as nearly as possible) an equipotential surface for the corresponding magnetic scalar potential (expanded, for example, in a combination of spherical harmonics and offset-monopole terms). More generally, the mean-square tangential component of the coronal magnetic field on the source surface should be minimized [Schulz et al., Solar Phys., 60, 83-104, 1978] with respect to any adjustable parameters (e.g., external spherical-harmonic expansion coefficients) of the field model. Solar wind should then be regarded as flowing not quite radially, but rather in a straight line along the outward normal to the source surface, and the heliospheric B field should follow a corresponding generalization of Parker's spiral [Levine et al., Solar Phys., 77, 363-392, 1982].
SH13B-1548
The MHD simulation of interplanetary space and heliosphere by using the boundary conditions of time-varying magnetic field and IPS-based plasma
We present our new boundary treatment to introduce the temporal variation of the observation-based magnetic field and plasma parameters on the inner boundary sphere (at 30 to 50 Rs) to the MHD simulation of the interplanetary space and the simulation results. The boundary treatment to induce the time-variation of the magnetic field including the radial component is essentially same as shown in our previous AGU meetings and newly modified so that the model can also include the variation of the plasma variables detected by IPS (interplanetary scintillation) observation, a ground-based remote sensing technique for the solar wind plasma. We used the WSO (Wilcox Solar Observatory at Stanford University) for the solar magnetic field input. By using the time-varying boundary condition, smooth variations of heliospheric MHD variables during the several Carrington solar rotation period are obtained. The simulation movie will show how the changes in the inner heliosphere observable by the ground-based instrument propagate outward and affects the outer heliosphere. The simulated MHD variables are compared with the Ulysses in-situ measurement data including ones made during its travel from the Earth to Jupiter for validation, and we obtain better agreements than with the simulation with fixed boundary conditions.
SH13B-1549
Mass Measurements of Coronal Mass Ejections Using the SECCHI-COR2 Coronagraphs
The twin Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) COR2 coronagraphs of the Solar Terrestrial Relations Observatory (STEREO) provide images of the solar corona from two view points in the solar system. Since their launch in late 2006, the STEREO Ahead (A) and Behind (B) spacecraft have been slowing separating from Earth at a rate of 22.5 degrees per year. By the end of 2007, the two spacecraft were separated by more than 40 degrees from each other. At this time, we began to see large- scale differences in the morphology and total intensity between coronal mass ejections (CMEs) observed with SECCHI-COR2 on STEREO-A and B. Because the CME emission is due to Thomson scattering, the intensity of an observed CME is dependent on the angle it makes with the observed plane-of-the-sky. From the intensity images, we can calculate the integrated line of sight electron density and mass. We demonstrate that is is possible to simultaneously derive the direction and true total mass of the CME if we make the simple assumption that the same mass should be observed in COR2-A and B.
SH13B-1550
Relationship between a CME-driven shock and a coronal metric type II burst
It has been a long-standing controversy whether coronal metric type II bursts are generated by CME-driven shocks or flare blast waves. Using unprecedented high-cadence observations from STEREO/SECCHI, we investigate the relationship between a metric type II event and a shock driven by the 2007 December 31 CME. The CME occurs at the east limb and its evolution is observed from about 1.1 to several tens of solar radii. The existence of the CME-driven shock is indicated by the deflection of coronal structures before the CME impinges on them, the best evidence for shocks in imaging observations. The earliest deflection of distant coronal structures occurs at 00:51:22 UT, about 2.6 min before the metric type II onset. The CME- driven shock emerges from the corona and produces a break point in the streamer north of the CME, which allows us to follow the shock propagation in imaging observations for the first time. We also have a continuous frequency coverage of the radio dynamic spectrum by combining observations from STEREO/SWAVES, BIRS and Learmonth, which successfully establishes the connection between the metric and decametric-hectometric (DH) type II bursts. The CME speed is about 600 km/s at the time of the metric type II onset, larger than the Alfven speed 420 - 490 km/s determined from the band splitting of the metric type II burst. The shock height-time curve determined from the metric and DH type II bands is consistent with the shock propagation obtained from the streamer deflection. These results provide unambiguous evidence that the metric type II burst is caused by the CME-driven shock. Implications are also discussed for particle acceleration and space weather forecasting.
SH13B-1551
Relationship betwwen of Coronal Mass Ejections and EIT Post Flare Arcades
Our recent study indicates the orientation of a halo CME elongation may correspond to the orientation of the
underlying flux rope. This is a continuation of the research and here we compare orientation angles of
elongated LASCO CMEs, both halo and partial to the EIT post eruption arcades (PEA). Data for 100 events
had been analyzed and er report the following: i) it is further supported that majority of halo CMEs are
elongated in the direction of the axial field of PEA arcades; ii) this relationship holds true for partial CME and
those events that originate further from the disk center. There is also an indication that events in the
northern hemisphere generally exhibit better correlation that those in the southern hemisphere.
http://www.bbso.njit.edu/~vayur/
SH13B-1552
STEREO Observations of a post-CME Current Sheet
Ray-like features in the wake of Coronal Mass Ejections (CMEs) are often interpreted as current sheets produced by the eruption. The 3D geometry of such post-CME current sheets is largely unknown and its knowledge should place important constraints on CME physics and coronal conditions. An example of a post-CME current sheet was observed on April 9th 2008, in the aftermath of the 'cartwheel' CME, which was observed by Hinode, SoHO, STEREO and TRACE. The CME and the corresponding current sheet were well-observed by both STEREO spacecraft, which were separated by about 48 degrees the day of the event. We present here an analysis of the 3D morphology of the current sheet using data from the COR1 and COR2 coronagraphs from both STEREO spacecraft. We will attempt various forward models (e.g., slabs, cylinders) of the current sheet as seen by the COR1 and COR2 coronagraphs from both STEREO spacecraft. This will characterize the 3D geometry of the current sheet and more precisely its shape and its real width and length. Our forward modeling will also supply the radial variation of the density along the current sheet. This information will supply some estimates of the temperature and magnetic field distributions in and out the current sheet respectively.
SH13B-1553
Interactions of Multiple CMEs with Complex Interplanetary Medium as Revealed by STEREO
Since the launch of STEREO in November 2006, continuous white-light observations of solar transients on their way to the Earth have been made possible. STEREO/SECCHI observations have also revealed the complexity and dynamic structure of the interplanetary medium. In this talk, we will discuss the significance of 3-D numerical simulations in the interpretation of observations taken by SECCHI. Our focus will be on a series of two ejections on January, 24-25, 2007, which have been simulated with the Space Weather Modeling Framework (SWMF). We will discuss the appearance of coronal mass ejections (CMEs) and dense streams in the Heliospheric Imagers' field-of-view. Detailed comparisons between the real and simulated time-elongation plots will be presented. We will also discuss how observations of CME-CME interaction can be distinguished from the interaction of CMEs with dense streams in the solar wind using the simulations.
SH13B-1554
SMEI Remote Sensing and the 3D Reconstruction of Corotating Heliospheric Structures
We report observations and 3D reconstructions of corotating heliospheric structures observed by the Solar
Mass Ejection Imager (SMEI). Observations of the inner heliosphere have been carried out on a routine
basis by SMEI since its launch in early 2003, and these have been used to measure and map the outward
flow of several-hundred CMEs. Most of these observations use short-term variations of brightness from one
SMEI orbit to the next (every 102 minutes) to track outward motion. The disadvantage of these orbit–to-orbit
analyses is that they cannot measure features that remain stationary relative to the Sun-Earth line (or those
which corotate with the Sun) and change slowly over time periods of several days. At UCSD we provide
measurements of heliospheric structures relative to a long-term base and, even in these observations, there
is little evidence of long-term stationary-standing density structures that corotate. By employing a kinematic
model of the solar wind, we reconstruct three-dimensional (3D) solar wind structures from multiple observing
lines of sight through the outward-flowing solar wind. By including interplanetary scintillation (IPS) velocity
observations from STELab, Japan or from Ooty, India we can extract both the solar wind density and velocity
from these analyses to compare with "ground truth" measurements from multi-point, in-situ solar wind
measurements from the STEREO, SOHO, Wind, and ACE spacecraft. We define the heliospheric structures
by these 3D velocity analyses, and they show that while the velocities map large regions near the ecliptic that
corotate, the dense structures that front and follow these regions are far more tenuous.
http://smei.ucsd.edu
SH13B-1555
Instant Stereoscopic Tomography of Active Regions with STEREO/EUVI
We develop a novel 3D reconstruction method of the coronal plasma
of an active region by combining stereoscopic triangulation of loops
with density and temperature modeling of coronal loops with a filling
factor equivalent to tomographic volume rendering. Because this method
requires only a stereoscopic image pair in multiple temperature filters,
which are sampled within ~1 minute with the recent STEREO/EUVI
instrument, this method is about 4 orders of magnitude faster than
conventional solar rotation-based tomography. We reconstruct the 3D
density and temperature distribution of active region NOAA 10955 by
stereoscopic triangulation of 70 loops, which are used as a skeleton for
a 3D field interpolation of some 7000 loop components, leading to a 3D model
that reproduces the observed fluxes in each stereosocpic image pair with an
accuracy of a few percent (of the average flux) in each pixel. With
the stereoscopic tomography we infer also a differential emission measure
(DEM) distribution over the entire temperature range of T~0.01-10 MK,
with predictions for the transition region and hotter corona in soft X-rays.
The tomographic 3D model provides also large statistics of physical
parameters. We find that the EUV loops with apex temperatures of
T = 1- 3 MK tend to be super-hydrostatic, while hotter loops
with T = 4-7 MK are near-hydrostatic. The new
3D reconstruction model is fully independent of any magnetic field data
and is promising for future tests of theoretical magnetic field models
and coronal heating models.
http://www.lmsal.com/~aschwand/eprints/2008_stereo3.pdf
SH13B-1556
Determination of CME 3D Trajectories From Stereoscopic Analysis of STEREO Coronagraph Data
We present results demonstrating that the 3D trajectory (velocity and direction) of a CME can be determined from stereoscopic analysis of a series of simultaneous coronagraph image pairs from the STEREO A and B spacecraft. It has been demonstrated that stereoscopic analysis (aka triangulation) of bright coronal features such as loops can be used to determine their 3D location and geometry. In these cases, the emission from the feature comes from relatively localized volumes. This is not the case for bright features in white light images, which may capture scattered light from an extended volume. Even though line of sight (LOS) effects dominate the observed structure seen in white light coronagraph images of STEREO CMEs, we find that by "tiepointing" the bright leading edge of the CME in both images of a stereo pair, we are able to determine the 3D trajectory using stereoscopy. This technique has been validated previously using synthetic white light stereoscopic image pairs. Here, to validate our results, we compare our 3D trajectories with CME trajectories determined by a more sophisticated forward-modeling method developed by Thernisien et al (Ap. J. 2006).
SH13B-1557
Comparison of Interplanetary Magnetic Clouds Observed by ACE and STEREO
The solar wind observations by STEREO A and B, together with the ACE spacecraft provide an unprecedented opportunity to examine three-dimensional structures of interplanetary magnetic clouds (MCs). The purpose of this study is to get a better insight into their spatial extent, differences in their detailed structures depending on the geometry of spacecraft encounter, and possible deformation due to interactions with other solar wind structures. For this purpose, we surveyed the STEREO and ACE data for the period from January 2007 through February 2008. As a result, we found that each of the three spacecraft encountered four or five well-defined MC during this period, in which the separation of STEREO A (B) from the Earth changed from 0 to 22 (-24) degrees. The observations from 21 to 23 May, 2007 provide a data set that is the most appropriate to our purpose. ACE detected two MCs (No. 1, May 21/2300 – May 22/1300; No.2, May 23/0300 – May 23/1200), and a less evident MC-like structure in between. Interestingly, the MC No. 1 was observed by STEREO B in a more beautiful form, with only a "remnant-like" structure observed by STEREO A, whereas the MC No.2 was observed by STEREO A in a more beautiful form than observed by ACE. It is supposed that these two MCs observed by ACE provide some evidence for deformation due to MC- MC interactions, although the analysis is not completed yet. On another topic, we need to admit that the probability for the same MCs to be observed by two spacecrafts is low despite the small separation between them. This observational fact can be explained by the direction of MC axis obtained from model fittings. This implies that we can obtain observational information about the spatial extent of MC only for those MCs with axes nearly parallel to the ecliptic plane.
SH13B-1558
Propagation and Decoupling of ICMEs and interplanetary shocks
The tracking of a solar storm from the Sun to 1~AU is one of the crucial issues for space weather forecasting. We use white light, remote radio and in-situ measurements to study the propagation of ICME/shock events. We compare these observations with two simple 1-D HD models: analytical and numerical, which focus on the transferring of momentum from the CME to the shock. The aim of the study is to understand how a fast CME/shock decelerates in the interplanetary medium.
SH13B-1559
The Solar Wind Power from Magnetic Flux
Observations of the fast, high latitude solar wind throughout Ulysses' three orbits show that solar wind power correlates remarkably well with the Sun's total open magnetic flux. These observations support a recent model of the solar wind energy and particle sources, where magnetic flux emergence naturally leads to an energy flux proportional to the strength of large-scale magnetic field. This model has also been shown to be consistent with X-ray observations of the Sun and a variety of other stars over 12 decades of magnetic flux. The observations reported here show that the Sun delivers ~ 600 kW/Wb to power the solar wind, and that this power to magnetic flux relation has been extremely stable over the last 15 years. Thus, the same law that governs energy released in the corona and from other stars also applies to the total energy in the solar wind.
SH13B-1560
First STEREO observation of a quiet sun CME
Streamer-blowouts form a particular class of CMEs characterized by a slow rise and swelling of the streamer that can last for days. While they are more massive than the average CME, their slow development complicates their association with features/activity in the low corona and hampers studies on their initiation mechanism(s). This paper reports on the first observation from 2 viewpoints of a streamer blowout CME. The event was observed by the SECCHI/COR2 A instrument as a typical flux-rope type CME, while a very faint partial halo was observed in COR2-B. The CME erupted from the east limb in the COR2 A field of view. EUVI-171 A images show a bright feature above the limb, traveling from the southern hemisphere towards the equator after which it slowly rises into the coronagraphic fields of view developing into the flux-rope structure CME. At the time of eruption the separation between the two STEREO spacecraft is sufficiently large (54 deg) to observe the source region face-on in STEREO-B. However, inspection of EUVI B data didn't reveal any particular source region, other than the quiet sun. No flaring activity could be related to the eruption. This observation shows unambiguously that a CME eruption does not necessarily have clear on-disk signature. Also it sheds light on the long-standing question of the necessity of having a flare for producing a CME. This result supplies strong constraints for CME initiation models. This type of observation could not have been achieved without the multi-viewpoint observations by STEREO.
SH13B-1561
Measurements of the Gegenschein brightness from the Solar Mass Ejection Imager (SMEI)
The Gegenschein is a faint diffuse component of the zodiacal light centered upon the antisolar point; this has now been viewed by the Solar Mass Ejection Imager (SMEI) for over 5 years. SMEI provides unprecedented near-full-sky photometric maps each 102-minute orbit, using data from 3 unfiltered CCD cameras. Its 0.1% photometric precision enables observation over long periods of time, of heliospheric structures having surface brightness down to several S10's (an S10 is the equivalent brightness of a 10th magnitude star spread over one square degree). When individual bright stars are removed from the maps and an empirical sidereal background subtracted, the residue is dominated by the zodiacal light. The sky coverage and duration of these measurements enables a definitive characterization. We describe the analysis method for these data, characterize the average Gegenschein brightness distribution, present empirical formulae describing its shape, and discuss its variation with time.