SH31A-0220
Numerical Simulations of MHD Waves in the Sun
Investigation of propagation, conversion, and scattering of MHD waves in the Sun is very important for understanding the mechanisms of transformation of the acoustic waves into different types of MHD waves. Such studying is also an essential part of developing robust local helioseismology techniques and diagnostics of subsurface magnetic fields. In this studying we investigate excitation, propagation, and conversion of different kinds of MHD waves in presence of the background inclined magnetic field. Waves are generated by the localized force and pressure sources with different frequencies placed at different depths. We have developed a complete linear 3D MHD numerical model to investigate influence of the magnetic field on wave properties and helioseismology measurements in realistic solar conditions. The results show that the magnetic field effects can substantially change the properties of the surface gravity waves (f-mode), but their influence on the acoustic-type waves (p-modes) is rather moderate. We find that magnetic field can lead to a collimation of the wave front. We also observe formation of Alfven waves in our simulations. The numerical modeling and new data from the HMI instrument on SDO will substantially advance our knowledge of the wave interaction with magnetic fields on the Sun and improve the local helioseismology diagnostics.
SH31A-0221
Comparison of a CME Flux-rope Model with LASCO data
The theoretical flux rope model (Chen 1989, 1996) of CME dynamics is investigated and compared with height-time curves of flux rope CME observations from LASCO. This model has been shown by Krall et al. (2001) to be a good match to numerous observed CME events. It is useful to study the model parametric dependences of CME initial acceleration, which is important for understanding the driving mechanisms of the ejections. STEREO will be able to provide data of the lower parts of the corona, capturing the initial acceleration of CMEs. The physics-based flux rope model is a low dimensional model comprising two second-order ordinary differential equations for the acceleration of the height Z(t) and the minor radius a(t) for the toroidal plasma loop. Given an initial parameter vector, an MHD-stable equilibrum is found that is a partial torus with two stationary footpoints separated by a distance Sf and anchored in the massive photosphere. The equilibrium flux rope is embedded in a background corona of finite pressure pc and magnetic field Bc and balances the J × B Lorentz force, gravity, and pressure gradient force. Injection of poloidal flux (toroidal current) serves as a direct drive toward destabilization and eruption. A code solves in seconds the dynamical evolution of the system in the d=4 state space for a given set of initial physical parameters (μ5 = \{Z0,Sf,a0,\bar{p}/pc,Bc\}), model coronal magnetic field, model solar wind, and the functional form of the flux injection dΦp(t)/dt. A physically acceptable range of parameters is sampled, and comparison with CME height-time data yields optimal parameters by the inverse method. Both the Very Fast Simulated Annealing Method (VFSA) and the Genetic Algorithm (GA) are used for optimization, and results are compared. The average relative variance of the model height versus time curves with the data sets are reported. The work is supported by NSF grant ATM-0638480 and the U.S. Department of Energy.
SH31A-0222
Evidence of Coupled Large-scale Propagating MHD Waves in the EUV Corona
We identify TRACE and SOHO-EIT EUV observations that contain EIT waves or evidence of EIT waves in the form of loop oscillations. In each case, we find instances of a "precursor" to the EIT wave--a much weaker wave pulse that appears instigated by the same source as the EIT wave, and travels in front of the pulse along the same trajectory. In each case, the wave "precursor" leads to some form of coronal dynamics; we observe either loop brightenings or, in one case, the initiation of an EIT wave and a sympathetic coronal mass ejection. These "precursors" are particularly notable in that they travel significantly faster--at least 3 × - 5 × faster--than their corresponding EIT waves, achieving minimum velocities of 1300-1600 km/s. We postulate that these wave "percursors" are, in fact, MHD modes coupled to the EIT waves, and may be a fast- mode-like component correlated with the EIT waves' corresponding slow-mode-like component.
SH31A-0223
How do CME-Shocks Look Like?: Study of Shock Geometry.
We use raytracing software to simulate white light coronagraph images of common 3D shock-like geometries, i.e. spherical and bow-shock type. We obtain the density profiles for different projections, shock thickness, and background and upstream densities. The results are compared to density profiles obtained from analyzing LASCO coronagraph images of CMEs that are good candidates to drive a shock due to their high velocities (V>1500 km/s). This work is funded by the LWS TR&T program.
SH31A-0224
Shock Structure of a Flare/CME Event in the low Corona
We study the MHD processes related to a flare/CME event in the lower solar corona using numerical simulations. Our initial state is an isothermal gravitationally stratified corona with an embedded flux rope magnetic field structure. The eruption is driven by applying an artificial force to the flux rope, enabling us to study the shock structures created by CMEs with different height-time profiles. The results show that as the flux rope rises, a shock structure is formed, reaching from ahead of the flux rope all the way to the solar surface. Thus, two main shock fronts are created, one front moving away from the Sun and another sweeping the solar surface. The relation to observed wave phenomena on the solar disk, and formation times of the CME-driven shocks are discussed.
SH31A-0225
Preliminary Results of Metrics Analysis of the ENLIL Heliospheric Cone Model While Studying Halo CME Propagation to the L1 Point.
We performed metrics analysis of the ENLIL heliospheric cone model by studying halo CME propagation and evolution to the L1 point and comparing the result to ACE observations. A cone model-based halo CME representation is inserted into the combined WSA-ENLIL or MAS-ENLIL model. We simulated a number of geomagnetic storms and series of events selected by community campaigns, including the October 2003 Halloween Storm CME and the recent fall AGU storm on December 15, 2006. We will present a set of such simulations and we will analyze the quality of the match between different solar wind parameters in the model and in the observations. In addition, we will study whether there are any systematic time lags between model outputs and observations by ACE. We also describe real-time setup for the ENLIL cone model to trigger CME alert capability at the Community Coordinated Modeling Center.
SH31A-0226
On-disk Observation of a Sympathetic CME in SOHO-EIT
We present the first observation of a sympathetic coronal mass ejection (CME) for which there is an obvious initiation mechanism. We observe a CME instigated from AR 10484 and an EIT wave traveling into AR 10486, where another CME is initiated. We note that, while the second CME appears driven by the first, the actual driver reaches it before the EIT wave. We hypothesize that the driver of the sympathetic CME is not the EIT wave itself, but is rather a decoupled Moreton wave. In such a case, a Moreton wave and an EIT wave are instigated at the same source, but then travel separately along similar trajectories, due to their differing speeds. This observation also yields much faster velocities for EIT waves than have been previously observed, as well as a possible instance of a channeled dimming region.
SH31A-0227
Validating one-point inversion solutions of the elliptic cone model for full halo CMEs
By using the elliptic cone model as a geometric proxy of the CME flux rope structure, we have established an one- point approach to invert geometric properties of frontside disk full-halo CMEs, such as the CME propagation direction, shape and angular widths. This work presents an algorithm for determining the radial speed and acceleration of full-halo CMEs on the basis of the apparent speed and acceleration observed on the sky-plane. Since there is some uncertainty in the one-point determination of the CME propagation direction, this work provides a way to estimate the confidence level of the inverted elliptic cone model parameters. http://sun.stanford.edu/~xuepu/PUBLICATION/FALL.ppt
SH31A-0228
Relationship between CME initial speed and magnetic helicity of magnetic clouds
In order to understand the relationship between solar and interplanetary phenomena, we have examined the initial properties of coronal mass ejections (CMEs) and magnetic helicity of magnetic clouds (MCs) for 24 CME- MC pairs. MCs are fitted with the linear force-free cylindrical model to obtain MC parameters (orientation, size, magnetic field magnitude, impact parameter, chirality, etc). The relative helicity per unit length of MC is calculated by \frac{HMC}{L}=\frac{4π B02}{α}\int0RJ12(α r)rdr. Comparing the square of CME initial speeds (VCME2) with the magnetic helicities (HMC, we find that there is a positive correlation between VCME2 and HMC, and the linear correlation coefficient (CC) between the two parameters is 0.52. We obtain a better correlation (CC=0.61) for 17 events whose impact parameter (the shortest distance of the satellite to the MC axis normalized by MC radius) is less than 0.5. Considering that the magnetic force in a flux rope is intimately related to magnetic helicity, our result supports that the magnetic force is responsible for the CME eruption. From this result we suggest that the high speed CME is associated with large magnetic helicity.
SH31A-0229
Compositional variations in magnetic clouds with ACE/SWICS
Magnetic Clouds (MCs) are a subgroup of Interplanetary Coronal Mass Ejections (ICMEs) showing a smooth rotation in their magnetic field vector and often enhanced magnetic field strength. From ICME studies a wide variety of compositional anomalies compared to normal solar wind is known (Richardson and Cane 2004). Enhanced iron charge states, enhanced O7/O6 ratios, and enhanced helium to proton ratios are common examples. From fitting the magnetic field inside a MC the trajectory of a spacecraft through the flux-rope MC can be reconstructed, allowing us to obtain spatially resolved compositional data. The considered MCs were observed from 2001 to 2007 using the magnetometer and the SWICS (Solar Wind Ion Composition Spectrometer) instrument onboard ACE (Advanced Composition Explorer). A total number of about 50 MCs were investigated, most of them were taken from the WIND list which ends in early 2006. We have completed the survey up to mid 2007 and also present the new MCs. The MCs were investigated for spatial heterogeneity with the aim to find trends for distinct compositional features.
SH31A-0230
Optical Flow of CMEs in SECCHI HI1
The SECCHI HI1 coronagraph is providing impressive new data showing the evolution of CMEs as they propagate towards Earth. We have applied an optical flow technique to the HI1 data to estimate the projected velocity of the CME. The optical flow technique we applied has previously been used to analyze SOHO-LASCO-C2 coronagraphic data. Here, we present the analysis of two CMEs observed in HI1-A on 2007 April 20 and 2007 July 9.
SH31A-0231
The effect of the magnetic topology of the Magnetic Clouds over the Solar Energetic Particle Events
We have simulated the effect of the magnetic topology of the Magnetic Clouds (MCs) over the solar energetic particle event (SEPe) fluxes (0.5-100 MeV) provided by solar flares. When a SEPe passes through a MC a characteristic behaviour in the data corresponding to the ion and electron fluxes is observed: a depression after a strong maximum of the flux. Using our cross-section circular and elliptical MC models we have tried to explain that effect, understanding the importance of the topology of the MC. In sight of the results of the preliminary analysis we conclude that the magnitude of the magnetic field seems not to play a significant role but the helicoidal topology associated with topology of the MCs. This work has been supported by the Spanish Comisión Internacional de Ciencia y Tecnologia (CICYT), grant ESP2005-07290-C02-01 and ESP2006-08459. This work is performed inside COST Action 724.
SH31A-0232
GCR Modulation by Small-Scale Features in the Interplanetary Medium
In an effort to uncover the properties of structures in the interplanetary medium (IPM) that modulate galactic cosmic rays (GCR) on short time-scales (from hours to days), we study periods of differing conditions in the IPM. We analyze GCR variations from spacecraft both inside and outside the magnetosphere, using the High Sensitivity Telescope (HIST) on Polar and the Spectrometer for INTEGRAL (SPI). We seek causal correlations between the observed GCR modulations and structures in the solar wind plasma and interplanetary magnetic field, as measured concurrently with ACE and/or Wind. Our analysis spans time-/size-scale variations ranging from classic Forbush decreases (Fds), to substructure embedded within Fds, to much smaller amplitude and shorter duration variations observed during comparatively benign interplanetary conditions. We compare and contrast the conditions leading to the range of different GCR responses to modulating structures in the IPM.
SH31A-0233
The effect of reconnection on a confined flux rope
Coronal mass ejections are among the most energetic events in our solar system, but their initiation mechanisms are still not well known. One possibility is loss of stability of a twisted flux rope confined by an overlying arcade. We present here a continuation of our research studying the role of reconnection on this system. We examine the relationship between critical-current reconnection and stability of a simple confined flux rope in simulations free from numerical reconnection. The current work focuses on imposing various reconnection rates on the system to determine how reconnection effects the stability of the confined rope.
SH31A-0234
Transport in the Interplanetary Medium of Coronal Mass Ejections
Coronal mass ejections (CMEs) are large scale structures of plasma and magnetic field expelled from the Sun, generally observed with coronographs in white light,and which are ejected into the interplanetary medium with a wide range of speeds. Due to its interaction with the surrounding medium, the interplanetary remmants of CMEs (ICMEs) suffer possitive or negative acceleration depending on their initial speed. This process of acceleration can be understood as a momentum transference between the ICMEs and the ambient solar wind. In this work, we consider the motion of an ICME in the solar wind as the motion of two immiscible fluids. An analytical study of the role of the drag force in the process of momentum interchange is presented. By comparing the analytical results with observations we obtain a good estimation of the drag coefficient.
SH31A-0235
High-resolution measurement of beryllium-10 content in the Dome Fuji shallow ice core during the Maunder Minimum
The production rate of the beryllium-10 in the atmosphere is basically proportional to the intensity of incoming galactic cosmic rays which show 11 year periodicity associated with the state of solar magnetic field. In order to examine the feasibility of detecting the 11 year solar cycle in the Dome Fuji shallow ice core covering over 3000 years, we measured the Be-10 content with high temporal resolution of 0.7-1.0 years. The Be-10/Be-9 ratio is measured by the Accelerator Mass Spectrometer (AMS) at the Micro Analysis Laboratory, Tandem accelerator (MALT), at the University of Tokyo. We report the preliminary data of the Be-10 concentration in the Dome Fuji shallow ice core around the 17th and the 18th century including the era of the Maunder Minimum. The average content of Be-10 in the ice core for this period is about 105 atoms/g. The 11 year periodicity is clearly detected with amplitude of about 30 %. We compare the obtained Be-10 data with the sunspot data and the other beryllium-10 data to evaluate the validity of our measurement and to examine the accuracy of the dating of the ice sheets for this period. Based on the results, we discuss the variation of solar cycle and the magnetic polarity during the Maunder Minimum.
SH31A-0236
A Statistical Study of the Ejecta - Shock Standoff Distance of Geoeffective Events
e study the interplanetary transport of 57 coronal mass ejections (CMEs), which are part of the events responsible for large geomagnetic storms of solar cycle 23 listed in the CDAW database. The interplanetary counterparts of these CMEs (ICMEs) were shock-driving and have caused intense (Dst < -100) geomagnetic storms. We study the statistical behavior of the standoff distance and time between the ICME and the shock. We divided our events into two groups, 1) events where there is likely a one-to-one relationship between the CMEs and ICMEs (unique events) and 2) events where multiple CMEs may be associated with a single ICME. We find that the standoff time of the unique events follows a normal distribution whit a mean of 7.6 hr. and a sigma σ = 4.7 hr. The standoff distance of unique events also follows a normal distribution with a mean of ~ 0.1 AU and a sigma of ~ 0.05 AU. We did not found any relationship between the position of the AR,associated to the low coronal CME activity, and the standoff distance. On the other hand there seems to be a linear relationship between the CME speed and the standoff distance.
SH31A-0237
Solar Eruptions and Large-scale Magnetic Fields
We study the magnetic morphology and evolution of solar flares and coronal dimmings associated with Coronal Mass Ejections (CMEs) and ambient magnetic fields of source regions. The study helps to understand interactions between magnetic structures of local and global scales and their effects on the energetics of flares and CMEs. We analyze a dozen active regions which produced flare-dimming-CME events and the preliminary results will be presented.
SH31A-0238
Assessment and Validation of MHD Models for the Solar Corona and Inner Heliosphere
We describe the status of a model assessment and validation project for testing MHD codes that simulate the solar corona and inner heliosphere. The goal of the project is to test MHD codes by applying firm empirical constraints to their boundary conditions in the corona and at 1 AU. The project has produced a database of coronal and solar wind observations from SOHO, ACE, Wind, and Ulysses. In addition to the database, software tools for comparing these data sets to the outputs for the MHD model codes under test will be demonstrated. The first step is to take the plasma parameters that are produced from the model codes and apply forward modeling to simulate the coronal observations of emission lines (H I Lyman alpha and O VI 103.2 nm). In situ solar wind data are used not only to provide benchmarks near 1 AU but also to provide coronal constraints for the coronal source regions of the solar wind. Future stages will involve making more direct comparisons of the plasma properties predicted from the model codes through the use of empirical coronal and solar wind models. We also describe a set of metrics that are used for making comparisons between the model code outputs and the empirical data. This work is supported by NASA under Grants NNX07AB98G to the Smithsonian Astrophysical Observatory and NNX07AB99G to the University of Michigan.