Magnetic Fields in Coronal Mass Ejection Source Regions I Posters
Presiding: D Choudhary, Department of Physics and Astronomy, California State University, Northridge; B Welsch, Space Sciences Laboratory, University of California, Berkeley
SH51C-01 0830h
A Mechanism for the Flux Cancellation Caused by Emerging Magnetic U-Loops in the Sun
We used three-dimensional MHD simulation to study the evolution of U-shaped magnetic field lines (U-loops) in a flux cancellation region on the Sun. Emergence of U-loops is thought to be a process for causing flux cancellation at the solar surface, although the physical mechanism for this process is not obvious because the mass tends to accumulate at the dipped part of U-loops thereby reducing the buoyancy. Our flux emergence simulation reveals that a temporary siphon flow plays a key role in enhancing the buoyancy of the dipped part of U-loops and helps it emerge into the solar atmosphere against the gravity. By applying a model of emerging U-loops to an observed flux cancellation region, we study a possible configuration of magnetic field lines related to flux cancellation.
SH51C-02 0830h
Solar magnetic configuration and the 2003 October-November events
Large-scale magnetic fields in 2003 October-November have been calculated using a potential field source surface model in order to study the fast halo CMEs occurred in this period. The calculation shows that these CMEs were associated spatially with open field areas or occurred at the boundaries of two open field regions with like magnetic polarity. We investigate possible relationships between such configurations of magnetic field and fast halo CMEs here. SOHO is a project of international cooperation between ESA and NASA.
SH51C-03 0830h
Magnetic structures of active regions and their link to coronal mass ejections
olar coronal mass ejections (CMEs) are a principal link that connects the chain of events in the solar atmosphere, interplanetary space and the earth's magnetic environment. The central objective of our study is to advance our understanding of physical processes in CMEs and related phenomena, including their ultimate origin, precursors and near sun evolution as well as their link to the interplanetary phenomena. Earlier studies unanimously suggest that there is a straightforward relationship between the magnetic fields of erupted filaments and magnetic clouds at 1AU. However, the situation is more complicated and less understood in the case of eruptions from solar active regions. We combined photospheric magnetograms, chromospheric and coronal images as well as solar wind data of high spatial and temporal resolution in order to i) determine the basic characteristics of the initial pre-eruption magnetic configuration in an active region and ii) find a link between these characteristics and the magnetic fields in interplanetary CMEs (ICMEs) at 1AU. Our results show a good correspondence between the directions of the helical magnetic fields in interplanetary ejecta and in the source active regions. We will also demonstrate how the combination of the solar surface and solar wind data may be used to discriminate between different CME models and to predict the sign of the interplanetary magnetic field at 1AU.
http://www.bbso.njit.edu/~vayur/
SH51C-04 0830h
Photospheric sources of very fast coronal mass ejections
We identified photospheric sources for 39 very fast (v > 1100 km/s) front-side coronal mass ejections that erupted between 1999 and 2001. For our study we used data on CMEs and their sources provided by the CME Catalog, SOHO spacecraft (LASCO, EIT, MDI), Big Bear Solar Observatory (Halpha, magnetograms), Mount Wilson Observatory (sunspot drawings) and Joint USAF/NOAA active region summary. Our results are as follows. We distinguished three different groups of active regions which are responsible for very fast CMEs: 1) Complex delta spots (21 events). This group of active regions is characterized by the presence of at least two large opposite polarity sunspots located close to each other. 2) Simple delta spots (8 events). A typical configuration of this type consists of one large twisted tadpole-shaped sunspot, surrounded by many small satellite-sunspots. 3) Extended magnetic regions, which consist of two adjacent decaying active regions or a new active region emerging inside a decaying active region.
http://www.bbso.njit.edu/~vayur/
SH51C-05 0830h
CME and associated phenomena on May 12, 1997
The multispectral observations of NOAA active region No. 8038 during 10-13 May 1997 are presented. The observations of MDI/SOHO magnetograms show that in this active region continual but discrete growth and decay of magnetic field was taking place indicating either continuous evolution of magnetic flux or emergence of new flux region. The movie of these magnetograms reveal two important results that the major opposite polarities of pre-existing region were approaching towards each other, and a small north polarity flux i.e. moving magnetic feature (MMF) was ejecting out from major north polarity at a quasi-periodicity of about 10 hrs during 10-13 May 1997. It appears that as a result of flux cancellation by one such ejected north polarity flux with a newly emerged south polarity flux around 04:30 UT on 12 May 1997, a blast wave generated, seen by EIT/SOHO, producing CME and a moderate but long enduring 1B/C1.3 solar flare. The observations in Hα, soft X-ray, hard X-ray, ionospheric absorption, radio and interplanetary scintillations in association to this flare are presented in detail.. The multiwavelength observations of the flare showed occurrence of at least two phases of energy release, first at 04:42 and second at 04:47 UT. We propose a qualitative model to interpret the observations, which, however, also explains the generation of CME and associated flare with two stages of energy release. The occurrence of type II radio burst at 04:54 UT was perhaps due to shock produced by the plasmoid erupted during second energy release at higher altitude in the corona. It appears that the plasmoid traversed through shock in the interplanetary medium so as to enhance the scintillation index on 14 May as inferred from IPS observations.
SH51C-06 0830h
Magnetic Flux Emergence and the Initiation of Filament Eruptions and CMEs as Observed by the EUV Imaging Telescope on SOHO
Solar observations over more than twenty years (e.g., Gaizauskas and Svestka, 1987, summarizing the "Flare Build-up Study", Feynman and Martin, 1995, and more recently, Wang and Sheeley, 1999) have demonstrated that emergence of new magnetic flux in the vicinity of quiescent filament fields frequently leads to the eruption of those filaments, given polarity orientations favorable for magnetic reconnection. Concurrently, models of the interaction of such magnetic flux configurations have been developed to explain the initiation of flares (e.g., Priest and Forbes, 2002) and coronal mass ejections (Chen et al., 2002). We have used observations made in the 195 Angstrom (Fe XII) band by the EUV imaging Telescope (EIT) on SOHO to identify instances of emerging flux, indicated by new EUV emission, and subsequent eruption of a quiescent filament in a search for coronal changes that might appear as a result of merging magnetic fields. Limiting our study to quiescent filaments distant from active regions, we have identified events in which a slow increase in filament height begins shortly (a few hours) after first appearance of an EUV emission source either within or beside the filament channel. For long filaments, the apex of the rising filament appears to lie above the developing EUV source, implying that the field supporting the filament is locally interacting with the emerging field. Transient EUV features at onset of the eruptive phase include low-lying loops over the neutral line and, more rarely, localized sources apparently associated with the rising filament. No evidence of reconfiguring of an overlying corona (only faintly detected by the EIT) prior to CME initiation has been found. Our results support the hypothesis that at least in some instances the emergence of new magnetic field leads to a loss of filament equilibrium and a coronal mass ejection. This work is supported by NASA Intergovernmental Transfer W-10118 to NOAA's Space Environment Center. SOHO is a project of international cooperation between ESA and NASA.
SH51C-07 0830h
The Thermal Structure of AR 8038 During the May 1997 Event
During May 1997 active region AR 8038 was the site from which all solar flares originated. In particular, on May 12 a halo CME was associated with the only major flare of the day. We present a study of the thermal structure of AR 8038 obtained using our computational MHD model. Our algorithm solves the resistive and viscous full MHD equations in 3D. The energy equation includes thermal conduction parallel to the magnetic field, a radiation loss term, and parametric heating. The surface magnetic flux is prescribed as boundary condition. The initial potential field is sheared to obtain an energized configuration. Then we advance the MHD/thermodynamic model and look for a steady state. From the plasma properties it is possible to calculate emissions in the extreme ultraviolet and X-ray bands and compare the images with the observations. Work supported by NASA and the Center for Integrated Space Weather Modeling (an NSF Science and Technology Center).
SH51C-08 0830h
Magnetic field configurations at CME initiation sites*
Different magnetic field configurations are proposed or required for CME initiations by different models. In particular, "breakout" model (Antiochos, 1998; Antiochos et al., 1999) requires a mutiflux system that allows closed flux transfer between different systems and energy release during the euption of an underlying sheared structure. On the other hand, Linker et al. (2003) showed with MHD simulations that adequate amount of flux cancellation at the neutral line at the base of a single arcade structure may also lead to an eruption of a sheared structure. Debates are on going between different CME initiation models. We found, using observational data and PFSS model extrapolations, that both multiflux system and single arcade configuration exist at CME source regions. We present these cases and our analyses of the magnetic field topology and other characteristics of the events. *work suppoted by NSF/ATM, DOD/solarMURI, and the Center for Integrated Space Weather Modeling (an NSF Science and Technology Center).
SH51C-09 0830h
Energetics of AR 0486 from line-of-sight and vector magnetograms
Over two weeks in October/November 2003, the Sun featured unusually strong activity, with three large sunspot groups (including the largest one of this solar cycle), twelve X-class flares (including the strongest ever recorded), numerous halo coronal mass ejections (two with near-recorded speeds) and two significant proton storms. Eight of the twelve X-class flares originated from active region AR 10486. To understand the reasons of this peculiar activity, we investigate the evolution of the coronal magnetic field configuration as well as the energetics of AR 10486 before and after the X17.2 flare on October 28. To determine the coronal magnetic fields, we use potential and nonlinear force-free reconstruction techniques using line-of-sight (SOHO/MDI) and vector (MSO/IVM, Huairou, BBSO) magnetograms on the photosphere as boundary conditions. We identify the source region of the flare as related to the existence of null point or separator field line evidenced in a reversed-Y magnetic configuration. From the 3D configurations we derive the magnetic energy budget which can be released during the impulsive phase of the flare. The estimated free magnetic energy is enough to trigger an X-class flare. The continuous evolution of the magnetic energy derived from the potential field extrapolations indicates that the flare does not modify the distribution of magnetic field on the photosphere. We also study the distribution of energy before and after the flare using different vector magnetic field measurements.
SH51C-10 0830h
Boundary Flows in Solar Active Regions
We present a general technique to calculate the flow field at the altitude where vector magnetic field measurements of solar active regions have been obtained. The velocity field vector is reconstructed fully by solving the ideal induction equation of magnetohydrodynamics for the cross-field velocity component and by utilizing the Doppler velocity information to calculate the field-aligned velocity component. Because solving the induction equation is an under-determined problem, we have formulated our technique in such a way as to provide a unique solution of the induction equation when the vertical (normal to the boundary) component of the cross-field velocity is prescribed. We provide examples of various possible choices for the cross-field vertical velocity and we discuss the respective results. Moreover, we showcase the validity of our technique by predicting the particular area of NOAA active region 8210 from which a flare and a CME were triggered, using the reconstructed velocity field vector.
SH51C-11 0830h
Magnetic Field Configuration of Flare Locations in NOAA10486
The active region NOAA 10486 was the site of large solar flares that were associated with the coronal mass ejections. The initial trigger of these flares occurred at the sites where there was emergence of new flux in addition to the large magnetic shear. Several other large active regions also show that flux emergence is an essential property of such locations. In this paper, we present the magnetic field characteristics of NOAA10486 and compare them with similar active regions of past solar cycles.
SH51C-12 0830h
Clustering Properties of Active Centers During Solar Cycle~23
We continue our study (Pojoga and Cudnik, 2002, Solar Phys. 208, 17) of the distribution of solar magnetic regions during the current solar cycle in order to determine more accurately the characteristics of active region clusters. Synoptic magnetic maps from Kitt Peak National Solar Observatory and H-alpha observations of active regions taken at the Prairie View Solar Observatory are used. We identify clusters of activity by comparing the positions of active centers in successive Carrington rotations. An activity complex is considered if the active center persists for a minimum of 4 solar rotations and its position between two rotations is confined to an interval of ±5 degrees in latitude and ±15 degrees in longitude. The characteristics of clusters, such as lifetimes, rotation rates, and flaring properties are re-examined for the whole period. Our results show that a large percentage of active regions (40 - 50%) is involved in the clustering process. The activity complexes or nests are compact in size and exhibit latitude-dependent rotation rates that are close to (and slightly higher than) the differential rotation of recurrent sunspots. Our analysis reveals a great number of complex nests, which also exhibit high flaring rates, either converging, diverging or parallel. Different characteristics of the nests suggest that they are maintained by repeated injections of magnetic flux rather than by the evolution of the surface magnetic fields. We also examine the link between various nest characteristics and the progression of the solar cycle and compare these results with those from previous activity cycles. Examples of a few nests are shown, emphasizing the evolution of their size, activity level and rotation rate.