SH41C-01 INVITED 

Solar Reconnection

* Antiochos, S K (antiochos@nrl.navy.mil), Naval Research Laboratory, Code 7675, Washington, DC 20375, United States

High spatial and temporal resolution observations from SOHO, TRACE, Hinode, and STEREO prove dramatically that the photosphere is never simple and the corona is never quiet. The photosphere exhibits a constantly evolving, multipolar flux distribution on scales ranging from the magnetic carpet to active region complexes. The corona exhibits brightenings and jetting on a vast range of temporal and spatial scales: from small transient spicules, to long-lived coronal loops, to giant coronal mass ejections. We present theoretical and numerical results demonstrating that magnetic reconnection is the physical process underlying all of this activity. These results also show that the topology of the solar field is the key to understanding why solar activity exhibits such an apparently wide variety of forms. Conservation of magnetic helicity turns out to be the critical condition that distinguishes between the different types of reconnection in the solar corona. We discuss the implications of our results for interpreting the latest observations from Hinode and STEREO. This work was supported, in part, by NASA, ONR, and the NSF. http://solartheory.nrl.navy.mil

SH41C-02 

On the filamentary structure of energetic electrons during flares

* Drake, J (drake@umd.edu), UC Berkeley, 7 Gauss Way, Berkeley, CA 74720-7450, United States Swisdak, M (swisdak@umd.edu), U Maryland, IREAP University of Maryland, College Park, MD 20770, United States Shay, M (shay@udel.edu), U Delaware, Department of Physics and Astronomy 217 Sharp Lab, Newark, DE 19716, United States

Simulations and analytic arguments are presented that demonstrate that magnetic reconnection in the tenuous high temperature corona does not occur as a single large-scale x-line. Rather the narrow current layers that form at x-lines form secondary magnetic islands at small spatial scales. An electron acceleration model based on the interaction of particles with many contracting islands has been developed. A consequence of particle acceleration in any multi-island system is that energetic particles are released in narrow streams with characteristic widths of the order of the electron skin depth. This is because electrons are released from islands as they reconnect with the macro-scale field of the corona or magnetosphere. The characteristic width of the released energetic electron streams correspond to the width of the reconnection dissipation region. Thus, energetic electrons do not propagate away from the reconnection site in the corona as a single large-scale front but as a filamentary web. As a result, the return current problem is transformed: the narrow filaments of energetic particles propagate parallel to the magnetic field as kinetic Alfven waves with propagation speeds comparable to the thermal velocity of the energetic particles. Simple estimates suggest that the conversion of particle to kinetic Alfven wave energy is efficient so that the wave and particle energy propagates together as a radiation front from the corona toward the solar surface. The structure and dynamics of this radiation front are being explored.

SH41C-03 

Observational Evidence of the Role of Collisionless Magnetic Reconnection in Self- Organization of Solar and Stellar Coronae

Mullan, D (mullan@udel.edu), University of Delaware, Department of Physics and Astronomy 104 The Green 217 Sharp Laboratory, Newark, DE 19716, United States * Cassak, P A (pcassak@udel.edu), University of Delaware, Department of Physics and Astronomy 104 The Green 217 Sharp Laboratory, Newark, DE 19716, United States Shay, M A (shay@udel.edu), University of Delaware, Department of Physics and Astronomy 104 The Green 217 Sharp Laboratory, Newark, DE 19716, United States

Magnetic reconnection is widely accepted to be the driver of eruptive activity in the solar corona. However, questions about how a large amount of magnetic energy can accumulate before an eruption without triggering fast reconnection, why fast magnetic reconnection begins abruptly, and under what coronal conditions an eruption occurs remain unanswered. Observations of solar and stellar flares have revealed similar phenomenologies and power law statistics, suggesting that eruptions in solar and stellar coronae are driven by the same physical process. The existence of power law statistics has prompted the suggestion that solar and stellar coronae are self-organized, but the physical foundation of this theory has been lacking. We present observational evidence from 107 flare events in 37 sun-like stars that solar and stellar coronae self-organize into a state in which the coronal plasma is marginally collisional. This corroborates a recent model in which coronal eruptions are initiated by a catastrophic onset of collisionless magnetic reconnection [1]. These results demonstrate that the dynamics of magnetic reconnection play an active role in constraining the conditions of solar and stellar coronae. [1] P. A. Cassak, M. A. Shay, and J. F. Drake, Phys. Rev. Lett., 95, 235002 (2005).

SH41C-04 

Physical Properties in the Post-CME Current Sheet

* Ko, Y (yko@cfa.harvard.edu), Harvard-Smithsonian Center for Astrophysics, 60 Garden Steet, MS-50, Cambridge, MA 02138, United States Raymond, J C (jraymond@cfa.harvard.edu), Harvard-Smithsonian Center for Astrophysics, 60 Garden Steet, MS-50, Cambridge, MA 02138, United States

Post-CME current sheet is a common feature associated with solar eruptions as inferred by CME models. Magnetic reconnection within the current sheet should produce observational signatures, such as heated plasma, bursty outflows and accelerations, that can be used to test various models. Thin ray-like features in the corona appeared shortly after the eruption have been observed by white light coronagraphs on SMM, SOHO/LASCO and MLSO/MK4. They are believed to be the observational evidence of the post-CME current sheet. Spectroscopic observations from SOHO/UVCS also supports its existence by the observations of highly ionized emission lines that exist co-spatially with those features observed in white light. We present the first attempt to model the time-dependent density, temperature and ionic charge state evolution following the magnetic reconnection within a post-CME current sheet, and discuss the observational consequences implied from our results.

SH41C-05 

CME Initiation and Shock Formation in Complex Active Regions: Comparing the April 21 and August 24, 2002 CME Events

* Lugaz, N (nlugaz@ifa.hawaii.edu), Institute for Astronomy-Univ. of Hawaii, 2680 Woodlawn Dr, Honolulu, HI 96822, United States Roussev, I I (iroussev@ifa.hawaii.edu), Institute for Astronomy-Univ. of Hawaii, 2680 Woodlawn Dr, Honolulu, HI 96822, United States Sokolov, I V (igorsok@umich.edu), CSEM - Univ. of Michigan, 2455 Hayward St, Ann Arbor, MI 48109, United States

Complex active regions (ARs) often exhibit complicated magnetic topology with multiple null points and quasi- separators, as well as flux emergence and shearing motions. Our newly developed model for the initiation of a Coronal Mass Ejection (CME) mimics one consequence of flux emergence by studying the effects of the shearing of the two footprints of a small-scale dipole in the vicinity of an AR. Reconnection with the overlaying and neighboring magnetic fields results in an eruption whose footprints change location in a jump-like manner. We employed the Space Weather Modeling Framework to apply this model of CME initiation to the April 21 and August 24, 2002 ejections (from ARs 9906 and 10069, respectively). Those CMEs had similar properties, but their associated Solar Energetic Particle (SEP) events greatly differed. The studied ARs also displayed the complex magnetic topology required in our model of CME initiation. We discuss the initial evolution of the coronal magnetic field via reconnection at the pre-existing null points and quasi-separator, as well as the influence of the global magnetic field on the shock geometry and its possible implication for SEP production. We also compare the simulated events with relevant observations.

SH41C-06 INVITED 

Causes and Consequences of Reconnection in the Laboratory

* Prager, S C (scprager@wisc.edu), University of Wisconsin, 1150 University Ave, Madison, WI 53706, United States

Study of reconnection in the toroidal laboratory configuration known as the reversed field pinch reveals numerous features that are likely shared in part by magnetospheric and solar plasmas. In the MST experiment, reconnection is impulsive temporally and global spatially. Multiple, coupled reconnections occur, spread globally throughout the plasma. During a sudden reconnection event, the magnetic energy in the plasma is reduced by about ten percent, while the ion thermal energy increases several-fold (in one hundred microseconds). The reconnections rearrange the magnetic structure and lead to chaotic field line wander. MHD theory and nonlinear computation predicts the occurrence of multiple reconnections (nonlinearly coupled), magnetic energy release and, to some extent, the impulsive onset. But two-fluid Hall effects are measured to be strong as well, as also predicted by theory. Theoretical work is underway to explain the ion heating, which is strongest for heavier ions (as also occurs in the solar wind).

SH41C-07 

Experimental merging, coalescence, reconnection, and bouncing of two flux ropes

* Intrator, T (intrator@lanl.gov), Los Alamos National Laboratory, P-24 Plasma Physics, Mail Stop E526, Los Alamos, NM 87545, United States Sun, X (xsun@lanl.gov), Los Alamos National Laboratory, P-24 Plasma Physics, Mail Stop E526, Los Alamos, NM 87545, United States Furno, I (furno@lanl.gov), Los Alamos National Laboratory, P-24 Plasma Physics, Mail Stop E526, Los Alamos, NM 87545, United States Ryutov, D (ryutov1@llnl.gov), Lawrence Livermore National Laboratory Lawrence Livermore National Lab, 7000 East Avenue, Livermore, CA 94550, United States Dorf, L (ldorf@lanl.gov), Los Alamos National Laboratory, P-24 Plasma Physics, Mail Stop E526, Los Alamos, NM 87545, United States Lapenta, G (lapenta@lanl.gov), Los Alamos National Laboratory, T-15 Plasma Theory, Los Alamos, NM 87545, United States

Dynamics of magnetic flux ropes are of fundamental importance to the Earth's magnetosphere, solar eruptions, and other astrophysical phenomena. In the solar plasmas, flux ropes that emerge through the convection zone may interact with the pre-existing flux ropes on the photosphere. The dynamics may be related to the eruption trigger mechanism. During the emerging process, only those with preferred amounts of twist can survive the interaction with surrounding plasmas. Although their total helicity is expected to remain conserved, the twist could be transferred into writhe via the kink instability. These magnetic reconnection events occurring in nature are three dimensional processes. However, most experimental efforts to understand reconnection have concentrated in two dimensions. There are few experiments concerning the merging of flux ropes, and our Reconnection Scaling Experiment is the only one with fully 3D geometry, that includes finite length flux ropes and adjustable boundary conditions between line tied and non line tied. We report the experimental results on the merging, coalescence, and bouncing, of two flux ropes for strong and moderate guide field. http://wsx.lanl.gov

Author(s) (2007), Title, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract #####-##.