SH51D-01 INVITED
A Cross Comparison of Physical Processes in the Genesis of Coronal Mass Ejections and Plasmoids in the Earth's Magnetic Tail
Both coronal mass ejections (CMEs) and plasmoid formation in the geomagnetic tail have been characterized in terms of models that involve a slow build-up of magnetic energy followed by its sudden release. In each case the model invokes a growth phase during which the magnetic energy is stored, a trigger mechanism which releases this stored energy, and a recovery phase during which the field relaxes to a relatively low energy state. Because of these shared principles, researchers working on these two phenomena often ask similar questions. For example, "How long must the growth phase be in order to store sufficient energy?," "What is the physics of the trigger mechanism?," and "What is the role of magnetic reconnection during each phase?". There are, however, some fundamental differences between models of CMEs and plasmoid formation that prevent a one-model-fits- all approach. The field configurations prior to onset are quite different as are the properties of the plasmas in which the two phenomena occur. We assess the commonalities and differences within each phenomenon and try to determine the areas of research where a direct comparison is useful.
SH51D-02
Role of Collisionless Reconnection in the Sudden Onset of Flares and Substorms: a Comparative Study
Magnetic reconnection is widely believed to play an important role in magnetospheric substorms and solar flares. However, observations impose powerful constraints on theories of reconnection. Since the plasmas in the corona and the magnetosphere are characterized by very high values of the Lundquist number, it is likely that the relevant regime of reconnection is collisionless, and described by a generalized Ohm's law. Observations of substorms and flares demonstrate that they are generically not quasi-steady but impulsive phenomena, characterized not only by rapid growth, but a sudden change in the time-derivative of the reconnection rate, which places an additional burden on theory. We will present strong theoretical evidence that such fast and impulsive signatures can be obtained for both flares and substorms within the framework of two-fluid or Hall MHD theory, subject to the caveat that there are unresolved questions on how the present theoretical results on fast reconnection scale to large systems. Results of analytic theory and simulations will be presented for various system sizes, and comparisons will be made with in situ satellite measurements and RHESSI/SOHO/TRACE observations. The role of secondary instabilities of thin current sheets such as ballooning (for substorms) and tearing (for flares) will be discussed.
SH51D-03 INVITED
A Comparison of the Formation and Evolution of Magnetic Flux Ropes in the Solar Corona and Earth's Magnetotail
Magnetic reconnection plays a fundamental role in the energization of solar and magnetospheric plasma and the reconfiguration of solar and geomagnetic fields. Coronal mass ejections (CMEs), and their interplanetary counterparts (ICMEs), often show evidence of a twisted flux rope structure that is nearly identical - though of vastly different spatial scale - as plasmoids observed in the Earth's magnetotail. This paper compares and contrasts the formation and evolution of CMEs and plasmoids. We demonstrate that magnetic reconnection in the solar corona and the Earth's magnetotail create similar magnetic structures, but that post-eruption dynamics and the magnetic and plasma differences of the heliosphere and magnetosphere lead to different evolutions and impacts on their surroundings.
SH51D-04
What mirror mode waves in the solar wind are telling us about the solar corona
We have observed two quite distinct sources of mirror mode waves. Behind the bow shock in the magnetosheath and along the magnetopause, we see mirror mode waves grow from the pressure anisotropy imposed by the shock or the solar wind plasma. We also have observed mirror mode waves in the Saturnian magnetosphere growing from the pressure anisotropy imposed by mass loading from the E-ring torus. These mirror mode waves last a long time and are convected radially away from Saturn. By analogy, the solar wind mirror mode waves could be either generated by shocks or by mass-loading followed by radial transport from the inner corona. We see little evidence in Interplanetary CMEs or the solar wind that these mirror mode waves are caused by shock compressions. We test the radial transport hypothesis by examining the occurrence rate of mirror mode waves in the solar wind at 0.72 AU (with Pioneer Venus Orbiter data), at 1 AU with STEREO, and at 5 AU with Ulysses.
SH51D-05
Sheaths: A Comparison of Magnetospheric, ICME, and Heliospheric Sheaths
When a supersonic flow encounters an obstacles, shocks form to divert the flow around the obstacle. The region between the shock and the obstacle is the sheath, where the supersonic flow is compressed, heated, decelerated, and deflected. Supersonic flows, obstacles, and thus sheaths are observed on many scales throughout the Universe. We compare three examples seen in the heliosphere, illustrating the interaction of the solar wind with obstacles of three very different scales lengths. Magnetosheaths form behind planetary bow shocks on scales ranging from tens to 100 planetary radii. ICME sheath form behind shocks driven by solar disturbances on scale lengths of a few to tens of AU. The heliosheath forms behind the termination shock due to the obstacle presented by the interstellar medium on scale lengths of tens to a hundred AU. Despite this range in scales some common features have been observed. Magnetic holes, possibly due to mirror mode waves, have been observed in all three of these sheaths. Plasma depletion layers are observed in planetary and ICME sheaths. Other features observed in some sheaths are wave activity (ion cyclotron, plasma), energetic particles, transmission of Alfven waves/shocks, tangential discontinuities turbulence behind quasi-parallel shocks, standing slow mode waves, and reconnection on the obstacle boundary. We compare these sheath regions, discussing similarities and differences and how these may relate to the scale lengths of these regions.
SH51D-06
CME's low Mach number leads to a low Beta magnetosheath which alters their interaction with the magnetosphere
In this paper we illustrate some expectations for the interaction between low Mach number solar wind (often characteristic of CMEs) and the magnetosphere. A result of the low (Alfven) Mach number solar wind is the formation of a low thermal beta magnetosheath downstream of the Earth's bow shock. Because of such properties, magnetic forces become prominent and largely rule the properties of the magnetosheath flow and of its coupling with the magnetosphere. We first illustrate such effects by use of spacecraft data (a case when Cluster was adequately located in the magnetosehath) and MHD simulations for such a low Mach number solar wind case. We generally predict (a) high-velocity flow jets in the magnetosheath adjacent to the magnetopause, (b) reduced flows in other regions of the magnetosheath, (c) asymmetric shapes for the magnetopause, and (d) anomalous magnetic-field stretching of the dipolar portions of the magnetosphere, which we relate to the occurrence of sawtooth events.
SH51D-07 INVITED
A Comparison Between Particle Acceleration Processes during Explosive Solar Events and in the Earth's Magnetosphere
Despite being a fundamental and universal phenomenon, the acceleration of charged particles in heliophysical plasmas has remained poorly understood. The International Heliophysical project provides a unique opportunity to compare and contrast between observations and theoretical models of particle acceleration in the solar corona, the interplanetary medium, and in geospace. Near the Sun, charged particles are sometimes accelerated to relativistic energies when the coronal magnetic field reorganizes itself during massive explosions known as solar flare and coronal mass ejection (CMEs) events. In addition, if the CMEs are fast enough they drive shock waves as they propagate through the solar corona and the interplanetary medium and can accelerate particles to relativistic energies. The Earth's magnetosphere system is characterized by regions dominated by the terrestrial dipolar field, magnetospheric activity driven by the solar wind, and the bow shock standing in the solar wind. Detailed observations have been amassed of energetic particles at the bow shock, in the radiation belts, and the magnetotail, which allow the effects of geometry, length scales and solar wind driving to be investigated. In this paper, we discuss the similarities and highlight the main differences between the causes and consequences of the various physical processes responsible for accelerating particles near the Sun, in interplanetary space, and in and around the Earth's magnetosphere.