HR: 15:12h
AN: SM53C-04 INVITED     [Abstracts]
TI: Surprising New Results on the Structure of the Diffusion Region
AU: * Daughton, W
EM: william-daughton@uiowa.edu
AF: University of Iowa, 511 Van Allen Hall, Iowa City, IA 52242, United States
AB: The prevailing understanding of collisionless reconnection is based on the notion that the diffusion region has a multi-scale structure consisting of an outer ion-scale region and an inner electron-scale region that is presumed to remain microscopic (electron scale) in both the inflow and outflow directions. As a consequence, it has been argued that the reconnection rate is controlled by the ions and is insensitive to details of the electron physics. In contrast to this conventional picture, new results from large-scale fully kinetic simulations indicate that the electron diffusion region expands in time to form an elongated current layer with a width on the order of the electron meandering orbit but a length that can exceed tens of ion inertial lengths. As a result, the electron layer forms a bottleneck limiting the reconnection rate. Furthermore, this extended electron current sheet periodically becomes unstable to the formation of secondary islands leading to a reconnection process that is inherently unsteady. Although scaling these results to realistic parameter regimes remains a significant challenge, it already seems clear that the length of the electron diffusion region will be much larger than previously thought, with a length at the magnetopause of ~ 500 km rather than the expected ~ 8 km. These results have major implications for the study of reconnection and require a thorough re-examination of the previous theories. Similarly, the diagnostics for identification of the diffusion region and interpretation of observational data need to be reconsidered for both existing missions such as Cluster as well as upcoming missions such as the Magnetospheric Multiscale mission.
DE: 7526 Magnetic reconnection (2723, 7835)
DE: 7835 Magnetic reconnection (2723, 7526)
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Joint Assembly