HR: 0800h
AN: SM51A-03    [Abstracts]
TI: Agyrotropy: An Observable Probe of Magnetic Topology
AU: * Scudder, J
EM: jack-scudder@uiowa.edu
AF: University of Iowa, Room 203 Van Allen Hall, Iowa City, IA 52242, United States
AU: Daughton, W
EM: william-daughton@uiowa.edu
AF: University of Iowa, Room 203 Van Allen Hall, Iowa City, IA 52242, United States
AU: Karimabadi, H
AF: University of California San Diego, Department of Electrical and Computing Engineering, San Diego, CA , United States
AB: Claims for traversal of magnetic separatrices and electron diffusion region transits are many, though few, if any, are theoretically certain. The reason for this on the edge of the MMS era is that there is no clearly agreed upon observable for this type of identification that has a theoretical basis. All too often data signatures are interpreted as, or circularly defined to be, those of the magnetic separatrices or the electron diffusion region. Examples of such identifications are a burst of electric field noise, parallel electric fields, heat flux layers, or "bursts" of energetic particles. The purpose of this presentation is to discuss an observable, electron agyrotropy, that agilely illuminates the boundaries of magnetic topology. For this study fully kinetic simulations of reconnecting layers have been used with open boundary conditions including guide and anti-parallel geometries and multiple island equilibria. Unlike observations, the actual magnetic topology in the simulations can be determined using the vector potential; the same simulation run can be used to compute the observable electron agyrotropy from the pressure tensor of the PIC particles in the code. In this way the patterns of agyrotropy are demonstrated to "paint" the mathematical separatrices of the vector potential. Even in time dependent geometries the electron agyrotropy provides a clear indication of the location of such layers. Since non-zero agyrotropy reflects an electron distribution that is not cylindrically symmetrical about the magnetic field direction, its detection would be a strong local signature that unusually thin layers are being traversed. Because these layers are structured in space, they can support electric fields from the off diagonal elements of the pressure tensor of the type required to explain collisionless magnetic reconnection. As it is a local measurement, the pattern of agyrotropy can be found by orchestrating simultaneous independent measurements using an array of spacecraft such as Cluster or MMS. If detectors are routinely intercalibrated to the level that agyrotropy is routinely small, interesting experimental discoveries can be made by delineating locales where the agyrotropy is too large to be explained by intercalibration errors. As a word of caution, agyrotropy detection need not imply the detection of magnetic separatrices or even the diffusion region, since non-zero electron agyrotropy is a well known property of the Harris sheet in the presence of a background plasma. However, this agyrotropy is not large by the standards of PIC reconnecting sites, so sorting events by the size of agyrotropy would help to guarantee identifications.
DE: 7526 Magnetic reconnection (2723, 7835)
DE: 7827 Kinetic and MHD theory
DE: 7835 Magnetic reconnection (2723, 7526)
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Joint Assembly