


ICS13 Abstract View 

Kinetic Effects in Magnetotail Dynamics: Emergence of FiniteWidth Reconnection Exhausts and the Occurrence of Localized Reconnection Onset 
Pritchett, P.L., pritchet@physics.ucla.edu (1) 
3D particleincell simulations are used to investigate two aspects of magnetic reconnection in a magnetotail configuration: (1) the emergence of finitewidth exhaust structures from a X line and (2) the localized onset of reconnection in response to the imposition of a nearEarth, highlatitude electric field. Both issues are addressed using an initial plasma sheet configuration that consists of a 2D dipole field joined to an asymptotic tail equilibrium with finite B_{z}.
An earthwardmoving reconnection jet from a finite X line is found to separate initially into two segments of width ~1015 d_{i} each. The dawnward segment moves ahead of the duskward one due to a finite iongyroradius effect and continues to intensity, while the latter is buffeted by the return flows generated by the former and stagnates. The leading front develops the characteristic structure of a sharp B_{z} increase and density drop on a 12 d_{i} scale. The current associated with this B_{z} increase is carried mainly by the electrons, and the jet front is the site of a Region 1 sense fieldaligned current system. Close to the dipole region the ion velocity distribution behind the front contains a drop out in parallel phase space at speeds of ~1.52.5 V_{A}.
It has been difficult to understand the emergence of localized (in y) reconnection flow channels in the tail. Unlike the case of a localized driving E_{y} applied in the lobes, which spreads rapidly across the tail due to the high Alfven speed, a localized E_{y} imposed at high latitude on the earthward boundary remains localized and creates a B_{z} reduction region that stretches duskward. This leads to a dawndusk asymmetry with a thinner current sheet and weakened B_{z} on the duskward edge of the flow channel. Eventually, this leads to localized reconnection with a tilted X line and the emergence of strong earthward and tailward flows. The significance for substorm onset will be discussed.

(1) Department of Physics & Astronomy, UCLA, Los Angeles, CA 900951547, USA 



