Kinetic structure and dynamics of guide-field magnetic reconnection

J. F. Drake (University of Maryland), M. Swisdak, M. Shay, 
M. Hesse, and C. Cattell 

The impact of an initial guide magnetic field on the structure and
dynamics of magnetic reconnection has been explored with full particle
simulations and analytic analysis. Generally fast magnetic
reconnection with a guide field is driven by the dispersive kinetic
Alfven dynamics rather than whistler dynamics. The transition from
anti-parallel to guide field reconnection, the role of non-gyrotropic
pressure in breaking the frozen-in condition, the structure of the
parallel electric field and the role of turbulence will be
discussed. Surprises are that the transition from anti-parallel to
guide field reconnection occurs when the initial axial field is around
0.1 of the reversed field, leading to the question as to whether true
anti-parallel reconnection exists in nature. Guide field reconnection
is much more susceptible to secondary island formation than
anti-parallel reconnection, consistent with MRX observations and the
formation of flux ropes (FTE's) at the magnetopause. Parallel electric
fields are much more localized transverse to the flux surfaces than
had been previously believed and become structured along B, rather
than smooth due to the deveopment of turbulence in the form of
electron-holes and double layers. Consistent with observations in the
auroral ionosphere and magnetosphere, large-scale parallel electric
fields probably do not exist in nature.