Extension of the electron dissipation region in collisionless Hall MHD reconnection

Details Extension of the electron dissipation region in collisionless Hall MHD reconnection Extension of the electron dissipation region in collisionless Hall MHD reconnection

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm21a1556s&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SM21A-1556

Physics

Plasma Physics

[2753] Magnetospheric Physics / Numerical Modeling, [7835] Space Plasma Physics / Magnetic Reconnection, [7999] Space Weather / General Or Miscellaneous

Scientific paper

Recent space based observations and numerical work have suggested that in collisionless plasmas the electron diffusion region may extend to lengths on the order of tens of ion inertial lengths (di=c/ωpi), whereas Hall MHD simulations have typically produced more cusp-like reconnection geometries with lengths on the order of di. This raises the following question: is it possible to realize elongated electron current sheets within the framework of a Hall MHD model by means of a generalized Ohm’s law that includes additional closure terms (such as hyper-resistivity), to parameterize physical processes of kinetic origin? If so, it may facilitate greatly the capability of global multi-fluid models to represent the effects of kinetic physics at small scales. Here present Sweet-Parker type scaling arguments in the context of hyper-resistive Hall MHD. Our numerical experiments suggest that both cusp-like and modestly more extended geometries are realizable. However, the length of the electron dissipation region, which is taken as a parameter by several recent studies, is found to depend explicitly on the level of hyper-resistivity. Furthermore, although hyper-resistivity can produce more extended electron dissipation regions, the length of the region remains smaller than one ion skin depth for the largest values of hyper-resistivity considered here-significantly shorter than current sheets seen in many recent kinetic studies. The length of the electron dissipation region is found to depend on electron inertia as well, scaling like (me/mi)3/8. However, the thickness of the region appears to scale similarly, so that the aspect ratio is at most very weakly dependent on (me/mi).

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