Three Dimensional Mesoscale Reconnection and its Relation to Magnetotail Dynamics

The mesoscale structure of reconnection is explored using a two-fluid code with the Hall effect and electron inertia. Previous full particle simulation studies of 3-D reconnection have shown that the system self-organizes into a quasi 2-D x-line configuration. However, these kinetic models were limited to relatively small systems. In a mesoscale systems (with scale length around 20 R_e) we show that reconnection becomes intriniscally 3-D. In relatively thick current sheets we find that reconnection occurs in widely separated localized patches whose intrinsic scale length is of the order of 10 c/ω _pi or 1 - 4 R_e in the Earth's magnetotail. There is no tendency for magnetic x-lines to spread and become quasi 2-D. The spatial scale of these patches are consistent with cross tail length scales of bursty bulk flows (BBFs), as inferred from multiple satellite observations. In thinner current sheets multiple finite length x-lines form in the cross tail direction which lead to a global release of magnetic energy. The implications for these results on the conditions under which the magnetotail releases magnetic energy in localized regions (BBFs) or through more global processes (substorms) are discussed.