Dynamics of thin current sheets associated with magnetotail reconnection

Abstract

We have examined the detailed structure of thin current sheets and their evolution during a substorm interval on 24 August 2003, when Cluster experienced several rapid current sheet crossings within a couple of ion gyrotimes. These crossings took place during an interval of high‐speed ion flows with BZ reversals and signatures of accelerated electrons, suggesting crossing of the reconnection region. On the basis of four‐point observations with a tetrahedron scale of ∼200 km, we could quantify for the first time the thickness of the current sheet, which was comparable to or less than one ion inertia length, and resolve some internal structures such as multiple peaks within these thin current sheets. Different patterns in jX and in electron anisotropy were identified during the current sheet crossings: two crossings during tailward flow interval exhibited a quadrupole‐type Hall current in the ion diffusion region without a guide field, while one crossing during earthward flow showed a current system as predicted in the ion diffusion region under the presence of a guide field. Multiple flux rope type signatures or transient skewed structures are observed in the thin current sheets, particularly in regions where signatures of electron acceleration are observed. These observations suggest that three‐dimensional localized/transient structures could play an essential role in the dynamics of the thin current sheets, while a gross X‐line picture can be established only in an average sense.