Unexpected vertical current sheets in the magnetotail associated with northward IMF

Fast magnetic field polarity changes detected in the quiet magnetotail by a spacecraft are usually attributed to thin cross-tail current sheet crossings. On September 14, 2001, Cluster registered several such events. However the IMF was northward for the previous 24 h and the formation of a thin current sheet was very unlikely. The multi-point analysis revealed that these sheets were almost vertically oriented, had strong shear and vanishing normal magnetic components and therefore should be interpreted as boundaries between two independent magnetic field domains (flux tubes), rather than crossings of the main cross-tail current sheet. We suggest that such anomalous configuration might form in the course of high-latitude reconnection of geomagnetic lobe and interplanetary field lines when IMF is northward.