Characteristics of field-aligned currents associated with magnetic flux ropes in the magnetotail: A statistical study

Abstract

We present an investigation of 35 magnetic flux ropes encountered by Cluster in the Earth's magnetotail during the years between 2001 and 2004. The study shows that the parallel current dominates inside 86% of the identified flux ropes and 71% of the flux ropes are surrounded by the draping regions where the parallel current is comparable to the perpendicular component and steeply changes its direction. Namely, magnetic field is nearly force-free in 86% of the identified flux ropes while it considerably deviates from the force-free in the draping region. Therefore, the observations indicate that energy conversion should take place in the draping region. Moreover, the core fields for most the flux ropes come from the interplanetary magnetic field.