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Two consecutive magnetic flux ropes, separated by less than 30 s(Dt 30 s), are observed within one magnetic reconnection diffusion region without strong guide field in the Earth’s magnetotail by Cluster multispacecraft. The flux ropes are characterized by bipolar signatures of the south–north magnetic field component Bz accompanied with strong core magnetic field By, intense current J and density depletions inside of them. In spite of the small but non-trivial global scale negative guide field(–By), there exists a directional change of the core fields of two flux ropes, i.e.,-Byfor the first one, and Byfor the second one. The directions of the core fields are the same as the ambient cross-tail magnetic field component(By) just outside of flux ropes. Therefore, we suggest that the core field of flux ropes is formed by compression of the local preexisting Byand that the directional change of core field is due to the change of local preexisting By. Such a change in ambient Bymight be caused by some microscale physics.
Two consecutive magnetic flux ropes, separated by less than 30 s (Dt 30 s), are observed within one magnetic reconnection diffusion region without strong guide field in the Earth’s magnetotail by Cluster multispacecraft. The flux ropes are characterized by bipolar signatures of the south-north magnetic field component Bz accompanied with strong core magnetic field By, intense current J and density depletions inside of them. In spite of the small but non-trivial global scale negative guide field (-By), there exists a directional change of of the core fields of two flux ropes, ie, -Byfor the first one, and Byfor the second one. The directions of the core fields are the same as the ambient cross-tail magnetic field component (By) just outside of the flux ropes. , we suggest that the core field of flux ropes is formed by compression of the local preexisting By and that the directional change of core field is due to the change of local preexisting By. Such a change in ambient Bymight be caused by some microscale physics.