Patchy reconnection and evolution of multiple plasmoids in the Earth's magnetotail: Effects on near‐Earth current system

Abstract

Reconnection during substorms in the near‐Earth magnetotail occurs in a complicated way. Local instabilities can trigger anomalous resistivity in several spatial regions, which may initially be well separated from each other. As time progresses, the resulting plasmoids grow larger until they reach the dimension of the entire system and start to interact with each other. Satellite observations show that this expansion occurs rapidly during the downtail travel after plasmoid development when −10 RE > XGSM > −30 RE [Ieda et al., 1998]. In this paper we study the interaction of two and three plasmoids and their coalescence, as well as the current system seen near the Earth brought about by the reconnection regions. In the numerical experiments, resistivity is prescribed at localized patches which are placed at different downtail locations. We compare the magnitude of the influence the reconnection sites have on the near‐Earth current system. We find that not only the relative position of the resistivity patches but also the absolute distance from the Earth play roles in the relative amplitude of the field‐aligned currents associated with the individual reconnection events.