The Core Field Enhancement Caused by Pressure Loss in the Flux Rope Structures in the Magnetotail

Abstract

The plasmoids in the Earth's magnetotail, which are closely correlated with magnetospheric substorms, might be the structures with various magnetic topologies. Most plasmoids are flux rope like structures ith large core fields. The MHD simulations show that the occurrence of various magnetic structures in the magnetotail might be related to different distributions of the cross‐tail component By. However, the core field strength of flux rope structures shown in the previous simulations is much lower than that in the ambient lobe. In this paper, we consider that the pressure loss caused by extension of helical field lines to the flank regions and introduce the modificative terms to the MHD equations. In two cases with uniform initial By distribution, the recurrent formation and successive ejection of flux rope structures are illustrated under the action of plasma inflow caused by the dawn‐dusk electric field. It is noticeable that in the cases with the modificative terms, a reduction of the averaging magnitude of peak pressure values and a considerable enhancement of the averaging strength of core magnetic field are exhibited for the multiple magnetic structures. Moreover, in case 1 with a lower background By (By0 = 1nT) the relative amplitude of core field By enhancement is larger than that in case 2 (By0 = 2nT).