A simulation study of forced reconnection processes and magnetospheric storms and substorms

Abstract

We simulate, on the basis of a two‐dimensional incompressible MHD code, the plasma dynamics of a long magnetotail (∼200 RE) under a constant and time‐varying driving force delivered from the solar wind. It is found that under a constant driving force the magnetic fields in the magnetotail tend to reconnect impulsively and the formation of X line and plasmoids occurs intermittently and repeatedly every 2–4 hours. Under a time‐varying driving force the post‐driven phase of a plasmoid formation and the spontaneous reconnection process are also studied. Our results show that magnetic reconnection in the magnetotail during magnetospheric substorms and storms is basically a driven process. A complete sequence of the event, going from the gradual pile‐up of magnetic flux to the formation and the antiearthward convection of the new X line and to the ejection of plasmoids from the antiearthward end of the magnetotail, requires the presence of the driving force. The simulation results may also be useful in unifying the different interpretations (1) of the plasmoid formation and plasma sheet thinning and (2) of the relative importance of magnetotail processes with respect to the direct solar wind effects during substorms.

Hybrid Modeling of the Formation of Thin Current Sheets in Magnetotail Configurations

“…A comparison between the two panels indicates that only a very small fraction of the applied electric field can be recovered in the center of the current sheet. This result confirms earlier and concurrent investigations of MHD simulations which exhibit similar features (Birn and Schindler, 1985;Lee et al, 1985).…”

Plasmoid Formation in Current Sheet with Finite Normal Magnetic Component

“…The formation of plasmoids has been mostly investigated for the Earth's magnetotail configuration in the context of the substorm onset problem [1-3, [5][6][7][8]. In those studies the weakly 2D current sheet with finite B n is used to model the initial static equilibrium of near-Earth magnetotail plasma.…”

A 2.5 dimensional MHD simulation of multiple‐plasmoid‐like structures in the course of a substorm

“…It was found that under a constant driving force delivered from the solar wind the formation of plasmoids occurs intermittently and repeatedly every 2 to 4 hours. The authors suggested that the repeated occurrence of plasmolds was associated with impulsive changes of the AE index superposed on a highly enhanced average level and some of the impulsive changes of the AE index were definitely associated with auroral substorm activity [Lee et al, 1985]. However, in their model a constant plasma mass density P0 is adopted and the variations of temperature and density are not investigated within the context of incompressible fluid.…”

“…The core field generation in plasmoids can be also explained in terms of Hallgenerated currents which can naturally lead to core field strengths that even exceed the ambient lobe field in the magnitude. In order to study the origin and the evolution of plasmolds a simulation study of forced reconnection processes has been carried out by Lee et al [1985]. It was found that under a constant driving force delivered from the solar wind the formation of plasmoids occurs intermittently and repeatedly every 2 to 4 hours.…”