A scenario covering all phases of nightside convection with the roles of ion drifts and reconnection determined from the observed field‐aligned currents

Abstract

The rate of transfer of magnetic flux into the nightside dipole‐like region is a function of the field‐aligned current (FAC) intensity and Nt–Nd, where Nt and Nd are the total number of plasma sheet ions on flux tubes in the near‐Earth tail and just inside the dipole‐like region. In addition, for slowly varying convection, the FAC intensity is a function of the magnetic flux in the tail. The above two relationships provide the basis for a scenario for convection. Convection bays and steady state occur if there is an ample supply of flux tubes with a small value of Nt in the near‐Earth tail. The growth phase occurs when a major increase in dayside reconnection leads to an increase in the amount of tail flux, which in turn causes increased convection into the nightside dipolar region. The plasma sheet thins until the predipolarization phase starts (reconnection or some similar process). The reconnection provides magnetic flux with reduced Nt, and also produces a change in the field‐aligned currents, both of which increase the dipolarization rate after electrical coupling with the ionosphere is established. At that time, either a pseudobreakup or a substorm onset will occur. The recovery phase is a convection toward a steady state, in which the plasma undergoes redistribution in latitude, local time, radial distance, and energy. It can be either fairly localized or magnetosphere‐wide, depending on the changes that have occurred in the dayside reconnection rate.