Effects of the large‐scale electric field on particle drifts in the near‐Earth tail

Abstract

Large‐scale electric field contributes to the charged particle drift motion directly through the E × B drift and indirectly through energization caused by magnetic drifts parallel to the electric field and through pitch angle changes due to magnetic field gradients perpendicular to the electric field. In this paper, we describe these effects on particle drifts in the near‐Earth tail, where the electric field pattern can be expected to be complex, especially near the inner edge of the plasma sheet. We use the Tsyganenko 1989 model to describe the near‐Earth tail magnetic field. The ionospheric Heppner‐Maynard model is mapped to the magnetosphere to model various electric field structures that are not included in a simple model that combines the corotation electric field with a constant cross‐tail convection electric field. The simple model is used as a reference when the results deduced from the Heppner‐Maynard model are discussed. Because these field models are numerically tedious, the bounce‐averaged drift equations are used. They also provide a practical way to include complex electric field models. In addition, we study the electric field mapping in a stretched magnetic field configuration typical for substorm growth phases. Furthermore, it is shown that the inductive electric field associated with temporal stretching during substorm growth phases can be comparable to the typical values of the convective electric field due to earthward plasma convection.