ИСТИНА

Magnetic energy release during magnetic reconnection in the magnetotail leads to fast plasma flows transporting thermal energy toward the inner magnetosphere. The interaction of the ambient plasma with such flows is controlled by forces at the flow's leading edge near as a sharp enhancement of the equatorial magnetic field component there, which has been called a dipolarization front. In this study, we examine the kinetic plasma structure of those equatorial magnetic field perturbations observed behind dipolarization fronts. Using statistical observations of dipolarization fronts in the near-Earth magnetotail by Time History of Events and 19 Macroscale Interactions during Substorms (THEMIS) mission, we show that these perturbations are sub-ion scale (scale is below ion gyroradius) magnetic field depressions (magnetic holes), mostly observed around the equatorial plane, and drift dawnward. They are populated by hot, transversely anisotropic electrons, likely heated at the front. Combining spacecraft observations and analytical estimates, we suggest that these holes result from the ballooning/interchange instability at the dipolarization front. They likely represent a nonlinear stage of magnetic field perturbations associated with front instability, and serve to transport hot electrons across the front. We discuss the possible role of the holes in scattering and heating electrons and ions in the dipolarized magnetotail.