The frontside boundary layer of the magnetosphere and the problem of reconnection

TLDR

It is suggested that diffusive entry of magnetosheath plasma and/or heating of detached plasmasphere plasma forms the low‑latitude boundary layer. The study presents Heos 2 plasma and magnetic‑field data from the frontside boundary layers of the magnetosphere. Observations show that the low‑latitude boundary layer is thinner, less turbulent, and exhibits a density jump at the magnetopause, ruling out large‑scale reconnection at the front and indicating that reconnection is transient in the cusp, eroding magnetic flux and producing short‑term large‑amplitude perturbations.

Abstract

Further Heos 2 plasma and magnetic field data obtained in the frontside boundary layers of the magnetosphere are presented. They reveal that the low‐latitude extension of the entry layer is of a somewhat different nature. The most pronounced difference with respect to the entry layer in the cusp region is the substantial density jump at the magnetopause. Furthermore, the low‐latitude boundary layer tends to be thinner and less turbulent, and the flow velocity inside the layer is always lower than that of the adjacent magnetosheath. This observation excludes large‐scale reconnection at the front of the magnetosphere as the origin of the layer. It is suggested that diffusive entry of magnetosheath plasma and/or heating of detached plasma from the plasmasphere leads to the formation of the layer. It appears likely that reconnection is dominantly occurring as a transient process in the cusp region and accompanies the eddy convection inside the entry layer. As a consequence, magnetic flux is being eroded from the front of the magnetosphere. This is in agreement with the signature of short‐term large‐amplitude magnetic perturbations observed in the low‐latitude boundary layer.