Introduction


Magnetospheric boundary layer is a region close to the Earth's magnetopause in which magnetosheath plasma has strong influence. It can be divided into four parts:

  1. Plasma mantle
  2. Entry layer
  3. Exterior cusps
  4. Low-latitude boundary layer, LLBL

However, some researchers don't define the entry layer at all as a separate region. A n additional boundary called the free-flow boundary has been suggested to exists between the exterior cusp and the magnetosheath (this is the boundary that is often plotted as a dashed line in schematic figures of the magnetosphere).

Boundary layer is a very special region, not only because of the presence of magnetosheath plasma, but also because of the still uncertain topology. Also the mapping of the boundary layer regions to low altitude is not quite certain yet, although it is clear that these spatially vast regions map into a very limited region around the low altitude cusps. The mapping can be studied either by using advanced magnetic field models, or by low-altitude measurements of

Charged-particle precipitation characteristics seem to be the best (low-altitude) means to categorize the boundary layers. Dayside auroral precipitation from these regions is responsible for the daytime zone of soft precipitation, or the cusp/cleft precipitation.

The recent loss of Cluster satellites was a bad blow to the in situ study of the Earth's boundary regions.

Plasma mantle


The plasma mantle was first defined by Rosenbauer et al. (1975). It

Figure: Formation of the plasma mantle. Low-energy ions (blue) take longer to mirror from the ionosphere than do higher energy ions (red), and are thus convected further across field lines, giving decreasing energy and density with deeper penetration into the mantle (towards the magnetosphere).

Entry layer

The entry layer was first defined by Haerendel and Paschmann (1975) and Paschmann et al. (1976). It

Exterior cusp

Low-latitude boundary layer

References