Structuring of LLBL by IMF Orientation

by

Oleg L. Vaisberg
26 September 2001

Interball measurements within the low-latitude boundary layer (LLBL) indicate that most of LLBL crossings fall into two categories: (1) highly structured LLBL and (2) weakly structured LLBL. The highly structured LLBL is usually associated the interplanetary magnetic field (IMF) and/or magnetosheath magnetic field has a negative B_Z component, while the weakly structured LLBL is usually observed while IMF and&/or magnetosheath magnetic field has a positive B_Z component. Two types of the LLBL differ not only in observed variations of number density distribution but also in temperature and velocity pattern.

The ion velocity distributions within highly structured LLBL are quite variable and often consist of two or three magnetosheath-type components with different velocities parallel to the magnetic field. The ion velocity distributions within weakly structured LLBL consist of two components and show significantly smaller variations compared to the highly structured LLBL. These characteristics indicate that two types of LLBL have different sources.

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