The Diamagnetic Cavity in the Exterior Cusp and "Stagnation Region" as it is Seen From Interball-Tail.

Interball-Tail orbits were traced in the special coordinate system based on the Tsyganenko-96 geomagnetic field model which moves relative to GSM depending on the season and interplanetary conditions. Plasma parameters and magnetic field magnitude in this system indicate an existence of spatially confined region where magnetic field is significantly less than the Tsyganenko-96 model prediction, and plasma number density is close to the magnetosheath plasma density. The ion temperature in this region is unexpectedly high and convection velocity is small. This is generally inconsistent with the model which consideres the cusp as a region of reconnected field lines convection. This region was statistically investigated to clarify the problems as follows: 1) the mechanism of plasma heating in the "diamagnetic cavity", 2) the nature of the magnetopause in this region, 3) the reason of plasma stagnation.