Fine structure of the polar cusp as deduced from the plasma wave and plasma measurements Original Research Article

Plasma waves are one of the most significant features of plasma. They are a very sensitive indicator of the boundaries and inner structure of different regions in space plasmas. The data gathered onboard Interball 1 and Magion 4 in the polar cusp indicate that plasma wave intensity changes very rapidly with a characteristic period of the order of 1–50 seconds, which differs from the satellite rotation period. Comparison with plasma data suggests that it could be associated with real inner structure of the polar cusp. A similar effect has been seen in the data from Prognoz 8 and Freja satellites. CLUSTER data also confirm these effects. The analysis of the wave and plasma data from these satellites associated with fine (filamentary) structures in the cusp is given in this paper. This kind of filamentary structure plasma is often associated with nonlinear stage of the current instabilities or nonlinear evolution of the Alfven waves. The polar cusp can be used as a laboratory for studies of the plasma non-linear processes. Discussion of possible source of this fine structure is presented at the end of this paper.