Anisotropy of proton fluxes in neutral sheet region measured by DOK2 on Interball-1

The anisotropy of proton fluxes measured by DOK2 in a wide energy range (20–400 keV) during four crossings of the neutral sheet is discussed. In two cases, the satellite moves earthward whereas it moves tailward in other two. The bipolar proton fluxes are observed in the whole energy range. All events are observed during quiet geomagnetic field intervals with the predominate IMF Bx component and in the course of the growth phase of a small geomagnetic substorm, when the Interball-1 satellite was located in the plasma sheet and crossed the neutral line at a distance of ∼26RE. Changes of proton energy spectra during the crossings were observed. Observations indicate a crossing of the region where reconnection of magnetic field lines takes place. The positions of the neutral point were consistent with the NENL model.