Variations of the boundaries of plasma precipitations and auroral luminosity in the nighttime sector

A statistical study of the positions of the boundaries of different areas o f auroral precipitations in the nighttime sector and their comparison with the boundaries of the auroral luminosity have been carried out on the basis of data of low-altitude satellites of the DMSP series obtained in 1986. Da ta on the boundary position of plasma precipitations were used to determine their dynamics, depending on the level of magnetic activity. The equatorwa rd boundary of the diffuse luminosity closely coincides with the location o f the plasmapause. The difference is observed only in the region of local g eomagnetic midnight, under a very high level of magnetic activity, when the boundary of the diffuse luminosity is located at lower latitudes. In night hours, the equatorward boundary of the oval of discrete auroral coincides with the position of the inner boundary of the central plasma sheet, and it s poleward boundary coincides with the area of the sharp decrease in the en ergy flux of structured precipitations accompanied by significant softening of the spectrum of electron precipitation. A band of soft electron precipi tations is located between the poleward boundary of the auroral oval and po lar cap. The width of the band decreases with the growth in magnetic activi ty. During intense disturbances, the boundary of the polar cap tends to coi ncide with the high-latitude boundary of the auroral oval.