Specific features of the characteristics of midlatitude substorm and nonsubstorm Pi2 geomagnetic pulsations and their generation conditions

The specific features of the diurnal and seasonal variations in different characteristics of two Pi2 geomagnetic pulsation groups (observed during magnetospheric substorms and when these substorms are absent) and the pulsation generation geophysical conditions have been experimentally studied based on observations at the Borok midlatitude observatory. It has been indicated that the dynamics of the occurrence frequency of Pi2 substorm and nonsubstorm bursts and their amplitude, duration, and intervals between peaks depending on the local time and season is identical in many respects. It has been found that substorm Pi2 bursts are mostly observed when the IMF is sunward and the solar wind electric field (Ey) is positive, whereas nonsubstorm bursts are observed when the IMF is antisunward and Ey is negative. The fundamental differences in the diurnal and seasonal variations in index α, which characterizes the slope of the distribution function of the two-group Pi2 burst amplitudes, have been revealed. It has been found that the index α value substantially depends on Ey and the IMF longitude (ψ). It has been assumed that the plasma sheet turbulence of the metastable magnetotail is responsible for reconnection and the generation of substorm and nonsub-storm Pi2 pulsation bursts.