Midlatitude bursts of PiB geomagnetic pulsations and night airglow during stormtime sawtooth events

Abstract

We explore bursts of broadband pulsations (PiBs) and airglow using the ISTP midlatitude observatories during substorm activations in the course of severe magnetospheric storms. We detected bursty pulsations in the Pi1B short-period range not only when the boundary of the auroral and field-aligned currents (FACs) region was near Irkutsk, but also when the boundary was up to 10° northward. Earlier, we associated such events with sharp pulses of the solar wind (SW) ram pressure, Pd, and/or to fast substorm-related variations in FACs during superstorms. In this paper, we show observations of such bursty phenomena during substorm sawtooth events (STEs) in the course of two storms both with and without strong Pd pulses or their moderate variations. The possibility of periodic substorm activations during STEs by a global magnetotail instability and excitation of the nighttime Alfvén resonator is discussed. We suppose and test a technique for timing the substorm explosive phase onset by the start of the surge in the spectral power of Pi1B pulsations.