We reveal previously unknown quasi-periodic (QP) VLF emissions at the unusually high-frequency band of ~ 7–11 kHz by applying the digital filtering of strong sferics to the ground-based VLF data recorded at Kannuslehto station (KAN). In one event, the spectral–temporal forms of the emissions looked like a series of giant bullets, with very abrupt cessation. In the second event, the modulation period was about 3 min under the absence of the simultaneous geomagnetic pulsations.

A non-typical 1-4 kHz hiss was studied. It shows a sequence of separated noise bursts with strange “mushroom-like” shapes in the frequency-time domain, each lasting several minutes. This sequence could be a result of the modulation of the VLF hiss electron-cyclotron instability by Pc5 geomagnetic pulsations. This strange “mushroom-like” shape of the considered VLF hiss could be a combined mutual effect of the magnetospheric ULF-VLF wave interaction and the ionosphere waveguide propagation.