Non-typical ground-based quasi-periodic VLF emissions observed at L∼5.3 under quiet geomagnetic conditions at night

► Non-typical quasi-periodic (QP) VLF emissions have been recently found. ► These emissions were observed under conditions of quiet geomagnetic activity (Kp=0). ► The night-time and early morning QP event was reported here for the first time. ► These were auto-oscillations of the cyclotron instability of the radiation belts.