Abstract

Very low frequency (VLF) emissions of natural origin were identified for the first time by analyzing 1‐hr ground‐based magnetic field spectrograms in the 0.2‐ to 39‐kHz frequency range. Data were used from the Kannuslehto radio receiver (L‐shell ~5.5), recorded during different campaigns between 2006 and 2019. The spectrograms exhibit banded structures, which consist of several strip elements that vary in time and frequency over the event duration. Statistical analysis of 95 events shows that they are observed in the frequency range that extends from 2 to ~37 kHz, and mainly appearing above 16 kHz. The events span from 4 to 110 min and occur in the evening sector (~17–01 magnetic local time), mostly during quiet geomagnetic conditions. Furthermore, they are primarily left‐handed polarized and are associated with bursts of lightning‐related radio emissions such as sferics and tweeks.