VLF banded structured events observed in the 5–39 kHz frequency range in Finland

Analysis of very low frequency (VLF) radio waves provides us the remarkable possibility of investigating the response of both the lower ionosphere and magnetosphere to a diversity of transient and long-term physical phenomena originating on Earth (e.g., atmospheric waves) or in space (e.g., CMEs). In this work, broadband VLF data measured at Kannuslehto, in northern Finland, is used to characterize a new type of VLF emissions displaying a strip-like structure observed in the 5–39 kHz frequency range. Analyzing campaigns from 2006 to 2022, we found that this emission can be observed either in the high VLF frequency ranges or spanning from low to high frequency ranges. We also found that the events last usually less than 1 hour, occur during evening hours, and during quiet geomagnetic conditions. We discuss the seasonal dependence of this kind of events by analyzing a complete year during 2022. We also discuss whether their origin might be due to plasma instabilities in the magnetosphere, as in the case of auroral hiss.