Conjugate Ionospheric Electron Density Irregularities Induced by Very Low Frequency Transmissions at North West Cape, Australia

Abstract This study investigates the characteristics of ionospheric electron density irregularities induced by very low frequency (VLF) wave transmissions from North West Cape (NWC), Australia, using Swarm‐A satellite data from January 2014 to September 2024. The VLF‐induced irregularities at NWC are pronounced late at night, during equinoxes and June solstice, and under conditions of low solar activity. Similar climatological behavior, but with lower irregularity intensity, is observed at the magnetic conjugate location. These results suggest that ionospheric perturbations associated with VLF transmissions are more effective under tenuous ionospheric conditions. Irregularities at the NWC site are predominantly associated with plasma density depletions, whereas those at the conjugate location are mainly characterized by density enhancements. The plasma depletions at NWC can be attributed to enhanced chemical reactions between oxygen ions and molecular species resulting from atmospheric heating. However, the physical mechanism underlying the density enhancements at the conjugate location remains unclear.