A large-scale ionospheric depletion by intense radio wave heating
A large (100 km N/S), stable, smoothly‐structured and significant depletion (15% in number density) of the daytime Tromsø F‐region was produced inadvertently during a Heater polarisation and beam‐forming procedure. We show that the depletion coincided with the passage of an atmospheric gravity wave of natural origin which served as a large‐scale ‘seed‘ depletion for the self‐focussing instability