Associations between VLF hiss and HF radar echoes from field‐aligned ionization

A strong association was found between the occurrence of VLF hiss in the 1- to 10-kc/s band and 18-Mc/s radar echoes from F-region field-aligned irregularities. Owing to the geometry involved, the irregularities are located within the auroral zone ionosphere through which the VLF signals are believed to pass. Between September 1, 1963, and March 17, 1964, thirty-three hiss events were observed, of which thirty-two were associated with 18-Mc/s radar returns. On occasion, the two phenomena showed a very close time correlation. The discussion presented is based on data obtained by dividing the records into 2-hour time intervals and examining these intervals for the occurrence of each phenomenon.