A Study of Whistling Atmospherics. III. Observations at Closely Spaced Stations

Whistling atmospherics were recorded simultaneously at four stations with separations of about 150 km during the winter of 1960. Individual whistlers showed the same dispersions at all stations but significant differences in strength were sometimes observed. These features and the diffuseness of the whistlers are consistent with the idea of the energy emerging from the ionosphere through localized regions of size of the order of 100 km or less. A method has been developed of obtaining amplitude-frequency profiles. These were sometimes fairly flat but the less diffuse whistlers tended to show abrupt (up to 100 dB (kc/s)-') changes of amplitude of up to more than 20 dB for frequency ranges of about half a kilocycle per second. Such changes were, on occasions, dissimilar at the four stations.