Diurnal distribution of ELF, VLF, and LF noise at high latitudes as observed by Alouette 2

Statistical studies have been made of the diurnal and latitudinal occurrence and intensity patterns of ELF, VLF, and LF whistler-mode noise emissions observed with the Alouette 2 satellite. The ELF emissions occur characteristically below 1 kHz, are peculiar to the daylight hours, and show a peak in average intensity in the invariant latitude range of 50°–70°. In the VLF range, broadband emissions extending upward from the LHR frequency show a maximum average intensity near local noon and a Λ of about 77°. Along the auroral oval toward earlier and later hours, they show a decreasing intensity. The apparent high-frequency end of this emission band extends upward from 100 kHz to the local fN or fH frequency in the LF range. The LF emissions were studied at a fixed frequency of 200 kHz, and maximum intensities were found along the day and evening portions of the auroral oval. This type of noise also shows a latitude dependence on Kp similar to that of the auroral phenomena. A second region of peak intensity, at about the position of the nighttime plasmapause, appears in the LF statistical results, but a complete study has not been made of that region.