Occurrence distributions of VLF hiss and saucer emissions over the southern polar region

Occurrence regions of VLF hiss and saucer emissions over the southern polar region have been studied statistically from Isis 1 and 2 VLF data which were received at Syowa station ( L =6.0), Antarctica. It is found that saucers occur both in the dayside and in the nightside just as VLF hiss emissions, and spatial distribution of the saucer emission region is quite similar to the distribution of downward field‐aligned currents given by Iijima and Potemra [1976]. It is also found that saucers are observed at an altitude range of 500–4000 km in winter, while they are observed only at altitudes higher than 3000 km in summer. These results suggest that saucers are excited by upflowing ionospheric electron fluxes and that the growth rate depends on the electron density of the background.