Abstract:

The postnoon sector at cusp latitude is a abnormal plasma process region. It has been found that the postnoon sector at cusp latitudes is often characterized by the secondary maximum of the activities or intensities of space physical phenomena (to adjacent region):Stronger upward field aligned current;the maximum of downward low energy electron stream; the maximum of upward ion flux;the maximum of electron density in the ionosphere F region and so on.The substancial reason that causes the abnormal in this region is not understood well yet. In this paper the electric field intensity data of aurora hiss at South Pole Station (geomagnetic latitude about 75°) in 1986 were analized statistically.The relationship between the occurrence of VLF aurora hiss and Ap index is examined also. The results show the secondary maximum of occurrence of 31-38kHz VLF emissions in the postnoon sector exists and the position of the maximum agrees with the abnormal plasma region mentioned above and that there is a good correlation between occurrence and Ap index.