极尖纬度午后极光嘶声的极大发生率

极尖纬度午后区是一个异常等离子体过程区，已发现该区在低地磁扰动条件下，多种空间物理现象活动强度极大（相对邻区）：强的向上场向电流，向下低能电子流极大，向上离子通量极大，Ｆ层电子密度极大等等。导致该区异常的根本原因尚不清楚。本文利用南极点站（磁纬约７５°）的极光嘶声的电场强度进行统计分析，发现该区３１－３８ｋＨｚ波段极光嘶声的发生率极大。本文还分析了该区极光嘶声发生率与地磁活动指数Ａｐ的关系，结果表明，它们之间有明显的相关关系。

THE MAXIMUM OF VLF HISS OCCURRENCE IN THE POSTNOON SECTOR AT CUSP LATTITUDES

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.