THE EFFECT OF IMF By ON THE MLT DISTRIBUTION OF THE OCCURRENCE OF VLF HISS

The effect of the interplanetary magnetic field dawn-dusk component (IMF B_y) on the MLT distribution of VLF hiss occurrence is analysed in this paper by using 31-38kHz VLF data observed at the south pole station (invarent latitude about 75°). It is foUnd that IMF B_y influnces the distribution of the VLF occurrence stronly, especially at the day side. The asymmytry of VLF occurrence at pre-noon MLT region and at post-noon MLT region at cusp latitude exists.The peak of the VLF occurrence is much more higher at post-noon sector than at pre-noon sector when positive B_y but the peak of VLF occurrence at postnoon becomes bigger when is negative B_y. This B_y control is related to the B_y control of magnetospheric plasma convection patterns and the distribution of electrons precipitation.