Relation between the VLF noise variations and the sector structure of the interplanetary magnetic field

The variations in amplitudes of a very low frequency (VLF) noise recorded i n Yakutsk during periods when the Earth passes the sector boundaries of the interplanetary magnetic field (IMF) were considered using the method of su perimposed epochs. The amplitude of the VLF noise sharply decreases on the second day after the change from the positive sector to the negative one in summer in night hours and increase in the second half of the positive sect or in night hours both in summer and in winter. The effect of the amplitude increase does not depend on the evenness of the solar-cycle number and man ifests itself mainly in the maximum of solar activity. The minimum of the a mplitude of the VLF noise falls approximately on the middle of the negative sector of the IMF and also does not depend on the solar activity.