Stimulation of Pc 1 micropulsations by controlled VLF transmissions

During controlled VLF transmission experiments from a site near Anchorage, Alaska (L = 4), Pc 1 micropulsations, which can be associated with the VLF transmission program, were observed by detectors at College, Alaska; Dunedin, New Zealand; and Macquarie Island. The micropulsation event started shortly after the transmitter began sending a simple repetitive pulse program at 6.6 kHz. The program consisted of a 5-s-long pulse transmitted every 30 s. Following the onset of the event a complex sequence of micropulsations appeared between 1.0 and 1.33 Hz. During the simple repetitive program the pulsations recurred every 90 s. The micropulsations began 15 min after satellite 1972-76B, at low altitude in the conjugate region of the transmitter, observed proton fluxes which could be identified on a one-for-one basis with irregularly spaced pulses from the transmitter. Calculations suggest that the 6.6-kHz whistler mode wave and a 1-Hz hydromagnetic wave resonate with protons of the same parallel velocity near L = 4.0. The observations suggest that the micropulsations were stimulated by the VLF transmissions, the protons playing a role in the interaction.