New observations of the low frequency interplanetary radio emissions

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Abstract
Recent Voyager 1 observations reveal reoccurrences of the low frequency interplanetary radio emissions. Three of the new events are weak transient events which rise in frequency from the range of 2–2.3 kHz to about 3 kHz with drift rates of ∼1.5 kHz/year. The first of the transient events begins in mid‐1989 and the more recent pair of events both were first detected in late 1990. In addition, there is an apparent onset of a 2‐kHz component of the emission beginning near day 70 of 1991. The new transient emissions are barely detectable on Voyager 1 and are below the threshold of detectability on Voyager 2, which is less sensitive than Voyager 1. The new activity provides new opportunities to test various theories of the triggering, generation, and propagation of the outer heliospheric radio emissions and may signal a response of the source of the radio emissions to the increased solar activity associated with the recent peak in the solar cycle.