A Fresh Look at Jovian Decametric Radio Emission Occurrence Probabilities in the CML-Io Phase Plane

The occurrence of Jovian decametric emission (DAM) is sporadic as observed from ground-based instruments. When the timing intervals of observed occurrences of Jovian DAM are compared to all periods when Jupiter was observable, a set of Jovian DAM emission occurrence probabilities can be created. These probabilities are usefully plotted as a function of Jovian system III (magnetospheric) central meridian longitude (CML-III) and Io's phase measured from superior geocentric conjunction (SGC), producing a CML-Io phase plane. It has been known since 1964 that Jovian DAM tends to have higher occurrence probabilities in different regions of the CML-Io phase plane, leading to the identification of different Io-related and non-Io-related DAM components.

AJ4CO Observatory, located in High Springs, Florida, USA, has been observing Jupiter when it is within ~4.5 hours of transit since October, 2013. The primary instrument used for observing Jovian DAM is a swept-frequency (16 to 32 MHz) dual polarization spectrograph fed by an eight-element phased array of terminated folded dipoles. A high-speed digital spectrograph with a tunable 2 MHz bandwidth was also used from 2013 to 2016 to observe emission at higher time resolution.

We analyze the dynamic spectra of Jovian DAM observed at AJ4CO Observatory from 2013 through 2020 to measure emission timing intervals and classify the emission into four types: L (for wideband L bursts), S (for wideband S bursts), N (for narrowband continuous emission), and T (for narrowband trains of S bursts).

For this presentation, we show CML-Io phase plane probabilities categorized by radio frequency, polarization, emission type, and emission arc shape. We show how the various high-probability DAM regions within the phase plane change with each parameter and with various combinations of parameters. We present updated definitions of the DAM component phase plane boundaries and discuss how the DAM components appearing in various parts of the CML-Io phase plane may differ from one another.