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