decametric radio emission was discovered in 1955 by B.F. Burke and
K.L. Franklin at the frequency of 22.2 MHz. The emission has an upper cutoff
frequency of 39.5 MHz. It can be detected from ground-based stations from
the upper cutoff frequency of the emission down to the cutoff frequency
of the terrestrial ionosphere which is usually around 5 to 10 MHz.
The peak of the intensity of the emission occurs at around 8 MHz. The emission
occurs in episodes called "storms". A storm can last from a few minutes
to several hours.
Two distinctive types of bursts can be received during a storm. The L bursts (L for Long) are bursts that vary slowly in intensity with time. They last from a few seconds to several tens of seconds and have instantaneous bandwidth of a few MHz. The S bursts (S for Short) are very short in duration, have instantaneous bandwidth of a few kHz to a few tens of kHz, and drift downward in frequency at a rate of typically -20 MHz/sec. They arrive at rates from a few to several hundred bursts per second. In a 5 kHz bandwidth receiver they last for only a few milliseconds. Sometimes both types of bursts can be heard simultaneously.
In order to study the wide band structure of the Jovian decametric radio emission, the University of Florida operates a broadband radio spectrograph. The spectrograph covers the frequency range from 18 to 36 MHz and uses the conical log spiral array. Please click on the link below for examples of wide band dynamic spectra of Jovian decametric radio emission.
The Jovian decametric radio emission is always received against the galactic background radio emission. The galactic background radio emission is generated by relativistic electrons spiraling in the weak galactic magnetic field.
The probabilities of detecting the emission depend strongly on the values of the Jovian central meridian longitude (CML), the Io Phase, and the Jovicentric declination of the Earth (DE). The CML is the value of the System III longitude of Jupiter facing the Earth. The Io Phase is the angle of Io, one of Jupiter's moons, with respect to superior geocentric conjunction. The combination of CML and Io phase values that have increased probabilities of emission are called sources. The sources are named Io-A, Io-B, and Io-C for the Io-controlled emission and A, B, and C for the Non-Io controlled emission.
The emission is usually either right (RH) or left hand (LH) circularly or elliptically polarized, depending on the source.