Local time dependence of Jovian radio emissions observed by Galileo

Galileo has been in orbit around Jupiter since December 1995. All the orbit s are equatorial and elliptical, with apogees between 60 R-J - 142 R-J and perigees from 8 - 12 R-J. Since orbit injection, the plasma wave instrument (PWS) has been collecting data over specific intervals of each of the orbi ts at all local times and a range of different radial distances. We present the results of a survey of the data for the frequency range 300 kHz to 5.6 MHz, which includes the hectometric (HOM) and low-frequency decametric (DA M) emissions. The results indicate that both the HOM and DAM emission are m ore intense and occur more frequently in the midnight sector of Jupiter. Th is is in analogy to Earth and consistent with a magnetic substorm source fo r a portion of the radio emissions in this frequency range. Another peak in the power levels is observed on the Jovian dayside in the local time range 11 hrs. < LT < 12 hrs. This peak does not have a terrestrial counterpart. We speculate that this dayside peak may be a result of sampling near perige e, but we cannot rule out the possibility that this is not the case.