Characterization of Jovian hectometric sources with Juno: statistical position and generation by shell-type electrons

Abstract

The Juno orbiter has been exploring the polar magnetosphere of Jupiter since mid-2016. Thanks to its unique polar trajectory, it has crossed regularly the north- ern and southern sources of auroral hectometric radiation, acquiring pioneer radio, magnetic and electron in situ measurements. By conducting a survey of the first 10 perijoves, we show evidence of a systematic spatial conjugacy between the crossed hectometric sources and the zone of diffuse aurora. In the framework of the elec- tron Cyclotron Maser Instability (CMI), we used electron distribution functions measured by JADE-E to derive (i) the CMI expected growth rate, (ii) the asso- ciated electron energy and (iii) the emission frequency. We then compared these values to the wave properties measured by Waves. In addition to the two CMI sources of free energy already identified in the literature (loss cone and conics), we show that shell-type electrons of about 1—5 keV are driving emission below the electron cyclotron frequency (as at Earth and Saturn).