Reply to Comment by Lamy et al. on “Locating the source field lines of Jovian decametric radio emissions”

At Jupiter, part of the auroral radio emissions are controlled by the Galilean moons Io,&#160;Europa and Ganymede. Until now, they have been remotely detected using ground-based radio-telescope or electric antenna aboard spacecraft. The polar trajectory of the Juno&#160;orbiter leads to cross the magnetic flux tube connected to these moons, or their tail, and&#160;gives a direct in-situ measurements of the characteristics of these decametric moon induced radio emissions&#160;(such as the electron population, size of the source, and beaming&#160;angle and growth rate of the emission). In this study,&#160;we focus on the crossing of the Ganymede flux tube. The study of Juno/JADE-E and&#160;Juno/Waves data leads to an estimated source size of a few 100s km,&#160;an electron population of energy&#160;E= 8&#177;2 keV and an emission beaming angle&#160;of&#160;&#952;= 80&#177;2&#176;&#160;from the magnetic field lines. Finally, this crossing of a decametric radio emission induced by a moon brings us new constrains on the Cyclotron Maser Instability process

Download Full-text

The low-frequency source of Saturn’s kilometric radiation

Science ◽

10.1126/science.aat2027 ◽

2018 ◽

Vol 362 (6410) ◽

pp. eaat2027 ◽

Cited By ~ 9

Author(s):

L. Lamy ◽

P. Zarka ◽

B. Cecconi ◽

R. Prangé ◽

W. S. Kurth ◽

...

Keyword(s):

Source Region ◽

Low Frequency ◽

Auroral Oval ◽

Emission Region ◽

Radio Emissions ◽

Cyclotron Maser ◽

Frequency Source ◽

Field Lines ◽

Plasma Measurements

Understanding how auroral radio emissions are produced by magnetized bodies requires in situ measurements within their source region. Saturn’s kilometric radiation (SKR) has been widely used as a remote proxy of Saturn’s magnetosphere. We present wave and plasma measurements from the Cassini spacecraft during its ring-grazing high-inclination orbits, which passed three times through the high-altitude SKR emission region. Northern dawn-side, narrow-banded radio sources were encountered at frequencies of 10 to 20 kilohertz, within regions of upward currents mapping to the ultraviolet auroral oval. The kilometric waves were produced on the extraordinary mode by the cyclotron maser instability from 6– to 12–kilo–electron volt electron beams and radiated quasi-perpendicularly to the auroral magnetic field lines. The SKR low-frequency sources appear to be strongly controlled by time-variable magnetospheric electron densities.

Download Full-text