Jovian longitudinal control of Io-related radio emissions

Journal Article · Mon Jan 15 04:00:00 EST 1979 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/156777· OSTI ID:6463754

Dessler, A J; Hill, T W

We propose a theoretical model to explain the control that Jupiter's rotational phase exercizes over Io-related radio emissions. Longitudinal asymmetries in the conductivity and electron content of Jupiter's ionosphere are generated by variations in the mirror altitudes of energetic electrons trapped in Jupiter's magnetosphere. Energetic electrons are absorbed by the atmosphere preferentially in regions where, because of higher-order magnetic moments, the low-altitude magnetic field strength, and hence the mirror altitude of trapped particles, is a decreasing function of Jovian longitude. In such regions, the lower edge of the trapped radiation is lost into the atmosphere, and the resulting electron-impact ionization causes an increase in both the conductivity and the charged particle content of the ionosphere. When the flux tube threading Io passes into such regions of weakening surface magnetic field (specifically, a negative longitudinal gradient), a low-pressure electric arc can be struck in Jupiter's atmosphere that results in enhancement of the Birkeland (magnetically field-aligned) current between Io and the Jovian ionosphere. Thus Io excites detectable low-frequency (dekametric) radio emission when its flux tube encounters a relative weakening of the magnetic field strength at its foot. The location of the principal negative longitudinal gradient in the surface field strenght, as extrapolated from the Pioneer 11 flyby, is in reasonable accord with the longitude of the ionospheric region from which the principal Io-related emissions are observed to arise.

• Research Organization: Department of Space Physics and Astronomy, Rice University
• OSTI ID: 6463754
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 227:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640107* -- Astrophysics & Cosmology-- Planetary Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ATMOSPHERES
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELECTROMAGNETIC RADIATION
ELECTRONS
ELEMENTARY PARTICLES
FERMIONS
FLUID MECHANICS
HYDRODYNAMICS
IONIZATION
JUPITER PLANET
LEPTONS
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
MECHANICS
MOTION
PHYSICAL PROPERTIES
PLANETARY ATMOSPHERES
PLANETARY MAGNETOSPHERES
PLANETS
RADIATIONS
RADIOWAVE RADIATION
ROTATION