Astron. Astrophys. 347, 1039-1045 (1999)

Jupiter's magnetic field as revealed by the synchrotron radiation belts

II. Change of the 2-D brightness distribution with

G.A. Dulk ¹, Y. Leblanc ¹, R.J. Sault ² and S.J. Bolton <sup>3

1</sup> CNRS-URA 264, Departement de Recherche Spatiale, Observatoire de Paris, F-92195 Meudon, France
² Australia Telescope National Facility, CSIRO, Epping, NSW 1710, Australia
³ Jet Propulsion Laboratory, Pasadena, CA, USA

Received 29 March 1999 / Accepted 30 April 1999

Abstract

We analyze the magnetic equatorial component of Jupiter's radio synchrotron radiation belts using two-dimensional images recorded by the Australia Telescope Compact Array and the Very Large Array over a period of several years, during which , the Earth's declination seen from Jupiter, changed from to near 0^o. The brightness distribution of the belts changed markedly. When there is a pronounced east-west asymmetry where the brightness of a region traversing the east limb is markedly different from that of the same region traversing the west limb, 180^o of rotation later. At most longitudes the brightness at east limb passage is larger than at west limb passage. However, when , the east-west asymmetry essentially disappears. When it is predicted that the east-west asymmetry will be as at -2.9^o, but reversed.

We show how these changes of appearance are simply related to and the warp of Jupiter's field as described by the "magnetic declination". The radius, latitude and brightness of the locus of maximum intensity is determined by electrons of pitch angle , and its longitudinal variation depends entirely on the magnetic field of Jupiter, and not on the energy distribution of the relativistic electrons. We compare the observations with calculations from three magnetic field models and find them to be consistent in general but discrepant in detail. The differences are attributed to uncertainties in the field models, which were generated with few constraints coming from the low latitudes and small radii of the synchrotron radiation belts.

Key words: magnetic fields plasmas radiation mechanisms: non-thermal planets and satellites: individual: Jupiter radio continuum: solar system

Send offprint requests to: G.A. Dulk

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Contents

• 1. Introduction
• 2. Observations and imaging
  • 2.1. Sample images showing the east-west asymmetry
  • 2.2. Brightness vs. in the dipole equator
• 3. Brightness and the magnetic field
  • 3.1. Brightness and in the dipole equator
  • 3.2. Brightness and in the true magnetic equator
  • 3.3. Residual asymmetry at
  • 3.4. Radius and latitude of the magnetic equator of 1.2 G
• 4. Discussion and conclusion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: June 6, 1999
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