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Astron. Astrophys. 319, 282-289 (1997)


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The radiation belts of Jupiter at 13 and 22 cm

II. The asymmetries and the magnetic field

G.A. Dulk 1, 2, Y. Leblanc 1, R.J. Sault 3, H.P. Ladreiter 4 and J.E.P. Connerney 5

1 CNRS-URA 264, Departement de Recherche Spatiale, Observatoire de Paris, F-92195 Meudon, France
2 Department of Astrophysical, Planetary and Atmospheric Sciences, University of Colorado, Boulder, CO 80309, USA
3 Australia Telescope National Facility, CSIRO, Epping, NSW 2121, Australia
4 Space Research Institute, University of Graz, Graz, Austria
5 Planetary Magnetospheres Branch, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA

Received 11 April 1996 / Accepted 17 June 1996

Abstract

Observations of Jupiter at 13 and 22 cm made with the Australia Telescope in July 1995, reported in Paper I (Leblanc et al. 1996), are interpreted by comparing with models of the magnetic field. The field models used are the O6 and a new, 4th degree and order model due to one of us (JEPC), denoted H4.

1) From our 3-D reconstruction we derive the variation with longitude [FORMULA] of the latitude and radial distance of peak radio emissivity: [FORMULA], and [FORMULA]   [FORMULA]. These values are in good agreement with the location of the magnetic equator on a surface of constant total field [FORMULA]  G.

2) We present the variation with [FORMULA] of the latitude and radial distance of high-latitude peaks in linearly-polarized brightness from a similar 3-D reconstruction. Comparing with calculations from the H4 model, these "mirror points" are in good accord with calculated latitudinal and radial variations for electrons with pitch angle [FORMULA] on L shell [FORMULA]   [FORMULA].

3) The variations with [FORMULA] (Paper I) of the brightness of regions traversing the east and west limbs (the east-west asymmetry) are compared with field model calculations that take into account the warp of the magnetic equator, i.e. the magnetic declination [FORMULA] and the Earth's jovicentric declination [FORMULA] that was [FORMULA] during our observations. The generally excellent agreement allows us to account for the brightness minimum near [FORMULA], the maximum near [FORMULA], and the fact that the bright spot near [FORMULA] is fainter when crossing the west limb than when crossing the east limb.

4) From the results of (3) we are able to predict the form of the east-west asymmetry when the Earth is at other declinations, up to [FORMULA]. Some published results substantiate the prediction.

The observations are in better agreement with model H4 than with O6. The discrepancies that remain can be used to improve the field models or further explore the properties of the synchrotron-emitting electrons.

Key words: Jupiter – radio emission – magnetosphere – radiation belts

Send offprint requests to: G.A. Dulk

© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998

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