Multifrequency analysis of the Jovian electron-belt radiation during the Cassini flyby of Jupiter

¹ Southwest Research Institute, Space Science Department, San Antonio, Texas, USA
e-mail: dsantoscosta@swri.edu; sbolton@swri.edu
² Berkeley Astronomy Department, University of California, Berkeley Ca, USA
e-mail: imke@berkeley.edu
³ The University of Melbourne, 3010 Victoria, Australia
e-mail: rsault@nrao.edu
⁴ Jet Propulsion Laboratory/Caltech, Pasadena Ca, USA
e-mail: michael.janssen@jpl.nasa.gov; steven.m.levin@jpl.nasa.gov

Received: 27 March 2014
Accepted: 10 June 2014

Abstract

Aims. We examine Very Large Array (VLA) observations of Jupiter to present evidence of fluctuations in the emission produced by the electron belt in January 2001. Investigating the source of fluctuations will provide new opportunities to discuss the scenarios of temporal changes in Jupiter’s synchrotron radiation (i.e., the electron belt) in future data analysis and modeling work.

Methods. To discuss the electron belt dynamics during the Cassini flyby of Jupiter, we compare the radio measurements from 2−3 January 2001 with VLA observations obtained on 20−21 December 1988, when viewing geometry and array configuration are comparable. All data are scaled to a standard Earth-Jupiter distance of 4.04 AU for comparison purposes. Brightness distribution maps with identical spatial resolutions and cartography of the equatorial radiation are constructed and examined at the wavelengths of ~21 cm and ~90 cm.

Results. Rotation-averaged maps show that the emission from the equatorial zones of maximum intensity is weaker by ~5−40%, but the brightness distribution is spatially more extended on 2−3 January 2001, resulting in a total emission at both wavelengths stronger by ~35%. Between observation periods, the brightness distributions are observed to evolve differently during the planet rotation. Tomographic reconstructions of the equatorial radiation support our conclusion that the electron-belt population was differently distributed around the planet in December 1988 and January 2001.

Conclusions. Our analysis of VLA data sets suggests that the spatial distribution of the electron belt on 2−3 January 2001 is different from that usually observed. Our knowledge of solar activity at the time of the Cassini flyby of Jupiter suggests that the emission from the electron radiation belt was responding to external influences, most likely to solar wind structures rather than to solar radio flux, on a timescale of days to a couple of weeks. Combined results from a multisource data analysis – including spacecraft and radio observations – are needed to confirm this relationship.