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Electron Signatures of Satellite Sweeping in the Magnetosphere of Uranus

Cooper, J. F. and Stone, E. C. (1991) Electron Signatures of Satellite Sweeping in the Magnetosphere of Uranus. Journal of Geophysical Research A, 96 (A5). pp. 7803-7821. ISSN 0148-0227. doi:10.1029/90JA02629.

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The Voyager 2 Cosmic Ray System found large-scale macrosignatures of satellite sweeping for MeV electrons near the orbits of the satellites Miranda, Ariel, and Umbriel in the magnetosphere of Uranus. Due to the large magnetic inclinations of satellite orbits at Uranus, sweeping rates vary along the orbits with the McIlwain L parameter. However, no evidence was found, where expected, for fresh sweeping signatures at such positions. Although the maximal electron intensity occurs near Voyager 2's minimum L (4.67) as predicted by the Q_3 field model, the intensity minima in the macrosignatures show large outward displacements (≤0.5 R_U) from minimum-L positions of the associated satellites. These radial displacements increased with measured electron energy and at higher magnetic latitudes. Pitch angle distributions are generally more anisotropic outside the macrosignatures and more isotropic within, as determined from comparison of inbound and outbound intensity profiles at different latitudes. These anisotropy measurements provide the basis for latitudinal flux extrapolation, which when coupled with power law scaling of spectral distributions allow the calculation of phase space density profiles. The latter show local minima in the macrosignatures and are indicative of distributed electron sources in the inner magnetosphere and/or nonadiabatic transport processes such as pitch angle scattering and magnetospheric recirculation. Preliminary diffusion coefficients with values D_(LL) ∼ 10^(−7)–10^(−6) RS² and radial dependence D_(LL) ∼ L^3–L^4 have been estimated for the macrosignatures. The low-order L dependence of D_(LL) is consistent with diffusion driven by ionospheric dynamo. However, quantitative modeling of radial and pitch angle diffusion is required to assess the formative processes for the macrosignatures before more physically meaningful transport parameters can be determined.

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Additional Information:Copyright 1991 by the American Geophysical Union. (Received January 2, 1990; revised November 16, 1990; accepted November 21, 1990.) We thank R. E. Vogt for his contributions during the Jupiter and Saturn encounters as principal investigator for the CRS. Our present work owes a great debt to D. L. Chenette' s pioneering contributions to CRS data analysis during the encounter with Uranus. We are also indebted to M. Acufia, J. E. P. Connerney, and N. Ness for providing B and L coordinates prior to publication for Voyager 2 and the satellites from the Q_3 model for the planetary magnetic field. We thank A. C. Cummings, M. Tranh, D. Burke, and J. Weger of Caltech for technical assistance in the performance of laboratory experiments to evaluate the responses of CRS detectors to energetic electrons. The continued productivity of the CRS experiment has also been due in part to technical support provided by W. E. Althouse, T. Garrard, and R. Burrell at Caltech, N. Lal at Goddard Space Flight Center, and O. Divers at the Jet Propulsion Laboratory. The principal data analysis for this report was carded out during J. Cooper's residence as a postdoctoral fellow at Caltech under the support of NASA contracts NAS7-918 and NGR 05-002-160. J.F.C. also thanks J.P. Wefel of the Department of Physics and Astronomy at Louisiana State University for cooperation and support during completion of the final manuscript. Partial support was provided at LSU by ONR grant N-00014-90-J-1466 and NASA grant NAG 2-528. Additional support was provided to J. Cooper by ST Systems Corporation (STX). The Editor thanks L. Hood and B. Randall for their assistance in evaluating this paper.
Group:Space Radiation Laboratory
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NASANGR 05-002-160
ST Systems Corporation (STX)UNSPECIFIED
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Space Radiation Laboratory1989-31
Issue or Number:A5
Record Number:CaltechAUTHORS:20140505-091935345
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ID Code:45480
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Deposited On:05 May 2014 23:50
Last Modified:10 Nov 2021 17:04

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