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Three‐dimensional convective flows of energetic ions in Jupiter's equatorial magnetosphere
Author(s) -
Waldrop L. S.,
Roelof E. C.,
Fritz T. A.
Publication year - 2015
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2015ja021103
Subject(s) - magnetosphere , physics , plasma sheet , jovian , convection , jupiter (rocket family) , geophysics , solar wind , plasma , astrophysics , computational physics , saturn , mechanics , astronomy , nuclear physics , planet , spacecraft
From 1995 to 2003, the Galileo Energetic Particles Detector (EPD) measured the three‐dimensional distribution of protons, oxygen, and sulfur ions with total energies between 0.1 and 1 MeV throughout the equatorial Jovian magnetosphere. We perform a spherical harmonics expansion of the measured distributions through the second order and use the resulting anisotropy coefficients to identify purely convecting distributions and derive ion flow velocities via the Compton‐Getting effect. We demonstrate that the second‐order harmonic terms are an essential diagnostic in excluding spurious gradient anisotropies in the velocity derivation. This analysis unambiguously confirms that energetic ion flows in the azimuthal direction are significantly slower than rigid planetary corotation by an amount that is local time dependent, a phenomenon that is qualitatively consistent with expectations of plasma mass loading within an asymmetric magnetic field configuration. However, both the polar and radial components of the ion flows exhibit unexpected and poorly understood global morphology. Consistently northward and inward flows are observed near the dayside and predusk sectors of the equatorial inner magnetosphere, while southward and outward flows are observed within the plasma sheet in the predawn middle magnetosphere. The persistence of southward convection in this region, which is operative regardless of whether the spacecraft was transiting the plasma sheet from the northern magnetic lobe or from the southern lobe, is inconsistent with contemporary models of dynamical plasma sheet motion, while the distinctive local time asymmetries imply that the solar wind is a significant driver of plasma convection at radial distances as small as 15 R J .