Jay Alan Ansher

Anisotropy and proton density in the Io plasma torus derived from whistler wave dispersion

During the Voyager 1 encounter with Jupiter, a large number of whistler waves were observed. Previous studies have examined the dispersion of these waves and made estimates of the electron and light ion (i.e., proton) densities. The current paper reexamines this data, taking into account the revised temperatures of the torus species the additional data on ion composition from the Voyager UVS instrument and the role of thermal anisotropy on the plasma densities. These refinements in the density model drastically alter the implications of the whistler wave data. Both the thermal and the nonthermal species must be anisotropic to fit the whistler dispersions. The thermal component must have T⊥/T‖ > 1.75 and the nonthermal component 3 < T⊥/T‖ < 10, The equatorial proton density is low, under 60 cm−3 in all cases. This results in a proton abundance (L shell proton content relative to the total ion content) of no more than 10%, approximately a factor of two lower than the conclusions of previous whistler analysis. At the high latitudes, the implied electron density results in a plasma frequency of under 20 kHz. Finally, it is evident from this analysis that not all of the whistler waves were propagating along the magnetic field lines, as was commonly assumed in previous work.

Determination of the quiet time current sheet thickness using Geotail CPI data and nonlinear dynamics modeling

[1] In this paper we present a survey of the quiet (Kp < 1+) current sheet thickness for X GSE between -20 R E and -80 R E as determined from an ion distribution function signature of nonlinear particle dynamics in current sheet-like magnetic fields. The signature manifests itself as a series of peaks in the ion distribution function whose separation depend on the fourth root of the energy and parameters that describe the current sheet structure. We have found clear evidence of the distribution function signature throughout the entire region of interest. Analysis of the data shows that the current sheet thickness is remarkably uniform in the region under study with an average thickness of 0.76 ± 0.56 R E . This result is consistent with measurements of the quiet time current sheet thickness made using other techniques.