Computer Science
Scientific paper
Nov 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt.........9f&link_type=abstract
Thesis (PHD). THE UNIVERSITY OF MICHIGAN , Source DAI-B 58/05, p. 2472, Nov 1997, 110 pages.
Computer Science
Magnetosphere
Scientific paper
The high latitude ionosphere and polar wind outflow at Saturn were studied with a sophisticated numerical model. The importance of the polar wind as a source of plasma to the Saturnian magnetosphere was analyzed. In addition, we wished to better understand the data that was taken during the fly-by missions to Saturn, and we developed a tool that may be used in future studies during the Cassini mission. The time-dependent and gyrotropic continuity, momentum, and energy equations with heat flow were solved for a quasineutral, currentless plasma comprised of H+ and H3+ ions. In addition, the electron temperature equation was solved. This coupled set of equations was solved with a combination Godunov and Crank-Nicolson scheme. The model was run to steady-state with several neutral atmospheric temperatures (Tn) and variations on the densities of the neutral species. The model produced reasonable agreement with electron densities derived from Voyager 1 radio occultation data at 73o at and above the observed peak with a neutral atmosphere that was consistent with observations. In order to match the observed profile throughout the entire observed region, it was necessary to include additional losses due to either methane or water at lower altitudes, and to increase the source of ions (by increasing the amount of H2). Plasma is expected to be transported upward above ≈2000 km, and steady-state fluxes to the magnetosphere were estimated to be on the order of 2× 107/ cm-2s-1. With a downward heat flux of 20× 10-3 ergs cm-2s-1 applied to the electrons at the top of the simulation, their temperature reached values of ≈7000 K. The temperatures of the positive species significantly departed from the neutral temperature at altitudes of ≈3000-3500 km above the 1-bar pressure level (nH2≈ 108) when Tn = 800 and 1000 K. Time-dependent simulations revealed that H+ is the dominant ion throughout most of the ionosphere 3 hours after the sun sets, and that the altitude of the electron peak rises during the night. An asymmetry in the source of H3+ to the magnetosphere is expected, as the flux of H3+ becomes negligible by the end of the night.
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