Ground-based observations of Saturn's auroral ionosphere over three days: Trends in HI temperature, density and emission with Saturn local time and planetary period oscillation

摘要

On 19-21 April 2013, the ground-based 10-m W.M. Keck II telescope was used to simultaneously measure HI emissions from four regions of Saturn's auroral ionosphere: (1) the northern noon region of the main auroral oval; (2) the northern midnight main oval; (3) the northern polar cap and (4) the southern noon main oval. The H-3(+) emission from these regions was captured in the form of high resolution spectral images as the planet rotated. The results herein contain twenty-three H-3(+) temperatures, column densities and total emissions located in the aforementioned regions - ninety-two data points in total, spread over timescales of both hours and days. Thermospheric temperatures in the spring-time northern main oval are found to be cooler than their autumn-time southern counterparts by tens of K, consistent with the hypothesis that the total thermospheric heating rate is inversely proportional to magnetic field strength. The main oval H-3(+) density and emission is lower at northern midnight than it is at noon, in agreement with a nearby peak in the electron influx in the post-dawn sector and a minimum flux at midnight. Finally, when arranging the northern main oval H-3(+) parameters as a function of the oscillation period seen in Saturn's magnetic field the planetary period oscillation (PPO) phase - we see a large peak in H-3(+) density and emission at similar to 115 degrees northern phase, with a full-width at half-maximum (FWHM) of similar to 44 degrees. This seems to indicate that the influx of electrons associated with the PPO phase at 90 is responsible at least in part for the behavior of all H(3)(+)parameters. A combination of the H-3(+) production and loss timescales and the 10 uncertainty in the location of a given PPO phase are likely, at least in part, to be responsible for the observed peaks in H-3(+) density and emission occurring at a later time than the peak precipitation expected at 90 PPO phase. (C) 2015 Elsevier Inc. All rights reserved.