TY - JOUR

T1 - Ground-based observations of Saturn’s auroral ionosphere over three days

T2 - trends in H3+ temperature, density and emission with Saturn local time and planetary period oscillation

AU - O’Donoghue, James

AU - Melin, Henrik

AU - Stallard, Tom S.

AU - Provan, G.

AU - Moore, Luke

AU - Badman, Sarah V.

AU - Cowley, Stan W.H.

AU - Baines, Kevin H.

AU - Miller, Steve

AU - Blake, James S.D.

N1 - This is the author’s version of a work that was accepted for publication in Icarus. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Icarus, 263, 2016 DOI: 10.1016/j.icarus.2015.04.018

PY - 2016/1/1

Y1 - 2016/1/1

N2 - On 19–21 April 2013, the ground-based 10-m W.M. Keck II telescope was used to simultaneously measure View the MathML sourceH3+ 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 View the MathML sourceH3+ emission from these regions was captured in the form of high resolution spectral images as the planet rotated. The results herein contain twenty-three View the MathML sourceH3+ 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 View the MathML sourceH3+ 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 View the MathML sourceH3+ 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 View the MathML sourceH3+ density and emission at ∼115° northern phase, with a full-width at half-maximum (FWHM) of ∼44°. 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 View the MathML sourceH3+ parameters. A combination of the View the MathML sourceH3+ 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 View the MathML sourceH3+ density and emission occurring at a later time than the peak precipitation expected at 90° PPO phase.

AB - On 19–21 April 2013, the ground-based 10-m W.M. Keck II telescope was used to simultaneously measure View the MathML sourceH3+ 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 View the MathML sourceH3+ emission from these regions was captured in the form of high resolution spectral images as the planet rotated. The results herein contain twenty-three View the MathML sourceH3+ 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 View the MathML sourceH3+ 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 View the MathML sourceH3+ 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 View the MathML sourceH3+ density and emission at ∼115° northern phase, with a full-width at half-maximum (FWHM) of ∼44°. 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 View the MathML sourceH3+ parameters. A combination of the View the MathML sourceH3+ 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 View the MathML sourceH3+ density and emission occurring at a later time than the peak precipitation expected at 90° PPO phase.

KW - Ionosphere

KW - Saturn

KW - Aurora

KW - Magnetosphere

U2 - 10.1016/j.icarus.2015.04.018

DO - 10.1016/j.icarus.2015.04.018

M3 - Journal article

VL - 263

SP - 44

EP - 55

JO - Icarus

JF - Icarus

SN - 0019-1035

ER -