Conjugate observations of Saturn’s northern and southern H3+ aurorae

O'Donoghue, James and Stallard, Tom S. and Melin, Henrik and Cowley, Stan W. H. and Badman, Sarah V. and Moore, Luke and Miller, Steve and Tao, Chihiro and Baines, Kevin H. and Blake, James (2014) Conjugate observations of Saturn’s northern and southern H3+ aurorae. Icarus, 229. pp. 214-220. ISSN 0019-1035

Abstract

We present an analysis of recent high spatial and spectral resolution ground-based infrared observations of H3+ obtained with the 10-m Keck II telescope in April 2011. We observed H3+ emission from Saturn’s northern and southern auroral regions, simultaneously, over the course of more than 2 h, obtaining spectral images along the central meridian as Saturn rotated. Previous ground-based work has derived only an average temperature of an individual polar region, summing an entire night of observations. Here we analyse 20 H3+ spectra, 10 for each hemisphere, providing H3+ temperature, column density and total emission in both the northern and southern polar regions simultaneously, improving on past results in temporal cadence and simultaneity. We find that: (1) the average thermospheric temperatures are 527 ± 18 K in northern Spring and 583 ± 13 K in southern Autumn, respectively; (2) this asymmetry in temperature is likely to be the result of an inversely proportional relationship between the total thermospheric heating rate (Joule heating and ion drag) and magnetic field strength – i.e. the larger northern field strength leads to reduced total heating rate and a reduced temperature, irrespective of season, and (3) this implies that thermospheric heating and temperatures are relatively insensitive to seasonal effects.