Conjugate observations of Saturn’s northern and southern H[superscript + subscript 3] aurorae

We present an analysis of recent high spatial and spectral resolution ground-based infrared observations of H[superscript + subscript 3] obtained with the 10-m Keck II telescope in April 2011. We observed H[superscript + subscript 3] 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 H[superscript + subscript 3] spectra, 10 for each hemisphere, providing H[superscript + subscript 3] 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.

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