TY - JOUR

T1 - Conjugate observations of Saturn’s northern and southern H3+ aurorae

AU - O'Donoghue, James

AU - Stallard, Tom S.

AU - Melin, Henrik

AU - Cowley, Stan W. H.

AU - Badman, Sarah V.

AU - Moore, Luke

AU - Miller, Steve

AU - Tao, Chihiro

AU - Baines, Kevin H.

AU - Blake, James

PY - 2014/2

Y1 - 2014/2

N2 - 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.

AB - 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.

KW - Saturn

KW - Aurorae

KW - Magnetosphere

KW - Ionosphere

KW - Aeronomy

U2 - 10.1016/j.icarus.2013.11.009

DO - 10.1016/j.icarus.2013.11.009

M3 - Journal article

VL - 229

SP - 214

EP - 220

JO - Icarus

JF - Icarus

SN - 0019-1035

ER -