Simultaneous Infrared Observations of the Jovian Auroral Ionosphere and Thermosphere

Abstract

Simultaneous observations of $H_3^{+}$ and $H_2$ in Jupiter's northern infrared aurora were conducted on 02 June 2017 using Keck-NIRSPEC to produce polar projection maps of $H_3^{+}$ radiance, rotational temperature, column density, and $H_2$ radiance. The temperature variations within the auroral region are $\sim 700-1000$ K, generally consistent with previous studies, albeit with some structural differences. Known auroral heating sources including particle precipitation, Joule heating, and ion drag have been examined by studying the correlations between each derived quantity, yet no single dominant mechanism can be identified as the main driver for the energetics in Jupiter's northern auroral region. It appears that a complex interaction exists between the heating driven by various mechanisms and the cooling from the $H_3^{+}$ thermostat effect. Comparisons between the $H_3^{+}$ temperature and the line-of-sight ion velocity in the reference frame of (a) the planetary rotation and (b) the neutral atmosphere further suggest that the local thermodynamic equilibrium effect may play an important role in thermospheric heating at Jupiter. Along with previously reported heating events that occurred in both the lower and upper atmosphere, it is speculated that the heating source may originate from an altitude above Jupiter's stratosphere but below the peak altitude of $H_3^{+}$ overtone and $H_2$ quadrupole emissions.