Concurrent ultraviolet and infrared observations of the north Jovian aurora during Juno’s first perijove

The UltraViolet Spectrograph (UVS) and the Jupiter InfraRed Auroral Mapper
(JIRAM) observed the polar aurora during the perijove phase of the first Juno orbit (PJ1)
on 27 August 2016. The UVS passband includes H2 bands that are directly excited by
collisions of auroral electrons with H2. The JIRAM L-band imager includes some of the
brightest H3+ features between 3.3 and 3.6
μ
m. The intensity if this IR emission depends on
both the column density of H3+ and the temperature in the emitting region. A series of
spatial scans obtained every 30 s is used to build up images of the polar regions. JIRAM’s
spatial resolution was about 100 km/pixel during most of the observations reported here
while UVS has a substantially lower resolution (about 250 km/pixel). Concurrent
observations were obtained during about 70 min in the north. We present a set of
simultaneous ultraviolet and infrared images and point out similarities and di
ff
erences in
their morphology and brightness distribution. The time evolution in the two spectral
domains will be described and interpreted in terms of energy of the auroral electrons, time
history of the precipitation and lifetime of the H3+ ions. Ultraviolet color ratio maps
visualize the spatial distribution of the characteristic energy of the primary auroral electrons.
Other supporting information is provided by the H3+ temperatures and column density
maps derived from the analysis of JIRAM spectra covering the 2-5 μm interval.