Simultaneous UV Images and High-latitude Particle and Field Measurements
During an Auroral Dawn Storm at Jupiter
Abstract
We present multi-instrument Juno observations on day-of-year 86, 2017
that link particles and fields in Jupiter’s polar magnetosphere to
transient UV emissions in Jupiter’s northern auroral region known as
dawn storms. Juno ranged from 42ºN - 51ºN in magnetic latitude and 5.8
– 7.8 jovian radii (1 RJ = 71,492 km) during this period. These dawn
storm emissions consisted of two separate, elongated structures which
extended into the nightside, rotated with the planet, had enhanced
brightness (up to at least 1.4 megaRayleigh) and high color ratios. The
color ratio is a proxy for the atmospheric penetration depth and
therefore the energy of the electrons that produce the UV emissions.
Juno observed electrons and ions on magnetic field lines mapping to
these emissions. The electrons were primarily field-aligned,
bi-directional, and, at times, exhibited sudden intensity decreases
below ~10 keV coincident with intensity enhancements up
to energies of ~1000 keV, consistent with the high color
ratio observations. The more energetic electron distributions had
characteristic energies of ~160 – 280 keV and downward
energy fluxes (~70 – 135 mW/m2) that were a significant
fraction needed to produce the UV emissions for this event. Magnetic
field perturbations up to ~0.7% of the local magnetic
field showing evidence of upward and downward field-aligned currents,
whistler mode waves, and broadband kilometric radio emissions were also
observed along Juno’s trajectory during this timeframe. These high
latitude observations show similarities to those in the equatorial
magnetosphere associated with dynamics processes such as interchange
events, plasma injections, and/or tail reconnection.