Detection and Characterization of Circular Expanding UV-Emissions Observed in Jupiter's Polar Auroral Regions

Abstract

Jupiter's polar auroral region hosts UV auroral emissions that relate to the magnetospheric dynamics from the outer magnetosphere. Juno-UVS has discovered intriguing features characterized by expanding emission circles of UV-brightness <140 kR. These events are located at the border of the previously defined swirl region, nearby the polar dark region. The features expand into a circular shape up to ∼1,000 km in radius, at expansion velocities from 3.3 ± 1.7 up to 7.7 ± 3.5 km/s, as measured over the four best observed cases. Using color ratio measurements as a proxy for the depth of the recorded features, the mean electron energy responsible for these emissions is 80–160 keV. Events occurring in the outer magnetosphere at distances >100 RJ are likely causing for these features. Dayside magnetopause reconnection and Kelvin-Helmholtz instabilities resulting from the shear flows near the magnetopause are expected to generate field-aligned currents that could potentially be the cause of these features.