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

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 R_J 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.