TY - GEN

T1 - Transient Flashes in Saturn’s UV Aurora

T2 - An Analysis of Hubble Space Telescope 2013-2017 Campaigns and Cassini Magnetic Field Measurements

AU - Qin, Tianshu

PY - 2022

Y1 - 2022

N2 - Transient flashes in Saturn’s auroral images correspond to ∼1 h quasiperiodic (QP) pulsations in in-situ particle and wave measurements at high latitudes. A previous investigation by Bader et al. (2019) showed these events mostly take place near dusk and link to magnetodisc reconnection. In this study, we examined northern auroral images from Hubble Space Telescope’s (HST) 2013-2017 campaigns, identified 29 short-lived, recurrent features and examined simultaneous magnetometer (MAG) data collected by the Cassini orbiter. We found, when HST observation cadence permitted, a flash lifetime of 4-17 min (subject to uncertainties related to exposure times), and a 40-70 min periodicity in occurrence. A heat map was constructed to illustrate the aggregate occurrence of transient auroral signatures, and it shows a strong preference in both local time, 14-19 LT, and latitude, 75-85 ̊. These transient flashes are identified in either the presence or absence of Saturn’s main auroral oval, indicating the lackingof dependence on the main emission power. The concurrent magnetic field pulsations generally take a sawtooth shape rather than a sinusoid, and the local field strength can experience a change varying significantly from 0.5 to 5.0 nT (depending on the range of Cassini). The QP pulsation events were all detected when the spacecraft was in the southern hemisphere and are usually seen with a less bent-back field, suggesting closed field lines in a more dipolar configuration. One of the identified field pulsation events (in 2014-100) indicates that these features could occur at the ∼21 LT region, in agreement with the spatial location of an identified, atypical flash (2016-232). We also found the ionospheric footprint of the spacecraft must be close to the region of flashes for magnetic field pulsations to be detected, indicating a localised rather than global driving process.

AB - Transient flashes in Saturn’s auroral images correspond to ∼1 h quasiperiodic (QP) pulsations in in-situ particle and wave measurements at high latitudes. A previous investigation by Bader et al. (2019) showed these events mostly take place near dusk and link to magnetodisc reconnection. In this study, we examined northern auroral images from Hubble Space Telescope’s (HST) 2013-2017 campaigns, identified 29 short-lived, recurrent features and examined simultaneous magnetometer (MAG) data collected by the Cassini orbiter. We found, when HST observation cadence permitted, a flash lifetime of 4-17 min (subject to uncertainties related to exposure times), and a 40-70 min periodicity in occurrence. A heat map was constructed to illustrate the aggregate occurrence of transient auroral signatures, and it shows a strong preference in both local time, 14-19 LT, and latitude, 75-85 ̊. These transient flashes are identified in either the presence or absence of Saturn’s main auroral oval, indicating the lackingof dependence on the main emission power. The concurrent magnetic field pulsations generally take a sawtooth shape rather than a sinusoid, and the local field strength can experience a change varying significantly from 0.5 to 5.0 nT (depending on the range of Cassini). The QP pulsation events were all detected when the spacecraft was in the southern hemisphere and are usually seen with a less bent-back field, suggesting closed field lines in a more dipolar configuration. One of the identified field pulsation events (in 2014-100) indicates that these features could occur at the ∼21 LT region, in agreement with the spatial location of an identified, atypical flash (2016-232). We also found the ionospheric footprint of the spacecraft must be close to the region of flashes for magnetic field pulsations to be detected, indicating a localised rather than global driving process.

KW - Aurora

KW - Magnetosphere

KW - Saturn

U2 - 10.17635/lancaster/thesis/1681

DO - 10.17635/lancaster/thesis/1681

M3 - Master's Thesis

PB - Lancaster University

ER -