TY - JOUR

T1 - Saturn's northern auroras and their modulation by rotating current systems during late northern spring in early 2014

AU - Kinrade, Joe

AU - Badman, Sarah Victoria

AU - Provan, G.

AU - Cowley, S. W. H.

AU - Lamy, Laurent

AU - Bader, Alexander

N1 - This is a peer reviewed version of an article which has been published in final form at https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018JA025426 This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for self-archiving.

PY - 2018/8/1

Y1 - 2018/8/1

N2 - The Hubble Space Telescope imaged Saturn's northern ultraviolet auroras during February‐June 2014, when Saturn's northern and southern magnetic perturbation fields were locked in anti‐phase and matched in rotation period (~10.69 h). During this coalescence period, we test for evidence of rotational modulation of the auroras using the latest rotating current system model and kilometric radio phases derived from Cassini measurements. While we see modulation of auroral intensity in the rotating frames of the planetary period current systems, the pattern is opposite to that expected and is dominated by an asymmetric local time profile that peaks at dawn. Enhancement of the north emission by rotating upward field aligned currents (FACs) is expected to peak at magnetic longitudes of ~90°, whereas here the intensity increased at ~270°. This unexpected finding is attributed to the presence of non‐PPO dynamics having affected the auroral morphology, together with insufficient sampling of the rotational system orientations provided during such HST campaigns. Rotational modulation is clearest at dawn regardless of the pattern's orientation, suggesting that the physical relationship between rotating FACs and auroral intensity is not direct, having a local time dependence that is not generally observed in the rotating FAC magnitudes. We also find no statistically significant planetary period oscillation of the auroral circle position, but the mean centre was offset from the spin pole by ~3° latitude toward early morning local times. Mean auroral boundaries were located at equatorward and poleward colatitudes of 15.0±2.8° and 12.4±3.0°.

AB - The Hubble Space Telescope imaged Saturn's northern ultraviolet auroras during February‐June 2014, when Saturn's northern and southern magnetic perturbation fields were locked in anti‐phase and matched in rotation period (~10.69 h). During this coalescence period, we test for evidence of rotational modulation of the auroras using the latest rotating current system model and kilometric radio phases derived from Cassini measurements. While we see modulation of auroral intensity in the rotating frames of the planetary period current systems, the pattern is opposite to that expected and is dominated by an asymmetric local time profile that peaks at dawn. Enhancement of the north emission by rotating upward field aligned currents (FACs) is expected to peak at magnetic longitudes of ~90°, whereas here the intensity increased at ~270°. This unexpected finding is attributed to the presence of non‐PPO dynamics having affected the auroral morphology, together with insufficient sampling of the rotational system orientations provided during such HST campaigns. Rotational modulation is clearest at dawn regardless of the pattern's orientation, suggesting that the physical relationship between rotating FACs and auroral intensity is not direct, having a local time dependence that is not generally observed in the rotating FAC magnitudes. We also find no statistically significant planetary period oscillation of the auroral circle position, but the mean centre was offset from the spin pole by ~3° latitude toward early morning local times. Mean auroral boundaries were located at equatorward and poleward colatitudes of 15.0±2.8° and 12.4±3.0°.

U2 - 10.1029/2018JA025426

DO - 10.1029/2018JA025426

M3 - Journal article

VL - 123

JO - Journal of Geophysical Research: Space Physics

JF - Journal of Geophysical Research: Space Physics

SN - 2169-9402

ER -