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Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - Saturn's dayside ultraviolet auroras
T2 - Evidence for morphological dependence on the direction of the upstream interplanetary magnetic field
AU - Meredith, C. J.
AU - Alexeev, I. I.
AU - Badman, S. V.
AU - Belenkaya, E. S.
AU - Cowley, S. W. H.
AU - Dougherty, M. K.
AU - Kalegaev, V. V.
AU - Lewis, G. R.
AU - Nichols, J. D.
N1 - ©2014. American Geophysical Union. All Rights Reserved. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
PY - 2014/3
Y1 - 2014/3
N2 - We examine a unique data set from seven Hubble Space Telescope (HST) "visits" that imaged Saturn's northern dayside ultraviolet emissions exhibiting usual circumpolar "auroral oval" morphologies, during which Cassini measured the interplanetary magnetic field (IMF) upstream of Saturn's bow shock over intervals of several hours. The auroras generally consist of a dawn arc extending toward noon centered near similar to 15 degrees colatitude, together with intermittent patchy forms at similar to 10 degrees colatitude and poleward thereof, located between noon and dusk. The dawn arc is a persistent feature, but exhibits variations in position, width, and intensity, which have no clear relationship with the concurrent IMF. However, the patchy postnoon auroras are found to relate to the (suitably lagged and averaged) IMF B-z, being present during all four visits with positive B-z and absent during all three visits with negative B-z. The most continuous such forms occur in the case of strongest positive B-z. These results suggest that the postnoon forms are associated with reconnection and open flux production at Saturn's magnetopause, related to the similarly interpreted bifurcated auroral arc structures previously observed in this local time sector in Cassini Ultraviolet Imaging Spectrograph data, whose details remain unresolved in these HST images. One of the intervals with negative IMF B-z however exhibits a prenoon patch of very high latitude emission extending poleward of the dawn arc to the magnetic/spin pole, suggestive of the occurrence of lobe reconnection. Overall, these data provide evidence of significant IMF dependence in the morphology of Saturn's dayside auroras.
AB - We examine a unique data set from seven Hubble Space Telescope (HST) "visits" that imaged Saturn's northern dayside ultraviolet emissions exhibiting usual circumpolar "auroral oval" morphologies, during which Cassini measured the interplanetary magnetic field (IMF) upstream of Saturn's bow shock over intervals of several hours. The auroras generally consist of a dawn arc extending toward noon centered near similar to 15 degrees colatitude, together with intermittent patchy forms at similar to 10 degrees colatitude and poleward thereof, located between noon and dusk. The dawn arc is a persistent feature, but exhibits variations in position, width, and intensity, which have no clear relationship with the concurrent IMF. However, the patchy postnoon auroras are found to relate to the (suitably lagged and averaged) IMF B-z, being present during all four visits with positive B-z and absent during all three visits with negative B-z. The most continuous such forms occur in the case of strongest positive B-z. These results suggest that the postnoon forms are associated with reconnection and open flux production at Saturn's magnetopause, related to the similarly interpreted bifurcated auroral arc structures previously observed in this local time sector in Cassini Ultraviolet Imaging Spectrograph data, whose details remain unresolved in these HST images. One of the intervals with negative IMF B-z however exhibits a prenoon patch of very high latitude emission extending poleward of the dawn arc to the magnetic/spin pole, suggestive of the occurrence of lobe reconnection. Overall, these data provide evidence of significant IMF dependence in the morphology of Saturn's dayside auroras.
KW - POLAR IONOSPHERIC FLOWS
KW - RECONNECTION
KW - MAGNETOSPHERE
KW - MAGNETOPAUSE
KW - CONVECTION
KW - JUPITERS
KW - DYNAMICS
KW - DRIVEN
KW - CYCLE
KW - EARTH
KW - Auroral phenomena
KW - Hubble Space Telescope
KW - Saturn
KW - Solar wind dependence
U2 - 10.1002/2013JA019598
DO - 10.1002/2013JA019598
M3 - Journal article
VL - 119
SP - 1994
EP - 2008
JO - Journal of Geophysical Research: Space Physics
JF - Journal of Geophysical Research: Space Physics
SN - 2169-9402
IS - 3
ER -