Stability within Jupiter’s polar auroral ‘Swirl region’ over moderate timescales

Stallard, T. S., Clarke, J. T., Melin, H., Miller, S., Nichols, J. D., O'Donoghue, J. ORCID: https://orcid.org/0000-0002-4218-1191, Johnson, R. E., Connerney, J. E. P., Satoh, T. and Perry, M. (2016) Stability within Jupiter’s polar auroral ‘Swirl region’ over moderate timescales. Icarus, 268. pp. 145-155. ISSN 0019-1035 doi: 10.1016/j.icarus.2015.12.044

Abstract/Summary

Jupiter’s Swirl region, poleward of the main auroral emission, has been characterised in previous obser- vations as having highly variable auroral emission, changing dramatically across the region on a two- minute timescale, the typical integration time for UV images. This variability has made comparisons with H3+ emission difficult. Here, we show that the Swirl region in H3+ images is characterised by relatively stable emission, often with an arc of emission on the boundary between the Swirl and Dark regions. Coadding multiple UV images taken over the approximate lifetime of the H3+ molecule in the ionosphere, show similar structures to those observed in the H3+ images. Our analysis shows that UV auroral morphol- ogy within Jupiter’s Swirl region is only highly variable on short timescales of 100s, an intrinsic prop- erty of the particle precipitation process, but this variability drops away on timescales of 5–15 min. On moderate timescales between 10 and 100 min, the Swirl region is stable, evolving through as yet unknown underlying magnetospheric interactions. This shows that observing the UV aurora over time- scales 5–15 min resolves clear auroral structures that will help us understand the magnetospheric origin of these features, and that calculating the variability over different timescales, especially >15 min, pro- vides a new and important new tool in our understanding of Jupiter’s polar aurora.