Tom Stallard

Once every two decades, Jupiter, Saturn and the Sun move into close alignment with each other, so that Saturn moves periodically into Jupiter's extended magnetotail. Observations from Voyager 2 show that this rare alignment results in dramatic changes to Saturn's aurora, with the radio emission decreasing by two orders of magnitude. However, since that observation, we have no measurements of this event and no real understanding of how the auroral region changes in brightness or currents, or how the thermosphere might change as a result of changing auroral inputs. Here. we present a series of ground-based observations of the H3+ auroral emission from Saturn across a period of two months, hoping to observe the auroral changes during a jovian magnetotail crossing. Our preliminary results show some tantilizing results - during the final observations of the sequence, Saturn's aurora appears to drop away significantly in brightness, resulting in apparently dramatic changes in the ion winds observed. On one night the entire polar cap appears to super rotate. On subsequent nights, very dim aurora appear to match with strange ion flows that, in some cases, appear to be in anti-phase with the planetary period - perhaps hinting at an ionosphere controlled solely by the atmosphere, within the usual middle magnetosphre breakdown. These results are highly preliminary. We intend to re-analyse them and ensure that these very unusual dynamics are not an artefact of calibration - if they remain, this presents the first strong evidence of what processes occur on a planet when removed from the influence of the solar wind.