| Autor: |
Kita, H., Kimura, T., Tao, C., Tsuchiya, F., Murakami, G., Yamazaki, A., Yoshioka, K., Ebert, R.W., Wilson, R.J., Allegrini, F., Clark, G., Connerney, J. E. P., Gladstone, G. R., Yoshikawa, I., Fujimoto, M. |
| Zdroj: |
Journal of Geophysical Research - Space Physics; December 2019, Vol. 124 Issue: 12 p10209-10218, 10p |
| Abstrakt: |
We summarize Jupiter's ultraviolet (UV) auroral response to solar wind dynamic pressure variations during Juno's approach to Jupiter in 2016. The response time of Jupiter's aurora to external drivers has thus far been unknown owing to a sparsity of upstream in situ solar wind measurements. Combining the Juno solar wind observations with continuous UV aurora data obtained by Hisaki EXCEED (Extreme Ultraviolet Spectroscope for Exospheric Dynamics) and Juno UV spectrograph, the UV aurora brightenings in response to three major shock arrivals showed time lags of 10–15 hr. These time lags are longer than the time required for ballistic propagation of the shocks by the solar wind. In addition to that puzzle, while an enhancement in the UV auroral power was observed with an increase in dynamic pressure to ~0.03 nPa, no associated brightening was observed with a dynamic pressure elevation of >0.1 nPa. These imply that internal magnetospheric aspects need to be taken into consideration to fully resolve the issue. Jovian ultraviolet aurora are emitted from hydrogen molecules in Jupiter's atmosphere when energetic electrons precipitate from the magnetosphere to excite the atmospheric molecules. The Jovian magnetosphere is always under the influence of the solar wind. Variation in the solar wind affects magnetospheric dynamics and thus the Jovian aurora intensity. The solar wind‐magnetosphere interaction is well studied for Earth, and the issue of aurora response to the solar wind is also well studied for Earth, but the issue remains open for Jupiter. Here we obtain the response time of aurora brightening upon intensification of the solar wind, which is a very fundamental quantity, to find it to be too long to be explained by a simple propagating model that assumes the solar wind as the dominant driver. Furthermore, some small variations in solar wind shocks led to aurora brightenings, while larger variations did not trigger other events. The characteristics discussed in this paper provide good case studies to validate theories or numerical simulations of how Jovian aurora may respond to changes in the solar wind. We compare Jupiter's ultraviolet aurora variation observed by Hisaki with changes in the upstream solar wind conditions observed by JunoTransient brightenings responded to major solar wind shocks with ~10 hr lag time, which is inconsistent with a solar wind propagation modelA brightening triggered by a dynamic pressure elevation of 0.03 nPa was detected, whereas a 0.1 nPa elevation did not trigger a brightening |
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