By Ruoyan Wang (University of Leicester)
We have simultaneously observed line-of-sight ionospheric and thermospheric winds in Jupiter using the Keck II telescope and produced one of the first global maps of both ion and neutral flows in the same layer of any atmosphere. Since ionospheric currents are through the relative motion of ions within the neutral atmosphere, comparing these two maps produces a global map of the "effective" ion drifts, the E x B flows that drive upper ionospheric currents. To the surprise of the Jupiter community, this upper atmospheric "effective" ion drift is dominated by two sunward blue-shifted jets associated with the dawn and dusk main auroral region, highly reminiscent of ionospheric flows seen on Earth. This discovery is directly opposite to the expected rotationally symmetric breakdown in corotation driven by the plasma-heavy magnetosphere. Our result suggests that the asymmetric currents close in the upper ionosphere, while the closure of breakdown-in-corotation currents occurs deep in the lower ionosphere, resulting in powerful upward auroral currents penetrating through overlying regions of downward currents associated with the asymmetric currents. Such a mechanism could potentially explain the complex switching generation of Jupiter's main auroral emissions observed by the Juno mission. Moreover, this study highlights the importance of the neutral atmosphere and interactions between ions and neutrals on other planets, including Earth, making Jupiter an important global comparator for future studies of these interactions.
See full paper for further details:
Wang, R., Stallard, T. S., Melin, H., Baines, K. H., Achilleos, N., Rymer, A. M., Ray, R. C., Nichols, J. D., Moore, L., O'Donoghue, J., Chowdhury, M. N., Thomas, E. M., Knowles, K. L., Tiranti, P. I., Miller, S. (2023). Asymmetric Ionospheric Jets in Jupiter's Aurora. Journal of Geophysical Research: Space Physics, 128, e2023JA031861. https://doi.org/10.1029/2023JA031861.
By Domenico Trotta (Imperial College London)
Shock waves, i.e., abrupt transitions between supersonic and subsonic flows, are present in a large variety of astrophysical systems, and are pivotal for efficient energy conversion and particle acceleration in our universe [1]. Despite decades of research, the mechanisms by which particles are accelerated at shocks are a matter of debate, and are crucial to several applications, ranging from explaining acceleration of cosmic rays to the highest energies [2] to the study of space weather phenomena [3].
Shocks in the heliosphere are unique, being directly accessible by spacecraft exploration, thus providing the missing link to the remote observations of astrophysical systems. Interplanetary (IP) shocks are generated because of solar activity phenomena, such as Coronal Mass Ejections (CMEs), and play an important role in the energetics of the heliosphere where they propagate [4].
The ground-breaking NASA Parker Solar Probe (PSP, [5]) and ESA Solar Orbiter [6] missions are probing the previously unexplored inner heliosphere, providing datasets with unprecedented resolutions.
We used such novel observational window to report direct PSP observations of a CME-driven shock as close to the Sun as 0.07 A, making it the closest to the Sun direct observation of a shock wave to date. The shock then reached Solar Orbiter at 0.7 AU, enabling us to study the evolution of the shock throughout its propagation in the heliosphere.
We characterized the shock and its environment. At PSP, we found a sharp shock with moderate strength, and investigated how switchbacks, fundamental constituents of the near-Sun environment, are processed by the shock crossing. In contrast, the Solar Orbiter observations revealed a very structured shock transition, with shock-accelerated protons with energies of up to 2 MeV. The differences between the two shocks are due to both evolution effects and the large-scale geometry of the event, crossed by the spacecraft in two points only. This study elucidates how the local features of IP shocks and their environments can be very different as they propagate through the heliosphere.
See full publication for further information:
Trotta et al., ApJ, 962, 2 (2024), DOI: 10.3847/1538-4357/ad187d
References:
[1] Bykov et al., SSRv, 2015, 14 (2019)
[2] Amato&Blasi, Adv. Sp. Res., 62, 10 (2018)
[3] Klein&Dalla, SSRv, 212, 1107 (2017)
[4] Reames et al., ApJ, 483, 512 (1997)
[5] Fox et al., SSRv, 204, 7 (2016)
[6] Muller et al., A&A, 642, A1 (2020)
This resource is a collation of PhD student adverts from the MIST Community.
Please note that the list is not exhaustive and is not intended to be an accurate capture of all studentships in the MIST community.
Please feel welcome to share and distribute this resource to any interested parties. Potential PhD applications should direct all enquiries about individual adverts to the named contact.
If you have any suggestions on how we can improve this resource, you can contact us as This email address is being protected from spambots. You need JavaScript enabled to view it..