Speaker: Dr Licia Ray (Lancaster)
Title: Jupiter’s Alfvén Surface and Implications for Magnetotail Behaviour
Abstract: Jovian magnetospheric plasma is coupled to the ionosphere through Alfvén waves. Alfvén waves enable the transport of angular momentum and energy between the planet and magnetospheric plasma, a process that ultimately generates Jupiter’s bright auroral emissions. However, past the Alfvén radius, the location where the radial velocity is greater than the Alfvén velocity, magnetospheric plasma is effectively decoupled from the planet, with fluctuations in the local magnetosphere no longer communicated back to the planet. Determining Jupiter’s Alfvén surface is critical for interpreting drivers of auroral emissions, in situ data, and applications of numerical models. Previous studies that calculated the location of the Alfvén radius assumed an azimuthally symmetric magnetosphere and local-time independent magnetic field. Here, we employ a statistical description of the magnetic field that includes local time effects. We find a minimum Alfvén radius of 30 RJ (Jupiter radii) at 6 LT, with plasma decoupled from the planet in the post-dusk through dawn sector. Furthermore, no Alfvén radius exists within 60 RJ between 8 and 20 LT. Our results have implications of the interpretation of Jupiter’s magnetotail behaviour and we suggest that it may behave similar to the heliospheric current sheet. Our results highlight the importance of local time considerations in MI coupling studies at Jupiter and offer new interpretations for local time dependent measurements and observations, such as the spatial distribution of reconnection events, outflow events with strong radial components, and the dark polar collar in the auroral region.