Ionospheric Outflow at Jupiter and Saturn

<p>Ionospheric outflow is the outward flow of atmospheric plasma, initiated by a loss of equilibrium along the magnetic field. Terrestrial ionospheric outflow presents as a polar wind triggered by the Dungey cycle, which drives much of Earth’s magnetospheric dynamics. At Saturn, Felici et al. [2016] observed ionospheric outflow in the lobes at 36 R<sub>S</sub>. Interestingly, at Jupiter, Valek et al. [2019] reported ionospheric outflow on magnetic field lines with invariant latitudes between Io’s auroral signatures and the main auroral emission, lower than the polar cap.</p><p>At Jupiter and Saturn, the rapid rotation of the planet, coupled with an internal plasma source inside each magnetosphere, results in the Vasyliunas cycle, by which material is circulated throughout the system, eventually being lost down the magnetotail. This constant churning likely results in a system where ionospheric outflow occurs more readily at mid-to-high planetary latitudes that map to the middle magnetosphere, rather than solely at polar latitudes. Furthermore, ionospheric outflow at the Jupiter and Saturn will be affected by strong centrifugal forces and auroral currents, which are near omnipresent in each magnetosphere.</p><p>Using a 1-dimensional, hydrodynamic, multi-fluid model, we determine the ionospheric outflow in the jovian and saturnian systems. Our model includes the effect of centrifugal forces and auroral field-aligned currents, both of which act to enhance outflow rates from previous studies. We find that ionospheric outflow may provide a significant contribution to the jovian and saturnian systems, with the mass source rates of 18.7 – 31.7 kg s<sup>-1</sup>and 5.5-17.7 kg s<sup>-1</sup>, respectively, where the range reflects the sensitivity to the assumed initial atmospheric conditions.</p>

The Polar Wind Modulated by the Spatial Inhomogeneity of the Strength of the Earth’s Magnetic Field

<p>When the geomagnetic field is weak, the small mirror force allows precipitating charged particles to deposit energy in the ionosphere. This leads to an increase in ionospheric outflow from the Earth’s polar cap region, but such an effect has not been previously observed because the energies of the ions of the polar ionospheric outflow are too low, making it difficult to detect the low-energy ions with a positively charged spacecraft. In this study, we found anti-correlation between ionospheric outflow and the strength of the Earth’s magnetic field. Our results suggest that the electron precipitation through the polar rain can be a main energy source of the polar wind during periods of high levels of solar activity. The decreased magnetic field due to spatial inhomogeneity of the Earth’s magnetic field and its effect on outflow can be used to study the outflow in history when the magnetic field was at similar levels.</p>