Small scale structures in the footprint tails of the Galilean moons observed by JIRAM

<p>The Jovian Infrared Auroral Mapper (JIRAM) on board Juno is a spectro-imager which is observing the<br>atmosphere of Jupiter and its auroral emission using its two imagers in the L (3.3-3.6μm) and M bands (4.5-<br>5.0μm) and a spectrometer (2-5 μm spectral range).<br>The highly elliptic orbit of Juno and the unprecedented resolution of the JIRAM imager allowed to retrieve<br>wealth of details about the morphology of moon-related aurorae. This phenomenon is due to the jovian magnetic<br>field sweeping past the Galiean moons, which generate Alfven waves travelling towards the ionosphere and set<br>up field aligned currents. When the associated electrons reach the ionosphere, they interact with the hydrogen<br>and make it to glow. In particular, the tails of the footprints showed a spot-like substructure consistently, which<br>were investigated using the L-band of the imager from perijove 4 to perijove 30. This feature was observed close<br>to the footprints, where the the typical distance between spots lies between 250km and 500km. This distance<br>decreases to 150km in a group of three observations in the northern emisphere when each moon is close to 250 ◦<br>west longitude. No correlation with orbital parameters such as the longitude of the moons was found so far,<br>which suggests that such morphology is almost purely due to ionospheric processes.<br>Moreover, during PJ 13 a long sequence of images of the Io footprint was shot and it revealed that the<br>secondary spots appears to corotate with Jupiter. This behaviour is observed also during orbits 14 and 26.<br>During these sequences JIRAM clearly observed the Io footprint leaving behind a trail of ”footsteps” as bright<br>spots.<br>The characteristics of these spots are incompatible with multiple reflection of Alfven waves between the two<br>emispheres. Instead, we are currently investigating ionospheric processes like the feedback instability (FI) as a<br>potential candidate to explain the generation of the observed small scale structure. This process relies on local<br>enhacement of conductivity in the ionosphere, which is affected by electron precipitation. Order of magnitude<br>estimates from the FI are compatible with the inter-spot distance and the stillness of the spots.</p>

Modeling of SEP induced auroral emission at Mars: Contribution of precipitating protons and effects of crustal fields

<p>Solar Energetic Particle (SEP) and the Imaging UltraViolet Spectrograph (IUVS) instruments on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft have discovered diffuse aurora that spans across nightside Mars, which resulted from the interaction of Solar Energetic Particles (SEPs) with Martian atmosphere [Schneider et al., 2015]. Previous models showed that 100 keV monoenergetic electron precipitation should have been at the origin of the low altitude (~60 km) peak of the limb emission, however, no models were able to reproduce the observed emission profiles by using the observed electron energy population [e.g. Haider et al., 2019]. Previous auroral emission models did not take into account the contribution of MeV proton precipitation, although MeV proton can penetrate down to ~60 km altitude as well [e.g., Jolitz et al., 2017]. This study aims to model SEP induced diffuse auroral emission by both electrons and protons.</p><p>We have developed a Monte-Carlo collision and transport model of SEP electrons and protons with magnetic fields on Mars. We calculated limb intensity profile of CO<sub>2</sub><sup>+</sup> ultraviolet doublet (UVD) due to precipitation of electrons and protons with energy ranging 100eV-100keV and 100eV-5MeV, respectively, during December 2014 SEP event and September 2017 SEP event by using electron and ion fluxes observed by MAVEN/SEP, SWEA and SWIA.</p><p>The calculated peak limb intensity of CO<sub>2</sub><sup>+</sup> UVD due to precipitation of protons is 3-5 times larger than that due to precipitation of electrons during both December 2014 and September 2017 SEP events, which suggests that protons can make brighter CO<sub>2</sub><sup>+</sup> UVD emission than electrons. Peak altitude of limb intensity profiles of CO<sub>2</sub><sup>+</sup> UVD due to precipitation of electrons and protons are both 10 - 20 km higher than the observation, a discrepancy could be explained by the uncertainty in the electron and proton fluxes that precipitate into the nightside Mars.</p><p>We have tested an effect of crustal field on the emission of CO<sub>2</sub><sup>+</sup> UVD. CO<sub>2</sub><sup>+</sup> UVD emission due to the precipitating electrons are depleted by a factor of 10 in the region of open crustal field and disappeared in the region of closed and parallel crustal field, whereas emission due to the precipitating protons does not change significantly. Further observations of diffuse aurora in the crustal field region should be needed to constrain the origin of diffuse aurora on Mars.</p>

Cloud Cover and Aurora Contamination at Dome A in 2017 from KLCAM

Dome A in Antarctica has many characteristics that make it an excellent site for astronomical observations, from the optical to the terahertz. Quantitative site testing is still needed to confirm the site’s properties. In this paper, we present a statistical analysis of cloud cover and aurora contamination from the Kunlun Cloud and Aurora Monitor (KLCAM). KLCAM is an automatic, unattended all-sky camera aiming for long-term monitoring of the usable observing time and optical sky background at Dome A. It was installed at Dome A in January 2017, worked through the austral winter, and collected over 47,000 images over 490 days. A semi-quantitative visual data analysis of cloud cover and auroral contamination was carried out by five individuals. The analysis shows that the night sky was free of clouds for 83 per cent of the time, which ranks Dome A highly in a comparison with other observatory sites. Although aurorae were detected somewhere on an image for nearly 45 per cent of the time, the chance of a point on the sky being affected by an aurora is small. The strongest auroral emission lines can be filtered out with customized filters.

AGN-driven outflows and the AGN feedback efficiency in young radio galaxies

Active galactic nuclei (AGN) feedback operated by the expansion of radio jets can play a crucial role in driving gaseous outflows on galaxy scales. Galaxies hosting young radio AGN, whose jets are in the first phases of expansion through the surrounding interstellar medium (ISM), are the ideal targets to probe the energetic significance of this mechanism. In this paper, we characterise the warm ionised gas outflows in a sample of nine young radio sources from the 2 Jy sample, combining X-shooter spectroscopy and Hubble Space Telescope imaging data. We find that the warm outflows have similar radial extents (∼0.06−2 kpc) as radio sources, consistent with the idea that “jet mode” AGN feedback is the dominant driver of the outflows detected in young radio galaxies. Exploiting the broad spectral coverage of the X-shooter data, we used the ratios of trans-auroral emission lines of [S II] and [O II] to estimate the electron densities, finding that most of the outflows have gas densities (log(ne cm−3) ∼ 3 − 4.8), which we speculate could be the result of compression by jet-induced shocks. Combining our estimates of the emission-line luminosities, radii, and densities, we find that the kinetic powers of the warm outflows are a relatively small fraction of the energies available from the accretion of material onto the central supermassive black hole, reflecting AGN feedback efficiencies below 1% in most cases. Overall, the warm outflows detected in our sample are strikingly similar to those found in nearby ultraluminous infrared galaxies, but more energetic and with higher feedback efficiencies on average than the general population of nearby AGN of similar bolometric luminosity; this is likely to reflect a high degree of coupling between the jets and the near-nuclear ISM in the early stages of radio source evolution.

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>