Periodic shearing motions in the Jovian magnetosphere causing a localized peak in the main auroral emission close to noon

Recently, a transient localized brightness enhancement has been observed in Jupiter's main auroral emission close to noon by Palmaerts et al. (2014). We use results from three-dimensional global MHD simulations to understand what is causing this localized peak in the main emission. In the simulations, the peak occurs every rotation period and is due to shearing motions in the magnetodisk. These shearing motions are caused by heavy flux-tubes being accelerated to large azimuthal speeds at dawn. The centrifugal force acting on these flux-tubes is then so high that they rapidly move away from the planet. When they reach noon, their azimuthal velocity decreases, thus reducing the centrifugal force, and allowing the flux-tubes to move back closer to Jupiter. The shearing motions associated with this periodic phenomenon locally increase the field aligned currents in the simulations, thus causing a transient brightness enhancement in the main auroral emission, similar to the one observed by Palmaerts et al. (2014).Comment: accepted for publication on 2018/04/25 by Planetary and Space Scienc

Numerical simulations of shear-induced consecutive coronal mass ejections

Methods: Stealth CMEs represent a particular class of solar eruptions that are clearly distinguished in coronagraph observations, but they don't have a clear source signature. A particular type of stealth CMEs occurs in the trailing current sheet of a previous ejection, therefore, we used the 2.5D MHD package of the code MPI-AMRVAC to numerically simulate consecutive CMEs by imposing shearing motions onto the inner boundary. The initial magnetic configuration consists of a triple arcade structure embedded into a bimodal solar wind, and the sheared polarity inversion line is found in the southern loop system. The mesh was continuously adapted through a refinement method that applies to current carrying structures. We then compared the obtained eruptions with the observed directions of propagation of an initial multiple coronal mass ejection (MCME) event that occurred in September 2009. We further analysed the simulated ejections by tracking the centre of their flux ropes in latitude and their total speed. Radial Poynting flux computation was employed as well to follow the evolution of electromagnetic energy introduced into the system. Results: Changes within 1\% in the shearing speed result in three different scenarios for the second CME, although the preceding eruption seems insusceptible to such small variations. Depending on the applied shearing speed, we thus obtain a failed eruption, a stealth, or a CME driven by the imposed shear, as the second ejection. The dynamics of all eruptions are compared with the observed directions of propagation of an MCME event and a good correlation is achieved. The Poynting flux analysis reveals the temporal variation of the important steps of eruptions. For the first time, a stealth CME is simulated in the aftermath of a first eruption, through changes in the applied shearing speed.Comment: 11 pages, 12 figures, to be published in "Astronomy & Astrophysics", and the associated movies will also be available on the journal's websit

Modeling magnetospheric fields in the Jupiter system

The various processes which generate magnetic fields within the Jupiter system are exemplary for a large class of similar processes occurring at other planets in the solar system, but also around extrasolar planets. Jupiter's large internal dynamo magnetic field generates a gigantic magnetosphere, which is strongly rotational driven and possesses large plasma sources located deeply within the magnetosphere. The combination of the latter two effects is the primary reason for Jupiter's main auroral ovals. Jupiter's moon Ganymede is the only known moon with an intrinsic dynamo magnetic field, which generates a mini-magnetosphere located within Jupiter's larger magnetosphere including two auroral ovals. Ganymede's magnetosphere is qualitatively different compared to the one from Jupiter. It possesses no bow shock but develops Alfv\'en wings similar to most of the extrasolar planets which orbit their host stars within 0.1 AU. New numerical models of Jupiter's and Ganymede's magnetospheres presented here provide quantitative insight into the processes that maintain these magnetospheres. Jupiter's magnetospheric field is approximately time-periodic at the locations of Jupiter's moons and induces secondary magnetic fields in electrically conductive layers such as subsurface oceans. In the case of Ganymede, these secondary magnetic fields influence the oscillation of the location of its auroral ovals. Based on dedicated Hubble Space Telescope observations, an analysis of the amplitudes of the auroral oscillations provides evidence that Ganymede harbors a subsurface ocean. Callisto in contrast does not possess a mini-magnetosphere, but still shows a perturbed magnetic field environment. Callisto's ionosphere and atmospheric UV emission is different compared to the other Galilean satellites as it is primarily been generated by solar photons compared to magnetospheric electrons.Comment: Chapter for Book: Planetary Magnetis

Propagation of an Earth-directed coronal mass ejection in three dimensions

Solar coronal mass ejections (CMEs) are the most significant drivers of adverse space weather at Earth, but the physics governing their propagation through the heliosphere is not well understood. While stereoscopic imaging of CMEs with the Solar Terrestrial Relations Observatory (STEREO) has provided some insight into their three-dimensional (3D) propagation, the mechanisms governing their evolution remain unclear due to difficulties in reconstructing their true 3D structure. Here we use a new elliptical tie-pointing technique to reconstruct a full CME front in 3D, enabling us to quantify its deflected trajectory from high latitudes along the ecliptic, and measure its increasing angular width and propagation from 2-46 solar radii (approximately 0.2 AU). Beyond 7 solar radii, we show that its motion is determined by an aerodynamic drag in the solar wind and, using our reconstruction as input for a 3D magnetohydrodynamic simulation, we determine an accurate arrival time at the Lagrangian L1 point near Earth.Comment: 5 figures, 2 supplementary movie

4pi Models of CMEs and ICMEs

Coronal mass ejections (CMEs), which dynamically connect the solar surface to the far reaches of interplanetary space, represent a major anifestation of solar activity. They are not only of principal interest but also play a pivotal role in the context of space weather predictions. The steady improvement of both numerical methods and computational resources during recent years has allowed for the creation of increasingly realistic models of interplanetary CMEs (ICMEs), which can now be compared to high-quality observational data from various space-bound missions. This review discusses existing models of CMEs, characterizing them by scientific aim and scope, CME initiation method, and physical effects included, thereby stressing the importance of fully 3-D ('4pi') spatial coverage.Comment: 14 pages plus references. Comments welcome. Accepted for publication in Solar Physics (SUN-360 topical issue

Response of Jupiter's auroras to conditions in the interplanetary medium as measured by the Hubble Space Telescope and Juno

We present the first comparison of Jupiter's auroral morphology with an extended, continuous and complete set of near-Jupiter interplanetary data, revealing the response of Jupiter's auroras to the interplanetary conditions. We show that for ∼1-3 days following compression region onset the planet's main emission brightened. A duskside poleward region also brightened during compressions, as well as during shallow rarefaction conditions at the start of the program. The power emitted from the noon active region did not exhibit dependence on any interplanetary parameter, though the morphology typically differed between rarefactions and compressions. The auroras equatorward of the main emission brightened over ∼10 days following an interval of increased volcanic activity on Io. These results show that the dependence of Jupiter's magnetosphere and auroras on the interplanetary conditions are more diverse than previously thought

The Physical Processes of CME/ICME Evolution

As observed in Thomson-scattered white light, coronal mass ejections (CMEs) are manifest as large-scale expulsions of plasma magnetically driven from the corona in the most energetic eruptions from the Sun. It remains a tantalizing mystery as to how these erupting magnetic fields evolve to form the complex structures we observe in the solar wind at Earth. Here, we strive to provide a fresh perspective on the post-eruption and interplanetary evolution of CMEs, focusing on the physical processes that define the many complex interactions of the ejected plasma with its surroundings as it departs the corona and propagates through the heliosphere. We summarize the ways CMEs and their interplanetary CMEs (ICMEs) are rotated, reconfigured, deformed, deflected, decelerated and disguised during their journey through the solar wind. This study then leads to consideration of how structures originating in coronal eruptions can be connected to their far removed interplanetary counterparts. Given that ICMEs are the drivers of most geomagnetic storms (and the sole driver of extreme storms), this work provides a guide to the processes that must be considered in making space weather forecasts from remote observations of the corona.Peer reviewe

Improving predictions of high-latitude Coronal Mass Ejections throughout the heliosphere

Predictions of the impact of coronal mass ejections (CMEs) in the heliosphere mostly rely on cone CME models, whose performances are optimized for locations in the ecliptic plane and at 1 AU (e.g., at Earth). Progresses in the exploration of the inner heliosphere, however, advocate the need to assess their performances at both higher latitudes and smaller heliocentric distances. In this work, we perform 3-D magnetohydrodynamics simulations of artificial cone CMEs using the EUropean Heliospheric FORecasting Information Asset (EUHFORIA), investigating the performances of cone models in the case of CMEs launched at high latitudes. We compare results obtained initializing CMEs using a commonly applied approximated (Euclidean) distance relation and using a proper (great circle) distance relation. Results show that initializing high-latitude CMEs using the Euclidean approximation results in a teardrop-shaped CME cross section at the model inner boundary that fails in reproducing the initial shape of high-latitude cone CMEs as a circular cross section. Modeling errors arising from the use of an inappropriate distance relation at the inner boundary eventually propagate to the heliospheric domain. Errors are most prominent in simulations of high-latitude CMEs and at the location of spacecraft at high latitudes and/or small distances from the Sun, with locations impacted by the CME flanks being the most error sensitive. This work shows that the low-latitude approximations commonly employed in cone models, if not corrected, may significantly affect CME predictions at various locations compatible with the orbit of space missions such as Parker Solar Probe, Ulysses, and Solar Orbiter.Peer reviewe

Contrôle du dopage dans la croissance épitaxiale d'arséniure de gallium

Nous présentons nos résultats récemment acquis dans la maîtrise du niveau et du profil de dopage de couches d'arséniure de gallium préparées par épitaxie en phase vapeur. Nous décrivons un procédé de dopage par rétrodiffusion, et exposons nos méthodes de caractérisation