Dimitrios Millas

The structure of Jupiter's magnetosphere reflects the combined effects of a strong intrinsic field and an extended hinged current sheet whose morphology varies with solar wind forcing. We present a study of Jupiter's magnetodisc that combines the UCL‐AGA magnetodisc code with Khurana's generalized, hinged current sheet models (1992/2022) to fit Juno MAG data from orbits PJ6–PJ12 and PJ34 using a “rolling‐window” approach. Periods of relative stability (“quiescent” magnetosphere) are identified during each pass, reducing the impact of transient solar‐wind and reconfiguration events. The underlying magnetospheric parameters are then determined and current sheet morphology constrained. Estimated magnetopause distances are also obtained and compared to the results obtained by Joy et al. (2002, https://doi.org/10.1029/2001ja009146 ), showing most probable subsolar standoff distances between 46 and 64 and results consistent with dawn‐dusk asymmetry and/or a cushion region along the dusk flank. This approach reveals substantial per‐perijove magnetospheric and current sheet geometry variability, as well as capturing changes in hot‐plasma content and effective magnetodisc radius within a single pass. Correlations between model parameters link extended magnetospheres to larger magnetic field sweepback onset distances, with weaker negative trends linking magnetospheric compression with the Alfvén wave propagation speed and hot plasma content with the distance at which hinging becomes significant. Finally, both MDISC + Khurana model variants are shown to match, and often outperform, the optimized Connerney (2020) baseline current disc model across most perijoves analyzed.

A number of observations of astrophysical jets, at different scales, have shown that jets are often non-uniform outflows in their cross-section. Their structure is believed to play an important role in their overall stability. In this work, we combine analytical methods and numerical simulations to investigate the stability of non-uniform jets originating from active galactic nuclei. We adopt a standard ‘spine and sheath’ model, using a fast, light inner spine and a heavier, slower outer sheath. In the first part of this work, we conduct a linear stability analysis, finding the time-scales for the growth of the instabilities and the corresponding eigenfunctions. We focus on the nature of the physical processes that dominate and drive the destabilization of configurations. In the second part, we examine the evolution of the perturbed jets through relativistic 3D numerical simulations using the pluto code. Starting with the eigenfunctions found in the first part as initial conditions, we derive instability growth times and evolution which are in good agreement with the linear analysis.

Solar activity, ranging from the background solar wind to energetic coronal mass ejections (CMEs), is the main driver of the conditions in the interplanetary space and in the terrestrial space environment, known as space weather. A better understanding of the Sun-Earth connection carries enormous potential to mitigate negative space weather effects with economic and social benefits. Effective space weather forecasting relies on data and models. In this paper, we discuss some of the most used space weather models, and propose suitable locations for data gathering with space weather purposes. We report on the application of Representer analysis (RA) and Domain of Influence (DOI) analysis to three models simulating different stages of the Sun-Earth connection: the OpenGGCM and Tsyganenko models, focusing on solar wind—magnetosphere interaction, and the PLUTO model, used to simulate CME propagation in interplanetary space. Our analysis is promising for space weather purposes for several reasons. First, we obtain quantitative information about the most useful locations of observation points, such as solar wind monitors. For example, we find that the absolute values of the DOI are extremely low in the magnetospheric plasma sheet. Since knowledge of that particular sub-system is crucial for space weather, enhanced monitoring of the region would be most beneficial. Second, we are able to better characterize the models. Although the current analysis focuses on spatial rather than temporal correlations, we find that time-independent models are less useful for Data Assimilation activities than time-dependent models. Third, we take the first steps toward the ambitious goal of identifying the most relevant heliospheric parameters for modeling CME propagation in the heliosphere, their arrival time, and their geoeffectiveness at Earth.

Supernovae and astrophysical jets are two of the most energetic and intriguing objects in the universe. We examine an interesting scenario that involves the interaction of these two extreme phenomena, motivated by observations of the W50-SS433 system: a jet launched from the microquasar SS433 (an X-ray binary) located inside a supernova remnant, W50. These observations revealed a unique morphology of the remnant, attributed to the presence of the jet. We performed full 3D relativistic hydrodynamic simulations to better capture the interaction between the remnant and the jet and post-processed the data with a radiative transfer code to create emission maps.

Relativistic jets from active galactic nuclei (AGN) often display a non-uniform structure and are, under certain conditions, susceptible to a number of instabilities. An interesting example is the development of non-axisymmetric, Rayleigh-Taylor type instabilities in the case of differentially rotating two-component jets, with the toroidal component of the magnetic field playing a key role in the development or suppression of these instabilities. We have shown that higher magnetization leads to stability against these non-axisymmetric instabilities. Using ray-casting on data from relativistic MHD simulations of two-component jets, we now investigate the effect of these instabilities on the synchrotron emission pattern from the jets. We recover many well known trends from actual observations, e.g., regarding the polarization fraction and the distribution of the position angle of the electric field, in addition to a different emitting region, depending on the stability of the jet.