Data-driven numerical simulations of the Parker Spiral and interplanetary propagation of solar transients

The accurate reconstruction of the plasma and magnetic field parameters in the ambient interplanetary medium is fundamental to reproduce the interplanetary propagation of solar disturbances such as solar energetic particles (SEPs), stream and corotating interaction regions (SIRs and CIRs), and coronal mass ejections (CMEs), both for understanding the physics of these phenomena and for applications in space weather forecasting. The small-scale features of the ambient solar wind, in fact, affect the evolution, arrival times, and geo-effectiveness of solar transients.
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\nThe Reverse In situ and MHD Approach (RIMAP) is a hybrid analytical-numerical method to reconstruct the heliosphere on the ecliptic plane from in situ measurements acquired by spacecraft with heliocentric orbits. RIMAP uses the in situ measurements as boundary conditions for a MHD simulation based on the PLUTO code, combining ballistic and MHD approaches in order to preserve the small-scale variability of the solar wind flow lines and thus offering a structured, realistic background medium for modelling the propagation of solar eruptions.
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\nIn this dissertation, after an introduction about the main topics and models of heliospheric physics and the magnetohydrodynamics equations, we present the detailed description of the novelties of the RIMAP model, and its application to the measurements acquired by spacecraft at 1 AU in correspondence of solar minima configurations.
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\nThen, one of these reconstructions is used as a background medium to propagate an interplanetary CME. The perturbation is modelled as a spheroidal, homogeneous plasma cloud without internal magnetic flux rope. We use an artificial, passive tracer to quantify the mixing at 1 AU between ambient solar wind material and the one with coronal eruption origins, in order to evaluate the fraction of plasma measured in situ that can be traced back to its sources on the Sun.
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\nThe RIMAP reconstruction is also carried out using measurements acquired by NASA’s Parker Solar Probe (PSP) during its seventh solar encounter, in January 2021, between 20 and 40 solar radii. This was the time of the first quadrature between PSP and ESA-NASA’s Solar Orbiter (SolO), which at the time was orbiting the Sun around 0.5 AU and providing remote sensing observations of the solar corona via the Metis coronagraph. The RIMAP reconstruction connects density and wind speed estimates inferred from the coronal features observed by Metis/SolO between 3 and 6 solar radii to the measurements acquired by PSP at 21.5 solar radii along the corresponding plasma streamline. Thus, the magnetic connection between the inner corona and the super Alfvénic wind is reconstructed with a high degree of accuracy with a detailed data-driven MHD simulation.
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\nFinally, we describe the possible future developments of the RIMAP technique such as the extension to a two-fluids treatment, the testing of different models of magnetized coronal mass ejections, the simulation of solar wind switchbacks, and the extension to full three-dimensional boundaries, using coronagraphic observations to infer the input parameters.

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