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The solar wind (SW) is a vital component of space weather, providing a background for solar transients such as coronal mass ejections, stream interaction regions, and energetic particles propagating toward Earth. Accurate prediction of space weather events requires a precise description and thorough understanding of physical processes occurring in the ambient SW plasma. Ensemble simulations of the three-dimensional SW flow are performed using an empirically-driven magnetohydrodynamic heliosphere model implemented in the Multi-Scale Fluid-Kinetic Simulation Suite (MS-FLUKSS). The effect of uncertainties in the photospheric boundary conditions on the simulation outcome is investigated. The results are in good overall agreement with the observations from the Parker Solar Probe, Solar Orbiter, Solar Terrestrial Relations Observatory, and OMNI data at Earth, specifically during 2020-2021. This makes it possible to shed more light on the properties of the SW propagating through the heliosphere and perspectives for improving space weather forecasts. 

Abstract Large-scale disturbances generated by the Sun’s dynamics first propagate through the heliosphere, influence the heliosphere’s outer boundaries, and then traverse and modify the very local interstellar medium (VLISM). The existence of shocks in the VLISM was initially suggested by Voyager observations of the 2-3 kHz radio emissions in the heliosphere. A couple of decades later, both Voyagers crossed the definitive edge of our heliosphere and became the first ever spacecraft to sample interstellar space. Since Voyager 1’s entrance into the VLISM, it sampled electron plasma oscillation events that indirectly measure the medium’s density, increasing as it moves further away from the heliopause. Some of the observed electron oscillation events in the VLISM were associated with the local heliospheric shock waves. The observed VLISM shocks were very different than heliospheric shocks. They were very weak and broad, and the usual dissipation via wave-particle interactions could not explain their structure. Estimates of the dissipation associated with the collisionality show that collisions can determine the VLISM shock structure. According to theory and models, the existence of a bow shock or wave in front of our heliosphere is still an open question as there are no direct observations yet. This paper reviews the outstanding observations recently made by the Voyager 1 and 2 spacecraft, and our current understanding of the properties of shocks/waves in the VLISM. We present some of the most exciting open questions related to the VLISM and shock waves that should be addressed in the future. 

Since the launch on 2018 August 12, the Parker Solar Probe (PSP) has completed its first five orbits around the Sun, having reached down to ~28 solar radii at perihelion 5 on 2020 June 7. More recently, the Solar Orbiter (SolO) made its first close approach to the Sun at 0.52 AU on 2020 June 15, nearly 4 months after the launch. Using a 3D heliospheric MHD model coupled with the Wang-Sheeley-Arge (WSA) coronal model using the Air Force Data Assimilative Photospheric flux Transport (ADAPT) magnetic maps as input, we simulate the time-varying inner heliosphere, including the trajectories of PSP and SolO, during the current solar minimum period between 2018 and 2020. Above the ADAPT-WSA model outer boundary at 21.5 solar radii, we solve the Reynolds averaged MHD equations with turbulence and pickup ions taken into account and compare the simulation results with the PSP solar wind and magnetic field data, with particular emphasis on the large-scale solar wind structure and magnetic connectivity during each solar encounter. 

Abstract Drawing connections between heliospheric spacecraft and solar wind sources is a vital step in understanding the evolution of the solar corona into the solar wind and contextualizing in situ timeseries. Furthermore, making advanced predictions of this linkage for ongoing heliospheric missions, such as Parker Solar Probe (Parker), is necessary for achieving useful coordinated remote observations and maximizing scientific return. The general procedure for estimating such connectivity is straightforward (i.e., magnetic field line tracing in a coronal model) but validating the resulting estimates is difficult due to the lack of an independent ground truth and limited model constraints. In its most recent orbits, Parker has reached perihelia of 13.3R_⊙and moreover travels extremely fast prograde relative to the solar surface, covering over 120° longitude in 3 days. Here we present footpoint predictions and subsequent validation efforts for Parker Encounter 10, the first of the 13.3R_⊙orbits, which occurred in November 2021. We show that the longitudinal dependence of in situ plasma data from these novel orbits provides a powerful method of footpoint validation. With reference to other encounters, we also illustrate that the conditions under which source mapping is most accurate for near‐ecliptic spacecraft (such as Parker) occur when solar activity is low, but also require that the heliospheric current sheet is strongly warped by mid‐latitude or equatorial coronal holes. Lastly, we comment on the large‐scale coronal structure implied by the Encounter 10 mapping, highlighting an empirical equatorial cut of the Alfvèn surface consisting of localized protrusions above unipolar magnetic separatrices.