[1] Collisionless shocks due to mass-loading were first discussed to describe the solar wind flow around a cometary atmosphere, showing its choking effects on the flow. Recent observations have led to an increased interest in mass-loading occurring in the solar corona due to both sungrazing comets and collisional debris production by sunward migrating interplanetary dust particles. The 1-D simulations with a hydrodynamic model have illustrated the impact on the solar wind from abrupt mass-loading in the coronal region. Full 3-D magnetohydrodynamic (MHD) simulations using a solar corona model based on the Block-Adaptive-Tree-Solarwind-Roe-Upwind-Scheme code provide a more realistic coronal environment for modeling specific events applicable to modeling the mass-loaded coronal wind. A specific application is introduced modeling the mass-loading effects from a sungrazing comet.Citation: Rasca, A. P., M. Horányi, R. Oran, and B. van der Holst (2014), Modeling solar wind mass-loading in the vicinity of the Sun using 3-D MHD simulations,

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The most surprising result from the first solar encounters by the Parker Solar Probe (PSP) is the large amount of brief magnetic field reversals often referred to as switchbacks. Switchbacks have previously been observed further downstream in the solar wind by spacecraft such as Helios 2 at 62 R s from the Sun. However, these observations lack a distinct proton temperature increase detected inside switchbacks by PSP, implying that they are evolving over time to eventually reach a pressure balance at the switchback boundaries. We look at the evolution of switchback boundaries as a function of radial distance from the Sun, from closest approach at 35.7 R s during PSP’s first two encounters to beyond 80 R s . Using magnetic field and proton data from PSP’s FIELDS and SWEAP instruments, we perform a day-by-day superposed epoch analysis of the 25 switchbacks with the sharpest step-like boundaries. During both encounters we found the proton temperature spikes to gradually decline before vanishing completely around 55 R s . Magnetic reversals and velocity spikes also steadily drop in magnitude, but eventually flatten out instead of disappearing. Most interestingly, proton temperature change ΔT p across switchback boundaries is found to reach 2 × 105 in magnitude below 40 R s during PSP’s outbound trajectory, but is an order of magnitude less on the inbound trajectory, suggesting a possible common change in switchback characteristics near closest approach during both encounters.