As a star spins-down during the main sequence, its wind properties are affected. In this work, we investigate how the Earth's magnetosphere has responded to the change in the solar wind. Earth's magnetosphere is simulated using 3D magnetohydrodynamic models that incorporate the evolving local properties of the solar wind. The solar wind, on the other hand, is modelled in 1.5D for a range of rotation rates Ω from 50 to 0.8 times the present-day solar rotation (Ω ). Our solar wind model uses empirical values for magnetic field strengths, base temperature and density, which are derived from observations of solar-like stars. We find that for rotation rates 10Ω , Earth's magnetosphere was substantially smaller than it is today, exhibiting a strong bow shock. As the sun spins down, the magnetopause standoff distance varies with Ω −0.27 for higher rotation rates (early ages, ≥ 1.4Ω ), and with Ω −2.04 for lower rotation rates (older ages, < 1.4Ω ). This break is a result of the empirical properties adopted for the solar wind evolution. We also see a linear relationship between magnetopause distance and the thickness of the shock on the subsolar line for the majority of the evolution (≤ 10Ω ). It is possible that a young fast rotating Sun would have had rotation rates as high as 30 to 50Ω . In these speculative scenarios, at 30Ω , a weak shock would have been formed, but for 50Ω , we find that no bow shock could be present around Earth's magnetosphere. This implies that with the Sun continuing to spin down, a strong shock would have developed around our planet, and remained for most of the duration of the solar main sequence.

We study coronal mass ejection (CME)-driven shocks and the resulting post-shock structures in the lower corona (2-7 R ). Two CMEs are erupted by modified Titov-Démoulin (TD) and Gibson-Low (GL) type flux ropes (FRs) with the Space Weather Modeling Framework. We observe a substantial pile-up of density compression and a narrow region of plasma depletion layer (PDL) in the simulations. As the CME/FR moves and expands in the solar wind medium, it pushes the magnetized material lying ahead of it. Hence, the magnetic field lines draping around the CME front are compressed in the sheath just ahead of the CME. These compressed field lines squeeze out the plasma sideways, forming PDL in the region. Solar plasma being pushed and displaced from behind forms a strong piled-up compression (PUC) of density downstream of the PDL. Both CMEs have comparable propagation speeds, while GL has larger expansion speed than TD due to its higher initial magnetic pressure. We argue that high CME expansion speed along with high solar wind density in the region is responsible for the large PUC found in the lower corona. In case of GL, the PUC is much wider, although the density compression ratio for both the cases is comparable. Although these simulations artificially initiate out-of-equilibrium CMEs and drive them in an artificial solar wind solution, we predict that PUCs, in general, will be large in the lower corona. This should affect the ion profiles of the accelerated solar energetic particles.

[1] We present a comparison between two simulations of coronal mass ejections (CMEs), in the lower corona, driven by different flux rope mechanisms presented in the literature. Both mechanisms represent different magnetic field configurations regarding the amount of twist of the magnetic field lines and different initial energies. They are used as a "proof of concept" to explore how different initialization mechanisms can be distinguished from each other in the lower corona. The simulations are performed using the Space Weather Modeling Framework (SWMF) during solar minimum conditions with a steady state solar wind obtained through an empirical approach to mimic the physical processes driving the solar wind. Although the two CMEs possess different initial energies (differing by an order of magnitude) and magnetic configurations, the main observables such as acceleration, shock speed, Mach number, and Bn (the angle between the shock normal and the upstream magnetic field) present very similar behavior between 2 and 6 R . We believe that through the analysis of other quantities, such as sheath width and postshock compression (pileup and shock indentation compressions), the effect of different magnetic configurations and initializations can be distinguished. We discuss that coronal models that employ a reduced value of polytropic index (g) may significantly change the energetics of the CME and that the background solar wind plays an important role in the CMEs' shock and sheath evolution.

The Sun continually emits mass, momentum, and energy in the form of magnetized and ionized plasma from its outermost layer known as the solar wind (Hundhausen, 2012). The variation in energy content is closely related to the solar cycle. During the minimum activity phase, the predominant solar structures are the coronal holes (CH), from where the fast solar wind streams continuously emanate (Schwenn, 2006;Gosling, 1997; Gosling et al., 1976, and references therein). The interaction of ambient solar wind and fast solar wind forms the regions known as co-rotating interaction regions or CIR's (Alves et al., 2006;Smith & Wolfe, 1976). During the maximum solar activity phase, the predominant large-scale solar structures are the sunspots and active regions, where continuous magnetic reconfigurations release a large amount of magnetized plasma into the interplanetary space known as Coronal Mass Ejections (CME). A subclass of CMEs identified in the interplanetary medium is the magnetic clouds (MC) (Burlaga & Burlaga, 1995;Burlaga et al., 1998) An important characteristic of MC concerns its signature observed by the satellite when crossing the flux tube magnetic structure, which can be seen as an intense magnetic field with smooth rotation and low plasma beta value, also being able to be defined as a force-free structure having cylindrical symmetry (see, Kilpua et al., 2017;Goldstein, 1983, for more details). These MC-type solar and interplanetary structures in comparison to structures that are predominant in the minimum of solar activity can intensely and abruptly affect the magnetosphere-ionosphere system and upper atmosphere if they have a southward-directed interplanetary magnetic field (IMF) component through magnetic reconnection (Dungey, 1961). The primary evidence of the abrupt penetration of mass, momentum, energy, and magnetic flux into the inner regions of the magnetosphere is the emergence of magnetic storms and substorms (Chapman & Ferraro, 1933;Gonzalez et al., 1994), together with global perturbations in the particle flux which make up the ring current (RC) and the Radiation Belts (RB) that are highly influenced by the occurrence of