Solar Wind Properties and Geospace Impact of Coronal Mass Ejection-Driven Sheath Regions : Variation and Driver Dependence

We present a statistical study of interplanetary conditions and geospace response to 89 coronal mass ejection-driven sheaths observed during Solar Cycles 23 and 24. We investigate in particular the dependencies on the driver properties and variations across the sheath. We find that the ejecta speed principally controls the sheath geoeffectiveness and shows the highest correlations with sheath parameters, in particular in the region closest to the shock. Sheaths of fast ejecta have on average high solar wind speeds, magnetic (B) field magnitudes, and fluctuations, and they generate efficiently strong out-of-ecliptic fields. Slow-ejecta sheaths are considerably slower and have weaker fields and field fluctuations, and therefore they cause primarily moderate geospace activity. Sheaths of weak and strong B field ejecta have distinct properties, but differences in their geoeffectiveness are less drastic. Sheaths of fast and strong ejecta push the subsolar magnetopause significantly earthward, often even beyond geostationary orbit. Slow-ejecta sheaths also compress the magnetopause significantly due to their large densities that are likely a result of their relatively long propagation times and source near the streamer belt. We find the regions near the shock and ejecta leading edge to be the most geoeffective parts of the sheath. These regions are also associated with the largest B field magnitudes, out-of-ecliptic fields, and field fluctuations as well as largest speeds and densities. The variations, however, depend on driver properties. Forecasting sheath properties is challenging due to their variable nature, but the dependence on ejecta properties determined in this work could help to estimate sheath geoeffectiveness through remote-sensing coronal mass ejection observations.Peer reviewe

Power spectra in the sheath of shock-driven ICMEs

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Acceleration of an interplanetary shock through the magnetosheath: a global hybrid simulation

According to most observations and simulations, interplanetary shocks slow down when they propagate through the magnetosheath. In this article, we present results from a self-consistent global hybrid PIC simulation of an interplanetary shock which, by contrast, accelerates as it propagates through the magnetosheath. In this simulation, the solar wind upstream of the interplanetary shock is set up with an Alfvén Mach number MA = 4.5 and the interplanetary magnetic field (IMF) is set up to be almost parallel to the y direction in GSE coordinate system. The ‘planet’ is modelled as a magnetic dipole with no tilt: the dipole is in the GSE’s z direction. In the ecliptic plane (Oxy), which contains the interplanetary magnetic field (IMF), the magnetic field lines are piling up against the magnetopause, and the velocity of the interplanetary shock decreases from 779 ± 48 km/s in the solar wind down to 607 ± 48 km/s in the magnetosheath. By contrast, in the noon-meridian plane (Oxz), which is perpendicular to the IMF, the velocity of the interplanetary shock in the magnetosheath can reach values up to 904 ± 48 km/s. This study suggests that interplanetary shocks can accelerate as they propagate through the magnetosheath. This finding, reported here for the first time, could have important implications for space weather, as it corresponds to the case where an interplanetary shock catches up with a low Alfvén Mach number solar transient such as an interplanetary coronal mass ejection

Statistics of the fluctuations in Sheaths preceding Magnetic Clouds

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Kinetic simulation of magnetic field generation and collisionless shock formation in expanding laboratory plasmas

International audienc

Biermann-Battery-Mediated Magnetic Reconnection in 3D Colliding Plasmas

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