Geometry, Kinematics and Heliospheric Impact of a Large CME-driven Shock in 2017 September. (arXiv:1811.10162v1 [astro-ph.SR])

Geometry, Kinematics and Heliospheric Impact of a Large CME-driven Shock in 2017 September. (arXiv:1811.10162v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Liu_Y/0/1/0/all/0/1">Ying D. Liu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhu_B/0/1/0/all/0/1">Bei Zhu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhao_X/0/1/0/all/0/1">Xiaowei Zhao</a>

A powerful coronal mass ejection (CME) occurred on 2017 September 10 near the
end of the declining phase of the historically weak solar cycle 24. We obtain
new insights concerning the geometry and kinematics of CME-driven shocks in
relation to their heliospheric impacts from the optimal, multi-spacecraft
observations of the eruption. The shock, which together with the CME driver can
be tracked from the early stage to the outer corona, shows a large oblate
structure produced by the vast expansion of the ejecta. The expansion speeds of
the shock along the radial and lateral directions are much larger than the
translational speed of the shock center, all of which increase during the flare
rise phase, peak slightly after the flare maximum and then decrease. The near
simultaneous arrival of the CME-driven shock at the Earth and Mars, which are
separated by 156.6$^{circ}$ in longitude, is consistent with the dominance of
expansion over translation observed near the Sun. The shock decayed and failed
to reach STEREO A around the backward direction. Comparison between ENLIL MHD
simulations and the multi-point in situ measurements indicates that the shock
expansion near the Sun is crucial for determining the arrival or non-arrival
and space weather impact at certain heliospheric locations. The large shock
geometry and kinematics have to be taken into account and properly treated for
accurate predictions of the arrival time and space weather impact of CMEs.

A powerful coronal mass ejection (CME) occurred on 2017 September 10 near the
end of the declining phase of the historically weak solar cycle 24. We obtain
new insights concerning the geometry and kinematics of CME-driven shocks in
relation to their heliospheric impacts from the optimal, multi-spacecraft
observations of the eruption. The shock, which together with the CME driver can
be tracked from the early stage to the outer corona, shows a large oblate
structure produced by the vast expansion of the ejecta. The expansion speeds of
the shock along the radial and lateral directions are much larger than the
translational speed of the shock center, all of which increase during the flare
rise phase, peak slightly after the flare maximum and then decrease. The near
simultaneous arrival of the CME-driven shock at the Earth and Mars, which are
separated by 156.6$^{circ}$ in longitude, is consistent with the dominance of
expansion over translation observed near the Sun. The shock decayed and failed
to reach STEREO A around the backward direction. Comparison between ENLIL MHD
simulations and the multi-point in situ measurements indicates that the shock
expansion near the Sun is crucial for determining the arrival or non-arrival
and space weather impact at certain heliospheric locations. The large shock
geometry and kinematics have to be taken into account and properly treated for
accurate predictions of the arrival time and space weather impact of CMEs.

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