Geocoronal Solar Wind Charge Exchange Process Associated With the 2006‐December‐13 Coronal Mass Ejection Event.

We report the discovery of a geocoronal solar wind charge exchange (SWCX) event corresponding to the well‐known 2006 December 13th coronal mass ejection (CME) event. Strong evidence for the charge exchange origin of this transient diffuse emission is provided by prominent non‐thermal emission lines at energies of O7+, Ne9+, Mg11+, Si12+, Si13+. Especially, a 0.53 keV emission line that most likely arises from the N5+ 1s15p1 → 1s2 transition is detected. Previously, the forecastability of SWCX occurrence with proton flares has been disputed. In this particular event, we found that the SWCX signal coincided with the arrival of the magnetic cloud inside CME, triggered with a time delay after the proton flux fluctuation as the CME shock front passed through the Earth. Moreover, a spacecraft orbital modulation in SWCX light curve suggests that the emission arises close to the Earth. The line of sight was found to always pass through the northern magnetospheric cusp. The SWCX intensity was high when the line of sight passed the dusk side of the cusp, suggesting an azimuthal anisotropy in the flow of solar‐wind ions inside the cusp. An axisymmetric SWCX emission model is found to underestimate the observed peak intensity by a factor of about 50. We suggest this discrepancy is related to the azimuthal anisotropy of the solar‐wind flow in the cusp. Plain Language Summary: We discovered compelling observational evidence of the coronal mass ejection (CME) interacting with Earth's magnetosphere by the Suzaku satellite. The signal arises from a process called charge exchange, in which heavily charged ions within the CME interact with neutral hydrogen within Earth's magnetosphere. This specific process, known as solar wind charge exchange (SWCX), was associated with the CME event occurred on 2006 December 13th during the solar minimum. This event provided us with a unique opportunity to gain insights into the interplanetary consequences of CMEs. Despite a delay relative to the shock wave associated with the CME, the SWCX coincided with the arrival of a magnetic cloud. This suggests that solar wind ions were guided along magnetic field lines into a region near Earth called the cusp, through a process known as magnetic reconnection. Additionally, we observed that SWCX emissions were most pronounced when the satellite's line of sight passed through the dusk region of the cusp. This indicates that the CME ejecta may have followed a path along the Parker spiral—a magnetic field pattern twisted by solar rotation—resulting in the solar wind arriving from a direction distinct from that of the Sun. Key Points: We discover a solar wind charge exchange event with Suzaku X‐ray satellite driven by the 2006‐December‐13th coronal mass ejectionThe solar wind charge exchange (SWCX) occurrence time coincides with the CME magnetic cloud arrival. It is a useful knowledge in space weather forecastingWe modeled the light curve variation of the SWCX. The result indicates that the solar‐wind flow is anisotropic in the cusp [ABSTRACT FROM AUTHOR]