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Lockwood, M.; Owens, M. J.; Barnard, L. A.
Journal of geophysical research. Space physics, March 2023, 2023-03-00, 20230301, Volume: 128, Issue: 3Journal Article
We study Universal Time (UT) variations in the magnetospheric response to Coronal Mass Ejection (CME) impacts, using the example of the two CMEs that led to the destruction of 38 out of 49 Starlink satellites in early February 2022. We employ the Expanding‐Contracting Polar Cap model to analyze the variation in the size of the ionospheric polar caps and an eccentric dipole model of the geomagnetic field and thereby quantify the UT variations caused by the inductive effect of the diurnal motions of the geomagnetic poles in a “geocentric‐solar” frame of reference (i.e., a frame with an X axis that points from the center of the Earth to the center of the Sun). The results show that use of a quasi‐steady convection model predicts a similar global power deposition into the thermosphere as that inferred here, but does not give the same division of that power between the northern and southern hemispheres. We demonstrate that, through the combined effects of the Russell‐McPherron dipole‐tilt mechanism on solar‐wind magnetosphere coupling and of the diurnal polar cap motions in a geocentric‐solar frame, the power deposited varies significantly with the arrival UT of the CMEs at Earth. We also show that in the events of early February 2022, both CMEs arrived at almost the optimum UT to cause maximum thermospheric heating. Plain Language Summary We use a recent well‐publicized space‐weather event as an example of a previously‐overlooked aspect of the behavior of near‐Earth space. The event took place in early February 2022, when 38 out of 49 Starlink satellites burned up in Earth's atmosphere because two Coronal Mass Ejections (CMEs) emitted from the Sun hit the Earth and had a larger heating effect on the upper atmosphere than expected. The new element that we introduce is the effect of the eccentricity of Earth's magnetic field which is reflected in the offset of the magnetic pole from the geographic pole being considerably greater in the southern hemisphere than in the northern hemisphere. This introduces a daily variation into the response of Earth's magnetosphere to a given solar wind disturbance and we show that the effect would have been less severe during the February 2022 event had the CMEs arrived either earlier or later than they did. Key Points Analysis of the CME effects causing the loss of 38 Starlink satellites shows that the terrestrial response to a CME depends on its impact UT UT effects are caused by diurnal motions of the poles and the eccentric nature of the geomagnetic field Joule heating dominated in the southern polar cap during the first CME and initially during the second but later was dominant in the north
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