ICON Observations of Equatorial Ionospheric Vertical ExB and Field‐Aligned Plasma Drifts During the 2020–2021 SSW

Previous studies have revealed large anomalies in vertical ExB drift during the sudden stratospheric warming (SSW), and little attention focused on the behaviors of field‐aligned plasma drift. We report the first simultaneous observations of the equatorial ionospheric vertical ExB and field‐aligned plasma drifts and neutral winds during the 2020–2021 SSW, using the Ionospheric Connections Explorer (ICON) satellite measurements. The downward ExB drift is observed in the afternoon equatorial topside ionosphere in longitudes of ∼180°–270°E, in good agreement with the Jicamarca incoherent scatter radar measurements. What is more, the ICON records the afternoon northward disturbance in field‐aligned plasma drift, which is mainly due to the disturbance meridional wind. The enhanced semidiurnal tides maybe contribute to the disturbances in equatorial topside plasma drifts and neutral winds. This study indicates that the field‐aligned motion is an important factor in the ionosphere‐thermosphere responses to SSW. Plain Language Summary Previous studies have revealed that the sudden stratospheric warming causes large anomalies in the low‐latitude ionosphere via the vertical ExB plasma drift driven by the E region wind dynamo. However, ionospheric electron density distributions are not only influenced by the vertical ExB drifts, but also by the plasma drifts along geomagnetic field lines driven by the F region neutral wind and plasma pressure gradient and gravity. In the past studies, little attention focused on the behaviors of the F region field‐aligned plasma drifts during the sudden stratospheric warming (SSW). Ionospheric Connections Explorer (ICON) provides the first simultaneous observations of the E and F region neutral winds and topside ionospheric vertical ExB and field‐aligned plasma drift. The results show that the enhanced semidiurnal tides can cause the significant disturbances in both the F region vertical ExB and field‐aligned plasma drift and neutral winds during the 2020–2021 SSW. The observed neutral wind and plasma drift will likely impact Earth's ionospheric plasma environment and imply a substantial impact of the lower atmosphere on ionospheric space weather. Key Points The Ionospheric Connections Explorer satellite observes the afternoon downward plasma drift during sudden stratospheric warming (SSW) Disturbance in the F region neutral wind and their contribution to the field‐aligned plasma drift during SSW are observed for the first time The e