Poleward Disturbances in Thermospheric Winds During the 3–4 November 2021 Geomagnetic Storm

Abstract This study focuses on ionosphere‐thermosphere coupling over North America during the 3–4 November 2021 strong geomagnetic storm (Kp 8−). We comprehensively analyze storm‐time ionospheric and thermospheric disturbances using data from ground‐based instruments at Poker Flat, Millstone Hill, and Urbana, as well as satellite observations and model data. Significant features of ionosphere‐thermosphere dynamics during the storm include (a) equatorward (−300 m/s) and poleward (50 m/s) surges at Millstone Hill (42.37 glat) and a poleward surge (75 m/s) at Urbana (40.13 glat) in the magnetic local time (MLT) post‐midnight sector, (b) ion velocities greater than −1,500 m/s at Poker Flat accompanied by a deep ionospheric trough moving to latitudes as low as 40 glat suggesting SAPS activity, (c) a widespread electron density depression in the morning hours due to an extended composition disturbance zone and (d) Large‐Scale Traveling Ionospheric Disturbances (LSTIDs) related to disturbances in equatorward winds in the post‐poleward wind interval. Results show that the equatorward and poleward surges were not accompanied by LSTIDs, which suggests that the extreme disturbances in meridional winds could have mainly been caused by SAPS forcing, due to ion drag and pressure gradients, rather than equatorward propagating Traveling Atmospheric Disturbances (TADs). Furthermore, the MLT location of Millstone Hill and Urbana indicates that during the disturbances both stations would have been located within the eastward backflow sector of the SAPS, which likely contributed to the complicated ion‐neutral dynamics.