Thermospheric and Ionospheric Planetary Wave Variability Associated With the 2018 SSW

Abstract

This study investigates thermospheric and ionospheric planetary wave (PW) variability during the 2018 sudden stratospheric warming (SSW) using exospheric temperature (Tex) retrieved from ionosonde observations at Beijing and Wuhan. Pronounced Q5DW and Q10DW variability was identified in both observed NmF ₂ and retrieved Tex. Comparisons with F10.7, IMF Bz, and Ap indices, together with model simulations, are used to evaluate possible contributions from geomagnetic forcing. The Q5DW shows substantial temporal correspondence with the Ap index and model simulations, indicating nonnegligible contributions from geomagnetic forcing. In contrast, although pronounced Q10DW variability is also present in the Ap index and model simulations, its onset timing and subsequent temporal evolution show large differences from those in the observed NmF ₂ and retrieved Tex. Independent SABER and MLS temperature observations reveal pronounced westward‐propagating zonal‐wavenumber‐1 Q10DW‐W1 and Q5DW‐W1 variability in the middle atmosphere during the SSW interval. The middle‐atmospheric Q10DW‐W1 and thermospheric Q10DW show broadly similar temporal evolution and station‐dependent development, with pronounced and sustained enhancements becoming evident earlier near Beijing than near Wuhan. Correlation analysis further shows strong temporal correspondence between their fitted amplitude envelopes, with maximum correlations of approximately 0.91 and 0.93 for SABER and 0.95 and 0.92 for MLS near Beijing and Wuhan, respectively. Moreover, the vertical phase structure of Q10DW‐W1 exhibits clear downward phase progression near Beijing and Wuhan, indicating possible upward propagation. These combined observations provide support for a possible SSW‐related middle‐atmosphere‐thermosphere connection associated with the Q10DW.