Predictability of the Ionosphere-Thermosphere during Sudden Stratospheric Warmings

We investigate the predictability of the ionosphere-thermosphere (IT) region during sudden stratospheric warmings (SSWs) by using subseasonal hindcasts in the Community Earth System Model, version 2 with the Whole Atmosphere Community Climate Model (CESM2[WACCM6]) to force the lower boundary of the TIEGCM. The extension of subseasonal hindcasts into the IT region enables the first comprehensive investigation of IT predictability during SSWs. By systematically analyzing 14 major SSW events occurring between 2000 and 2023, we demonstrate that SSWs drive enhanced predictability in the IT system, although this enhancement is highly spatially dependent and varies by event. Hindcasts initialized 4–10 days prior to SSW onset demonstrate high skill in predicting SSW-driven O/N2 anomalies at high latitudes and Total Electron Content (TEC) anomalies in the low-latitude American and Eastern Pacific sectors. Furthermore, we identify a distinct enhancement in short-term forecast skill during the post-SSW recovery phase. During this interval, the window of useful predictability (anomaly correlation coefficient > 0.6) extends by approximately 1 day for TEC and up to 2 days for thermospheric composition relative to climatological baselines. These results suggest that the dominant source of predictability evolves from active vertical coupling during the SSW onset to stabilization and persistence during the recovery, establishing SSWs as a critical window of opportunity for space weather forecasting.