Quiet Time Ionosphere‐Thermosphere Predictability During Sudden Stratospheric Warmings in TIE‐GCM

Abstract 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 TIE‐GCM. The extension of subseasonal hindcasts into the IT region enables the first comprehensive investigation of IT predictability during SSWs. By systematically analyzing 15 major SSW events occurring between 2000 and 2023, we find that hindcast skill in the IT system is enhanced during SSW periods relative to the climatological baseline, although this enhancement is highly spatially and event dependent. Hindcasts initialized 4–10 days prior to SSW onset demonstrate high skill in predicting SSW‐driven O/N 2 anomalies at middle to 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) increases by approximately 1 day for TEC and up to 2–3 days for O/N 2 in specific regions (e.g., the Southern Hemisphere) relative to climatological baselines.