Observation of Shortwave Fadeout Events Using Chinese Dual Auroral Radar Network (CN‐DARN) During the Severe Solar Storm in May 2024

Abstract

Shortwave fadeout (SWF) is a typical dayside high‐frequency radio disturbance caused by solar flare‐induced ionospheric ionization enhancement. Using newly built Chinese Dual Auroral Radar Network (CN‐DARN) observations, we investigate two X‐flare‐driven SWFs during the May 2024 geomagnetic superstorm (SYM‐H = −518 nT), on 10 May (pre‐storm) and 11 May (storm main phase). Comparative analysis reveals strong ionospheric negative storm modulations on SWF characteristics: a prominent Doppler flash (line‐of‐sight velocity peak 137 m/s, exceeding prior records) preceded the pre‐storm SWF, but none was detected for the event during the main phase of the storm. The latter showed layered radar backscatters (E‐vs. F‐region reflections) with divergent interruption durations (∼20 vs. ∼80 min); F‐region backscatters had abnormally prolonged recovery (>3 hr to quiet‐time levels), while E‐region signals and the pre‐storm SWF recovered in ∼1 hr. We also find radar transmission frequency and local time impact SWF observations. These results highlight ionospheric negative storm effects on flare‐induced SWFs, clarify their characteristics in complex ionospheric conditions, and support their accurate forecasting.