Investigating the Source and Characteristics of Winter Daytime MSTIDs Using the Chinese Dual Auroral Radar Network (CN‐DARN)

Abstract

Medium‐scale traveling ionospheric disturbances (MSTIDs) are important wave‐like perturbations in the ionosphere. Although some previous studies have been conducted, the source of winter daytime MSTIDs remains unclear. Using joint observations from the Chinese Dual Auroral Radar Network (CN‐DARN) of the Chinese Meridian Project Phase II, the Atmospheric Infrared Sounder (AIRS), and ERA5 Reanalysis data, this study provides observations linking stratospheric polar vortex variability, gravity wave (GW) activity, and daytime MSTIDs over the Asian mid‐latitudes. We analyzed an exceptionally strong polar vortex event in February 2025. The observation of pronounced MSTIDs activity by CN‐DARN was accompanied by remarkably intense gravity wave activity during the same event. In contrast, we examined the same period in 2024, which was a typical polar vortex breakdown event. We found that GW activity was weak, and the occurrence rate of MSTIDs was very low. The analysis results show that daytime MSTIDs propagated predominantly southward with propagation azimuths ranging from 129° to 177° (measured clockwise from geographic north), horizontal phase velocities of 110–218 m/s, and periods of 20–24 min during February 2025. Comparative analysis suggests that polar vortex activity is likely a source of wintertime daytime MSTIDs. We performed WACCM‐X simulations to investigate daytime neutral winds at 200 km altitude during different polar atmospheric activities in winter. The simulation results indicate that stronger northwestward neutral winds occur at middle and high latitudes during polar vortex events than during polar vortex breakdown events, which favors the propagation of southward MSTIDs. This study establishes a link between the polar vortex, GWs, and MSTIDs in the Asian sector, advancing the understanding of MSTID sources and characteristics.