Daytime Ionospheric F‐Region Topside Irregularities Associated With Significant Density Enhancement at Low Latitudes During the 12 November 2025 Magnetic Storm

Abstract In this study, daytime F‐region irregularities were observed at low latitudes during the main phase of the 12 November 2025 strong magnetic storm, causing intense very high frequency radar echoes ranging hundreds of kilometers in altitude. They were generated mainly at the F‐region topside, associated with significant plasma density enhancement possibly driven by storm‐time electric field polarity transition from eastward to westward, or meridional wind. The enhanced plasma density could provide favorable downward density gradient for generating the daytime irregularities via gradient drift instability at F‐region topside under westward storm‐time electric field. The irregularities occurred over a large zonal region spanning thousands of kilometers. The study provides new possibility of low‐latitude F‐region irregularities different from the major irregularity types over low latitudes, which could be the first report of its kind at this region.