Complex Ionospheric Irregularity Echoes Observed by Low Latitude Long Range Ionospheric Radar

Abstract Using the Low lAtitude long Range Ionospheric raDar (LARID) at Dongfang (19.2°N, 108.8°E), Hainan Island, China, we report a unique case of complex ionospheric irregularities observed on 9 June 2024. The most interesting aspect is the first‐time long‐range (∼2,000 km) detection of daytime ionospheric irregularities and post‐sunset band‐like irregularity structures by HF radar at low latitudes. By incorporating VHF radar and global navigation satellite system (GNSS) rate of total electron content index (ROTI) observations, the radio wave propagation modes of the ionospheric irregularity events observed by LARID and evolution of these ionospheric irregularities were analyzed. The daytime ionospheric irregularity echoes observed by LARID over the Indian Ocean exhibited westward drift, evident in both echo patterns and Doppler velocities. These ionospheric echoes were likely backscattered from E region field aligned irregularities by the “downleg” of the 1‐hop HF ray path. The post‐sunset irregularity echoes observed by LARID over Indian Ocean manifested as a band‐like structure. This structure was closely attached to the bottom of ground/sea scatter echoes and showed the same range variation as the ground/sea scatters. GNSS ROTI observation revealed that irregularities primarily appeared south of the magnetic equator and drifted eastward across the eastern longitudes in later hours. Analysis indicates that the displacement of small‐scale irregularities within the equatorial plasma bubble event along the magnetic field likely contributed to the band‐like irregularity structure observed by LARID and the asymmetric irregularity distribution observed by GNSS.