Development of Low Latitude Long Range Ionospheric Radar for Observing Plasma Bubble Irregularities and Preliminary Results

The Low lAtitude long Range Ionospheric raDar (LARID), which consists of two high frequency (HF) radars looking toward the east and west of Hainan Island, respectively, has been developed and installed at Dongfang (19.2 degrees N, 108.8 degrees E, dip lat. 13.8 degrees N), China. This paper describes the system design of LARID and its first observational results of equatorial plasma bubble (EPB) irregularities. The antenna array of LARID is composed of a west-looking array and an east-looking array. Each array consists of 20 log-periodic antennas for transmission and reception and 4 log-periodic antennas for interferometry, and has a beam steering capability in the azimuth angles of +/- 24 degrees due the boresight pointing east (or west). Observational results show that the LARID is capable of detecting backscatter echoes from EPB irregularities and the ground, with a distance of 4,000 km or more away from Hainan Island. Multiple EPB structures were continuously observed on 17 April 2023, with eastward drifts ranging between 70 and 130 m/s. Based on ray tracing simulations, the backscatter echoes of EPB irregularities were due to the 0.5-hop and 1.5-hop propagation modes. The distances between the successive EPB structures were estimated ranging between 500 and 900 km in longitude. The LARID observations, together with other instruments in the East and Southeast Asian sector, provided a clear picture of longitudinal variation of EPBs in 90-125 degrees E. It is expected that the LARID will provide an important tool to study the generation and evolution of EPBs and their short-term prediction in East and Southeast Asia. A Low lAtitude long Range Ionospheric raDar (LARID) operating at 8-22 MHz has been developed and installed at Hainan Island, China First long-range observations of equatorial plasma bubble (EPB) irregularities and their zonal drifts by the LARID were presented The LARID is expected to play an important role in the study of EPB and its short-term forecasting in East and Southeast Asia