[P-EM13] Coupling Processes in the Atmosphere-Ionosphere System

[PEM13-P03] Daytime 150-km field-aligned irregularity echoes observed by a VHF radar at Chumphon, Thailand

*Yuichi Otsuka¹, Kornyanat Hozumi², Michi Nishioka², Takuya Tsugawa², Susumu Saito⁵, Pornchai Supnithi ³, Punyawi Jamjareegulgarn⁴ (1.Institute for Space-Earth Environmental Research, Nagoya University, 2.National Institute of Information and Communications Technology, 3.King Mongkut's Institute of Technology Ladkrabang, 4.King Mongkut's Institute of Technology Ladkrabang, Prince of Chumphon Campus, 5.Electronic Navigation Research Institute)

Keywords:150-km echo, radar, FAI, equatorial ionosphere, ionospheric irregularity

Daytime Field-Aligned Irregularities (FAIs) around an altitude of 150 km, so-called 150-km FAIs, have been observed with VHF radars in the equatorial regions. We report the 150-km FAIs observed with the 39.65 MHz VHF radar at Chumphon, Thailand, which has been operating since January 2020. The Chumphon radar is composed of a linear array of 18 three-element Yagi antennas. For the E-region and 150-km FAI echo measurements, the radar beam is allocated to 10 directions from -48 to 60 deg in azimuth around the north with a step of 12 deg. The 150-km FAI echos were observed frequently during a period between May and August 2020. The echo intensity of the 150-km echoes shows zonal asymmetry while the echo intensity of E-region FAIs does not depend on the azimuth. The 150-km FAI echo intensity is higher on the eastward beams than the westward beams. The most intense echo is observed at 36-46 deg east with respect to the magnetic north, on average.The altitude of the echo appearance also shows the zonal asymmetry. The echo altitude increases with viewing from the east to west by approximately 5 deg between -45 deg and 45 deg in azimuth. This zonal asymmetry of the echo intensity and altitude is consistent with that of the 150-km FAI echoes observed by the EAR (Equatorial Atmosphere Radar) at Kototabang, Indonesia, located at approximately 10 deg south in the almost same longitude as Chumphon, whereas the echo intensity of the 150-km echo over Kototabang is highest at 6 deg east from the north.