[P-EM13] Study of coupling processes in solar-terrestrial system

[PEM13-03] Study of ionospheric E-region irregularities by Equatorial Atmosphere Radar during annular solar eclipse

*Tatsuhiro Yokoyama¹, Rieko Takagi¹, Mamoru Yamamoto¹, Kornyanat Hozumi², Chihiro Tao², Hiroyuki Shinagawa² (1.Research Institute for Sustainable Humanosphere, Kyoto University, 2.National Institute of Information and Communications Technology)

Keywords:Equatorial Atmosphere Radar, Ionosphere, Solar eclipse, 150-km echoes

The plasma irregularities generated in the ionosphere cause scintillation of radio waves, which seriously degrades electronic navigation by Global Navigation Satellite System (GNSS). A phenomenon called 150-km echoes is one of the plasma irregularities in the E-region. However, the generation mechanism of the plasma irregularities, especially 150-km echoes, has not been clarified yet. A solar eclipse is one of the phenomena that cause plasma irregularities. In order to clarify the ionospheric E-region irregularities during the annular solar eclipse on December 26, 2019, we observed and analyzed the ionospheric conditions during the eclipse in Southeast Asia, with the Equatorial Atmospheric Radar (EAR) and 5 ionosondes, and compared them with simulations by GAIA, a physical model for the neutral and ionized atmospheres. The EAR has been focusing on the 150-km echoes since 2007. We performed a long-term statistical analysis using these results. A statistical analysis revealed that the occurrence of 150-km echoes is inversely correlated with not only the solar activity but also the geomagnetic disturbance due to changes in the electric field and neutral wind caused by the geomagnetic disturbance. The ionosonde observations during the eclipse revealed that the maximum electron density decreased due to the eclipse. Contrary to the previous observations, it was found that it took longer time for the maximum electron density to reach the minimum value at the sites where the obscuration was larger. It is suggested that the plasma transport by electric field or neutral wind may play an important role in such plasma density variation during the eclipse. The EAR observations revealed that the eclipse blocked the photoelectrons, which likely prevented the 150-km echoes, and that the E-region electric field fluctuation caused by the eclipse affected the E-region Doppler velocity . The gap between GAIA simulations and EAR observations is due to the deviation of the neutral atmosphere density and temperature in the model from the reality.