Imaging Radar Observations of the Daytime F-Region Irregularities in Low-Latitudes of China

Hainan COherent scatter Phased Array Radar has recorded four patches of daytime F-region field-aligned irregularities on 31 May 2021, and it is the first time to investigate the daytime irregularities by the radar imaging technique. In-beam radar images are plotted on the curved plane transverse to the geomagnetic field lines. The displayed daytime irregularities present the obliquely elongated band-like structures and the corresponding scatter regions extend to hundreds of kilometers in range and narrow to a few kilometers in the zonal direction. The diffuse and isolated structures were also observed in the radar images. The radar image sequences indicate that the irregularities were continuous in height as they drifted westward. The daytime irregularities maintained the oblique elongated structures that resemble the morphological features of the nighttime equatorial plasma bubbles. Combined with the in situ satellite measurements, these daytime F-region irregularities are interpreted to be the remnants of the previous night's bubbles and come from the higher altitudes near the magnetic equator.