Unexpected High Occurrence of Daytime F‐Region Backscatter Plume Structures Over Low Latitude Sanya and Their Possible Origin

Abstract

AbstractIonospheric F‐region irregularity backscatter plumes are commonly regarded as a nighttime phenomenon at equatorial and low latitudes. Using the Sanya (18.4°N, 109.6°E, dip lat. 12.8°N) VHF radar, F‐region backscatter echoes were observed at daytime during 0700–1800 LT, with an unexpected high occurrence in June solstice of solar minimum. Radar interferometry and ICON satellite in situ results show that the daytime F‐region echoes were from plume structures consisting of field‐aligned irregularities. The daytime echoing structures appeared mostly above 350 km altitude, extending up to 650 km or more with apparent westward drifts at times. We surmise that the daytime F‐region echoes were due to equatorial plasma bubble irregularities generated on the previous night around 100–125°E, where the irregularities could survive unexpectedly long time, beyond sunrise as vertically elongated fossil plumes. Under the ionospheric background dynamics, the fossil plumes could be elevated to high altitudes and drift zonally over Sanya.