Seasonal Variation of Daytime Electron Density Irregularity Distributions in the Bottom and Top Sides of the Low Latitude F Region

The occurrence rate of daytime electron density irregularities in the low‐latitude F region around the solar minimum exhibits different seasonal patterns in the Northern Asian sector (near 110°E longitude), depending on the data set used. This study examines this discrepancy using Beidou total electron content (TEC) data and vertical TEC profiles from the radio occultation experiment onboard the Constellation Observing System for Meteorology, and Ionosphere, and Climate (COSMIC) during the period 2017–2019. At the northern low latitudes near 110°E, the irregularity occurrence rate derived from Beidou TEC data is higher around the December solstice than around the June solstice. This seasonal behavior is opposite to that from the in situ satellite measurements on the topside. The irregularity distributions derived from COSMIC TEC profiles reveal altitudinal variations in seasonal occurrence patterns: the occurrence rate is higher around the December solstice than around the June solstice in the bottom side (150–250 km altitude) of the F region, whereas the seasonal pattern on the topside (450–700 km altitude) exhibits the opposite behavior. These seasonal patterns on the bottomside and topside are consistent with those derived from the Beidou TEC and in situ satellite measurements, respectively. These findings suggest that Beidou TEC perturbations during the daytime primarily represent irregularities on the bottom side. We interpret the altitudinal difference in the irregularity distribution as a result of differences in the sources of irregularities at different altitudes.