Global Observations of Day-to-Day Longitudinal Structures of Equatorial Ionization Anomaly by using FORMOSAT-7/COSMIC-2

Abstract:

Forcing from the lower atmosphere is one of the major sources of day-to-day variability in the ionosphere. However, lack of daily observations of global electron density means that investigation of such variations has to mostly rely on model predictions or requires several days or months of measurements to be combined. With the global ionosphere specification (GIS) constructed by assimilating slant total electron content from radio occultation measurements from the FORMOSAT-7/COSMIC-2 and global positioning system receivers, hourly profiles of global 3D electron density are now available to examine daily ionospheric variations based of observations. In this study, the day-to-day variability of equatorial ionization anomaly (EIA) at different longitudes are investigated by using the GIS electron density profiles during 2019-2020. The crest density often appears as an extended single peak structure or as broken double peaks, and the pattern repeats with an approximate periodicity of 2–3 days. Such peculiar EIA features are prominently seen during local noon hours and appear over Asian longitude sectors in the September equinox, but seems to exist over the Pacific sector throughout the year. Vertical electron density structures show that such EIA variations become most pronounced around 300 km altitude, which also persists in integrated ionospheric electron contents. Tidal analysis is carried out to understand the possible driving forces that cause such day-to-day variabilities. Further, the day-to-day tidal amplitude changes during 2019-2020 are examined to investigate how the daily variations of EIA density is accounted by corresponding variabilities of the forcing from below.