Latitudinal Dependence of Daytime Electron Density Bite‐Out in the Ionospheric F2‐Layer

Abstract

AbstractDaytime bite‐out in diurnal variations of the F2‐layer electron density often occurs in the equatorial ionosphere, while it was less reported at mid‐latitudes. In this paper, the climatology of daytime bite‐out was investigated using ionosonde measurements in the East Asia sector. The bite‐out can take place at both low‐ and mid‐latitudes and mainly in summer months; and it significantly depends on latitudes. The bite‐out appears as foF2 stays stable or slightly decreases for hours in early morning and then enhances till late afternoon at equatorial ionization anomaly (EIA) crest latitudes. It becomes more significant and durative at mid‐latitudes; foF2 increases and reaches a peak in the morning and then continuously declines till afternoon. In particular, the diurnal variation pattern of foF2 is nearly opposite to that of photoionization at the higher‐latitude station Yakutsk at solar maximum. Moreover, the bite‐out is more remarkable at solar minimum (maximum) than at solar maximum (minimum) at low‐latitudes (mid‐latitudes). The trans‐equator plasma outflow caused by neutral winds and the upward thermal diffusion can result in the bite‐out in the EIA crest region, while the subsequent field‐aligned plasma influx induced by the fountain effect ceases it. At mid‐latitudes, the diurnal variation magnitudes of the thermospheric composition and photoionization production rate are also important factors determining bite‐out degree in addition to neutral wind‐induced downward transport and the upward thermal diffusion.