Evaluation of Atmospheric 3‐Day Waves as a Source of Day‐to‐Day Variation of the Ionospheric Longitudinal Structure

We report for the first time the day‐to‐day variation of the longitudinal structure in height of the F2 layer (hmF2) in the equatorial ionosphere using multi‐satellite observations of electron density profiles by the Constellation Observing System for Meteorology, Ionosphere and Climate‐2 (COSMIC‐2). These observations reveal a ∼3‐day modulation of the hmF2 wavenumber‐4 structure viewed in a fixed local time frame during January 30–February 14, 2021. Simultaneously, ∼3‐day planetary wave activity is discerned from zonal wind observations at ∼100 km by the Ionospheric Connection Explorer (ICON) Michelson Interferometer for Global High‐Resolution Thermospheric Imaging (MIGHTI). This signature is not observed at ∼180–250 km altitudes, suggesting the dissipation of this wave below the F‐region. We propose that the 3‐day variation identified in hmF2 is likely caused by the planetary wave‐tide interaction through the E‐region dynamo. Plain Language Summary The F‐region ionosphere at ∼200–400 km altitudes often shows global‐scale structures and variations that are attributed to neutral atmospheric tides and planetary waves propagating from the lower atmosphere. Previous observations have identified 3‐day planetary waves at E‐region altitudes (∼100 km), but the vertical extent of these waves has not yet been determined due to lack of high altitude observations. For this study, we use newly obtained concurrent atmospheric and ionospheric observations that provide the necessary coverage. Our study provides the first observational evidence of the vertical propagation of a 3‐day planetary wave across both E‐ and F‐region altitudes. The results suggest that this wave causes the day‐to‐day variation of the four‐peaked longitudinal structure in the equatorial ionosphere through modulating the E‐region dynamo rather than direct propagation into the F‐region. Key Points First examination of 3‐day wave activity across ∼100–250 km altitudes and the ionospheric peak height change using coordinated satellites Ionospheric longitudinal structure shows a ∼3‐day variation coinciding the planetary wave observed in atmospheric winds at ∼100 km altitude The neutral atmospheric 3‐day wave signature is not observed at ∼180–250 km altitudes, suggesting the modulation of tides in the E‐region