Zonally Symmetric Planetary Wave Signatures in F-Region Electron Densities

Planetary waves (PW) originating from the stratosphere and mesosphere induce significant oscillations in the F-region ionosphere at periods of 2–20 days. It appears intriguing because PWs cannot propagate directly into the ionosphere, raising questions about the mechanisms responsible for their periodicities in this region. Wavenumber-period spectra of electron density (Ne) variability in PW periods derived from COSMIC-2 (Constellation Observing System for Meteorology, Ionosphere, and Climate-2) observations demonstrate that roughly half of the variability is associated with zonally symmetric (S0) oscillations. However, the variability associated with zonally symmetric oscillations remains an open question, because it cannot be due to straightforward E-region dynamo action. This work focuses on unravelling the possibilities behind the S=0 vacillations in the F-region ionosphere. We investigate two possible explanations. The first hypothesis proposes that longitudinal asymmetries in conductivities modify wind-driven currents and generate polarization electric fields that map into the F-region through vertical ion drifts. Local time–resolved PW analyses show that s = 0 amplitudes during morning hours are consistent with the rapid increase in conductivities at dawn in the E-region. These results suggest that conductivity gradients may play a key role in mapping PW variability into zonally symmetric F-region oscillations. The second hypothesis considers the in-situ generation through nonlinear ion–neutral (hydromagnetic) coupling during solar maximum. It suggested that the modulation of s = 1 PW oscillation in the electric field by the wave-1 zonal variation in the magnitude of the geomagnetic field may produce zonally symmetric oscillation in the F-region.