Characteristics of ionospheric wavenumber structures in COSMIC-2 RO observations

High-rate radio occultation (RO) in COSMIC2 (FORMOSAT7) enables us to investigate the continuous variability of the ionosphere at a Spatio-temporal resolution which was unthinkable a few decades ago. We present unique characteristics of ionospheric wavenumber structures observed using COSMIC2 RO data, not reported before. Altitude-longitude maps of normalized electron density of local time ionosphere in the Equatorial Ionization Anomaly (EIA) region, indicate wavenumber structures with vertically tilted phase fronts. The longitudinal extent of a tilted wavenumber 4 (WN4) phase front approximates its zonal wavelength in the local-time ionosphere, i.e., ~90⁰ in longitudes. WN4 filtered component indicates a more significant tilt (when visible), with a larger longitudinal extent of a wavenumber structure in the vertical plane. High latitudinal resolution investigation of wavenumber structure presents a significant difference in the characteristics of wavenumber structures at different geomagnetic latitudes within the EIA region. During the daytime WN4 structure in the EIA crest region is out of phase with respect to that in the EIA trough region. However, the two were observed to be in phase with each other during the nighttime. These characteristics also vary with altitude. Above 400 km WN4 structure in the EIA crest and trough region is seen to be in phase with each other at all local times. CREST. These results highlight that, while the direct role of non-migrating tides, which provides the vertical tilt to the wavenumber structure, maybe the dominant mechanism, however, electrodynamical transport of plasma in the EIA region driven by eastward zonal electric field during the daytime also plays a significant role in the formation of wavenumber structure. During the nighttime, in the absence of the fountain effect, wavenumber structures are driven by the direct forcing of non-migrating tides within the EIA region. The results will be presented and discussed in light of existing knowledge of the formation of wavenumber structures and the impact of non-migrating tides on the local-time ionosphere.