Temporal modulations of the longitudinal structure in F2 peak height in the equatorial ionosphere as observed by COSMIC

This study investigates the temporal variability of longitudinal structure in F-2 layer peak height (h(m)F(2)) in the equatorial ionosphere. For this study, electron density profiles retrieved from the radio occultation measurements by the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) are fitted with a two-layer Chapman function to determine h(m)F(2). The h(m)F(2) values in the magnetic equatorial region display a four-peaked longitudinal structure that has been identified in other ionospheric observations. The four-peaked structure is likely the signature of the forcing by the eastward propagating nonmigrating diurnal tide with zonal wave number 3 (DE3). Further analysis for the period of prominent four-peaked structure over August-September 2008 finds that this structure exhibits a 5 day periodicity. Coincidentally, the all-sky interferometric meteor radar's wind measurements at Thumba (8.5 degrees N, 77 degrees E) in India for the mesosphere and lower thermosphere indicate strong 5 day planetary waves within that time period. The observed temporal periodicity of the four-peaked longitudinal structure in h(m)F(2) could thus be attributed to the interaction of DE3 with a 5 day planetary wave.