Modeling the daytime, equatorial ionospheric ion densities associated with the observed, four-cell longitude patterns in E x B drift velocities

Previous studies have quantified the longitude gradients in E x B drift associated with the four-cell tidal structures and have confirmed that these sharp gradients exist on a day-to-day basis. For this paper, we incorporate the Ion Velocity Meter (IVM) sensor on the Communications/Navigation Outage Forecasting System satellite to obtain the daytime, vertical E x B drift velocities at the magnetic equator as a function of longitude, local time, and season and to theoretically calculate the F region ion densities as a function of altitude, latitude, longitude, and local time using the Global Ionosphere Plasmasphere model. We compare calculated ion densities assuming no longitude gradients in E x B drift velocities with calculated ion densities incorporating the IVM-observed E x B drift at the boundaries of the four-cell tidal structures in the Peruvian and the Atlantic longitude sectors. Incorporating the IVM-observed E x B drift velocities, the ion density crests rapidly converge to the magnetic equator between 285 and 300 degrees E geographic longitude, are absent between 300 degrees and 305 degrees, and move away from the magnetic equator between 305 degrees and 340 degrees. In essence, the steeper the longitude gradient in E x B drifts, the steeper the longitude gradient in the equatorial anomaly crest location.