Using the Arecibo ISR data to understand the role of the secular variations on the topside ionosphere

The Incoherent Scatter Radar (ISR) technique is a well-established tool for research in the upper atmospheric physics field and is still the most powerful ground-based technique for probing the ionosphere. The ISR at Arecibo Observatory (18.35°N, 66.75°W, which is at a geomagnetic latitude of ~30°N, or 46.7° dip latitude) has a very large aperture, which makes it uniquely suited for sensitive investigations of topside ionosphere parameters during low solar activity. The daily quiet-time variation of the thermal plasma in the upper ionosphere/protonosphere is determined by (1) diffusion along the magnetic flux tube and (2) electromagnetic drift (V) caused by an electric field E, which moves the plasma perpendicular to the magnetic field (B). The focus of this study is to characterize the responses of the ionosphere above the F region peak to the secular changes along the last 30 years based on ISR data exploring the main processes aforementioned. Thus, we present an analysis of the electron density and temperature variations at topside ionosphere for Equinoxes and a comparison of them with the predictions made by the SUPIM-INPE (Sheffield University Plasmasphere Ionosphere Model – INPE).