ALBERT

Description: In this study, we perform the first comprehensive comparison of ion density (Ni) in the topside ionosphere measured by the Langmuir probe (LP) and faceplate (FP) of the thermal ion imager on board Swarm satellites. Our results show a systematic difference between the LP and FP derived Ni values, and the systematic difference shows prominent dependences on solar flux, local time, and season. Although both Ni datasets show generally good linear regression with electron density (Ne) measurements from the incoherent scatter radar (ISR) located at Jicamarca, the Ni derived from LP shows an additional dependence on the solar flux, while such a dependence cannot be seen in the FP-derived Ni. We suggest that the solar flux dependence of LP-derived Ni is related to the ion compositions change at Swarm altitude, which has not been properly accounted for in the LP processing algorithm. More light ions (e.g., H+), diffusing down from the plasmasphere to the Swarm altitude, seem to cause the overestimation of Ni from LP during low solar activity. A linear relation between the Swarm LP-derived Ni and ISR Ne is derived, and such a function is recommended to be implemented into further updates of the Swarm LP plasma density data.

Description: The International Reference Ionosphere (IRI) model is recognized as the official standard for Earth's ionosphere by the International Standardization Organization, the International Union of Radio Science, the Committee on Space Research, and the European Cooperation for Space Standardization. As requested by these organizations, IRI is an empirical model representing the primary ionospheric parameters based on the long data record that exists from ground and space observations of the ionosphere. The core model describes monthly averages of the electron density, electron temperature, ion temperature, and ion composition globally in the altitude range from 60 to 2,000 km. Over time additional parameters were added in response to community requests, this includes the equatorial ion drift, the occurrence probability of spread-F, auroral boundaries and the electron content from the bottom of the ionosphere to a user-specified altitude. We will present the latest version of the model, which includes several improvements and new models for the ion temperature, the ion drift, the D-region electron density, and the electron density in the topside and plasmasphere. A special focus in recent years has been on assimilative methods to bring IRI predictions closer to real-time conditions with the help of measured parameters. An overview of these methods will be provided and we will discuss the future plans for the IRI model. A comprehensive description of the model was recently published in Reviews of Geophysics (Bilitza et al., doi:10.1029/2022RG000792) providing a deeper understanding of the model architecture, its scientific background and its mathematical formalism.

Description: Modeling of the topside ionosphere (from F peak to ~2000 km) suffers from a scarcity of data because ground ionosondes only reach up to the F peak. Millions of topside ionograms had been recorded by the Alouette 1,2 and ISIS 1,2 satellites between 1962 and 1990 that were never fully analyzed. The satellites carried topside sounders, the satellite equivalent of the ground-based ionosonde, and provided the first global view of the topside ionosphere. The topside sounders were designed as analog systems that recorded ionograms on 35 mm film for analysis by visual inspection. Many nations participated in the data analysis process that involved manual scaling of the ionograms and inversion into electron density profiles. But because of the tedious manual process only a small percentage of the recorded ionograms was converted to electron density profiles. We were able to digitize a significant portion of the 60 satellite years of analog data before the tapes were discarded. In a second step we worked with a team at the University of Massachusetts Lowell who developed the Topside Ionogram Scalar with True-Height inversion (TOPIST) software for the automated scaling and inversion of the traces on the digital ionograms into electron density profiles thus avoiding the very limiting manual process. As a result of our project close to a million digital topside ionograms and electron density profiles are now available for browsing/plotting/downloading at NASA's Space Physics Data Facility (https://spdf.gsfc.nasa.gov). We will review some of the science results based on the digital data.