Abstract
The global statistical median behavior of the electron temperature (Te) in the topside ionosphere was investigated through in-situ data collected by Langmuir Probes on-board the European Space Agency Swarm satellites constellation from the beginning of 2014 to the end of 2020. This is the first time that such an analysis, based on such a large time window, has been carried out globally, encompassing more than half a solar cycle, from the activity peak of 2014 to the minimum of 2020. The results show that Swarm data can help in understanding the main features of Te in the topside ionosphere in a way never achieved before. Te data measured by Swarm satellites were also compared to data modeled by the empirical climatological International Reference Ionosphere (IRI) model and data measured by Jicamarca (12.0°S, 76.8°W), Arecibo (18.2°N, 66.4°W), and Millstone Hill (42.6°N, 71.5°W) Incoherent Scatter Radars (ISRs). Moreover, the correction of Swarm Te data recently proposed by Lomidze was applied and evaluated. These analyses were performed for two main reasons: (1) to understand how the IRI model deviates from the measurements; and (2) to test the reliability of the Swarm dataset as a new possible dataset to be included in the underlying empirical dataset layer of the IRI model. The results show that the application of the Lomidze correction improved the agreement with ISR data above all at mid latitudes and during daytime, and it was effective in reducing the mismatch between Swarm and IRI Te values. This suggests that future developments of the IRI Te model should include the Swarm dataset with the Lomidze correction. However, the existence of a quasi-linear relation between measured and modeled Te values was well verified only below about 2200 K, while for higher values it was completely lost. This is an important result that IRI Te model developers should properly consider when using the Swarm dataset.
Highlights
We aimed to investigate the effect of the application of the Lomidze correction on Swarm Te measurements through a comparison with International Reference Ionosphere (IRI)-modeled values for the period 2014–2020 for all the three Swarm satellites
The main statistical median features of the topside ionosphere Te were investigated on a global basis through data collected by Langmuir Probes (LPs) on-board Swarm satellites from the beginning of 2014 to the end of 2020
Swarm Te measured data were compared with corresponding values modeled by IRI, and with data measured by Jicamarca, Arecibo, and Millstone Hill Incoherent Scatter Radars (ISRs), to evaluate the reliability of both Swarm data and IRI model in the description of the spatial, diurnal, and seasonal trends of Te in the topside ionosphere
Summary
The ionosphere is a plasma medium consisting of ions and electrons with a neutral component that, for most of the cases, are not in thermal equilibrium. Since the early satellites and rockets missions in the 1950s and 1960s [1], a bulk of evidence has been accumulated demonstrating the non-thermal equilibrium between ions, electrons, and neutrals in the ionosphere. Plasma temperature (ions plus electrons) usually exceeds the neutral one by a factor strongly dependent on altitude, time, and location; large differences among ion and electron temperatures are observed.
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