Climatology of Deep O+ Dropouts in the Night‐Time F‐Region in Solar Minimum Measured by a Langmuir Probe Onboard the International Space Station

• Published in: Journal of geophysical research. Space physics 2022-07, Vol.127 (7), p.n/a
• Main Authors: Debchoudhury, Shantanab, Barjatya, Aroh, Minow, Joseph I., Coffey, Victoria N., Parker, Linda N.
• Format: Article
• Language: English
• Subjects: Altitude; Astronomical instruments; Atmospheric models; Climate; Climate models; Climatology; climatology of topside plasma compostion; Composition; Dropouts; Electron density; Empirical models; Exosphere; Geographical locations; Global climate; Hemispheres; International Space Station; in‐situ measurement; Ion density; Ion density (concentration); Ionosphere; Ions; Langmuir probe; Multinational space ventures; Orbits; Parameters; Solar cycle; Solar minimum; Space stations; Sweeping; topside O+ composition; Units of measurement; Wind variations; Winter
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2022JA030446

The Floating Potential Measurement Unit onboard the International Space Station includes a Wide sweeping Langmuir Probe that has been operating in the F‐region of the ionosphere at ∼400 km since 2006. While traditional Langmuir probe estimates include critical plasma parameters like electron density and temperature, we have also extracted the O+ percentage from the total ion constituents. This O+ composition data set from the recent minimum in the Solar Cycle 24 reveals orbits with dropouts in O+ to below 80% of the total background ion density at International Space Station orbital altitudes. The observed O+ percentages during these dropouts are much lower than the values predicted by the International Reference Ionosphere 2016 (IRI2016) empirical model. In this paper, we present the climatology of these O+ dropouts with their dependency on season, local time and geographical location. The results show that the lowered O+ percentages are more significant in the winter hemispheres and are routinely observed for orbits in the pre‐sunrise periods. The patterns in O+ dropouts can be explained in part from the lowering of the O+/H+ transition height during solar minimum along with patterns in neutral wind variation. Plain Language Summary The plasma environment experienced by the International Space Station (ISS) is of key importance to the space physics community. A suite of instruments on the ISS has been operating since 2006 that consist of a spherical Langmuir probe, called the Wide sweeping Langmuir Probe, which is a sensor that periodically collects information about the density and energy of the ambient electrons. Recently, we presented a technique to also infer the composition of O+ ions relative to the total ion density which is an important parameter in understanding the interaction between the terrestrial atmosphere with the exosphere. Results from the most recent period of solar minimum reveal dropouts in O+ densities compared to predictions from empirical models. We show global climatology plots from 2018 to 2019 and observe that these large dropouts in O+ are more prevalent in the post‐midnight region of the winter hemisphere. Past studies have discussed increased presence of lighter H+ ions at higher orbital altitudes, but the fact that O+ dropouts are observed even at ISS altitudes is striking and one of the prominent features of solar minimum. Key Points O+ percentages often drop below 80% at International Space Station altitudes during solar