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

摘要

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.