Langmuir Probe observations of O+ depletions in the post-midnight sector during the Solar Cycle 24 minimum
Abstract
The Floating Potential Measurement Unit (FPMU) on board the International Space Station (ISS) includes a spherical wide-sweeping Langmuir Probe (WLP) that has been operated intermittently for over 14 years. More than 80% of these observations span the most recent solar cycle 24 from 2011 to 2019, and therefore FPMU has been in a unique position to monitor the variability of the F-region ionosphere at ~400 km altitude. While traditional Langmuir Probe estimates include electron density and temperature, we have extracted ion composition information from the ion saturation region of the Langmuir probe, assuming O+ and H+ to be the only constituents. One of the striking findings from the dataset is the presence of deep O+ depletions in the post-midnight sector during solar minimum in the years 2018-2019. The O+ abundance can drop to less than 75% for many orbits for pre-dawn local times, and are significantly more than predictions from the International Reference Ionosphere (IRI) model. In this study, we present the climatology of these extreme O+ depletions and their seasonal and longitudinal dependence for the solar minimum. The depletions are present for both equatorial and mid-latitudes and are deeper for the hemisphere in local winter.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMSA52A..08D