[P-EM12] Coupling Processes in the Atmosphere-Ionosphere System

[PEM12-18] Variability and Distribution of Nighttime Low Latitude Ionospheric Irregularities and Vertical Plasma Drift Observed by FORMOSAT-5 Advanced Ionospheric Probe In-Situ Measurements from 2017 – 2020

*Loren Chang^1,2, Yueh-Chun Hsieh^1,2, Chi-Kuang Chao^1,2, Yi Duann^1,2, Cornelius Csar Jude H. Salinas^3,4, Jann-Yenq Liu^1,2, Charles C.H. Lin⁵ (1.Department of Space Science and Engineering, National Central University, Taoyuan City, Taiwan, 2.Center for Astronautical Physics and Engineering, National Central University, Taoyuan City, Taiwan, 3.NASA Goddard Space Flight Center, Greenbelt, MD, USA, 4.Goddard Earth Sciences Technology and Research II, University of Maryland, Baltimore County, MD, USA, 5.Department of Earth Sciences, National Cheng Kung University, Tainan City, Taiwan)

Keywords:ionosphere, irregularity, FORMOSAT-5, Advanced Ionospheric Probe

Irregularities in ionospheric plasma distribution can result in severe scintillation and disruption to the radio frequencies utilized for satellite communications and navigation. In the low latitudes, these irregularities can include Equatorial plasma bubbles (EPBs) and Travelling Ionospheric Disturbances (TIDs). EPBs are irregularities manifesting in low latitude nighttime ionosphere plasma density that can extend along magnetic field lines with zonal scales on the order of 100 km or less, while TIDs are propagating wave disturbances. High frequency in-situ measurements of ionospheric plasma aboard spacecraft in Low Earth Orbit (LEO) are a direct measurement of irregularities in plasma density, and are therefore valuable for resolving EPB and TID occurrences, variability, and relation to other ionospheric parameters that are believed to play a driving role in the formation of such irregularities, such as vertical plasma drift. In this study, we utilize observations taken over a three-year period between 2017 – 2020 by the Advanced Ionospheric Probe (AIP) carried aboard the FORMOSAT-5 satellite to examine the spatial, seasonal, and interannual variability of low latitude ionospheric irregularities and vertical ion drift during this time. AIP provides in-situ measurements of ion density and vertical ion drift in the low to mid-latitude ionosphere at approximately 720 km altitude with local times between 22:00 – 23:00 local time. Our global scale results resolve distinct and inter-annually recurrent seasonal patterns in the distribution of nighttime ionospheric irregularities and vertical plasma drift during this time. Elevated occurrences of ion density irregularities are resolved along the Equatorial Ionization Anomaly (EIA) latitudes, with notable lower occurrences along the low and equatorial magnetic latitudes extending from the Atlantic to the East Asian sectors in boreal winter, as well as over distinct patches over the American sector, Indian Ocean, and Western Pacific sectors during the boreal summer. It is also notable that the occurrences of ion density irregularities over the Atlantic and African sectors were higher in 2018 compared to the two latter years in this study. In comparison, the spatial and interannual variation of the co-located vertical ion drifts were much more consistent during the years examined, indicating that the driver for the observed interannual variability in ion density irregularities cannot be attributed to the vertical ion drift at the same time and location of the observations.