[P-EM13] Coupling Processes in the Atmosphere-Ionosphere System

[PEM13-P10] Formosat-5/Advanced Ionosphere Probe observes Night-time Top-side Ionospheric density responses to Quasi-6-day wave events

*Cornelius Csar Jude Salinas^1,2, Loren Chang^1,2, Yosuke Yamazaki³, Astrid I Maute⁴, Chi-Kuang Chao¹, Jann-Yenq LIU¹, Charles Lin⁵, Liying Qian⁴ (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.GFZ Potsdam, Potsdam, Germany, 4.High Altitude Observatory National Center for Atmospheric Research, Boulder, Colorado, USA, 5.Department of Earth Science, National Cheng Kung University, Tainan, Taiwan)

Keywords:Ionosphere, Electron Density, Planetary-waves

The quasi-6-day wave (Q6DW) is a westward planetary-scale wave with zonal wavenumber 1 and with a period of around 6 days. It is prominent and recurrent in the mesosphere and lower thermosphere (MLT) region especially around equinox seasons. Although it peaks in the MLT region, it has been shown to affect the ionosphere and thermosphere. In this work, we show that the Q6DW component of night-time top-side (at ~710 km) ionospheric density observed by Formosat-5/Advanced Ionospheric Probe (F-5/AIP) enhances during Q6DW events. Formosat-5 is in a repeating sun-synchronous orbit which allows it to pass over the same grid-point in just 2 days. At the same time, AIP observes night-time (~10 pm local-time) ionospheric ion density at ~710 km. This region is the roughly the bottom of the top-side ionosphere. Thus, this allows us to observe short-term variabilities in the top-side night-time ionosphere. This work takes advantage of this sampling to calculate the quasi-6-day wave (Q6DW) component of night-time top-side ion density as observed by F5/AIP from January 2018 to December 2019. This work also calculates the Q6DW component of upper mesospheric geopotential height as observed by the Microwave Limb Sounder onboard the Aura satellite to determine Q6DW events. From 2018 to 2019, MLS observes around 4 clear Q6DW events. We report that F-5/AIP also observes an increase in Q6DW amplitudes in ion density during these Q6DW events. We then compared these observations to simulations of electron density at ~400 km by the Specified Dynamics – Whole Atmosphere Community Climate Model with Ionosphere/Thermosphere eXtension (SD-WACCM-X) from 2018 to 2019. Electron density at ~400 km is a frequently used proxy for electron density at around 700 – 800 km. Simulations also show an enhancement in the Q6DW component of ~10 pm local-time electron density at ~400 km during instances when the Q6DW component of upper mesospheric geopotential height enhances. Model diagnostics have revealed that the Q6DW affects night-time electron density via the night-time vertical drift. Further diagnostics will be done to determine how the Q6DW in neutral winds drive the night-time vertical drift.