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

[PEM13-26] Ionospheric topside diffusive flux and the formation of summer nighttime ionospheric electron density enhancement over Millstone Hill

*Yihui Cai^1,4,6,7、Xinan Yue^1,6,7、Wenbin Wang²、Shun-Rong Zhang³、Huixin Liu⁴、Jiuhou Lei⁵ (1.Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China、2.High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO, USA、3.Haystack Observatory, Massachusetts Institute of Technology, Westford, MA, USA、4.Department of Earth and Planetary Science, Kyushu University, Fukuoka, Japan、5.CAS Key Laboratory of Geospace Environment, University of Science and Technology of China, Hefei, China、6.College of Earth and Planetary Sciences, University of the Chinese Academy of Sciences, Beijing, China、7.Beijing National Observatory of Space Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China)

キーワード：Millstone Hill ISR, Topside ionospheric O+ diffusivev flux, Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM), Mid-latitude summer nighttime anomaly (MSNA)

The topside ionospheric O+ diffusive flux has rarely been studied, but it is not only important for analyzing the relative contributions of various physical processes (such as ambipolar diffusion, neutral winds, and electric fields) and chemical processes to the ionospheric structure. It is also significant to study the dynamics and mass coupling between the ionosphere and the plasmasphere, for example, it is an upper boundary condition necessary for the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM). We performed a statistical analysis of the O+ diffusive flux in the topside ionosphere using Millstone Hill (42.6°N, 288.5°E) ISR data from 1970 to 2018. We obtained its characteristics as a function of solar activity, geomagnetic activity, altitude, local time, and season. Furthermore, the new specification of the topside O+ diffusive flux was used to drive the TIEGCM, which provides new insight into the competing roles of topside diffusive flux, neutral winds, and electric fields in forming the mid-latitude summer nighttime ionospheric electron density enhancement (MSNA). Simulations indicate that while magnetic meridional winds, which turn equatorward before sunset, are essential to sustain the daytime ionization near dusk, the topside diffusive flux is critically important for the formation and timing of the summer evening density peak. This new finding from the Millstone Hill observations may lead to an ultimate understanding of the more generic MSNA features in both the Northern and Southern Hemispheres.