Climatology Analysis of the Daytime Topside Ionospheric Diffusive O⁺ Flux Based on Incoherent Scatter Radar Observations at Millstone Hill

Abstract

This paper reports the characteristics of the topside ionospheric O + diffusive flux (   O E) during both geomagnetically quiet (0 ≤ Kp ≤ 2) and moderate (2 < Kp ≤ 4) times using incoherent scatter radar observations at Millstone Hill (42.6°N, 288.5°E) for solar minimum from 1970 to 2018.changes from upward to downward at a fixed height is earlier than 18 SLT in spring and winter, but later than 18 SLT in summer and autumn. We also found that an increase in geomagnetic activity decreases the vertical gradient of plasma density during the daytime in all seasons, resulting in a ∼20 km increase in the transition height and an earlier transition time near dusk in spring, autumn, and winter, but a larger transition height change of about 20-50 km and a later transition time in summer. The change in the seasonal variations of the upwardresults from the competition between the variations of plasma diffusive velocity and density when the geomagnetic activity increases, as well as the changes in plasma vertical density profiles.

Ionospheric Topside Diffusive Flux and the Formation of Summer Nighttime Ionospheric Electron Density Enhancement Over Millstone Hill

“…The ISR dataset used in this study is the same as that in Y. Cai et al. (2021). The zenith measurement of Millstone Hill ISR (42.6°N, −71.5°W, inv.…”

“…A key feature of this study is the use of sophisticated topside diffusive flux ($${{\Phi}}_{O+}$$) derived from the Millstone Hill ISR data. A statistical $${{\Phi}}_{O+}$$ specification has been recently developed using the radar's long‐term observations from 1970 to 2018 (Y. Cai et al., 2021). This data‐informed $${{\Phi}}_{O+}$$ was implemented in the TIEGCM as the upper boundary condition for the model ionosphere plasma density solver.…”

“…A statistical 𝐴𝐴 Φ𝑂𝑂+ specification has been recently developed using the radar's long-term observations from 1970 to 2018 (Y. Cai et al, 2021). This data-informed 𝐴𝐴 Φ𝑂𝑂+ was implemented in the TIEGCM as the upper boundary condition for the model ionosphere plasma density solver.…”

Altitude Extension of the NCAR‐TIEGCM (TIEGCM‐X) and Evaluation

“…To explore the effect of the upper boundary on the performance of the TIEGCM, Y. Cai, Wang, et al. (2021) used incoherent scatter radar observations at Millstone Hill (42.6°N, 288.5°E) from 1970 to 2018 to analyze the various characteristics of the topside ionospheric O + diffusive flux in detail and further incorporated the parameterized O + diffusive flux into the upper boundary condition to solve the O + continuity equation in the TIEGCM. They used the data‐informed TIEGCM to successfully produce the mid‐latitude summer nighttime anomaly and proposed that the topside diffusive flux is critically important for the formation and timing of the summer evening density peak (Y. Cai et al., 2022).…”

“…Liu et al., 2018) were developed with the TIEGCM as the core. Since the TIEGCM was developed, much work has been done to improve it, including adding migrating and nonmigrating tides at the lower boundary (Hagan et al., 2001), revising the solar irradiance and photoelectron inputs (Solomon & Qian, 2005), modifying the upper boundary heat flux (Lei et al., 2007), revising the auroral precipitation inputs (Emery et al., 2008), applying variable eddy diffusivity at the lower boundary (Qian et al., 2009), enabling the inclusion of helium as the fourth major neutral constituent (Sutton et al., 2015), adding a new module that includes both anomalous electron heating and electron‐neutral cooling rate correction associated with the Farley‐Buneman instability (J. Liu et al., 2016), achieving high‐resolution geographic longitude‐latitude coordinates (0.625° × 0.625°) to resolve critical mesoscale structures (Dang et al., 2021), and optimizing the upper boundary conditions to solve the O + continuity equation (Y. Cai, Wang, et al., 2021; Y. Cai et al., 2022). In this study, the TIEGCM was successfully extended upward by four scale heights, resulting in an upper boundary height of up to ∼1,200 km at solar maximum.…”