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1. The NCAR-TIEGCM Version 3.0

   https://doi.org/10.22541/essoar.174835358.89263150/v1  

   Wu, Haonan; Wang, Wenbin; Pham, Kevin H; Lin, Dong; Rao, Nikhil; Wiltberger, Michael; Lu, Gang; Wu, Qian; Liu, Han-Li; Qian, Liying; et al (May 2025, ESS Open Archive)

   A new version of the US National Science Foundation National Center forAtmospheric Research (NSF NCAR) thermosphere-ionosphere-electrodynamicsgeneral circulation model (TIEGCM) has been developed and released. Thispaper describes the changes and improvements of the new version 3.0since its last major release (2.0) in 2016. These include: 1) increasingthe model resolution in both the horizontal and vertical dimensions, aswell as the ionospheric dynamo solver; 2) upward extension of the modelupper boundary to enable more accurate simulations of the topsideionosphere and neutral density in the lower exosphere; 3) improvedparameterization for thermal electron heating rate; 4) resolvingtransport of minor species N(2D); 5) treating helium as a major species;6) parameterization for additional physical processes, such as SAPS andelectrojet turbulent heating; 7) including parallel ion drag in theneutral momentum equation; 8) nudging of prognostic fields near thelower boundary from external data; 9) modification to the NO reactionrate and auroral heating rate; 10) outputs of diagnostic analysis termsof the equations; 11) new functionalities enabling model simulations ofcertain recurrent phenomena, such as solar flares and eclipse. Wepresent examples of the model validation during a moderate storm andcompare simulation results by turning on/off new functionalities todemonstrate the related new model capabilities. Furthermore, the modelis upgraded to comply with the new computer software environment at NSFNCAR for easy installation and run setup and with new visualizationtools. Finally, the model limitations and future development plans arediscussed. 

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2. Observation of Quiet‐Time Mid‐Latitude Joule Heating and Comparisons With the TIEGCM Simulation

   https://doi.org/10.1029/2024JA032578  

   Day, E K; Grocott, A; Walach, M‐T; Wild, J A; Lu, G; Ruohoniemi, J M; Coster, A J (September 2024, Journal of Geophysical Research: Space Physics)

   Abstract Joule heating is a major energy sink in the solar wind‐magnetosphere‐ionosphere system and modeling it is key to understanding the impact of space weather on the neutral atmosphere. Ion drifts and neutral wind velocities are key parameters when modeling Joule heating, however there is limited validation of the modeled ion and neutral velocities at mid‐latitudes. We use the Blackstone Super Dual Auroral Radar Network radar and the Michigan North American Thermosphere Ionosphere Observing Network Fabry‐Perot interferometer to obtain the local nightside ion and neutral velocities at ∼40° geographic latitude during the nighttime of 16 July 2014. Despite being a geomagnetically quiet period, we observe significant sub‐auroral ion flows in excess of 200 ms⁻¹. We calculate an enhancement to the local Joule heating rate due to these ion flows and find that the neutrals impart a significant increase or decrease to the total Joule heating rate of >75% depending on their direction. We compare our observations to outputs from the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM). At such a low geomagnetic activity however, TIEGCM was not able to model significant sub‐auroral ion flows and any resulting Joule heating enhancements equivalent to our observations. We found that the neutral winds were the primary contributor to the Joule heating rates modeled by TIEGCM rather than the ions as suggested by our observations. 

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3. The Ionospheric Lunar Tidal Response to the 2020–2021 Sudden Stratospheric Warming Observed by COSMIC‐2, ICON and Modeled by SD‐WACCMX, TIE‐GCM

   https://doi.org/10.1029/2025JA034731  

   Aggarwal, Deepali; Kumar, Sunil; Martinez, B C; Pedatella, Nicholas; Lu, Xian; Oberheide, Jens (February 2026, Journal of Geophysical Research: Space Physics)

   Abstract This study examines how the breakdown of the stratospheric polar vortex influences lunar semidiurnal (M2) tides in F‐region electron density using Global Ionospheric Specification (GIS) data from the Constellation Observing System for Meteorology, Ionosphere, and Climate‐2 (COSMIC‐2). During the 2020–2021 Sudden Stratospheric Warming (SSW) event—marked by an exceptionally disrupted polar vortex—we observe up to a 16% enhancement in the M2 lunar tide at low latitudes (equatorial ionization anomaly) around 300 km altitude relative to the mean state. The response of M2 in vertical plasma drifts measured by the ion velocity meter on board the Ionospheric Connection Explorer satellite shows similar variability. Whole‐atmosphere model simulations using the Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (SD‐WACCM‐X) reproduce consistent M2 tidal signatures in E‐region zonal winds, F‐region vertical drifts, and electron density. To quantify the relative contributions of electrodynamics and neutral winds, we analyzed the ion continuity equation using the National Center for Atmospheric Research Thermosphere–Ionosphere–Electrodynamics General Circulation Model with SD‐WACCM‐X as the lower boundary. Results show M2 tides impact F‐region electron densities primarily through vertical plasma drifts, which increase by ∼114% during the SSW, while transport by neutral winds rises by ∼43%. These findings confirm that vertical drifts dominate lunar tide transport, with neutral winds providing a secondary contribution. 

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4. Hybrid Simulations of Interstellar Pickup Ions at the Solar Wind Termination Shock Revisited

   https://doi.org/10.3847/1538-4357/ada89c  

   Giacalone, Joe; Kornbleuth, M; Opher, M; Gkioulidou, M; Köta, J; Puzzoni, E; Richardson, J D; Zank, G P (February 2025, The Astrophysical Journal)

   Abstract We revisit previous hybrid simulations of the heating and acceleration of interstellar pickup ions (PUIs) at the solar wind termination shock. In previous simulations, a relatively cold initial distribution of PUIs was assumed; and while the resulting shock-heated distribution was consistent with Voyager 2 LECP measurements at about 30 keV, the intensity of the distribution downstream of the shock in the ~1–10 keV energy range was lower than predictions based on analysis of energetic neutral atoms (ENAs) from the Interstellar Boundary Explorer-Hi and Cassini's Ion and Neutral Camera. Here we perform new simulations with more realistic initial PUI distributions. We assume the distribution is a partially filled spherical shell in velocity space with a radius that varies from 320 to 640 km s⁻¹. We then use the distributions downstream of the shock from these new simulations to estimate the ENA flux spectrum and compare with observations. We find that the predicted ENA spectrum from the new simulations much better matches the observations over a broad range of energies. We conclude that the hybrid simulations provide reasonable predictions for the distribution of charged particles in the energy range from ~0.5 to 50 keV. 

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5. Importance of lower atmospheric forcing and magnetosphere-ionosphere coupling in simulating neutral density during the February 2016 geomagnetic storm

   https://doi.org/10.3389/fspas.2022.932748  

   Maute, Astrid; Lu, Gang; Knipp, Delores J.; Anderson, Brian J.; Vines, Sarah K. (August 2022, Frontiers in Astronomy and Space Sciences)

   During geomagnetic storms a large amount of energy is transferred into the ionosphere-thermosphere (IT) system, leading to local and global changes in e.g., the dynamics, composition, and neutral density. The more steady energy from the lower atmosphere into the IT system is in general much smaller than the energy input from the magnetosphere, especially during geomagnetic storms, and therefore details of the lower atmosphere forcing are often neglected in storm time simulations. In this study we compare the neutral density observed by Swarm-C during the moderate geomagnetic storm of 31 January to 3 February 2016 with the Thermosphere-Ionosphere-Electrodynamics-GCM (TIEGCM) finding that the model can capture the observed large scale neutral density variations better in the southern than northern hemisphere. The importance of more realistic lower atmospheric (LB) variations as specified by the Whole Atmosphere Community Climate Model eXtended (WACCM-X) with specified dynamics (SD) is demonstrated by improving especially the northern hemisphere neutral density by up to 15% compared to using climatological LB forcing. Further analysis highlights the importance of the background atmospheric condition in facilitating hemispheric different neutral density changes in response to the LB perturbations. In comparison, employing observationally based field-aligned current (FAC) versus using an empirical model to describe magnetosphere-ionosphere (MI) coupling leads to an 7–20% improved northern hemisphere neutral density. The results highlight the importance of the lower atmospheric variations and high latitude forcing in simulating the absolute large scale neutral density especially the hemispheric differences. However, focusing on the storm time variation with respect to the quiescent time, the lower atmospheric influence is reduced to 1–1.5% improvement with respect to the total observed neutral density. The results provide some guidance on the importance of more realistic upper boundary forcing and lower atmospheric variations when modeling large scale, absolute and relative neutral density variations. 

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