This study uses WACCM-X whole atmospheric model simulations to investigate long-term trends in ionospheric day-to-day variability over the past century (1921–2015), validated against Wuhan ionosonde observations spanning 1947–2024. The analysis examined F-layer critical frequency (foF2) standard deviations normalized by monthly means, performing time-slice simulations under perpetual solar minimum conditions to isolate atmospheric perturbation effects. The simulations reveal three primary findings:

First, ionospheric day-to-day variability trends maximize at approximately ±1% of seasonal mean per decade, with stronger nighttime trends (±2%) than daytime (±1%). Second, geomantic secular variation dominates trends over the American-Atlantic sector, while increasing greenhouse gases (GHG) control the Asia-Pacific region patterns, producing negative mid-latitude trends with longitudinal wavenumber-4 structure. Third, the GHG-driven negative trend (approximately −0.8% per decade at mid-latitudes) correlates with weakening SE2 semidiurnal tidal day-to-day variability, suggesting tidal modulation as the underlying mechanism. These findings demonstrate that ionospheric weather-like variability undergoes significant long-term climate change impacts.

This study uses TIE-GCM model simulations to investigate sporadic E (Es) layer enhancement mechanisms during the May 2024 super geomagnetic storm (Dst minimum: −412 nT). The analysis examined vertical ion convergence (VIC)—a key indicator for Es layer formation—driven by neutral wind shear at 100–130 km altitude. The simulations reveal three primary effects:

First, VIC was significantly enhanced over East Asia-Australia and Pacific sectors within the 40°S–40°N latitude band, with enhancement patterns exhibiting clear "equatorward propagation" from high to low latitudes during the storm recovery phase. Second, VIC enhancement occurred predominantly during local nighttime (16:00–04:00 LT) and decreased with descending altitude due to increased ion-neutral collision frequencies. Third, zonal wind shear dominated the VIC enhancement, specifically through dramatically strengthened westward winds (exceeding 150 m/s at some altitudes) induced by storm-driven equatorward winds via Coriolis force. These findings demonstrate that super geomagnetic storm impacts extend into the mesosphere-lower thermosphere, modulating ionospheric E-region irregularities and affecting radio communications.

This study systematically evaluates high-latitude Joule heating in the recently released TIE-GCM version 3.0 model by comparison with EISCAT incoherent scatter radar measurements from two September campaigns (2005 and 2009). The analysis tested multiple convection forcing models under varying geomagnetic activity levels (low: Kp < 2, moderate: 2 < Kp < 6, high: Kp > 6). The simulations reveal four primary effects:

First, data-assimilated convection models (AMIE and AMGeO) improved agreement with EISCAT-derived Joule heating rates by 8%, 28%, and 54% for low, moderate, and high geomagnetic activity compared to empirical models (Heelis and Weimer). Second, increasing horizontal grid resolution from 2.5° to 1.25° produced approximately 20% higher Joule heating rates across all activity levels. Third, AMIE-driven runs better reproduced the magnitude of heating rates, while AMGeO-driven runs captured the vertical profile shape more accurately. Fourth, internal model time step resolution (ranging from 1 to 30 seconds) had no measurable effect on Joule heating calculations. These findings establish best practices for modeling high-latitude energy inputs in thermosphere-ionosphere systems.

This study uses a sophisticated climate model (CESM2/WACCM-X) to predict how Earth's upper atmosphere (100–500 km altitude) will respond to a worst-case CO₂ increase scenario by 2090, where concentrations nearly triple from ~350 ppm to ~1,000 ppm. The simulations reveal three primary effects:

First, thermospheric temperature, neutral density, and electron density decrease overall due to CO₂'s cooling effect, with electron density showing a transition from increase to decrease above ~220 km altitude. Second, the north-south (meridional) wind circulation accelerates by 5–10 m/s, especially during June, indicating a faster global wind pattern. Third, atmospheric tides—24-hour cycles weaken above 200 km but strengthen below it, while 12-hour cycles weaken throughout the thermosphere. These dynamical changes align with predictions from another model (GAIA), confirming that CO₂-induced cooling accelerates upper-atmospheric circulation. The findings help anticipate impacts on satellites, navigation systems, and space weather.

This study uses multiple simultaneous observations (ICON, GOLD, COSMIC-2, GPS-TEC) to investigate ionospheric responses during the January 2021 sudden stratospheric warming (SSW) event at equatorial and low latitudes. Unlike typical SSW events, the observations reveal three primary effects:

First, ionospheric peak electron density (NmF2) and total electron content (TEC) decreased during both morning and afternoon periods without the typical semi-diurnal variations observed in other SSW events. Second, this depletion was primarily driven by reductions in the column O/N₂ ratio (decreasing by 9.3–17.2% depending on latitude) and solar radiation (F10.7 declined ~10%), rather than conventional E × B drift or neutral wind transport mechanisms. Third, thermospheric observations revealed enhanced SW2 (10–15 m/s increase) and M2 (5–8 m/s increase) tidal amplitudes after SSW onset, suggesting enhanced tidal "mixing effects" that increased downward atomic oxygen transport. These findings highlight composition-driven coupling processes as the dominant mechanism during this SSW event.​

This study uses ICON satellite observations to investigate how Earth's F-region thermosphere (200–400 km altitude) responds to the January 2021 sudden stratospheric warming (SSW) event at middle-low latitudes. Two atmospheric models (NRLMSISE-00 and TIEGCM) served as baselines to isolate SSW-driven changes from seasonal variations. The observations reveal three primary effects: First, atomic oxygen density decreased in the middle thermosphere but increased in the upper thermosphere during afternoon hours, with transition levels varying by local time and latitude—governed by the balance between upwelling (causing decreases) and adiabatic cooling (causing increases). Second, molecular nitrogen density increased at all altitudes, with enhancements growing stronger at higher altitudes (up to 15–20%). Third, neutral temperature decreased throughout the F-region, particularly in morning sectors (approximately 5–6% cooling), supporting previous thermospheric cooling predictions. These altitude-dependent composition and temperature changes demonstrate strong vertical coupling during SSW events.