Research

This study uses the GAIA atmospheric model to investigate for the first time how increasing CO₂ concentration affects sporadic E (Es) layer formation at 90–120 km altitude. Simulations were conducted for normal (315 ppm) and doubled CO₂ (667 ppm) levels to evaluate changes in vertical ion convergence (VIC)—the key parameter driving Es formation through wind shear mechanisms. The simulations reveal three primary effects:

First, VIC is significantly enhanced globally in the 100–120 km altitude range, with particularly strong increases over East Asia and the Pacific sector. Second, VIC hotspots shift downward by approximately 5 km (from ~120 km to ~115 km) and exhibit substantial changes in their diurnal patterns, with VIC persisting longer into nighttime hours. Third, this enhancement results equally from two mechanisms: reduced ion-neutral collision frequency (due to thermospheric cooling-induced density decreases) and changes in zonal wind shear (likely driven by altered atmospheric tides). These findings suggest future Es layers will be more intense, last longer, and form at lower altitudes, potentially disrupting HF/VHF communication systems.

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 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.

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.

Using the Community Earth System Model with thermosphere-ionosphere extension (CESM WACCM-X), this study investigates how increasing greenhouse gas concentrations affect the ionosphere and thermosphere's response to geomagnetic storms. The May 2024 geomagnetic superstorm is simulated under four different CO2 scenarios, ranging from present-day levels (403 ppmv) to nearly doubled concentrations (918 ppmv) projected for 2084. The results show that higher CO2 concentrations significantly weaken the absolute response of both the ionosphere and thermosphere to geomagnetic storms. Specifically, the thermosphere neutral density response decreases by 20-25% and the ionospheric response weakens by up to 50% as CO2 levels increase from current to future projected levels. However, when expressed as relative changes compared to background conditions, the storm responses actually strengthen with higher CO2 concentrations, primarily because the background neutral densities become much smaller in a high-CO2 atmosphere. The weakening absolute response occurs due to reduced Joule heating at higher altitudes, which is the primary energy source driving storm-time changes in the upper atmosphere. This study provides the first comprehensive assessment of how climate change may alter space weather impacts on Earth's upper atmosphere.

This paper has received much attention from the public. Here are links from CNN, Astronomy, and NCAR.

https://www.astronomy.com/science/satellites-face-new-challenges-from-solar-storms/

https://edition.cnn.com/2025/08/14/climate/solar-storms-satellites-global-warming

https://news.ucar.edu/133035/atmosphere-changes-so-will-its-response-geomagnetic-storms

https://www.kyushu-u.ac.jp/f/63050/2508_Huixin_climate_change_geomagnetic_storms_UCAR_new.pdf

Using 37 ground-based ionosondes distributed globally and space-based COSMIC-2 radio occultation observations, this study investigates the responses of Es layers to the May 2024 super geomagnetic storm. The results show that Es layers were significantly enhanced during the recovery phase of geomagnetic storm. In addition, the enhanced Es layers mainly occurred over Southeast Asia, Australia, the South Pacific and the East Pacific. The temporal evolution of foEs disturbances over the Asian-Australian sector clearly shows the “wave propagation” characteristics from high to low latitudes, indicating that the enhancements of the Es layers are most likely caused by the disturbed neutral winds in the E region. This study presents observational evidence for the downward impacts of the geomagnetic storm on the E-region ionosphere.

The Medium-Scale Traveling Ionospheric Disturbances (MSTIDs) can be excited by many sources. Among those magnetic reconnections has been proposed as a potential driver for dayside MSTIDs, but direct evidence has been limited. Using ground-based radar data from the Super Dual Auroral Radar Network on December 14, 2012, we observed quasi-periodic multiple MSTIDs propagating from auroral latitudes to mid latitudes near magnetic local noon, which showed one-to-one correspondences to intermittent lobe reconnections with periodicities of about 20–30 minutes. Simultaneous EISCAT Svalbard incoherent scatter radar data revealed enhanced electric field and Joule heating within the cusp region following each lobe reconnection. These multi-instrument observations strongly suggest lobe reconnection as a possible driver for the dayside MSTID.

Using the Fe+ layer as a proxy for Es layer, in this study, we investigated the structural and dynamic characteristics of the large-scale Es layers extending thousands of kilometers over East Asia by using a 3-D Es layer numerical model driven by neutral winds from the Whole Atmosphere Community Climate Model with thermosphere and ionosphere eXtension model (WACCM-X). The simulation results show that the Es layer is a tilted blanket rather than a narrow flat band. In addition, the Es layers mainly occur in the 3-D spatial position of the convergent vertical wind shear. The apparent horizontal velocity (~300-400 m/s) of Es structure is mostly westward and northward, which is different from the ion drift velocity (~100 m/s). This indicates that Es structure can develop rapidly over a large area simultaneously rather than drifting from one location to the next. COSMIC targets the locations of Es layers with all intensities that including much smaller intensity at a given time from a global perspective. The migration speed of hotspot of Es layer occurrence recorded by COSMIC satellites matches the apparent velocity. The GNSS receivers track the dense ion clusters (foEs > 14 MHz) to measure the drift direction and speed of extremely strong Es layer, which matches the ion drift velocity.

In 2018, Mars experienced a Planet Encircling Dust Event (PEDE-2018), which had significant impacts on the atmosphere. In this study, we examined changes in wave signatures (amplitudes and apparent wavelengths) associated with PEDE-2018. In-situ density measurements from the NGIMS (Neutral and Ion Gass Mass Spectrometer) instrument on MAVEN spacecraft allowed us to analyze densities of both neutrals and ions, providing insights into ion-neutral coupling in the upper atmosphere. As shown in Figure 5, we found that the rates of larger wavelengths enhanced during PEDE-2018 for both neutrals and ions (wavelengths are apparent along MAVEN trajectory, with a much larger horizontal than vertical scale).  Moreover, high correlations among the wavelengths of various species (Figure 6, not shown here) were derived under both low-dust and PEDE-2018 conditions, may implying ion-neutral coupling and common dominant wave sources.

The thermosphere, which is the neutral atmosphere that makes up most of the upper atmosphere, was generally believed to be "unaffected by magnetic fields. However, our papers published in 2005 and 2006 have changed this perception. By using the world's first high-precision accelerometer, which precisely measures gravity onboard a satellite, for thermospheric observations, we discovered anomalous thermospheric density anomalies (EMA) and thermospheric wind jets in the magnetic equatorial region. These discoveries revealed for the first time that the magnetic field dominates the behavior of the neutral atmosphere through atmosphere-plasma interaction, and provided a new perspective on thermospheric ionospheric dynamics. In addition, the accelerometer-based thermospheric observation method developed from our research has greatly stimulated research in the difficult-to-observe thermospheric region, and has become a pillar of upper atmosphere research in recent decades. This has stimulated research in the thermospheric region, which is difficult to observe.