Qian Wu

A balloon borne Fabry Perot interferometer called High altitude Interferometer WIND observation (HIWIND) flew from Wanaka, New Zealand (44.69S, 169.14E) in April 2025 to observe mid‐latitude thermospheric winds in the southern hemisphere for the first time. The HIWIND results were compared with Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) simulations. The HIWIND observed a stronger poleward (southward) meridional and eastward zonal wind during the daytime compared to the model. The ionospheric density profiles from TIEGCM were compared with those from the COSMIC 2 satellite observations. The peak heights of the ionospheric F2 layer electron density in the observations were lower than those in the model, suggesting that the meridional winds in the real world were stronger than those in the model, which is consistent with the HIWIND and TIEGCM wind comparisons. The source of the weaker simulated winds is not known and is a topic for future studies.

Simultaneous observations of ion drifts and neutral winds have been conducted at Jang Bogo Station (JBS), Antarctica since 2017 using a Dynasonde and a Fabry‐Perot Interferometer, respectively. This study presents the results of a comparison between these two measurements to investigate the impacts of ion drifts on neutral winds in the Southern polar cap during winter. The results observationally demonstrate that neutral winds are largely weaker than ion drifts, suggesting that the neutral winds rarely reach a statistical steady‐state. However, thermosphere‐ionosphere‐electrodynamics general circulation model simulations show the opposite trend, significantly underestimating ion drifts. Neutral winds are also found to have different characteristics depending on the magnetic local time sectors, being weaker on the dayside than on the nightside of the polar cap, which is possibly explained if the previous histories of the neutrals before being observed are considered. Additionally, changes in neutral winds due to ion drag are more noticeable in the duskside than in the dawnside due to differences in collision frequency, which is primarily dependent on the diurnal variations of ionospheric density at JBS.

Recent thermospheric wind observation by a balloon borne instrument HIWIND over New Zealand in April 2025 combined with ground based Fabry Perot interferometer observations in Brazil provides a good opportunity to examine the longitudinal variations in the southern mid latitude region. The results showed noticeable longitudinal variations, which could be generated by nonmigrating tides propagating from the lower atmosphere. HIWIND also provided the first southern hemisphere daytime thermospheric wind observations. Combined HIWIND data with COSMIC 2 radio occultation observations of ionosphere profiles in the southern hemisphere we will examine the interaction between the ionosphere and thermosphere. Using the first principle model TIEGCM we simulated the southern hemisphere thermospheric winds and ionosphere profiles to compare with the HIWIND and COSMIC observations. HIWIND results help to reveal significant discrepancy between observations and simulations and point toward the direction for future improvement of the simulations.

This study presents the results from a climatological analysis of thermospheric winds (~ 250 km altitude) in the southern polar cap, based on the first long-sterm ground-based Fabry–Perot Interferometer (FPI) observations at Jang Bogo station (JBS; 80°S geomagnetic latitude), Antarctica, during 2014 − 2022. The winds exhibit pronounced diurnal variations, characterized by persistent anti-sunward flow across all magnetic local time sectors with a slight duskward tilt, primarily driven by ion drag in combination with day-to-night pressure gradients. The seasonal and solar activity dependencies show enhanced wind magnitudes during equinoxes and under high solar activity, likely reflecting stronger ion drag from increased ionospheric densities. The wind patterns are further modulated by increasing geomagnetic activity, which intensifies wind speeds and enhances the duskward tilts, associated with the strengthening of the dusk-side ionospheric convection cell. The orientation of the interplanetary magnetic field (IMF) also influences wind behaviors: a negative IMF Bz component increases wind magnitudes, while the IMF By component induces directional asymmetry by modulating ionospheric convection. These results offer new ground-based constraints on thermospheric wind circulation in the southern polar cap and its possible mechanisms over nearly a solar cycle. Graphical Abstract:

A new version of the US National Science Foundation National Center for Atmospheric Research (NSF NCAR) thermosphere‐ionosphere‐electrodynamics general circulation model (TIEGCM) has been developed and released. This paper describes the changes and improvements of the new version (3.0) since its last major release (2.0) in 2016. These include: (a) increasing the model resolution in both the horizontal and vertical dimensions, as well as in the ionospheric dynamo solver; (b) upward extension of the model upper boundary to enable more accurate simulations of the topside ionosphere and neutral density in the lower exosphere; (c) improved parameterization for thermal electron heating rate; (d) resolving transport of minor species N( ² D); (e) treating helium as a major species; (f) parameterization for additional physical processes, such as SAPS and electrojet turbulent heating; (g) including parallel ion drag in the neutral momentum equation; (h) nudging of prognostic fields near the lower boundary from external data; (i) modification to the NO reaction rate and auroral heating rate; (j) outputs of diagnostic analysis terms of the equations; (k) new functionalities enabling model simulations of certain recurrent phenomena, such as solar flares and eclipses. We present examples of the model validation during a moderate storm and compare simulation results by turning on/off new functionalities to demonstrate the related new model capabilities. Furthermore, the model was upgraded to comply with the new computer software environment at NSF NCAR for easy installation and run setup and with new visualization tools. Finally, the model limitations and future development plans are discussed.

This study characterizes the main ionospheric trough (MIT) using a newly implemented detection method applied to ground‐based Global Navigation Satellite System data. The MIT is a region of plasma depletion occurring primarily in the nighttime sub‐auroral F‐region ionosphere. Analysis is based on ground‐based ionosphere total electron content (TEC) measurements from 2012 to 2024 and is applied to both hemispheres. The data are sorted by geomagnetic condition and season. We characterize MIT dynamics and compare the results with previous studies. Detection algorithm limitations, hemispheric asymmetry, trough depth, boundary wall steepness and position are statistically quantified and visualized. Main conclusions include: (a) Automatic trough detection is highest during geomagnetically active winter in the northern hemisphere (NH). (b) This detection method creates synoptic views of the trough which we can use to demonstrate control of sub‐auroral polarization streams (SAPS) over the dusk/afternoon sector and influence of storm onset on the MIT. (c) There is a noticeable morning preference for the southern hemisphere (SH) trough. (d) The dawn‐side SH trough appears equatorward relative to the NH, potentially due to influence from polar convection patterns. The dusk‐side NH trough appears slightly equatorward of the SH trough as a response to SAPS. (e) The deepest trough occurs during dawn hours and demonstrates more consistent longitudinal patterns during quiet local winter. (f) The steepest trough boundary is at the poleward wall with a positive gradient at 12–15 local time in NH summer. Synoptic maps illustrate asymmetries in the trough structure and the influence of density plumes.

Plasma irregularities in the ionosphere induce scintillation of radio signals. Radio occultation (RO) observations of the Global Navigation Satellite Systems (GNSS) signals from low Earth orbit (LEO) allow monitoring of the ionospheric scintillation. Under certain conditions, it is possible to localize (geolocate) plasma irregularities along the line‐of‐sight between the GNSS and LEO satellites. While several techniques have been considered for the localization, in this study we use the back propagation (BP) of complex RO signals (phase and amplitude) measured at a high rate (HR), 50–100 Hz. Our method is based on a numerical solution of the wave equation, originally proposed for geolocation in 2002, with some modifications. We consider theoretical aspects of the BP technique, including assumptions, approximations and limitations, and perform numerical modeling of radio wave propagation. We investigate geolocation by BP for two regions with aligned and mis‐aligned irregularities and explain multi‐valued geolocations. We focus on the equatorial F region, consistent with the COSMIC‐2 observation sampling and use the IGRF‐13 model of the Earth's magnetic field to define the orientation of plasma irregularities. We use our method for processing of COSMIC‐2 HR scintillation data collected from the precise orbit determination antennas for 2 years: 2021 and 2023 (years with low and high solar activity). The results, represented by gridded monthly maps of geolocations, show clear seasonal and interannual variations. Additionally, we present comparison of the geolocations obtained independently from L1 and L2 signals for a 2‐month period.

A new version of the US National Science Foundation National Center for Atmospheric Research (NSF NCAR) thermosphere-ionosphere-electrodynamics general circulation model (TIEGCM) has been developed and released. This paper describes the changes and improvements of the new version 3.0 since its last major release (2.0) in 2016. These include: 1) increasing the model resolution in both the horizontal and vertical dimensions, as well as the ionospheric dynamo solver; 2) upward extension of the model upper boundary to enable more accurate simulations of the topside ionosphere and neutral density in the lower exosphere; 3) improved parameterization for thermal electron heating rate; 4) resolving transport of minor species N(2D); 5) treating helium as a major species; 6) parameterization for additional physical processes, such as SAPS and electrojet turbulent heating; 7) including parallel ion drag in the neutral momentum equation; 8) nudging of prognostic fields near the lower boundary from external data; 9) modification to the NO reaction rate and auroral heating rate; 10) outputs of diagnostic analysis terms of the equations; 11) new functionalities enabling model simulations of certain recurrent phenomena, such as solar flares and eclipse. We present examples of the model validation during a moderate storm and compare simulation results by turning on/off new functionalities to demonstrate the related new model capabilities. Furthermore, the model is upgraded to comply with the new computer software environment at NSF NCAR for easy installation and run setup and with new visualization tools. Finally, the model limitations and future development plans are discussed.

The space weather event on 10–11 May 2024 was a high‐impact geomagnetic storm, resulting in a SYM‐H index decrease to −518 nT, the lowest level registered in several decades. We investigated the response of the Earth's ionosphere during the main phase of this storm using a comprehensive data set of ionospheric observations (in situ plasma density and/or Total Electron Content (TEC)) from twenty Low‐Earth‐Orbit satellites such as COSMIC‐2, Swarm, GRACE‐FO, Spire, DMSP, and Jason‐3, orbiting at altitudes between 320 and 1,330 km. We found that ionospheric response followed a classical development pattern with the largest positive effects occurred at low and middle latitudes in daytime and evening sectors, associated with significant intensification of the Equatorial Ionization Anomaly (EIA) by the super fountain effect. The greatest effects occurred in the Pacific and American longitudinal sectors, which were in daylight, between 19 and 24 UT on 10 May 2024. This time overlaps with a period of steady southward IMF Bz and favorable conditions for long‐lasting penetration electric fields. The EIA crest‐to‐crest separation expanded to 40–60° in latitude with the largest poleward excursion of the crest to ∼27° magnetic latitude. The extreme EIA expansion with crest separation up to 60° in latitude along with a giant plasma bite‐out near the magnetic equator were observed in the dusk/evening sector over South America. The ground‐based TEC showed an enhancement up to ∼200 TECU, while satellites detected an increase in topside TEC up to ∼100–155 TECU, indicating key contribution of the topside ionosphere into the ground‐based TEC.

Penetrating and disturbed electric fields develop during geomagnetic storms and are effective in driving remarkable changes in the nightside low latitude ionosphere over varying time periods. While the former arrive nearly instantaneously with the changes in the solar wind electric field, the latter take more time, requiring auroral heating to modify upper atmospheric winds globally, leading to changes in the thermospheric wind dynamo away from the auroral zones. Such changes always differ from the quiet time state where the winds are usually patterned after daytime solar heating. We use the Multiscale Atmosphere‐Geospace Environment model (MAGE) and observations from the NASA Ionospheric Connection Explorer (ICON) mission to investigate both during the 7–8 July 2022 geomagnetic storm event. The model was able to simulate the penetrating and disturbed electric fields. The simulations showed enhanced westward winds and the wind dynamo induced upward ion drift confirmed by the ICON zonal wind and ion drift observations. The simulated zonal wind variations are slightly later in arrival at the low latitudes. We also see the penetrating electric field opposes or cancels the disturbed electric field in the MAGE simulation.