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During the storm on 3 and 4 November 2021, the Global‐scale Observations of the Limb and Disk (GOLD) mission observed well separated equatorial ionization anomaly (EIA) crests post sunset on 3 November, but merged EIA on 4 November. We used the Whole Atmosphere Community Climate Model‐eXtended to simulate the EIA structures during the two nights. The simulations show two separated post sunset EIA crests on 3 November but merged post sunset EIA crests on 4 November, which are qualitatively consistent with the GOLD observations. Numerical simulations and Ionospheric Connection Explorer neutral wind observations illustrate that the formation of merged EIA crests was due to several hours of downward E ×${\\times} $  B drifts before and after sunset. Further diagnostic analysis revealed that it was mainly driven by westward electric fields caused by the disturbance dynamo electric field during the recovery phase of the storm. Plain Language Summary The Ionospheric equatorial ionization anomaly (EIA) occurs almost every day and has been studied extensively. A large number of studies have shown that EIA has usually two separated electron density crests around ±$\\pm $ 15° off the magnetic equator in the ionosphere. A structure of merged EIA with just one density crest located near the magnetic equator was observed by a satellite on 4 November 2021. We successfully simulate the merged EIA structure using a first‐principles model. Analysis of the model results reveals that thermospheric neutral winds were disturbed by a geomagnetic storm on 3 and 4 November 2021; the disturbance dynamo electric field due to the disturbed winds changed the usual drift pattern of the plasma, which eventually drive the ionospheric plasma to move toward the magnetic equator causing the merged EIA structure. Key Points Merged equatorial ionization anomaly (EIA) structure was observed by Global‐scale Observations of the Limb and Disk during the storm of 3 and 4 November 2021 This EIA structure was successfully reproduced by Whole Atmosphere Community Climate Model‐eXtended simulations Model diagnostic analysis reveals that the merged EIA was mainly driven by disturbance dynamo electric fields during the storm

Leveraging observations by two NASA missions—GOLD (Global‐scale Observations of the Limb and Disk) and ICON (Ionospheric Connection Explorer), we investigate concurrent responses of thermospheric composition, temperatures, and neutral winds to the geomagnetic storm on 3–4 November 2021, as well as their interplay at low and middle latitudes. The synergetic observations reveal remarkable depletions up to 60%–70% in GOLD O/N2, along with large enhancements in GOLD temperatures poleward of 30° in the middle thermosphere. Meridional winds from ICON observations are altered by ∼100 m/s equatorward of 25°N latitude and at 250 km, characterized by a reversal of prevailing northward winds to geomagnetic storm‐driven southward winds. This study fills a need, after a decade‐long gap, for observing concurrent and co‐located responses of composition, temperatures, and neutral winds in the thermosphere to geomagnetic storms. Plain Language Summary Geomagnetic storms, arising from solar wind shocks emitted from the Sun, deposit a large portion of the absorbed solar energy into the Earth's high‐latitude atmosphere through Joule heating and high energy particle heating. Accurate prediction of the responses to geomagnetic storms in the thermosphere‐ionosphere is one of the core scientific objectives of space weather. The recently launched Global‐scale Observations of the Limb and Disk (GOLD) and Ionospheric Connection Explorer (ICON) missions provides an unparalleled opportunity to assess storm‐induced concurrent changes in multiple key parameters. During a G3 geomagnetic storm on 3 November 2021, GOLD observed the substantial changes of 60%–70% in thermosphere column density ratios of atomic oxygen to molecular nitrogen and temperatures. Exceptional meridional winds of 100–200 m/s were also seen by ICON over a broad altitude range. Such observations fill a decades‐long need for simultaneous observations of the key variables in the ionosphere‐thermosphere system. Key Points Remarkable depletions in O/N2 and enhancements in temperature, up to 60%–70%, are seen by Global‐scale Observations of the Limb and Disk during the geomagnetic storm Averaged southward wind deviations of ∼100 m/s are observed by Ionospheric Connection Explorer, coincident with the largest gradient in O/N2 depletions Both O/N2 and temperatures recover rapidly from the disturbed states to pre‐storm states

We report a new ionosphere phenomenon: Equatorial ionization anomaly (EIA) discontinuity (EIAD), based on OI 135.6 nm radiance observations from the Global Observations of Limb and Disk (GOLD), ground‐based total electron content maps and in‐situ ion density data from Constellation Observing System for Meteorology, Ionosphere, and Climate‐2. The EIAD occurs when the OI radiance of the EIA crest has a local minimum, at a fixed UT, with the radiance in the local longitude region being weaker than that on the east and west sides. In the GOLD field‐of‐view, EIAD follows the seasonal variations of EIA. EIAD appears more often over the Atlantic Ocean and Africa than over South America. It occurs more in the southern crest during the December solstice, and more in the northern crest during both equinoxes. EIAD can occur under both quiet and disturbed times. Plain Language Summary The equatorial ionization anomaly (EIA) is very dynamic and can exhibit various structures. Here we report a newly discovered EIA structure: EIA discontinuity, namely the EIA crest shows a lower electron density in the middle longitude range than in east and west longitude ranges. We first show the observation of EIA discontinuity observed concurrently by a geo‐stationary orbit satellite, a low‐earth‐orbit satellite and ground‐based global positioning system receiver. Then a statistical study illustrates that the EIA discontinuity is mostly captured in field‐of‐view of the geo‐stationary satellite in one hemisphere. It obeys the seasonal variation of EIA. The occurrence is higher in the spring equinox than in the fall equinox. Near the December solstices, it appears more in the southern crest. In both equinoxes, it appears more often in the northern crest. In August, its occurrence increases with the increase of solar irradiance. The EIA discontinuity can occur under both geomagnetically quiet and disturbed times. Key Points Equatorial ionization anomaly (EIA) discontinuity is the EIA crest with a weaker electron density in a longitude region than longitudes to the east and west Statistical study shows that its occurrence has a preference in Atlantic Ocean and Africa than America within the Global Observations of Limb and Disk field‐of‐view EIA discontinuity can occur under both geomagnetically quiet and disturbed times

We investigate in detail the occurrence and evolution of ionospheric equatorial plasma bubbles (EPBs) during a moderate storm on 17 September 2021, using Global‐scale Observations of the Limb and Disk (GOLD) observations and Whole Atmosphere Community Climate Model‐eXtended (WACCM‐X) simulations. GOLD observations show that there were no EPBs on 16 September before the storm but EPBs occurred after the storm commencement on 17 September. The EPBs extended to ∼30° magnetic latitude. A diagnostic analysis of WACCM‐X simulations reveals that the rapid enhancement of prompt penetration electric fields (PPEFs) after the sudden storm commencement is the main reason that triggered the occurrence of the EPBs. Further quantitative analysis shows that vertical plasma drifts, which are enhanced by the PPEF, played a dominant role in strengthening the Rayleigh‐Taylor instability, leading to the occurrence of the EPBs and the large latitudinal extension of the EPBs to ∼30° magnetic latitude during the night of 17 September.

The ratio of O to N2 number densities (O/N2) at different altitudes is an important parameter in describing thermospheric neutral composition changes and their effects on the ionosphere during geomagnetic storms. However, storm‐induced vertical variations in O/N2 and its dependence on the O and N2 perturbations are still not fully understood. Here, the Thermosphere/Ionosphere Electrodynamics General Circulation Model simulations were used to investigate the responses of thermospheric composition at different pressure levels to the super geomagnetic storm occurred on November 20 and 21 in 2003. Our analysis shows that the behaviors of O/N2 perturbations on different pressure levels are similar above ∼180 km altitude. In the middle and low thermosphere of below ∼300 km, the storm‐time O/N2 decrease is mainly caused by a large reduction of O number density. However, N2 enhancement plays a vital role in O/N2 decreases in the upper thermosphere. The O/N2 enhancement is mainly attributed to the N2 decreases at all pressure levels. The changes of O and N2 number densities at a constant pressure level can be explained by the perturbations of their mass mixing ratio (mmr) and total mass density (ρ). The regions of the O/N2 decrease are characterized by the O mmr decrease and N2 mmr enhancement, whereas the regions of the O/N2 increase are characterized by the O mmr increase and N2 mmr decrease. The ρ value that shows the decrease globally at most pressure levels during the storm either enhance or reduce the O and N2 perturbations. Plain Language Summary The column O/column N2 density ratio (∑O/N2) was usually used to describe thermospheric neutral composition responses to geomagnetic storms and the storm effects on ionospheric plasma density. However, thermospheric circulation changed considerably during the storm, resulting in discrepancies in composition at different altitudes. Additionally, the daytime electron density changes during geomagnetic storms are more related to those of local O/N2 at a given altitude, not the ∑O/N2. Therefore, it is important to fully understand the storm‐induced vertical variations in O, N2 and O/N2 perturbations. In this paper, the vertical variations in O/N2 and its dependence on the O and N2 perturbations during the 20–21 November 2003 storm are investigated by the numerical simulations. Our results shows that the behaviors of O and N2 perturbations depend much on the altitude, but those of O/N2 on different pressure levels are similar, especially above ∼180 km. This study helps us better understand the physical process of storm‐time ∑O/N2 variations based on the observations. Key Points In middle and low thermosphere of below ∼300 km, storm‐time decreases of the ratio of O/N2 volume density are mainly caused by O reduction In the upper thermosphere, N2 enhancement plays a vital role in the decreases of the ratio of O/N2 volume density during the storm At all pressure levels, storm‐time increases of the ratio of O/N2 volume density depend more on the N2 decreases

This paper investigates the midlatitude ionospheric disturbances over the American/Atlantic longitude sector during an intense geomagnetic storm on 23 April 2023. The study utilized a combination of ground‐based observations (Global Navigation Satellite System total electron content and ionosonde) along with measurements from multiple satellite missions (GOLD, Swarm, Defense Meteorological Satellite Program, and TIMED/GUVI) to analyze storm‐time electrodynamics and neutral dynamics. We found that the storm main phase was characterized by distinct midlatitude ionospheric density gradient structures as follows: (a) In the European‐Atlantic longitude sector, a significant midlatitude bubble‐like ionospheric super‐depletion structure (BLISS) was observed after sunset. This BLISS appeared as a low‐density channel extending poleward/westward and reached ∼40° geomagnetic latitude, corresponding to an APEX height of ∼5,000 km. (b) Coincident with the BLISS, a dynamic storm‐enhanced density plume rapidly formed and decayed at local afternoon in the North American sector, with the plume intensity being doubled and halved in just a few hours. (c) The simultaneous occurrence of these strong yet opposite midlatitude gradient structures could be mainly attributed to common key drivers of prompt penetration electric fields and subauroral polarization stream electric fields. This shed light on the important role of storm‐time electrodynamic processes in shaping global ionospheric disturbances.

ICON observations were used to investigate local time (LT) and latitudinal variations of thermospheric meridional winds in the middle‐high thermosphere (160–300 km) during quiet times in 2020 June and December. At middle‐low latitudes (10°S–40°N), meridional winds were predominantly equatorward in the summer hemisphere while mostly poleward in the winter hemisphere. The meridional winds showed that the diurnal variation was dominant between ∼20°N and ∼40°N, but the semi‐diurnal variation played a leading role at lower latitudes (below ∼20°N) during solstice months. Thermosphere‐Ionosphere Electrodynamics General Circulation Model reproduced the ICON observed meridional wind variations qualitatively. A model diagnostic analysis shows that the pressure gradient force dominated the semi‐diurnal variation of the winds, while the Coriolis force played a leading role in the diurnal variation in June. In December, LT variations of meridional winds were primarily driven by pressure gradient and ion drag forces. During both months, the vertical viscosity was important, tending to balance the effects of pressure gradients. Additionally, semi‐diurnal variations of low‐latitude meridional winds in June were more affected by upward propagating tides than those in December. Key Points ICON‐observed F‐layer meridional winds show that diurnal and semidiurnal variations dominate at ∼20°N–40°N and 10°S–∼20°N respectively In June, pressure gradient force dominated the semi‐diurnal variation, and Coriolis force had a leading role in the diurnal variation Semi‐diurnal variations of meridional winds at low latitudes in June were more affected by upward propagating tides than those in December

Severe environmental pollution resulting from improper emissions of volatile organic gases (VOCs) has posed significant menaces to human health, ecosystem security, and the pursuit of socially sustainable development. Herein, we present a convenient approach to crafting conductive gas-sensitive nanocomposites with double-percolation microstructure by employing a blend of thermoplastic polyurethane (TPU) and polycaprolactone (PCL) as the compositing matrix, combined with multi-walled carbon nanotubes (MWCNTs) as the functional nanofiller. The analysis of the interface energy between the components inside the nanocomposites revealed that MWCNTs were preferentially dispersed within the TPU phase. By adjusting the TPU-to-PCL ratio and the adding sequence of components during compositing, a two-phase continuous matrix structure and a double-percolation conductive microstructure were attained, which was benefited to the enhancement of electrical conductivity. When the mass ratio of TPU-to-PCL was fixed at 50:50, the lowest resistivity of the TPU/PCL/MWCNTs nanocomposite, measuring 2.57 × 10 5 Ω·m was achieved when MWCNTs were initially blended with TPU followed by PCL. Gas-sensitive assessments of the TPU/PCL/MWCNTs nanocomposite revealed its exceptional selectivity, responsiveness, and recovery to formaldehyde, surpassing other targeted VOCs such as benzene, xylene, ammonia, and ethanol. Notably, gas responsiveness to formaldehyde at 25 °C and 500 ppm registers at 74% for the TPU/PCL/MWCNTs nanocomposites. Furthermore, responsiveness exhibits a robust linear correlation with increasing formaldehyde concentration.

The ratio of O to N 2 number densities (O/N 2 ) at different altitudes is an important parameter in describing thermospheric neutral composition changes and their effects on the ionosphere during geomagnetic storms. However, storm‐induced vertical variations in O/N 2 and its dependence on the O and N 2 perturbations are still not fully understood. Here, the Thermosphere/Ionosphere Electrodynamics General Circulation Model simulations were used to investigate the responses of thermospheric composition at different pressure levels to the super geomagnetic storm occurred on November 20 and 21 in 2003. Our analysis shows that the behaviors of O/N 2 perturbations on different pressure levels are similar above ∼180 km altitude. In the middle and low thermosphere of below ∼300 km, the storm‐time O/N 2 decrease is mainly caused by a large reduction of O number density. However, N 2 enhancement plays a vital role in O/N 2 decreases in the upper thermosphere. The O/N 2 enhancement is mainly attributed to the N 2 decreases at all pressure levels. The changes of O and N 2 number densities at a constant pressure level can be explained by the perturbations of their mass mixing ratio (mmr) and total mass density ( ρ ). The regions of the O/N 2 decrease are characterized by the O mmr decrease and N 2 mmr enhancement, whereas the regions of the O/N 2 increase are characterized by the O mmr increase and N 2 mmr decrease. The ρ value that shows the decrease globally at most pressure levels during the storm either enhance or reduce the O and N 2 perturbations. The column O/column N 2 density ratio (∑O/N 2 ) was usually used to describe thermospheric neutral composition responses to geomagnetic storms and the storm effects on ionospheric plasma density. However, thermospheric circulation changed considerably during the storm, resulting in discrepancies in composition at different altitudes. Additionally, the daytime electron density changes during geomagnetic storms are more related to those of local O/N 2 at a given altitude, not the ∑O/N 2 . Therefore, it is important to fully understand the storm‐induced vertical variations in O, N 2 and O/N 2 perturbations. In this paper, the vertical variations in O/N 2 and its dependence on the O and N 2 perturbations during the 20–21 November 2003 storm are investigated by the numerical simulations. Our results shows that the behaviors of O and N 2 perturbations depend much on the altitude, but those of O/N 2 on different pressure levels are similar, especially above ∼180 km. This study helps us better understand the physical process of storm‐time ∑O/N 2 variations based on the observations. In middle and low thermosphere of below ∼300 km, storm‐time decreases of the ratio of O/N 2 volume density are mainly caused by O reduction In the upper thermosphere, N 2 enhancement plays a vital role in the decreases of the ratio of O/N 2 volume density during the storm At all pressure levels, storm‐time increases of the ratio of O/N 2 volume density depend more on the N 2 decreases

To investigate gravity wave (GW) perturbations in the midlatitude mesopause region during boreal equinox, 433 h of continuous Na lidar full diurnal cycle temperature measurements in September between 2011 and 2015 are utilized to derive the monthly profiles of GW-induced temperature variance, T′2, and the potential energy density (PED). Operating at Utah State University (42° N, 112° W), these lidar measurements reveal severe GW dissipation near 90 km, where both parameters drop to their minima (∼ 20 K2 and ∼ 50 m2 s−2, respectively). The study also shows that GWs with periods of 3–5 h dominate the midlatitude mesopause region during the summer–winter transition. To derive the precise temperature perturbations a new tide removal algorithm suitable for all ground-based observations is developed to de-trend the lidar temperature measurements and to isolate GW-induced perturbations. It removes the tidal perturbations completely and provides the most accurate GW perturbations for the ground-based observations. This algorithm is validated by comparing the true GW perturbations in the latest mesoscale-resolving Whole Atmosphere Community Climate Model (WACCM) with those derived from the WACCM local outputs by applying this newly developed tidal removal algorithm.