Abstract. Advances in lidar technology have enabled the detection of Metal Ion Clouds (MICs) at altitudes between 120–300 km in the Earth’s thermosphere. Observations from a Ca+ lidar in Beijing, China, reveal that these MICs are characterized by tightly packed, stripe-like structures that span extensive areas, covering hundreds to thousands of square kilometers. Some of these stripes extend downward to the Main Metal Layer (MML) around 100 km, and some clouds descend with tidal winds and merge into the underlying MML. While arriving the altitudes of Mesosphere and Low-Thermosphere (MLT), they lead to an increase in Sporadic-E (Es) layer density, and even trigger the formation of a new Es layer. The metal ions in the upper thermosphere will eventually sink into the MML and significantly affect its density variations. The striped structure of MICs and their direct effects on Es and MML suggest they originate from meteoroid trails, challenging traditional views on meteoric input.

Abstract. Gravity waves (GWs) play an important role in balancing the energy budget of the mesosphere and lower thermosphere (MLT) by heating/cooling the background atmosphere. The global heat fluxes and heating rates generated by non-breaking GWs are derived from SABER observations during 2002–2025. The derived heat fluxes are mainly downward and cool the background atmosphere, with peaks occurring at 80–100 km. Around 35 °N, the monthly mean heat flux and heating rate are ~−0.7 Kms−1 and ~−12 Kday−1, with standard deviations of ~1.1 Kms−1 and ~20 Kday−1, respectively. Global GW-induced heat fluxes and heating rates exhibit stronger annual and weaker semiannual oscillations, with the stronger peak in summer hemisphere. Moreover, these quantities show notable interhemispheric and seasonal asymmetries, with larger summer amplitudes occurring at the northern high latitudes. Such interhemispheric asymmetry agrees with the colder summer mesopause at northern high latitudes. However, the heat fluxes and heating rates derived here are ~0.3−0.5 times the values lidar observations and are ~0.5 times the theoretical values and breaking GWs. These underestimations are induced by the uncertainties of GW propagation directions, observational filter, and limited GW wavelengths observable by SABER.

This study presents a climatological analysis of the systematic zonal differences in Equatorial Plasma Bubbles (EPBs) morphology, leveraging continuous observations from NASA's Global-scale Observations of the Limb and Disk (GOLD) mission between January 2023 and May 2025. Within the GOLD field of view, which continuously scans the nighttime ionosphere over the Americas and the Atlantic Ocean, a pronounced longitudinal asymmetry is uncovered: although backward C-shaped EPBs dominate overall, forward C-shaped EPBs occur more frequently in the western longitudinal sector than in the eastern sector. Statistical results demonstrate that this zonal morphological difference is a recurrent phenomenon, the occurrence of which follows the same seasonal pattern as the local EPB rates, being most frequent around equinoxes. Its occurrence rate increases with solar activity (F10.7 index) but shows no significant correlation with geomagnetic activity (Kp index). The magnetic longitudinal demarcation line between these morphological regions approximates a normal distribution, peaking around 25.9 degrees in magnetic longitude-a value notably close to the region of maximum magnetic declination. Analysis incorporating ionospheric zonal drift velocities from ROCSAT-1 data suggests that this morphological dichotomy originates from longitudinal variations in the latitudinal distribution of the plasma zonal drift, which is itself governed by the geomagnetic configuration. These findings provide robust, long-term observational evidence for the control of large-scale geomagnetic field geometry on the morphology of ionospheric plasma depletion.

Auroras have been observed at unusual latitudes of China over the past couple of years, which may be a direct result of the north magnetic pole’s drift and intense solar activity. However, the specific impact on the Asian space environment remains unknown. Here, we present auroral activities recorded in southern Inner Mongolia (~37.2° N in magnetic latitude) and the resulting ionospheric environmental changes detected by the Chinese Dual Auroral Radar Network (CN-DARN) during a recent severe geomagnetic storm. Leveraging the wide spatial coverage and continuous high time resolution monitoring capabilities of the CN-DARN, comprehensive analysis of ground-based and space-based multi-source data reveals that CN-DARN has captured the spatiotemporal evolution characteristics of dawnside subauroral polarization streams (SAPS). The study identifies a direct link between auroral intensification and dawnside SAPS acceleration for the first time, establishing a mechanistic connection between auroral activity and ionospheric convection dynamics in subauroral region. Moreover, the observations show that the ionospheric irregularities with high velocity of 1,000 m/s induced by the dawnside SAPS have propagated to Mohe (~ 48.6° N in magnetic latitude), the northernmost region of China. The research also reveals that intense auroral particle precipitation caused severe degradation of high-frequency (HF) communications in the Asian region. This study represents the first comprehensive investigation of auroral activity observed at unusual latitudes of China, unraveling the impact of auroral activities on the ionospheric environment of Asian mid-to-high latitudes. It also showcases the critical capabilities of the Chinese Meridian Project in addressing space environmental challenges of Asia.

Abstract During the geomagnetic storm on 10 May 2024, neutral density measurements from 14 Tianmu, Swarm, and GRACE‐FO satellites at ∼510 km altitude, combined with total electron content (TEC) observations, enabled the first global observational comparison of large‐scale traveling atmospheric and ionospheric disturbances (LSTADs/TIDs) via snapshots and keograms. LSTADs/TIDs exhibited similar wavefronts aligned with geomagnetic latitude, spanning 90–180° in longitude, originating from auroral or cusp Joule heating regions on both day and night sides. They propagated along overlapping meridional trajectories at 450–1,100 m/s. LSTADs lag LSTIDs by ∼30 min due to the phase polarization and differing observation heights. Besides, rare instantaneous neutral density enhancements were detected at low to mid latitudes during storm onset. These findings provide near‐continuous global observational insights into storm‐time thermosphere‐ionosphere wave coupling and demonstrate a feasible approach for future global LSTADs monitoring through empirical mode decomposition adaptive filtering of multi‐satellite data.

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument aboard the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite measure temperature and species globally from the stratosphere to the lower thermosphere since January 2002. The nighttime temperatures measured by the same sodium LiDAR at two adjacent middle latitude locations are used as the benchmark to assess the long-term stability of SABER temperature measurement in the mesosphere and lower thermosphere (MLT) during 2002-2024. The temperature differences (Delta T) between the concurrent observations from SABER and LiDAR are within +/- 5 K, with standard deviations (STDs) of 10-15 K in most years at 86-98 km. The drifts of Delta T are of -0.4-1.7 K/decade and the drifts of STDs are 0.2-1.7 K/decade at 86-98 km. However, they are statistically insignificant under a confidence level of 95%. Moreover, the Delta T and its STDs do not depend on solar activities. These comparisons show that the temperatures measured by SABER and the sodium LiDAR coincide well with each other at least in the region where the sodium concentration is high (86-98 km) and the LiDAR measurement is most accurate. The accuracy and precision of the SABER temperature measurement displays no significant systematic change or solar activity dependency.

Using a recognition model of atmospheric gravity waves (AGWs), we identified 519 AGW events from the OH airglow images observed at the Dandong and Lhasa stations from 2015 to 2017. The 317 AGW events detected at the Dandong station have wavelengths ranging from 30 to 60 km, periods from 14 to 20 min, horizontal speeds from 30 to 60 m/s, and relative intensities from 0.4% to 0.6%, respectively. The parameters of 202 events recorded at the Lhasa station mainly vary within 15-35 km in horizontal wavelength, 4-6 min in period, 40-100 m/s in horizontal velocity, and 0.1%-0.3% in relative intensity. The occurrence rate peaks in winter and summer at Dandong and the peak in summer are absent at Lhasa because of the lack of convective weather. The seasonal propagation directions of the waves are influenced by both the wind field-filtering effect and the distribution of wave sources. In spring, because of the southeastward background wind field, fewer southeastward events are observed at the Dandong station. The situation at the Lhasa station is similar. In summer, both the Lhasa and Dandong stations are dominated by northeastward AGWs, which can be attributed to the southwestward wind. In autumn, ray-tracing results show that the events at Dandong mainly originate from wind shear, whereas the events at the Lhasa station are triggered by convective weather. The location of the wave sources determines the trend of the propagation directions at the Dandong and Lhasa stations in autumn. In winter, because of the eastward wind, more events are propagating to the southwest at the Dandong station.

Abstract Geomagnetic storms, through the complex modulation of space weather, can disrupt observational instruments. During certain storms, digisonde observations exhibit complete echo disappearances, a phenomenon that has not been systematically investigated. We conducted a statistical analysis of this phenomenon using digisonde data from three stations of the Chinese Meridian Project (Mohe:122.2°E, 53.3°N; Wuhan:114.3°E, 30.3°N; Fuke:109.7°E, 19.3°N) over a solar cycle from January 2011 to April 2025, encompassing 351 geomagnetic storms. Results show that digisonde echo disappearances occur only during moderate (min Dst between −100 and −50 nT) and strong (min Dst ≤ −100 nT) storms, and not during minor storms (−50 nT < min Dst ≤ −30 nT). Both the occurrence and duration of these disappearances show a clear latitudinal dependence, highest at Mohe, intermediate at Wuhan, and lowest at Fuke. Disappearances occur more frequently at night and during the storm recovery phase than in daytime and the main phase. Seasonally, occurrence peaks in autumn, followed by spring and winter, and is lowest in summer. These disappearances may be linked to D‐region absorption during geomagnetic storms and storm‐driven changes in ionospheric electron density. These findings have practical implications for the operation of ionosphere instruments and for mitigating geomagnetic‐storm effects.

Abstract The auroral‐like sporadic E‐layer is typically observed at altitudes between 100 and 150 km within the South American Magnetic Anomaly region. However, the occurrence of an unusual layer event detected above this altitude range on 18 July 2017 has raised intriguing questions regarding the physical processes responsible for the substantial vertical displacement of this layer. The interplanetary medium conditions during the event exhibited characteristics consistent with the recovery phase of a geomagnetic storm driven by a complex solar wind structure, occurring after substorm activity. To address this atypical layer occurrence, we examined the magnetospheric conditions using the BATS‐R‐US model with two experiments: one including the actual geomagnetic dipole inclination and another omitting it. These configurations allow for a discussion of the energy deposition processes under the prevailing interplanetary medium conditions. Also, the dynamics of the inner radiation belt were investigated through analysis of the magnetic field power spectral density and low‐energy electron flux measurements from the Van Allen Probes mission to verify electron precipitation. Plasma wave observations and their characterization also revealed atypical behavior, in which a non‐standard confinement of hiss waves (200 and 500 Hz) occurred simultaneously with an electron flux decrease (<1 keV), an integrated ionization rate between 250 and 300 km, and the formation of a peculiar layer. Finally, although this magnetic storm was moderate, we demonstrate that particle precipitation significantly impacted the atmosphere, as evidenced by pronounced ozone depletion in the mesosphere with magnitudes substantially stronger when compared to the extreme storm of May 2024.

Abstract. A compact solid etalon Fabry-Perot interferometer (SEFPI) with an effective aperture diameter of 70 mm has been developed for ground-based measurements of upper atmospheric winds and temperatures at an altitude of approximately 250 km. Unlike conventional FPIs employing air-spaced etalons, the SEFPI uses a solid etalon, enabling a more compact, lightweight, and cost-effective instrument design, while requiring stringent thermal stabilization. Laboratory validation using an acousto-optic frequency shifter (AOFS) to generate controlled Doppler shifts demonstrated the SEFPI’s high measurement accuracy, with an average wind uncertainty of 0.42 m/s and a root mean square error (RMSE) of 0.61 m/s. Field comparison validation was conducted via coincident ground-based measurements with two interferometry techniques. The first employed a Dual-Channel Optical Interferometer (DCOI), while the second utilized a well-established FPI employing a 100 mm diameter air-spaced etalon. The SEFPI measurements exhibited strong agreement with both instruments, yielding Pearson correlation coefficients exceeding 0.84. Statistical analysis yielded an overall mean wind difference of 1.88 m/s relative to the co-located DCOI instrument and 5.58 m/s relative to the conventional FPI located 502 km away. Temperature comparisons between the two FPIs revealed a correlation coefficient of 0.86 and an average difference of 62.38 K.

The Scale-Invariant Feature Transform (SIFT) algorithm detects key points and generates descriptors in images, enabling features matching across different images for object recognition and tracking. We derived the zonal drift velocities of equatorial plasma bubbles (EPBs) by tracking SIFT key points in GOLD Nmax data. Zonal drift velocities varied from similar to 40 m/s to similar to 160 m/s and exhibited prominent seasonal variations: the average drift velocity for different longitudes peaks around the Northern Hemisphere's winter solstice month and reaches its minimum near the summer solstice month. The results show that the zonal drift speeds of EPBs are larger during high solar activity, while intense geomagnetic activity suppresses eastward drift velocities. This study represents the first application of the SIFT algorithm to satellite airglow images. Our findings reveal climatological variations in ionospheric zonal drifts, providing new observational foundations for advancing the understanding of ionospheric electrodynamic processes.

Abstract. Severe thunderstorms drive vertical coupling through electrical processes associated with transient luminous events (TLEs) and dynamical processes associated with atmospheric gravity waves (AGWs). On 19 May 2022, an exceptionally intense thunderstorm outbreak occurred over the northern Bay of Bengal–Himalayan foothill region. The storm system produced more than 100 red sprites, 16 secondary gigantic jets, and at least four ghosts, accompanied by visible concentric airglow ripples. This event represented the first large-scale detection of a massive red sprite outbreak in China. From a dynamical perspective, concentric gravity waves (CGWs) were observed from the stratosphere to the thermosphere using coordinated satellite and ground-based airglow observations. AIRS measurements revealed concentric wave structures in the stratosphere above the convective source region, while ground-based airglow imagers detected CGWs in the OH, OI 557.7 nm, and OI 630.0 nm emission layers. CGWs in the mesosphere and lower thermosphere (MLT) propagated northeastward for more than 3000 km, suggesting propagation within favorable MLT ducting structures. In contrast, thermospheric CGWs observed in the OI 630.0 nm emission exhibited horizontal phase speeds of 260–280 m s⁻¹. Reverse ray-tracing analysis indicates a preferred source altitude near 150 km, suggesting that these waves were likely secondary gravity waves generated by the dissipation and breaking of upward-propagating primary gravity waves. Their asymmetric occurrence is likely attributable to Doppler-induced dissipation associated with thermospheric background winds. These observations provide a rare example of simultaneous electrical and dynamical coupling from the troposphere to the thermosphere during an extreme convective event.

The zonal neutral wind is generally believed as the driving source of zonal drift of the equatorial plasma bubbles (EPBs). Comparing their correlations is crucial for understanding the zonal drift of EPBs. However, studies on their relationship by utilizing ground-based observational data are very limited, especially in the Chinese sector. In this study, we conducted a statistical comparison between the EPB zonal drift velocity estimated from an All-Sky Airglow Imager (ASAI) and the zonal neutral wind obtained from a Fabry-Perot Interferometer (FPI) and a Dual-Channel Optical Interferometer (DCOI) deployed at the Fuke (; , dip latitude similar to 9.7 degrees N) station over more than 1 yr, from June 2023 to December 2024. The results show that the zonal drift velocities of over 50% EPB events are generally consistent with the zonal neutral wind velocities. For the remaining cases, the EPB zonal drift velocity differs from the zonal neutral wind velocity, with more pronounced deviations observed around midnight. Before midnight, events with EPB zonal drift velocities lower than the wind velocity outnumber those with higher velocities. After midnight, this trend reverses, with higher EPB velocities becoming more frequent. Additionally, the differences between EPB zonal drift velocity and zonal neutral wind velocity exhibit seasonal variations and are modulated by geomagnetic activity. These results provide valuable insights for advancing our understanding of the patterns and physical mechanisms governing EPB zonal drift.

On the two consecutive days of February 26-27, 2014, the all-sky airglow imager in Qujing observed Equatorial Plasma Bubbles (EPBs) dissipating more rapidly than those that appeared before and after. While these rapidly dissipating EPBs were present, the Hainan COherent-scatter Phased Array Radar (HCOPAR) detected Field-Aligned Irregularities (FAIs) within them. These FAIs first descended and then rose. The vertical extent of the fluctuations exceeded 100 km. Observations from four ionosondes at different latitudes showed a consistent pattern over the two nights. The F-layer height initially ascended and then rapidly descended. Plasma from higher altitudes was compressed to lower altitudes, which resulted in a significant increase in peak density. As a result, Nighttime Ionosphere Enhancement (NIE) occurred. At first, the FAIs descended along with the F-layer. After a while, they began to rise again. The downward movement is believed to have accelerated the decay of EPBs in the NIE region.

In this study, we investigate the source and dynamics of a mesoscale gravity wave (MGW) observed over northern China. On January 12, 2010, an OH airglow imager at the Xinglong station (40.2 degrees N, 117.4 degrees E) detected an MGW propagating from southwest to northeast, consistent with the background wind direction. The wave exhibited a horizontal wavelength of 125 +/- 7.6 km, an observed period of 25 +/- 3.2 min, and a phase speed of 83 +/- 12.4 m/s. The momentum flux and the energy FLux of the MGW were approximately 24.93 m(2)/s(2) and 1.08 x 10(-5) W/m(2), respectively, from the airglow imaging observation. During propagation, wave breaking generated secondary ripples with wavelengths of 5-12 km. These ripples were likely caused by wind shear, as measured by the Doppler meteor radar at Shisanling (40.3 degrees N, 116.2 degrees E). According to OH emission profiles from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite, the height of the OH airglow layer was similar to 81 km during the MGW propagation event. A separate northwestward-propagating small-scale gravity wave with a wavelength of similar to 35 km was also observed. The backward ray-tracing analysis conducted with European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis data indicated that the jet system near the Tibetan Plateau served as the source for the MGW.

Chemical heating from exothermic reactions is a key component of the upper mesosphere-lower thermosphere (UMLT) energy budget, yet its quantification remains uncertain. We derive a new data set of heating rates at 22:00 local time for seven major reactions using Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) OH (9-6) limb emissions, collocated with Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature and ozone profiles. The retrieval assumes chemical equilibrium for ozone and HOx and applies updated Einstein coefficients from HITRAN-2020. Consistent with earlier studies, the relative importance of individual reactions varies systematically with altitude: the hydrogen + ozone reaction (H+O-3) provides the leading contribution below similar to 92 km, whereas three-body oxygen recombination (O+O+M) dominates above this level. Other reactions make a substantial contribution across much of the 80-96 km region, accounting for roughly one-third to one-half of the total chemical heating above similar to 86 km. The derived latitude-altitude heating structures of the dominant reactions are significantly modulated by atmospheric tides. In the equatorial zone, these heating rates exhibit a pronounced semiannual cycle that tracks seasonal changes in temperature and key reactants. Relative to previous SCIAMACHY-based estimates, the updated data set yields lower heating rates from H+O-3. An uncertainty assessment indicates similar to 30 % uncertainty for H+O-3 and similar to 45 %-80 % for O+O+M. These results refine and consolidate current understanding of chemical heating and its variability in the UMLT.

AbstractThe storm‐time temperature difference with respect to its quiet‐time expectation (ΔT) in the mesosphere and lower thermosphere were studied during the extreme storms on 2024 Mother's Day and 2003 Halloween Day. The storm‐time ΔT were determined by performing daily zonal running mean on the temperature profiles in the ascending and descending nodes separately. The storm‐time ΔT had peak values of ≥25 K and extended downward to ∼100 km globally. Above 105 km, the global mean ΔT had values of ≥20 K in the early morning and of ≥15 K in the late afternoon during storm‐time. At high latitudes, the storm‐time ΔT was larger in the late afternoon than in the early morning. This is opposite to that at middle and low latitudes. Adiabatic warming/cooling caused by the heating‐induced circulation changes outside of the auroral oval is likely responsible for the local time and latitude dependence of the storm‐time ΔT.

Atomic hydrogen (H) is crucial for understanding photochemistry and the energy budget in the mesopause region. However, there is still no consensus on the H abundance in this region. This study presents a new hydrogen data set derived from Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY) OH(9–6) band spectra, collocated with temperature and ozone profiles from other remote sensing instruments. H number densities peak at 82–87 km and range from to , depending on season and latitude. Two other H data sets obtained from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) are presented for comparison: those from Mlynczak et al. (2018, https://doi.org/10.1029/2018GL077377 ) and Panka et al. (2021, https://doi.org/10.1029/2020GL091053 ) are approximately 30% lower and 50% higher than the SCIAMACHY data at peak altitudes, respectively. Additionally, the H number density retrieved in this study partly shows better agreement with the only direct rocket in situ measurements than those from SABER.

F-region Field-Aligned Irregularities (FAIs) observed by the Hainan Coherent Scatter Phased Array Radar (HCOPAR) and the Equatorial Plasma Bubbles (EPBs) observed by four All-Sky Airglow Imagers (ASAIs) in the night of 4 November 2023 were compared. The spatiotemporal distribution of the FAIs was nearly consistent with that of the EPBs. However, certain FAIs were located outside the EPBs. Oblique band-like echoes extended beyond the EPBs between 12:30 and 13:30 UT, with the opposite line-of-sight velocities of the echo components above and below. Electrostatic reconnection between adjacent bubbles was considered a driving mechanism for the irregularities extending outward. Between 14:30 and 15:30 UT, certain FAIs were located outside the eastern wall of the bubble. The upward electric field component in the westward tilted bubble will transport the plasma from eastern wall and make the high density gradient region extend outside the bubble, and the irregularities appeared due to the polarization electric field extending outside the bubble.