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Abstract Geological Culture Villages Towns (GCV(T)s) serve as rich repositories of geological resources, embodying significant historical and cultural values that mirror the dynamic interplay between Earth's evolution and human societies. Despite their importance, the theoretical underpinnings of GCV(T)s have not been thoroughly explored and elucidated. This study explores the relationship between geological culture and societal development, revealing the linkage between geological culture and societal advancement with the aim of promoting a harmonious coexistence between humanity and the environment. Focusing on 96 GCV(T)s in China, this study employs spatial analytical techniques such as the nearest-neighbor index, kernel density analysis, geographic connectivity, and geographic detector to scrutinize the spatial distribution patterns and identify key influencing factors. The findings reveal that (1) GCV(T)s exhibit uneven distribution, with concentrations in the Yangtze River Delta region, Beijing-Tianjin-Hebei region, and Shanxi-Gansu and Ningxia Provinces. (2) These sites tend to be situated in areas characterized by active geological formations, abundant geological relics, higher elevations, gentle topography, and ample rainfall. (3) The establishment and evolution of GCV(T)s are shaped by a complex interplay of geological heritage, natural factors, and human interventions. While the selection and spatial arrangement of these sites are predominantly influenced by geological and natural factors, the innovative development of their geological cultural heritage is driven by humanistic considerations. Overall, the distribution and evolution of GCV(T)s stem from multifaceted interactions among diverse factors. Recognizing this intricate web of influences is crucial for safeguarding geocultural diversity and formulating conservation strategies for geoheritage protection. The development of GCV(T)s transcends mere geoheritage preservation, it embodies a pivotal stride toward safeguarding the varied and multi-dimensional global geoheritage.

Abstract Digitalized natural history collections serve as vital ecological and evolutionary research resources. Specimen retrieval based on morphological features allows for the rapid acquisition of similar specimens from these collections, aiding in maximizing the utilization of their resources and catering to the requirements of related research. However, achieving this objective requires effective feature extraction and representation techniques. We developed a phenotype encoding network (PENet), a deep learning‐based model that combines hashing methods to automatically extract and encode discriminative features into hash codes. We evaluated the performance of PENet on six data sets, including a newly constructed beetle data set (6566 images), which covers over 60% of the genera within the six subfamilies of Scarabaeidae. Phenotype encoding network showed high performance in feature extraction and image retrieval, allowing users to input an image of a specimen and efficiently retrieve all specimens with similar morphology. Two visualization methods, t‐SNE and Grad‐CAM, were used to evaluate the representation ability of the hash codes. Additionally, by using the hash codes generated from PENet, a phenetic distance tree was constructed based on the beetle data set. The result indicated that the hash codes could reveal the phenetic distances and relationships among categories to a certain extent. PENet provides an automatic and efficient method to extract and represent morphological discriminative features. The generated hash code can be used as a low‐dimensional carrier of these features, enabling efficient specimen retrieval. Moreover, the distance information carried by these hash codes suggests their potential in systematics, deserving further exploration.

Developing short-term forecasting models for global atmospheric temperature and wind in near space is crucial for understanding atmospheric dynamics and supporting human activities in this region. While numerical models have been extensively developed, deep learning techniques have recently shown promise in improving atmospheric forecasting accuracy. In this study, convolutional long short-term memory (ConvLSTM) and convolutional gated recurrent unit (ConvGRU) neural networks were applied to build for short-term global-scale forecasting model of atmospheric temperature and wind in near space based on the MERRA-2 reanalysis dataset from 2010–2022. The model results showed that the ConvGRU model outperforms the ConvLSTM model in the short-term forecast results. The ConvGRU model achieved a root mean square error in the first three hours of approximately 1.8 K for temperature predictions, and errors of 4.2 m/s and 3.8 m/s for eastward and northward wind predictions on all 72 isobaric surfaces. Specifically, at a higher altitude (on the 1.65 Pa isobaric surface, approximately 70 km above sea level), the ConvGRU model achieved a RMSE of about 2.85 K for temperature predictions, and 5.67 m/s and 5.17 m/s for eastward and northward wind. This finding is significantly meaningful for short-term temperature and wind forecasts in near space and for exploring the physical mechanisms related to temperature and wind variations in this region.

In order to test the influence of the structural design of a no-tillage corn precision planter on vibration stability performance, a vibration model was constructed with the help of MATLAB/Simulink, and it was concluded that the vibration response curve of the no-tillage corn precision planter was relatively smooth. Based on the theory of the discrete element method (DEM), taking the planting apparatus of the no-tillage corn precision planter as the research object, firstly, a DEM single-factor test was carried out to investigate the effects of the slot inclination angle, number of slots, and rotational speed of the planter plate on the disturbance performance. Then, a three-factor, three-level orthogonal test was conducted with the maximum amount of seed discharging, the minimum average speed, and the minimum average kinetic energy as the final optimization objectives, and the qualified rate of seed discharging and the leakage rate as the evaluation indexes. The results show that the larger the inclination angle, the higher the number of slots, and the faster the rotational speed, the more violent the particle disturbance. At the same time, when the slot inclination angle of the planter plate is 60°, the number of slots is 20, and the rotational speed is 55 rpm, the seed discharge efficiency is the highest, at this time, the seed discharge qualification rate of maize particles is 95%, and the leakage rate is 3%; the results of this test can provide technical support for the research of the same kind of precision sowing equipment in the future.

Vat photopolymerization (VPP), as an additive manufacturing (AM) technology, can conveniently produce ceramic parts with high resolution and excellent surface quality. However, due to the inherent brittleness and low toughness of ceramic materials, manufacturing defect-free ceramic parts remains a challenge. Many researchers have attempted to use carbon fibers as additives to enhance the performance of ceramic parts, but these methods are mostly applied in processes like fused deposition modeling and hot pressing. To date, no one has applied them to VPP-based AM technology. This is mainly because the black carbon fibers reduce laser penetration, making it difficult to cure the ceramic slurry and thus challenging to produce qualified ceramic parts. To address this issue, our study has strictly controlled the amount of carbon fibers by incorporating trace amounts of carbon fiber powder into the original ceramic slurry with the aim to investigate the impact of these additions on the performance of ceramic parts. In this study, ceramic slurries with three different carbon fiber contents (0 wt.%, 0.1 wt.%, 0.2 wt.%, and 0.3 wt.%) were used for additive manufacturing. A detailed comparative analysis of the microstructure, physical properties, and mechanical performance of the parts was conducted. The experimental results indicate that the 3D-printed alumina parts with added carbon fibers show varying degrees of improvement in multiple performance parameters. Notably, the samples prepared with 0.2 wt.% carbon fiber content exhibited the most significant performance enhancements.

Alumina (Al2O3) ceramics are widely used in electronics, machinery, healthcare, and other fields due to their excellent hardness and high temperature stability. However, their high brittleness limits further applications, such as artificial ceramic implants and highly flexible protective gear. To address the limitations of single-phase toughening in Al2O3 ceramics, some researchers have introduced a second phase to enhance these ceramics. However, introducing a single phase still limits the range of performance improvement. Therefore, this study explores the printing of Al2O3 ceramics by adding two different phases. Additionally, a new gradient printing technique is proposed to overcome the limitations of single material homogeneity, such as uniform performance and the presence of large residual stresses. Unlike traditional vat photopolymerization printing technology, this study stands out by generating green bodies with varying second-phase particle ratios across different layers. This study investigated the effects of different contents of sepiolite fiber (SF) and 316L stainless steel (SS) on various aspects of microstructure, phase composition, physical properties, and mechanical properties of gradient-printed Al2O3. The experimental results demonstrate that compared to Al2O3 parts without added SF and 316L SS, the inclusion of these materials can significantly reduce porosity and water absorption, resulting in a denser structure. In addition, the substantial improvements, with an increase of 394.4% in flexural strength and an increase of 316.7% in toughness, of the Al2O3 components enhanced by incorporating SF and 316L SS have been obtained.

Circadian rhythm sleep–wake disorders (CRSWDs) are becoming increasingly common in modern societies due to lifestyle changes. The detrimental effects of CRSWDs on sleep and psychological health have attracted considerable attention recently. Alternative remedies for the treatment of CRSWDs have also gained attention in recent years owing to the limitations of medications. Several in vivo and clinical investigations have shown that acupuncture, one of the most important components of traditional Chinese medicine (TCM), has been shown to modulate sleep-related circadian rhythms. Owing to the lack of research on the mechanism and effectiveness of acupuncture in treating CRSWDs, clinical applications of acupuncture have not gained popularity. This paper reviews the acupuncture methods, acupoint selection, and biochemical indicators supplied by in vivo and clinical studies to explore the effectiveness of acupuncture, and summarizes the circadian rhythm mechanisms and the acupuncture characteristics on circadian rhythm. The neurochemical mechanisms linked to acupuncture in treating CRSWDs are also outlined from the perspective of the central and peripheral biological clocks. Lastly, the inadequacy of previous studies on CRSWDs and conflicting results regarding acupuncture are explored and future research directions are envisioned.

C–N bond cross-coupling is fundamental in organic chemistry, but the readily available organic fluorides are unsuitable as coupling substrates. Here, we realize defluorinative cross-coupling with amines via a silylboronate-mediated strategy.

Spread F (SF) in the ionosphere can be observed frequently in mid-latitude regions. It is suggested that atmospheric gravity waves play a significant role for the seeding of mid-latitude SF. Previous research suggested that the source of travelling ionospheric disturbances (TIDs) over China is in the southeastern and northeastern edge of the Qinghai-Tibet Plateau, however, until now there have been no ground-based observations of the ionosphere in this region. Recently, an advanced digital ionosonde was installed at Zhangye station (39.2°N, 100.54°E, Dip Lat 29.6°N) in the northeastern edge of the Qinghai-Tibet Plateau. It is an opportunity to verify the effect of gravity waves on the formation of mid-latitude SF by comparing it with observations in other regions of the Chinese sector. In this study, statistical analysis of SF recorded at Zhangye station during 2017–2022 was carried out. Results show that diurnal, seasonal and solar cycle characteristics of the occurrence rate of SF are similar with previous studies. At Zhangye station, the maximum occurrence rate of SF is during the post-midnight period in summer and winter. The occurrence rate of SF events have a negative relationship with solar activity. There is no obvious relationship between the occurrence rate of SF and geomagnetic activity. Comparing observations of other stations in the mid-latitude region, we found that the occurrence rates of SF (the annual maximum rates are from 33.83% to 53.29%) are much higher at Zhangye station. Further studies show that ionospheric disturbances can be observed frequently at Zhangye station, especially in autumn and winter. Gravity waves/TIDs in the northeast of the Qinghai-Tibet Plateau are suggested to explain the abnormal higher occurrence rate of SF at Zhangye station.

A wide variety of small-amplitude waves widely exist in the ionosphere and have significant effects on the evolution of equatorial plasma bubbles. In this paper, we simulated equatorial plasma bubbles (EPB) seeded by vertical neutral wind perturbations with wavelengths of 125 km and 250 km, and compared the morphology characteristics of plasma bubble structures with those under random noise perturbations in the background density. The numerical results showed that both vertical winds and random background noise perturbations can contribute to the growth of plasma bubbles, and the perturbations under additional random background noise can promote the growth of the plasma bubble structures faster. Additionally, several processes of the nonlinear behavior of bifurcated EPB structures, including bifurcation, pinching, and small-scale turbulent structures, were successfully obtained. Our simulation captured supersonic flows within the low-density plasma structures characterized by vertical velocities of about 1.5 km/s, which is consistent with experimental studies found in the literature.

Evolutionary and functional analyses alongside new fossil specimens expand our understanding of rolling-into-ball behaviour in pill scarab beetles.

Parametric decay instability (PDI) is an important process in ionospheric heating. This paper focuses on the frequency and wavevector matching condition in the initial PDI process, the subsequent cascade stage, and the generation of strong Langmuir turbulence. A more general numerical model is established based on Maxwell equations and plasma dynamic equations by coupling high-frequency electromagnetic waves to low-frequency waves via ponderomotive force. The primary PDI, cascade process, and strong Langmuir turbulence are excited in the simulation. The matching condition in the initial PDI stage and cascade process is verified. The result indicates that the cascade ion acoustic wave may induce or accelerate the formation of cavitons and lead to the wavenumber spectrum being more enhanced at 2kL (where kL is the primary Langmuir wavenumber). The wavenumber spectra develop from discrete to continuous spectra, which is attributed to the caviton collapse and strong Langmuir turbulence.

Meteor radar is one of the key tools for studying the atmospheric dynamics in the mesosphere and lower thermosphere. The physical parameters obtained by meteor radar inversion can provide important statistical information for research. The daily and annual variations in meteor azimuth distribution detected by meteor radars contain information about meteor source regions and patterns related to the rotation and revolution of the Earth. Using the meteor parameters from two meteor radars located in Mohe (53.5° N, 122.3° E) and Wuhan (30.6° N, 114.4° E), this study calculates the variation patterns in the meteor azimuth distribution over the two sites over 1 year. Additionally, this study introduces the variable, Max_Azi, to describe the position of the peak of azimuth distribution. The peak value of azimuth distribution is calculated by Gaussian fitting to quantify the variation patterns in azimuth distribution. This study provides complementary information on the azimuth distribution in high and middle latitudes. The results indicated that the azimuth distribution variation for the Mohe meteor radar is consistent with the Earth’s revolution model.

Recently, kilometer-scale Martian ionospheric irregularities have been measured by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission (Fowler et al., 2020). In this study, we carried out a simulation of these irregularities, assuming a uniform Martian zonal neutral wind and a cosinusoidal perturbation of the plasma density as the seeding source. Results show that a vertical electric field shear could be induced by such a plasma density perturbation. We find that the vertical electric field shear causes a velocity shear of the plasma between the topside and bottomside ionosphere, which in turn is able to produce kilometer-scale ionospheric irregularities — irregularities of a smaller scale than were seen in previous simulations (Jiang CH et al., 2021). These kilometer-scale variations with altitude, in plasma density and magnetic field profiles, are comparable to the MAVEN observations.

The theoretical development of Schumann Resonances has spanned more than a century as a form of global natural electromagnetic resonances. In recent years, with the development of electromagnetic detection technology and the improvement in digital processing capabilities, the connection between Schumann Resonances and natural phenomena, such as lightning, earthquakes, and Earth’s climate, has been experimentally and theoretically demonstrated. This article is a review of the relevant literature on Schumann Resonance observation experiments, theoretical research over the years, and a prospect based on space-based observations. We start with the theoretical background and the main content on Schumann Resonances. Then, observations and the identification of Schumann Resonance signals based on ground and satellite data are introduced. The research and related applications of Schumann Resonances signals are summarized in terms of lightning, earthquakes, and atmosphere. Finally, the paper presents a brief study of Schumann Resonances based on the China Seismo-Electromagnetic Satellite (CSES) and preliminary ideas about how to improve the identification and application of space-based Schumann Resonances signals.

A regioselective carbosilylation of alkenes is a powerful strategy to access functionalized silylated alkanes. In this study, the authors report a catalyst-free carbosilylation of alkenes using silyl boronates and organic fluorides, mediated by t BuOK, and synthesise various silylated alkanes with tertiary or quaternary carbon centres.

The electron density (Ne), ion density (Ni), and electron temperature (Te) statistics recorded by the DEMETER satellite payload ISL (Instrument Sonde de Langmuir) were used to study the disturbance characteristics of the ionosphere before solid earthquakes of magnitude 6 or higher in Japan during the summer of 2005–2009, to provide more information and methods for the coupling mechanism and short-range earthquake prediction. In this paper, the region of ±10° of the epicenter is divided into 1°×1° pixels, and the background field of each parameter is constructed using data without earthquakes and relatively calm space weather. We also define a measure of the perturbation intensity of ionospheric parameters relative to the background field during the occurrence of earthquakes. The analysis results of the four Japanese earthquakes from space and time show an excellent synchronization in the time and area of the anomalies in ionospheric parameters of the four cases. All four instances showed Ne abnormalities, and three showed Ni and Te anomalies, in which Ne and Ni increased or decreased abnormally, while Te increased abnormally every time, and the anomalies mainly occurred about 9–12 days before the earthquake. This paper eliminates the influence of solar, geomagnetic, and satellite data defects on the experimental results as much as possible in data screening and method selection. The results partially agree with the conclusions reported in the existing literature, and the obtained anomalies are somewhat related to the ionospheric precursors of earthquakes.

The ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2) is known as the ionospheric equivalent slab thickness (EST, also known as τ), and it is a crucial indicator of the ionosphere. Using TEC and NmF2 data from the years 2010 to 2017, this work conducts a comprehensive statistical analysis of the ionospheric slab thickness in Beijing, which is in the midlatitude of East Asia. The outcomes show that the τ have different diurnal variations at different seasons for high/low-solar-activity years. On the whole, daytime τ significantly greater than nighttime τ in summer, and it is the opposite for the τ in winter regardless of the solar cycle, whereas the τ during equinox shows different morphology for high/low-solar-activity years. Specifically, daytime τ is larger than nighttime τ during equinox in years of high-solar activity, while the opposite situation applies for the τ during equinox in years of low-solar activity. Moreover, the pre-sunrise and post-sunset peaks are most pronounced during winter for low-solar-activity years. In summer, there is a great increase in τ during the morning hours when compared with other seasons. Furthermore, the τ decreases with the solar activity during nighttime, whereas it seems there is no correlation between daytime τ and solar activity. This paper explained the primary diurnal variations in τ across different seasons during high-/low-solar-activity years by analyzing relative fluctuations of TEC and NmF2 throughout the corresponding period. In addition, based on the disturbance index (DI), which is calculated by instantaneous τ and its corresponding median, this paper found that the storm-time τ might increase when compared with its median value during the daytime, while it may both increase and decrease during the nighttime, especially around dawn and dusk hours. To further analyze the physical mechanism, an example on 2 October 2013 is also presented. The results indicate that the positive disturbance of τ during the main phase of a geomagnetic storm might be caused by the prompt penetration electric field and neutral wind during the storm, and the τ increases during the early recovery phase might be due to the disturbance dynamo electric field as well as the neutral wind during the storm. Moreover, there is a negative disturbance of τ in the recovery phase during the most disturbed sunrise hours, and it might be due to the electric field reversal, neutral wind or other factors during this period. This paper notes the differences of τ in midlatitude between different longitudinal sectors from the related climatology and storm-time behavior, as it would be helpful to improve the current understanding of τ at midlatitudes in East Asia.

This paper presents a circularly polarized turnstile antenna for a meteor radar system. The antenna employs a pair of turnstile radiators, a 1:2 power divider and a 90° phase shifter. After a series of simulations and optimizations, the maximum circularly polarized gain at 39 MHz is 5.9 dBic with 96° 3 dB beam width. The simulated axial ratio below 3 dB is from −39° to 39° within the band of interest. Then, the proposed antenna is fabricated and applied to a meteor radar system. Two tests are carried out for radiation characteristics demonstration. In the first test, the VSWR of the proposed antenna is below 1.2 at 38.5–39.5 MHz and keeps good agreement with simulation results. However, the meteor azimuth distribution is illogical when the output results are compared with the Australian meteor detection radar (ATRAD) meteor detection. To address the problem, baluns are investigated and introduced for balanced feeding. The 1:1 unbalance–balance transformer has been used to improve the radiation characteristics of the designed antenna. The final test results show that the meteor radar system with the improved antenna achieves better performances in meteor counts and meteor azimuth distribution.

A new protocol enabling the formation of trifluoromethyl compounds from acyl fluorides has been developed. The combination of FLUOLEAD® and Olah’s reagent in solvent-free conditions at 70 °C initiated the significant deoxyfluorination of the acyl fluorides and resulted in the corresponding trifluoromethyl products with high yields (up to 99%). This strategy showed a great tolerance for various acyl fluorides containing aryloyl, (heteroaryl)oyl, or aliphatic acyl moieties, providing good to excellent yields of the trifluoromethyl products. Synthetic drug-like molecules were also transformed into the corresponding trifluoromethyl compounds under the same reaction conditions. A reaction mechanism is proposed.

The characteristics of high-frequency (HF) electromagnetic (EM) wave propagation can be affected when EM waves propagate in the ionosphere. When ionospheric irregularities appear in the ionosphere, they can have a serious impact on the propagation of HF EM waves. In this study, the propagation of HF EM waves in ionospheric irregularities was investigated by numerical simulation. First, a two-dimensional model of plasma bubbles was used to produce ionospheric irregularities in the ionosphere. A ray-tracing method was then utilized to simulate the propagation of HF radio waves in these ionospheric irregularities. Results showed that the propagation of HF radio waves in the ionosphere was more complex in ionospheric irregularities than without ionospheric irregularities. In addition, corresponding ionograms were synthesized by radio rays propagated in the ionosphere with these irregularities. The synthesized ionograms were then compared with the experimental ionograms recorded by an ionosonde. Results showed that spread F could be simulated on the ionograms when ionospheric irregularities occurred in the ionosphere. This result was consistent with the ionosonde observations.

In this study, we present three experiments carried out at the EISCAT (European Incoherent Scatter Scientific Association) heating facility on October 29 and 30, 2015. The results from the first experiment showed overshoot during the O-mode heating period. The second experiment, which used cold-start X-mode heating, showed the generation of parametric decay instability, whereas overshoot was not observed. The third experiment used power-stepped X-mode heating with noticeable O-mode wave leakage. Parametric decay instability and oscillating two-stream instability were generated at the O-mode reflection height without the overshoot effect, which implies suppression of the thermal parametric instability with X-mode heating. We propose that the electron temperature increased because X-mode heating below the upper hybrid height decreased the growth rate of the thermal parametric instability.

Abstract The generation and evolution of artificial plasma clouds is a complicated process that is strongly dependent on the background environment and release conditions. In this paper, based on a three-dimensional two-species fluid model, the evolution characteristics of artificial plasma clouds under various release conditions were analyzed numerically. In particular, the effect of ionospheric density gradient and ambient horizontal wind field was taken into account in our simulation. The results show that an asymmetric plasma cloud structure occurs in the vertical direction when a nonuniform ionosphere is assumed. The density, volume, and expansion velocity of the artificial plasma cloud vary with the release altitude, mass, and initial ionization rate. The initial release velocity can change the cloud's movement and overall distribution. With an initial velocity perpendicular to the magnetic field, an O+ density cavity and two bumps exist. When there is an initial velocity parallel to the magnetic field, the generated plasma cloud is bulb-shaped, and only one O+ density cavity and one density bump are created. Compared to the cesium case, barium clouds expand more rapidly. Moreover, Cs+ clouds have a higher density than Ba+ clouds, and the snowplow effect of Cs+ is also stronger.

As a companion paper to Zhou RX et al. (2020), this study describes application of the automatic detection and analysis module to identify all the tweek atmospherics detectible in the WHU ELF/VLF receiver data collected at Suizhou station during the period of 3 February through 29 February 2016. Detailed analysis of the identified low-latitude tweek events reveals that the occurrence rate varies considerably — from 800 to 6000 tweeks per day, and exhibits a strong diurnal and local time dependence, the peak occurring before local midnight. The diurnal variation of identified tweeks was similar to that of the lightning data obtained by the World-Wide Lightning Location Network (WWLLN).. Estimates of the propagation distance and ionospheric reflection height of tweek atmospherics suggest that the majority (~92%) of the low latitude tweeks originate from the lightning activity within a radius of 4000 km and that they are very likely to reflect from the lower ionospheric D-region at the height range of 75–85 km. At these lower ionospheric reflection altitudes, ~74% of the corresponding electron densities from the tweek spectral measurements are within 24.5–27.5 cm-3. The daily variation of estimated D-region electron densities in the considered period (February 2016) also exhibits a small overall increasing trend from early to later in the month.

As a dispersive wave mode produced by lightning strokes, tweek atmospherics provide important hints of lower ionospheric (i.e., D-region) electron density. Based on data accumulation from the WHU ELF/VLF receiver system, we develop an automatic detection module in terms of the maximum-entropy-spectral-estimation (MESE) method to identify unambiguous instances of low latitude tweeks. We justify the feasibility of our procedure through a detailed analysis of the data observed at the Suizhou Station (31.57°N, 113.32°E) on 17 February 2016. A total of 3961 tweeks were registered by visual inspection; the automatic detection method captured 4342 tweeks, of which 3361 were correct ones, producing a correctness percentage of 77.4% (= 3361/4342) and a false alarm rate of 22.6% (= 981/4342). A Short-Time Fourier Transformation (STFT) was also applied to trace the power spectral profiles of identified tweeks and to evaluate the tweek propagation distance. It is found that the fitting accuracy of the frequency–time curve and the relative difference of propagation distance between the two methods through the slope and through the intercept can be used to further improve the accuracy of automatic tweek identification. We suggest that our automatic tweek detection and analysis method therefore supplies a valuable means to investigate features of low latitude tweek atmospherics and associated ionospheric parameters comprehensively.

In this study, we simulated the electron density disturbance at night in the bottom of the ionosphere caused by the electrostatic field in a thundercloud. The simulation was conducted using the charge of the thundercloud as the source, by incorporating a more up-to-date conductivity profile, and using the ion chemistry model for the lower ionosphere. The results revealed that a thundercloud charge of 30–100 C can cause a disturbance in the electron density in the lower ionosphere, decreasing to 40% of the original value or increasing to 160% of the original value. The electron density disturbance occurs mainly below an altitude of 80 km, and its peak is located at an altitude of 70 km, with a regional horizontal radius of about 50–75 km. The simulation results of this study improve the theory of Salem et al and extend the original one-dimensional model to three-dimensional space.

Spread-F (SF) is one of the most important types of the ionospheric irregularities as it causes ionospheric scintillation which can severely affect the performance and reliability of communication, navigation, and radar systems. The ionosonde provides the most effective and economical way to study the ionosphere and SF. However, the manual identification of SF from an ionogram is boring and hard work. To automatically identify SF on the ionogram and extend the study of SF into the middle and low latitudes of East Asia, this paper presents a statistical analysis of SF in this region, based on the naïve Bayesian classifier. The results showed that the accuracy of automatic identification reached up to 97% on both the validation datasets and test datasets composed of Mohe, I-Cheon, Jeju, Wuhan, and Sanya ionograms, suggesting that it is a promising way to automatically identify SF on ionograms. Based on the classification results, the statistical analysis shows that SF has a complicated morphology in the middle and low latitudes of East Asia. Specifically, there is a peak of occurrence of SF in the summer in I-Cheon, Jeju, Sanya, and Wuhan; however, the Mohe station has the highest occurrence rate of SF in December. The different seasonal variations of SF might be due to the different geographic local conditions, such as the inland-coastal differences and formation mechanism differences at these latitudes. Moreover, SF occurs more easily in the post-midnight hours when compared with the pre-midnight period in these stations, which is consistent with the previous results. Furthermore, this paper extracts the frequency SF (FSF) index and range SF (RSF) index to characterize the features of SF. The results shows that the most intense FSF/RSF appeared in the height range of 220–300 km/1–7 MHz in these stations, although there are different magnitude extensions on different season in these regions. In particular, strong spread-F (SSF) reached its maximum at the equinox at Sanya, confirming the frequent SSF occurrence at the equinox at the equator and low latitudes. These results would be helpful for understanding the characteristics of SF in East Asia.

E-region field-aligned irregularities (FAIs) are a hot topic in space research, since electromagnetic signal propagation through ionospheric irregularities can undergo sporadic enhancements and fading known as ionospheric scintillation, which could severely affect communication, navigation, and radar systems. However, the range resolution of very-high-frequency (VHF) radars, which is widely used to observe E-region FAIs, is limited due to its bandwidth. As a technology that is widely used in atmosphere radars to improve the range resolution of pulsed radars by transmitting multiple frequencies, this paper employed the multifrequency radar imaging (RIM) technique in a Wuhan VHF radar. The results showed that the range resolution of E-region FAIs greatly improved when compared with the results in traditional single-frequency mode, and that finer structures of E-region FAIs can be obtained. Specifically, the imaging results in multifrequency mode show that E-region FAIs demonstrate an overall descending trend at night, and it could be related to the tides or gravity waves due to their downward phase velocities or even driven by downwind shear. In addition, typical quasi-periodic (QP) echoes with a time period of around 10 min could be clearly seen using the RIM technique, and the features of the echoes suggest that they could be modulated by gravity waves. Furthermore, the RIM technique can be used to obtain the fine structure of irregularities within a short time period, and the hierarchical structure of E-region FAIs can be easily found. Therefore, the multifrequency imaging RIM technique is suitable for observing E-region FAIs and their evolution, as well as for identifying the different layers of E-region FAIs. Combined with the RIM technique, a VHF radar provides an effective and promising way to observe the structure of E-region FAIs in more detail to study the physical mechanism behind the formation and evolution of ionospheric E-region irregularities.

Abstract Statistical analysis of spread F (SF), recorded at Puer (PUR, 22.7° N, 101.05° E, Dip Latitude 12.9° N) during 2015–2016, was carried out to reveal its characteristics at the northern equatorial ionization anomaly. In our study, SF was categorized into four types, frequency spread F (FSF), range spread F (RSF), mix spread F (MSF) and strong range spread F (SSF). The statistical results presented that FSF and MSF were dominant over Puer. Most types of SF appeared mostly in summer months, except the maximum occurrence of SSF in equinox months. Moreover, observations of SF events also showed that the solar activity and magnetic activity dependence of SF varied with seasons. Compared with observations at other region, the present results suggest that medium-scale traveling ionospheric disturbances (MSTIDs) may play a key role in generation of SF in low-latitude region.

Phosphorylation is one of the most important posttranslational modifications and regulates the physiological process. While recent studies highlight a major role of phosphorylation in the regulation of sleep–wake cycles to a lesser extent, the phosphoproteome in the suprachiasmatic nucleus (SCN) is not well-understood. Herein, we reported that the EA treatment elicits partial reparation of circadian rhythmicity when mice were exposure to constant darkness for long time. We investigated the effects of EA on circadian rhythms in constant darkness between EA stimulation and free-running control. Next, mass spectrometry–based phosphoproteome was utilized to explore the molecular characteristics of EA-induced phosphorylation modification in the SCN. A total of 6,192 distinct phosphosites on 2,488 proteins were quantified. Functional annotation analysis and protein–protein interaction networks demonstrated the most significant enriched phosphor-proteins and phosphosites involved in postsynapse and glutamatergic synapse. The current data indicated that most of the altered molecules are structural proteins. The target proteins, NMDAR and CAMK2, were selected for verification, consistent with the results of LC–MS/MS. These findings revealed a complete profile of phosphorylation modification in response to EA.

The defluorosilylation of aryl fluorides to access aryl silanes was achieved under transition-metal-free conditions via an inert C–F bond activation. The defluorosilylation, mediated by silylboronates and KOtBu, proceeded smoothly at room temperature to afford various aryl silanes in good yields. Although a comparative experiment indicated that Ni catalyst facilitated this transformation more efficiently, the transition-metal-free protocol is advantageous from a green chemistry perspective.

The ionospheric equivalent slab thickness (EST, also named τ) is defined as the ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2), and it is a significant parameter representative of the ionosphere. This paper presents a comprehensive statistical study of the ionospheric slab thickness at Yakutsk, located at the high latitude of East Asia, using the GPS-TEC and ionosonde NmF2 data for the years 2010–2017. The results show that the τ has different diurnal and seasonal variations in high- and low-solar-activity years, and the τ is greatest in the winter, followed by the equinox, and it is smallest in the summer in both high- and low-solar-activity years, except during the noontime of low-solar-activity years. Specifically, the τ in inter of high-solar-activity year shows an approximate single peak pattern with the peak around noon, while it displays a double-peak pattern with the pre-sunrise and sunset peaks in winter of the low-solar-activity years. Moreover, the τ in the summer and equinox have smaller diurnal variations, and there are peaks with different magnitudes during the sunrise and post-sunset periods. The mainly diurnal variation of τ in different seasons of high- and low-solar-activity years can be explained within the framework of relative variation of TEC and NmF2 during the corresponding period. By defining the disturbance index (DI), which can visually assess the relationship between instantaneous values and the median, we found that the geomagnetic storm would enhance the τ at Yakutsk. An example on 7 June 2013 is also presented to analyze the physical mechanism. It should be due to the intense particle precipitation and expanded plasma convection electric field during the storm at high-latitude Yakutsk station. The results would improve the current understanding of climatological and storm-time behavior of τ at high latitudes in East Asia.

In this paper, a statistical analysis of the diurnal, seasonal and solar cycle variation in the TEC longitudinal difference in midlatitudes of East Asia is presented using CODE GIMs data in 2015–2019. Moreover, the empirical neutral wind model HWM-14 and geomagnetic field model IGRF-2020 were employed to analyze the influence of geomagnetic configuration-neutral wind mechanism on the TEC longitudinal difference, and the F2 layer peak electron density (NmF2) data from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) were also used to study the role of local electron density in the TEC longitudinal difference. For the high solar activity year, the results show that east-west TEC longitudinal difference index Re/w is negative in the noon and positive at evening-night. Moreover, the longitudinal difference of daytime TEC is most evident in summer, less in autumn and least in spring and winter, while the nighttime difference is most obvious in equinox, followed by summer and winter during nighttime. The model simulation shows that the TEC longitude difference around noon is mainly caused by the zonal wind-declination mechanism, and a 4-h time delay seems to be an optimal result for the vertical drift velocity to cause the longitudinal TEC difference during pre-noon hours. At night, the uplifting electron flux, which is a product of local electron density and vertical drift velocity, shows a good correlation with Re/w, indicating that the local electron density is also an important factor affecting the TEC longitudinal difference during the nighttime. Moreover, there was about a 3-h time delay between the TEC longitudinal variations and the uplifting electron flux at night. For the low solar activity years, the western TEC is greater than eastern TEC during most of the year except in the summer nighttime. The TEC diurnal variation in the east and west suggested that the nighttime Re/w should be related to other physical process, such as the midlatitude summer nighttime anomaly (MSNA) in the east and the ionospheric nighttime enhancement (INE). The current study provides evidence for the longitudinal difference of NmF2 in East Asian midlatitudes and geomagnetic configuration-neutral wind mechanism proposed in previous studies and finds some new features which need further studying to improve our current understanding of ionospheric longitudinal difference in the low solar activity years. The results provide new insight into TEC longitudinal variations at midlatitudes, and they can contribute to understanding the ionosphere-thermosphere coupling system.

Ground-based oblique incidence sounding (OIS) is an important means to investigate the ionosphere. As the OIS ionogram is a visual representation of the OIS parameters, such as group distance and maximum usable frequency (MUF), it is of great significance for improving the quality and the range resolution. This will facilitate the automatic interpretation and inversion of OIS ionograms to obtain the fine structure and spatial–temporal evolutions of the ionosphere. In this paper, a novel OIS signal processing scheme is proposed based on the Eigenspace-based (ESB) beamforming technology and Capon high-resolution range profile (HRRP). First, by applying the ESB beamformer to a compact L-shaped antenna array, the energy of the OIS signals received by multiple antennas can be added, while the interference and noise will be suppressed. Subsequently, the Capon HRRP algorithm is used to improve the range resolution. This is achieved due to the slow variation in the characteristics of the ionosphere resulting in good short-term coherence of the narrowband signals. The experimental results show that the two-stage signal-processing method significantly improves the imaging quality of OIS ionograms. In particular, the structure inside the ionosphere and its temporal and spatial evolution can be observed more precisely after the range resolution of the OIS ionogram is improved; therefore, it has great application potential.

Abstract We report a statistical study of medium-scale traveling ionospheric disturbances (MSTIDs) during 2014–2017 in the low-latitude China region using the Hong Kong Continuously Operating Reference Stations network with a baseline length of 10–15 km. Polynomial fitting and the multichannel maximum entropy method are utilized to derive MSTID parameters from global positioning system total electron content data. We find that MSTIDs can be sorted into three types in this region. One type is daytime MSTIDs, which are mainly distributed during 1000–1700 local time (LT) in spring, autumn and winter. The second type is nighttime MSTIDs, which mainly occur from 2200 to 0300 LT in spring and summer. The third type is morning MSTIDs, mainly occurring from 0500 to 0700 LT in spring and autumn. No clear difference in the MSTID parameters is distinguishable between the cyclone period and non-cyclone period, which may be due to the distance restriction for cyclone identification and different propagation distances of the primary gravity waves (GWs) and secondary GWs.

The data assimilation algorithm is a common algorithm in space weather research. Based on the GNSS data from the China Crustal Movement Observation Network (CMONOC) and the International Reference Ionospheric Model (IRI), a fast three-dimensional (3D) electron density nowcasting model for China and its adjacent regions was developed. Unlike the traditional Gaussian background covariance model, the error covariance of the IRI model, based on the IGS grid TEC data, is estimated in this work. Due to the large scale of the high-resolution covariance matrix, it cannot be stored and calculated directly on a personal computer. The covariance localization (CL) technique is introduced to sparse the covariance matrix while removing the pseudo-correlation of the covariance matrix. After localization, the covariance matrix can be converted into a sparse matrix for storage and calculation, which greatly reduces the computer memory requirement of the assimilation model and improves the calculation speed of the model. Based on this algorithm, a series of experiments were carried out in this work. The experimental results show that this algorithm can effectively assimilate the observed GNSS to the background field, make up for the temporal and spatial limitations of the observed data, and improve the accuracy of the ionospheric electron density nowcast. Compared with the digisonde observed foF2 (the critical frequency of the ionospheric F2 layer), the RMSE of the assimilation model is 0.44 MHz lower than that of the IRI model.

The lower atmosphere forcing plays an important role in forming the sporadic E (Es) layer in the ionosphere. In this study, a comparative study of the Es layer recorded by ionosondes at the middle latitude regions was carried out between the plateau and plain regions in China. The two ionosonde stations (Zhangye, 39.21°N, 100.54°E and Beijing, 40.25°N, 116.25°E) are located at the Qinghai–Tibet Plateau and North China Plain, respectively. The data during the year 2018 were used to reveal the characteristics of the Es layer. The occurrence probability, the critical frequency (foEs) and the base virtual height (h’Es) were considered in this study. Results show that: (1) The diurnal and seasonal variations of the occurrence probability between these two regions are similar. The maximum occurrence probability is at noontime and in the summer season. However, the Es at Zhangye occurred more frequently than Beijing at nighttime and in winter to early spring. (2) Similar to previous studies, the maximum value of foEs at Beijing mainly occurred in summer. Interestingly, the maximum value is in winter at Zhangye station. (3) The characteristics of the anomaly of the Es layer at Zhangye are mostly consistent with the characteristics of atmospheric gravity waves in the Qinghai–Tibet Plateau. Therefore, compared with observations at Beijing, the anomalies of the Es layer at Zhangye (at night and in winter to spring) might be attributed to gravity waves in the lower atmosphere over the Qinghai–Tibet Plateau.

Poly l-lactic acid (PLLA) was limited in the further orthopaedic application due to its insufficient mechanical property and poor bioactivity. Graphene oxide (GO) is an effective reinforcement, whereas silicon-doped hydroxyapatite (Si-HA) possesses excellent bioactivity, but either GO or Si-HA tends to aggregate in PLLA matrix. In this study, a GO@Si-HA nanosystem was achieved by in-situ growth of Si-HA on GO, and then incorporated into PLLA scaffold fabricated by laser sintering technology. On one hand, Si-HA on the surface of GO effectively prevented the aggregation of GO by acting as a barrier between GO nanosheets. On the other hand, GO hindered the aggregation of Si-HA by means of anchoring Si-HA. Results displayed that the compressive strength and modulus of the PLLA/GO@Si-HA composite scaffold were enhanced by 85% and 120%, respectively. Meanwhile, the scaffold exhibited significantly improved bioactivity, and consequently promoted cell adhesion, proliferation and differentiation. The developed PLLA/GO@Si-HA composite scaffold with excellent mechanical properties and superior bioactivity could serve as a promising substitute for bone repairing.

This study investigates the variations of middle and low latitude sporadic-E (Es) layers in response to a geomagnetic storm. Es layers are observed by five ionosondes located in the Eastern Asian sector. The critical frequencies of Es layers (foEs) at six stations increased in sequence from high latitude stations to low latitude stations after IMF/Bz turning southward. Lomb–Scargle analysis shows the amplification of semidiurnal oscillation amplitude in the vertical height of Es layers during geomagnetic disturbance. Modeling results of the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) show the enhancement of the wind field in the mesosphere and the lower thermosphere (MLT) region. Our study provides evidence that the enhanced wind field in the MLT region during the storm period could result in the enhancement of Es layers at middle and low latitude.

The sporadic E (Es) layer is a thin layer of ion plasma enhancement in the E-region ionosphere, typically at altitudes of 90–120 km with vertical and horizontal extent of several or several tens of kilometers. As the transition region between the lower and upper atmosphere, this layer is of critical importance for ionospheric studies. The most economical but effective method to observe this layer is using ionosonde, which, however, is incapable of capturing the finer structure or the internal inhomogeneity of the Es layer as the range resolution is on the order of kilometers. To overcome this limitation, we employ the frequency domain interferometry (FDI) technique, a technique that has been successfully applied to the analysis of some radar and sonar measurements. Here, we use the Es layer measurements near Wuhan, China (114°22′E, 30°30′N) on 8 June 2021 as examples to showcase the capability of this technique. Our results show that the spatial resolution of ionosonde imaging is remarkably increased: the complexity of the internal fine structure in the Es layer can be well observed in the FDI-processed ionograms, whereas the intrinsic range resolution is several kilometers. Moreover, by comparing the ionograms obtained with and without the FDI technique, it is found that the FDI-processed ionogram is particularly suitable for the observation of evolutional processes in the Es layer, as well as the identification of different types of Es layer. With this level of spatial resolution, ionosonde, in combination with the FDI technique, opens the possibility for more refined observations of the Es layer.

In this study, a method is proposed to carry out automatic inversion of oblique ionograms to extract the parameters and electron density profile of the ionosphere. The proposed method adopts the quasi-parabolic segments (QPS) model to represent the ionosphere. Firstly, numerous candidate electron density profiles and corresponding vertical traces were, respectively, calculated and synthesized by adjusting the parameters of the QPS model. Then, the candidate vertical traces were transformed to oblique traces by the secant theorem and Martyn’s equivalent path theorem. On the other hand, image processing technology and characteristics of oblique echoes were adopted to automatically scale the key parameters (the maximum observable frequency and minimum group path, etc.) from oblique ionograms. The synthesized oblique traces, whose parameters were close to autoscaled parameters, were selected as the candidate traces to produce a correlation with measured oblique ionograms. Lastly, the proposed algorithm searched the best-fit synthesized oblique trace by comparing the synthesized traces with oblique ionograms. To test its feasibility, oblique ionograms were automatically scaled by the proposed method and these autoscaled parameters were compared with manual scaling results. The preliminary results show that the accuracy of autoscaled maximum observable frequency and minimum group path of the ordinary trace of the F2 layer is, respectively, about 91.98% and 86.41%, which might be accurate enough for space weather specifications. It inspires us to improve the proposed method in future studies.

Objective. The aim of this study was to demonstrate the peripheral mechanisms of chrono-acupuncture by observing acupuncture at different time points affecting relative proteins to regulate the cytoskeleton of fibroblasts differently. Methods. A total of 108 male SD rats (180–220 g) that have basic pain threshold within 3–10 s were selected and randomly divided into group A (n = 72) and control group (n = 36). After the succession of modeling with CFA injection, the rats in group A were randomly divided into model group and acupuncture group, each group containing 36 rats. Then according to the different treatment time, each group was randomly classified into 6 subgroups (ZT0, ZT4, ZT8, ZT12, ZT16, and ZT20), each subgroup containing 6 rats (n = 6). On the second day of successful modeling, the rats in the acupuncture group received acupuncture treatment at the corresponding time point, while the control group and the model group were only tied up at the corresponding time point without any treatments. Methods of operation: use 0.5-inch needles, puncture the rats’ “Zusanli” on the affected limb, with Twirling manipulation for a minute after every five minutes; the treatment lasts thirty minutes in total. After 7 days of treatments, the skin and subcutaneous tissue of rats’ acupoint area of “Zusanli” on the affected limb were taken and then stained by immunofluorescence double staining method to observe the expression of the fibroblast cytoskeleton F-actin and β-tubulin under the LSCM while using western blot to observe the expression of P38MAPK/P-P38MAPK. Results. The expression of the cytoskeleton F-actin and β-tubulin at acupoint area in the acupuncture group was significantly higher than that in the control and model group. The effect of acupuncture on the restructure of the fibroblast cytoskeleton is different at different time points, the most effective time point was at ZT12 while the least at ZT16. Acupuncture can decrease the high expression of P-P38MAPK/P38MAPK in the model group, and the effect has time differences. The expression of P-P38MAPK/P38MAPK increased more significantly at ZT16 than ZT12. Conclusion. The remodeling difference of fibroblast cytoskeleton after receiving acupuncture treatment could be one of the peripheral bases of the chrono-acupuncture.

The poor safety performance of the construction industry is a global concern. Workers’ unsafe behaviors (WUBs) are viewed as critical causes of construction accidents. Thus, it has been a leading research topic to identify antecedents of WUBs and establish reliable models to explain WUBs. Cognitive biases (CBs) are salient antecedents of WUBs. However, the relationships between CBs and WUBs are not further explored in construction safety management. As such, this study selected three prevalent CBs, i.e., availability bias (AB), confirmation bias (FB), and overconfidence, and investigated the relationships between the three CBs and WUBs and the functions of RPs in these relationships among tunnel construction workers. We established six multiple regression models. Research results show that CBs can directly influence RPs and WUBs, RPs are antecedents of WUBs, and the mediating effect of RPs on the relationships between CBs and WUBs is salient. In detail, AB and FB explain more ERP and overconfidence explains more BRP. AB and FB indirectly influence more WUBs through ERP, while overconfidence indirectly affects more WUBs through BRP. The study provides a novel theoretical paradigm for conceptualizing CBs and their relationships with RPs and WUBs. The research results can also guide managers to take debiasing measures to decrease workers’ unsafe behaviors on the construction site.

Whistler-mode chorus waves are regarded as an important acceleration mechanism contributing to the formation of relativistic and ultra-relativistic electrons in the Jovian radiation belts. Quantitative determination of the chorus wave driven electron scattering effect in the Jovian magnetosphere requires detailed information of both ambient magnetic field and plasma density and wave spectral property, which however cannot be always readily acquired from observations of existed missions to Jupiter. We therefore perform a comprehensive analysis of the sensitivity of chorus induced electron scattering rates to ambient magnetospheric and wave parameters in the Jovian radiation belts to elaborate to which extent the diffusion coefficients depend on a number of key input parameters. It is found that quasi-linear electron scattering rates by chorus can be strongly affected by the ambient magnetic field intensity, the wave latitudinal coverage, and the peak frequency and bandwidth of the wave spectral distribution in the Jovian magnetosphere, while they only rely slightly on the background plasma density profile and the peak wave normal angle, especially when the wave emissions are confined at lower latitudes. Given the chorus wave amplitude, chorus induced electron scattering rates strongly depend on Jovian L-shell to exhibit a tendency approximately proportional to LJ3. Our comprehensive analysis explicitly demonstrates the importance of reliable information of both the ambient magnetospheric state and wave distribution property to understanding the dynamic electron evolution in the Jovian radiation belts and therefore has implications for future mission planning to explore the extreme particle radiation environment of Jupiter and its satellites.

The trapping layer refers to the atmospheric layer with vertical gradient of atmospheric refractivity less than −157 N-Units/km or vertical gradient of atmospheric modified refractivity 0 M-unit/km, which has a significant impact on radar and radio communication systems. Based on COSMIC and other radio occultation data, we show the statistical characteristics of the global trapping layer during 2005–2020.The statistical results show that the occurrence rate of the trapping layers is mainly concentrated between 50°S and 50°N, and higher occurrences of the trapping layers with more than 50% mainly occur in the boundary area between ocean and land, such as the northwest coastal area of Mexico, the west coastal area of Africa, the Mediterranean Sea, the Red Sea and the Arabian Sea, and the northwest area of Australia, etc. The altitude of the trapping layer is lower near the land and increases with the distance away from the coastline. The intensity is mainly between 6 M-unit and 24 M-unit (an M-unit is the unit of atmospheric modified refractivity), and the average value in some regions is above 24 M-unit, such as in the Arabian Sea area. In addition, the thickness of the trapping layer is between 50 and 240 m, and is generally larger over the ocean than over the land. These results reveal that the generation of the trapping layer is the result of the interaction of various background environmental factors such as radiation band migration, trade winds, monsoons, solar radiation heating, sea–land breezes and so on.

High power microwave (HPM) injection into the troposphere to block the chain of chlorofluorocarbons (CFCs) or injection into the stratosphere to promote ozone generation are two feasible methods to artificially affect the ozone number concentration. Based on Maxwell’s equations and current density control equations, this study adopts the finite difference time domain (FDTD) method to quantitatively analyze the process of HPM injection into different heights of atmosphere. By taking consideration of the main atmospheric components and the major chemical reactions in the atmospheric, the decomposition of CFCs and the change of the ozone number density is also quantitatively simulated in response to the injection of single pulse microwaves. The numerical simulation results show that under the injection of high power microwaves, the number density of electrons increased exponentially with time, reaching a maximum value of 1017cm-3, and it increased considerably with the pulse time of injected high power microwaves and finally saturates when the state of atmospheric breakdown occurs. The decomposition of CFCs mainly occurs in the electron relaxation process, and the decomposition rate can reach 6% according to the simulation result. Before the atmosphere breaks down occurs, increase of microwave intensity or pulse width facilitates the production of more free electrons, which can consequently lead to a considerable increase in the ozone number density in ozone layer for a prolonged period.

In this study, detection and three-dimensional (3D) imaging of lightning plasma channels are presented using radar interferometry. Experiments were carried out in Leshan, China with a 48.2 MHz VHF radar configured with an interferometric antenna array. The typical characteristics of lightning echoes are studied in the form of amplitude, phase, and doppler spectra derived from the raw in-phase/quadrature (I/Q) data. In addition, the 3D structure of lightning channels is reconstructed using the interferometry technique. The localization results of lightning are verified with the locating results of lightning detection networks operating at VLF ranges, which indicate the feasibility of using VHF radar for lightning mapping. The interpretation of the observational results is complicated by the dendric structure of lightning channel and the overlap between passive electromagnetic radiations and return echoes. Nevertheless, some parts of the characteristics of lightning are still evident. The observational result of return echoes shows good consistency with the overdense assumption of lightning channels. The transition from the overdense channel to the underdense channel in the form of amplitude and phase is clearly observed. This technique is very promising to reveal the typical characteristics of lightning return echoes and structure of lightning propagation processes.

This study presents observations of nighttime spread F/ionospheric irregularities and spread Es at low and middle latitudes in the South East Asia longitude of China sectors during the recovery phase of the 7–9 September 2017 geomagnetic storm. In this study, multiple observations, including a chain of three ionosondes located about the longitude of 100°E, Swarm satellites, and Global Navigation Satellite System (GNSS) ROTI maps, were used to study the development process and evolution characteristics of the nighttime spread F/ionospheric irregularities at low and middle latitudes. Interestingly, spread F and intense spread Es were simultaneously observed by three ionosondes during the recovery phase. Moreover, associated ionospheric irregularities could be observed by Swarm satellites and ground-based GNSS ionospheric TEC. Nighttime spread F and spread Es at low and middle latitudes might be due to multiple off-vertical reflection echoes from the large-scale tilts in the bottom ionosphere. In addition, we found that the periods of the disturbance ionosphere are ~1 h at ZHY station, ~1.5 h at LSH station and ~1 h at PUR station, respectively. It suggested that the large-scale tilts in the bottom ionosphere might be produced by LSTIDs (Large scale Traveling Ionospheric Disturbances), which might be induced by the high-latitude energy inputs during the recovery phase of this storm. Furthermore, the associated ionospheric irregularities observed by satellites and ground-based GNSS receivers might be caused by the local electric field induced by LSTIDs.

The ionograms, which were recorded by the ionosonde located at Pu’er station (PUR, 22.7° N, 101.05° E, Dip Latitude 12.9° N) in the Southwest of China in the year of 2016, were used to study the ionospheric behavior of the ordinary critical frequency of the F2 layer (foF2) in the region of the northern equatorial ionization anomaly. To verify the performance of the International Reference Ionosphere (IRI) over the Southwest of China, a comparative study of the observed foF2 and the latest version of the International Reference Ionosphere (IRI-2016) was carried out. We found that the foF2 in equinox months is greater than summer and winter. Moreover, a higher frequency of the observed bite-out of foF2 in January and April than other months and the IRI-2016 cannot represent the bite-out of foF2 in diurnal variations. Compared to the observations at Pu’er Station, the IRI-2016 underestimated foF2 for most time of the year. The IRI with the International Radio Consultative Committee (CCIR) option overestimated foF2 is higher than that with the International Union of Radio Science (URSI) option. Furthermore, the normalized root mean square error of foF2 from the IRI-2016 with the CCIR option is less than that with the URSI.

This paper describes a novel sounding system for which the functions of the medium frequency (MF) radar and the ionosonde are integrated on the same hardware platform and antenna structure, namely the middle atmosphere-ionosphere (MAI) system. Unlike the common MF radar, MAI system adopts the pseudo-random (PRN) phase-coded modulation technology, which breaks the limitation of the traditional monopulse mode. Through the pulse compression, only a small peak power is needed to achieve the signal-to-noise ratio (SNR) requirement. The excellent anti-jamming performance is also very suitable for the ionospheric sounding. One transmitting and six receiving modes are adopted for the MF sounding. While neglecting the structure of the T/R switches, the coupling interference between the transmitter and the receiver may also be avoided. Moreover, by employing a miniaturized antenna array composed of progressive-wave antennas for the MF receiving and ionospheric sounding, the MAI system takes account of the requirements of the inversion algorithms of MF radar and the large bandwidth need for the ionospheric sounding concurrently. Such an antenna structure can also greatly simplify the system structure and minimize the difficulty of deployment. The experiments verified the availability of the system scheme and its engineering application significance. Through further analysis of the sounding data, the wind field of the mesosphere, the electron density of D layer and electron density profile from layers E to F were obtained at the identical location. The capability of MAI system can play an important role in studying the interaction and coupling mechanism between the mesosphere and ionosphere.