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By using fast ionogram observations, we report the first simultaneous observations of ascending ion layers at equatorial and low latitudes. The ionosonde measurements at Sanya (18.3°N, 109.6°E; dip lat. 12.2°N) and Chumphon (10.7°N, 99.4°E; dip lat. 3.8°N) show that a high Es layer, which might contain metallic ions, was directly lifted upward from the local E region to F region bottomside at morning hours, in a pattern similar to the vertical drift of the F region background ionosphere driven by the daytime eastward electric field. A statistical analysis with Sanya ionosonde measurements shows that the low latitude ascending ion layer is not a rare phenomenon, with a maximum occurrence of 22% during equinox. The results indicate that at the latitudes far away from the magnetic equator, the local E region metallic ions could be directly brought into the F region with the ascending layer. It can be expected that fast ionogram measurements, which can easily capture the rapid evolution of the background ionosphere, will play an important role in studying the formation of some unexpected high altitude metallic layers. [ABSTRACT FROM AUTHOR]

The observations of short-duration meteor showers at different geographic locations are important for well understanding of their outbursts. Using the four all-sky interferometric meteor radars at Mohe (53.49°N, 122.34°E), Beijing (40.3°N, 116.19°E), Wuhan (30.54°N, 114.34°E), and Ledong (18.44°N, 108.97°E) in China, four outbursts (2011, 2012, 2018, and 2019) of the October Draconid meteor shower were observed between 2011 and 2021. The October Draconid meteor velocity was concentrated around 22∼23 km s−1, with an active duration of 6∼9 h and a main peak around the solar longitude 194.73°∼195.63°. When comparing the hourly rates of the October Draconid meteor shower for different years at Mohe, a maximum (minimum) of peak flux was observed in 2012 (2011). The radiants and orbit parameters of the October Draconid meteors derived from the radars at different latitudes are consistent, except that the weighted mean echo height during the peak activity at Mohe was always lower than that at other stations. [ABSTRACT FROM AUTHOR]

Previous theoretical simulations showed the generation of double‐layer structures of E‐region field‐aligned irregularities (FAIs). In this study, we report the double‐layer structures of E‐region FAIs observed by an all‐sky radar at low latitude Ledong (18.4°N, 109°E), China. These FAIs appeared at the altitudes ∼90 and 110 km respectively. Both layers displayed quasi‐periodic patterns with synchronized spatial features, that is, being manifested as spatially separated patches or wavelike structures over similar longitudes at the two layers simultaneously. The neutral wind observations revealed the existence of wind shears at two separated altitudes where the double FAI layers occurred. The two wind shears created two vertically separated sporadic E layers and possibly drove the generation of the double‐layer FAIs via gradient drift instability. The synchronized spatial features of the FAIs at the two layers could be modulated by gravity waves. Plain Language Summary: The E‐region field‐aligned irregularities (FAIs) were observed usually in a form of single layer. Due to the limited field of view of narrow‐beam radars which were traditionally employed for observing ionospheric irregularity, the spatial morphology and evolution of E‐region FAIs in a small region were resolved. Owing to the recently developed capability of all‐sky radars in observing E‐region irregularities, the spatial features of E‐region irregularities over a larger zonal region up to hundreds of kilometers in the horizontal plane can be derived. Further, the spatial features of E‐region irregularities in the vertical direction can be unambiguously determined. Utilizing an all‐sky radar at low latitude Ledong, China, a case of double‐layer structures of E‐region FAIs, which occurred at ∼90 and 110 km altitudes respectively, was observed. The double layers of FAIs spanned a zonal coverage ∼250 km, showing as synchronized spatially separated quasi‐periodic patches or wavelike structures in two layers. Especially, the wavelike structures synchronized in the two layers could provide solid evidence for the crucial role of gravity waves in modulating E‐region irregularities. In combination with the collocated ionosonde Es and neutral wind observations, the physical mechanisms responsible for the generation of the double‐layer E‐region FAIs were discussed. Key Points: Double layer structures of E‐region field‐aligned irregularity (FAI) were observed at low latitude by an all‐sky radarBoth layers of FAIs were quasi‐periodic type and synchronously manifested as spatially separated patches or wavelike structuresThe double‐layer FAIs were likely generated by wind shear driven gradient drift instability and modulated by gravity waves [ABSTRACT FROM AUTHOR]

• A moderate geomagnetic storm could trigger unseasonal post-sunset EPBs. • The periodic EPBs, with spacings of ∼ 650–870 km, extended to middle latitudes. • Enhanced F layer upward drifts alone may not be enough to trigger unseasonal EPBs. In the East and Southeast Asia, equatorial plasma bubbles (EPBs) mainly occur at post-sunset in equinoctial months. On 7–8 July 2022, a moderate geomagnetic storm occurred, with minimum Dst of −85 nT. This storm could trigger unseasonal post-sunset EPBs over the East/Southeast Asian sector. Observations from GNSS TEC/scintillation receivers, VHF coherent radar and ionosonde show that on 7 July, a few clusters of EPBs, which caused strong amplitude scintillations and significant TEC fluctuations, occurred over a wide latitude range, from low to middle latitudes up to ∼ 32°N. The EPB irregularities at middle latitudes drifted westward, with velocities of about 97 m/s. Before the generation of EPBs, apparent background ionospheric disturbances were detected. An abrupt rise of ionospheric F layer, with upward drifts of about 33 m/s was observed near sunset at low latitudes. It is suggested that the moderate geomagnetic storm was the main reason for the generation of unseasonal post-sunset EPBs. The prompt penetration of eastward electric field caused by the geomagnetic storm could lead to the abrupt rise of F layer near sunset and promote the growth of Rayleigh-Taylor instability. The background ionospheric disturbance could act as a seeding role for the unseasonal EPBs. [ABSTRACT FROM AUTHOR]

It has been found that the total electron content (TEC) and the ionospheric electric fields indicated by the geomagnetic data showed inconsistent changes with each other at the mid- and low latitudes in both the American and the Asian–Australian sectors during geomagnetic quiet time (GQT) from 30 November to 8 December 2019 (Kpmax = 1.7). Meanwhile, the effects of thermospheric compositions are still indistinct. In this work, we analyze the mid/low-latitude ionospheric variations during this period, utilizing multi-instrument observations. The vertical drift velocities from the Ionospheric Connection Explorer (ICON) show significant variations and are in line with the changes in TEC at low latitudes in both of the two sectors. The zonal electric fields are supposed to play the main role in the TEC changes. This is also confirmed by the ionospheric F2 layer parameters data from the ionosonde stations at Sanya in the Asian–Australian sectors. The correlation between the variations in the geomagnetic H component (ΔH) and ionospheric F-layer electric fields can be affected by solar activity levels. The geomagnetic data ΔH sometimes may not indicate the magnitude of the electric fields in the F-region ionosphere under geomagnetic quiet conditions. The column density ratio of atomic oxygen (O) to molecular nitrogen (N2) (∑O/N2) from the Global Scale Observations of the Limb and Disk (GOLD) showed a strong enhancement at mid-latitudes in the American sector on 30 November. It is speculated that the neutral compositions should make a minor contribution to the changes in TEC during this event, compared with the electric fields. [ABSTRACT FROM AUTHOR]

Using Global Navigation Satellite Systems (GNSS) observation data for developing a high-precision ionospheric Total Electron Content (TEC) model is one of the essential subjects in ionospheric physics research and the application of satellite navigation correction. In this study, we integrate the Empirical Orthogonal Function (EOF) method with the TEC data provided by the Center for Orbit Determination in Europe (CODE), and observed by the dense GNSS receivers operated by the Crustal Movement Observation Network of China (CMONOC) to construct a regional ionospheric TEC model over China. The EOF analysis of CODE TEC in China from 1998 to 2010 shows that the first-order EOF component accounts for 90.3813% of the total variation of the ionospheric TEC in China. Meanwhile, the average value of CODE TEC is consistent with the spatial and temporal distribution characteristics of the first-order EOF base function, which mainly reflects the latitude and diurnal variations of TEC in China. The first-order coefficient after EOF decomposition shows an obvious 11-year period and semi-annual variations. The maximum amplitude of semi-annual variation mainly appears in March and October, which is closely associated with the variation in geographical longitude, the semi-annual change of the low-latitude electric field, and the ionospheric fountain effect. The second-order coefficient has an evident annual variation, the minimum amplitude mainly occurs in March, August, and September, and the amplitude values in the high solar activity years are more significant than those in the low solar activity years. The third-order coefficient mainly shows the characteristics of annual variation, and the fourth-order coefficient shows the noticeable semi-annual and annual variations. The third and fourth-order coefficients are both modulated by the solar activity index F10.7. The ionospheric TEC model in China, driven by CMONOC real-time GNSS observation data, can better reflect the latitude, local time and seasonal variation characteristics of ionospheric TEC over China. In particular, it can clearly show the spring and autumn asymmetry of ionospheric TEC in the low latitudes. The root mean square error of the absolute error between the model and the actual observation is mainly distributed around 2.45 TECU (1 TECU = 1016 electrons/m2). The values of the TEC model constructed in this study are closer to the actual observed values than those of the CODE TEC in China. [ABSTRACT FROM AUTHOR]

Ionospheric total electron content (TEC) is an important parameter in ionospheric researches and applications. However, the determination of the absolute value of TEC can be greatly influenced by the differential code biases (DCBs) estimation. Nowadays, there are more and more Global Navigation Satellite System (GNSS) signals available all over the world, which allow us to solve TEC and DCBs with the hypothesis of local spherical symmetry (LSS) imposed on the dual-frequency observations from only one individual station. For comparison, the results based on the global ionospheric map (GIM) act as a reference in this article. On the one hand, different combinations of Global Positioning System (GPS), GLONASS, and BeiDou Navigation Satellite System (BDS) are considered to illustrate the significance of multi-GNSS observations, with the mixed GPS, GLONASS, and BDS combination performing best when compared to the referenced results. On the other hand, different parameters in LSS condition are taken into account to investigate the suitable geometric constraint of LSS, with the differential longitude, latitude, and epoch suggested to be 3.0°, 0.6°, and 4 min, respectively. Moreover, a group of detailed comparisons from several different stations also show that the combined DCBs and ionospheric TEC derived from our method are compatible with those from the GIM-aided method, especially in the low-latitude area. In summary, with the advantage of the multi-GNSS signals from an individual station, our method can estimate the ionospheric TEC and DCBs independently, which could provide a potential tool in the future real-time applications. [ABSTRACT FROM AUTHOR]

The physical properties of meteoroids producing meteor plasma non-field-aligned irregularities (NFAI) in the Earth's atmosphere are poorly known. Here we report a complete picture of a fireball and mesospheric NFAI that it produced for the first time. Simultaneous radar and optical observations were made by the recently completed facility, Meteor and ionospheric Irregularity Observation System. The observations show that the mesospheric NFAI were clustered into three patches where the optical meteor flares took place, instead of being generated continuously along the whole meteor path. It is very likely that nanometer-or-larger-sized dust particles could be directly generated via meteoroid fragmentation at the flaring points and thus promote the generation of NFAI patches. The properties of the parent meteoroid show a chondrite type and a Jupiter family comet orbit, with Na/Mg and Fe/Mg intensity ratios of 1.5 and 1, respectively, photometric mass of about 4 g, and fragmentation strengths of around 10–74 kPa. The results suggest that the direct generation of dust particles, which was previously observed in the atmospheric disintegration of a kiloton-scale meteoroid, could be extended to the much smaller gram-scale meteoroids. Since meteoroids having such characteristics or more fragile material are not unusual, further studies leading to a better understanding of meteor mass deposition in the upper atmosphere, which consider the dust particles directly generated via gram-scale meteoroid fragmentation, are extremely important. [ABSTRACT FROM AUTHOR]

In this study, we investigate the ionospheric storm effects in the Chinese sector during 2 October 2013 geomagnetic storm. The TEC map over China sector (1° × 1°) and eight ionosondes data along the longitude of 110°E are used to show significant positive ionospheric phases (enhancements in TEC and ionospheric peak electron density NmF2) in the high-middle latitude region and the negative effects at the low latitude and equatorial region during the storm. A wave structure with periods about 1–2 h and horizontal speed about 680 m/s, propagating from the high latitudes to the low latitudes is observed in electron densities within the height region from 200 to 400 km, which is caused by the combined effects of neutral wind and the large-scale traveling disturbances (LSTIDs). In the low latitude regions, compared with those in the quiet day, the ionospheric peak heights of the F2 layer (hmF2) in the storm day obviously increase accompanying a notably decrease in TEC and NmF2, which might be as a result of the eastward prompt penetration electric field (PPEF) evidenced by the two magnetometers and the subsequent westward disturbance dynamo electric fields (DDEF). The storm-time TEC enhancement mainly occurs in the topside ionosphere, as revealed from the topside TEC, bottomside TEC and GPS TEC. [ABSTRACT FROM AUTHOR]

A Meteor and ionospheric Irregularity Observation System (MIOS) - optical subsystem, which currently consists of 26 video cameras (4 spectrographs) at two stations Sanya (18.3°N, 109.6°E) and Ledong (18.4°N, 109°E) separated by about 70 km was developed. One of the major goals of MIOS is to study how the entry of meteoroids into the Earth's atmosphere changes the ionosphere through combining measurements of optical meteor with radar specular and non-specular meteor echoes and ionospheric irregularity echoes. This paper outlines the MIOS optical subsystem design for optical meteor detecting and methods for inferring physical and chemical properties. The spectrum and common volume optical trail observations from the two stations allow identifying emissions from meteor and atmospheric species, and calculating the meteor velocity, trajectory and orbital parameters. Preliminary results of meteors detected by the MIOS optical subsystem during July-August 2019 are presented and discussed. [ABSTRACT FROM AUTHOR]

Ionospheric F‐region irregularity backscatter plumes are commonly regarded as a nighttime phenomenon at equatorial and low latitudes. Using the Sanya (18.4°N, 109.6°E, dip lat. 12.8°N) VHF radar, F‐region backscatter echoes were observed at daytime during 0700–1800 LT, with an unexpected high occurrence in June solstice of solar minimum. Radar interferometry and ICON satellite in situ results show that the daytime F‐region echoes were from plume structures consisting of field‐aligned irregularities. The daytime echoing structures appeared mostly above 350 km altitude, extending up to 650 km or more with apparent westward drifts at times. We surmise that the daytime F‐region echoes were due to equatorial plasma bubble irregularities generated on the previous night around 100–125°E, where the irregularities could survive unexpectedly long time, beyond sunrise as vertically elongated fossil plumes. Under the ionospheric background dynamics, the fossil plumes could be elevated to high altitudes and drift zonally over Sanya. Plain Language Summary: Equatorial plasma plumes, which are known as vertically elongated irregularity structures over the magnetic equator, have been widely accepted as being generated at nighttime. The plumes usually disappear before sunrise. At daytime, there are very few reported cases of F‐region backscatter echoes. It is still not clear what caused the daytime echoes. During November 2016 to August 2020, the Sanya VHF radar was operated for observing F‐region echoes at daytime. The observations show that the daytime F‐region echoing structures could appear at any time during 0700–1800 LT, with a maximum occurrence around 0900 LT. Radar interferometry and ICON satellite in situ results reveal that these daytime echoes were from field‐aligned irregularities, which are shown as plume structures in the topside ionosphere. It is suggested that the plume structures could be remnants of equatorial plasma bubble (EPB) irregularities generated on the previous night around 100–125°E. They rise to high altitudes and drift zonally together with background plasma, causing the daytime F‐region backscattering structure over Sanya. Our results indicate that the EPBs could maintain their vertically elongated structures and meter‐scale irregularities at F‐region topside for much longer time than previously thought and have important implications for understanding their dynamics. Key Points: An unexpected high occurrence of daytime F‐region backscatter echoing structure was detected over low latitude Sanya during June solsticeInterferometry shows that the daytime F‐region echoes were backscattered from plume structures consisting of field‐aligned irregularitiesThe daytime plume structures over Sanya could be remnants of nighttime equatorial plasma bubbles generated ~100–125°E [ABSTRACT FROM AUTHOR]

• A practical deep-learning method (DIAS) is proposed to automatically scale E, F1, F2 traces in ionograms. • The scaling accuracy of the ionograms provided by DIAS is higher than that by ARTIST routine, close to that by human experts. • Real-time ionogram scaling by DIAS has potential application in global ionospheric weather nowcasting. Scientists can study the global ionospheric weather by manually or automatically scaling ionograms recorded by global ionosondes to obtain characteristic values of D, E, F regions in the ionosphere. Therefore, fast and accurate ionogram scaling is crucial to real-time space weather monitoring, which is closely related to the performance of space-borne and ground-based technological systems as well as life on earth. The significant increase in data collections during recent years makes an impossible task for human experts to manually scale large amounts of ionograms in time. While the scaling accuracy of traditional automatic methods is less than that by human experts, making them insufficient for scientific tasks. Deep-learning is currently attracting immense research interest in many scaling tasks due to its powerful ability to deal with huge data collections. In this study, we present a deep-learning method for ionogram automatic scaling (DIAS) that can rapidly scale ionograms precisely from the ionosonde data. We trained and tested on data recorded by Wuhan ionosonde located at 114.4° E and 30.5° N. Our results show that the proposed deep-learning method improved the precision and recall rate by 8%, 17%, respectively, compared to using Automatic Real-Time Ionogram Scaling with True-height (ARTIST), which is the most-widely-used automatically scaling routine, in scaling E, F1 and F2 layers. The scaling accuracy of the ionograms provided by our deep-learning model is close to that by human experts, which suggests that the ionograms provided by our deep-learning method can be applied directly to global ionospheric weather nowcasting. Therefore, this study may contribute greatly to improve our knowledge of the ionospheric space. [ABSTRACT FROM AUTHOR]

An Ionospheric Observation Network for Irregularity and Scintillation in East/Southeast Asia was recently deployed. Using ionospheric total electron content (TEC) from the two crossed Beidou geostationary satellite receiver chains of the network along 110°E and 23°N and Doppler velocity measurements from the Sanya (18.3°N, 109.6°E) portable digital ionosonde, we report first observations of low latitude TEC oscillations synchronized over a wide longitude range in East/Southeast Asia, which occur at nighttime, after the main phase of the geomagnetic storm on 20 April 2018. A comparison among TEC and Doppler velocity and interplanetary magnetic field (IMF) Bz component shows that the periodic TEC enhancements correlate with F region downward plasma drifts and IMF Bz southward turnings. The results suggest that the quasiperiodic southward turnings of IMF Bz could produce multiple short‐lived westward prompt penetration electric fields, which contribute to driving the nighttime low latitude TEC oscillations simultaneously over the wide longitude range. Plain Language Summary: Regional‐scale positive/negative ionospheric storm effects have been widely investigated using GPS total electron content (TEC) and ionosonde observations. Here we report significant nighttime TEC oscillations detected at latitudes lower than the equatorial ionization anomaly crest in the longitudes of 95–120°E by the Ionospheric Observation Network for Irregularity and Scintillation in East/Southeast Asia during geomagnetic storm. Periodic TEC enhancements are nearly synchronized over the wide longitude range, in close association with downward plasma drifts at low latitude. The good consistence between the changes of plasma vertical drift and of interplanetary magnetic field Bz polarity indicates that multiple short‐lived westward prompt penetration electric fields could drive the periodic downward plasma drifts, which are very likely to cause low‐pressure region of topside ionosphere at low latitude and subsequent flowing of plasma from higher latitudes (equatorial ionization anomaly crest) to the low‐pressure region. The extra plasma sourced from higher latitudes, which is against the loss of increased recombination due to F region height decrease, could contribute to the TEC oscillations. Compared with the TEC measurements by GPS receiver network that are affected by satellite motion, the Ionospheric Observation Network for Irregularity and Scintillation in East/Southeast Asia, which measures TEC at fixed ionospheric pierce points along the same longitude/latitude by receiving Beidou geostationary satellite signals, provides a unique means for fine‐scale observations of ionospheric perturbations not previously possible. Key Points: We report first IONISE observations of low latitude TEC oscillations synchronized over a wide longitude range at nighttimeThe TEC oscillations were likely driven by multiple westward PPEFs due to southward turnings of IMF BzThe IONISE provides a unique means for fine‐scale observations of ionospheric perturbations along the same longitude/latitude [ABSTRACT FROM AUTHOR]

This paper reports a special midlatitudinal medium‐scale traveling ionospheric disturbance (MSTID) event, accompanied by a poleward surge of airglow depletion/enhancement and a bifurcation of depletion during the magnetically quiet period. These special structures were generated during a decreasing height of ionosphere with nighttime plasma density enhancement and increment of airglow emission intensity possibly caused by a passing‐by midnight brightness wave. We suggest that the interaction of the passing‐by MSTID and nighttime plasma density enhancement resulted in the poleward surge and bifurcation of airglow depletion. The nighttime plasma density enhancement could feed the high plasma density to interact with the airglow depletions of MSTID, causing the poleward surge and bifurcation of airglow depletion by the secondary gradient drift instability. The poleward surged airglow enhancement within two adjacent depletions of MSTID is also firstly reported in this study. Plain Language Summary: It was generally believed that the midlatitudinal ionosphere is fairly quiescent until the first report of airglow structure of the medium‐scale traveling ionospheric disturbance by Garcia, Kelley, Makela, and Huang (2000, https://doi.org/10.1029/1999JA000305). Kelley et al. (2000, https://doi.org/10.1029/2000GL000022) and Garcia, Kelley, Makela, Sultan, et al. (2000, https://doi.org/10.1029/1999JA000306) further reported magnetically storm‐time "intense mid‐latitude spread F" events accompanied by poleward surged bifurcations of airglow depletions, which caused the severe perturbations of GPS signal. Those two events were most likely the interactive result of airglow depletion and enhanced plasma density region from the equatorial ionization anomaly crest region driven by magnetic storms. In this paper, we report a very similar airglow event accompanied by a poleward surged airglow depletion/enhancement and a bifurcation of depletion but occurred at magnetically quiet time in Xinglong, China. We suggest that the interaction of the passing‐by medium‐scale traveling ionospheric disturbance and the nighttime plasma density enhancement/nighttime increment of airglow emission intensity from a possible source of midnight brightness wave resulted in the poleward surged bifurcation of aiglrow depletion, most likely driven by the secondary gradient drift instability. This event can broaden our knowledge on the dynamical process of midlatitudinal ionosphere and provide a new guidance for further investigation of the midlatitudinal special airglow events. Key Points: MSTID with a poleward surged airglow depletion/enhancement and a bifurcation of depletion occurred during the magnetically quiet timeSecondary gradient drift instability could have developed the poleward surged bifurcation of depletionThis event is suggested to be caused by the interaction between MSTID and NPDE [ABSTRACT FROM AUTHOR]

The International Reference Ionosphere (IRI) is the most frequently used community empirical model. The latest version IRI2016 provides three options for the F2 peak height hmF2: AMTB2013, SHU-2015, and BSE-1979. In this paper, we used the hmF2 data derived by the ionosondes at Mohe, Beijing, Wuhan and Sanya ranging from year 2007 to 2016 to assess the performance of these three options in the model. The results show that the variability of the observed hmF2 versus local time, seasons and levels of solar activity could be reproduced well by the three options. However, the SHU-2015 option performs best at these four stations, followed by BSE-1979, and the AMTB2013 option is worst. Generally, the AMTB2013 and BSE-1979 options overestimate the hmF2 values, while the SHU-2015 option mainly underestimates the hmF2 values. This is the first evaluations of the three IRI2016 hmF2 options by manually scaled ionosonde data over China area to our knowledge. Overall, we recommend the usage of SHU-2015 hmF2 option over China region when using IRI2016 model in terms of hmF2 calculation. [ABSTRACT FROM AUTHOR]

On the basis of multiple observations of ionosondes, meteor radars, magnetometers and GNSS receivers, we present the response of the equatorial and low latitude ionosphere over the West Pacific Ocean Sector to an X1.2 solar flare that peaked at 1:48 UT on 15 May 2013. The geomagnetic H component observations indicate the equatorial electrojet strength over the East Asia region is obviously enhancement during the flare. After the end time of solar flare, the ionosonde observations at Guam, an ionosonde station near the geomagnetic equatorial region, show the decrease of the peak height of ionospheric F2 layer which is related to the decrease of the eastward electric field. Simultaneous strong southern wind is observed by meteor radar over Sanya, a geomagnetic low latitude station, which probably product the westward dynamo electric field and further result in the decrease of vertical drift velocity over the geomagnetic equatorial region. In addition, GNSS total electron content (TEC) observations from six stations in the researching region show the TEC enhancement only appears nearby the geomagnetic equator region. [ABSTRACT FROM AUTHOR]

Based on the one-month (October, 2014) wind observations of 11 radars distributed in both hemispheres along the 120°E meridian during a radar campaign, this article reports on improvements of the tidal mapping technique proposed before (Yu et al., 2013) by extending the latitude coverage to the global scale (from pole to pole). We first present the tidal components decomposed from the wind observations at different stations. It is revealed that the tidal components are stronger at stations in the Northern Hemisphere than in the Southern Hemisphere. Then, Hough mode decomposition is performed to extract the contributions of different tidal modes for each decomposed tidal component. The expected dominant mode, (1, 1) mode, is the strongest. The trapped (1, −2) mode also contributes a lot to the diurnal component. Yet for the semidiurnal component, (2, 4) mode along with (2, 5) mode make considerable contributions. In contrast, (3, 5) mode has the strongest amplitude for the terdiurnal component. At last, the tidal mapping technique proposed before is improved to get the pole-to-pole structure of each tidal component, based on the extracted tidal modes. The mapped tidal components successfully construct the general latitudinal and altitudinal distributions, compared with the Thermosphere Ionosphere Mesosphere Energetics and Dynamics Doppler Interferometer (TIDI) observations and Global Scale Wave Model (GSWM-09) results. Comparison of the predicted and observed tidal wind (for example, at Wuhan Station) indicates the capability of the mapping technique for reproducing the local time and altitude variations of the original observations. [ABSTRACT FROM AUTHOR]

In this paper, the ionospheric total electron content (TEC) is derived from 250 Global Navigation Satellite Systems (GNSS) receivers over China. The GNSS TEC data are utilized to study the diurnal and day-to-day variability of ionosphere, ionospheric east–west differences and to construct regional ionospheric map. The GNSS–TEC curves clearly show sunrise and sunset enhancements in the diurnal variation. The peak value of TEC is lower in January 2015 than in May 2014. There is 2 h difference in the occurrence time of TEC maximum/minimum between May and January. Compared with the observations of Global Positioning System (GPS) and Global Navigation Satellite System (GLONASS), the measurements from the Geostationary Earth Orbit (GEO) satellites of BeiDou Navigation Satellite System (BDS) clearly present the ionospheric day-to-day variability and east–west differences in a region with small longitude differences (3.52–11.31°). The east–west differences in TEC are more obvious in larger longitude differences at 11:30 local time on 23 January 2015. The maximum east–west difference in TEC is about 7 total electron content unit (TECU, 1 TECU = 10 16 el m −2 ) in longitude difference of 11.31°. Our analysis shows that the TEC for east–west small longitude differences may be associated with the east–west gradient of geomagnetic declination. Based on 250 GNSS stations, a regional TEC map constructed by Kriging method can well capture the main spatial structure of ionosphere in China. A comparison between TEC maps obtained by Kriging method and provided by Jet Propulsion Laboratory displays that there are large deviations in the North of China, which is mainly caused by the difference in the number of used GNSS stations. In addition, comprehensive investigation presents that GNSS has more advantages over GPS and GLONASS in the ionosphere research over China. [ABSTRACT FROM AUTHOR]

Equatorial spread-F (ESF) backscatter plumes are often observed in radar range-time-intensity (RTI) maps at low latitude. Except case studies, few statistical investigations on the onset locations of scintillation-producing ESF plumes at given sites have been conducted. In this study, a statistical analysis is carried out on onset locations of ESF backscatter plumes observed at a low-latitude location Sanya (18.4°N, 109.6°E; dip lat 12.8°N) during equinoctial months of 2013. By employing a tracing method to locate backscatter plumes, we estimate the onset longitudes of periodic plumes obtained from the Sanya VHF radar five-beam steering measurements. The results show that the inter-plume distances (in longitude) are mostly confined within 200-600 km, and the ESF plumes producing ionospheric scintillations over Sanya are almost exclusively generated at the longitudes of 94°-110°E. The results indicate the necessity to monitor ESF plume initial generation in the longitude region of 94°-110°E to better understand the day-to-day variability in the occurrence of ionospheric scintillations over Sanya. [ABSTRACT FROM AUTHOR]

In this paper, we developed a two-dimensional ionospheric assimilation model that assimilates the observations of peak electron density of F2-layer (NmF2) and the peak height of F2-layer (hmF2) derived from five ionosonde stations along the 120°E meridian, using three-dimensional variation techniques (3DVAR) based on a physics-based ionosphere theoretical model. The assimilation system can well produce the assimilated results along the 120°E meridian plane by using the data of NmF2 and hmF2 at five ionosonde stations from Mohe (52.0°N) to Sanya (18.3°N). The root mean square error (RMSE) between the analysis results of the assimilation model and the ionosonde observations is much lower than that between the results from international reference ionosphere (IRI) and the ionosonde observations. In addition, we carried out the assimilation test by taking the IRI results as the observations to check the assimilated results in the regions without observations. The assimilated result in the southern hemisphere (RMSE=0.29) is much worse than that in the northern hemisphere (RMSE=0.10) because no observations in the southern hemisphere were used. If the data derived from the four ionosonde stations in Australia are used, the assimilated result in the southern hemisphere would be much more accurate. In addition to NmF2 and hmF2, the assimilation model can also adjust the total electron content (TEC). The RMSE between the TEC after assimilation and the observed GPS TEC is much lower than that between the TEC from the IRI model and the observed GPS TEC. [ABSTRACT FROM AUTHOR]

The Global Positioning System (GPS) L-band ionospheric scintillation produced by electron density irregularities in the ionospheric E- and F-regions, is mainly a low- and high-latitude phenomenon. In this study, the statistical behavior of GPS ionospheric scintillation over a Chinese low-latitude station Sanya (18.3°N, 109.6°E; dip lat: 12.8°N) has been investigated. A detailed study on the seasonal and solar activity dependence of scintillation occurrence during July 2004–December 2012 show that the amplitude scintillation pattern, with a maximum occurrence during equinox of solar maximum, agrees with plasma bubble observations by in situ satellites in this longitude. A few daytime periodic scintillation events are found during June solstice months of solar minimum. Interestingly, a significant equinoctial asymmetry of scintillation onset time is found in 2011–2012. The initiation of scintillation during September–October is on average earlier than that of March–April about 25 min. Meanwhile, the zonal drifts of irregularities estimated using two spatially separated GPS receivers over Sanya show a similar behavior during the two equinoxes, slowly decreasing from 150 m/s at post-sunset to 50 m/s near midnight. The possible mechanisms responsible for the occurrence characteristics of GPS scintillation over Sanya, and relevant aspects of the zonal drifts of the irregularities are discussed. [ABSTRACT FROM AUTHOR]

We present a multi-instrument experiment to study the effects of tropospheric thunderstorms on the mesopause region and the lower ionosphere. Sodium (Na) lidar and ionospheric observations by two digital ionospheric sounders are used to study the variation in the neutral metal atoms and metallic ions above thunderstorms. An enhanced ionospheric sporadic E layer with a downward tidal phase is observed followed by a subsequent intensification of neutral Na number density with an increase of 600 cm−3 in the mesosphere. In addition, the Na neutral chemistry and ion-molecule chemistry are considered in a Na chemistry model to simulate the dynamical and chemical coupling processes in the mesosphere and ionosphere above thunderstorms. The enhanced Na layer in the simulation obtained by using the ionospheric observation as input is in agreement with the Na lidar observation. We find that the intensification of metallic layered phenomena above thunderstorms is associated with the atmospheric tides, as a result of the troposphere-mesosphere-ionosphere coupling. [ABSTRACT FROM AUTHOR]