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The occurrences of equatorial plasma bubble (EPB) irregularities over Asian and American sectors often show a different behavior due to significantly different geometries of the geomagnetic field. By using the GPS total electron content observations over equatorial and low latitudes sectors of Asian (about 120°E) and American (about 60°W) during 1997–2018, we present a comparative study of long-term occurrences of EPB kilometer-scale irregularities over the two longitude sectors. The results show that post-sunset EPB irregularities over the Asian sector were positively correlated with solar activity. However, in the American sector, such a positive dependence was not apparent in 2000–2002, which could be partly induced by limited data available during the high occurrence season of solar maximum when the GPS receivers frequently lost lock. The geomagnetic disturbance tends to inhibit the generation of EPB irregularities over both sectors during post-sunset but enhance their generation during post-midnight. The latitudinal distribution of EPB irregularities exhibited a double-peak structure centered within ± 10° (dip lat.), with the latitudinal limit below ± 25° at solar maximum in both sectors and below ± 20° and ± 10° at solar minimum in American and Asian sectors, respectively. Specifically, in the American sector, the occurrence rates were about two times higher than those in the Asian sector, and the occurrence rates in the northern hemisphere were apparently lower than those in the southern hemisphere. The enhanced ionization by particle precipitation over the South Atlantic Magnetic Anomaly region could cause the north–south asymmetry of occurrence rates of EPB irregularities. The results help in designing experiments to understand better the generation of EPB irregularities under the future international meridian circle project. [ABSTRACT FROM AUTHOR]

All-sky meteor radars are primarily used for meteor observations. This paper reports the first observations of ionospheric E-region field-aligned irregularities (FAIs) from a conventional all-sky meteor radar located at Wuhan (31°N, 114°E) for the period of March–June 2018. E-region FAI echoes evident in range-time intensity (RTI) maps show quasiperiodic striations with positive and negative slopes, which are consistent with multiple FAI structures moving across the wide beam of the meteor radar. A statistical analysis shows that out of a total of 111 d, there are 73 d with E-region FAI echoes detected by the meteor radar. The FAI events correspond well with the presence of sporadic-E layers which provide the necessary plasma density gradient for the development of gradient drift instability producing FAIs. The results demonstrate the capability of conventional meteor radars to make simultaneous routine observations of meteors and ionospheric E-region FAIs through incorporating RTI and spectral analysis into the online realtime data processing. Meteor radar observations could potentially address the limitations of ionospheric radars, which cannot provide simultaneous measurements of neutral winds and irregularity structures, and thereby contribute to better understanding of the dynamical processes producing E-region irregularities. [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]

Interferometry plays an important role in revealing fine-scale structures of ionospheric irregularity. By placing an additional receiving array of four 5-element Yagi antennas in the north of the main East-West array of the Sanya VHF radar, multiple interferometry baselines with components parallel and perpendicular to the magnetic meridian are formed. These baselines allow us to study the three-dimensional (3D) behavior of low-latitude ionospheric field-aligned irregularity (FAI) over Sanya. Using multiple non-collinear receiving baselines, an experiment for which the Sanya VHF radar operated as an interferometer was performed on 10 July 2013. Ionospheric E-region FAI echoes with periods of several minutes were observed during 0745-0915 UT; mean Doppler velocity was around −30 m/s with spectral widths of about 50 m/s. The interferometry results show fine-scale structures of E-region FAI with a zonal scale size of 15 km or less. In addition, we found that the periodic variations of echo intensity shown in radar range-time-intensity (RTI) maps were produced by spatially separated E-region irregularity patches. The patches drifted westward with a velocity of about 40-60 m/s and could be associated with propagating gravity waves. These results provide a clearer picture of the characteristics of FAI and thus help to investigate the generation and dynamics of low-latitude ionospheric irregularities in the Chinese sector. [ABSTRACT FROM AUTHOR]

In this paper, winds derived from OH Meinel 892.0 nm detection by an FPI (Fabry-Perot Interferometer) are compared with the simultaneous wind measurements from a meteor radar during April-May of 2010. The peak height of OH Meinel 892.0 nm is about 87 km. The variations of FPI wind at 87 km mostly have the similar track to meteor radar wind at 87 km, and the data values of FPI wind mainly fall into the range of meteor radar wind. However, there are still quantitative differences between the observations of the two systems. The best cross-correlation occurs in meridional winds from two systems in April of 2010. An obvious wave signal with 0.2 cycle/d frequency is found in meridional winds observed by both FPI and meteor radar. [ABSTRACT FROM AUTHOR]

Sanya VHF radar (18.4°N, 109.6°E, dip latitude 12.8°N) at Hainan Island is the first coherent backscatter radar for sounding low-latitude ionospheric irregularities in the mainland of China. In this paper, we present the first results of low-latitude ionospheric E and F region irregularities using the radar data during the period from February 2009 to March 2010. The Doppler velocity of radar echoes from E region field aligned irregularities (FAIs) was about several tens of meters per second, while the Doppler spectral width was appreciably larger than the velocity, and could reach one hundred meters per second, indicating that the observed E region FAIs belonged to type 2 irregularities. The observations of range time intensity (RTI) maps of FAIs showed that E region irregularities most often occurred at night within the altitude range 85-115 km, and were rarely observed at afternoon hours. The percentage occurrence of E region FAIs maximized during spring months (Feb.-May) with a peak value over 80%. The heights at which the strongest echo related FAIs occurred were mainly around 100 km, lower than h'Es and the difference is mostly 10-20 km. December solstice seemed to be the minimum period of occurrence when the FAI echoes were commonly detected at a narrow altitude range 90-100 km. Moreover, simultaneous radar and GPS observations during spread F events in the pre-midnight hours of solar minimum revealed that significant GPS L band scintillations coincided with the appearance of F region plasma plume structures, which extended up to 450 km in altitude. [ABSTRACT FROM AUTHOR]

The data observed by a spectral airglow temperature imager (SATI) at Beijing National Observatory of Space Environment from July 23, 2008 to July 31, 2009 are used to study night mesopause temperature in Beijing. From variations of temperature at 87 and 94 km obtained from OH (6-2) and O (0-1) airglow spectra, temperature at night is shown lowest in the summer and highest in the winter. In summer, average temperature at 87 km is 173.9 K, lower than average temperature 180.1 K at 94 km. But in winter, average temperature at 87 km is 201.2 K, higher than average temperature 194.8 K at 94 km. The altitude of mesopause in Beijing is below 87 km in summer and above 94 km in winter. There are about 120-150 days when the mesopause locates below 87 km, which is in agreement with the results of SABER/TIMED. Variations of temperatures at 87 and 94 km are analyzed by harmonic method. Our results show that amplitudes of annual oscillation of temperature at 87 and 94 km are 17.5 and 7.8 K respectively. Amplitudes of semi-annual oscillation at 87 and 94 km are 1.6 and 5.3 K, which are smaller than those of annual oscillation. Although there are differences among different observations because of different locations and different instruments, our results are in general agreement with observation at similar latitude as Beijing. [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]