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Trans-ionospheric communication of radio waves can be affected by ionospheric scintillation which can lead to a complete loss of lock. Scintillation is more prevalent in the ionospheric equatorial anomaly region, and at high latitudes, which is one of the main concerns of space weather services. In this paper, we present the first time a technique to derive a near-real-time ionospheric scintillation index S4 regional mapping based on Kriging method using six low latitude stations in Southern China. The result is compared with the Global Ionospheric Scintillation Propagation Model (GISM) and ionospheric irregularity index represented by the rate of change total electron content index (ROTI) to assess the validation and accuracy of output of Kriging method. It shows that our map could reflect better the regional characteristic and variations of S4 in the Southern China. The lower mean absolute errors and the mean square errors indicate that the results of Kriging method are relatively true and reliable, which could be considered monitoring and warning regional ionospheric scintillation activities under disturbed space weather conditions.

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.

Recently, Jiang et al., (2016) reported daytime spread F at Puer station (22.7oN, 101.05oE, Dip Lat 12.9oN). As a continual work, daytime spread F at middle latitudes was investigated in this study through ionograms recorded by an ionosonde installed at Zhangye (ZHY, 39.4oN, 100.0oE, Dip Lat 29.6oN) in the Northwest of China. The ionosonde at ZHY station recorded daytime spread F three times on 6 January, 2017. The first case occurred at approximately 06:45 LT and disappeared at about 08:35 LT. The second and third cases lasted from 09:50 LT to 10:30 LT and from 11:10 LT to 11:30 LT, respectively. In addition, Swarm satellite observations were used to reveal the possible mechanism in this study. Results show that daytime spread F observed in this study might be attributed to Traveling Ionospheric Disturbances (TIDs)/atmospheric gravity waves induced by a geomagnetic storm. However, the physical processes might be different for these cases. Ionospheric instabilities produced by local F region electric field might be contributed to the first case. The second and third cases might be attributed to off-vertical reflections from wave-like ionospheric structure generated by TIDs/atmospheric gravity waves.

In this paper, a regional 3-D ionospheric electron density specification over China and adjacent areas (70°E–140°E in longitude, 15°N–55°N in latitude, and 100–900 km in altitude) is developed on the basis of data assimilation technique. The International Reference Ionosphere (IRI) is used as a background model, and a three-dimensional variational technique is used to assimilate both the ground-based Global Navigation Satellite System (GNSS) observations from the Crustal Movement Observation Network of China (CMONOC) and International GNSS Service (IGS) and the ionospheric radio occultation (RO) data from FORMOSAT-3/COSMIC (F3/C) satellites. The regional 3-D gridded ionospheric electron densities can be generated with temporal resolution of 5 min in universal time, horizontal resolution of 2° × 2° in latitude and longitude, and vertical resolution of 20 km between 100 and 500 km and 50 km between 500 and 900 km. The data assimilation results are validated through extensive comparison with several sources of electron density information, including (1) ionospheric total electron content (TEC); (2) Abel-retrieved F3/C electron density profiles (EDPs); (3) ionosonde f o F 2 and bottomside EDPs; and (4) the Utah State University Global Assimilation of Ionospheric Measurements (USU-GAIM) under both geomagnetic quiet and disturbed conditions. The validation results show that the data assimilation procedure pushes the climatological IRI model toward the observation, and a general accuracy improvement of 15–30% can be expected. Thecomparisons also indicate that the data assimilation results are more close to the Center for Orbit Determination of Europe (CODE) TEC and Madrigal TEC products than USU-GAIM. These initial results might demonstrate the effectiveness of the data assimilation technique in improving specification of local ionospheric morphology.

A technique is developed to derive two-dimensional maps of total electron content (TEC) over China and adjacent areas using Global Navigation Satellite System (GNSS) data from the Crustal Movement Observation Network of China (CMONOC) and the International Global Navigation Satellite System Service (IGS). A revised self-calibration of pseudo-range errors (SCORE) algorithm is used to derive the TEC and to determine the Differential Code Biases (DCBs) simultaneously. The accuracy and validity of this technique is verified in two ways. Firstly, the estimated TEC is compared with the results derived using DCBs from Center for Orbit Determination of Europe (CODE) under different solar activity conditions and seasons; secondly, sample TEC along the receiver-to-satellite ray paths are simulated by NeQuick model and are reprocessed by this TEC derivation technique to make the accuracy test. Two-dimensional maps of vertical TEC of ionospheric pierce points (IPPs) are obtained accordingly with a time resolution of 30 s. The data interpolating empirical orthogonal functions (DINEOF) technique is then used to make the extrapolation for the unknown or missing data points. The optimal EOF modes for data reconstruction are specified via cross-validation method. The regional TEC distribution over China and adjacent areas is scaled into grid size of 1° × 1° for each 5 min, which can well reflect the characteristic of large-scale regional variations and temporal evolution as well as the small-scale local features of ionosphere.

In this paper, a regional total electron content (TEC) mapping technique over China and adjacent areas (70 degrees E-140 degrees E and 15 degrees N-55 degrees N) is developed on the basis of a Kalman filter data assimilation scheme driven by Global Navigation Satellite Systems (GNSS) data from the Crustal Movement Observation Network of China and International GNSS Service. The regional TEC maps can be generated accordingly with the spatial and temporal resolution being 1 degrees x1 degrees and 5min, respectively. The accuracy and quality of the TEC mapping technique have been validated through the comparison with GNSS observations, the International Reference Ionosphere model values, the global ionosphere maps from Center for Orbit Determination of Europe, and the Massachusetts Institute of Technology Automated Processing of GPS TEC data from Madrigal database. The verification results indicate that great systematic improvements can be obtained when data are assimilated into the background model, which demonstrates the effectiveness of this technique in providing accurate regional specification of the ionospheric TEC over China and adjacent areas.

Variability of vertical TEC recorded at Fuzhou (26.1°N, 119.3°E, geomagnetic latitude 14.4°N), Xiamen (24.5°N, 118.1°E, geomagnetic latitude 13.2°N), Nanning (22.8°N, 108.3°E, geomagnetic latitude 11.4°N), China, during the low solar activity in 2006–2007 have been analyzed and discussed. Remarkable seasonal anomaly was found over three stations with the highest value during spring and the lowest value during summer. The relative standard deviation of VTEC is over 20% all the time, with steady and smooth variation during daytime while it has a large fluctuation during nighttime. The biggest correlation coefficient was found in the VTEC-sunspot pair with a value of over 0.5. It seems that solar activity has a better correlation ship than geomagnetic activity with the variation of VTEC and better correlations are found with more long-term data when comparing our previous study. The results of comparing observation with model prediction in three sites reveal again that the SPIM model overestimates the measured VTEC in the low latitude area.

Surface electromyogram (sEMG) signal has been applied to gesture recognition successfully. However, performance of gesture recognition degrades due to noise, which is unavoidable in practical environment. This study aims to propose a gesture recognition system using a multiple classifier system (MCS) based on random subspace. Our method makes a decision using a signal which is less sensitive to noise. Each base classifier is trained using the subset of channels selected randomly. The influence of a base classifier by a noisy sample is measured by sensitivity, defined as the perturbation of an output of a classifier. The final decision of the MCS is determined according to the output of the based stable classifiers fused by majority vote. Experimental results show that the proposed method achieves better classification performance in comparison with its base classifier and the random subspace method in terms of accuracy and robustness to noise.

GPS-derived vertical TEC recorded at Xiamen (24.5 degrees N, 118.1 degrees E, geomagnetic latitude 13.2 degrees N), China, during year 2006 is analyzed for the first time and compared to that predicted by ionosphere model SPIM recommend by ISO. A manifest seasonal anomaly is found with the high value during equinoctial season and low value during summer and winter season. Relative standard deviation for VTEC shows high value at around midnight and before sunrise. The correlation analysis exhibits that the variation of VTEC has a very weak relation with geomagnetic and solar activities (Dst, AP, SSN and F10.7). Comparative results reveal that the SPIM overestimates the observed VTEC at most of the time. (C) 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.

This paper presents small scale (duration ⩽1 h, ΔTEC ⩾ 1TECU) night-time total electron content (TEC) enhancements observed at the equatorial anomaly region in China, for the first time. The data is from a GPS receiver chain established in 2005 by Institute of Center for Space Science and Applied Research, Chinese Academy of Sciences and a GPS receiver of International GPS Service (IGS), located between Fuzhou (26.1°N, 119.3°E) and Nanning (22.8°N, 108.3°E). Two other GPS observations of IGS taken at higher latitude were also used to investigate the localization of such phenomenon. The characteristics of the night-time TEC enhancement are examined with two case studies. The TEC increases about 1–3TECU, intermittently. While the night-time TEC enhancement mainly occurs at the equatorial anomaly region, it can be observed at middle latitude as well. The spatial size of the enhancement region is less than 5° in longitude. The primary statistical study shows that the TEC enhancement is more often observed in spring and autumn, but rarely in summer. It has no dependence on geomagnetic activity. The enhancement can occur both before and after midnight.

Using a self-consistent quasi-electrostatic (QE) field model, the magnitude of QE is calculated at altitudes from 0km to 90km due to a sudden discharge of thunderstorm cloud. It is assumed that a positive charge of 200C is displaced to ground within 1ms. The numerical results show that the QE field obtained is greater than the breakdown field of neutral atmosphere at height above the thunderstorm about 65~78 km, 1 ms after the initiation of the discharge, and it decreases very quickly 0.5 s later. Because the thermal and ionization time scale are very short at the ionospheric height, the local nighttime lower ionosphere should be substantially affected by the relative large QE field. By solving the Boltzmann equation numerically, it is shown that the electron distribution function has a high-energy tail at some altitudes, for example at 73 km, and the averaged electron energy is about 3~6 eV at heights of 63~78 km. The results also show that the electron density increases between 65km and 78 km, and the maximum peak becomes three orders larger than the ambient value at about 73 km. Such an effect is much larger than that caused by the electromagnetic pulse which is produced by the lightning stroke current.