Total Electron Content Disturbances Research Articles

Multi-dimensional distribution of near-field ionospheric disturbances produced by the 2015 Mw7.8 Nepal earthquake

Ionospheric anomalies possibly associated with large earthquakes, particularly coseismic ionospheric disturbances, have been detected by global positioning system (GPS). A large Nepal earthquake with magnitude Mw7.8 occurred on April 25, 2015. In this paper, we investigate the multi-dimensional distribution of near-field coseismic ionospheric disturbances (CIDs) using total electron content (TEC) and computerized ionospheric tomography (CIT) from regional GPS observational data. The results show significant ionospheric TEC disturbances and interesting multi-dimensional structures around the main shock. Regarding the TEC changes, coseismic ionospheric disturbances occur approximately 10–20min after the earthquake northeast and northwest of epicentre. The maximum ridge-to-trough amplitude of CIDs is up to approximately 0.90 TECU/min. Propagation velocities of the TEC disturbances are 1.27±0.06km/s and 1.91±0.38km/s. It is believed that the ionospheric disturbances are triggered by acoustic and Rayleigh waves. Tomographic results show that the three-dimensional distribution of ionospheric disturbances obviously increases at an altitude of 300km above the surrounding epicentre, predominantly in the entire region between 200km and 400km. Significant ionospheric disturbances appear at 06:30 UT from tomographic images. This study reveals characteristics of an ionospheric anomaly caused by the Nepal earthquake.

Features of TEC behaviour over the low-latitude North-American region during the period of medium solar activity

The study is focused on Total Electron Content (TEC) behavior in low-latitude North-American region within the twelve-year period from 2005 to 2016. The obtained systematic (regular) TEC variations (diurnal, seasonal patterns) conform to the known tendencies described by climatological TEC models. TEC variations during disturbances have a number of distinctive features. The majority of positive TEC enhancements occur already with Dst <−30nT. The intensity of TEC change does not depend on Dst-index minimum value. Almost all cases of day-time TEC disturbances are accompanied by night-time disturbances with the possibility of relative night-time deviations being larger that is confirmed by data of low-orbit satellites CHAMP and DMSP. The simultaneity of changes of critical frequencies of the ionosphere with changes of TEC during disturbances was observed at Ramey (Puerto Rico) and Eglin (U.S.A.) stations when ionosonde data was available. This proves that TEC reflects the character of ionospheric disturbances. Spatial non-synchronism of TEC change that was sometimes observed can be explained by local character of the area covered with positive TEC disturbance. It was shown the potential provided by local GNSS networks for the detailed analysis of TEC variations over the considered region and estimation of the ionosphere state in near-real time.

Influence of January 2009 stratospheric warming on HF radio wave propagation in the low-latitude ionosphere

We have considered the influence of the January 23–27, 2009 sudden stratospheric warming (SSW) event on HF radio wave propagation in the equatorial ionosphere. This event took place during extremely low solar and geomagnetic activity. We use the simulation results obtained with the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) for simulating environmental changes during the SSW event. We both qualitatively and quantitatively reproduced total electron content disturbances obtained from global ground network receiver observations of GPS navigation satellite signals, by setting an additional electric potential and TIME-GCM model output at a height of 80 km. In order to study the influence of this SSW event on HF radio wave propagation and attenuation, we used the numerical model of radio wave propagation based on geometrical optics approximation. It is shown that the sudden stratospheric warming leads to radio signal attenuation and deterioration of radio communication in the daytime equatorial ionosphere.

Total electron content disturbances during minor sudden stratospheric warming, over the Brazilian region: A case study during January 2012

AbstractThe effects of sudden stratospheric warming (SSW) on ionosphere have been investigated by several scientists, using different observational techniques and model simulations. However, the minor SSW event during January 2012 is one of those that are less studied. Influences of several types of possible drivers—minor SSW event, changing solar flux, moderate geomagnetic storm on 22–25 January, and one of the largest solar proton events on 23–30 January—make it a challenging period to interpret. In the present study, the GPS‐total electron content (TEC) measurements from a network of 72 receivers over the Brazilian region are considered. This network of 72 GPS‐TEC locations lies between 5°N and 30°S (35°) latitudes and 35°W and 65°W (30°) longitudes. Further, two chains of GPS receivers are used to study the response of the equatorial ionization anomaly (EIA) in the Brazilian eastern and western sectors, as well as its day‐to‐day variability before and during the SSW‐2012. It was noted that the TEC is depleted to the order of 30% all over the Brazilian region, from equator to beyond the EIA regions and from east to west sectors. It is also noticed that the EIA strengths at the east and west sectors were weakened during the SSW‐2012. However, the Brazilian eastern sector was found to be more disturbed compared to the western sector during this SSW‐2012 event.

Ionospheric TEC disturbance study over seismically region in China

Using data of Crustal Movement Observation Network of China (CMONOC) and IGS (International GNSS Service), we attempt to give a statistical behavior of the total electron content (TEC) perturbation before 30Mw6.0+ earthquakes from 2000 to 2010 in China. Results show that TEC anomalies are detected before 20 earthquakes, nearly 67%. The anomalies represent positive before most events and occur mostly within 2–6days before the shocks, significantly during the afternoon period, 12–20LT. To verify the reliability of the anomalous behavior of TEC detected in the statistical study, we analyze variations of TEC over two regions during a period of low solar and geomagnetic activity in April-October 2008. In southwest China, during that time, six large earthquakes with magnitude M≧6.0 occurred. And a ‘check-region’ with same geomagnetic latitudes as the epicentral area is selected. Known that the decisive role in the ionosphere state is performed by space weather effects, we compare the TEC variations with time series of EUV solar radiation, Bz component of the interplanetary magnetic field (IMF), index of geomagnetic activity Dst and planetary index Kp, respectively. It is found that, both in the two regions, the observed anomalies in the regional TEC are in good correlation with the variations of above index. We detect different levels of TEC anomalies before the 6 earthquakes, and most of them are amost certainly dominated by space weather expect for Wenchuan case. The work illustrates the difficulties of searching precursors of earthquake in the ionosphere, but also, it reminds the importance for considering the effect of atmospheric waves on the ionosphere as well as the applicability of statistical approach.

Влияние внезапного стратосферного потепления в январе 2009 г. на распространение коротких радиоволн в экваториальной ионосфере

For the first time, we consider the effect of the January 23–27, 2009 sudden stratospheric warming (SSW) event on HF radio wave propagation in the equatorial ionosphere. This event took place during extremely low solar and geomagnetic activity. We use the simulation results obtained with the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) for simulating environmental changes during the SSW event. We both qualitatively and quantitatively reproduce total electron content disturbances obtained from global ground network receiver observations of GPS navigation satellite signals, by setting an additional electric potential and TIME-GCM model output at a height of 80 km. In order to study the influence of this SSW event on HF radio wave propagation and attenuation, we use the numerical model of radio wave propagation based on geometrical optics approximation. It is shown that a sudden stratospheric warming leads to radio signal attenuation in the day-time equatorial ionosphere.

GPS–TEC response to the substorm onset during April 5, 2010, magnetic storm

We consider disturbances of total electron content (TEC) of the high-latitude ionosphere provided by the GPS global navigation satellite system before and during the magnetic storm on April 5, 2010. Simultaneously, we examine magnetic data from all available magnetometer arrays in the northern hemisphere, augmented with data from scanning photometers and riometers. The substorm onset, during both non-storm and storm periods, is found to cause significant enhancement of TEC scintillations characterized by the TEC time derivative dTEC. Comparison of 2D maps of the spectral power of magnetic fluctuations in the Pc5 band (1–10 mHz) and dTEC during substorms shows a good spatial and temporal correspondence between them. Both magnetic and ionospheric fluctuations tend to concentrate inside the auroral oval, the boundaries of which are determined from the OVATION model. The time–space evolution of TEC scintillations is rather similar to that of ultra-low-frequency magnetic fluctuations, but not to that of the ionospheric electrojet. GPS signal phase slips, resulting in non-physical TEC jumps (>1 TECu/min), occur predominantly inside the auroral oval and in the vicinity of its equatorward boundary.

TEC variations and ionospheric disturbances during the magnetic storm in March 2015 observed from continuous GPS data in the Southeast Asia region

TEC variations and ionospheric disturbances during the magnetic storm in March 2015 observed from continuous GPS data in the Southeast Asia region

Large ionospheric TEC depletion induced by the 2016 North Korea rocket

A rocket called Kwangmyongsong-4 was launched from North Korea at 00:30UT on February 7, 2016. We investigated ionospheric total electron content (TEC) depletions induced by the rocket using the Global Navigation Satellite System (GNSS) stations in South Korea. A sudden depletion in TEC variations appeared ∼6min after the rocket launch. The drops in slant TEC exceeded 17 TEC unit (TECU) and those in vertical TEC were approximately 7 TECU. It is remarkable that the TEC drop by the 2016 Kwangmyongsong-4 rocket is larger (almost by three times) than that by the 2012 Unha-3 rocket. There are the differences of the background TEC values at the 2012andthe 2016 cases. These results suggest that the difference of the background electron density affects the magnitude of TEC depletion. The horizonal velocity of the rocket was 1.6km/s, which was estimated from horizontal distances with an initial time of TEC disturbances. However, the 2012 Unha-3 rocket (∼2.5km/s) moved faster horizontally than the 2016 Kwangmyongsong-4 rocket. Furthermore, when the rocket moved from high latitudes to low latitudes, TEC disturbances reduced gradually, and then, the depletion persisted for a longer time at the west side (the right side of southern direction).

Observations of conjugate MSTIDs using networks of GPS receivers in the American sector

AbstractThis study has used total electron content (TEC) values from an extended network of GPS receivers and a highly developed processing to characterize the conjugacy of medium‐scale traveling ionospheric disturbances (MSTIDs) over the American continent. It was found that midlatitude nighttime MSTIDs, also named electrobuoyancy waves, map into the opposite hemisphere but the amplitude of the TEC disturbance in the Southern Hemisphere is between 8 and 13% of the amplitude in the original hemisphere. The periods of the MSTIDs vary between 50 and 65 min. MSTID dynamics is presented for two days: 20 August 2012 and 17 June 2012. On the first day, MSTIDs entered into the American sector shortly before 4 UT, last for 3 h, drifted at an average speed of 200 m/s, and dissipated in the Caribbean region. In the Northern Hemisphere, the MSTIDs were directed southwestward (SW) and 60° from south. In the Southern Hemisphere, they moved northwestward (NW) or ~60° from north. The MSTID velocity changed through the night from ~300 m/s to ~150 m/s, but the propagation direction did not vary. On 17 June 2012 a series of wide MSTIDs were seen traveling across the Caribbean region that exited through the western coast of Central America. These MSTIDs last for ~5 h. Number density measured with the DMSP‐F15 and DMSP‐F17 satellites confirm the notion that the MSTIDs consist of rising and falling sheets of plasma density driven by electric fields likely set by a Perkins‐type instability. These observations support the notion that gravity waves can seed and boost the growth of the nighttime MSTIDs.

Dynamics of the level of total electron content disturbance at high and middle latitudes according to GPS data

We study the level of total electron content (TEC) disturbance in ionospheric mid-latitude and high-latitude regions, which occurred during 2013. TEC behavior is calculated using data from two GPS stations: MOND (Mondy) and NRIL (Norilsk). TEC variations are estimated from dual-frequency phase measurements for all radio signal paths. We analyze the TEC variations in two time ranges: 10 and 40 min. These ranges correspond to medium- and large-scale ionospheric disturbances respectively. The TEC disturbance level is characterized using a special index WTEC. It allows us to receive multi-day continuous series of average TEC variation intensity. We reveal that at high latitudes WTEC variations correlate well with AE ones. The correlation between WTEC and Dst variations is much lower. The minimum level of TEC disturbance is independent of the season in the Arctic region; diurnal WTEC variations are more pronounced for medium-scale ionospheric disturbances than for large-scale ones. At mid-latitudes, the WTEC variation concurs with Dst and Kp variations only during strong magnetic storms. The minimum level of TEC disturbance is higher in summer than in winter. At middle latitudes, the sunset terminator generates gravity waves. In the Arctic region, terminator-induced waves are not observed.

Analysis of traveling ionospheric disturbances (TIDs) in GPS TEC launched by the 2011 Tohoku earthquake

AbstractTraveling ionospheric disturbances (TIDs) have been detected using various measurement techniques, including HF sounders, incoherent scatter radars, in situ measurements, and optical techniques. However, observations of TIDs have tended to be sparse and there is a need for additional observations to provide new scientific insight into the geophysical source phenomenology and wave propagation physics. The dense network of GPS receivers around the globe offers a relatively new data source to observe and monitor TIDs. In this paper, we use total electron content (TEC) measurements from ~4000 GPS receivers throughout the continental United States to observe TIDs associated with the 11 March 2011 Tohoku tsunami. The tsunami propagated across the Pacific to the U.S. west coast over several hours, and we show that corresponding TIDs were observed in the US. Using this network of GPS receivers we present a 2D imaging of TEC perturbations and calculate various TID parameters, including horizontal wavelength, speed, and period. Well‐formed, planar TIDs were detected over the west coast of the U.S. ~10 h after the earthquake. Fast Fourier transform analysis of the observed waveforms revealed that the period of the wave was 15.1 min with a horizontal wavelength of 194.8 km, phase velocity of 233.0 m/s, and an azimuth of 105.2° (propagating nearly due east in the direction of the tsunami wave). These results are consistent with the TID observations in airglow measurements from Hawaii earlier in the day and with other GPS TEC observations.

Динамика возмущенности полного электронного содержания в высоких и средних широтах по данным GPS

We study the level of total electron content (TEC) disturbance in ionospheric mid-latitude and high-latitude regions during 2013. TEC behavior is calculated using data from two GPS stations: MOND (Mondy) and NRIL (Norilsk). TEC variations are calculated from two-frequency phase measurements for all radio rays. We analyze the TEC variations in two time ranges: 10 and 40 min. These ranges correspond to middle- and large-scale ionospheric disturbances respectively. The TEC disturbance level is characterized using the special index WTEC. WTEC allows us to receive multi-day continuous series of average TEC variation intensity. We reveal that at high latitudes WTEC variations agree well with AE ones. The correlation between WTEC and Dst variations is much less. The minimum level of TEC disturbance is independent of the season in the Arctic region; diurnal WTEC variations are more pronounced for medium-scale ionospheric disturbances than for large-scale ones. At mid-latitudes, the WTEC behavior agrees well with the Dst and Kp variations only during strong magnetic storms. The minimum level of TEC disturbance is higher in summer than in winter. At mid-latitudes, the sunset terminator generates gravitational waves. In the Arctic region, terminator-generated waves are not observed.

Observation of TEC perturbation associated with medium‐scale traveling ionospheric disturbance and possible seeding mechanism of atmospheric gravity wave at a Brazilian sector

AbstractIn the present study, we document daytime total electron content (TEC) disturbances associated with medium‐scale traveling ionospheric disturbances (MSTIDs), on few chosen geomagnetically quiet days over Southern Hemisphere of Brazilian longitude sector. These disturbances are derived from TEC data obtained using Global Navigation Satellite System (GNSS) receiver networks. From the keograms and cross‐correlation maps, the TEC disturbances are identified as the MSTIDs that are propagating equatorward‐eastward, having most of their average wavelengths longer in latitude than in longitude direction. These are the important outcomes of the present study which suggest that the daytime MSTIDs over Southern Hemisphere are similar to their counterparts in the Northern Hemisphere. Another important outcome is that the occurrence characteristics of these MSTIDs and that of atmospheric gravity wave (AGW) activities in the thermosphere are found to be similar on day‐to‐day basis. This suggests a possible connection between them, confirming the widely accepted AGW forcing mechanism for the generation of these daytime MSTIDs. The source of this AGW is investigated using the Geostationary Operational Environmental Satellite system (GOES) and Constellation Observing System for Meteorology, Ionosphere, and Climate satellite data. Finally, we provided evidences that AGWs are generated by convection activities from the tropospheric region.

On forecasting ionospheric total electron content responses to high-speed solar wind streams

Conditions in the ionosphere have become increasingly important to forecast, since more and more spaceborne and ground-based technological systems rely on ionospheric weather. Here we explore the feasibility of ionospheric forecasts with the current generation of physics-based models. In particular, we focus on total electron content (TEC) predictions using the Global Ionosphere-Thermosphere Model (GITM). Simulations are configured in a forecast mode and performed for four typical high-speed-stream events during 2007–2012. The simulated TECs are quantified through a metric, which divides the globe into a number of local regions and robustly differentiates between quiet and disturbed periods. Proposed forecast products are hourly global maps color-coded by the TEC disturbance level of each local region. To assess the forecasts, we compare the simulated TEC disturbances with global TEC maps derived from Global Positioning System (GPS) satellite observations. The forecast performance is found to be merely acceptable, with a large number of regions where the observed variations are not captured by the simulations. Examples of model-data agreements and disagreements are investigated in detail, aiming to understand the model behavior and improve future forecasts. For one event, we identify two adjacent regions with similar TEC observations but significant differences in how local chemistry versus plasma transport contribute to electron density changes in the simulation. Suggestions for further analysis are described.

Disturbances of the upper atmosphere and ionosphere caused by acoustic-gravity wave sources in the lower atmosphere

The results of observations of acoustic-gravity waves in the troposphere and the ionosphere at middle latitudes during periods of passage of the solar terminator are presented. Tropospheric observations were performed using a lidar. The frequency characteristics of variations of the tropospheric parameters are determined based on observations of the intensity of the scattered lidar signal. The characteristics of variations of the total electron content (TEC) in the atmosphere are determined from data collected by GPS navigation satellites. An analysis of the observational data showed that the spectrum of variations of the atmospheric and ionospheric parameters is indicative of acoustic-gravity waves (AGW) propagating from the lower atmosphere. Modeling studies of the vertical propagation of AGW from the Earth’s surface showed that such waves quickly (within ~15 min) reach altitudes of the upper atmosphere (~300 km). The refraction and dissipation of waves in the upper atmosphere produces perturbations of the background state of the atmosphere and gives rise to the waveguide propagation of infrasonic wave components. The observed manifestations of TEC disturbances caused by AGW propagating from the lower atmosphere can be explained by the diurnal variation of the altitude of the ionosphere and the waveguide propagation of infrasonic waves.

Application of the models of the middle and upper atmosphere to simulation of total electron content perturbations caused by the 2009 stratospheric warming

Sudden stratospheric warming (SSW) is a unique atmospheric phenomenon, which consists in a rapid rise of temperature at altitudes of ~30–40 km in high latitudes of the winter, typically, northern hemisphere. Modeling SSW effects in the mesosphere, thermosphere, and ionosphere is a challenging problem, because it must be done on a global scale, with consideration of numerous physical and chemical processes. This paper reports the results of calculations of the characteristics of total electron content (TEC) perturbations for the conditions of the SSW event in January 2009. The calculations are performed using the Global Self-Consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) supplemented by the lower boundary conditions in the form of space–time distributions of the basic parameters of the mesosphere at an altitude of 80 km, as calculated by the SOCOL, KASIMA, and TIME GCM models. The simulation results show that, for some versions, the spatial distribution of total electron content disturbances ΔTEC shows a qualitative agreement with experimental data; however, the values of ΔTEC in all variants of calculations proved to be an order of magnitude lower than the measured.

Atmospheric resonant oscillations by the 2014 eruption of the Kelud volcano, Indonesia, observed with the ionospheric total electron contents and seismic signals

Acoustic waves from volcanic eruptions are often observed as infrasound in near fields. Part of them propagate upward and disturb the ionosphere, and can be observed with Total Electron Content (TEC) data from Global Navigation Satellite System (GNSS) receivers. Here we report TEC variations after the 13 February 2014 Plinian eruption of the Kelud volcano, East Java, Indonesia, observed with regional GNSS networks. Significant disturbances in TEC were detected with six GNSS satellites, and wavelet analysis showed that harmonic oscillations started at ∼16:25 UT and continued for ∼2.5 h. The amplitude spectrum of the TEC time series showed peaks at 3.7 mHz, 4.8 mHz and 6.8 mHz. Long-wavelength standing waves with a wide range of wavelength trapped in the lower atmosphere are excited by the Plinian eruption. Amplitude spectra of the ground motion recorded by seismometers, however, had frequency components at discrete wave-periods. The condition for the resonant oscillations between the atmosphere and the solid Earth is satisfied only at these discrete wave-period and horizontal wavelength pairs, therefore efficient energy transfer from the atmospheric standing waves to the solid Earth Rayleigh waves occurred at discrete periods and resulted in the harmonic ground motion.

Statistical characteristics of seismo-ionospheric GPS TEC disturbances prior to global Mw ≥ 5.0 earthquakes (1998–2014)

Pre-earthquake ionospheric anomalies are still challenging and unclear to obtain and understand, particularly for different earthquake magnitudes and focal depths as well as types of fault. In this paper, the seismo-ionospheric disturbances (SID) related to global earthquakes with 1492Mw≥5.0 from 1998 to 2014 are investigated using the total electron content (TEC) of GPS global ionosphere maps (GIM). Statistical analysis of 10-day TEC data before global Mw≥5.0 earthquakes shows significant enhancement 5 days before an earthquake of Mw≥6.0 at a 95% confidence level. Earthquakes with a focal depth of less than 60km and Mw≥6.0 are presumably the root of deviation in the ionospheric TEC because earthquake breeding zones have gigantic quantities of energy at shallower focal depths. Increased anomalous TEC is recorded in cumulative percentages beyond Mw=5.5. Sharpness in cumulative percentages is evident in seismo-ionospheric disturbance prior to Mw≥6.0 earthquakes. Seismo-ionospheric disturbances related to strike slip and thrust earthquakes are noticeable for magnitude Mw6.0–7.0 earthquakes. The relative values reveal high ratios (up to 2) and low ratios (up to −0.5) within 5 days prior to global earthquakes for positive and negative anomalies. The anomalous patterns in TEC related to earthquakes are possibly due to the coupling of high amounts of energy from earthquake breeding zones of higher magnitude and shallower focal depth.

Study of the thermospheric and ionospheric response to the 2009 sudden stratospheric warming using TIME‐GCM and GSM TIP models: First results

AbstractThis paper presents a study of mesosphere and low thermosphere influence on ionospheric disturbances during 2009 major sudden stratospheric warming (SSW) event. This period was characterized by extremely low solar and geomagnetic activity. The study was performed using two first principal models: thermosphere‐ionosphere‐mesosphere electrodynamics general circulation model (TIME‐GCM) and global self‐consistent model of thermosphere, ionosphere, and protonosphere (GSM TIP). The stratospheric anomalies during SSW event were modeled by specifying the temperature and density perturbations at the lower boundary of the TIME‐GCM (30 km altitude) according to data from European Centre for Medium‐Range Weather Forecasts. Then TIME‐GCM output at 80 km was used as lower boundary conditions for driving GSM TIP model runs. We compare models' results with ground‐based ionospheric data at low latitudes obtained by GPS receivers in the American longitudinal sector. GSM TIP simulation predicts the occurrence of the quasi‐wave vertical structure in neutral temperature disturbances at 80–200 km altitude, and the positive and negative disturbances in total electron content at low latitude during the 2009 SSW event. According to our model results the formation mechanisms of the low‐latitude ionospheric response are the disturbances in the n(O)/n(N2) ratio and thermospheric wind. The change in zonal electric field is key mechanism driving the ionospheric response at low latitudes, but our model results do not completely reproduce the variability in zonal electric fields (vertical plasma drift) at low latitudes.