Ionospheric response to an intense solar flare in equatorial and low latitude region

Space Weather and the Global Positioning System

Earth’s atmospheric layers are subjected to continuous changes in near-earth space. Hence, the space weather needs to be investigated, and the most reliable method is using satellite system. Widely used technique is Global Positioning System (GPS) which is primarily designed for tracking and navigation. Ionosphere, one of the earth’s atmospheric layers which contains free electrons, is highly affected by space weather like solar flares, geomagnetic storms and seasons. Since the GPS satellite signal travels through the ionosphere, its propagation is affected, and signal gets delayed by plasma of free electron known as total electron content (TEC). TEC not only depends on space weather but also on geographic location, specially the low latitude region (23° above and below the equator). Indian subcontinent falls under this low latitude region, and hence, satellite system applications like precise positioning, navigation, tracking and satellite communication are affected. Hence to correct the GPS delay, accurate estimation of TEC is necessary. In this paper, TEC and rate of TEC (ROT) are calculated, and the variation of the TEC is analyzed. The ionospheric delay, TEC and ROT are calculated for GPS data received on March 10, 2013, from the dual-frequency GPS receiver of NovAtel make located in K L University, Guntur, India (Lat: 16.44° N/Long: 80.62° E). The analysis presented in this paper will help in precise estimation of composition of ionosphere which will improve navigational accuracy.

The ionospheric total electron content (TEC) in the low-latitude Singapore region (geographic latitude 01.37° N, longitude, 103.67° E, geomagnetic latitude 8.5° S) for 2010 to 2011 was retrieved using the data from global positioning system (GPS)-based measurements. The observed TEC from GPS is compared with those derived from the latest International Reference Ionosphere (IRI)-2012 model with three options, IRI-Nequick (IRI-Neq), IRI-2001, and IRI-01-Corr, for topside electron density. The results showed that the IRI-Neq and IRI-01-Corr models are in good agreement with GPS-TEC values at all times, in all seasons, for the year 2010. For the year 2011, these two models showed agreement at all times with GPS-TEC only for the summer season, and for the period 11:00 to 24:00 UT hours (19:00 to 24:00 LT and 00:00 to 08:00 LT) during the winter and equinox seasons. The IRI-2012 model electron density profile showed agreement with constellation observing system for meteorology, ionosphere, and climate (COSMIC) radio occultation (RO)-based measurements around 250 to 300 km and was found to be independent of the options for topside density profiles. However, above 300 km, the IRI-2012 model electron density profile does not show agreement with COSMIC measurements. The observations (COSMIC and GPS) and IRI-2012-based data of TEC and electron density profiles were also analyzed during quiet and storm periods. The analysis showed that the IRI model does not represent the impact of storms, while observations show the impact of storms on the low-latitude ionosphere. This suggests that significant improvements in the IRI model are required for estimating behavior during storms, particularly in low-latitude regions.

The upward looking ionospheric total electron content (TEC) from the MetOp‐A and TSX satellites during 2008–2015 has been used to systematically study the longitudinal variations of the topside ionosphere and plasmasphere. The results of this study are summarized as follows: (1) There are significant longitudinal variations in the topside ionosphere and plasmasphere at low latitudes. The TEC maximum during the June solstice over the Western and Central Pacific Ocean corresponds to a TEC minimum at the same location during the December solstice, but the opposite behavior occurs over South America and the Atlantic Ocean. (2) During the solstices, the relative longitudinal variations in the geomagnetic equatorial region do not have a strong dependence on local time and solar activity. (3) The TEC in the winter hemisphere decreases with increasing solar activity, especially at higher altitudes and at night. The topside TEC depletion with solar activity depends on longitude. (4) The solstice‐like longitudinal pattern lasts much longer than the equinox‐like patterns, with the June solstice pattern lasting the longest. Furthermore, the equinox‐like longitudinal patterns occur in March when expected, whereas they extend from the autumnal equinox until the end of October. (5) The longitudinal variations of upward looking TEC are different from the corresponding longitudinal variations of electron densities around the F2 peak and orbital altitudes. This indicates that the topside ionosphere structure is strongly influenced by the physical processes in the topside region, rather than being a pure reflection of the ionospheric F2 peak structure.

The present paper investigates the alterations in ionospheric Total Electron Content (TEC) over a low latitude location Bangalore (Geographic latitude 12.9 ∘ N {12.9^{\circ }}\hspace{2.38387pt}\text{N} and longitude 77.6 ∘ E {77.6^{\circ }}\hspace{2.38387pt}\text{E} ; Geomagnetic latitude 4 . 5 ∘ N 4.{5^{\circ }}\hspace{2.38387pt}\text{N} ) in India, corresponding to the new Moon and full Moon days which are associated with abnormality in the eastward Equatorial Electrojet (EEJ) currents. It has been well established that even during certain geomagnetic quiet days, the EEJ current direction is reversed, resulting in a westward electrojet current called Counter Electrojet (CEJ) which is more prominent around the new Moon and full Moon days, favored by Sun–Moon–Earth alignments and lunar orbital characteristics. The Global Positioning System (GPS) derived TEC at Bangalore is investigated for full Moon and new Moon and their adjacent days during the period 2008–2015. The presence of CEJ during these days suggests the foremost role of driving EEJ current over the equator in the alterations of spatiotemporal distributions of TEC over the low latitude region. The deviations in quiet time TEC during new Moon and full Moon days are quantified in this study that may give a thrust towards modeling of lunar tidal effects in the flipped ionospheric parameter over the Indian region. The study would also support analysis of future solar eclipse effects on ionosphere those involve additional photoionization production/recombination processes corresponding to the passage of lunar shadow and cooling effects. Moreover, the results underpin modeling and mitigation of ionospheric error in the satellite-based positioning, navigation, and communication applications.

Well organized and systematic study of sun-earth connection is vital. The fact that the state and conditions of space are influenced by solar activity, makes the space weather domain a field of vibrant research. Solar flares are rapid expulsions of electromagnetic radiation from the Sun's active regions. These complex transient excitations, mainly in soft X-rays (0.1 – 10nm), and extreme ultraviolet (10 – 121.6 nm) resulting in ionospheric response, have been a subject of keen interest over decades. Studies show a clear indication of Coronal Mass Ejections (CMEs) associated with flares and prominences. This is of prime importance, as the research on flare associated CMEs does have some underlying impacts to be revealed. The sudden enhancement of X-ray and extreme ultraviolet irradiance during flares raises the density of the ionosphere through enhanced photoionization. Sudden ionospheric disturbances due to the enhancement of plasma density is crucial and the total electron content (TEC) is a potent measure of the ionospheric response. Present study focuses on the analysis of ionospheric plasma irregularities and TEC variation due to M and X class solar flares in the beginning of solar cycle 25. We considered intense flares in the period 2019 - 2024, due to the solar activity growth at the ascending part of the solar cycle 25. Out of these, 15 M class and 15 X class flares are chosen to study plasma instabilities and TEC variations. On the basis of multiple observations from GNSS receivers and satellite missions, we present how flare characteristics affect flare responses in the ionosphere and the formation of large-scale travelling ionospheric disturbances, during intense solar flares. The estimation of enhanced TEC (ΔTEC) shows that the peak enhancement in TEC is highly correlated with peak enhancement in X-ray flux during solar flares. Plasma density shows significant escalations on flare days than on non-flare days. More intense X-class flare provoked a more significant response in the ionosphere than the less intense M class flare. In addition to this, our study also expands in relating the same to flare associated CMEs in the given solar cycle. The CMEs whose source regions are known, can be used to draw out valid conclusions on CME - flare association and how this impacts the ionospheric responses. The growing space weather effects has also led to an increase in space weather research that aims to enumerate the sun-earth connection more precisely. The investigation on variation of both TEC and plasma density leads to better understanding of the ionospheric response to flare activity to a remarkable extent.

The Global Positioning System (GPS) applications are highly vulnerable to the ionospheric space weather effects. Modelling and forecasting the ionospheric effects such as time delays for GPS signals are important for real time alerts of space weather effects on GPS services. In the present work, the performance of Neural Networks (NN) model is compared with International Reference Ionosphere (IRI) models. The ionospheric Total Electron Content (TEC) observations have been collected during 2015 year, descending phase of 24th solar cycle, over three Indian low latitude GPS stations namely, Bengaluru (Geographic coordinates: 13.02°N and 77.57°E), near to geomagnetic equator, Guntur (Geographic coordinates: 16.37°N and 80.37°E), which is at Equatorial Ionization Anomaly (EIA) and Lucknow (Geographic coordinates: 26.83°N and 80.92°E), which is beyond EIA region. The performance of NN model in predicting the ionospheric TEC values is compared with IRI (IRI-2012 and IRI-2016) models during test period, October–December 2015 over three Indian low latitude regions. It is observed that IRI models (IRI-2012 and IRI-2016) have shown more the temporal differences with GPS-VTEC during sunrise hours compared to sunset hours over three low latitude regions. The performance of IRI-2016 model has apparently better than IRI-2012 model. However, it is observed that IRI-2016 model has large discrepancies over Bengaluru and Guntur station due to high VTEC fluctuations at equatorial and low latitudes. The NN models are well predicted the measured diurnal mean VTEC variations with the less errors, ±5 TECU but the differences of IRI models are ±15 TECU over all the three stations. Later, GPS-data for 10 years, 2009–2018, is collected over Bengaluru station during 24th solar cycle. The performance of NN model is validated during 2016, 2017 and 2018 years over Bengaluru GPS station. The error measurements and experimental results reported that the measured GPS-VTEC values are well predicted by NN model compared to IRI-2016 model over equatorial and low latitude GPS stations.

Ionospheric peak electron density (NmF2) and total electron content (TEC) are the essential measures of ionospheric variability for modeling their effects on navigation and communication system applications. The global and regional models have their limitations in predicting ionospheric variations at the low latitude Indian region, mainly due to the anomalous electron density gradients and equatorial ionization anomaly (EIA) effects. In this paper, ionospheric TEC characteristics are modeled based on canonical correlation analysis (CCA) with Global Positioning System (GPS)-TEC observations and NmF2 values at a northern low latitude station Bangalore (13.02° N and 77.57° E) during the 2017 period. The decomposed CCA modes consist of CCA patterns and their corresponding amplitudes. The short-term variations (diurnal) are reproduced by the CCA patterns, whereas the long-term variations (yearly) are reproduced by their corresponding amplitudes. The first three CCA modes represent the ionospheric features such as diurnal, sunrise and sunset enhancements, semiannual, annual, and solar-cycle variations. Further, the temporal structures of NmF2 are effectively replicated by the CCA model. NmF2 (CCA) showed relatively higher linearity (0.99) and lower RMSE (0.31 TECU), whereas NmF2 (IRI2016) showed lower linearity (0.92) and higher RMSE (1.45 TECU) with the measured-NmF2 values. Hence, the CCA approach could be an effective method for characterizing the NmF2 variations over the low latitude region.

Anomaly effects of 6–10 September 2017 solar flares on ionospheric total electron content over Saudi Arabian low latitudes

<p>The present study investigates the variation of Total Electron Content (TEC) using Global Positioning System (GPS) satellites from four equatorial to mid-latitudes stations over a period of one year. The stations are Port Blair (11.63°N, 92.70°E), Agartala (23.75°N, 91.25°E), Lhasa (29.65°N, 91.10°E) and Urumqi (43.46°N, 87.16°E). The diurnal, monthly and seasonal variations of TEC have been explored to study its latitudinal characteristics. Analysis of TEC data from these stations reveals the characteristics of latitudinal variation of Equatorial Ionospheric Anomaly (EIA). To validate the latest IRI 2012 model, the monthly and seasonal variations of GPS-TEC at all the four stations have been compared with the model for three different topside options of electron density, namely, NeQuick, IRI-01-corr and IRI-2001. TEC predictions from IRI-2001 top side electron density option using IRI 2012 model overestimates the observed TEC especially at the low latitudes. TEC from IRI- NeQuick and IRI-01-corr options shows a tendency to underestimate the observed TEC during the day time particularly in low latitude region in the high solar activity period. The agreement between the model and observed values are reasonable in mid latitude regions. However, a discrepancy between IRI 2012 derived TEC with the ground based observations at low latitude regions is found. The discrepancy appears to be higher in low-latitude regions in comparison to mid latitude regions. It is concluded that largest discrepancy in TEC occur as a result of poor estimation of the hmF2 and foF2 from the coefficients.</p>

Performance evaluation of ionospheric time delay forecasting models using GPS observations at a low-latitude station

The Total Electron Content (TEC) is a vital and most dominant ionosphere parameter that can cause Global Positioning System (GPS) signal delays, signal degradation and in extreme cases loss of lock. This results into inefficient operations of ground and space based Global Navigation Satellite System (GNSS) applications. Ionosphere range delay on GPS signals is a major error source for GPS positioning and Navigation. Earlier research has shown that the ionosphere is highly variable at low latitude and equatorial regions. Since India located near to the equator, the gradient of equatorial ionization anomaly between the through and the crest is very sharp, which results in large variation of ionospheric electron content. In this thesis the seasonal variation of ionosphere TEC is compared for several stations (Bangalore(12.96°N, 77.5667°E), Hyderabad (17.36°N, 78.47°E), Lucknow (26.8000° N, 80.9000° E), Port Blair (11.6683° N, 92.7378°E)) in India from 2013 to 2014. The observed TEC from GPS is compared with those derived from the International Reference Ionosphere (IRI)-2012 model (IRI-NeQuick and IRI-2001). From the Results we observed that TEC achieves its highest value during the summer, moderate TEC values in the winter and minimum in equinox seasons. And also observed that as the longitude increases the TEC variability is more in the ionosphere. The study of TEC variability is, therefore useful for GNSS users in order to minimize errors where high level of accuracy in measurements is required.

Ionospheric total electron content response to September-2017 geomagnetic storm and December-2019 annular solar eclipse over Sri Lankan region

Development of multivariate ionospheric TEC forecasting algorithm using linear time series model and ARMA over low-latitude GNSS station

Evaluation of long-term variability of ionospheric total electron content from IRI-2016 model over the Indian sub-continent with a latitudinal chain of dual-frequency geodetic GPS observations during 2002 to 2019