Abstract This study investigates characteristics of ionospheric irregularities over the East–West Asian equatorial region using the Rate of TEC Index (ROTI) derived from Global Navigation Satellite System (GNSS) measurements. Data from four stations (GUAM, PIMO, CUSV, and IISC) were analyzed for 2008–2023, covering solar cycle (SC) 24 and the ascending phase of SC 25. While our findings are generally aligned with previous research, this work presents new insights into the complex behavior of ionospheric scintillation in this sector. A key finding is the significant spatial variability in irregularity occurrence, with stations at similar magnetic dip (11–13°) exhibiting varying activity levels. Notable longitudinal asymmetries were also identified, particularly at GUAM, which shows reduced autumnal activity, likely due to local differences in Pre‐Reversal Enhancement (PRE) and magnetic declination. Our study shows a clear daily pattern: scintillation begins after sunset (18:00–19:00 LT), peaks in the late evening (20:00–21:30 LT), and declines by early morning. A slight increase in ROTI is consistently observed just before sunrise at all locations. Temporally, results show dependence on the 11‐year SC and a distinct seasonal pattern, with activity concentrated in equinoctial months. The spring maximum is generally stronger than the autumn one across stations. Finally, although the long‐term trend follows the SC, the relationship is non‐linear. Outliers, such as anomalous activity in 2019, demonstrate that while the Sunspot Number (SSN) is a primary long‐term driver, scintillation is also modulated by short‐term geophysical phenomena.

This study investigates the response of the South American ionosphere to the December 19-20, 2015, geomagnetic storm using multi-instrument satellite and ground-based data. An interplanetary shock triggered prompt penetration electric fields (PPEFs) during the storm's initial phase, initiating rapid DP2 currents and significant equatorial electrojet (EEJ) fluctuations, particularly in Jicamarca, Peru. Our analysis shows that dayside field-aligned currents (FACs) are the primary drivers of the observed DP2 fluctuations. The South Atlantic Magnetic Anomaly (SAMA) also induced a westward geomagnetic gradient-induced current at the equatorward boundary, which suppressed the EEJ current at Sao Luiz during the magnetically quiet period. During the storm's main phase, eastward PPEFs enhanced ionospheric irregularities at several Global Positioning Satellite (GPS) stations: Sao Luiz (14.8 %), Cuiaba (11.4 %), and Jatai (15.5 %) in Brazil; Tucuma (33.6 %) and Rio Grande (33.2 %) in Argentina; and all Peruvian GPS stations (5.8-57.6 %), with Arequipa showing the highest percentage. Conversely, irregularities were inhibited at Eusebio (-31.5 %), Sao Jose dos Campos (-11.8 %), and Campo Grande (-4.8 %) in Brazil, and Rosario (-9.4 %) and Villegas (-0.8 %) in Argentina, relative to a magnetically quiet day, which was attributed to the interplay between westward disturbance dynamo electric fields (DDEF) and PPEF. Joule heating, peaking at 14:35 UT on 20 December drove equatorward disturbance winds that generated the DDEF and modulated irregularities during the recovery phase. Westward DDEF suppressed post-sunset irregularities across most Brazilian and Argentine stations (-50.2 % to-10.1 %), but slightly enhanced post-midnight ionospheric irregularities at Cuiaba (+4.3 %) and Tucuma (+21.1 %). All Peruvian stations recorded post-midnight enhancements (+14.8 % to +136.7 %), with Arequipa showing the highest increase. We quantified the delayed magnetic response of the disturbance dynamo (Ddyn) relative to Joule heating, revealing propagation delays of approximately 6, 8.5, and 8.2 h in Brazil, Argentina, and Peru, respectively. Ddyn exhibited strong spatiotemporal variability, including spatial anomalies associated with the SAMA. The Peruvian sector dominated the Ddyn power (59.0 %), followed by Brazil (35.1 %) and Argentina (5.9 %). Evidence of interhemispheric FAC asymmetry, attributed to seasonal variability, was also observed. These findings significantly advance our understanding of storm-time low-latitude electrodynamics and their regional variability. (c) 2025 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

The Available TEC data from seven (07) GPS stations located in the West African zone were used to determine the calculated temporal distribution of Equatorial Plasma Bubble (EPB) occurrence. We also used the ROTI to detect and evaluate irregularities associated with plasma bubbles. The detection and localization of EPBs were achieved by applying software for the detection and localization of sub-ionized plasma bubbles. The study reveals a variability of EPBs which depend on local time of day, season and solar activity. The diurnal variation of EPBs follows the diurnal variation of the ROTI. It shows EPBs associated with a ROTI higher than 3 TECU/mn at night between sunset around 19.00LT and local midnight. They are lower during the few hours after midnight. Seasonal variation shows a significantly higher occurrence during the two equinoxes than during the two solstices. The annual variation of EPBs occurrence is higher during periods of high solar activity (2001, 2014, 2024) and low or virtually absent during periods of solar minima (2008-2009, 2018-2019).

This manuscript examines the performance of two ionospheric models, AfriTEC and NeQuick 2, at station BF01 (lat. 12.3714° N, long. −1.5197° W) in Ouagadougou, Burkina Faso, situated in the West African equatorial region. The study is aimed at aiding in selecting an appropriate ionospheric model for this region, where in situ data are scarce. It involves comparing the VTEC values derived from RINEX files obtained at station BF01 with those provided by the two models, AfriTEC and NeQuick 2. Two periods were distinguished: a period of high solar activity (Rz ≥ 50) between 2013 and 2015 and a period of low solar activity (Rz < 50) from 2016 to 2021. The results show that during periods of high solar activity, both models underestimate VTEC with relative differences of up to −60%. However, AfriTEC is closer to the RINEX values during hours of strong sunlight. Between 2016 and 2021, the performance of the models gradually improves, with AfriTEC being more stable and more consistent with the RINEX data, especially during periods of VTEC peak. NeQuick2 performs less well during hours of strong sunshine and at night, with greater deviations from the RINEX data. From this study, it emerges that AfriTEC is the most suitable ionospheric model for predicting VTEC at station BF01.

This study investigates the ionospheric response to four major geomagnetic storms that occurred on 14 July 2012, 17 March 2013, 2 October 2013, and 27 February 2014, focusing on variations in the vertical total electron content (VTEC). VTEC data were obtained from 13 GNSS stations distributed across low, mid, and high-latitude regions along longitudes between 20E and 40E. For each event, the mean VTEC of the five geomagnetically quietest days of the corresponding month was used as a reference to characterize storm-time deviations.The results reveal diverse and complex ionospheric responses. The 14 July 2012 storm is characterized by a nighttime VTEC depletion at the equatorial ionization anomaly (EIA) trough, a transient intensification of the EIA, pronounced oscillations, interhemispheric asymmetries, and a subsequent suppression of the EIA, while high latitudes exhibit persistent depletion. The 17 March 2013 storm shows a pre-storm enhancement of VTEC, followed by oscillatory behavior, a transition from positive to negative storm effects, interhemispheric asymmetries, and EIA suppression. Similarly, the 2 October 2013 storm exhibits an early VTEC enhancement, marked oscillations, high-latitude depletion, and a transition from positive to negative effects at mid-latitudes, with relatively weak responses at low latitudes.

This study examines the deviation in ionospheric total electron content (TEC) over Nepal during 49 geomagnetic storms of solar cycle 24. For this investigation, the daily RINEX files downloaded from the UNAVCO website are used to calculate the TEC on GPS measurements only. The study shows the increase and decrease in TEC during the event days. The increase or decrease in percentage TEC is compared to a reference quiet day. Among 49 selected storms in 26 stormy days the TEC has increased and in 23 stormy days the TEC has decreased. The maximum deviation in TEC is found during the recovery phase geomagnetic storm of 2010-08-04 and 2012-07-16. During storm on 2010-08-04 it is 101.97

A processing application has been developed to detect and characterize localized plasma decreases: Equatorial plasma bubbles. The algorithm used is based on an automated search for negative STEC variations during a GPS satellite passage. First, an example of detection is shown. The method used has been applied to available data from seven (7) stations in West Africa, and the results over several years of measurements are presented. A study of spatial behavior was also carried out. The results show that the location of EPB bubbles depends on magnetic position. Bubbles are more present near the position of the North and South Equatorial Anomaly (EIA) ridges, but exist near the magnetic equator. Beyond 30° of inclination, bubbles are rarely present. The study of EPB characteristics also revealed durations mostly between 10 and 25 min, and maximum depths between 5 and 25 TECU.

Numerous raw data concerning the ionosphere exist almost everywhere in Africa. However, these data are underexploited due to the lack of simple methods to extract ionospheric parameters from the data. This paper presents a method for extracting vertical total electron content (VTEC) using Global Navigation Satellite System-Continuously Operating Reference Station (GNSS-CORS) raw data recorded between 01/01/2013 and 12/31/2021 at station BF01 (Latitude = 12.3714 N and Longitude = -1.5197 W) in Ouagadougou, Burkina Faso, located at the trough of ionization in the West African equatorial zone. This station is one of the stations in Burkina Faso that recorded data better continuously during the period of this study. This work involves the determination of VTEC using dual-frequency GPS measurements. Thus, the raw GNSS-CORS data in "T02" format were first converted into "Receiver INdependent Exchange Format" (RINEX) into time files in steps of 1 s. These files were then reorganized into daily files with 30 s steps, before being used for VTEC extraction. For this purpose, scripts were developed and run in Matlab. The extracted VTEC is saved in text and graphics files. With the result obtained, it is possible to dimension some fundamental characteristics of the ionosphere at low latitudes. It is also possible to produce spatio-temporal maps of TEC variations over Burkina Faso and even for the whole of West Africa at least if the CORS networks of neighboring countries are known. Key words: Global navigation satellite system-continuously operating reference station (GNSS-CORS), vertical total electron content (VTEC), Receiver INdependent Exchange Format (RINEX), ionosphere.

This paper presents the regular variations of the Vertical Total Electron Content (VTEC) at station BF01 (Lat. = 12.3714 N and Long. = -1.5197 W) in Ouagadougou (Burkina Faso) located in the trough of the equatorial ionisation anomaly near the northern ridge of the West African zone. The period studied runs from 2013 to 2021. The VTEC is extracted from the raw Global Navigation Satellite System - Continuously Operating Reference Station (GNSS-CORS) data recorded at station BF01 during the study period. The analysis of diurnal variations showed three types of profiles with a dominant profile being the Dome type. Generally speaking, the daily VTEC profiles show a minimum at dawn between 4:00 UT and 6:00 UT followed by a rapid increase from sunrise to a maximum around 15:00 UT, then a gradual decrease in the late afternoon and during the night to reach the minimum just before sunrise. On some days, a second nocturnal maximum is observed between 19:00 UT and 20:00 UT. Seasonal and annual variations revealed that for each year, the highest VTEC values are observed during the equinox, although with higher values at the March equinox. It was also found that the lowest VTEC values are recorded at the summer solstice in each year. The regular variations in the VTEC at station BF01 during the study period therefore highlight three anomalies: the semi-annual anomaly, the equinoctial asymmetry and the winter anomaly. Furthermore, the VTEC at station BF01 in Ouagadougou evolves in phase with the sunspot cycle.

The quasi-biennial oscillation (QBO) signals at two Equatorial ionization anomaly (EIA) crests of the ionosphere have been studied using the continuous GNSS network data in Vietnam and adjacent regions during the 2008- 2021 period. The monthly mean EIA crests amplitudes are calculated. The Lomb-Scargle periodogram method was applied to the residuals of the EIA crests magnitudes, DTEC, which are obtained from subtracting the fittings with solar index, F10.7. The Lomb-Scargle spectrum shows the quasi-biennial component in the residuals DTEC with the picks at 18, 25, and 29-30 months. The ionosphere QBO at two EIA crests was found out by the band-pass filter centered at 25 months with haft-power points at 17 and 33 months. The zonal wind data at 50 hPa (~ 20 km) of the tropical equatorial stratosphere is used as the stratosphere QBO (SQBO) to consider the relationship between the SQBO and the obtained ionosphere QBO. The direct comparison and the cross wavelet transform of the SQBO and ionosphere QBO data series show that during 2008-2009, the ionosphere QBO signal is low, the SQBO and ionosphere QBO are in phase during the 2010-2013 and 2018-2021 periods, but anti-phase during the 2014-2017 period. For the 2010-2013, 2014-2017 and 2018-2021 periods, the correlation coefficients are 0.623, 0.637, -0.646 in the northern crest, and 0.571, 0.53, -0.530 in the southern crest, respectively. Furthermore, we also observed that the SQBO and the ionosphere QBO signals were shortened during the 2015-2016 period, approximately 1.5 years. Previous studies showed that the ENSO (El Niño - Southern Oscillation) warm phase, also known as El-Niño existed during 2015-2016. The results of this study allow us to assume that the SQBO influences the ionosphere QBO. Our results show that the SQBO is the main factor affecting the ionospheric QBO at two EIA crests. However, the physical theoretical interpretation of the mechanisms of action is a challenge for scientists and requires further research.

Space weather science has been a growing field in Africa since 2007. This growth in infrastructure and human capital development has been accompanied by the deployment of ground-based observing infrastructure, most of which was donated by foreign institutions or installed and operated by foreign establishments. However, some of this equipment is no longer operational due to several factors, which are examined in this paper. It was observed that there are considerable gaps in ground-based space-weather-observing infrastructure in many African countries, a situation that hampers the data acquisition necessary for space weather research, hence limiting possible development of space weather products and services that could help address socio-economic challenges. This paper presents the current status of space weather science in Africa from the point of view of some key leaders in this field, focusing on infrastructure, situation, human capital development, and the research landscape.

In this article, we analyze vertical total electron content (VTEC) over Nepal for 4 periods: March 14–25, 2015, June 18–29, 2015, May 24–June 4, 2017, and September 3–14, 2017. In each period, there are quiet geomagnetic days and intense geomagnetic stormy days. The VTEC observed during these periods has observed both positive and negative ionospheric storms. We compared VTEC Receiver-Independent Exchange Format (RINEX) observations with the Global Ionospheric Map (GIM), Centre for Orbit Determination in Europe (CODE), and IGS working group (IGSG). We found in RINEX observation of the VTEC a noon bite out profile with predominance of morning and afternoon peaks and a nighttime peak, but this was not noticeable clearly with CODE and IGSG models. The comparison between RINEX TEC, CODE, and IGSG models shows that the GIM model does not estimate RINEX VTEC over Nepal. The disagreement between VTEC CODE/IGSG and VTEC RINEX is important during geomagnetically quiet periods, while there is good agreement between VTEC CODE/IGSG and VTEC RINEX during strong geomagnetic storms. We also find a greater disagreement between the models and the data at the equinoxes when the VTEC is larger. It is, therefore, necessary to introduce data from Nepal stations into the models CODE and IGSG in order to improve them.

Scintillation due to ionospheric plasma irregularities remains a challenging task for the space science community as it can severely threaten the dynamic systems relying on space-based navigation services. In the present paper, we probe the ionospheric current and plasma irregularity characteristics from a latitudinal arrangement of magnetometers and Global Navigation Satellite System (GNSS) stations from the equator to the far low latitude location over the Indian longitudes, during the severe space weather events of 6–10 September 2017 that are associated with the strongest and consecutive solar flares in the 24th solar cycle. The night-time influence of partial ring current signatures in ASYH and the daytime influence of the disturbances in the ionospheric E region electric currents (Diono) are highlighted during the event. The total electron content (TEC) from the latitudinal GNSS observables indicate a perturbed equatorial ionization anomaly (EIA) condition on 7 September, due to a sequence of M-class solar flares and associated prompt penetration electric fields (PPEFs), whereas the suppressed EIA on 8 September with an inverted equatorial electrojet (EEJ) suggests the driving disturbance dynamo electric current (Ddyn) corresponding to disturbance dynamo electric fields (DDEFs) penetration in the E region and additional contributions from the plausible storm-time compositional changes (O/N2) in the F-region. The concurrent analysis of the Diono and EEJ strengths help in identifying the pre-reversal effect (PRE) condition to seed the development of equatorial plasma bubbles (EPBs) during the local evening sector on the storm day. The severity of ionospheric irregularities at different latitudes is revealed from the occurrence rate of the rate of change of TEC index (ROTI) variations. Further, the investigations of the hourly maximum absolute error (MAE) and root mean square error (RMSE) of ROTI from the reference quiet days’ levels and the timestamps of ROTI peak magnitudes substantiate the severity, latitudinal time lag in the peak of irregularity, and poleward expansion of EPBs and associated scintillations. The key findings from this study strengthen the understanding of evolution and the drifting characteristics of plasma irregularities over the Indian low latitudes.

This paper presents the variations of the rate of change of Total Electron Content (TEC) index (ROTI), characterizing the occurrence of ionospheric plasma irregularities over Vietnam and neighboring countries in the Southeast Asian region using the continuous GPS data during the 2008-2018 period. The results showed that the occurrence of strong ROTI in all stations is maximum in equinox months March/April and September/October and depends on solar activity. The ROTI is weak during periods of low solar activity and strong during periods of high solar activity. There is an asymmetry between the two equinoxes. During maximum and declining phases of 2014-2016, occurrence rates in March equinox are larger than in September equinox, but during the descending period of 2010-2011, the occurrence rates in September equinox at almost all stations are larger than in March equinox. The correlation coefficients between the monthly occurrence rate of irregularities and the F10.7 solar index at the stations in the equatorward EIA crest region are higher than at those in the magnetic equatorial and the poleward EIA crest regions. The irregularity occurrence is high in the pre-midnight sector, maximum between 2000 LT to 2200 LT. The maximum irregularity occurrence is located around 4-5° degrees in latitude equator-ward away from the anomaly crests.

This study presents the first prediction results of a neural network model for the vertical total electron content of the topside ionosphere based on Swarm-A measurements. The model was trained on 5 years of Swarm-A data over the Euro-African sector spanning the period 1 January 2014 to 31 December 2018. The Swarm-A data was combined with solar and geomagnetic indices to train the NN model. The Swarm-A data of 1 January to 30 September 2019 was used to test the performance of the neural network. The data was divided into two main categories: most quiet and most disturbed days of each month. Each category was subdivided into two sub-categories according to the Swarm-A trajectory i.e. whether it was ascending or descending in order to accommodate the change in local time when the satellite traverses the poles. Four pairs of neural network models were implemented, the first of each pair having one hidden layer, and the second of each pair having two hidden layers, for the following cases: 1) quiet day-ascending, 2) quiet day-descending, 3) disturbed day-ascending, and 4) disturbed day-descending. The topside vertical total electron content predicted by the neural network models compared well with the measurements by Swarm-A. The model that performed best was the one hidden layer model in the case of quiet days for descending trajectories, with RMSE = 1.20 TECU, R = 0.76. The worst performance occurred during the disturbed descending trajectories where the one hidden layer model had the worst RMSE = 2.12 TECU, (R = 0.54), and the two hidden layer model had the worst correlation coefficient R = 0.47 (RMSE = 1.57),In all cases, the neural network models performed better than the IRI2016 model in predicting the topside total electron content. The NN models presented here is the first such attempt at comparing NN models for the topside VTEC based on Swarm-A measurements. (C) 2020 COSPAR. Published by Elsevier Ltd. All rights reserved.

This paper presents an international cooperation which has successfully developed research capacities in the scientific disciplines of sun–earth relations and space weather in many countries over the world during the past decades. This success was based on the deployment of scientific instruments in countries that did not have them, on the sharing of knowledge and research tools, on thesis supervision and on the integration of researchers trained in their country. This article will only focus on aspects of training conducted by ICTP, Boston College, ICG, SCOSTEP and GIRGEA. We will highlight what has been enhanced in international cooperation to achieve this success and what remains to be done.

We use GPS networks to measure the vertical Total Electron Content (VTEC) variations at low latitude, in three longitude sectors: America, Europe-Africa and Asia, collected during the period 2013-2017. This period corresponds to the increasing phase of the solar cycle 24 (SC#24) observed around 2013-2014 as well as the decreasing phase around 2014-2017. Our results discussed a morphological analysis of regular variations in ionization during different phases of solar activity: daytime variations, seasonal and semi-annual variations and variations based on the solar cycle 24 in three longitude sectors. In all longitude sectors, the highest VTEC values are displayed during the two months of the spring, located after sunrise and before sunset. The lowest values are found during the summer and winter seasons. We found that the winter anomaly and the presence of equinoxial peaks are the most pronounced effects in VTECs in the increasing and decreasing phase of the SC#24. A strong asymmetry is detected between equinoxial peaks and the location of peaks occurring in March/April and October/November at maximum in the solar flux variations during the increase phase. We show that the daily VTEC maximum values were registered between 14:00 and 16:00 LT and the minimum values between 4:00 and 6:00 LT. Double ionization peak in the morning and evening is observed in VTEC annual variations, due to the proximity of the equatorial fountain stations. From the statistical analysis part, we observed practically the same distribution of the different classes of VTEC (two peaks, bell-shaped and plateau-shaped) variations in the three sectors of longitude. These observations indicate longitudinal variation in the presence of the winter anomaly in the Equatorial Ionized Anomaly (EIA) region. Additionally, we can note a longitudinal variation of the spring-autumn VTEC asymmetry in the EIA region during the five years 2013-2017. We observe also that the occurrence of nocturnal peak recorded around 19 local time (LT) shows the same characteristics as the vertical drift E x B (B: magnetic field is perpendicular to E: electric field.) with respect to solar cycle, season and longitude. Three essential characteristics we noted: 1) the occurrence of the nocturnal peak generally follows the solar cycle. 2) The occurrence of the nocturnal peak is generally stronger at the equinoxes than at the solstices. 3) The occurrence of the nocturnal peak is stronger in the Europe-Africa and America sectors than in the Asia sector. As a result, nocturnal peak occurrence is well related to the PRE at the origin of the GNSS signal scintillations. (C) 2021 COSPAR. Published by Elsevier B.V. All rights reserved.

In this study, we analyse the climatology of ionosphere over Nepal based on GPS-derived vertical total electron content (VTEC) observed from four stations as defined in Table 1: KKN4 (27.80∘ N, 85.27∘ E), GRHI (27.95∘ N, 82.49∘ E), JMSM (28.80∘ N, 83.74∘ E) and DLPA (28.98∘ N, 82.81∘ E) during the years 2008 to 2018. The study illustrates the diurnal, monthly, annual, seasonal and solar cycle variations in VTEC during all times of solar cycle 24. The results clearly reveal the presence of equinoctial asymmetry in TEC, which is more pronounced in maximum phases of solar cycle in the year 2014 at KKN4 station, followed by descending, ascending and minimum phases. Diurnal variations in VTEC showed the short-lived day minimum which occurs between 05:00 to 06:00 LT (local time) at all the stations considered, with diurnal peaks between 12:00 and 15:00 LT. The maximum value of TEC is observed more often during the spring equinox than the autumn equinox, with a few asymmetries. Seasonal variation in TEC is observed to be a manifestation of variations in solar flux, particularly regarding the level of solar flux in consecutive solstices.

The thickness parameters that most empirical models use are generally defined by empirical relations related to ionogram characteristics. This is the case with the NeQuick model that uses an inflection point below the F2 layer peak to define a thickness parameter of the F2 bottomside of the electron density profile, which is named B2. This study is focused on the effects of geomagnetic storms on the thickness parameter B2. We selected three equinoctial storms, namely 17 March 2013, 2 October 2013 and 17 March 2015. To investigate the behavior of the B2 parameter before, during and after those events, we have analyzed variations of GNSS derived vertical TEC (VTEC) and maximum electron density (NmF2) obtained from manually scaled ionograms over 20 stations at middle and low latitudes of Asian, Euro-African and American longitude sectors. The results show two main kinds of responses after the onset of the geomagnetic events: a peak of B2 parameter prior to the increase in VTEC and NmF2 (in ~60% of the cases) and a fluctuation in B2 associated with a decrease in VTEC and NmF2 (~25% of the cases). The behavior observed has been related to the dominant factor acting after the CME shocks associated with positive and negative storm effects. Investigation into the time delay of the different measurements according to location showed that B2 reacts before NmF2 and VTEC after the onset of the storms in all the cases. The sensitivity shown by B2 during the studied storms might indicate that experimentally derived thickness parameter B2 could be incorporated into the empirical models such as NeQuick in order to adapt them to storm situations that represent extreme cases of ionospheric weather-like conditions.

Abstract. In this study, we analyze the climatology of ionosphere over Nepal based on GPS derived VTEC observed from four stations: KKN4 (27.80° N, 85.27° E), GRHI (27.95° N, 82.49° E), JMSM (28.80° N, 83.74° E), DLPA (28.98° N,82.81° E) during years 2008 to 2018. The study illustrates the diurnal, monthly, annual, seasonal and solar cycle variations of VTEC during all time of solar cycle 24. The results clearly revel the presence of equinoctial asymmetry in TEC which is more pronounced in maximum phases of solar cycle in year 2014 at KKN4 station followed by descending, ascending and minimum phases. Diurnal variation of VTEC showed short-lived day minimum which occurs between 5:00 to 6:00 LT at all the stations considered with diurnal peak between around 12:00 to 15:00 LT. The maximum value of TEC is observed during spring equinox than autumn equinox with a few anomalies. Similarly, winter anomalies are noticed during increasing and maximum phases of the solar cycle2011 and 2014 from almost all stations taken in the study.