GPS TEC Research Articles

Prediction of GPS TEC during the X9.3 Solar Flare for DGAR low latitude station by using OKSM

The effect of solar flares on the ionospheric regions of earth, which in turn affects signals of the various Global Navigation Satellite Systems, is a very important criterion to be considered in satellite communication. In this paper, we are investigating the prediction capability of the Kriging based Model and its effect on calculating the signal delay of GPS system on 6.9.2017during which NASA have observed a solar flare which have recorded X9.3 on solar storm scale. The GPS data used in this paper for prediction of TEC is taken from the DGAR Island station. The Vertical Total Electron Content data for GPS is predicted from 3rd September 2017 to 7th September 2017 by using the previous collected 6 days of TEC data of the low latitude DGAR station from IONOLAB and also by using the input parameters like Kp index, SSN, Ap index and Dst index. The predicted results are validated by comparing them with IRI 2016 and IRI PLAS 2017 model collected during the same dates.

GPS TEC Scintillations and TEC depletion as seen from Hetauda and NAST, Nepal for 2016

We analyzed Global positing System Total Electron Content (GPS-TEC) data of stations Hetauda (27.414 0N and 85.051 0E) and NAST (27.656 0N and 85.327 0E), Nepal which are a part of UNAVCO.We obtained the variation of rate of TEC index (ROTI) and S4 index throughout the year 2016 for the two stations involved for the 32 all the Pseudo-Random Noise (PRN) numbers barring PRN number 4 which was inactive throughout the year. We chooses two stations data which are almost 40 km in distance and correlated the value of ROTI index with ROTI index and S4 index with S4 index and found that the ROTI index of Hetauda is well correlated with ROTI index of NAST with the highest being 94% for PRN 10 and the lowest being -13% for PRN 1. An extremely low correlation between S4 index of Hetauda and S4 index of NAST was observed with the highest correlation being 8% in PRN 3, 32 and the lowest correlation of -15% in PRN 12.
 BIBECHANA 18 (2) (2021) 87-94

Statistics of GPS TEC at the northern EIA crest region of the Indian subcontinent during the solar cycle 24 (2013-2018): comparison with IRI-2016 and IRI-2012 models

Statistics of GPS TEC at the northern EIA crest region of the Indian subcontinent during the solar cycle 24 (2013-2018): comparison with IRI-2016 and IRI-2012 models

Daytime Equatorial Spread F‐Like Irregularities Detected by HF Doppler Receiver and Digisonde

AbstractDaytime equatorial spread F (ESF) is not as common as nighttime ESF due to the presence of a highly conducting E‐layer during the daytime which counteracts the development of F‐layer plasma irregularities. This study presents two rare daytime ESF‐like events which occurred over an interval ∼2 h and were detected by the HF Doppler receiver located in Lagos (LAG: geographic: 3.27°E, 6.48°N; dip latitude −1.72°) and the Lowell Digisonde at Ilorin (ILR; 4.68°E, 8.50°N; dip latitude −1.25°), managed by Lowell GIRO Data Center (LGDC). Analysis of the first event revealed ∼30 min periodic oscillations in iso‐heights of ionospheric electron density. Shorter period (∼15 min) oscillations appeared simultaneously in HF Doppler measurements and these oscillations lasted nearly 3 h. Close inspection of the ionograms from ILR during this interval (1500–1800 UT) showed the occurrence of small‐scale spreading in the F‐layer trace which varied in altitude as the disturbance progressed. Computation of the linear growth rate of the collisional Rayleigh‐Taylor instability showed that the plasma instability was seeded by a traveling ionospheric disturbance (TID). The characteristics of the second event suggest that horizontal stratifications in plasma density distribution at the reflecting ionospheric layer were responsible for the spread F traces in the ionograms. Analysis of GPS TEC data from Nigeria during these events revealed the presence of wave structures consistent with TIDs.

Analysis of Ionosphere disturbance caused by the Lokon Volcano Eruption using GPS TEC data

Eruption of Mount Lokon has the potential to cause danger to the community. The study of the ionospheric disturbances triggered by Lokon activity is very important to determine eruptive behavior. TEC anomaly before eruption is succesfully detected using correlation methods. Based on GPS TEC data from the GNSS satellite it was concluded that the TEC anomaly occurred three days before the eruption on July 14th, 2011. Using leveling method and polynomial technique, eruption effects on ionosphere were be determined. Eruption on July 2011 caused ionospheric disturbance. These results will be important considerations in decision making related to disaster mitigation

Multi-Experiment Observations of Ionospheric Disturbances as Precursory Effects of the Indonesian Ms6.9 Earthquake on August 05, 2018

Taking the 2018 Ms6.9 Indonesia earthquake as a case study, the ionospheric perturbations in very low frequency (VLF) transmitters recorded by China Seismo-Electromagnetic Satellite (CSES) were mainly investigated, as well as the multi parameters of the plasma and electromagnetic field. The characteristics of electron density (Ne), GPS TEC, ULF electric field, ion drift velocity, and ionosphere height were extracted and compared with the features of the signal-noise ratio (SNR) from VLF transmitters of NWC at the southern hemisphere and JJI at the northern hemisphere. Most disturbances in VLF radio waves occurred along the orbits near the epicenter within 10 days before the earthquake. Along these orbits, we observed simultaneous modulations in the Ne and ULF electric field, as well as the changed ion drifting directions. There was also high spatial correspondence between both SNR and ionospheric height anomalies over the epicentral and its magnetic conjugate regions. Combined with the multi observations, these results suggest that the genesis of perturbations in signals emitted by VLF transmitters on satellite was more likely related to the overlapped electric field in the preparation area of the earthquake.

Multi-instrument observations of SCIPS: 1. ISR and GPS TEC results

An uninterrupted multi-day (6–8 May 2013) ionospheric F-region event with features indicative of medium-scale traveling ionospheric disturbances (MSTIDs) was detected with the Millstone Hill (MH) incoherent scatter radar (ISR). It was later identified, with the addition of Global Positioning System total electron content (GPS-TEC) imaging, as a novel ionospheric phenomenon. This phenomenon is herein termed semi-coherent ionospheric pulsing structures (SCIPS). The presumptive-MSTIDs in this multi-day event had a ~1 h period and were observed during calm-to-minor geomagnetic conditions using both the vertical-looking (Zenith) and steerable (Millstone Hill Steerable Antenna, or MISA) MH ISR systems. To image the MH MSTID events on a larger horizontal scale than is possible with ISR systems alone, a dense network of GPS TEC receivers was leveraged. The ISR-observed event was located in the GPS-TEC data geographically centered on the MH location with a ~100 km resolution (pixel size). However, keogram analysis of the GPS-TEC data revealed that the event had coherency across the continental United States. The same technique additionally exposed similar events occurring globally throughout the observing period. Our multi-instrument approach allows us to conclude that the event was comprised of large-scale and continuously forced, semi-coherent ionospheric pulsing structures (SCIPS) that masqueraded as MSTIDs when viewed locally. The GPS-TEC images show that the SCIPS were stationary in longitude on a global scale, but appeared to propagate in a southward direction in the Northern Hemisphere. It was not possible to obtain direct imaging in the southern hemisphere due to the smaller number of receivers. The SCIPS appear to originate at high latitudes and, in several instances, were coherent across over 10,000 km. The apparent high latitude source location, ubiquity, and large-scale coherence of the SCIPS suggest unexpected impulsive auroral oval sources containing enough energy to continually force the observed MSTID-like structures even during low geomagnetic activity periods.

Responses of the African equatorial ionization anomaly (EIA) to some selected intense geomagnetic storms during the maximum phase of solar cycle 24

This study investigates the morphology of the GPS TEC responses in the African Equatorial Ionization Anomaly (EIA) region to intense geomagnetic storms during the ascending and maximum phases of solar cycle 24 (2012–2014). Specifically, eight intense geomagnetic storms with Dst ≤ −100 nT were considered in this investigation using TEC data obtained from 13 GNSS receivers in the East African region within 36–42°E geographic longitude; 29°N–10°S geographic latitude; ± 20°N magnetic latitude. The storm-time behavior of TEC shows clear positive and negative phases relative to the non-storm (median) behavior, with amplitudes being dependent on the time of sudden commencement of the storm and location. When a storm starts in the morning period, total electron content increases for all stations while a decrease in total electron content is manifested for a storm that had its sudden commencement in the afternoon period. The TEC and the EIA crest during the main phase of the storm is significantly impacted by the geomagnetic storm, which experiences an increase in the intensity of TEC while the location and spread of the crest usually manifest a poleward expansion.

Investigation of ionospheric TEC anomalies caused by space weather conditions

This study examines the influence of space weather conditions on ionospheric TEC variations at different latitudes around the world. According to the space weather condition indices (geomagnetic storm-activity indices, solar activity indices, magnetic field change indices, plasma density and proton flux indices) different time periods were chosen. GPS observations were used to obtain TEC data derived from International GNSS Service (IGS) stations located at northern and southern hemisphere latitude regions (equatorial, mid-latitude and high latitude). GPS TEC data were evaluated associated with the space weather conditions using 15-day running median statistical analysis method. The results showed that besides the commonly used geomagnetic storm-activity and solar activity indices, plasma density, magnetic field change and particle flux indices are also important in determining whether there is any TEC anomaly in the ionosphere. This study illustrated that all indices should be examined in the applications associated with the ionosphere and particularly in the research of pre-earthquake ionospheric anomalies.

Characterization of Ionospheric Delay and Forecasting Using GPS-TEC over Equatorial Region, Malaysia

This paper investigates the characteristic of the ionospheric delay and forecasting using modified statistical Holt-Winter method over Malaysia. This was carried out by using dual frequency GPS Ionospheric Scintillation and TEC Monitor (GISTM) receivers installed at the National University of Malaysia (UKM) (geographic coordinates 2.55°N, 101.46°E and geomagnetic coordinates 7.10°S, 174.05°E), and Langkawi national observatory (Langkawi) (geographical coordinates 6.19°N, 99.51°E and geomagnetic coordinates 3.39°S, 172.42°E), during 2011. In this work, the Holt-Winter forecasting method is modified to provide a better forecasting result over Malaysia. The diurnal, monthly, and seasonal variations of actual ionospheric delay have been analyzed and compared with forecasted ionospheric delay. Based on the results, the diurnal variability of ionospheric delay was maximal mostly between 12:00– 17:00 LT, and minimal nearly at 05:00 LT. The maximum monthly ionospheric delays occurred in October, which is attributed to the geomagnetic storm disturbance that caused increase in ionospheric delay. The lowest seasonal ionospheric delay occurred in the summer and the highest was during the equinox. The maximum ionospheric delay on a quiet day was around 41.9 TECU, while it reached up to 86.6 TECU during the geomagnetic storm. The Holt-Winter method exhibited the highest difference between the measurements and the forecasts in March, with an error of 6%. Hence, the modified Holt-Winter method forecast ionospheric delay effectively during quiet and disturbed periods over Malaysia.

On the Co‐Seismic Ionospheric Disturbances (CIDs) in the Rapid Run Ionosonde Observations Over Allahabad Following Mw 7.8 Nepal Earthquake on April 25, 2015

AbstractWe present high‐resolution ionosonde observations at Allahabad (25.43°N, 81.84°E) near anomaly crest location in India along with GPS TEC to investigate the possible signatures of co‐seismic disturbances (CIDs) in the ionosphere during Mw7.8 Nepal Earthquake that occurred at 06:11:26 UT on 25 April 2015. The epicenter of the earthquake (28.147°N, 84.708°E) was located at ~77 km north‐west of Kathmandu with a shallow depth of 15 km. The mechanical shock disturbances produce Rayleigh waves and Rayleigh wave induced acoustic gravity waves (AGWs) during earthquake which propagate into the ionosphere and produced plasma density fluctuations due to collisions. The manifestation of these waves produces ‘wiggles' or ‘cusps' in the ionograms known as Multiple‐Cusp Signatures (MCS). The detection of multiple cusps in the ionograms at Allahabad indicates the altitude structure of Rayleigh wave and it's induced AGWs. To confirm co‐seismic signatures in ionosonde further, we scaled the ionograms at iso‐density and iso‐heights along with foF2 (MHz) and h'F (km). The periodogram and wavelet analysis suggest the presence of acoustic gravity waves and gravity waves with frequencies in the range of 0.7‐1.5 mHz over the altitude range of 180‐250 km. The foF2 variations show wave like oscillations having frequency of 0.5 mHz after the onset of earthquake. The GPS TEC also show signatures of co‐seismic perturbations having frequencies in the range of 2‐4 mHz and are propagated to southward with a speed of 0.5‐1.0 km/s. These results suggest that there exists a good coupling between seismic activity and ionized density perturbations after Nepal earthquake.

Performance Evaluation of Adjusted Spherical Harmonics Ionospheric Model Over Indian Region

The ionosphere is perceived to be a predominant source of ranging error of Global Navigation Satellite System (GNSS) signals to degrade the positional accuracy. The suitable ionospheric model is necessary to improve the positional accuracy of GNSS and Satellite-Based Augmentation System (SBAS) users. In this paper, the regional ionospheric model (RIM) over the Indian region is implemented based on the adjusted spherical harmonics function (ASHF) model from dense GPS TEC stations over the Indian region. Also, the evaluation of the different ASHF order models conducted to identify the proper order of the ASHF model for Indian low latitude ionospheric calm and adverse space weather conditions. The results confirm that the 4th order ASHF ionospheric model can identify the northern Equatorial Ionization Anomaly (EIA) TEC crest patterns over the Indian region. The comparison of the 4th order ASHF ionospheric model carried out with dual and single frequency ionospheric models like as Klobuchar model, Centre for Orbit Determination in Europe (CODE) Klobuchar model, NeQuick G model, BeiDou System (BDS2) model and CODE Global Ionospheric Maps (GIM) models. The outcome of the results indicates that the 4th Order ASHF ionospheric model would be potential for single and dual-frequency ionospheric models for GNSS and SBAS systems.

A New Ionospheric Model for Single Frequency GNSS User Applications Using Klobuchar Model Driven by Auto Regressive Moving Average (SAKARMA) Method Over Indian Region

The single-frequency users of Global Navigation Satellite System (GNSS) require an effective mathematical model that mitigate the dominant errors due to ionospheric delays. Klobuchar model approximately reduces ionospheric effect up to 50% through its coefficients in the navigation message, which is not sufficient for the GNSS single frequency users at critical applications. Hence, a new model, for Single Frequency GNSS User Applications using Klobuchar model driven by Auto Regressive Moving Average Method (SAKARMA) is proposed to forecast and enhance the precision of ionospheric delay estimations for GNSS users. The hourly VTEC maps are obtained from the Assimilated Indian Regional Vertical Total Electron Content (AIRAVAT) by the process of data assimilation using the Kalman filter exclusively for the Indian region (longitude: 65°E to 100°E; latitude: 5°N to 40°N) using 26 GPS TEC stations over Indian region. The accuracy of the SAKARMA model is investigated using the AIRAVAT maps for various Indian geographic regions during both geomagnetic quiet and disturbed conditions of September month in 2016 year. Furthermore, in order to test SAKARMA model, a dual-frequency Navigation with Indian Constellation (NavIC) receiver located at the KL Education Foundation, Guntur, India (geographic: 16.37°N, 80.37°E; geomagnetic: 7.44°N, 153.75°E) is used to collect the observations during 2 - 12 September 2017. Furthermore, SAKARMA model is also validated with Klobuchar model, Klobuchar-style coefficients provided by the Center for Orbit Determination in Europe (CODE) (CODKlob) Model, BeiDou System (BDS2) Model and NeQuick 2 Model over a low latitude NavIC station in forecasting the ionospheric delays. The experimental results of SAKARMA for NavIC have revealed that the MAPE for proposed SAKARMA model is 9-17% (accuracy: 83-91%), while 34-53% (accuracy: 47-66%) for the Klobuchar model. Thus, the results illustrate that the proposed SAKARMA model is capable of predicting the ionospheric delays for single frequency GNSS/NavIC users.

Perturbation Features Imprinted on Ionosphere by Successive Clusters of Strong Earthquakes: Role of Atmospheric Coupling Dynamics

The paper presents atmospheric coupling physics through identifying a few significant features imprinted on the ionosphere by certain unique seismic environments when a number of successive cluster of earthquakes ranging from 7.1 to 8.2 magnitudes occurred within about two weeks period, over the East-West Pacific zone covering 150° E to 70° W. Amongst the cases considered here are earthquakes of Chile Apr. 1, 2014 (M = 8.2) and Apr. 3, 2014 (M = 7.7), New Guinea Apr. 11, 2014 (M = 7.1) and Solomon Islands 13.04.2014 (M = 7.6). The main data source for the study is Global TEC with supplementary inputs from GPS observations taken at Guwahati (26° N, 92° E), an Appleton anomaly crest region. A few EQ events with epicenters in and around this anomaly zone are also taken in the study to focus on the seismic induced density features like Earthquake time Equatorial Anomaly (EEA) and Earthquake time Equatorial Anomaly Crest (EEAC) developed over the belt. Such anomalous modifications in TEC resulting to growths of EEA and EEAC covering Solomon Islands—New Guinea extending up to Chile along the fault lines for more than a month, are significant observations brought out in the paper. The GPS TEC data from Gauhati University are utilized in identifying the epicentre position through anomalous appearance of satellites beyond the Line Of Sight (LOS) observation. Finally, the seasonal role on enhancing the seismic induced E-field coupled by mutual interactive EQ preparatory effects of the three major events as well as in enhancement of EQ time radon emission through fault is invoked in explanation to the anomalous density features.

Analysis of signal strength, satellite visibility, position accuracy and ionospheric TEC estimation of IRNSS

The Indian Regional Navigation Satellite System (IRNSS) is an indigenously developed satellite navigation system to meet practical needs. The system, comprising a constellation of seven satellites in GEO orbit, has been fully operational since 2018. It is essential to evaluate the performance of the IRNSS continuously for various applications. As a part of ISRO field trial and data collection program an IRNSS Standard Positioning Service User Receiver (UR) placed at ACS College of Engineering (ACSCE), Bangalore, for independent field trial and data collection. The receiver is operational on a $24\times 7$ basis. A MATLAB Graphical User Interface has been developed to analyze and plot the data variation of signal strength, elevation angle, visibility of satellites, user position, position error, geometric dilution of precision (GDOP) and find the availability of the number of satellites plotted for every second based on the received data. From the results, it is observed that the signal strength (C/No) is good, i.e. above 40 dBHz, visibility of satellites at receiver location is good. The mean position at user location is found to be $X=1349700~\mbox{m}$, $Y = 6070902~\mbox{m}$, $Z = 1413860~\mbox{m}$ and latitude of 12.8914 degree, longitude of 77.465 degree and altitude of 739 m. The mean position from IRNSS is compared with Google map results showing a good match. The geometry distance of receiver location with respect to Earth center is estimated and observed. The RMS of position error for L1, L5 and dual frequency (L5+S) at ACSCE, Bangalore, is 9.7444 m, 6.6873 m and 5.6667 m, respectively. Hence, as expected the dual-frequency (L5+S) receiver gives an accurate position rather than the single-frequency signals. The IRNSS TEC is measured using Ionospheric group delay and the pseudo-range of L5 and S band which is collected from ACSCE receiver. A third order Savitzky-Golay-Filtered technique is used for TEC smoothing. RMSE between IRNSS TEC from pseudo-range and GPS TEC is 0.6482 TECU and the correlation coefficient is 0.9981. RMSE between IRNSS TEC from ionospheric delay of L5/S and GPS TEC is 1.971 TECU and the correlation coefficient is 0.9966. Finally, smoothed TEC values derived from pseudo-range measurements give a good result and can be used to generate daily TEC maps. In order to analyze the performance of IRNSS over the Indian region, we have chosen three other receiver stations located at Osmania University (Hyderabad), University of Burdwan (Bardhaman, West Bengal) and Shri Mata Vaishno Devi University (Katra, Jammu and Kashmir). Based on the results, we conclude that the IRNSS constellation is performing well and providing good signals for accurate user position determination and ionospheric data analysis.

Accuracy and consistency of different global ionospheric maps released by IGS ionosphere associate analysis centers

Due to the differences of ionospheric modeling methods and selected tracking stations, the accuracy and consistency of Global Ionospheric Maps (GIMs) released by Ionosphere Associate Analysis Centers (IAACs) are different. In this study, we evaluate and analyze in detail the accuracy and consistency of GIMs final products provided by six IAACs from three different aspects. Firstly, the comparison of these GIMs shows that the mean bias (MEAN) is related to the modeling methods of various IAACs. The variation trend of the standard deviation (STD) is consistent with the solar activities, and accompanied by certain seasonal and annual periodic variations. The MEAN between IGS and each center is about −1.3 to 1.0 TECU, and the STD is about 1.4–2.5 TECU. Secondly, the validation with GPS TEC shows that the STD of CODE is the smallest at various latitudes, and the STD is about 0.7–4.5 TECU. Thirdly, The validation with the Jason2 VTEC shows that the STD between Jason2 and IAACs is about 4.4–5.2 TECU. In addition, the STD between Jason2 and six GIMs in the areas with more tracking stations is better than that of the regions with fewer tracking stations in different latitude regions. Regardless of whether the tracking stations are more or less, the MEAN and STD in high solar activity are larger than in low solar activity.

Tropospheric and Ionospheric Anomalies Induced by Volcanic and Saharan Dust Events as Part of Geosphere Interaction Phenomena

In this work, we assessed the possible relation of ionospheric perturbations observed by Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER), Global Positioning System total electron content (GPS TEC), National Oceanic and Atmospheric Administration (NOAA)-derived outgoing longwave-Earth radiation (OLR), and atmospheric chemical potential (ACP) measurements, with volcanic and Saharan dust events identified by ground and satellite-based medium infrared/thermal infrared (MIR/TIR) observations. The results indicated that the Mt. Etna (Italy) volcanic activity of 2006 was probably responsible for the ionospheric perturbations revealed by DEMETER on 4 November and 6 December and by GPS TEC observations on 4 November and 12 December. This activity also affected the OLR (on 26 October; 6 and 23 November; and 2, 6, and 14 December) and ACP (on 31 October–1 November) analyses. Similarly, two massive Saharan dust episodes, detected by Robust Satellite Techniques (RST) using Spinning Enhanced Visible and Infrared Imager (SEVIRI) optical data, probably caused the ionospheric anomalies recorded, based on DEMETER and GPS TEC observations, over the Mediterranean basin in May 2008. The study confirmed the perturbing effects of volcanic and dust events on tropospheric and ionospheric parameters. Further, it demonstrated the advantages of using independent satellite observations to investigate atmospheric phenomena, which may not always be well documented. The impact of this increased detection capacity in reducing false positives, in the framework of a short-term seismic hazard forecast based on the study of ionospheric and tropospheric anomalies, is also addressed.

Ground-based Observations of the Polar Region Space Environment at the Jang Bogo Station, Antarctica

Jang Bogo Station (JBS), the second Korean Antarctic research station, was established in Terra Nova Bay, Antarctica (74.62°S 164.22°E) in February 2014 in order to expand the Korea Polar Research Institute (KOPRI) research capabilities. One of the main research areas at JBS is space environmental research. The goal of the research is to better understand the general characteristics of the polar region ionosphere and thermosphere and their responses to solar wind and the magnetosphere. Ground-based observations at JBS for upper atmospheric wind and temperature measurements using the Fabry-Perot Interferometer (FPI) began in March 2014. Ionospheric radar (VIPIR) measurements have been collected since 2015 to monitor the state of the polar ionosphere for electron density height profiles, horizontal density gradients, and ion drifts. To investigate the magnetosphere and geomagnetic field variations, a search-coil magnetometer and vector magnetometer were installed in 2017 and 2018, respectively. Since JBS is positioned in an ideal location for auroral observations, we installed an auroral all-sky imager with a color sensor in January 2018 to study substorms as well as auroras. In addition to these observations, we are also operating a proton auroral imager, airglow imager, global positioning system total electron content (GPS TEC)/scintillation monitor, and neutron monitor in collaboration with other institutes. In this article, we briefly introduce the observational activities performed at JBS and the preliminary results of these observations.

Short Term Single Station GNSS TEC Prediction Using Radial Basis Function Neural Network

TEC prediction models for 24 hours ahead have been developed from JOG2 GPS TEC data during 2016. Eleven month of TEC data were used as a training model of the radial basis function neural network (RBFNN) and 1 month of last data (December 2016) is used for the RBFNN model testing. The RBFNN inputs are the previous 24 hour TEC data and the minimum of Dst index during the previous 24 hours. Outputs of the model are 24 ahead TEC prediction. Comparison of model prediction show that the RBFNN model is able to predict the next 24 hours TEC is more accurate than the TEC GIM model.

Multi-instrumented observations of the equatorial F-region during June solstice: large-scale wave structures and spread-F

Typical equatorial spread-F events are often said to occur during post-sunset, equinox conditions in most longitude sectors. Recent studies, however, have found an unexpected high occurrence of ionospheric F-region irregularities during June solstice, when conditions are believed to be unfavorable for the development of plasma instabilities responsible for equatorial spread-F (ESF). This study reports new results of a multi-instrumented investigation with the objective to better specify the occurrence of these atypical June solstice ESF in the American sector and better understand the conditions prior to their development. We present the first observations of June solstice ESF events over the Jicamarca Radio Observatory (11.95° S, 76.87° W, ∼ 1° dip latitude) made by a 14-panel version of the Advanced Modular Incoherent Scatter Radar system (AMISR-14). The observations were made between July 11 and August 4, 2016, under low solar flux conditions and in conjunction with dual-frequency GPS, airglow, and digisonde measurements. We found echoes occurring in the pre-, post-, and both pre- and post-midnight sectors. While at least some of these June solstice ESF events could have been attributed to disturbed electric fields, a few events also occurred during geomagnetically quiet conditions. The late appearance (22:00 LT or later) of three of the observed events, during clear-sky nights, provided a unique opportunity to investigate the equatorial bottomside F-region conditions, prior to ESF, using nighttime airglow measurements. We found that the airglow measurements (630 nm) made by a collocated all-sky camera show the occurrence of ionospheric bottomside F-region perturbations prior to the detection of ESF echoes in all three nights. The airglow fluctuations appear as early as 1 hour prior to radar echoes, grow in amplitude, and then coincide with ESF structures observed by AMISR-14 and GPS TEC measurements. They also show some of the features of the so-called large-scale wave structures (LSWS) that have been detected, previously, using other types of observations and have been suggested to be precursors of ESF. The bottomside fluctuations have zonal spacings between 300 and 500 km, are aligned with the magnetic meridian, and extend at least a few degrees in magnetic latitude.