Post-midnight Hours Research Articles

Development of Cost-Effective GPS Receiver for Ionospheric Scintillation Monitoring Aided with IoT System

One of the applications of GPS receiver is to detect and measure the irregularities in satellites communication. Many of the studies conducted the research to analyses the transmission data through ionosphere layers. One of the subjects of the research is scintillation. One of the ionosphere scintillation parameters used for measuring the irregularities is amplitude scintillation (S4). However, the survey-grade or GISTM receiver, which is expensive, was commonly used to monitor the parameter. The other alternative is to used common geodetic GPS receiver that capable of collecting the parameters. This study used ZED-F9P with ANN-MB antenna and Raspberry Pi as the prototype to operate. The data collected during the autumnal equinox showed a pattern of strong ionospheric scintillation effects in the post-midnight hours. The study demonstrates the feasibility of using low-cost GNSS receivers for ionospheric monitoring, which has important implications for various applications such as navigation, communication, and space weather monitoring.

Seasonal morphology and solar activity dependence analysis of mid-latitude post-midnight enhancement using Global Ionospheric Map

In the mid-latitude ionosphere, the anomalous enhancement during nighttime is defined by an increase in electron density of the F2 region and/or total electron content. Studying this phenomenon is important because it enriches our understanding of the complex physical processes responsible for ionosphere formation. Furthermore, long-term investigations can reveal patterns and trends in ionospheric behavior, enabling more accurate predictions and improvements in ionosphere models. In this paper, we have investigated the mid-latitude post-midnight enhancement (MPE) utilizing Global Ionosphere total electron content (TEC) Maps (GIMs) during Low Solar Activity (LSA) years 2009, 2020 and High Solar Activity (HSA) year 2014. The investigation is done in the Northern and Southern Hemispheres during post-midnight hours (0–6 LT) focusing on the occurrence and strength of the MPE according to its seasonal morphology, in addition to the MPE occurrence dependence on the Interplanetary Magnetic Field (IMF) and the influence of the F10.7 on the strength of MPE. The findings indicate that the MPE occurrence and strength are more frequent and stronger during the winter solstice and depend on season, longitude, latitude, and level of solar activity. The MPE occurrence rate and strength reduce when solar activity is higher. The MPE occurrence rate shows a correlation with the IMF's By and Bz components. The negative correlation between F10.7 and MPE strength emphasizes solar activity's impact on MPE.

Investigation of the possible dependence of equatorial plasma bubble with travelling ionospheric disturbances using airglow-imager at Abuja

Airglow images obtained with the aid of a ground-based Airglow Imager (AGI) located at Abuja, Nigeria (Geographic: 7.39°E, 8.99°N; Dip latitude: −1.60°) have been used to study the possible relationship between the occurrence of Atmospheric Gravity Waves (AGWs) and Equatorial Plasma Bubbles (EPBs) to investigate the role AGW plays in the occurrence of EPB. Airglow images covering over two and half years (nighttime only), from June 2015 to August 2018 were used. Three filters of the airglow imager were used in this study, taking observation over 652 days (nights). Results show that AGW occurrence is random with no regular trend and very rare at the station compared with EPB. EPB is found to occur more frequently with local time and seasonal dependence. Peak occurrences of EPB are observed during the equinoctial months. Although concurrent occurrences of the two phenomena are very infrequent, results further show that whenever both phenomena occur simultaneously, the duration of occurrences tends to suggest there exists a relationship between them. The concurrent occurrence of the two phenomena is observed more during post-sunset than post-midnight hours whenever it happens. Although EPB occurs independently of AGW, the results show that on nights where we have concurrent occurrences, EPB occurrence tends to take place earlier than days of EPB occurrence without AGW. We, therefore, conclude from the results obtained in this study that, AGW is not the only factor that contributes to the occurrences of EPB at the station since the AGW observed might not have consistently propagated to the bottomside of the F layer due to its dissipation. However, whenever it occurs, AGW tends to influence the conditions that trigger the occurrence of EPB.

Seasonal Variation of the F2-Layer Critical Frequency and Comparison with the IRI-2016 Model during Two Extremes of Solar Activity Phase of Solar Cycle 22

Abstract: Introduction: The variation of the ionosphere is mostly studied using the critical frequency of the F2-layer (foF2) whose values can also be predicted by an ionospheric model. The widely used model for predicting ionospheric parameters is the International Reference Ionosphere (IRI). Aim: This paper aims to demonstrate how well the current International Reference Ionosphere (IRI-2016) model performs in predicting the critical frequency of the F2-layer (foF2) over two equatorial stations during two extremes of solar activity phase of solar cycle 22.. Methods: The hourly foF2 experimental data collected during the Maximum Phase of Solar Activity MPSA year (1989) and Minimum Phase of Solar Activity MnPSA year (1986) at Ougadougou (Geomagnetic Latitude 0.59 oN, Geomagnetic Longitude 71.46 oE) in the African longitudinal sector and Manila (Geomagnetic Latitude 3.4 oN, Geomagnetic Longitude 191.1 oE) in the Asia longitudinal sector as well as the predicted foF2 data by the IRI-2016 model were used in this study. Sunspot data from Zurich was utilized as a measure of solar activity phase. The foF2 data were grouped into four seasons before analysis began. Comparing the seasonal means of the experimental foF2 data and the IRI-2016 modeled foF2, it was possible to determine how closely the model matched the experimental data at the different seasons and longitudinal sectors Results: The results showed that the IRI-2016 model overestimate and underestimate the observed foF2 at different periods of the day during the equinox and solstice seasons. Observation showed that the highest positive and negative percentage deviations were observed mostly during the post-midnight hours. Observation also showed that Seasonal mean values of the IRI-2016 model of both options showed remarkable improvement at this two stations since their values have little difference from the observed foF2 values. Conclusion: The discrepancy (underestimation and overestimation) in the IRI-2016 model is found larger during MPSA year than during MnPSA year. The URSI option performs better than the CCIR option since its predicted values are much closer to the observed values. Both options of the model perform better in the Asian longitudinal sector than the African longitudinal sector.

Statistical Analysis of SF Occurrence in Middle and Low Latitudes Using Bayesian Network Automatic Identification

Spread-F (SF) is one of the most important types of the ionospheric irregularities as it causes ionospheric scintillation which can severely affect the performance and reliability of communication, navigation, and radar systems. The ionosonde provides the most effective and economical way to study the ionosphere and SF. However, the manual identification of SF from an ionogram is boring and hard work. To automatically identify SF on the ionogram and extend the study of SF into the middle and low latitudes of East Asia, this paper presents a statistical analysis of SF in this region, based on the naïve Bayesian classifier. The results showed that the accuracy of automatic identification reached up to 97% on both the validation datasets and test datasets composed of Mohe, I-Cheon, Jeju, Wuhan, and Sanya ionograms, suggesting that it is a promising way to automatically identify SF on ionograms. Based on the classification results, the statistical analysis shows that SF has a complicated morphology in the middle and low latitudes of East Asia. Specifically, there is a peak of occurrence of SF in the summer in I-Cheon, Jeju, Sanya, and Wuhan; however, the Mohe station has the highest occurrence rate of SF in December. The different seasonal variations of SF might be due to the different geographic local conditions, such as the inland-coastal differences and formation mechanism differences at these latitudes. Moreover, SF occurs more easily in the post-midnight hours when compared with the pre-midnight period in these stations, which is consistent with the previous results. Furthermore, this paper extracts the frequency SF (FSF) index and range SF (RSF) index to characterize the features of SF. The results shows that the most intense FSF/RSF appeared in the height range of 220–300 km/1–7 MHz in these stations, although there are different magnitude extensions on different season in these regions. In particular, strong spread-F (SSF) reached its maximum at the equinox at Sanya, confirming the frequent SSF occurrence at the equinox at the equator and low latitudes. These results would be helpful for understanding the characteristics of SF in East Asia.

Multifrequency Observations of Postmidnight Ionospheric Irregularities From an Anomaly Crest Location

AbstractThe paper reports occurrences of postmidnight to early morning ionospheric depletions in total electron content (TEC) observed using the Low Earth Orbiting satellite beacon from Calcutta (22.57°N, 88.36°E geographic, and 32°N magnetic dip) situated around the northern crest of the equatorial ionization anomaly (EIA) in the Indian longitude sector for the period 2015–2016. These results are novel and contrary to the usual scenario of equatorial ionospheric irregularities being dominant during the early evening to pre‐midnight hours of equinoctial months. The TEC depletions, commonly called “bite‐outs,” exhibit amplitudes of 1–2.5 TECU, with maximum depletion found near the northern crest of the EIA around subionospheric coordinates 25.8°N and 82.2°E. These bite‐outs exhibited seasonal variabilities, with maximum occurrences found during local summer months. The observed TEC depletions during postmidnight hours point toward irregularities, which are not generated over the magnetic equator and drifted along magnetic field lines. A case study of the observation of these ionospheric disturbances has also been presented across a spectrum of frequencies, namely 150 and 400 MHz (Low Earth Orbit satellites), 250 MHz (Geostationary satellites), and 1.5 GHz (GPS—Medium Earth Orbit satellites) to establish the presence of irregularities of different scale sizes even during postmidnight hours.

The role of global thermospheric zonal winds on the variability of equatorial ionospheric irregularities

We analyze the role of thermospheric winds on the variability of ionospheric plasma density irregularities for solar maximum periods using ionospheric plasma density profiles from the three Swarm satellites and zonal wind data from the Horizontal Wind Model 14 (HWM14). The results show that the plasma density irregularities are strongest during post-midnight hours compared to pre-midnight hours in the African – American longitude sector and this is associated with an enhancement in eastward zonal wind after midnight. In addition, the occurrence of plasma irregularities are observed to show a westward shift. The zonal wind reversal from westward to eastward during post-sunset hours is found to be very important for the generation and variability of plasma irregularities. In the African – American longitudinal sector, where plasma irregularities are the most intense, the eastward wind is strongest in December solstice than for the other seasons. Moreover, plasma irregularity during the December solstice is comparable to the Rayleigh-Taylor Instability mechanism (RTI) favored equinox seasons. But, plasma irregularities are weakest in the June solstice where the zonal eastward wind over geomagnetic equatorial region is weakest as compared to the other seasons. Zonal wind reversal from westward to eastward around post-sunset hours occurred early for seasons with stronger ionospheric irregularity activity whereas the reversal is delayed for the season with weakest ionospheric irregularity activity in the African – American sector. Our results are confirmations of the theoretical prediction on the role of eastward zonal wind in plasma instability growth rate by Kudeki et al. (2007).

Modeling and causative mechanism of OI 630.0 nm nightglow emission over Cachoeira Paulista (22.7oS, 45oW) – Brazil: Seasonal and temporal variability

The seasonal and temporal variability of the OI 630.0 nm nightglow emissions were observed over Cachoeira Paulista (22.7 o S, 45 o W; dip latitude −35°) in Brazil by multichannel photometer during 2014 and 2015. The temporal variation of the OI 630.0 nm nightglow intensity shows a peak during post-midnight hours ( ∼ 25 h 00 LT) during the summer. During autumn, this peak is shifted towards pre-midnight at ∼ 22 h 00 LT. It is noticed that this peak again shifted towards post-midnight at 26 h30 LT and 25 h30 LT during winter and spring, respectively. The intensity increases by a factor of 2–4 in the summer than that observed in other three seasons. The modelling of the nightglow measurements in 2015 is carried out by calculating the excitation rate, emission rate and intensity of OI 630.0 nm nightglow emission in the upper atmosphere at low latitudes. Our calculation suggests that the dissociative recombination of O 2 + with electrons is the main source for the OI 630.0 nm nightglow emission. We report that the model intensities are in good agreement with the measurements at Cachoeira Paulista for all four seasons and the model reproduces all features of peak intensities very well.

Irregular sleep-wake patterns in older adults with current or remitted depression

Background: Disturbed sleep and irregular sleep-wake patterns have been associated with poor outcomes in older adults. Sleep regularity however has not been studied in a sample with current or remitted major depression.Methods: 138 participants (63.8±8.6 years; n=27 current major depression, n=64 remitted, and n=47 healthy controls) were monitored using wrist-worn actigraphy. The Sleep Regularity Index (SRI), sleep-wake fragmentation and stability, sleep onset and offset timing, number of awakenings and measures from cosinor analysis were computed.Results: Compared with controls, older adults with current depression had lower SRI (p < 0.01), lower relative amplitude (p < 0.05), and higher activity during sleeping and post-midnight hours (p < 0.05). Older adults with remitted depression displayed lower activity during the day (p < 0.05), showed reduced average activity and lower amplitude than controls. Total sleep time, sleep timing, and number of awakenings did not differ between groups. All groups differed significantly in self-reported sleep quality and depression severity.Limitations: Longitudinal studies which examine how sleep-wake patterns change based on depressive episode recency, severity and how medications may influence these patterns are needed.Conclusions: Older adults with current or remitted major depression do not differ from controls on traditional sleep metrics but do report poor quality sleep and show differences in sleep regularity and rest-activity patterns. Reducing the risk of poor outcomes in both groups may be aided by interventions that help promote sleep regularity and increased activity.

Nighttime enhancements in the VTEC at anomaly crest region Bhopal: Solar and magnetic activity effects

Nighttime enhancement in the Vertical Total Electron Content (VTEC) of the ionosphere near equatorial ionization anomaly crest region in the Indian ionospheric sector has been studied during May 2016 to August 2017, a solar minimum period. VTEC data is obtained from a multi-frequency multi-constellation global navigation satellite system (GNSS) receiver installed at Bhopal (23.2°N, 77.4°E & MLAT 14.2°N). Only those enhancements which show VTEC enhancement ≥ 10% compared to the background has been considered in the study. Out of the total 105 cases of enhancement recorded during this period, 86 events occurred during pre-midnight and 19 during post-midnight hours. Enhancements in VTEC occurred in all seasons; more frequent however during summer than winter and equinox months. Some of the nighttime enhancements in VTEC resulted in the scintillations in the satellite signals as well. Peak amplitude of the enhancement maximizes in summer whereas its half amplitude duration maximizes during equinox month. The number of occurrences of nighttime enhancement in VTEC shows negative correlation with peak amplitude while they are positively correlated with half amplitude duration. We have found that the peak amplitude of nighttime enhancements in VTEC shows strong positive correlation while percentage occurrence shows strong negative correlation with solar and magnetic activities respectively. Other characteristics like half amplitude duration, time of peak and occurrence time of nighttime enhancement in VTEC show positive correlation with solar activity while they are insignificant with magnetic activity. The peak amplitude of pre-midnight enhancements in VTEC is highly correlated with the strength of equatorial electrojet strength. The results are compared with the earlier observations and possible mechanism is also discussed.

Modeled IMF By Effects on the Polar Ionosphere and Thermosphere Coupling

AbstractThere is still an inadequate understanding of how the interplanetary magnetic field (IMF) east‐west component (By) affects thermospheric composition, and other ionospheric and thermospheric fields in a systematic way. Utilizing the state‐of‐art first‐principles Coupled Magnetosphere Ionosphere Thermosphere (CMIT) modeling and TIMED/Global Ultraviolet Imager (GUVI)‐observed ΣO/N2 covering an entire solar cycle (year 2002–2016), as well as a neutral parcel trajectory tracing technique, we emphasize that not only the direction of By, but also its strength relative to the IMF north‐south component (Bz) that has important effects on high latitude convection, Joule heating, electron density, neutral winds, and neutral composition patterns in the upper thermosphere. The Northern Hemisphere convection pattern becomes more twisted for positive By cases than negative cases: the dusk cell becomes more rounded compared with the dawn cell. Consequently, equatorward neutral winds are stronger during postmidnight hours in negative By cases than in positive By cases, creating a favorable condition for neutral composition disturbances (characterized by low ΣO/N2) to expand to lower latitudes. This may lead to a more elongated ΣO/N2 depletion area along the morning‐premidnight direction for negative By conditions compared with the positive By conditions. Backward neutral parcel trajectories indicate that a lower ΣO/N2 parcel in negative By cases comes from lower altitudes, as compared with that for positive By cases, leading to larger enhancements of N2 in the former case.

A Statistical Study on The Local Time Dependence of Equatorial Spread F (ESF) Irregularities and Their Relation to Low‐Latitude Es Layers Under Geomagnetic Storms

AbstractIn this paper, we present a study on the local time dependence of equatorial spread F (ESF) irregularities and their relation to low‐latitude Es layers in response to geomagnetic storms using simultaneous observations of two ionosondes one located at Tirunelveli (8.73°N, 77.70°E), an equatorial station and other located at Hyderabad (17.36°N, 78.47°E), an off‐equatorial station during the years 2007–2015 that covers solar cycles 23 and 24. The Aarons criteria for the ESF irregularities for different seasons under geomagnetic storms are evaluated. In the category I, we noticed partial enhancement in prereversal enhancement (PRE) during postsunset resulting in ~30% occurrence of spread F instead of total inhibition during equinox and winter seasons. Also, occurrence of ESF in summer is suppressed by only ~75% due to partial increase in PRE. In category II, we observed presunrise height enhancement mostly during winter, which caused ESF to occur at ~50% followed by equinox and summer. The results presented here suggest that many are actually not following the Aarons criteria possibly due to not considering other background conditions. Accordingly, we examined the plausible role of low‐latitude Es layers on the generation of ESF irregularities under these categories during geomagnetic storms. We noticed the absence/presence of Es layers in both categories during postsunset and postmidnight hours resulting in increase/decrease of PRE due to modifications in the field‐line‐integrated Pederson conductivity. Accordingly, the results suggest that one of the plausible reasons for ESF irregularities not following Aarons criteria is linked to the variability of the low‐latitude Es layers.

Investigation of the relationship between the spatial gradient of total electron content (TEC) between two nearby stations and the occurrence of ionospheric irregularities

Abstract. The relation between the occurrence of ionospheric irregularities and the spatial gradient of total electron content (TEC) derived from two closely located stations (ASAB: 4.34∘ N, 114.39∘ E and DEBK: 3.71∘ N, 109.34∘ E, geomagnetic), located within the equatorial region, over Ethiopia, during the postsunset hours was investigated. In this study, the Global Positioning System (GPS)-derived TEC during the year 2014 obtained from the two stations were employed to investigate the relationship between the gradient of TEC and occurrence of ionospheric irregularities. The spatial gradient of TEC (ΔTEC∕Δlong) and its standard deviation over 15 min, σ(ΔTEC∕Δlong), were used in this study. The rate of change of TEC-derived indices (ROTI, ROTIave) were also utilized. Our results revealed that most of the maximum enhancement and reduction values in ΔTEC∕Δlong are noticeable during the time period between 19:00 and 24:00 LT. In some cases, the peak values in the spatial gradient of TEC are also observed during daytime and postmidnight hours. The intensity level of σ(ΔTEC∕Δlong) observed after postsunset show similar trends with ROTIave, and was stronger (weaker) during equinoctial (solstice) months. The observed enhancement of σ(ΔTEC∕Δlong) in the equinoctial season shows an equinoctial asymmetry where the March equinox was greater than the September equinox. During the postsunset period, the relation between the spatial gradient of TEC obtained from two closely located Global Navigation Satellite System (GNSS) receivers and the equatorial electric field (EEF) was observed. The variation in the gradient of TEC and ROTIave observed during the evening time period show similar trends with EEF with a delay of about 1–2 h between them. The relationship between σ(ΔTEC∕Δlong) and ROTIave correlate linearly with correlation coefficient of C=0.7975 and C=0.7915 over ASAB and DEBK, respectively. The majority of the maximum enhancement and reduction in the spatial gradient of TEC observed during the evening time period may be associated with ionospheric irregularities or equatorial plasma bubbles. In addition to latitudinal gradients, the longitudinal gradient of TEC has contributed significantly to the TEC fluctuations.

Significant Electric Field Perturbations in Low Latitude Ionosphere due to the Passage of Two Consecutive ICMEs During 6–8 September 2017

AbstractThis investigation shows that the significant electric field disturbances in the dip‐equatorial ionosphere during the geomagnetic storm of 6–8 September 2017 are due to the passage of two consecutive interplanetary coronal mass ejections (ICMEs). During the passage of the first ICME sheath, a long duration (∼10 hr) prompt penetration (PP) event is operational in which 60‐min periodic component is found to be present in vertical drift as well as in equatorial electrojet, but the 45‐min periodicity, though present, is not significant in equatorial electrojet. On 8 September, the shock associated with the second ICME enhances theFregion vertical plasma drift to ∼150 m/s in the evening hours which is one of the highest vertical drift ever measured over Jicamarca. The same PP electric field causes unusually large enhancement of the equatorial electrojet strength to ∼135 nT in the early morning hours over the Philippine sector. The disturbance dynamo (DD) that follows the storm causes an upward vertical drift of ∼55 m/s during postmidnight hours over Jicamarca which is one of the highest observed. These unusually large electric field perturbations cause significant changes in theFregion plasma fountain. It is shown that these electric field perturbations cannot be accounted by PP/DD electric field associated with the geomagnetic storm only and significant contribution from substorm is conspicuous. Therefore, the present investigation highlights the need to evaluate the role of substorm in unusually large electric field perturbations over equatorial ionosphere.

Long‐Lasting Latitudinal Four‐Peak Structure in the Nighttime Ionosphere Observed by the Swarm Constellation

AbstractIn this study, we provide for the first time observation of the latitudinal four‐peak structure of F region electron density in the nightside ionosphere. The special configuration of Swarm satellites, Swarm B having the chance to resample the regions of Swarm A/C with successively increasing time differences, provides an unprecedented opportunity to check the evolution of these nightside electron density peaks. Overall, the latitudinal four‐peak structures have very low occurrence rates, only 4% of the Swarm orbits. The two mid‐latitude peaks prefer to appear close to ±40° magnetic latitude, while the two low‐latitude peaks appear within ±20° magnetic latitude. Such latitudinal four‐peak structures can persist throughout the night until sunrise hours. No clear seasonal dependence is found for the two mid‐latitude peaks, while the two low‐latitude peaks are almost symmetric about the magnetic equator during equinoxes but are located at slightly higher latitudes in the summer hemisphere around solstices. The two low‐latitude peaks at late‐night hours are believed not to be remnants of the dusk‐side equatorial ionization anomaly (EIA) crests, as (a) example shows that Swarm A/C observe the development of shoulders at the flanks of the two EIA crests after sunset hours, and the shoulders become peaks 3 h later when Swarm B resamples the same region; (b) statistic results reveal that the two low‐latitude peaks during post‐midnight hours do not propagate towards the magnetic equator, as expected for EIA crests, but move slowly poleward. We suggest that the enhanced meridional wind at postmidnight hours is one possible driver for causing such latitudinal four‐peak structure of F region electron density. In addition, the simultaneous magnetic measurements from Swarm satellites are also analyzed, but they show no obvious diamagnetic effect that could help to maintain pressure balance within these electron density peaks.

Diurnal, seasonal and solar cycle variation in total electron content and comparison with IRI-2016 model at Birnin Kebbi

Abstract. The ionosphere is the major error source for the signals of global positioning system (GPS) satellites. In the analysis of GPS measurements, ionospheric error is assumed to be somewhat of a nuisance. The error induced by the ionosphere is proportional to the number of electrons along the line of sight (LOS) from the satellite to receiver and can be determined in order to study the diurnal, seasonal, solar cycle and spatial variations in the ionosphere during quiet and disturbed conditions. In this study, we characterize the diurnal, seasonal and solar cycle variation in observed total electron content (OBS-TEC) and compare the results with the International Reference Ionosphere (IRI-2016) model. We obtained TEC from a dual-frequency GPS receiver located at Birnin Kebbi Federal Polytechnic (BKFP) in northern Nigeria (geographic location: 12.64∘ N, 4.22∘ E; 2.68∘ N dip) for the period 2011–2014. We observed differences between the diurnal variation in OBS-TEC and the IRI-2016 model for all hours of the day except during the post-midnight hours. Slight post-noon peaks in the daytime maximum and post-sunset decrease and enhancement are observed in the diurnal variation in OBS-TEC during the equinoxes. On a seasonal scale, we observed that OBS-TEC values were higher in the equinoxes than the solstices only in 2012. However, in 2011, the September equinox and December solstice recorded a higher magnitude, followed by the March equinox, and the magnitude was lowest in the June solstice. In 2013, the December solstice magnitude was highest, followed by the equinoxes, and it was lowest in the June solstice. In 2014, the March equinox and December solstice magnitudes were higher than the September equinox and June solstice magnitude. The June solstice consistently recorded the lowest values for all the years. OBS-TEC is found to increase from 2011 to 2014, thus revealing solar cycle dependence.

Ionospheric VTEC variations over Pakistan in the descending phase of solar activity during 2016–17

This paper presents the variations of the ionospheric Vertical Total Electron Content (VTEC) observed over Pakistan at the verge of low- to mid-latitude regions during the years 2016–17 of the descending phase of the solar cycle. The study is conducted by considering the ionospheric measurements from dual frequency Global Navigation Satellite System (GNSS) receivers permanently installed at Islamabad (geomagnetic Lat. 25.44°N, Long. 148.83°E), Multan (geomagnetic Lat. 22.13°N, Long. 146.91°E) and Quetta (geomagnetic Lat. 22.50°N, Long. 142.73°E). The diurnal, seasonal and annual variations of VTEC over Pakistan are examined in the context of geomagnetic storm during 2016. This study shows high values during the March and September equinoctial months and lower values during the summer and winter solstices from VTEC estimations. Furthermore, higher, moderate and lower VTEC variations are recorded during the seasonal analysis in the equinoxes, summer solstice and winter solstice, respectively. The maximum seasonal VTEC values are observed during the post-sunrise hours between 11:00–17:00 LT and the minimum values are recorded during the post-midnight hours between 02:00–05:00 LT during each season at all the stations. Moreover, the effect of geomagnetic storm is detected in the ionospheric VTEC of the three different stations, which occurred on 13 October 2016. The initial phase of the storm caused no prominent effect on VTEC, while an enhancement in VTEC is registered in the main and recovery phases of the storm. The recorded VTEC from three different stations is correlated with the indices of the geomagnetic storm.

Mesospheric Temperature Inversions Observed in OH and O2 Rotational Temperatures From Mount Abu (24.6°N, 72.8°E), India

AbstractWe present a detailed investigation of upper mesospheric temperature inversions (MTIs) based on around 4.5 years of data of O2 and OH nightglow emission intensities (I(O2) and I (OH)) and temperature (T(O2) and T (OH)) corresponding to 94 and 87‐km altitudes. These measurements were carried out using Near‐Infrared Imaging Spectrograph from a low‐latitude location, Mount Abu (24.6°N, 72.8°E), in India. A total of 745 nights of Near‐Infrared Imaging Spectrograph observations is used, which showed the mean of T(O2) and T (OH) to be 199.6 and 203.0 K. However, there are nights that showed T(O2) greater than T (OH), which is considered as an indicator of upper MTIs. Among these nights, around 28% (209 out of 745) showed MTIs. It is found that 75% and 25% of MTIs occurred during premidnight and postmidnight hours. It was noted that maximum number of nights showed MTIs for a duration of around 4 hr followed by 3, 2, 5, and 6 hr. Investigation of causative mechanism for the upper MTIs revealed that although both wave dynamics and chemical heating by the exothermic reactions do work together, the in situ chemical heating process seems to be a more probable cause as compared to the vertical transport of energy from lower below. So far, such detailed statistics on MTIs does not exist in the published literature, and thus, the information presented in this work provides the necessary input for a greater understanding of the atmospheric temperature structure through modeling and simulation studies.

Plasma Dynamics Associated With Equatorial Ionospheric Irregularities

AbstractThe Communication/Navigation Outage Forecasting System satellite was operational from 2008, a period of deep solar minimum, to 2015, a period of moderate solar conditions. The behavior of the vertical plasma drift and the distribution of plasma depletions during the deep solar minimum of 2009 deviated substantially from the behavior that was observed during the solar moderate conditions encountered by the Communication/Navigation Outage Forecasting System satellite in 2014, which are typical of previous observations. Presented here are observations of the vertical drift of plasma depletions and the background plasma in which they are embedded. We find that depletions detected at local times after 2100 hr during solar minimum are typically found in background drifts that are weakly downward compared to the strongly downward background drifts observed during moderate solar activity levels. Additionally, at solar minimum, the drift within the depletions is upward with respect to the background as compared with observations at the same local times during solar moderate conditions for which the depleted plasma more nearly drifts with the background. We note that weak background plasma drifts observed throughout the night during solar minimum promote the continued growth of depletions that may evolve more slowly or be continuously generated to appear in the topside in the postmidnight hours.

Climatology of the Occurrence Rate and Amplitudes of Local Time Distinguished Equatorial Plasma Depletions Observed by Swarm Satellite

AbstractIn this study, we developed an autodetection technique for the equatorial plasma depletions (EPDs) and their occurrence and depletion amplitudes based on in situ electron density measurements gathered by Swarm A satellite. For the first time, comparisons are made among the detected EPDs and their amplitudes with the loss of Global Positioning System (GPS) signal of receivers onboard Swarm A, and the Swarm Level‐2 product, Ionospheric Bubble Index (IBI). It has been found that the highest rate of EPD occurrence takes place generally between 2200 and 0000 magnetic local time (MLT), in agreement with the IBI. However, the largest amplitudes of EPD are detected earlier at about 1900–2100 MLT. This coincides with the moment of higher background electron density and the largest occurrence of GPS signal loss. From a longitudinal perspective, the higher depletion amplitude is always witnessed in spatial bins with higher background electron density. At most longitudes, the occurrence rate of postmidnight EPDs is reduced compared to premidnight ones; while more postmidnight EPDs are observed at African longitudes. CHAMP observations confirm this point regardless of high or low solar activity condition. Further by comparing with previous studies and the plasma vertical drift velocity from ROCSAT‐1, we suggest that while the F region vertical plasma drift plays a key role in dominating the occurrence of EPDs during premidnight hours, the postmidnight EPDs are the combined results from the continuing of former EPDs and newborn EPDs, especially during June solstice. And these newborn EPDs during postmidnight hours seem to be less related to the plasma vertical drift.