Post-sunset Period Research Articles

Evaluation of Glycemic Control in Patients With Diabetes by a Continuous Glucose Monitoring System During the Month of Ramadan.

Ramadan presents challenges for patients with type 2 diabetes mellitus (T2DM) who choose to fast. Maintaining good glycemic control through regular monitoring during fasting is crucial. This study aims to evaluate and compare glycemic fluctuations in fasting and non-fasting T2DM patients during Ramadan. We conducted a prospective comparative study on 39 T2DM patients, divided into fasting and non-fasting groups based on the International Diabetes Federation - Diabetes and Ramadan Alliance (IDF-DAR) Practical Guidelines 2021. Each patient wore an iPro®2 Continuous Glucose Monitoring System (CGMS) device (Medtronic plc, Dublin, Ireland),for five to seven days, with consultations scheduled before, during, and after Ramadan. Glycated hemoglobin (HbA1c) levels were measured before and after Ramadan. The fasting risk score was calculated using the DAR guidelines. The fasting group included 29 fasting patients with an average fasting risk score of 2.7 according to the DAR guidelines, while the non-fasting group had 10 non-fasting patients with an average score of 6.55. The average HbA1c was estimated by the CGMS at 7.36% for fasting patients and 7.1% for non-fasting patients. In the fasting group, 80% of patients experienced at least one episode of hyperglycemia, averaging 4.03 episodes per day, predominantly occurring during pre-dawn (suhoor) and post-sunset (iftar) periods. Hypoglycemia occurred in 24% of fasting patients, mainly before iftar. In contrast, the non-fasting group had a higher average of 6.8 hyperglycemic episodes per day, with 50% of the group also experiencing hypoglycemia. Notably, a significant improvement in HbA1c was observed in the non-fasting group after Ramadan (7.77 ± 0.89 vs. 9.13 ± 1.99, p=0.037). No significant changes in HbA1c, weight, or body mass index were found in the fasting group. Pre-Ramadan education, risk stratification, and continuous monitoring during Ramadan are essential to prevent metabolic complications in T2DM patients, whether fasting or non-fasting. CGMSs reveal a high prevalence of hyperglycemia, especially in non-fasting patients, underscoring the need for tailored treatment adjustments to achieve optimal glycemic control.

Detection of GNSS ionospheric scintillations in multiple directions over a low latitude station

Abstract Analysis of huge data and detection of scintillation events by human visualization is expensive and time consuming process and also unfeasible in real time. In this paper, classical approaches namely Hard, Semi-Hard and Manual annotation rules are used for detection of the scintillations. For this, one week data is acquired from Septentrio PoLaRx5S GNSS scintillation monitoring Receiver corresponding to various constellations. Seven constellations namely GPS, GLONASS, Galileo, SBAS, BeiDou, QZSS and IRNSS-L5 signals during pre-sunset and post sunset hours are considered. The occurrence of scintillations due to pre-sunset and post sunset period by using hard and semi hard detection rules are analysed. It is observed that the occurrence of scintillations is more in post-sunset hours as compared to pre-sunset hours in all constellations. The performances of Semi Hard and Hard detection rules are compared with manual annotation by using confusion matrices statistical parameters namely accuracy, misclassification and precision. Identified scintillation signals coming from the least and worst affected directions. These results would be useful for early detection of scintillation without human inspection of scintillation events.

On the In Situ Observations of Irregularities During Rocket Flights From Thumba for Different Geophysical Conditions and the Associated Causative Mechanisms

AbstractElectron density and Neutral Wind (ENWi) probe and/or Langmuir probe were flown on three different rocket flights from equatorial station Thumba (8.5°N, 77°E), during daytime, eclipse time, and post sunset time respectively, of low solar activity period, to study ionization irregularities in the E region of the ionosphere. The spectral characteristics observed using the payloads were analyzed during the three different rocket flights. The 15 January 2010 solar eclipse event and “SOUREX 1” wind and electron density measurements confirm the validity of the wind shear theory for equatorial regions during the eclipse and post sunset periods, when electrojet is weak, using wind and electron density irregularity measurements from the same instrument (ENWi) for the first time. The spectral indices in the range of −1.2 to −1.78 and the strong wind shear due to gravity wave winds during the eclipse time as well as the post sunset time, confirm the role of neutral turbulence in the generation of irregularities in the 95–112 km altitude region. The spectral index of −2.0 to −2.7 and the presence of irregularities in the negative gradient regions establishes the role of wind‐driven gradient drift instability (GDI) in generating irregularities during the SOUREX 1 post sunset flight for altitudes below 93 km. Further, the role of gradient drift instability in triggering ionization irregularities during the daytime on 14 January 2010 is unraveled by the spectral index of −2.03 and the presence of irregularities in the positive gradient regions alone.

Analysis of ionospheric storm-time effects over the East African sector during the 17 March 2013 and 2015 geomagnetic storms

An analysis of the mechanisms that caused the storm-time effects during two geomagnetic storms that occurred on 17 March 2013 and 2015 is presented. We used Global Navigation Satellite System (GNSS) derived Total Electron Content (TEC) data over the trough (Addis Ababa, ADIS, 38.8^circE geographic longitude, 0.18^circN geomagnetic latitude) and near the crest (Mbarara, MBAR, 30.7^circE geographic longitude, 10.22^circS geomagnetic latitude) regions of East African sector. Magnetometer data over Addis Ababa (AAE) and Mbour (MBO) were also used to derive the disturbance in ionospheric currents during the two storm periods. The monthly median TEC values for a month within which the storm under consideration occurred were used as a measure of background variability to analyse the response of the ionosphere to the storms. The response of the ionosphere to a geomagnetic storm is considered to be significant when the magnitude of TEC deviation (|Delta TEC|) is ge 45%. During the storm main phase, the ionosphere over the East African trough responded positively to the 17 March 2015 geomagnetic storm at 1800 UT, whilst at the crest regions, there was no significant response to the two St. Patrick’s day geomagnetic storms. However, during the storm recovery phase of 17 March 2013 and 2015 storms, both the stations over the trough and crest regions of East Africa showed a positive response. We checked thermospheric [O]/[text {N}_2] changes as a result of the two storms. There were no appreciable changes in [O]/[text {N}_2] over this sector between 16 and 18 March 2013. We observed an appreciable change in [O]/[text {N}_2] between 16 and 18 March 2015. The [O]/[text {N}_2] increase was more pronounced/obvious on 18 March 2015. The positive ionospheric responses during the recovery phases of the two geomagnetic storms could not be attributed to changes in thermospheric [O]/[text {N}_2] because the responses were nighttime features. The southward turning of the z component of Interplanetary magnetic field (IMF Bz) led to enhanced eastward equatorial electric field (EEF) during 0725 UT (1025 LT) and 0645 UT (0945 LT) for 17 March 2013 and 17 March 2015 storms, respectively. We note that when the IMF Bz turned northward, the EEF turned westward. During the southward turnings of IMF Bz that took place at about 1435 UT (1735 LT) on 17 March 2013, eastward prompt penetration electric field (PPEF) occurred in the post-sunset period starting at about 1600 UT (1900 LT) and enhanced the Prereversal enhancement (PRE). The presence of westward PPEF at around 1500 UT (1800 LT) acted to suppress the PRE on 17 March 2015. The positive storm effects during the recovery phases of the two storms may be attributed to strong disturbed dynamo electric field (DDEF), which was eastward during the night. We may thus surmise that the ionospheric responses to geomagnetic storms of St. Patrick’s day over the equatorial and low-latitude region of Africa were as a result of the combined effect of equatorward neutral wind, PPEF and DDEF.Graphical

Ionospheric and magnetic signatures of extreme space weather events of 17 March and 23 June 2015 over the African sector

We have investigated responses of the African sector of the ionosphere to 17 March and 23 June 2015 severe geomagnetic storms. The vertical total electron content (TEC) measurements from Global Navigation Satellite System (GNSS) stations, which are located across the African continent, have been used to estimate the deviation of TEC (ΔTEC). The observed ionospheric response to these events was different at different locations. In the main phase of the 17 march 2015 storm, a significant positive ionospheric storm (ΔTEC maximum) occurred at Meli (245.8% enhancement) and Adis (105% enhancement) stations in the post-sunset period. On the other hand, during midnight negative ionospheric storms (ΔTEC minimum: ∼ 46%–68% depletion ) were observed at Dakr, Nklg, Wind, and Haro stations. The effects of 23 June 2015 storm are more pronounced during the initial phase. In the recovery phase of 23 June storm, negative storm effects observed at the eastern dip latitude and western equatorial stations. In contrast, at the northern and southern mid-latitude stations, we observed positive storm effect during the night periods. Night time TEC enhancement at mid-latitude stations probably caused by the vertical drift of the ionospheric plasma. We have also studied the magnetic signatures of the severe storms of 17 March and 23 June 2015 by analyzing their impacts on the horizontal (H-component) of the Earth’s magnetic field. By using a moving average filter, we have separated the effect of the magnetic disturbance (DP2) and the disturbance dynamo (Ddyn). The H-component analysis shows that there was maximum oscillation of DP2 and Ddyn currents occurrence when the IMF-Bz directed southward. In the main and recovery phases of the storm, this strong current oscillation is the driver for the development of positive ionospheric effect.

Statistical Study of the Ionospheric Slab Thickness at Yakutsk High-Latitude Station

The ionospheric equivalent slab thickness (EST, also named τ) is defined as the ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2), and it is a significant parameter representative of the ionosphere. This paper presents a comprehensive statistical study of the ionospheric slab thickness at Yakutsk, located at the high latitude of East Asia, using the GPS-TEC and ionosonde NmF2 data for the years 2010–2017. The results show that the τ has different diurnal and seasonal variations in high- and low-solar-activity years, and the τ is greatest in the winter, followed by the equinox, and it is smallest in the summer in both high- and low-solar-activity years, except during the noontime of low-solar-activity years. Specifically, the τ in inter of high-solar-activity year shows an approximate single peak pattern with the peak around noon, while it displays a double-peak pattern with the pre-sunrise and sunset peaks in winter of the low-solar-activity years. Moreover, the τ in the summer and equinox have smaller diurnal variations, and there are peaks with different magnitudes during the sunrise and post-sunset periods. The mainly diurnal variation of τ in different seasons of high- and low-solar-activity years can be explained within the framework of relative variation of TEC and NmF2 during the corresponding period. By defining the disturbance index (DI), which can visually assess the relationship between instantaneous values and the median, we found that the geomagnetic storm would enhance the τ at Yakutsk. An example on 7 June 2013 is also presented to analyze the physical mechanism. It should be due to the intense particle precipitation and expanded plasma convection electric field during the storm at high-latitude Yakutsk station. The results would improve the current understanding of climatological and storm-time behavior of τ at high latitudes in East Asia.

A Statistical Study of F‐Region 3.2‐m‐Scale Field‐Aligned Irregularities Occurrence and Vertical Plasma Drift Over Hainan: Solar Activity, Season, and Magnetic Activity Dependences

AbstractThe dependences of the nighttime low‐latitude F‐region 3.2‐m‐scale field‐aligned irregularities (FAIs) occurrence and vertical drift on solar activity, season, and magnetic activity during 2014–2017 are studied by using the coherent scatter radar located at Fuke (19.5°N, 109.1°E) and a nearby Digisonde at Sanya (18.4°N, 109.6°E), Hainan Island, China. The postsunset FAIs occurrence and vertical drift are closely related and modulated by the solar activity, especially for equinox. Utilizing the day‐to‐day comparison analysis, the threshold of the peak for the definitive postsunset FAIs generation during equinox was ∼30 m/s. The postmidnight FAIs occurrence in June solstice did not increase with the decreasing solar activity and is different from the nearby longitude 100°E reported by other studies. This difference is suggested to be due to the different Intertropical Convergence Zone activity between the two longitudes and reveals the highly localized and dynamic nature of irregularities, which clearly highlights the related challenges of space weather forecast. The SYM‐H and AE indices are used as indicators of the geomagnetic activity level, and the statistical results show that enhanced geomagnetic activity appears to weaken the evening and thus suppress the subsequent FAIs generation during the postsunset period. Westward substorm‐related overshielding electric field and/or disturbance dynamo electric field in the dusk side are suggested to play a role in the FAIs suppression during geomagnetic disturbances. This study contributes to the limited available statistical results in the Asian sector and is valuable for the holistic understanding of the global small‐scale FAIs occurrence pattern.

Investigation of equatorial plasma bubble irregularities under different geomagnetic conditions during the equinoxes and the occurrence of plasma bubble suppression

In this study, we investigated the behavior of equatorial plasma bubble irregularities under different geomagnetic conditions during March 2015 and September 2017. It was used Total Electron Content (TEC) data obtained from SGOC (6,89 oN, 79,87 oE), IISC (12,94 oN, 77,57 oE) and HYDE (17,40 oN, 78,50 oE) receiver stations which located between the trough and the crest of the equatorial ionization anomaly (EIA). We used the Rate of TEC change (ROT) and Rate of TEC change index (ROTI) to represent plasma bubbles irregularities. These indices are a well proxy for the ionospheric fluctuations and can be used to describe features of plasma bubbles irregularities. The equatorial plasma bubble irregularities for all stations were observed between 13 UT and 20 UT (during postsunset period) during equinoxes. The intensity level of ROTI during postsunset periods was greater than 1 TECU min−1. Also, the values of mean ROTI (ROTIave) between 13 UT and 20 UT have values greater than 0,4 TECU min−1 while the values of ROTIave at the other hours have values less than 0,4 TECU min−1. The geomagnetic activity has a significant effect on the occurrence of equatorial plasma bubbles irregularities. The occurrence rate of equatorial plasma bubble irregularities observed during postsunset hours increased as geomagnetic activity increases. It also was observed that the main phases of geomagnetic storms have the triggering effect of storms on equatorial plasma bubble irregularities observed at postsunset hours while the recovery phases of geomagnetic storms have the suppression effect of storms on equatorial plasma bubble irregularities. Asymmetry between two equinoxes was observed. The occurrence rate of equatorial plasma bubble irregularities in the March equinox was much larger than that of the September equinox. The occurrence probability of equatorial plasma bubbles for March Equinox was maximum with 45,1% at 17 UT while the occurrence probability of equatorial plasma bubbles for September Equinox was maximum with 11,5% at 16 UT. The enhancements and reductions in the latitudinal gradient of VTEC show similar behaviors with the occurrence of equatorial plasma irregularities. The EIA during postsunset hours contributes significantly to the occurrence of equatorial plasma bubbles irregularities.

Assessment of bottomside thickness parameters over magnetic equator and low latitudes during high solar activity of solar cycle 24

Bottomside thickness parameters of eight Digisonde stations over geomagnetic equator and low latitude regions have been investigated and compared with IRI model bottomside parameter during high solar activity (years 2013–2015) of the solar cycle 24. The studied years of each station rely on the GIRO data availability. The proposed B0 (B0_Pro) are computed by using the GIRO ionospheric data and the B0 expression in [16] with an average correction factor of “0.18733”. This average correction factor is derived from an average of 144 values of monthly average correction factors at eleven stations over geomagnetic equator and low latitude regions. The Results show that the seasonal variations of B0_Pro are in good agreements with those of B0_obs evidently as compared to B0_IRI at eight stations for all four seasons. For example, in the southern hemisphere, the absolute percentage distances between B0_Pro and B0_obs range from 13% to 33% with overall averages less than 26% and regional averages of 16.5%, but those between B0_IRI and B0_obs are higher. Moreover, the correlation coefficients between B0_Pro and B0_obs always are larger than 0.87 while excluding a lowest value of “0.7041”, but those between B0_IRI and B0_obs are lower. In the southern hemisphere, two remarkable features can always be reflected by B0_Pro for all studied stations. Meanwhile, in the northern hemisphere, the B0_Pro variations of each dip latitude has unique features at different locations, local times, and seasons. The inter-station differences of B0_Pro can be seen obviously in comparison with B0_IRI and described by the impacts of EEJ strength, vertical plasma drift, and PRE from local noontime to post-sunset periods. The remarkable findings from this present study may enhance the comprehension of bottomside variability and improve the IRI predictability in the future.

Nighttime equatorial 630-nm emission variability over Ethiopia

Two winters of nightglow intensity observations of the atomic oxygen 630-nm redline emission at Bahir Dar (11.6°N,37.4°E) were collected from measurements between November 2015 and March 2017 by the selection of 89 nights of quality data. The solar activity trend during the 2015–2017 period was decreasing with the solar flux activity varying within the range of 70 and 140 sfu (1SFU=10-22Wm-2Hz-1). The results have shown that for the first winter (2015–2016) for quiet geomagnetic activity and with the solar flux near the higher end of this range, the 630-nm intensity decreased significantly during the post-sunset period of 3–4 h. Also of note was that this trend was generally followed after midnight by a significant short-lived 630-nm brightness enhancement (fivefold). In the subsequent year of low solar fluxes, a similar significant decrease in the 630-nm intensity is seen starting from the early evening but for the remainder of the night the intensity remained generally constant with no significant sign of the post-midnight 630-nm enhancement of the previous year. During disturbed times the study of the temporal variations of the 630-nm intensity found a double peak structure that persisted beyond one day.

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.

Investigation of Spatiotemporal Morphology of Plasma Bubbles Based on EAR Observations

AbstractSpatiotemporal characteristics of equatorial plasma bubble (EPB) have been studied based on Equatorial Atmosphere Radar (EAR) fan sector observations from Kototabang. EPBs were characterized as either locally generated (whose genesis and subsequent evolution was observed in the fan sector maps) or drifted type (which drifted into fan sector scans from west). Investigation of the radar echo spectral width indicated that the drifted EPB could be less evolving type. Height of the F layer in the postsunset period over Kototabang and Chumphon were examined in the two types. Average peak h′F was higher in locally generated EPB cases than in drifted EPB cases (by ~25 km), which is also found to be statistically significant. This scenario has been visualized in terms of a standing large‐scale wave structure (LSWS) whose phase determine whether EPB will be seen evolving over EAR or drifted from a western longitude. Furthermore, low‐latitude sporadic E (Es) variabilities in the two cases were also examined. Es indicated an inverse relation with the peak h′F (which depends on crest/trough of LSWS). These results have been discussed in the light of earlier works on spatial morphology of EPB clusters, particularly in context to the possible generation mechanism of LSWS by the spatial inhomogeneity in the low‐latitude E region conductivity. Lesser occurrence of low‐latitude Es in locally generated EPB cases also signifies the vital role of E region conductivity on Rayleigh‐Taylor instability. These results highlight a need for networked spatial observation of low‐latitude Es.

Multi‐Instrumental Observation of Storm‐Induced Ionospheric Plasma Bubbles at Equatorial and Middle Latitudes

AbstractJune solstice is considered as a period with the lowest probability to observe typical equatorial plasma bubbles (EPBs) in the postsunset period. The severe geomagnetic storm on 22–23 June 2015 has drastically changed the situation. Penetrating electric fields associated with a long‐lasting southward IMF support favorable conditions for postsunset EPBs generation in the dusk equatorial ionosphere for several hours. As a result, the storm‐induced EPBs were progressively developed over a great longitudinal range following the sunset terminator. The affected area has a large longitudinal range of ~100° in the American sector and a rather localized zone of ~20° in longitude in the African sector. Plasma depletions of equatorial origin were registered at midlatitudes (30°–40° magnetic latitude) of both hemispheres in the African and American longitudinal sectors. We examine global features of the large‐scale plasma depletion by using a combination of ground‐based and space‐borne measurements—ground‐based Global Positioning System/Global Navigation Satellite System (GPS/GNSS) networks, Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) GPS Radio Occultation (RO), Swarm upward looking GPS data, and in situ plasma density observations provided by Swarm, Communications/Navigation Outage Forecasting System (C/NOFS), and Defense Meteorological Satellite Program (DMSP) missions. Joint analysis of the satellite observations revealed that these storm‐induced EPBs structures had extended over 500 km in altitude, at least from ~350 to ~850 km. These irregularities caused strong amplitude and phase scintillations of GPS/GNSS signals for ground‐based and space‐borne (COSMIC RO) measurements and seriously affected performance of navigation‐based services.

On Inconsistent ROTI Derived From Multiconstellation GNSS Measurements of Globally Distributed GNSS Receivers for Ionospheric Irregularities Characterization

AbstractThis study for the first time presents an investigation into the exploitation of multi‐Global Navigation Satellite System (GNSS) observations (Global Positioning System, Globalnaya Navigazionnaya Sputnikovaya Sistema, Galileo, and BeiDou) to characterize ionospheric plasma irregularities, based on the rate of change of total electron content index (ROTI) sampled at 1 s. It is demonstrated that the multi‐GNSS ROTIs can represent temporal evolutions of ionospheric plasma irregularities during a large geomagnetic storm. However, an inconsistency in the magnitudes of multi‐GNSS ROTIs is found among a variety of GNSS receivers (i.e., Javad, Leica, Trimble, and Septentrio). Through cross comparisons between GNSS receivers installed at zero/short baselines and validations by receivers distributed separately, it is observed that the magnitude of ROTI corresponding to each system differs between closely installed and even collocated receivers of different models, as well as between the GNSS signals on the same frequency. From 1‐year (i.e., 2015) data analysis, it is found that the magnitudes of multi‐GNSS ROTIs exhibit the dependence on the receiver type. Among the four GNSS receiver types, the largest discrepancy in the multi‐GNSS ROTIs is observed from Septentrio receivers, while the smallest one is shown by Trimble receivers. A one‐to‐one comparison indicates that the ROTI difference is noticeable and can increase to 4–6 TECu/min under ionospheric irregularities conditions, that is, in the postsunset period of 18–02 local time. To investigate the inconsistency, the effect of adopting different equivalent noise bandwidths in the tracking loop design is discussed, via cross comparisons between a GNSS software‐defined receiver and a collocated Septentrio receiver. The result shows that adopting 15‐ and 2‐Hz noise bandwidths in the tracking loop can cause 0.2‐ to 0.5‐TECu/min differences in the magnitude of ROTI, suggesting that the diverse tracking techniques deployed by various receivers are very likely a major contributor to the inconsistency of multi‐GNSS ROTIs.

Variability of the African equatorial ionization anomaly (EIA) crests during the year 2013

This paper discusses the variability of the position and magnitude of the crests of African Equatorial Ionization Anomaly during noon and post sunset periods. Total electron content data covered the year 2013, and were obtained from a chain of global positioning system receivers in both hemispheres around 37°E longitude. Local magnetometer data were used to infer the direction and magnitude of the E × B drift, while the solar extreme ultraviolet proxy index was used as a measure of solar activity. It was found that the time of formation of both crests varied from 1400 to 1700 local time. Additionally, the position of the crests was found to be asymmetric with respect to the magnetic equator. During the noon period, the position of the northern and southern crests varied from 4.91° to 7.36° and −9.17° to −12.62°, respectively. During the post-sunset period, it varied from 8° to 11.7° and −9° to −16°, respectively. Seasonally, with reference to the magnetic equator, both crests moved poleward during equinoxes and collapsed towards the equator during winter and summer. Equinoxes recorded the greatest crest magnitude followed by winter then summer over both hemispheres during the noon period. However, this trend persisted over the northern crest only during the post-sunset period. Overall, during the noon period, we recorded correlation coefficients of 0.67 and 0.68 between crest magnitudes and ΔH, a proxy for equatorial electrojet current, and 0.88 and 0.81 between crest positions and ΔH, for the northern and southern crests, respectively. During the Halloween day storm of 30 October 2013, a westward electric field inhibited the development of the post-sunset crests.

Characteristics of ionospheric scintillation climatology over Indian low-latitude region during the 24th solar maximum period

The amplitude and phase of L-band satellite signals are fluctuated randomly due to small scale electron density irregularity structures in the ionosphere which result in fleeting variations, known as ‘ionospheric scintillations’. The Global Navigation Satellite System (GNSS) is a profound remote sensing tool to monitor, model and forecast the ionospheric weather conditions. In this paper, the GNSS amplitude scintillation data has been analyzed during the year 2013 at Bengaluru (12.9°N, 77.59°E) and Lucknow (26.8467°N, 80.9462°E) stations to reinforce climatology of ionospheric scintillation over Indian low-latitude region. The probability of scintillation occurrence and their variations over equatorial and Equatorial Ionization Anomaly (EIA) regions in India are analyzed during various geomagnetic quiet and disturbed days, months and seasons. The annual occurrence of amplitude scintillations are mapped with the function of local time. It is observed from the experimental results that the probability of scintillations occurrences is higher over EIA region than over the equatorial region. The probability of scintillations is higher during March equinox and December solstice, and lowest during June solstice. Distribution of scintillations is intense during post–sunset period. The maximum percentage of scintillation occurrences at the two stations are recorded in November. Moreover, the highest percentage of scintillation occurrences took place on storm day (March 17, 2013) at the two stations. This work would be helpful for understanding the features of GNSS amplitude scintillations over Southern and Northern Indian regions. Moreover, these kinds of investigations are helpful for developing new algorithms to nowcast and forecast ionospheric scintillations over Indian Sub-continent.

Investigation on the Occurrence of Mid-Latitude E-Region Irregularity by Wuhan VHF Radar and Its Relationship With Sporadic E layer

By using the 2015–2016 data set of newly built Wuhan very high-frequency (VHF) radar, we investigate the occurrence of E-region field-aligned irregularities (FAIs) in mid-latitude China region for the first time. Wuhan E-region FAIs present the strongest occurrence of quasi-periodic (QP) echoes at postsunset period in the height range of 100–120 km and moderate occurrence of continuous echoes at postsunrise period in the height range of 90–100 km. Characteristics including temporal and altitudinal distribution, Doppler spectra and period of QP echoes are presented from a statistical point of view. We find that E-region FAIs observed by Wuhan VHF radar show strong linkage with the concurrent sporadic E layer observed by ionosonde. In general, Doppler spectra present type 2 feature with velocity in the range of ±50 m/s and width less than 50 m/s. Our results also indicate that mid-latitude E-region FAIs are closely associated with Es layer. Several mechanisms were proposed to interpret the mid-latitude E-region FAIs; however, further investigation is required to understand the generation with different ionospheric background and irregularity types.

Effects of Rayleigh-Taylor instability and ionospheric plasma bubbles on the global navigation satellite System signal

Ionospheric disturbances induced by various natural (e.g., earthquakes, volcanic eruption, thunderstorms, meteorite showers, solar eclipses) or anthropogenic (e.g., nuclear explosions, launching of space shuttles) processes can be detected through change in Total Electron Content (TEC) in the F-layer. These ionospheric perturbations can be captured by worldwide expanding geodetic (GNSS) networks, mainly during the day time, when the solar radiation ionizes the air molecules. However, during post-sunset period, strong ionospheric irregularities (known as Equatorial Plasma Bubbles, EPBs) develop due to the classical configuration for the Rayleigh-Taylor (R-T) instability that diffracts navigation and communication signals. Here we use various instances of ionospheric disturbances triggered by natural processes (e.g., earthquakes and volcanic eruption), in the recent decade to investigate the spatiotemporal and seasonal effects of ionospheric irregularities on the GNSS signals. Our study suggests that in the low-latitudinal region (e.g., Sumatra, Mexico), such ionospheric irregularities can mask the ionospheric perturbations due to the higher production rate of EPBs. Hence detection of such co-seismic TEC anomaly becomes difficult. However, in the high-latitudinal region (e.g., Iceland, Alaska), due to the lower production rate of EPBs, ambient ionospheric irregularities are insignificant and hence coseismic TEC anomalies can be captured even during night time. We argue that the production rate of EPBs further depends upon seasonal and longitudinal parameters on the globe.

Comparison of the human-baited double net trap with the human landing catch for Aedes albopictus monitoring in Shanghai, China

BackgroundHuman landing catch (HLC) is the most efficient method for Aedes monitoring, but it is not ethical due to its high risk of human exposure to pathogens. We designed trials to assess the performance of an alternative human-baited double net trap (HDN) for field Aedes albopictus monitoring compared with the standard HLC.MethodsOutdoor HDN and HLC catches were conducted simultaneously at 15 field sites on two sunny days in mid-July and August. The tests were performed 3 h apart: an early morning period (7:30–8:30 h), a pre-sunset period (16:30–17:30 h) and a post-sunset period (18:30–19:30 h). A total of 90 comparisons were made between the two methods. Field comparisons were designed to minimize half-hour bias and human-bait attraction bias.ResultsTwo mosquito species were collected by HDN and HLC, with the predominated species being Ae. albopictus (HDN: n = 1325, 97.35% of total; HLC: n = 531, 92.51% of total). A small proportion were adults of the Culex pipiens complex (HDN: n = 36, 2.65% of total; HLC: n = 43, 7.49% of total). Although the mean Ae. albopictus catch per hour of HLC was significantly higher than HDN (14.72 vs 5.90 per h, t(178) = 3.151, P = 0.003), there were significant positive spatial and temporal correlations between HLC and HDN for Ae. albopictus sampling among different sites and hours (r(90) = 0.785, P < 0.001; r(90) = 0.785, P < 0.001). Both methods proved that Ae. albopictus was most active during the hours before sunset and least active after sunset. No significant variation was observed in Ae. albopictus catch size of HDN between groups of more attractive and less attractive humans (3.38 vs 2.51 per 30 min, t(88) = 1.283, P = 0.201).ConclusionsWith moderate sampling efficiency, significantly positive spatial correlation with HLC, and less human-bait attraction bias, HDN appears to be a safer alternative to HLC for Ae. albopictus monitoring in Shanghai. With mosquito activity peaking in the pre-sunset hours, Ae. albopictus catches of HDN should be performed in the hours before dark. The trap design could be improved to make it more portable and easier for field operation.

Temporal evolution of the EIA along 95°E as obtained from GNSS TEC measurements and SAMI3 model

The total electron content (TEC) derived from GNSS measurements at a trans-hemispheric meridional chain of ground stations around 95°E longitude are used to study the quiet time inter-hemispheric structure and dynamics of the equatorial ionization anomaly (EIA) during the period March 2015 to February 2016. The stations are Dibrugarh (27.5°N, 95°E, 43° dip), Kohima (25.6°N, 94.1°E, 39° dip), Aizawl (23.7°N, 92.8°E, 36° dip), Port Blair (11.63°N, 92.71°E, 9° dip) and Cocos Islands (12.2°S, 96.8°E, 43° dip). The observation shows that the northern crest of the EIA lies in the south of 23°N (Aizawl) in all seasons but recedes further south towards the equator during December solstice. The largest poleward expansion of the northern (southern) EIA is observed in the March equinox (December solstice). The equinoctial and hemispherical asymmetry of TEC is noted. The winter anomaly is observed in the northern hemisphere but not in the southern hemisphere. The highest midday TEC over any station is observed in the March equinox. The TEC in southern summer (December solstice) is significantly higher than that in the northern summer (June solstice). The observed northern EIA contracts equatorward in the postsunset period of solstice but the southern EIA persists late into the midnight in the December solstice. The asymmetry may be attributed to the different geographic location of the magnetically conjugate stations. The SAMI3 simulations broadly capture the EIA structure and the inter-hemispheric asymmetry during solstices. The difference between observations and the SAMI3 is higher in March equinox and December solstice. The higher E × B vertical drift in the 90–100°E sector and the large geographic-geomagnetic offset in observing stations may have contributed to the observed differences.