High Solar Activity Research Articles

Determination of the Annual Optimal Reliable Frequency for Different Transmitter/Receiver Stations Distributed over the Iraqi Territory

This paper aimed to determine the Optimal Reliable Frequency (ORF) that can maintain certain connection link between different transmitter/receiver stations laid over the Iraqi territory. Three different transmitting sites were chosen as tested stations located in the northern, central, and southern regions of Iraq. These sites are Mosul, Baghdad, and Basra, respectively. In this study, the years 2009 and 2014, which represent the minimum and maximum years of solar cycle 24, were chosen to examine the effect of low and high solar activity on the determined ORF. The datasets of the Best Usable Frequency (BUF) were calculated using the ASAPS international communication model. An analytical study was made on the generated BUF parameter dataset of the annual time for the adopted years. Also, an analytical simulation was made for the suggested ORF parameter depending on the BUF parameter datasets. The results of this simulation showed that the suggested ORF parameter can be represented by polynomial equation of different orders. The suggested formula was determined depending on different tested parameters (path length, bearing, time (day) and BUF values). For this purpose, a certain program was built using a visual basic programing language (VB6). The suggested ORF parameter was investigated for the annual time for the three sites of the years 2009 and 2014.

Performance Evaluation of VTEC GIMs for Regional Applications during Different Solar Activity Periods, Using RING TEC Values

This paper presents a comparison of the vertical total electron content (vTEC) estimated over Italy using two different approaches: the GPS Global Ionosphere Maps (GIMs) and the so-called “calibration technique” developed by Ciraolo in 2007. The study has been carried out at a regional level by considering three Italian dual-frequency stations of the GPS permanent network “Rete Integrata Nazionale GPS (RING)”. The GPS receivers are permanently installed at Madesimo (geographical coordinates: 46.5 N, 9.4 E), Rome (geographical coordinates: 41.8 N, 12.5 E) and Resuttano (geographical coordinates: 37.7 N, 14.1 E), respectively in the north, center and south of Italy. Time windows selected for the analysis include periods of both low (July 2008 to June 2009) and high (September 2013 to August 2014) solar activity. The two datasets have also been studied considering both quiet and disturbed geomagnetic activity conditions. Moreover, the effects of an extreme geomagnetic storm have been investigated in March 2015 when the well-known St. Patrick storm occurred. Overall, GIM estimated values are always higher than those calibrated by the Ciraolo procedure for all the considered datasets. The differences between the two methods increase as the latitude decreases, and they increase as the solar activity intensifies. The outcomes of this study shall be helpful when applying GlMs at a regional level.

Signal‐In‐Space Performance Under Multiconstellation Environment From an Indian Low Latitude Station

AbstractGlobal Navigation Satellite System (GNSS) signals have become a useful tool to analyze signal‐in‐space performance in the presence of ionospheric perturbations with a view to improve the performance of satellite‐based systems and services. For this purpose, continuous monitoring of the signal tracking capabilities of commercial GNSS receivers is a priority, particularly from regions around the crests of Equatorial Ionization Anomaly (EIA), which experiences some of the worst‐case scenarios attributed to ionospheric effects. Ample investigations are reported in literature on GPS signal fading characteristics, while the same for GLONASS and Galileo are limited from Indian low latitude region. The present study aims to report cases of cycle slips and loss‐of‐lock observed independently at GLONASS L1 CA, L2 CA and Galileo L1 BC and E5a, along with a comparative study of robustness of L1 signal in three different constellations GPS, GLONASS, and Galileo, sharing more‐or‐less common ionospheric volume. Data analyzed in this study was recorded during March 2014, a period of high solar activity, from station Calcutta (22.58°N, 88.38°E geographic; magnetic dip 34.54°), located near the northern crest of EIA. Results of this study reveal GLONASS L2 CA to be most affected signal out of all, during periods of ionospheric scintillations. However, when constellations are compared for a particular frequency (L1), Galileo appears to be the least affected. Results of this study could be significant toward better understanding of scintillation effects on GNSS signals while developing more robust applications, especially for a low latitude station.

Implementing the MULTI-VP coronal model in EUHFORIA: Test case results and comparisons with the WSA coronal model

Context.In this study, we focus on improving EUHFORIA (European Heliospheric Forecasting Information Asset), a recently developed 3D magnetohydrodynamics space weather prediction tool. The EUHFORIA model consists of two parts covering two spatial domains: the solar corona and the inner heliosphere. For the first part, the semiempirical Wang-Sheeley-Arge (WSA) model is used by default; this model employs the potential field source surface and Schatten current sheet models to provide the necessary solar wind plasma and magnetic conditions above the solar surface, at 0.1 AU, which serve as boundary conditions for the inner heliospheric part. Herein, we present the first results of the implementation of an alternative coronal model in EUHFORIA, the so-called MULTI-VP model.Aims.After we replace the default EUHFORIA coronal setup with the MULTI-VP model, we compare their outputs both at 0.1 AU and 1 AU, for test cases involving high speed wind streams (HSSs). We select two distinct cases in which the standard EUHFORIA setup failed to reproduce the HSS plasma and magnetic signatures at Earth to test the performance of MULTI-VP coupled with EUHFORIA-heliosphere.Methods.To understand the quality of modeling with MULTI-VP in comparison with the default coronal model in EUHFORIA, we considered one HSS case during a period of low solar activity and another one during a period of high solar activity. Moreover, the modeling of the two HSSs was performed by employing magnetograms from different providers: one from the Global Oscillation Network Group (GONG) and the second from theWilcoxSpace Observatory (WSO). This way, we were able to distinguish differences arising not only because of the different models but also because of different magnetograms.Results.The results indicate that when employing a GONG magnetogram, the combination MULTI-VP+EUHFORIA-heliosphere reproduces the majority of HSS plasma and magnetic signatures measured at L1. On the contrary, the standard WSA+EUHFORIA-heliosphere combination does not capture the arrival of the HSS cases at L1. When employing WSO magnetograms, MULTI-VP+EUHFORIA-heliosphere reproduces the HSS that occurred during the period of high solar activity. However, it is unclear if it models the HSS during the period of low solar activity. For the same magnetogram and periods of time, WSA+EUHFORIA-heliosphere is not able to capture the HSSs of interest.Conclusions.The results show that the accuracy of the simulation output at Earth depends on the choice of both the coronal model and input magnetogram. Nevertheless, a more extensive statistical analysis is necessary to determine how precisely these choices affect the quality of the solar wind predictions.

Impact of the Ionosphere Disturbed by Rocket Plume on OTHR Radio Wave Propagation

AbstractThe main chemicals of rocket exhaust plume are released into the ionosphere, which cause three‐dimensional (3‐D) disturbances. By simulating the disturbance, we investigate the influence of ionospheric disturbance by the chemical release on the propagation of over‐the‐horizon radar (OTHR) waves. Based on the absorption simulation model, the absorption loss of OTHR waves caused by rocket plume was simulated. Using 3‐D digital ray tracing, we simulated the propagation path of radio waves in the “ionospheric hole” region. The simulation results show that the absorption loss of short waves decreases with an increase in the frequency and elevation angle of the ray. The absorption loss in the year of high solar activity is significantly higher than that in the year of low solar activity. The absorption value is largest at noon and smallest at night. In terms of seasonal variation, the absorption of radio waves is strongest in summer and weakest in winter. Additionally, the ionospheric hole area increases with the release time. The 6 MHz high‐frequency waves cannot reach the disturbance height and are completely reflected to the ground. Most of the 8 MHz radio waves are reflected to the ground, and some of them pass through the ionosphere. The radio waves at 10, 15, and 20 MHz can pass through the hole area of the ionosphere. Moreover, the ionospheric disturbance generated by the plume has a focusing effect on the propagation of OTHR shortwaves. With the increase in radio frequency, the focusing height gradually increases, and the focusing effect gradually weakens.

Precipitation in surrounding mountains instead of lowlands facilitated the prosperity of ancient civilizations in the eastern Qaidam Basin of the Tibetan Plateau

Precipitation fluctuation has been suggested as a crucial influencing factor in the evolution of ancient civilizations across the world. Nuomuhong culture (~3400–2450 BP) and Tuyuhun (313–663 CE) were unique ancient civilizations that developed in the eastern Qaidam Basin of the north Tibetan Plateau. However, how precipitation variation in the mountain–basin system has affected the rise and fall of these two ancient civilizations is not well understood. Based on analyses of grain size, magnetic susceptibility, Rb/Sr ratio, loss on ignition, and optically stimulated luminescence dates from an aeolian deposit sequence, lowland climate change in the Qaidam Basin during the late Holocene is reconstructed. The Rb/Sr ratio varies from 0.31 to 0.33 during ~2500–2300 BP, it increases from 0.33 to 0.44 during ~2300–1600 BP, and decreases from 0.44 to 0.29 during ~1600–1400 BP, suggesting the climate was relatively dry during ~2500–2300 BP and ~1600–1400 BP and relatively wet during ~2300–1600 BP in the lowlands of the eastern Qaidam Basin, which corresponded well to the gap between the Nuomuhong and Tuyuhun periods. However, the prosperous periods of the Nuomuhong and Tuyuhun were synchronous with high precipitation in the surrounding mountains. Therefore, high precipitation in the surrounding mountains nourished the expansion of oases and then facilitated the development of Nuomuhong and Tuyuhun, which was inconsistent with precipitation variation in the lowlands of eastern Qaidam Basin. The spatiotemporal pattern of precipitation in the mountain–basin system of the Qaidam Basin during the late Holocene was likely affected by solar activity through uplifting–subsiding air flow mechanism, with more precipitation in the mountain and less precipitation in the basin under higher solar activity. A cognitive model is provided to illustrate how solar activity affected the spatiotemporal patterns of precipitation in the mountain–basin structure of the eastern Qaidam, and then human settlement and civilization evolution during the late Holocene.

The three-dimensional ionospheric electron density imaging in Japan using the approximate Kalman filter algorithm

The three-dimensional ionospheric electron density (Ne) over Japan is retrieved by assimilating the ground-based total electron content (TEC) datasets into the International Reference Ionosphere (IRI) background model. To reduce the computational burdens encountered in the full Kalman filter (KF) algorithm, the simplified KF (SKF), a time-independent data assimilation scheme with no recursion, is adopted. The spatial resolution is 1°, 1°, and 30 km in latitude, longitude, and altitude, and the temporal resolution is 1 h. Regarding the quite geomagnetic condition, seasonal variations in the ionosphere were investigated firstly. The results show that the reconstructed Ne could well capture the seasonal ionospheric characteristics and semiannual anomaly. Subsequently, NmF2 (F2 layer peak electron density) values during April 3–9, 2013 (high solar activity) and 2018 (low solar activity) were reproduced and simulated by the SKF and IRI model, respectively. In contrast with the ionosonde data, the results indicated the reconstructed NmF2 was apt to capture the underlying trends of diurnal and annual variations more accurately. For the efficiency under the disturbed geomagnetic condition, we took a great geomagnetic storm that happened on August 26, 2018 as an example. The reproduced results also provided better imaging for Ne distributions by analyzing the vertical slices and profiles provided by SKF and IRI. It is suggested that the SKF algorithm is promising for ionospheric researches and practical applications in Japan.

Revealing the relationship between solar activity and COVID-19 and forecasting of possible future viruses using multi-step autoregression (MSAR).

The number of sunspots shows the solar activity level. During the high solar activity, emissions of matter and electromagnetic fields from the Sun make it difficult for cosmic rays to penetrate the Earth. When solar energy is high, cosmic ray intensity is lower, so that the solar magnetic field and solar winds affect the Earth externally and originate new viruses. In this paper, we assess the possible effects of sunspot numbers on the world virus appearance. The literature has no sufficient results about these phenomena. Therefore, we try to relate solar ray extremum to virus generation and the history of pandemics. First, wavelet decomposition is used for smoothing the sunspot cycle to predict past pandemics and forecast the future time of possible virus generation. Finally, we investigate the geographical appearance of the virus in the world to show vulnerable places in the world. The result of the analysis of pandemics that occurred from 1750 to 2020 shows that world’s great viral pandemics like COVID-19 coincide with the relative extrema of sunspot number. Based on our result, 27 pandemic (from 36) incidences are on sunspot extrema. Then, we forecast future pandemics in the world for about 110 years or 10 cycles using presented multi-step autoregression (MSAR). To confirm these phenomena and the generation of new viruses because of solar activity, researchers should carry out experimental studies.

Temperature and Humidity Regime of Roof Space in Buildings with Glass Roofs

The paper analyzes the temperature and humidity conditions of the roof space of buildings with translucent roofs in the winter period of operation. The work is based on the generalization of data from a number of field observations and monitoring of translucent roofs of atrium buildings in Moscow. It is established that the temperature and humidity regime of the sub-roof space of atrium buildings with translucent roofs in the winter period of operation has a significant impact on the load-bearing capacity and durability of the translucent filling of coatings (insulated glass units), as well as snow loads on translucent roofs. At the same time, an analysis of existing approaches to the design and calculation of translucent roofs atrium buildings has shown that the issue considered in this work is often not taken into account when assigning their design solutions, which further complicates their normal operation. It is established that when performing strength calculations of roof insulated glass units it is necessary to take into account the design conditions of the transitional spring-winter period, which is characterized by low outdoor temperatures and high solar activity. The thermal regime of translucent roofs of atrium buildings also has a significant impact on the formation of snow cover on similar structures, which is manifested in a different nature of the distribution of snow loads on translucent roofs, as well as on the amount of snow loads, which are several times less than the loads on similar deaf insulated roofs.

Evidence for the Significant Differences in Response Times of Equatorial Ionization Anomaly Crest Corresponding to Plasma Fountains During Daytime and Post‐Sunset Hours

AbstractBased on 10 years' (2010–2019) of vertical total electron content (VTEC) data from Ahmedabad (23.0°N, 72.6°E, dip angle 35.2°) and campaign based OI 630.0 nm airglow intensity measurements from Mt. Abu (24.6°N, 72.7°E, dip angle 38.0°), it is shown that plasma density over the equatorial ionization anomaly (EIA) crest region increases in varying degrees during post‐sunset hours (2000–2100 LT) in magnetically quiet periods. The post‐sunset peak in VTEC precedes the corresponding peak in airglow intensity. By comparing post‐sunset VTEC enhancements with ionosonde observations from Tirunelveli (8.7°N, 77.7°E, dip angle 1.7°), it is shown that pre‐reversal enhancement (PRE) of the zonal electric field causes these enhancements over the EIA crest region. These observations are supported by TEC measurements by GAGAN (GPS Aided Geo Augmented navigation), the Indian Satellite‐based Augmentation System (SBAS). Comparison of average VTEC variations with global empirical model drifts reveals that the post‐sunset enhancements in VTEC occurs ∼1.7 h after the PRE and are significant only during December solstice and equinoctial months in high solar activity years similar to seasonal variations in PRE amplitudes. This time delay (response time of EIA crest) is almost half compared to the average response time (3–4 h) associated with the daytime fountain. Based on the latitudinal gradient in SBAS‐TEC, it is proposed that the PRE drives plasma from 5°N to 10°N magnetic latitudes to the EIA crest region leading to shorter response time. These results show the important role of the PRE in conditioning the EIA crest region.

Climatology and seasonal variation of the thermospheric tides and their response to solar activities over Arecibo

A long-term statistical analysis of thermospheric tides in an altitude range from 150 to 400 km is presented. The analysis is based on a dataset with 31 multi-day experiments conducted from an incoherent scatter radar at Arecibo Observatory between 1984 and 2015. This is the first time that the climatological mean and seasonal variations of the thermospheric tides and their response to solar activities are reported using an extensive dataset. The climatological mean amplitude of diurnal tide (DT) is dominant while the amplitudes of the semidiurnal tide (SDT) and terdiurnal tide (TDT) are comparable. Below 250 km, the SDT and TDT phases show downward propagation with vertical wavelengths of 300 and 240 km, respectively. Above 250 km, the DT is the most prominent component except in autumn while the SDT dominates below 250 km except in winter. Above 250 km, the DT is the strongest in winter and its amplitude varies around 28 m/s. Below 250 km, the SDT is prominent in autumn and fluctuates around 35 m/s. The TDT is the most important in winter compared to the other three seasons and its amplitude is slightly less than 20 m/s. The DT and SDT amplitudes show the opposite response to solar activity. Above 250 km, the former increases with increasing solar activity while the latter is the opposite. The enhanced DT amplitude and its phase structure under the high solar activity indicates that the in-situ EUV radiation plays a major role in generating the thermospheric DT over Arecibo.

Equatorial anomaly according to the Interkosmos-19 data and IRI model: A comparison

The comparison of the IRI model with the foF2 distribution in the equatorial anomaly region obtained by topside sounding onboard the Interkosmos-19 satellite has been carried out. The global distribution of foF2 in terms of LT-maps was constructed by averaging Intercosmos-19 data for summer, winter, and equinox. These maps, in fact, represent an empirical model of the equatorial anomaly for high solar activity F10.7 ~ 200. The comparison is carried out for the latitudinal foF2 profiles in the characteristic longitudinal sectors of 30, 90, 210, 270, and 330°, as well as for the longitudinal variations in foF2 over the equator. The largest difference between the models (up to 60%) for any season was found in the Pacific longitudinal sector of 210°, where there are a few ground-based sounding stations. Considerable discrepancies, however, are sometimes observed in the longitudinal sectors, where there are many ground-based stations, for example, in the European or Indian sector. The discrepancies reach their maximum at 00 LT, since a decay of the equatorial anomaly begins before midnight in the IRI model and after midnight according to the Interkosmos-19 data. The discrepancies are also large in the morning at 06 LT, since in the IRI model, the foF2 growth begins long before sunrise. In the longitudinal variations in foF2 over the equator at noon, according to the satellite data, four harmonics are distinguished in the June solstice and at the equinox, and three harmonics in the December solstice, while in the IRI model only two and one harmonics respectively are revealed. In diurnal variations in foF2 and, accordingly, in the equatorial anomaly intensity, the IRI model does not adequately reproduce even the main, evening extremum.

From Hector Mine M7.1 to Ridgecrest M7.1 Earthquake. A Look from a 20-Year Perspective

The paper provides a comparative analysis of precursory phenomena in the ionosphere and atmosphere for two strong earthquakes of the same magnitude M7.1 that happened in the same region (North-East from Los Angeles) within a time span of 20 years, the Hector Mine and Ridgecrest earthquakes. Regardless of the similarity of their location (South-Eastern California, near 160 km one from another), there was one essential difference: the Hector Mine earthquake happened during geomagnetically disturbed conditions (essential in the sense of ionospheric precursors identification). In contrast, the quiet geomagnetic conditions characterized the period around the time of the Ridgecrest earthquake. The Hector mine earthquake happened in the middle of the rising phase of the 23-rd solar cycle characterized by high solar activity, while the Ridgecrest earthquake happened by the very end of the 24th cycle under very low solar activity conditions. We provide a comprehensive multi-factor analysis, determine the precursory period for both earthquakes and demonstrate the close similarity of ionospheric precursors. Unlike the majority of papers dealing with earthquake precursor identification based on the “abnormality” of observed time-series mainly determined by amplitude difference between “normal” (usually climatic) behavior and “abnormal” behavior with amplitudes exceeding some pre-established threshold, we used the technique of cognitive recognition of the precursors based on the physical mechanisms of their generation and the morphology of their behavior during the precursory period. These permits to uniquely identify precursors even in conditions of disturbed environment as it was around the time of the Hector Mine earthquake. We demonstrate the close similarity of precursors’ development for both events. The leading time of precursor appearance for the same region and similar magnitude was identical. For the Hector Mine it was 11 October 1999—5 days in advance—and for 2019 Ridgecrest it was 28 June—7 days before the mainshock and five days before the strongest foreshock.

Measurements of the time-dependent cosmic-ray Sun shadow with seven years of IceCube data: Comparison with the Solar cycle and magnetic field models

Observations of the time-dependent cosmic-ray Sun shadow have been proven as a valuable diagnostic for the assessment of solar magnetic field models. In this paper, seven years of IceCube data are compared to solar activity and solar magnetic field models. A quantitative comparison of solar magnetic field models with IceCube data on the event rate level is performed for the first time. Additionally, a first energy-dependent analysis is presented and compared to recent predictions. We use seven years of IceCube data for the moon and the Sun and compare them to simulations on data rate level. The simulations are performed for the geometrical shadow hypothesis for the moon and the Sun and for a cosmic-ray propagation model governed by the solar magnetic field for the case of the Sun. We find that a linearly decreasing relationship between Sun shadow strength and solar activity is preferred over a constant relationship at the 6.4σ level. We test two commonly used models of the coronal magnetic field, both combined with a Parker spiral, by modeling cosmic-ray propagation in the solar magnetic field. Both models predict a weakening of the shadow in times of high solar activity as it is also visible in the data. We find tensions with the data on the order of 3σ for both models, assuming only statistical uncertainties. The magnetic field model CSSS fits the data slightly better than the PFSS model. This is generally consistent with what is found previously by the Tibet AS−γ Experiment; a deviation of the data from the two models is, however, not significant at this point. Regarding the energy dependence of the Sun shadow, we find indications that the shadowing effect increases with energy during times of high solar activity, in agreement with theoretical predictions.7 MoreReceived 26 June 2020Accepted 11 December 2020DOI:https://doi.org/10.1103/PhysRevD.103.042005© 2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCosmic ray propagationMagnetic field generation & plasma dynamoSpace & astrophysical plasmaWave-wave, wave-particle interactionsPropertiesInterplanetary magnetic fieldTechniquesCherenkov detectorsCosmic ray & astroparticle detectorsCosmic rays & astroparticlesNeutrino detectorsTest-particle methodsGravitation, Cosmology & AstrophysicsPlasma PhysicsParticles & Fields

Estimating the Daytime Vertical E × B Drift From Magnetometer and C/NOFS Measurements and Comparison With Empirical Models Over the East African Sector

AbstractThis paper introduces a new approach of estimating the daytime horizontal geomagnetic field (ΔH)‐induced variations of vertical E × B drift velocity and evaluates its performance using Communication/Navigation Outage Forecasting Systems (C/NOFS) over the East African sector. H field at AAE (Addis Ababa magnetometer station) and ETHI (Adigrat magnetometer station in Ethiopia) and their immediate difference alongside with C/NOFS E × B drift were used for periodic polynomial fitting (PPF) a periodic basis. Knowledge of E × B drift is of utmost importance in space weather‐related predictions since it can significantly affect ionospheric density structures and dynamics. The periodic fitting illustrates better agreement with C/NOFS observation during 16:00–19:00 LT than 10:00–16:00 LT whose root‐mean‐square error (RMSE) increased from 9.2 to 12.67 m/s, respectively. Comparison of PPF, recent regional E × B model made by Dubazane and Habarulema (2018, https://doi.org/10.1029/2018SW001820) (E × BDub) and E × BIRI (vertical E × B estimates of International Reference Ionosphere [IRI]) was carried out using C/NOFS observation. Independent model validation shows that C/NOFS E × B values are closer to PPF estimates than E × BDub and E × BIRI over the region. Besides, the least squares model with physical inputs including local time (LT), day of the year (DOY), extreme ultraviolet (EUV) flux, and ΔH provides lowest RMSEs of about 5.36 and 7.41 m/s using a method of neural networking during low solar activity (LSA) and high solar activity (HSA), respectively.

Assessment of IRI-2016 hmF2 model options with digisonde, COSMIC and ISR observations for low and high solar flux conditions

The attempt of this work is to evaluate the three options (BSE-1979, AMTB-2013, SHU-2015) embedded in IRI-2016 for the F2 layer peak height (hmF2) estimation under low and high solar flux levels. We compare the model hmF2 with digisonde observations from Qaanaaq, Milllstone Hill, Ramey, Jicamarca and Port Stanley as well as Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) ionospheric radio occultation data over the five stations spanning from northern hemisphere to southern hemisphere. In the case of Millstone Hill, we also use incoherent scatter radar (ISR) measurements. For the comparison with digisonde data, SHU-2015 is the most accurate option for reproducing hmF2 at low and middle latitude stations (Milllstone Hill, Ramey, Jicamarca) with the smallest Root-Mean-Square-Error and the highest correlation with observations. At high latitude (Qaanaaq and Port Stanley), BSE-1979 becomes the best option. This is true for both low and high solar flux conditions. Similar results are obtained for the comparison between ISR and IRI-2016 hmF2 model options over Millstone Hill, where SHU-2015 option has the smallest deviations from the observation data in both low and high solar activity conditions. As for the comparison with COSMIC data, SHU-2015 edges out the other two options under low solar activity level with better performance at three stations. There is no optimal option under high solar activity level, which is to our surprise, cause SHU-2015 was developed based on a large amount of radio occultation data. At Jicamarca, all options show dramatic deviations from COSMIC observations, showing even negative correlations. We propose that the performance of the three options do not vary much with solar condition, while they differ a lot with location, for example, latitude.

Solar activity dependence of medium-scale traveling ionospheric disturbances using GPS receivers in Japan

In order to reveal solar activity dependence of the medium-scale traveling ionospheric disturbances (MSTIDs) at midlatitudes, total electron content (TEC) data obtained from a Global Positioning System (GPS) receiver network in Japan during 22 years from 1998 to 2019 were analyzed. We have calculated the detrended TEC by subtracting the 1-h running average from the original TEC data for each satellite and receiver pair, and made two-dimensional TEC maps of the detrended TEC with a spatial resolution of 0.15° × 0.15° in longitude and latitude. We have investigated MSTID activity, defined as delta I/overline{I}, where delta I and overline{I} are standard deviation of the detrended TEC and the average vertical TEC within the area of 133.0°–137.0° E and 33.0°–37.0° N for 1 h, respectively. From each 2-h time series of the detrended TEC data within the same area as the MSTID activity, auto-correlation functions (ACFs) of the detrended TEC were calculated to estimate the horizontal propagation velocity and direction of the MSTIDs. Statistical results of the MSTID activity and propagation direction of MSTIDs were consistent with previous studies and support the idea that daytime MSTIDs could be caused by atmospheric gravity waves, and that nighttime MSTIDs were caused by electro-dynamical forces, such as the Perkins instability. From the current long-term observations, we have found that the nighttime MSTID activity and occurrence rate increased with decreasing solar activity. For the daytime MSTID, the occurrence rate increased with decreasing solar activity, whereas the MSTID activity did not show distinct solar activity dependence. These results suggest that the secondary gravity waves generated by dissipation of the primary gravity waves propagating from below increase under low solar activity conditions. The mean horizontal phase velocity of the MSTIDs during nighttime did not show a distinct solar activity dependence, whereas that during daytime showed an anticorrelation with solar activity. The horizontal phase velocity of the daytime MSTIDs was widely distributed from 40 to 180 m/s under high solar activity conditions, whereas it ranged between 80 and 200 m/s, with a maximum occurrence at 130 m/s under low solar activity conditions, suggesting that gravity waves with low phase velocity could be dissipated by high viscosity in the thermosphere under low solar activity conditions.

Occurrence characteristics of equatorial plasma bubbles over Kisumu, Kenya during Solar maximum of Solar Cycle 24

Equatorial Plasma Bubbles (EPBs) are irregular plasma density depletions in the ambient electron density in the equatorial F-region ionosphere generated after sunset. EPBs are known to bring disruptions to telecommunication and navigation systems. This paper investigates the occurrence of EPBs over Kisumu, Kenya (Geomagnetic coordinates: 9.64o S, 108.59o E; Geographic coordinates: 0.02o S, 34.6o E) for a few selected quiet and storm days between 1st January 2013 and 31st December 2014 which was a high Solar activity period for Solar Cycle 24. The study brings out EPB occurrence pattern over Kisumu, Kenya for the selected quiet and storm days of 2013 and 2014. The Receiver Independent Exchange (RINEX) data was retrieved from the Kisumu high data-rate NovAtel GSV4004B SCINDA-GPS receiver. The data was unzipped and processed to obtain Vertical Total Electron Content (VTEC), amplitude scintillation (S4) and Universal Time (UT) which were then fed into MATLAB to generate VTEC and S4 plots against UT for each selected quiet and storm day within the years 2013 and 2014. The Total Electron Content (TEC) depletion depths and S4 index values between 16:00 and 20:00 UT for each selected quiet and storm day were extracted from the VTEC and S4 plots and used to plot TEC depletion depths and S4 plots. The Rate of Change of TEC (ROT) and Rate of Change of TEC Index (ROTI) between 16:00 and 20:00 UT were generated from VTEC and used to plot ROT and the corresponding ROTI plots against UT. TEC depletion depths and ROTI values for each selected quiet and storm day between 16:00 and 20:00 UT were extracted and used to plot TEC depletion depths and ROTI plots and S4 index and ROTI plots. In this study, the enhancement of S4 index corresponded well with TEC depletions, increased fluctuation of ROT and higher ROTI values between 16:00UT and 20:00UT for most days. This correspondence was used in inferring the occurrence of EPBs during the selected quiet and storm days of the years 2013 and 2014. The obtained results showed that the highest EPB occurrence was during March equinox with 33.33% occurrence in the year 2013 and 30.76% occurrence in the year 2014, followed by the September equinox which had 20.38% occurrence in 2013 and 17.26% occurrence in 2014. The seasonal variation of EPB occurrence was attributed to the variation in the daytime E x B drift velocities. Larger E x B drift velocities resulted in increased EPB occurrence in the equinoctial period (March, April, August and September) and November solstice period (November and December) while lower E x B drift velocities resulted in reduced EPB occurrence in the June solstice period (June and July). The percentage EPB occurrence in the year 2013 was 6.49% while in the year 2014 was 4.32%. The storm period had percentage EPB occurrence of 21.42% in the year 2013 and 21.88% in the year 2014 while the quiet period had percentage EPB occurrence of 18.75% in the year 2013 and 7.89% in the year 2014. These results clearly showed that the percentage EPB occurrence was higher during the storm period than in the quiet period. Hence the development of EPBs was enhanced by geomagnetic activity through several competing dynamics such as Prompt Penetration Electric Field (PPEF), Disturbance Dynamo Electric Field (DDEF) and reduction in electron density due to increased recombination rates. Â

Investigation of Satellite Trace (ST) and Multi-reflected Echo (MRE) ionogram signatures and its possible correlation to nighttime spread F development from Cyprus over the solar mini-max (2009–2016)

Multi-reflected echoes (MREs) and satellite traces (STs) are referred in literature as ionogram signatures of Travelling Ionospheric Disturbances (TIDs) which is a phenomenon that apparently drives spread F development mainly at nighttime mid-latitude ionosphere. A long-term statistical study has been undertaken to investigate the morphological aspect of these signatures over the lower midlatitude European station of Nicosia, Cyprus (35.19°N, 33.38°E geographic; magnetic dip. 29.38°N) by inspecting all ionograms recorded by the DPS-4D digisonde in the interval 2009–2016. The results underline the systematic manifestation of these TID signatures over Cyprus with a possible (although not quite clear) solar activity dependence and a distinctive seasonal and diurnal occurrence rate with a seasonal peak of STs during summer and of MREs during January to April. Based on the experimental results of the present study, the seasonal occurrence rate of MREs and STs is found to increase by 75% and 56% during high solar activity periods. Satellite traces are well known ionogram signatures of TIDs and mostly correlated to the nighttime spread F formation. The occurrence of mid-latitude spread Fs over European longitude sector normally increases during summer. The occurrences of TIDs are also prominent at this interval of the year over nighttime mid-latitude ionosphere. The presence of MREs as an ionogram signature of TIDs over mid-latitude ionosphere is unique in nature.

High-latitude polar pattern of ionospheric electron density: Scaling features and IMF dependence

We investigated the average polar patterns of ionospheric electron density and the corresponding patterns of scaling features as a function of interplanetary magnetic field orientation. The focus is on the Northern Hemisphere using electron density data recorded on-board ESA Swarm A satellite. The first- and second-order scaling exponents have been evaluated by means of the qth-order structure functions. We used electron density measurements over a period of 15 months from April 1, 2014 to June 30, 2015, which corresponds to the maximum of solar cycle 24 and which is characterized by an average value of the solar radio flux (F10.7) index equal to (140±30) sfu. Electron density, first- and second-order scaling exponents have been mapped and discussed for four main IMF orientations provided by By and Bz components under conditions of high solar activity. Large spatial changes of the second-order scaling exponent pattern are observed with a steepening of the associated spectral exponent in correspondence with the nightside polar cap trailing edge. Intermittency, defined as the departure from linearity of the dependence of scaling exponents on moment order q, is also evaluated finding that it is generally higher near the equatorward boundary of the auroral oval than elsewhere. On the whole, the found patterns of the electron density first- and second-order scaling exponents suggest the occurrence of turbulence at the high latitudes.