Ground-based Ionosonde Observations Research Articles

A comparison of FORMOSAT-3/COSMIC radio occultation and ionosonde measurements in sporadic E detection over mid- and low-latitude regions

The investigation of sporadic E or Es layers typically relies on ground-based or satellite data. This study compares the Es layers recorded in ionograms with those detected using GNSS L1 signal-to-noise ratio data from FORMOSAT-3/COSMIC radio occultation at mid and low latitudes. GPS radio occultation measurements of Es layers, during an 11-year time span of 2007–2017, within a 2° latitude × 5° longitude grid around each ionosonde site are compared to the Es recordings of the ionosonde. By comparing multi-year radio occultation data with recordings from six ionosonde stations at mid and low latitudes, it was discovered that at least 20% of the Es layer detection results between each ionosonde and its crossing GPS radio occultation measurements did not agree. The results show that the agreement between the two methods in Es detection is highly dependent on the season and local time. This study suggests that Es layer recordings from ground-based ionosonde observations have the best agreement with the Es layers detected by radio occultation data during daytime and local summers. The difference in the Es detection mechanisms between the two methods can explain the inconsistency between Es events measured by these two methods. The detection of Es layers in ionograms relies on the high plasma concentration in the E region, whereas signal scintillations caused by a large vertical gradient of the plasma density in the E region are considered a sign of Es occurrence in satellite techniques.

Determining the Day-to-Day Occurrence of Low-Latitude Scintillation in Equinoxes at Sanya during High Solar Activities (2012–2013)

Plasma irregularity in the equatorial and low-latitude ionosphere, which leads to ionospheric scintillation, can threaten the operation of radio-based communication and navigation systems. A method for forecasting scintillation activity is still pending. In this study, we examined the performance of ionospheric parameters, including the critical frequency (foF2), peak height of the F2-layer (hmF2), scale height (Hm) and virtual height (h’F), around local sunset from ground-based ionosonde observations, and also the characteristics of Equatorial Ionization Anomaly (EIA) derived from Gravity Recovery and Climate Experiment (GRACE) observations in equinoctial months (March–April and September–October) during high solar activities (2012–2013) at a low-latitude station at Sanya (18.3° N, 109.6° E; dip lat.: 12.8° N), China. Furthermore, the simplified linear growth rate of Rayleigh–Taylor (R–T) instability inferred from ionosonde measurements and EIA strength derived from GRACE observations were used to estimate the day-to-day occurrence of post-sunset scintillation. The results indicate that it is not adequate to determine whether scintillation in a low-latitude region would occur or not based on one ionospheric parameter around sunset. The simplified growth rate of R–T instability can be a good indicator for the day-to-day occurrence of scintillation, especially in combination with variations in EIA strength. An index including the growth rate and EIA variations for the prediction of the post-sunset occurrence of irregularity and scintillation is proposed; the overall prediction accuracy could be about 90%. Our results may provide useful information for the development of a forecasting model of the day-to-day variability of irregularities and scintillation in equatorial and low-latitude regions.

The Validation of FORMOSAT-3/COSMIC Measurements in the Middle Latitude Region of China with Ionosonde Observations during 2015–2018

We used ground-based ionosonde observations at Ganzi (31.2° N, 100.4° E) to validate the COSMIC measurement in the middle latitude region of China during low solar activity. First, eligible data pairs from two kinds of techniques were selected for the validation. Then, we investigated the consistency of the ionospheric parameters’ F layer peak density (NmF2) from selected data pairs at different local times in different seasons, and we also investigated the F layer peak height (hmF2). The correlation of the parameters (including NmF2 and hmF2) were good in general. The correlation coefficients of the NmF2 and hmF2 from all selected data pairs were 0.94 and 0.77, respectively. The correlation coefficients were higher in the daytime than those at night for both the NmF2 and hmF2. The correlation coefficients in different seasons were close to each other for both the NmF2 and hmF2. The NmF2 from the COSMIC tends to be overestimated during the whole day except in the morning; the hmF2 from the COSMIC tends to be overestimated in the morning and underestimated in the afternoon.

Auroral ionospheric E region parameters obtained from satellite- based far-ultraviolet and ground-based ionosonde observations – effects of proton precipitation

Abstract. Coincident auroral far-ultraviolet (FUV) and ground-based ionosonde observations are compared for the purpose of determining whether auroral FUV remote sensing algorithms that assume pure electron precipitation are biased in the presence of proton precipitation. Auroral particle transport and optical emission models, such as the Boltzmann 3-Constituent (B3C) model, predict that maximum E region electron density (NmE) values derived from auroral Lyman–Birge–Hopfield (LBH) emissions, assuming electron precipitation, will be biased by up to ∼20 % (high) for pure proton aurora, while comparisons between LBH radiances and radiances derived from in situ particle flux observations (i.e., Knight et al., 2008, 2012) indicate that the bias associated with proton aurora should be much larger. Surprisingly, in the comparisons with ionosonde observations described here, no bias associated with proton aurora is found in FUV-derived auroral NmE, which means that auroral FUV remote sensing methods for NmE are more accurate in the presence of proton precipitation than was suggested in the aforementioned earlier works. Possible explanations for the discrepancy with the earlier results are discussed.

Application of the Fengyun 3 C GNSS occultation sounder for assessing the global ionospheric response to a magnetic storm event

Abstract. The rapid advancement of global navigation satellite system (GNSS) occultation technology in recent years has made it one of the most advanced space-based remote sensing technologies of the 21st century. GNSS radio occultation has many advantages, including all-weather operation, global coverage, high vertical resolution, high precision, long-term stability, and self-calibration. Data products from GNSS occultation sounding can greatly enhance ionospheric observations and contribute to space weather monitoring, forecasting, modeling, and research. In this study, GNSS occultation sounder (GNOS) results from a radio occultation sounding payload aboard the Fengyun 3 C (FY3-C) satellite were compared with ground-based ionosonde observations. Correlation coefficients for peak electron density (NmF2) derived from GNOS Global Position System (GPS) and Beidou navigation system (BDS) products with ionosonde data were higher than 0.9, and standard deviations were less than 20 %. Global ionospheric effects of the strong magnetic storm event in March 2015 were analyzed using GNOS results supported by ionosonde observations. The magnetic storm caused a significant disturbance in NmF2 level. Suppressed daytime and nighttime NmF2 levels indicated mainly negative storm conditions. In two longitude section zones of geomagnetic inclination between 40 and 80∘, the results of average NmF2 observed by GNOS and ground-based ionosondes showed the same basic trends during the geomagnetic storm and confirmed the negative effect of this storm event on the ionosphere. The analysis demonstrates the reliability of the GNSS radio occultation sounding instrument GNOS aboard the FY3-C satellite and confirms the utility of ionosphere products from GNOS for statistical and event-specific ionospheric physical analyses. Future FY3 series satellites and increasing numbers of Beidou navigation satellites will provide increasing GNOS occultation data on the ionosphere, which will contribute to ionosphere research and forecasting applications.

Impact of geomagnetic variation over sub-auroral ionospheric region during high solar activity year 2014

The present work is an attempt to evaluate the impact of changing space weather condition over sub-auroral ionosphere during high solar activity year 2014. In view of this, the GPS based TEC along with Ionosonde data over Indian permanent scientific base “Maitri”, Antarctica (70°46′00″S, 11°43′56″E) has been utilized. The results suggested that the nature of ionospheric responses to the geomagnetic disturbances not only depended upon the status of high latitudinal electro-dynamic processes but also influenced by the seasonal variations. The results revel both negative and positive type of ionospheric response in a single year but during different seasons. The study suggested that the combination of equator-ward plasma transportation along with ionospheric compositional changes causes a negative ionospheric impact especially during summer and equinox seasons. However, the combination of pole-ward contraction of the oval region along with particle precipitation may lead to exhibit positive ionospheric response during the winter season. The plasma transportation direction has been validated with the help of convection boundary (HM boundary) deduced with the help of SuperDARN observations. The ground based ionosonde observations clearly provided the evidence of deep penetration of high energetic particles up to the E-layer heights which results a sudden and strong appearance of E-layer. The strengthening of E-layer is responsible for modification of auroral electrojet and field-aligned current system. Also, the sudden appearance of E-layer along with a decrease in F-layer electron density suggested the dominance of NO+ over O+ in a considered region under geomagnetic disturbed condition.

Auroral ionospheric E region parameters obtained from satellite-based far ultraviolet and ground-based ionosonde observations: 1. Data, methods, and comparisons.

A large number (~1000) of coincident auroral far ultraviolet (FUV) and ground-based ionosonde observations are compared. This is the largest study to date of coincident satellite-based FUV and ground-based observations of the auroral E region. FUV radiance values from the NASA Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) Global Ultraviolet Imager (GUVI) and the Defense Meteorological Satellite Program (DMSP) F16 and F18 Special Sensor Ultraviolet Spectrographic Imager (SSUSI) are included in the study. A method is described for deriving auroral ionospheric E region maximum electron density (NmE) and height of maximum electron density (hmE) from N2 Lyman-Birge-Hopfield (LBH) radiances given in two channels using lookup tables generated with the Boltzmann 3-Constituent (B3C) auroral particle transport and optical emission model. Our rules for scaling (i.e., extracting ionospheric parameters from) ionograms to obtain auroral NmE and hmE are also described. Statistical and visual comparison methods establish statistical consistency and agreement between the two methods for observing auroral NmE, but not auroral hmE. It is expected that auroral non-uniformity will cause the two NmE methods to give inconsistent results, but we have not attempted to quantify this effect in terms of more basic principles, and our results show that the two types of NmE observations are well correlated and statistically symmetrical, meaning that there is no overall bias and no scale-dependent bias.

Solar Transients Disturbing the Mid Latitude Ionosphere during the High Solar Activity

We investigate the effect of solar transients on the mid latitude ionosphere during the high solar activity period of solar cycle 23 i.e 2003 and 2004. A mid latitude station, Guangzhou (23.1N, 113.4E) was selected to carry out the investigation. The ionospheric behaviour at the selected station is characterized by considering the critical frequency of F2 layer (foF2) obtained by using the ground based Ionosonde observations. Then we selected two types of solar transients viz. solar flares and Coronal Mass Ejections (CMEs). To quantify the effect of solar flares we have considered the X-ray flux (1-8 Å) and EUV flux (26-34nm). Similarly to quantify the effect of CMEs, we have considered the geomagnetic storms, because during high solar activity the geomagnetic storms are caused by CMEs. From our analysis we conclude that during the geomagnetic storms the value of foF2 decreases as compared to quiet days thereby showing a negative effect. On the contrary we found that during solar flares there is sudden and intense increase in foF2. We also performed a correlation analysis to access the magnitude of association between changes in flux values and peak values of Dst during flares and storms with the corresponding changes and peak values of foF2. We found that a strong correlation exists between the enhancements/decrements in foF2 and enhancements in flux values and Dst. We conclude, while geomagnetic activity suppresses ionospheric activity the flares enhance the same.

Spatial features of Weddell Sea and Yakutsk Anomalies in foF2 diurnal variations during high solar activity periods: Interkosmos-19 satellite and ground-based ionosonde observations, IRI reproduction and GSM TIP model simulation

We studied the main morphology of the formation of summer ionospheric anomalies which includes the Weddell Sea Anomaly (WSA) and the Yakutsk Anomaly (YA) in terms of positive night-to-day foF2 differences. For this purpose, we have for the first time used topside sounding (Interkosmos-19 satellite) and ground-based (ionosonde) data as well as results from an empirical model (International Reference Ionosphere – IRI) and from a first-principles model (Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere – GSM TIP). The main spatial morphological characteristics of the WSA and YA are similar which points to a common cause for their occurrence. Our preliminary GSM TIP model results showed that the foF2 values at nighttime are greater than at daytime due to: (1) the horizontal plasma transport due to electromagnetic drift; (2) the vertical component of plasma transport along the geomagnetic field lines via meridional neutral wind; (3) the distribution of the neutral composition of the thermosphere.

Long‐term ionospheric trends based on ground‐based ionosonde observations at Kokubunji, Japan

Using monthly medians of ionosonde observations taken over a period including more than four solar cycles (1958–2003) at Kokubunji (35.71°N, 139.49°E), Japan and a linear regression model to eliminate solar and geomagnetic effects, we derive the long‐term trends of critical frequencies (foE,foF1, andfoF2), the E region height (h′E), and the F2 peak height (hmF2). The results show increasing trends forfoE (+0.002 MHz/yr),h′E (+0.189 km/yr), andfoF1 (+0.0107 MHz/yr) and decreasing trends forfoF2 (−0.0058 MHz/yr at noon and −0.0016 MHz/year at midnight) andhmF2 (−0.398 km/yr at noon and −0.505 km/year at midnight). We have also analyzed seasonal and diurnal trend variations. These trends differed for various times of day and months, even with altering signs (except forhmF2). An interesting phenomenon was observed for the first time; that is, the morphologies of the overall seasonal trend variations offoE andfoF1 were opposite each other to some extent, although the trends remained positive. A similar phenomenon was found for the seasonal trend variation ofhmF2 between local noon and midnight. In addition, comparison of the results from four regression models indicated that the differences induced by linear and quadratic models are slightly significant forfoF2 but not for other parameters. On the basis of the average offoF2 data obtained over 5 hours around noon, we have assessed the performance of each of these regression models. The performance differed depending on the month. The results showed that the quadratic model and the linear model that took saturation into consideration performed better than the linear ones which did not consider saturation. In addition, it was indicated that the effect of geomagnetic activity was not significant in regression models at this station.

Latitudinal variation of ionospheric slab thickness

The ionospheric slab thickness τ, defined as a ratio of the total electron content (TEC) to the F-region peak electron density N mF2, is a first order measure of the shape of the electron density profile. In the present study, we use GPS-derived TEC and vertical electron content estimates ITEC from ground-based ionosonde observations together with the corresponding f oF2 (F2 layer critical frequency) and h mF2 (F2 layer peak height) at 14 world-wide stations lying at different latitude regions from the geomagnetic equator to north pole. The period of study is during 2001–2002, which is close to the solar maximum phase of the 23rd solar cycle. Hourly values of TEC, ITEC, f oF2, h mF2 and τ during the period of study are used to compare τ values from the observation and model predictions using the International Reference Ionosphere extended towards the plasmapause with the plasmasphere option of the Russian standard model of the ionosphere, IRI*. For the three latitudinal zones (high, mid and low latitudes) the IRI* predictions of τ are compared with observed τ values for the bottomside ionosphere (below h mF2), topside ionosphere (between h mF2 and 1000 km), plasmasphere (from 1000 to 20,000 km), and the total height range through the ionosphere and plasmasphere. Significant overestimation of τ has been revealed when using IRI*, particularly for the topside ionosphere at high latitudes. Relation of the topside part of slab thickness with the topside half peak density height above the F2 layer peak provides new characteristic parameter for modeling of the topside shape of electron density profile.

Daytime F2-layer positive storm effect at middle and lower latitudes

Abstract. Daytime F2-layer positive storm effects at middle and lower latitudes in the winter thermosphere are analyzed using AE-C, ESRO-4 neutral gas composition data, ground-based ionosonde observations and model calculations. Different longitudinal sectors marked by the storm onset as 'night-time' and 'daytime' demonstrate different F2-layer positive storm mechanisms. Neutral composition changes in the 'night-time' sector with increased [O] and [N2] absolute concentrations, while (N2/O)storm/(N2/O)quiet\\approx1 at F2-layer heights, are shown to contribute largely to the background NmF2 increase at lower latitudes lasting during daytime hours. Storm-induced surges of the equatorward wind give rise to an additional NmF2 increase above this background level. The mid-latitude F2-layer positive storm effect in the 'daytime' sector is due to the vertical plasma drift increase, resulting from the interaction of background (poleward) and storm-induced (equatorward) thermospheric winds, but not to changes of [O] and [N2] concentrations.

Daytime F2-layer positive storm effect at middle and lower latitudes

<strong class="journal-contentHeaderColor">Abstract.</strong> Daytime F2-layer positive storm effects at middle and lower latitudes in the winter thermosphere are analyzed using AE-C, ESRO-4 neutral gas composition data, ground-based ionosonde observations and model calculations. Different longitudinal sectors marked by the storm onset as 'night-time' and 'daytime' demonstrate different F2-layer positive storm mechanisms. Neutral composition changes in the 'night-time' sector with increased [O] and [N₂] absolute concentrations, while (N₂/O)<i>_storm</i>/(N₂/O)<i>_quiet</i>\approx1 at F2-layer heights, are shown to contribute largely to the background N<i>_m</i>F2 increase at lower latitudes lasting during daytime hours. Storm-induced surges of the equatorward wind give rise to an additional N<i>_m</i>F2 increase above this background level. The mid-latitude F2-layer positive storm effect in the 'daytime' sector is due to the vertical plasma drift increase, resulting from the interaction of background (poleward) and storm-induced (equatorward) thermospheric winds, but not to changes of [O] and [N₂] concentrations.