Ground-based Ionosonde Research Articles

Observations of ionospheric disturbances associated with the 2020 Beirut explosion by Defense Meteorological Satellite Program and ground-based ionosondes

Abstract. A major explosion that released a significant amount of energy into the atmosphere occurred in Beirut on 4 August 2020. The energy released may have reached the upper atmosphere and generated some traveling ionospheric disturbances (TIDs), which can affect radio wave propagation. In this study, we used data from the Defense Meteorological Satellite Program (DMSP) and ground-based ionosondes in the Mediterranean region to investigate the ionospheric response to this historic explosion event. Our DMSP data analysis revealed a noticeable increase in the ionospheric electron density near the Beirut area following the explosion, accompanied by some wavelike disturbances. Some characteristic TID signatures were also identified in the shape of ionogram traces at several locations in the Mediterranean. This event occurred during a period of relatively quiet geomagnetic conditions, making the observed TIDs likely to have originated from the Beirut explosion, not from other sources such as auroral activities. These observational findings demonstrate that TIDs from the Beirut explosion were able to propagate over longer distances, beyond the immediate areas of Lebanon and Israel–Palestine, reaching the Mediterranean and eastern Europe.

The Influence of Sudden Stratospheric Warming on the Development of Ionospheric Storms: The Alma-Ata Ground-Based Ionosonde Observations

This paper examines the response of the ionosphere to the impact of two moderate geomagnetic storms observed on January 17 and 26–27, 2013, under conditions of strong sudden stratospheric warming. The study uses data from ground-based ionosonde measurements at the Alma-Ata ionospheric station (43.25 N, 76.92 E) combined with optical observation data (The Spectral Airglow Temperature Imager (SATI)). Ionosonde data showed that the geomagnetic storms under consideration do not generate ionospheric storms but demonstrate some unusual types of diurnal foF2 variations with large (up to 60%) deviations in foF2 from median values observed during the night/morning periods on 13–15 and 20–23 January, which do not have any relation to solar or geomagnetic activity. Wave-like disturbances in foF2, h’F, and daily averaged foF2 values with a quasi-period of 5–8 days and peak-to-peak amplitude from about 1 MHz to 2 MHz (from 20% to 40%) and ~40 km are observed during the period 9–28 January, after registration of the occurrence of the major SSW event on 6–7 January. The observed variations in the OH emission rate are found to be quite similar to those observed in the ionospheric parameters that assume a community of processes in the stratosphere/mesosphere/ionosphere system. The study shows that the F region of the ionosphere is influenced by processes in the lower ionosphere, in this case by processes associated with sudden stratospheric warming SSW-2013, which led to modification of the structure of the ionosphere and compensation of processes associated with the development of the ionospheric storms.

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.

Optimal Estimation Inversion of Ionospheric Electron Density from GNSS-POD Limb Measurements: Part I-Algorithm and Morphology

GNSS-LEO radio links from Precise Orbital Determination (POD) and Radio Occultation (RO) antennas have been used increasingly in characterizing the global 3D distribution and variability of ionospheric electron density (Ne). In this study, we developed an optimal estimation (OE) method to retrieve Ne profiles from the slant total electron content (hTEC) measurements acquired by the GNSS-POD links at negative elevation angles (ε < 0°). Although both OE and onion-peeling (OP) methods use the Abel weighting function in the Ne inversion, they are significantly different in terms of performance in the lower ionosphere. The new OE results can overcome the large Ne oscillations, sometimes negative values, seen in the OP retrievals in the E-region ionosphere. In the companion paper in this Special Issue, the HmF2 and NmF2 from the OE retrieval are validated against ground-based ionosondes and radar observations, showing generally good agreements in NmF2 from all sites. Nighttime hmF2 measurements tend to agree better than the daytime when the ionosonde heights tend to be slightly lower. The OE algorithm has been applied to all GNSS-POD data acquired from the COSMIC-1 (2006–2019), COSMIC-2 (2019–present), and Spire (2019–present) constellations, showing a consistent ionospheric Ne morphology. The unprecedented spatiotemporal sampling of the ionosphere from these constellations now allows a detailed analysis of the frequency–wavenumber spectra for the Ne variability at different heights. In the lower ionosphere (~150 km), we found significant spectral power in DE1, DW6, DW4, SW5, and SE4 wave components, in addition to well-known DW1, SW2, and DE3 waves. In the upper ionosphere (~450 km), additional wave components are still present, including DE4, DW4, DW6, SE4, and SW4. The co-existence of eastward- and westward-propagating wave4 components implies the presence of a stationary wave4 (SPW4), as suggested by other earlier studies. Further improvements to the OE method are proposed, including a tomographic inversion technique that leverages the asymmetric sampling about the tangent point associated with GNSS-LEO links.

Multi-Instrumental Observations of Midlatitude Plasma Irregularities over Eastern Asia during a Moderate Magnetic Storm on 16 July 2003

This study presents the observations of midlatitude plasma irregularities over Eastern Asia during a moderate magnetic storm on 16 July 2003. Multi-instrumental observations, including the ground-based ionosondes, the GNSS networks, and the CHAMP and ROCSAT-1 satellites, were utilized to investigate the occurrence and characteristics of midlatitude plasma irregularities. The midlatitude strong spread F (SSF) mainly occurred in the midnight–morning sector as observed by ionosondes over Japan during this storm. SSF was related to plasma depletions, which is also recorded by GNSS network in the form of the enhancement of the rate of total electron content (TEC) change index (ROTI). The possible mechanism for the generation of SSF is that the enhanced eastward electric fields, associated with the prompt penetration electric fields and disturbance dynamo electric fields, cause the uplift and latitudinal extension of equatorial plasma bubbles (EPBs) to generate the observed midlatitude SSF further. Meanwhile, plasma density increased significantly under the influence of this storm. In addition, other common type of spread F, frequency spread F (FSF), was observed over Japan on the non-storm day and/or at high latitude station WK545, which seems to be closely related to the coupling of medium-scale traveling ionospheric disturbances (MSTIDs) and sporadic E (Es) layer. The above results indicate that various types of midlatitude spread F can be produced by different physical mechanisms. It is found that SSF can significantly affect the performance of radio wave propagation compared with FSF. Our results show that space weather events have a significant influence on the day-to-day variability of the occurrence and characteristics of ionospheric F-region irregularities at midlatitudes.

Statistical validation of ionospheric electron density profiles retrievals from GOES geosynchronous satellites

In this paper, we discuss a novel retrieval of ionospheric electron density profiles using the Radio Occultation (RO) technique applied to measurements captured by the Global Positioning System (GPS) receivers onboard two Geostationary Operational Environmental Satellites (GOES). The GOES satellites operate at ~35,800 km altitude and are primarily weather satellites that operationally contribute continuous remote-sensing data for real-time weather forecasting, as well as near-Earth environment monitoring and Sun observations. The GPS receivers onboard GOES-16 and GOES-17 satellites can track GPS signals propagated through the Earth’s atmosphere, and although the receivers are primarily designed for navigation and station-keeping maneuvers, these GPS measurements that traverse the Earth’s atmosphere can be used to retrieve the ionospheric electron density profiles. This process poses a range of technical challenges. GOES RO links are different from the traditional low Earth orbit (LEO) RO geometry since the receiver is located in an orbit that is higher in altitude than the GPS constellation of transmitters. Additionally, the GPS receivers onboard GOES satellites provide only single-frequency GPS L1 observations and have clocks much less stable than those typically used for RO measurements. The geographical distribution of the retrieved GEO-based RO profiles was found to be uniquely constrained and repeatable based on the relative geostationary fixed positions in the Earth-Centered Earth Fixed reference frame with respect to the GPS constellation orbiting at lower altitude, and significantly different from the coverage patterns of LEO-based RO missions. We demonstrate the successful application of the proposed RO profiling technique with a statistically significant set of GPS observations from GOES-16 and GOES-17 satellites over several years of data collection. This enabled us to retrieve more than 10,000 ionospheric electron density profiles with a maximum altitude of up to 1000–2000 km, much higher than any existing LEO-based RO mission. We demonstrate good performance of GEO-based RO measurements for properly specifying the vertical distribution of ionospheric plasma density by comparing the profiles dataset from the GOES RO experiment with independent reference observations – ground-based ionosondes and LEO-based RO missions, as well as model simulation results provided by the empirical International Reference Ionosphere model. Over multiple years of observations, statistical analysis of discrepancies between the ionospheric F2 layer peak parameters (peak density and height) derived from geosynchronous GOES observations and reference measurements was conducted. This analysis reveals a very good agreement between GOES RO electron density profiles and independent types of measurements in both the F2 peak and the profile shape.

Nightside 135.6 nm emission enhancements of mid/low latitudes during geomagnetic storms as observed by the ionosphere PhotoMeter (IPM) on the Chinese meteorological satellite FY-3D

IPM has detected nightside 135.6 nm emission enhancements over a wide latitude range, from the sub-auroral latitudes to the equatorial regions during geomagnetic storms. Our work, presented in this paper, uses the data of IPM to understand these 135.6 nm emission enhancements during of geomagnetic storms and studies the variations of total electron content (TEC) and the F2 layer peak electron density (NmF2) in the region of enhanced emissions. Middle and low latitude emission enhancements are presented during several medium storms in 2018. The variations of both the integrated electron content (IEC) derived from the nighttime OI 135.6 nm emission by IPM and TEC from the International GNSS Service (IGS) relative to the daily mean of magnetically quiet days of per each latitude bin (30°≦geographic latitude < 40°, 15°≦geographic latitude < 30°, 0°≦geographic latitude < 15°, −15°≦geographic latitude < 0°, −30°≦geographic latitude < -15°, −40°≦geographic latitude < -30°) are investigated and show that on magnetically storm day, IEC by IPM always increases, while TEC from IGC may increase or decrease. Even if both increase, the increase of IEC is greater than that of TEC. From the comparison of IEC and TEC during magnetic storms, it can be seen that the enhancement of the nighttime 135.6 nm emissions is not entirely due to the ionospheric change. The time of IEC enhancements at each latitude bin is in good agreement, which mainly corresponds to the main phase time of the geomagnetic storm event and lasts until the recovery phase. The available ground-based ionosonde stations provide the values of NmF2 which match the 135.6 nm emissions measured by IPM in space and time. The variations of NmF2 squared can characterize the variations of the OI 135.6 nm emissions caused by O+ ions and electrons radiative recombination. The study results show that the OI 135.6 nm emission enhancements caused by O+ ions and electrons radiative recombination (where NmF2 squared increases) are obviously a contribution to the measured 135.6 nm emission enhancements by IPM. The contribution accounts for at least one of all contributions to the measured 135.6 nm emission enhancements by IPM. However, where the NmF2 squared provided by ionosonde decrease or change little (where the OI 135.6 nm emissions cause by O+ ions and electrons radiative recombination also decrease or change little), the emission enhancements measured by IPM at storm-time appear to come from the contributions of other mechanisms, such as energetic neutral atoms precipitation, or the mutual neutralization emission (O+ + O-→2O + hʋ (135.6 nm)) which also occupies a certain proportion in 135.6 nm airglow emission at night.

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.

Quiet-time seasonal behaviour of the ionosphere measured by the Ionosphere PhotoMeter (IPM) on the Chinese meteorological satellite FY-3D compared with the IRI2016 model predictions

In this paper, we examine the climatology structure of the mid-night ionosphere at approximately two o’clock local time of a low-solar-activity year and discrepancies between Ionosphere PhotoMeter (IPM) observations and IRI (International Reference Ionosphere) model-2016 predictions using (1) a global structure for the F2 layer peak electron density (NmF2) for four seasons, (2) the mean NmF2 values at different latitudes by month, and (3) the monthly distribution of the global average of NmF2. The data is collected by the IPM, a far-ultraviolet nadir- viewing photometer that has been aboard the second-generation, polar-orbiting Chinese meteorological satellite Feng-Yun 3D (FY-3D) since its launch on November 25th, 2017 and has provided excellent opportunities for many scientific investigations of the ionosphere. We collected night glow data under low geomagnetic activity (KP ≤ 4) during 2018, and the data obtained five days before and after a full-moon night were removed to prevent the influence of stray light. Before analysing the climatology of the ionosphere and comparing the results with those obtained from IRI2016, the accuracy of NmF2 measured by IPM was evaluated by comparison with data from ground-based ionosondes. A statistical comparative analysis of NmF2 measured by IPM and ionosonde indicated a difference of 20% at middle latitudes and 28% at low latitudes. The global behaviour of NmF2 measured by IPM and IRI for four seasons shows that the IRI model generally captures the morphology of the latitudinal structure and hemispheric asymmetry in NmF2 observed by IPM. A comparison between IPM-measured NmF2 and IRI-predicted NmF2 indicates that the former is systematically lower than the latter. The difference in the measurements and predictions can be as large as 300%.

First ICON-FUV Nighttime NmF2 and hmF2 Comparison to Ground and Space-Based Measurements.

The Far Ultra Violet (FUV) ultraviolet imager onboard the NASA-ICON mission is dedicated to the observation and study of the ionosphere dynamics at mid and low latitudes. We compare O+ density profiles provided by the ICON FUV instrument during nighttime with electron density profiles measured by the COSMIC-2 constellation (C2) and ground-based ionosondes. Co-located simultaneous observations are compared, covering the period from November 2019 to July 2020, which produces several thousands of coincidences. Manual scaling of ionogram sequences ensures the reliability of the ionosonde profiles, while C2 data are carefully selected using an automatic quality control algorithm. Photoelectron contribution coming from the magnetically conjugated hemisphere is clearly visible in FUV data around solstices and has been filtered out from our analysis. We find that the FUV observations are consistent with the C2 and ionosonde measurements, with an average positive bias lower than 1 × 1011 e/m3. When restricting the analysis to cases having an NmF2 value larger than 5 × 1011 e/m3, FUV provides the peak electron density with a mean difference with C2 of 10%. The peak altitude, also determined from FUV observations, is found to be 15 km above that obtained from C2, and 38 km above the ionosonde value on average.

Towards a Real-Time Description of the Ionosphere: A Comparison between International Reference Ionosphere (IRI) and IRI Real-Time Assimilative Mapping (IRTAM) Models

This paper focuses on a detailed comparison, based on the F2-layer peak characteristics foF2 and hmF2, between the International Reference Ionosphere (IRI), which is a climatological empirical model of the terrestrial ionosphere, and the IRI Real-Time Assimilative Mapping (IRTAM) procedure, which is a real-time version of IRI based on data assimilation from a global network of ionosondes. To perform such a comparison, two different kinds of datasets have been considered: (1) foF2 and hmF2 as recorded by 40 ground-based ionosondes spread all over the world from 2000 to 2019; (2) foF2 and hmF2 from space-based COSMIC/FORMOSAT-3 radio occultation measurements recorded from 2006 to 2018. The aim of the paper is to understand whether and how much IRTAM improves IRI foF2 and hmF2 outputs for different locations and under different diurnal, seasonal, solar and magnetic activity conditions. The main outcomes of the study are: (1) when ionosonde observations are considered for validation, IRTAM significantly improves the IRI foF2 modeling both in accuracy and precision, while a slight improvement in the IRI hmF2 modeling is observed for specific locations and conditions; (2) when COSMIC observations are considered for validation, no noticeable improvement is observed from the IRTAM side for both foF2 and hmF2. Indeed, IRTAM can improve the IRI foF2 description only nearby the assimilated ionosonde locations, while the IRI hmF2 description is always more accurate and precise than IRTAM one.

A Signature of 27 day Solar Rotation in the Concentration of Metallic Ions within the Terrestrial Ionosphere

Abstract We present observations during the interval 2006–2014 of 27 day and 13.5 day periodic oscillations in the ionospheric sporadic E (Es) layer. This is a thin, dense layer composed of metallic ions in the Earth’s upper atmosphere between 90 and 130 km. Lomb–Scargle spectral and wavelet analyses reveal that these pronounced periodicities observed from ground-based ionosondes and GPS/GNSS radio occultations are associated with high-speed solar winds generated from persistent coronal holes on successive 27 day solar rotations. The 27 day and 13.5 day oscillations in the Es layers are dependent on latitude, showing a higher magnitude of periodicities at low latitudes between 0° and 15° and at high latitudes between 45° and 90° (10%–14%) than those at midlatitudes between 15° and 45° (4%–10%). The 27 day and 13.5 day oscillations in the high-latitude Es layers correlate well with the geomagnetic activity Dst and Ap indices, and these periodic oscillations become more significant at the solar maximum (2000–2003 and 2011–2014) than at the solar minimum.

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.

Observations of equatorial plasma bubbles during the geomagnetic storm of October 2016

We investigated the variations of equatorial plasma bubbles (EPBs) in the East-Asian sector during a strong geomagnetic storm in October 2016, based on observations from the Beidou geostationary (GEO) satellites, Swarm satellite and ground-based ionosonde. Significant nighttime depletions of F region in situ electron density from Swarm and obvious nighttime EPBs in the Beidou GEO observations were observed on 13 October 2016 during the main phase. Moreover, one interesting feature is that the rare and unique sunrise EPBs were triggered on 14 October 2016 in the main phase rather than during the recovery phase as reported by previous studies. In addition, the nighttime EPBs were suppressed during the whole recovery phase, and absent from 14 to 19 October 2016. Meanwhile, the minimum virtual height of F trace (h’F) at Sanya (18.3°N, 109.6°E, MLAT 11.1°N) displayed obvious changes during these intervals. The h’F was enhanced in the main phase and declined during the recovery phase, compared with the values at pre- and post-storm. These results indicate that the enhanced nighttime EPBs and sunrise EPBs during the main phase and the absence nighttime EPBs for many days during the recovery phase could be associated with storm-time electric field changes.

Accuracy assessment of the quiet-time ionospheric F2 peak parameters as derived from COSMIC-2 multi-GNSS radio occultation measurements

The Constellation Observing System for Meteorology, Ionosphere, and Climate 2 (COSMIC-2) mission was launched into a low-inclination (24°) orbit on June 25, 2019. Six satellites, each with an advanced Tri-GNSS Radio-Occultation Receiver System (TGRS), provide a global and uniform data coverage of the equatorial region with several thousand electron density profiles daily. The COSMIC-2 electron density profiles, and specifically the derived ionospheric F2 peak parameters, are properly validated in this study with reliable “truth” observations. For this purpose, we used manually scaled ionograms from 29 ground-based ionosondes located globally at low and middle latitudes. For this validation campaign, we considered only geomagnetically quiet conditions in order to establish benchmark level of the new mission’s ionospheric observation quality and to evaluate the operational capability of the COSMIC-2 Radio Occultation (RO) payload at the background of normal day-to-day variability of the ionosphere. For reliable colocations between two independent techniques, we selected only COSMIC-2 RO profiles whose F2 peak point coordinates were within 5° of the closest ionosonde. Our comparison of the ionospheric F2 peak height (hmF2) derived from COSMIC-2 RO and ground-based ionosonde measurements showed a very good agreement, with a mean of ~5 and ~2 km at low and middle latitudes, respectively, while RMS error was of ~23 and ~14 km, respectively. That range corresponds to a deviation of only 6–9% from the reference, ionosonde observations. Examination of representative collocation events with multiple (2–5) simultaneous RO tracks near the same ionosonde with different RO geometry, multi-satellite and multi-GNSS combination give us observational evidence that COSMIC-2 RO-based EDPs derived from GPS and GLONAS links show good self-consistency in terms of the ionospheric F2 peak values and electron density profile shape. We can conclude that COSMIC-2 provides high quality data for specification the ionospheric electron density at the F2 peak region.

Using GNSS radio occultation data to derive critical frequencies of the ionospheric sporadic E layer in real time

The small-scale electron density irregularities in the ionosphere have a significant impact on the interruptions of Global Navigation Satellite System (GNSS) navigation and the accuracy of GNSS positioning techniques. The sporadic ionospheric E (Es) layer significantly contributes to the transient interruptions of signals (loss of lock) for GNSS tracking loops. These effects on the GNSS radio occultation (RO) signals can be used to derive the global location and intensity of Es layers as a complement to ground-based observations. Here we conduct statistical analyses of the intensity of Es layers, based on the scintillation index S4max from the FORMOSAT-3/COSMIC during the period 2006–2014. In comparison with simultaneous observations from an ionosonde network of five low-to-middle latitude ionosondes, the S4max indices from COSMIC, especially the small values, are linearly related to the critical frequency of Es layers (foEs). An accumulated period of less than 1 h is required to derive the short-term variations in real-time ionospheric Es layers. A total of 30.22%, 69.57% and 98.13% coincident hourly foEs values have a relative difference less than 10%, 30% and 100%. Overall, the GNSS RO measurements have the potential to provide accurate hourly observations of Es layers. Observations with S4max < 0.4 (foEs < 3.6 MHz), accounting for 66% of COSMIC S4 measurements, have not been used fully previously, as they are not easily visible in ground-based ionosonde data.

Observation of thermosphere and ionosphere using the ionosphere PhotoMeter (IPM) on the Chinese meteorological satellite FY-3D

The Ionosphere PhotoMeter (IPM) is a far ultraviolet nadir-viewing photometer that flew aboard the second-generation, polar-orbiting Chinese meteorological satellite Feng-Yun 3D (FY-3D), which was launched on November 25th, 2017. By observing far ultraviolet night-time OI 135.6 nm emissions, which are produced by the recombination of O+ ions and electrons, the F2 layer peak electron density (NmF2) can be deduced. During daytime IPM was designed to measure the OI 135.6 nm and N2 Lyman-Birge-Hopfield (LBH) band emissions, which would be used to infer the O/N2 ratio, a key diagnostic of neutral dynamics in the daytime. The paper shows the measurement results from IPM taken during its initial months of Operation. A quantitative comparison showing NmF2 from IPM and ground-based ionosondes is presented, and the correlation value R between the ground-based ionosondes and the satellite NmF2 is 0.91. The global O/N2 ratio distribution during geomagnetic storm on 25 through 30 August is presented and illustrated, which could show the latitudes of the ionospheric positive/negative storm in different longitude ranges. The O/N2 ratio significantly decreases during the main and recovery phase of the storm as expected. The correlation value R between the O/N2 ratio retrieved from IPM data and the ionospheric electron density provided by ground-based ionosondes during storms in August 2018 is about 0.78.

Effects in the Ionosphere after the Chilean Earthquake on February 27, 2010, According to Data of Ground-based Ionosondes

The paper analyzes the measurement data of the critical frequency (foF2) of the regular ionospheric F2-layer at a number of ground based stations of the vertical sounding of the ionosphere in order to detect disturbances in the ionosphere that followed the earthquake with a magnitude of M = 8.8. The earthquake occurred in Chile on February 27, 2010 at 0634 UT at an epicentral distance of 335 km from its capital city of Santiago. It was found that at significant distances (over 5000 km) from the earthquake epicenter under a quiet geomagnetic conditions, wave disturbances are observed in the behavior of foF2, exceeding approximately two standard deviations from the background level for three hours, with the maximum relative deviation of 20%. The analysis shows that the characteristics of disturbances in the ionosphere correspond in time to the arrival of a packet of acoustic-gravity waves excited in the atmosphere at the time of the seismic shock.

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.