Ground Ionosonde Research Articles

The Ionospheric Exploration Based on TJU#01 Meteorological Microsatellite Mission: Initial Results

AbstractThe global navigation satellite system radio occultation technique is achieving increasing significance and extensive promotion in the remote sensing of near‐earth atmosphere, climate, and ionosphere in recent three decades. Nowadays, many communities become interested in developing commercial mode in occultation measurement by launching massive nano‐ or cube satellite constellations at low costs. The TJU#01 is the first meteorological satellite of Tianjin Yunyao Aerospace Technology Co., Ltd. which was successfully launched into space on 7 December 2021. The occultation antenna onboard the satellite is able to probe both the ionosphere and atmosphere at multi‐frequencies including GPS, GLONASS, and BEIDOU systems. The microsatellite applies the same occultation antenna to receive both the atmospheric and ionospheric occultations at 100 and 1 Hz respectively. 100 Hz narrow band power and wide band power data are downloaded to the ground to generate high‐rate signal‐to‐noise ratio (SNR) series and applied to ionospheric scintillation exploration. In this paper, the primary parameters of the satellite and occultation antenna are introduced, as well as the ionospheric data processing methodologies. The initial ionospheric products of TJU#01 are evaluated after one‐month in orbit. The TJU#01 results have a good agreement with the co‐located ground ionosonde data and COSMIC‐2 observations. The new satellite and its follow‐on missions have great capabilities and potentials in the ionospheric and space weather researches.

Comparative Analysis of Global and Regional Ionospheric Responses during Two Geomagnetic Storms on 3 and 4 February 2022

The present work examines the spatial and temporal distribution of positive and negative TEC anomalies on the global and regional scale. To study the local response of the ionosphere, foF2 data from ground ionosonde stations and TEC data from Madrigal and CODE databases have been used. The relative deviation, which also determines the type of TEC response during geomagnetic storms on 3 and 4 February 2022, is considered. In the present study, the regions of positive and negative TEC anomalies and their evolution during storms are examined in detail. As a result of the study, estimates of the following were obtained: (i) the location of the sectors of the polar regions, in where the particle precipitation from the solar wind is observed, (ii) the mid-latitude regions, in which the mechanism of influence of the O/N2 ratio dominates, and (iii) the region around the equator, in which the influence of the electric field dominates. An attempt was made to determine which mechanism of influence of geomagnetic storms on the ionospheric electron density is dominant in different regions. The following main mechanisms are considered: (a) the additional ionization from the particles’ precipitation, (b) the change of the ratio of atomic oxygen (O) to molecular nitrogen (N2) due to the heating of the neutral air, and (c) the influence on the equatorial ionospheric anomaly.

Ionospheric response to the June 2015 geomagnetic storm in the South American region

The ionospheric dynamics in the South America (SA) sector during geomagnetic disturbed period from 21 to 24 June 2015 is investigated through ground ionosonde stations and Global Navigation Satellite System (GNSS) receivers, supported by Very Low Frequency (VLF) and magnetometer data. These disturbances were caused by 3 interplanetary shocks (IS) derived from 3 consecutives coronal mass ejections (CME) from the same solar active region; the first two CME were caused by filament eruptions, and the third was a much larger full halo CME, associated with a M2.6 solar flare. The first 2 shocks were compressive and did not cause an immediate response to the ionosphere in the analyzed region, while the third shock increased considerably the electron density from low to high-latitudes, triggering the second strongest geomagnetic storm of the 24th solar cycle. It was possible to observe the expansion of the crest of equatorial ionospheric anomaly (EIA) at midlatitudes and high-latitudes mainly due to prompt penetration electric field (PPEF) during the main phase and the recovery phase of the geomagnetic storm during the day.

Correction of Ionosphere Models Based on Ground Ionosonde Data

Correction of Ionosphere Models Based on Ground Ionosonde Data

3-D Ionospheric Tomography Using Model Function in the Modified L-Curve Method

Ionospheric tomography based on the observed total electron content along different satellite-receiver rays is a typically ill-posed inverse problem. Incorporating the electron density profiles data from COSMIC radio occultation technique and ground ionosondes, the Tikhonov regularization method is adopted to reconstruct the 3-D ionospheric electron density, and a regularization parameter is used to balance the weights between the prior (or background) information and real measurements. To determine the optimal regularization parameter, the model function in the modified L-curve method is used. This new method combines the advantages of the model function approach and L-curve criterion, and it has not only high accuracy, but also rapid convergence. To validate the effectiveness of this reconstruction algorithm, both the ideal test and real measurements test are carried out, and the results show that this algorithm can significantly improve the background model outputs.

Considering the potential of IAR emissions for ionospheric sounding

Knowledge of the ionospheric state allows us to adjust the forecasts of radio wave propagation, specify the environment models, and follow the changes of space weather. At present, probing of the ionosphere is produced by radio sounding with ground ionosondes, as well as by raying signals from satellites. We want to draw attention to the possibility of the diagnosis of the ionospheric parameters by detecting ultra-low frequency (ULF) electromagnetic emission generated in the so-called ionospheric Alfvén resonator (IAR). To do this, we present observations of the IAR emission made simultaneously for the first time at three stations using identical induction magnetometers. The stations are within one-hour difference of local time, two of them are mid-latitudinal; the third one is situated in the auroral zone. We compare frequency and frequency difference between adjacent harmonics of the observed multi-band emission with ionospheric parameters measured at the stations using ionosondes and GPS-observations. Diurnal variations of the ionospheric and ULF emission characteristics are also compared. The results show that there is quite a stable correlation between the resonant frequencies of the resonator bands and the critical frequency of the F2 layer of the ionosphere, namely, the frequency of the IAR emission varies inversely as the critical frequency of the ionosphere. This is due to the fact that the frequency of oscillation captured in the resonator is primarily determined by the Alfvén velocity (which depends on the plasma density) in the ionospheric F2 layer. The correlation is high; it varies at different stations, but is observed distinctly along the whole meridian. However, coefficients of a regression equation that connects the ionosphere critical frequency with DSB frequency vary significantly from day to day at all stations. The reason for such a big spread of the regression parameters is not clear and needs further investigation before we are able to develop a method for evaluating the ionosphere critical frequency using the IAR emission observations. Such a method may prove to be useful as an additional alternative to the basic method for probing the ionosphere using digisondes. This is especially important for auroral regions, where the presence of strong absorption, shielding by a lower layer, stratification, the presence of echoes, etc. make the sounding difficult.

Transionospheric radiosounding (Review)

The transionospheric radiosounding (TIS) method has naturally brought together the two most precise methods for scanning and monitoring the ionosphere (ionospheric radiosounding by airborne and ground ionosondes) into a single system. The subsequent development of TIS equipment has led to a qualitative change in the structure and operation of the ionospheric observatory, which greatly broadened the diagnostic capabilities of the ionospheric monitoring and expanded the ionospheric region monitored by the ground station. In fact, it can be said that a closed radiosounding system has been developed. It uses three branches of ionospheric multifrequency ray (or radio wave) fans to monitor the inner and outer ionosphere and to control both of these regions via transillumination of the ionosphere at the boundary of its radio transparency. The advantage of such a system is the full use of the entire range of radiated radio waves, each part of which is responsible for certain components of the diagnostic circuit. The paper presents the results of scientific studies obtained based on TIS data, which have led to the appearance of new and, to some extent, unexpected and previously unknown phenomena and effects. Special attention is paid to the modern stage of development of the TIS concept, which has good prospects for continuous monitoring of the polar ionosphere. It is questioned whether it is expedient to replace the term sounding with the term transillumination. It is noted that TIS was and remains the most precise method of ionosphere diagnostics.

Space weather effects on Earth's environment associated to the 24–25 October 2011 geomagnetic storm

Space weather studies have increased due to human society dependence on spaceborne and terrestrial infrastructure vulnerable to its effects. In this paper, we present an interdisciplinary study of the effects of solar activity on the Earth's environment; specifically, we focus on the effects on the ionosphere and the geomagnetic field. A timeline of effects occurring on the Earth produced by one of the first relevant events of the present solar cycle (24–25 October 2011) is given. We have analyzed the solar wind shockwave from satellite data, the storm‐time development, the ionospheric effects at global and local scales using the National Center for Atmospheric Research Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model fed with geomagnetic field‐aligned current data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment, and ground ionosonde data from both hemispheres, at Ebre Observatory and Port Stanley locations. We have compared observed geomagnetic variations at high latitudes with those modeled by the National Center for Atmospheric Research Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model. We have analyzed rapid geomagnetic variations (e.g., solar flare effect, storm commencement, Pi2) also on both hemispheres, at Ebre Observatory and Livingston Island locations. Finally, we have estimated geoelectric field and geomagnetically induced currents in the northeast of Spain (Catalonia) produced by this geomagnetic disturbance.

East‐west differences inF‐region electron density at midlatitude: Evidence from the Far East region

The global configuration of the geomagnetic field shows that the maximum east‐west difference in geomagnetic declination of northern middle latitude lies in the US region (~32°), which produces the significant ionospheric east‐west coast difference in terms of total electron content first revealed by Zhang et al. (2011). For verification, it is valuable to investigate this feature over the Far East area, which also shows significant geomagnetic declination east‐west gradient but smaller (~15°) than that of the US. The current study provides evidence of the longitudinal change supporting the thermospheric zonal wind mechanism by examining the climatology of peak electron density (NmF2), electron density (Ne) of different altitudes in the Far East regions with a longitude separation of up to 40–60° based on ground ionosonde and space‐based measurements. Although the east‐west difference (Rew) over the Far East area displays a clear diurnal variation similar to the US feature, that is negativeRew(West Ne > East Ne) in the noon and positive at evening‐night, the observational results reveal more differences including: (1) The noontime negativeRewis most pronounced in April–June while in the US during February–March. Thus, for the late spring and summer period negativeRewover the Far East region is more significant than that of the US. (2) The positiveRewat night is much less evident than in the US, especially without winter enhancement. (3) The magnitude of negativeRewtends to enhance toward solar maximum while in the US showing anticorrelation with the solar activity. The altitude distribution of pronounced negative difference (300–400 km) moves upward as the solar flux increases and hence produces the different solar activity dependence at different altitude. The result in the paper is not simply a comparison corresponding to the US results but raises some new features that are worth further studying and improve our current understanding of ionospheric longitude difference at midlatitude.

Comparison of the CHAMP radio occultation data with the Canadian advanced digital ionosonde in the Polar Regions

In this paper we present the results of the comparison of the retrieved electron density profiles of the Ionospheric Radio Occultation (IRO) experiment on board CHAMP (CHAllenging Minisatellite Payload), with the ground ionosonde profiles for the Polar Regions. IRO retrieved electron density profiles from CHAMP are compared with Canadian Advanced Digital Ionosonde (CADI) measurements at two vertical sounding stations well within the Polar Cap, Eureka (geog. 80°13′ N; 86°11′ W) and Resolute Bay (geog. 74°41′ N; 94°54′ W). We compared the ionospheric parameters such as the peak electron density of the F-layer (NmF 2) and the peak height of the F-layer (h mF 2) for a 3-year period, 2004–2006. CHAMP derived NmF 2 shows reasonable agreement with the ionosonde retrieved NmF 2 for both the stations (0.76 and 0.71 correlation coefficient, for Eureka and Resolute Bay, respectively) whereas the h mF 2 agreement is not that acceptable (0.25 and 0.37 correlation coefficient, respectively). The h mF 2 from vertical sounding showed less spread than the CHAMP h mF 2.

IRI 2001/90 TEC predictions over a low latitude station

Total electron content (TEC) over Tucumán (26.9°S, 294.6°W) measured with Faraday technique during the high solar activity year 1982, is used to check IRI 2001 TEC predictions at the southern crest of the equatorial anomaly region. Comparisons with IRI 90 are also made. The results show that in general IRI overestimates TEC values around the daily minimum and underestimates it the remaining hours. Better predictions are obtained using ground ionosonde measurements as input coefficients in the IRI model. The results suggest that for hours of maximum TEC values the electron density profile is broader than that assumed by the model. The main reason for the disagreement would be the IRI shape of the electron density profile. In a previous work using TEC measurements over Tucumán, obtained from GPS satellite signals during the high solar activity year 1999, a better agreement between IRI predictions and measurements has been observed. That better agreement was produced by the fact that 1999 GPS TEC measurements are 50% lower than those obtained by Faraday rotation technique during 1982. An equator ward movement of the southern peak of the EA plus the minor ionization level in 1999 could produce this reduction in TEC values. Moreover, it can be seen that in most of cases IRI TEC values around daily minimum show an hour displacement with respect to the experimental data.

Statistical correlation of spectral broadening in VLF transmitter signal and low-frequency ionospheric turbulence from observation on DEMETER satellite

Abstract. In our earlier papers we have found the effect of VLF transmitter signal depression over epicenters of the large earthquakes from observation on the French DEMETER satellite that can be considered as new method of global diagnostics of seismic influence on the ionosphere. At present paper we investigate a possibility VLF signal-ionospheric turbulence interaction using additional characteristic of VLF signal-spectrum broadening. This characteristic is important for estimation of the interaction type: linear or nonlinear scattering. Our main results are the following: – There are two zones of increased spectrum broadening, which are centered near magnetic latitudes Φ=±10° and Φ=±40°. Basing on the previous case study research and ground ionosonde registrations, probably it is evidence of nonlinear (active) scattering of VLF signal on the ionospheric turbulence. However occurrence rate of spectrum broadening in the middle-latitude area is higher than in the near-equatorial zone (~15–20% in comparison with ~100% in former area) that is probably coincides with the rate of ionospheric turbulence. – From two years statistics of observation in the selected 3 low-latitude regions and 1 middle-latitude region inside reception area of VLF signal from NWC transmitter we find a correlation of spectrum broadening neither with ion-cyclotron noise (f=150–500 Hz), which possibly means poor representation of the turbulence by the noise due to its mixture with natural ELF emission (which correlates with whistler), nor with magnetic storm activity. – We find rather evident correlation of ion-cyclotron frequency noise, VLF signal depression and weak correlation of spectrum broadening with seismicity in the middle-latitude region over Japan. But in the low-latitude regions we do not find such a correlation. Statistical decrease of VLF signal supports our previous case study results. However rather weak spectrum broadening-seismicity statistical correlation means probably that passive scattering prevails upon nonlinear (active) one.

November 2003 event: effects on the Earth's ionosphere observed from ground-based ionosonde and GPS data

Abstract. Intense late-cycle solar activity during October and November 2003 produced two strong geomagnetic storms: 28 October-5 November 2003 (October) and 19-23 November 2003 (November); both reached intense geomagnetic activity levels, Kp=9, and Kp=8+, respectively. The October 2003 geomagnetic storm was stronger, but the effects on the Earth's ionosphere in the mid-latitude European sector were more important during the November 2003 storm. The aim of this paper is to discuss two significant effects observed on the ionosphere over the mid-latitude European sector produced by the November 2003 geomagnetic storm, using data from ground ionosonde at Chilton (51.5° N; 359.4° E), Pruhonice (50.0° N; 14.6° E) and El Arenosillo (37.1° N; 353.3° E), jointly with GPS data. These effects are the presence of well developed anomalous storm Es layers observed at latitudes as low as 37° N and the presence of two thin belts: one having enhanced electron content and other, depressed electron content. Both reside over the mid-latitude European evening sector.

Comparison of ionospheric ionization measurements over Athens using ground ionosonde and GPS-derived TEC values

[1] GPS-derived TEC measurements (GPSTEC) represent the electron content up to 20,000 km, while a new ionosonde technique estimates the ionospheric electron content (ITEC) from ground ionosondes from the bottom of the ionosphere through the peak up to 1000 km. The two independent techniques were applied to determine ITEC and GPSTEC for Athens (38°N, 23.5°E) using the vertical Digisonde observations at Athens and GPSTEC maps produced by DLR/IKN for Europe using GPS measurements. Comparison of the two quantities over a 12-month time period shows a general agreement at daytime and a systematic deviation of ITEC towards lower values during nighttime. The diurnal variation of their residual values (ΔTEC) exhibits a morning minimum and an evening maximum, which can be explained in terms of ionospheric-plasmaspheric ionization exchange. The prominent evening enhancement, observed in all seasons around 1800–2000 LT, is attributed to the plasmaspheric bulge. The application of the superposed epoch analysis method on the daily ΔTEC values for several geomagnetic storms showed a rapid decrease of ΔTEC just after the storm initiation and a consecutive increase over a time period of 9 days, a behavior that is consistent with the plasmaspheric depletion and successive replenishment following storm activity. The daily variation of the ionospheric slab thickness is compatible with the variation of the thermospheric temperature within a day. Concerning the total slab thickness, this behavior is altered by the nighttime increase, which is most prominent in winter, and it is due to the lowering of the O+/H+ transition height. In summary, this analysis presents additional proof that the residuals ΔTEC = GPSTEC − ITEC provide information about the qualitative characteristics of the plasmaspheric dynamics as deduced from their diurnal behavior and their variation during geomagnetic storms.

F2 region maximum electron density height predictions for South American latitudes

Values of the F2 region maximum electron density height (hmF2) calculated using ground ionosonde data at South American latitudes are used to check the validity of the International Reference Ionosphere (IRI) to predict this variable. With this in mind we compare hmF2 predictions given by the model when measurements of critical frequency of F2 region and propagation parameter M(3000)F2 were used as input parameter in IRI (hmF2IRI‐Exp), against those obtained using the standard International Radio Consultative Committee (CCIR) option (hmF2IRI‐CCIR). In this paper we used hmF2IRI‐Exp values because hmF2 measurements were not available for the considered cases. Moreover, a comparison of the measured M(3000)F2 values with the CCIR predictions have been done. The results show that, in general, the standard predictions follow the diurnal tendency observed in the hmF2IRI‐Exp values. At low latitudes the hmF2IRI‐Exp values show oscillations not reproduced by the standard option. Cases with disagreements for 24 hours have been observed at high latitudes. Other cases with good agreement have been also obtained. The results suggest that, in general, the standard option of the model gives good hmF2 predictions at South American latitudes. Few cases showed deviation between 15 and 25%. As we expected, the obtained results suggest that the deviation between predicted and measured M(3000)F2 values is the main contribution for the deviation between hmF2IRI‐CCIR and hmF2IRI‐Exp. The comparison with the results obtained in previous work shows that the IRI performance in predicting M(3000)F2 and hmF2 is better than in predicting foF2.

The study of the electron density variability at fixed heights over San Juan and Tucuman

The electron density relative variability at fixed heights is studied using electron density profiles obtained from two Argentine ground ionosondes measurements. For midnight conditions, the results show that, in general, the variability increases with height reaching a maximum below the peak density. The highest variability was observed at 280 km of height for night equinox and high solar activity. Variability is considerably larger during night than during daytime at F region altitudes. An opposite but much smaller difference is seen al E region heights. At noon variability is larger at low solar activity than at high solar activity because of the smaller mean values.

Comparison between measured electron density at 600 km of altitude and IRI predictions

The electron density at 600 Km of altitude (N 600) predicted by IRI are compared with the measurements for a given particular time and place (not average) obtained with the Japanese Hinotori satellite. The results show disagreements among predictions and measurements when the model uses the CCIR and URSI options to obtain the peak characteristics. Good predictions are obtained for same cases using ground ionosonde data as input parameters in the model.

Signatures of polar cap patches in ground ionosonde data

The interpretation of localized density structures in the high‐latitude ionosphere as observed by ground ionosondes is a task that is complicated by the complexity of those structures and by the variety of processes that ionosonde waves undergo. To aid interpretation, we have performed a first‐order analysis of the shapes of traces seen in ionosonde displays. This has been done using an idealized model of a particular structure of current interest, a polar ionospheric patch. The patch is modeled as a spheroidal enhancement of density superposed on a horizontally stratified F layer. Ray tracing is used to find O‐ and X‐mode rays that reflect back to a ground ionosonde after total reflection. Theoretical curves are calculated for swept‐frequency (h'ƒ), fixed‐frequency (h't), and Doppler‐frequency (ƒDt) operational modes. The computed h'ƒ curves have U shapes, the h't curves are quasi‐hyperbolic, and the Doppler curves have reverse‐S shapes. By moving the patch through a series of horizontal separations from the ionosonde, the sequence of curves is calculated for a patch passing by an ionosonde. The theoretical traces have been compared with data from the Canadian advanced digital ionosondes (CADIs) at Resolute Bay, Eureka, and Alert. The CADI h'ƒ traces are observed usually to have incomplete U shapes, missing their lower‐frequency arms. In the light of the ray tracing the CADI results are consistent with the hypothesis that HF‐scattering irregularities are found on both the leading and trailing edges of patches but are stronger on the trailing edge. Similar results have been reported for scintillation‐causing irregularities. This points to the dominance of the gradient‐drift instability. The hyperbolic h't curves are asymmetric, having slower downsweeps than upsweeps. This can be caused by horizontal asymmetries in the patch density distribution. Often, polar patches seen by CADI are not single, isolated enhancements. Rather, they appear as composites of substructures, each of which mimics certain aspects of the single patch described by the present theoretical model.