Ionospheric Stations Research Articles

Электронная концентрация на высотах ионосферного слоя F1 в последнем минимуме (2007–2009 гг.) цикла солнечной активности

We present the results of the analysis of annual variations in daily electron density (N) at heights 140–160 km for the last solar minimum (2007–2009) obtained from digisonde measurements at the ionospheric station Irkutsk (52 °N, 104 °E). New coefficients of the known semi-empirical model (SEM) describing the connection between N and thermospheric characteristics are calculated to identify regularities of these variations. We have revealed that a characteristic feature of the annual N variations during the solar minimum is a change in their phase by 180° in a relatively narrow altitude interval (170–180 km). These results and the new SEM coefficients are original and important for atmospheric and ionospheric physics.

APPLICATION OF OBLIQUE IONOSPHERIC SOUNDING TO INCREASE THE ACCURACY CHARACTERISTICS OF THE OVER-THE-HORIZON RADAR

The over-the-horizon radar stations of the space wave are sensitive to changes in the ionosphere. For the accurate operation of such radars, it is necessary to have up-to-date information on the ionosphere at the reflection point of radio waves. The article gives an example of the implementation of a network of ionospheric stations working in the interests of the FG of the radar station with the example of the Australian system JORN. It is proposed to use the Russian vertical ionosondes Parus-A for ionospheric support of the radar. These ionosondes are also capable of performing oblique sounding at distances up to 2000 km. The results of oblique sounding by these ionosondes are shown on various routes on the territory of Russia: in the European part of the country, in Siberia and in the Far East. The features are explained and the analysis of the data is carried out. It is concluded that the problem is topical and that it can be solved. The potential is shown in the ionosonde Parus-A at the development stage and implemented later.

Ionospheric anomalies detected by ionosonde and possibly related to crustal earthquakes in Greece

Abstract. Ionosonde data and crustal earthquakes with magnitude M≥6.0 observed in Greece during the 2003–2015 period were examined to check if the relationships obtained earlier between precursory ionospheric anomalies and earthquakes in Japan and central Italy are also valid for Greek earthquakes. The ionospheric anomalies are identified on the observed variations of the sporadic E-layer parameters (h′Es, foEs) and foF2 at the ionospheric station of Athens. The corresponding empirical relationships between the seismo-ionospheric disturbances and the earthquake magnitude and the epicentral distance are obtained and found to be similar to those previously published for other case studies. The large lead times found for the ionospheric anomalies occurrence may confirm a rather long earthquake preparation period. The possibility of using the relationships obtained for earthquake prediction is finally discussed. Keywords. Ionosphere (Ionospheric disturbances)

Geomagnetic Storm Effects at F1 Layer Altitudes in Various Periods of Solar Activity (Irkutsk Station)

The influence of geomagnetic disturbances on electron density Ne at F1 layer altitudes in different conditions of solar activity during the autumnal and vernal seasons of 2003–2015, according to the data from the Irkutsk digital ionospheric station (52° N, 104° Е) is examined. Variations of Ne at heights of 150–190 km during the periods of twenty medium-scale and strong geomagnetic storms have been analyzed. At these specified heights, a vernal–autumn asymmetry of geomagnetic storm effects is discovered in all periods of solar activity of 2003–2015: a considerable Ne decrease at a height of 190 km and a weaker effect at lower levels during the autumnal storms. During vernal storms, no significant Ne decrease as compared with quiet conditions was registered over the entire analyzed interval of 150−190 km.

Winter Anomaly in the Critical Frequency of the E-Layer in the Nighttime Polar Cap

With the medians of the E-layer critical frequency foE measured at Resolute Bay and Casey ionospheric stations located in the polar caps of the Northern and Southern Hemispheres, it is found that these medians are higher at the nighttime hours (2100–0300 LT) in the local winter than in local summer. For Resolute Bay station, which is located above the Arctic Circle, the latter means that the foE median is higher at polar night than at polar day. Thus, the effect of a winter anomaly in the foE median in the nighttime polar cap is detected. The amplitude of that anomaly (the ratio of the local winter foE values to local summer values) could reach 15–20% and 10–15% for Resolute Bay and Casey stations, respectively. It is assumed that the winter anomaly in the foE median in the nighttime polar cap is caused by the winter–summer asymmetry in the accelerated electron energy fluxes precipitating into this region.

Long-term changes in the Delta foF2 parameter based on the data of two European ionospheric stations

Analysis of changes in the critical frequency foF2 in recent decades has been performed by determination of “Delta foF2” parameter. These values determine the mean change of foF2 values from the “etalon period” (1958–1980) to later periods. The results are compared with the determination of foF2 trends, which was performed in a series of previous publications of the authors. The data of two most reliable ionospheric stations of the European region, Slough and Juliusruh, are analyzed. The results confirm all principal conclusions obtained earlier, which were based on analysis of the trends. A systematic decrease of foF2 with time occurs (which corresponds to a negative trend), and the character of changes in the Delta values with season and local time on the whole agrees with the character of changes in the trend. It is shown that the results based on the data of both considered stations show good agreement.

Equinoctial spread-F occurrence at low latitudes in different longitude sectors under moderate and high solar activity

A comparative study aimed to investigate the equatorial and low-latitude spread-F occurrences for moderate solar activity (MSA) and high solar activity (HSA), was carried out considering concurrent observations made in some ionospheric stations, which identify three separate longitudinal sectors: Chiang Mai (CGM; 18.8° N, 98.9° E, mag. Lat. 13.2° N) and Chumphon (CPN; 10.7° N, 99.4° E, mag. Lat. 3.2° N), Thailand; Palmas (PAL; 10.2° S, 311.8° E, mag. Lat. 0.9° S) and São José dos Campos (SJC; 23.2° S, 314.1° E, mag. Lat. 14.0° S), Brazil; Tucumán (TUC; 26.9° S, 294.6° E, mag. Lat. 16.8° S), Argentina.Spread-F phenomena recorded during the equinoctial months of September and October 2010, March and April 2011, for MSA, March and April 2014, September and October 2014, for HSA, were classified in two different modes: range spread-F (RSF) and frequency spread-F (FSF). The satellite trace (ST) occurrence was also investigated as possible precursor of spread-F events. When comparing the results of equatorial (CPN and PAL) and low-latitude (CGM, SJC, and TUC) stations, some common features independently of the solar activity emerge: (1) a prevalence of RSF signatures is observed in the time interval 20:00–03:00 LT, while FSF occurrences prevail in the time interval 03:00–06:00 LT; (2) STs are confirmed to be a possible precursor of RSF occurrences.For HSA, at equatorial latitudes, spread-F occurrences in the Thai sector (CPN) are higher than those observed in the Brazilian sector (PAL).When comparing the results of low-latitude stations of CGM, SJC, and TUC some unusual aspects characterizing the morphology of spread-F occurrences emerge: (1) contrary to the Thai and Argentine sectors, in the Brazilian sector (SJC), RSF and FSF appearances in September, for HSA, are observed with relatively long persistence times between about 03:00-06:00 LT and 01:00-03:00 LT respectively, while balanced RSF and FSF occurrences with short persistence times are observed for months for MSA; (2) a prevalence of FSF at CGM during the first half of September for MSA, never observed in the Brazilian and Argentine areas.During years of LSA and MSA common morphological aspects are found at CGM and SJC, that is a predominance of FSF, with the lowest persistence times characterizing SJC. This suggests that the low-latitude behaviour of spread-F occurrences, under different levels of solar activity, at least in the longitude sectors here analysed, can be to a some extent generalized.

Quasi-wave variations in foEs during stratospheric warmings of 2008–2010 according to data from Kaliningrad ionospheric station

The results of analysis of variations in the sporadic layer critical frequency (foEs) for winter periods of 2008–2010 in which sudden stratospheric warmings were observed are presented in the paper. The data were obtained at Kaliningrad ionospheric station (54.6° N, 20° E) by a Parus digital ionosonde under the usual sounding regime with an interval of 15 min. Daily mean values of foEs were used for the analysis. Solar and geomagnetic activity remained low during the periods under study, making it possible to relate the quasiwave time variations in foEs to the parameters of stratospheric warmings. The results of spectral analysis performed on the basis of continuous wavelet transform showed that, during all warmings occurring in 2008–2010, time variations in foEs show the presence of wave processes with a period of an order of 5 days and longer ones with a period of ~10—11 days. These periods coincide with characteristic periods of planetary waves observed in the atmosphere during sudden stratospheric warnings.

Global empirical model of critical frequency of the ionospheric F2-layer for quiet geomagnetic conditions

Using the foF2 database obtained from satellites and ground-based ionospheric stations, we have constructed a global empirical model of the critical frequency of the ionospheric F2-layer (SDMF2—Satellite and Digisonde Data Model of the F2 layer) for quiet geomagnetic conditions (Kp < 3). The input parameters of this model are the geographical coordinates, UT, day, month, year, and the integral index F10.7 (day, τ = 0.96) of solar activity for a given day. The SDMF2 model was based on the Legendre method for the spatial expansion of foF2 monthly medians to 12 in latitude and 8 in longitude of spherical harmonics. The resulting spatial coefficients have been expanded by the Fourier method in three spherical harmonics with respect to UT. The effect of the saturation of critical frequency of the ionospheric F2-layer at high solar activity was described in the SDMF2 model by foF2 as a logarithmic function of F10.7 (day, τ = 0.96). The difference between the SDMF2 and IRI models is a maximum at low solar activity as well as in the Southern Hemisphere and in the oceans. The testing on the basis of ground-based and satellite data has indicated that the SDMF2 model is more accurate than the IRI model.

Stability of solar correction for calculating ionospheric trends

Abstract. Global climate change affects the whole atmosphere, including the thermosphere and ionosphere. Calculations of long-term trends in the ionosphere are critically dependent on solar activity (solar cycle) correction of ionospheric input data. The standard technique is to establish an experimental model via calculating the dependence of ionospheric parameter on solar activity from the whole analysed data set, subtract these model data from observed data and analyse the trend of residuals. However, if the solar activity dependence changes with time, the solar correction calculated from the whole data set may result in miscalculating the ionospheric trends. To test this, data from two European ionospheric stations – Juliusruh and Slough/Chilton – which provide long-term reliable data, have been used for the period 1975–2014. The main result of this study is the finding that the solar activity correction used in calculating ionospheric long-term trends need not be stable, as was assumed in all previous investigations of ionospheric trends. During the previous solar cycle 23 and the current solar cycle 24, the solar activity correction appears to be different from that for the previous period and the Sun seems to behave in a different way than throughout the whole previous era of ionospheric measurements. In future ionospheric trend investigations the non-stability of solar activity correction has to be very seriously taken into account, because it can substantially affect calculated long-term trends of ionospheric parameters.

Properties of the F2-layer critical frequency median in the nocturnal subauroral ionosphere during low and moderate solar activity

Based on an analysis of data from the European ionospheric stations at subauroral latitudes, it has been found that the main ionospheric trough (MIT) is not characteristic for the monthly median of the F2-layer critical frequency (foF2), at least for low and moderate solar activity. In order to explain this effect, the properties of foF2 in the nocturnal subauroral ionosphere have been additionally studied for low geomagnetic activity, when the MIT localization is known quite reliably. It has been found that at low and moderate solar activity during night hours in winter, the foF2 data from ionospheric stations are often absent in the MIT area. For this reason, a model of the foF2 monthly median, which was constructed from the remaining data of these stations, contains no MIT or a very weakly pronounced MIT.

Vertical plasma drift velocities in the polarization jet observation by ground Doppler measurements and driftmeters on DMSP satellites

Vertical and horizontal plasma drifts are investigated during the polarization jet (PJ) detection in the F2 ionospheric layer based on the Doppler measurements at the Yakutsk meridian chain of subauroral ionospheric stations. It is shown that the velocities of vertical and horizontal drifts are significantly higher than the background motion during PJ observation periods. The ionospheric plasma motion direction changes from upward to downward on the polar edge of the main ionospheric trough. Doppler measurements on the DPS-4 ionosondes are compared with the simultaneous measurements of the plasma drift on the DMSP satellites during their passage near the Yakutsk meridian. The two kinds of measurements are in good agreement with each other. During the magnetic storm of June 23, 2005, by measurements of the DMSP satellites, the velocities of upward plasma flows were 1.0–1.4 km/s at a satellite altitude of 850 km. In the ionospheric F region, this speed corresponds to 150 m/s. According to satellite measurements, the westward drift velocity reached 2.5 km/s. The development of the polarization jet in the ionosphere was accompanied by a tenfold decrease in the electron density in 15–30 min.

FoF2 vs solar indices for the Rome station: Looking for the best general relation which is able to describe the anomalous minimum between cycles 23 and 24

Analyses of the dependence of the F2layer critical frequency, foF2, on five widely used solar activity indices (F10.7, Lym-α, MgII, R and EUV0.1–50)are carried out considering noon values manually validated at the ionospheric station of Rome (41.8°N, 12.5°E, Italy) between January 1976 and December 2013, a period of time covering the last three solar cycles and including the prolonged and anomalous minimum of solar cycle 23/24 (years 2008–2009). After applying a 1-year running mean to both foF2 and solar activity indices time series, a second order polynomial fitting proves to perform better than a linear one, and this is specifically due to the very low solar activity of the last solar minimum and to the remaining saturation effect characterizing the high solar activity. A comparison between observed and synthetic foF2 values, the latter calculated by using the analytical relations found for every index, and some considerations made on the R parameter introduced by Solomon et al. (2013), suggest that MgII is the best index to describe the dependence of foF2 on the solar activity. Three main reasons justify this result: (1) the good sensibility of MgII to the variations of foF2 for low solar activity; (2) the reduced saturation effect characterizing MgII at high solar activity; (3) the poor influence of the hysteresis effect characterizing MgII at medium solar activity. On the other hand, the F10.7 index, widely used as input parameter for numerous ionospheric models, does not represent properly the last minimum; specifically, it is not able to describe the variations of foF2 under a solar activity level of F10.7=82·10–22 [JHz–1s–1m–2].

Empirical model of the main ionospheric trough for the nighttime winter conditions

For the first time we developed an empirical model of the main ionospheric trough, MIT, for quiet (Kp=2) nighttime (18:00–06:00 LT) winter conditions in the Northern and Southern hemispheres for all levels of solar activity. The model consists of two parts: (1) the MIT position model in terms of geographical latitude and longitude; (2) the MIT shape model in terms of the latitudinal–longitudinal foF2 variations in the range of 45–75°N latitudes in the Northern hemisphere and of 40–80°S in the Southern hemisphere. Thus, an empirical model of the quiet nighttime subauroral ionosphere has been developed. To construct this model the Interkosmos-19 and CHAMP satellites data have been used. The in-situ Ne measurements at the CHAMP heights were transformed to the electron density at F2 layer peak height (i.e. to NmF2 and then to foF2). In the frame of the model the diurnal and longitudinal variations in the MIT minimum position were revealed and studied in detail. Also the longitudinal and latitudinal variations in foF2 in the MIT region were investigated. Accuracy of the model was tested according to the ground-based ionospheric stations data. It is shown that the constructed model much more adequately reproduces the variations in the winter nighttime subauroral ionospheric structure, including the MIT position and shape variations, than the International Reference Ionosphere model (IRI-2012). The online version of the MIT model is available on the IZMIRAN website: http://www.izmiran.ru/ionosphere/sm-mit/ for free using and more detailed testing.

Ionospheric response under the influence of the solar eclipse occurred on 20 March 2015: Importance of autoscaled data and their assimilation for obtaining a reliable modeling of the ionosphere

This paper wants to highlight how the availability of measurements autoscaled at some reference ionospheric stations, and their assimilation by ionospheric models, was of crucial importance in determining, during the solar eclipse conditions occurred on 20 March 2015, a reliable representation of the ionosphere. Even though the solar eclipse falls in the recovery phase of the St. Patrick geomagnetic storm started on 17 March 2015, its influence on the ionospheric plasma seems undeniable. The reference ionospheric stations considered here are those of Rome (41°.8’ N, 12°.5’ E), and Gibilmanna (37°.9’ N, 14°.0’ E), Italy. Specifically, in a time interval including that of the eclipse, the electron density profiles autoscaled by the Automatic Real-Time Ionogram Scaler with True-height (ARTIST) system at San Vito (40°.6′ N, 17°.8′ E), Italy, which are here considered as the truth profiles, were compared with both the electron density profiles calculated by the IRI-SIRMUP-Profiles (ISP) model, after assimilating data recorded at Rome and Gibilmanna, and the electron density profiles provided by the IRI-CCIR model. The ISP and IRI-CCIR performances were then evaluated in terms of the root mean square errors made on the whole electron density profiles. The three-dimensional (3-D) electron density mappings of the ionosphere provided by ISP and IRI-CCIR models were also considered as the ionospheric environment by the ray tracing software tool IONORT to calculate quasi-vertical synthesized ionograms over the short radio link San Vito – Brindisi (40°.4′ N, 17°.6′ E), Italy. The corresponding synthesized values of foF2 and fxF2, obtained by IONORT-ISP and IONORT-(IRI-CCIR) procedures, were compared with those autoscaled by ARTIST from the vertical ionograms recorded at the truth site of San Vito. Some examples of IONORT-ISP and IONORT-(IRI-CCIR) synthesized ionograms are shown and discussed. Finally, comparisons in terms of foF2 deduced by long-term prediction and nowcasting maps are also shown. The results achieved in this work demonstrate how the assimilation of autoscaled data into the ionospheric models turned out to be valuable in providing a better representation of the ionospheric electron density under very unusual conditions.

Ionospheric vertical drift response at a mid-latitude station

Vertical plasma drift data measured at a mid-latitude ionospheric station Pruhonice (50.0°N, 14.6°E) were collected and analysed for the year 2006, a year of low solar and geomagnetic activity. Hence these data provide insight into the drift behaviour during quiet conditions. The following typical diurnal trend is evident: a significant decay to negative values (downward peak) at dawn; generally less pronounced downward peak at dusk hours. Magnitude of the downward drift varies during the year. Typically it reaches values about 20ms-1 at dawn hours and 10ms-1 at dusk hours. Maximum dawn magnitude of about 40ms-1 has been detected in August. During daytime the vertical drifts increases from the initial small downward drifts to zero drift around noon and to small upward drifts in the afternoon. Night-time drift values display large variability around a near zero vertical drift average. There is a significant trend to larger downward drift values near dawn and a less pronounced decrease of the afternoon upward vertical drifts near sunset. Two regular downward peaks of the drift associated with the dawn and dusk are general characteristics of the analysed data throughout the year 2006. Their seasonal course corresponds to the seasonal course of the sunrise and sunset. The duration of prevailing negative drift velocities forming these peaks and thus the influence of the dawn/dusk on the drift velocity is mostly 1.5–3h. The dawn effect on vertical drift tends to be larger than the effect of the dusk. The observed magnitude of the sunrise and sunset peaks show significant annual course. The highest variability of the magnitude is seen during winter. High variability is detected till March equinox and again after September equinox. Around solstice, both peaks reaches lowest values. After that, the magnitudes of the drift velocity increase smoothly till maxima in summer (August). The vertical drift velocity course is smooth between June solstice and September equinox. In general, the detected values of the observed vertical drift are of lower magnitudes compare to low latitudes. Drift data in midlatitudes seems to be more influenced by the atmospheric waves than data in lower latitudes.

Signature of a possible relationship between the maximum CME speed index and the critical frequencies of the F1 and F2 ionospheric layers: Data analysis for a mid-latitude ionospheric station during the solar cycles 23 and 24

We analyze temporal variations of two solar indices, the monthly mean Maximum CME Speed Index (MCMESI) and the International Sunspot Number (ISSN) as well as the monthly median ionospheric critical frequencies (foF1, and foF2) for the time period of 1996–2013, which covers the entire solar cycle 23 and the ascending branch of the cycle 24. We found that the maximum of foF1 and foF2 occurred respectively during the first and second maximum of the ISSN solar activity index in the solar cycle 23. We compared these data sets by using the cross-correlation and hysteresis analysis and found that both foF1 and foF2 show higher correlation with ISSN than the MCMESI during the investigated time period, but when significance levels are considered correlation coefficients between the same indices become comparable. Cross-correlation analysis showed that the agreement between these data sets (solar indices and ionospheric critical frequencies) is better pronounced during the ascending phases of solar cycles, while they display significant deviations during the descending phase. We conclude that there exists a signature of a possible relationship between MCMESI and foF1 and foF2, which means that MCMESI could be used as a possible indicator of solar and geomagnetic activity, even though other investigations are needed.

F2 region response to geomagnetic disturbances across Indian latitudes: O(1S) dayglow emission

AbstractThe morphology of ionospheric storms has been investigated across equatorial and low latitudes of Indian region. The deviation in F2 region characteristic parameters (foF2 and h′F) along with modeled green line dayglow emission intensities is examined at equatorial station Thiruvananthapuram (8.5°N, 76.8°E, 0.63°S geomagnetic latitude) and low‐latitude station Delhi (28.6°N, 77.2°E,19.2°N geomagnetic latitude) during five geomagnetic storm events. Both positive and negative phases have been noticed in this study. The positive storm phase over equatorial station is found to be more frequent, while the drop in ionization in most of the cases was observed at low‐latitude station. It is concluded that the reaction as seen at different ionospheric stations may be quite different during the same storm depending on both the geographic and geomagnetic coordinates of the station, storm intensity, and the storm onset time. Modulation in the F2 layer critical frequency at low and equatorial stations during geomagnetic disturbance of 20–23 November 2003 was caused by the storm‐induced changes in O/N2. It is also found that International Reference Ionosphere 2012 model predicts the F2 layer characteristic (foF2 and h′F) parameters at both the low and equatorial stations during disturbed days quite reasonably. A simulative approach in GLOW model developed by Solomon is further used to estimate the changes in the volume emission rate of green line dayglow emission under quiet and strong geomagnetic conditions. It is found that the O(1S) dayglow thermospheric emission peak responds to varying geomagnetic conditions.

Inverse problem of radiofrequency sounding of ionosphere

An algorithm for the solution of the inverse problem of vertical ionosphere sounding and a mathematical model of noise filtering are presented. An automated system for processing and analysis of spectrograms of vertical ionosphere sounding based on our algorithm is described. It is shown that the algorithm we suggest has a rather high efficiency. This is supported by the data obtained at the ionospheric stations of the so-called “AIS-M” type.

A regional adaptive and assimilative three-dimensional ionospheric model

A regional adaptive and assimilative three-dimensional (3D) ionospheric model is proposed. It is able to ingest real-time data from different ionosondes, providing the ionospheric bottomside plasma frequency fp over the Italian area. The model is constructed on the basis of empirical values for a set of ionospheric parameters Pi[base] over the considered region, some of which have an assigned variation ΔPi. The values for the ionospheric parameters actually observed at a given time at a given site will thus be Pi=Pi[base]+ΔPi. These Pi values are used as input for an electron density N(h) profiler. The latter is derived from the Advanced Ionospheric Profiler (AIP), which is software used by Autoscala as part of the process of automatic inversion of ionogram traces. The 3D model ingests ionosonde data by minimizing the root-mean-square deviation between the observed and modeled values of fp(h) profiles obtained from the associated N(h) values at the points where observations are available. The ΔPi values are obtained from this minimization procedure. The 3D model is tested using data collected at the ionospheric stations of Rome (41.8N, 12.5E) and Gibilmanna (37.9N, 14.0E), and then comparing the results against data from the ionospheric station of San Vito dei Normanni (40.6N, 18.0E). The software developed is able to produce maps of the critical frequencies foF2 and foF1, and of fp at a fixed altitude, with transverse and longitudinal cross-sections of the bottomside ionosphere in a color scale. fp(h) and associated simulated ordinary ionogram traces can easily be produced for any geographic location within the Italian region. fp values within the volume in question can also be provided.