Equivalent Slab Thickness Research Articles

Long term relationships of electron density with solar activity

Greenhouse gases such as carbon dioxide and methane that are causing climate change may cause long term trends in the thermosphere and ionosphere. The paper aims to contribute to explore long term effects in the ionosphere focusing on the impact of solar activity changes. Peak electron density data derived from vertical sounding measurements covering 65 years at the ionosonde stations Juliusruh (JR055), Boulder (BC840) and Kokubunji (TO536), have been utilized to estimate the long-term behavior of daytime ionospheric F2 layer ionization in relation to the solar 10.7 cm radio flux index F10.7. In parallel, Global Navigation Satellite System (GNSS) based vertical total electron content (TEC) data over the ionosonde stations in combination with the peak electron density data have been used to derive the equivalent slab thickness τ for estimating long-term behavior in the time period 1996-2022. A new approach has been developed for deriving production and loss term proxies for studying long-term ionization effects from F2 layer peak electron density and TEC data. The derived coefficients allow estimating the long-term variation of atomic oxygen and molecular nitrogen concentrations including their ratio during winter months. The noon-time slab thickness values over Juliusruh correlate well with the decrease of F10.7 and the F2 layer peak height and enable estimating the neutral gas temperature. The equivalent slab thickness decreases by about 20 km per decade in the period 1996-2022, indicating a thermospheric cooling by about 100 K per decade for Juliusruh. Whereas the oxygen concentration decreases, the loss term, considered as a proxy for molecular components of the neutral gas, in particular N2, increases with the long-term solar activity variation. Considering 11 years averages of the production and loss terms under wintertime conditions, the long-term study reveals for the O/N2 ratio a percentage decrease of 5% per decade and for F10.7 about 3.1% per decade in a linear approach referred to the year 1970. Linear models of 11 years averaged NmF2 and foF2 from corresponding F10.7 show a very close correlation with the temporal variation of F10.7 until about 1990. The root mean square errors are in the order of 1.0 -1.3 ‧1010m-3 for NmF2 and 0.03-0.05 MHz for foF2. After 1990 the linear models clearly deviate from F10.7 at all selected ionosonde stations indicating a non-local effect.

Ionospheric equivalent slab thickness ingestion into the NeQuick model

The ionospheric equivalent slab thickness (τ), defined as the ratio of the vertical total electron content (vTEC) to the ionospheric F2-layer electron density maximum (NmF2), is a parameter providing useful information on the shape of the vertical electron density profile. However, the use of this information is of difficult practical application in empirical ionosphere models, such as the NeQuick model, because by design they do not explicitly include τ as a modelling parameter. In this work, we investigated the opportunity of using measured τ values to improve the empirical modelling of the ionosphere vertical electron density profile by NeQuick. Measured τ values were obtained through NmF2 observations and vTEC measurements obtained between 2001 and 2019 by an ionosonde and a ground-based GNSS receiver, respectively, co-located at Rome ionospheric station (41.8° N, 12.5° E; Italy). NeQuick τ was obtained as the ratio between modelled NmF2 and vTEC values, the latter obtained by integration of the vertical profile. As a first step, τ values modelled by NeQuick were compared with corresponding values measured at Rome station to highlight diurnal, seasonal, and solar activity differences. Then, measured τ values were ingested in NeQuick through a three-parameter assimilation procedure which first assimilate F2-layer peak characteristics to constrain the F2-layer anchor point, and then assimilate vTEC to optimize the F2-layer shape through the NeQuick F2-layer thickness parameter, namely B2bot. The assimilation procedure provides information on how the NeQuick B2bot has to be modified to match measured τ values, and then on how the shape of the F2-layer profile has to be changed accordingly. Our results highlight that, in many cases, the NeQuick B2bot has to be increased to match observations, which has implications on the modelling of the NeQuick bottomside and topside effective scale heights.

Statistical Study of the Ionospheric Slab Thickness at Beijing Midlatitude Station

The ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2) is known as the ionospheric equivalent slab thickness (EST, also known as τ), and it is a crucial indicator of the ionosphere. Using TEC and NmF2 data from the years 2010 to 2017, this work conducts a comprehensive statistical analysis of the ionospheric slab thickness in Beijing, which is in the midlatitude of East Asia. The outcomes show that the τ have different diurnal variations at different seasons for high/low-solar-activity years. On the whole, daytime τ significantly greater than nighttime τ in summer, and it is the opposite for the τ in winter regardless of the solar cycle, whereas the τ during equinox shows different morphology for high/low-solar-activity years. Specifically, daytime τ is larger than nighttime τ during equinox in years of high-solar activity, while the opposite situation applies for the τ during equinox in years of low-solar activity. Moreover, the pre-sunrise and post-sunset peaks are most pronounced during winter for low-solar-activity years. In summer, there is a great increase in τ during the morning hours when compared with other seasons. Furthermore, the τ decreases with the solar activity during nighttime, whereas it seems there is no correlation between daytime τ and solar activity. This paper explained the primary diurnal variations in τ across different seasons during high-/low-solar-activity years by analyzing relative fluctuations of TEC and NmF2 throughout the corresponding period. In addition, based on the disturbance index (DI), which is calculated by instantaneous τ and its corresponding median, this paper found that the storm-time τ might increase when compared with its median value during the daytime, while it may both increase and decrease during the nighttime, especially around dawn and dusk hours. To further analyze the physical mechanism, an example on 2 October 2013 is also presented. The results indicate that the positive disturbance of τ during the main phase of a geomagnetic storm might be caused by the prompt penetration electric field and neutral wind during the storm, and the τ increases during the early recovery phase might be due to the disturbance dynamo electric field as well as the neutral wind during the storm. Moreover, there is a negative disturbance of τ in the recovery phase during the most disturbed sunrise hours, and it might be due to the electric field reversal, neutral wind or other factors during this period. This paper notes the differences of τ in midlatitude between different longitudinal sectors from the related climatology and storm-time behavior, as it would be helpful to improve the current understanding of τ at midlatitudes in East Asia.

On the global model of the ionospheric equivalent slab thickness

The equivalent slab thickness τ of the ionosphere links two of its parameters: the critical frequency foF2 and the total electron content TEC and, as a consequence, allows the determination of foF2 using TEC. Interest in the parameter τ has recently increased, as evidenced by a publication in Space Science Reviews 2022, 218:37, 1-65, which provides a historical overview of τ research, presents features of τ behavior in different regions of the globe under different solar activity conditions, and indicates directions for further research. This led to the following objectives for this paper: (1) estimating the correlation coefficient between foF2 and TEC, (2) testing a unique global model τ(NSTM) - the Neustrelitz equivalent Slab Thickness Model, (3) estimating the relation between τ and the Dst index. Using data from 78 stations divided into several longitude zones, it is shown for April 2022: (1) a high correlation between foF2 and TEC on a global scale is confirmed, but there is a large dependence on data quality, (2) each longitude zone has stations for which τ(NSTM) gives good agreement with experimental values and can be used in applications, (3) the correlation coefficient ρ(τ-Dst) is found to depend on longitude, which may have a physical nature.

Simulation of ionospheric parameters for September 2017

Modeling the parameters of the ionosphere is an important part of the process of studying the influence of space weather factors. This paper is devoted to modeling three parameters of the ionosphere (critical frequency foF2, total electron content TEC, and equivalent slab thickness τ) related to the possibility of determining foF2 on a global scale using TEC. Comparison of the model τ(IRI), τ(IRI-Plas) adapted to the observational TEC, τ(NSTM) with the observational median τ(med) for four ionosondes along the 30° E meridian in September 2017 showed the best fit for the IRI-Plas model. Using a polynomial approximation of τ(med) and the distribution of TEC along this meridian in the range of 30° N-70° N, the features of the response of TEC and foF2 to disturbances in September 2017 were revealed. The results for September 7-8, which showed positive enhancements of TEC and foF2, coincide with the results of other researchers. The similarity of this response with the response to the disturbance on September 27-28, which is not associated with a solar flare, is revealed. It is shown that the unique enhancement on September 11 during the magnetic storm recovery phase, identified in the Asian-Australian sector (Lei et al., 2018), is not observed at the 30° E meridian. The global longitudinal distributions of TEC at latitudes of 50° and 30° showed the locality of this phenomenon.

Statistical Study of the Ionospheric Slab Thickness at Yakutsk High-Latitude Station

The ionospheric equivalent slab thickness (EST, also named τ) is defined as the ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2), and it is a significant parameter representative of the ionosphere. This paper presents a comprehensive statistical study of the ionospheric slab thickness at Yakutsk, located at the high latitude of East Asia, using the GPS-TEC and ionosonde NmF2 data for the years 2010–2017. The results show that the τ has different diurnal and seasonal variations in high- and low-solar-activity years, and the τ is greatest in the winter, followed by the equinox, and it is smallest in the summer in both high- and low-solar-activity years, except during the noontime of low-solar-activity years. Specifically, the τ in inter of high-solar-activity year shows an approximate single peak pattern with the peak around noon, while it displays a double-peak pattern with the pre-sunrise and sunset peaks in winter of the low-solar-activity years. Moreover, the τ in the summer and equinox have smaller diurnal variations, and there are peaks with different magnitudes during the sunrise and post-sunset periods. The mainly diurnal variation of τ in different seasons of high- and low-solar-activity years can be explained within the framework of relative variation of TEC and NmF2 during the corresponding period. By defining the disturbance index (DI), which can visually assess the relationship between instantaneous values and the median, we found that the geomagnetic storm would enhance the τ at Yakutsk. An example on 7 June 2013 is also presented to analyze the physical mechanism. It should be due to the intense particle precipitation and expanded plasma convection electric field during the storm at high-latitude Yakutsk station. The results would improve the current understanding of climatological and storm-time behavior of τ at high latitudes in East Asia.

Validation of the models of the ionospheric equivalent slab thickness using data from African stations

Recently, the equivalent slab thickness τ of the ionosphere has attracted great attention. This is due to its role in determining the critical frequency foF2 from the data of the total electron content TEC, which is important in obtaining the characteristics of the high frequency HF radio waves propagation, especially during disturbances, when vertical sounding data may be absent. Currently, a global Neustrelitz equivalent Slab Thickness Model NSTM model has been developed, for the use of which it is sufficient to have 12 coefficients and an index of solar activity. On the other hand, empirical models, in particular the IRI-Plas model, in which TEC and the maximum density NmF2 are calculated, are also global and can provide values of τ on a global scale. These models can complement each other, but both need to be testing. Preliminary comparison of the NSTM model with the NGM model whose values were calculated as the quotient of values TEC(NTCM-GL) and NmF2(NPDM) has shown better performance for the τ(NSTM) model. In this paper, τ is compared for the NSTM and IRI-Plas models using the Grahamstown station data for 2001–2010. It is shown that both models reflect the diurnal and seasonal variations of the observational τ. To quantify the correspondence between the model and observational values of τ, standard metrics were used: the mean absolute error (MAE), the root mean-square-error (RMSE), the normalized root-mean-square error (NRMSE). The MAE values were 87.6 km for the NSTM model and 64.7 km for the IRI-Plas model in 2001. The corresponding values in 2007 were 70.2 km and 58 km. The RMSE values were 109.1 km for the NSTM model and 80 km for the IRI-Plas model in 2001. For low solar activity conditions, the RMSE values are 87.0 km and 73.1 km (that is, the values for IRI-Plas are also smaller than for NSTM). The NRMSE values are 25.2 % and 18.4 %, respectively, under high solar activity, and 21.2 % and 18.0 % under low solar activity. The greatest RMSE of the model values concern morning and evening hours: they can reach 180 km for the NSTM model and 120 km for the IRI-Plas model.

Testing of new ionospheric models along the meridian 110° E over the Northern Hemisphere

Despite the continuous improvement of the widely used empirical model international reference ionosphere (IRI), the recently appeared new models must be tested worldwide. Testing along the meridians has the advantage of dealing with the latitudinal dependent parameters. This paper uses new models of parameters foF2 (critical frequency), TEC (total electron content), and τ (equivalent slab thickness of the ionosphere), which are of great importance for evaluating the effects of space weather. IRI-Plas, NNT2F2, and NTSM models were tested using data from 6 ionosondes located along the meridian 110° E in March 2012. It is shown that the IRI-Plas model provides the closest values to experiment with respect to τ, while the NTSM model provides a rather limited reflection of the latitude dependence. Analyses of foF2(NNT2F2) have shown that, the NNT2F2 model provides good conformity with experimental values in this area, but it is very dependent on the TEC processing method. The latitudinal dependences of foF2 obtained with TEC and polynomial dependence τ(Appr) showed the presence of positive deviations from medians not only during disturbances but also quiet periods, longitudinally at the meridian.

Analytical Model Formulation of Steel Plate Reinforced Concrete Walls against Hard Projectile Impact

Steel plate reinforced concrete (SC) walls can effectively resist projectile impact by preventing the rear concrete fragments flying away, thus attracting much attention in defence technology. This work numerically and analytically investigated the hard projectile perforation of steel plate reinforced concrete walls. Impact resistance theories, including cavity expansion analysis as well as the petaling theory of thin steel plates were used to describe the cratering, tunneling and plugging phases of SC walls perforation. Numerical modeling of SC walls perforation was performed to estimate projectile residual velocity and target destructive form, which were validated against the test results. An analytical model for SC wall perforation was established to describe the penetration resistance featuring five stages, i.e., cratering, tunneling and plugging, petaling with plugging and solely petaling. Analytical model predictions matched numerical results well with respect to projectile deceleration evolution as well as residual velocity. From a structural absorbed energy perspective, the effect of front concrete panel and rear steel plate thickness combinations was also studied and analyzed. Finally, equivalent concrete slab thickness was derived with respect to the ballistic limit of SC walls, which may be helpful in the design of a protective strategy.

Morphologies of ionospheric-equivalent slab-thickness and scale height over equatorial latitude in Africa

• Ionospheric slab thickness (τ) and scale height (Hm) are probed over African. • Collocated GPS and Digisonde measurements aided extensive analysis of parameters. • Substantial increase in τ is realized during the post-sunset and solstice seasons. • The extracted Hm hardly evidence the effects of E × B drift and meridional wind. • Our results complement the relationships among bottomside and topside parameters. Accurate representation of ionospheric equivalent slab thickness (τ) and scale height (Hm) plays a crucial role in characterizing the complex dynamics of topside and bottomside ionospheric constituents. In the present work, we examined the corresponding morphologies of ionospheric profile parameters with collocated global positioning system (GPS) and Digisonde Portable Sounder (DPS) setups at an equatorial location in west Africa Ilorin (8.50°N, 4.68°E), during a low solar activity year 2010. The extracted τ from GPS and DPS in selected quiet periods confirm it to be a first-order measure of Hm over Africa. The seasonal analysis of τ shows substantial enhancement in the magnitude during the post-sunset and solstice seasons, of which December solstice manifests relatively higher values than June solstice. This result could be associated with the elevation of the meridional wind and drift in the parameters, which are more substantial during the post-noon and solstices. Therefore, at solstices, the post-night increase could indicate solar cycle dynamics during HSA (high solar activity) and LSA (low solar activity). However, the extracted Hm from its relationship with τ did not show visible effects of dynamics in E × B plasma drift and the meridional wind. In our study, a decline in morphologies of Hm and τ from December solstice to June solstice through the equinox is not consistent with the existing observations at mid-latitude. The results would complement the relationships between bottomside and topside profile peak parameters and dynamics of ionospheric constituents for a realistic representation and modeling of the ionosphere over African equatorial and low latitude regions. Thus, it also contributes to the global effort of improving ionospheric prediction and forecasting models.

Statistical Study of Ionospheric Equivalent Slab Thickness at Guam Magnetic Equatorial Location

The ionospheric equivalent slab thickness (τ) is defined as the ratio of the total electron content (TEC) to the F2-layer peak electron density (NmF2), and it is a significant parameter representative of the ionosphere. In this paper, a comprehensive statistical analysis of the diurnal, seasonal, solar, and magnetic activity variations in the τ at Guam (144.86°E, 13.62°N, 5.54°N dip lat), which is located near the magnetic equator, is presented using the GPS-TEC and ionosonde NmF2 data during the years 2012–2017. It is found that, for geomagnetically quiet days, the τ reaches its maximum value in the noontime, and the peak value in winter and at the equinox are larger than that in summer. Moreover, there is a post-sunset peak observed in the winter and equinox, and the τ during the post-midnight period is smallest in equinox. The mainly diurnal and seasonal variation of τ can be explained within the framework of relative variation of TEC and NmF2 during different seasonal local time. The dependence of τ on the solar activity shows positive correlation during the daytime, and the opposite situation applies for the nighttime. Specifically, the disturbance index (DI), which can visually assess the relationship between instantaneous τ values and the median, is introduced in the paper to quantitatively describe the overall pattern of the geomagnetic storm effect on the τ variation. The results show that the geomagnetic storm seems to have positive effect on the τ during most of the storm-time period at Guam. An example, on the 1 June 2013, is also presented to analyze the physical mechanism. During the positive storms, the penetration electric field, along with storm time equator-ward neutral wind, tends to increase upward drift and uplift F region, causing the large increase in TEC, accompanied by a relatively small increase in NmF2. On the other hand, an enhanced equatorward wind tends to push more plasma, at low latitudes, into the topside ionosphere in the equatorial region, resulting in the TEC not undergoing severe depletion, as with NmF2, during the negative storms. The results would complement the analysis of τ behavior during quiet and disturbed conditions at equatorial latitudes in East Asia.

Midlatitude climatology of the ionospheric equivalent slab thickness over two solar cycles

Midlatitude climatology of the ionospheric equivalent slab thickness over two solar cycles

Ionospheric Response along Meridian for the Certain Storm Using TEC and foF2

For a long time, the equivalent ionospheric slab thickness τ has remained in the shadow of ionospheric main parameters: the maximum density, NmF2 (or the critical frequency, foF2), and the total electron content. Empirical global models have been developed for these two parameters. Recently, several global models of τ have appeared concurrently. This paper compares τ of the Neustrelitz equivalent slab thickness model (NSTM), with τ(IRI-Plas) of the IRI-Plas model, and τ(Appr) of the approximation model, constructed along the 30° E meridian using data from several ionosondes. The choice of the model of the best conformity with observational data was made, which was used to study the effects of space weather during several magnetic storms in March 2012. The effects included: (1) a transition from negative disturbances at high latitudes to positive ones at low latitudes, (2) the super-fountain effect, which had been revealed and explained in previous papers, (3) a deepening of the main ionospheric trough. The efficiency of using τ(Appr) and τ(IRI-Plas) models for studying the effects of space weather has been confirmed. The advantage of the τ(Appr) model is its closeness to real data. The advantage of the τ(IRI-Plas) model is the ability to determine foF2 without ionosondes. The efficiency of the NSTM model is insufficient for a role of a global τ model due to the accuracy decreasing with the increasing latitude.

The Influence of Space Weather on the Relationship Between the Parameters TEC and foF2 of the Ionosphere

The critical frequency foF2 is an important parameter of the ionosphere, but its measurement data are often absent, especially during disturbances caused by the impact of space weather. The aim of this paper is to use the total electron content TEC to obtain foF2, which is necessary in such tasks as forecasting the maximum useable frequencies on HF paths, assimilation in the ionospheric models used in satellite wireless communication systems and for positioning. Formally, these parameters are linearly related through the equivalent slab thickness τ of the ionosphere, however, this relationship has not been practically studied for the southern hemisphere, since the thickness τ(IRI) of the International Reference Ionosphere IRI model can be used. This paper compares the efficiency of using τ(IRI) and various proposed options for determining experimental τ. The results are presented using the example of the March 2012-2017 disturbances and three stations in the southern hemisphere. Experimental medians τ(med) for a specific station in the current year and for other years, the median of another station, are used as τ. It is shown that the IRI model reacts only to negative disturbances. The use of various options for determining τ provides a 1.5-2 times better agreement with the real foF2. Especially, it concerns the long periods of enhancements of TEC (5-7 days), not connected in magnetic storms.

Latitudinal Dependence of the Ionospheric Slab Thickness for Estimation of Ionospheric Response to Geomagnetic Storms

The changes in the ionosphere during geomagnetic disturbances is one of the prominent Space Weather effects on the near-Earth environment. The character of these changes can differ significantly at different regions on the Earth. We studied ionospheric response to five geomagnetic storms of March 2012, using data of Total Electron Content (TEC) and F2-layer critical frequency (foF2) along the meridian of 70° W in the Northern Hemisphere. There are few ionosondes along this longitudinal sector: in Thule, Sondrestrom, Millstone Hill and Puerto Rico. The lacking foF2 values between the ionosondes were determined by using the experimental latitudinal dependences of the equivalent ionospheric slab thickness and TEC values. During geomagnetic storms, the following features were characteristic: (a) two-hours (or longer in one case) delay of the ionospheric response to disturbances, (b) the more prominent mid-latitude trough and (c) the sharper border of the EIA northern crest. During four storms of 7–17 March, the general tendency was the transition from negative disturbances at high latitudes to intense positive disturbances at low latitudes. During the fifth storm, the negative ionospheric disturbance controlled by O/N2 change was masked by the overall prolonged electron density increase during 21–31 March. The multiple correlation analysis revealed the latitudinal dependence of dominant Space Weather parameters’ impacts on foF2.

Global equivalent slab thickness model of the Earth’s ionosphere

The shape of the vertical electron density profile is a result of production, loss and transportation of plasma in the Earth’s ionosphere. Therefore, the equivalent slab thickness of the ionosphere that characterizes the width of vertical electron density profiles is an important parameter for a better understanding of ionospheric processes under regular as well as under perturbed conditions. The equivalent slab thickness is defined by the ratio of the vertical total electron content over the peak electron density and is therefore easy to compute by utilizing powerful data sources nowadays available thanks to ground and space based GNSS techniques. Here we use peak electron density data from three low earth orbiting (LEO) satellite missions, namely CHAMP, GRACE and FORMOSAT-3/COSMIC, as well as total electron content data obtained from numerous GNSS ground stations. For the first time, we present a global model of the equivalent slab thickness (Neustrelitz equivalent Slab Thickness Model – NSTM). The model approach is similar to a family of former model approaches successfully applied for total electron content (TEC), peak electron density NmF2 and corresponding height hmF2 at DLR. The model description focuses on an overall view of the behaviour of the equivalent slab thickness as a function of local time, season, geographic/geomagnetic location and solar activity on a global scale. In conclusion, the model agrees quite well with the overall observation data within a RMS range of 70 km. There is generally a good correlation with solar heat input that varies with local time, season and level of solar activity. However, under non-equilibrium conditions, plasma transport processes dominate the behaviour of the equivalent slab thickness. It is assumed that night-time plasmasphere–ionosphere coupling causes enhanced equivalent slab thickness values like the pre-sunrise enhancement. The overall fit provides consistent results with the mid-latitude bulge (MLB) of the equivalent slab thickness, described for the first time in this paper. Furthermore, the model recreates quite well ionospheric anomalies such as the Night-time Winter Anomaly (NWA) which is closely related to the Mid-latitude Summer Night-time Anomaly (MSNA) like the Weddell Sea Anomaly (WSA) and Okhotsk Sea Anomaly (OSA). Further model improvements can be achieved by using an extended model approach and considering the particular geomagnetic field structure.

Towards Cooperative Global Mapping of the Ionosphere: Fusion Feasibility for IGS and IRI with Global Climate VTEC Maps

Recommendations of the International Reference Ionosphere (IRI) Workshop 2017 in Taoyuan City, Taiwan and International GNSS Service (IGS) Workshop 2018 in Wuhan, China included establishment of an ionosphere mapping service that would fuse measurements from two independent sensor networks: IGS permanent GNSS receivers providing the vertical total electron content (VTEC) measurements and ionosondes of the Global Ionosphere Radio Observatory (GIRO) that compute the bottomside vertical profiles of the ionospheric plasma density. Using available GAMBIT software at GIRO, we introduced new VTEC products to its data roster: previously unavailable global average (climate) maps of VTEC and slab thickness based on climatological capabilities of IRI. Incorporation of the VTEC and τ maps into the GAMBIT Explorer environment provided data analysts with nearly 10-year history of the reference average VTEC records and opened access to the GAMBIT toolkit for evaluation and validation of the τ computations. This result is the first step towards establishing an infrastructure and the data workflow to provide GAMBIT users with the low latency and consistent quality and usability of the ionospheric weather-climate specifications. Combination of IGS-provided VTEC and GIRO-provided peak density of F2 layer NmF2 allows ground-based evaluation of the equivalent slab thickness τ, a derived property of the near-Earth plasma that characterizes the skewness of its vertical profile up to the GNSS spacecraft altitudes.

Validation of various ionospheric models in the high-latitudinal zone

When using ionospheric models, great importance is attached to their testing. The most widespread International Reference Ionosphere model is constantly being tested on a global scale, but the high latitude zone attracts special attention. In recent years, the Empirical Canadian High Arctic Ionospheric Model (E-CHAIM) has been proposed, aimed at high latitudes and having certain advantages. In this paper, both models are tested according to the Russian ionosondes Gorkovskaya (60.27˚ N, 29.38˚ E), Lovozero (67.97° N, 35.02° E), Norilsk (69.4° N, 88.1° E) in addition to the previous results of authors. The study period for Gorkovskaya and Lovozero stations has been increased to one year in conditions of low solar activity (May 2017-October 2018). For the Gorkovskaya station, the average absolute deviations |ΔfoF2| of the critical frequency for all months amounted to 0.33 MHz for the E-CHAIM model and 0.27 MHz for the IRI model. This corresponds to relative errors of 11.56% and 9.51%. For the Lovozero station, the absolute deviations were 0.34 MHz for the E-CHAIM model and 0.31 MHz for the IRI model. The corresponding relative errors were 11.8% and 11%. A comparison for the maximum height hmF2 was carried out for three options of the IRI model (AMTB2013, SHU2015, BSE1979) and the E-CHAIM model with experimental data. For the Norilsk station and the conditions of solar activity of an almost whole cycle, the AMTB2013 and SHU2015 options had no advantages anywhere over the BSE1979 and E-CHAIM options. In summer, the absolute deviations for all models lay in the range of 5–20 km, leading to a standard deviation not exceeding 20%. In winter, absolute deviations can reach 50–70 km, however, with the exception of one case, the standard deviation did not exceed 20%. For disturbed conditions, the results of determining foF2 by the E-CHAIM model were compared with an approach involving the usage of the total electron content TEC together with the equivalent slab thickness of the ionosphere. It was found that both approaches reproduce well the nighttime ionization enhancements associated with bursts of the AE index. The E-CHAIM model may overestimate the values of foF2, however, during positive disturbances both approaches underestimate the values of foF2. Using TEC can have a definite advantage over the E-CHAIM model, since TEC more objectively evaluates specific conditions.

A Statistical Study on the Winter Ionospheric Nighttime Enhancement at Middle Latitudes in the Northern Hemisphere

AbstractThe ionospheric electron density generally decreases after sunset under the effect of recombination, but sometimes, it increases, which forms an ionospheric nighttime enhancement (INE). In this research, the observations from two ionosondes in Mohe and Beijing and NASA's Jet Propulsion Laboratory‐Global Ionosphere Maps during the 24th solar cycle were used to explore the feature and mechanism of INE at midlatitudes. It shows that hmF2 always increases when INE occurs in summer, while it either rises or falls in winter. The increase of hmF2 has a significant contribution to INE in summer. For winter INE, however, the hmF2‐rising and the hmF2‐declining type INEs present no significant differences in durations and amplitudes, except that the former occurs slightly earlier than the latter. This suggests that the uplift of the ionosphere induced by equatorward thermospheric wind may not be a dominant factor for controlling the formation of winter INE at midlatitudes. We found that the electron density difference between the summer hemisphere and the winter hemisphere trends increases when the INE occurs in the winter hemisphere. This increased electron density difference between the two hemispheres is beneficial to the summer‐to‐winter interhemispheric plasma transport and the formation of INE in winter. Meanwhile, it is likely that the ionospheric equivalent slab thickness decreases during the winter INE due to downward transport from the topside. These indicate that downward plasma influxes from the topside ionosphere and the conjugate summer hemisphere play dominant roles for the formation of winter INE at middle latitudes.

Features of the Behavior of Ionospheric Parameters В0 and В1 in the High-Latitude Zone

The climatological features and behavior of the parameters B0_Neh_I, B1_Neh_I found from N(h) profiles calculated by the curves from the virtual heights during disturbances are studied based on data from the Norilsk station for 2003–2012. There is a greater similarity with the behavior in other latitudinal zones in that the values of B0_Neh_I are higher in summer than in winter and in years of active sun. The B1_Neh_I values are minimal in summer and maximal in winter; the scatter is from 1.3 to 3. Comparison with the IRI-2016 model showed relative deviations of the model values of B0_IRI_A from B0_Neh_I for B0_Neh_I by up to 100% in winter and 10–40% in summer. The winter values were 15–40% and the summer values were 8–50% for the parameter B1_Neh_I. Unlike other zones, the correlation coefficients between B0_Neh_I and the height of the hmF2 maximum, as well as those between B0_Neh_I and the equivalent slab thickness of the ionosphere τ, are lower. There are several types of reaction by the parameters TEC, foF2, B0_Neh_I, and B1_Neh_I to disturbances that, as a first approximation, can be represented as a table of five groups. In most cases, B0_Neh_I increases during disturbances, and B1_Neh_I decreases. The results were not found to depend on the disturbance level. There are large data gaps during disturbances. The total electron content (TEC) of the ionosphere is used to determine the sign of a disturbance.