Ionospheric F2 Layer Research Articles

A Comparison of PSO-based Neural Network Predictions of F2 Ionospheric Layer Critical Frequency in Malaysia with IRI-2016

This paper discussed the prediction of the equatorial ionospheric F2 layer critical frequencies, foF2, using a backpropagation neural network (BPNN) model in conjunction with a particle swarm optimization (PSO) algorithm, named as the BPNN–PSO model, for various solar and geomagnetic activities, and compared it with the IRI-2016 model. The critical frequency data were taken from an ionosonde located at Universiti Tun Hussein Onn Malaysia in Johor, Malaysia (1.86° N, 103.80° E). The model’s outputs were analyzed using root-mean-square error (RMSE). The BPNN–PSO model outperformed the IRI-2016 model during low, medium, and high solar activity. The BPNN–PSO model had the lowest RMSE of 0.20 MHz and performed best during periods of high solar activity. This is much better than the RMSE for IRI-2016 model, which was 2.95 MHz. In addition, compared with the IRI-2016 model, the BPNN–PSO model made accurate predictions during both quiet and geomagnetic storm conditions. The BPNN–PSO model had the lowest RMSE of 0.54 MHz during an intense storm, while the IRI-2016 model had the RMSE of 2.84 MHz during this storm.

A hybrid deep learning-based short-term forecast model for ionospheric foF2 in East Asia region

The short-term forecast of the critical frequency of the ionospheric F2 layer (foF2) is particularly challenging due to its nonlinear and non-stationary characteristics. To improve the short-term forecast accuracy of foF2, we propose a short-term hybrid deep learning model that integrates the improved complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN) and long short-term memory (LSTM) algorithms. The proposed model leverages the ICEEMDAN decomposition algorithm to expand foF2 time series data into multi-dimensional space and utilizes the LSTM algorithm to preserve long-term data information, capturing detailed changes in foF2 parameters and obtaining internal information about foF2. The 2014 and 2017 foF2 data from four observation stations located in Mohe, Beijing, Jeju, and Kokubunji in the mid-latitudes of East Asia were utilized for modeling and 1-hour forecast analysis. The forecast values of the proposed model align closely with the measured data, exhibiting minimal fluctuation in forecast error and effectively tracking the changing trend of foF2. The average root mean square error (RMSE) across the four stations in 2014 is 0.40 MHz, with a relative RMSE (RRMSE) of 7.11 % and a coefficient of determination (R2) of 0.98. The average RMSE in 2017 is 0.43 MHz, RRMSE is 7.68 %, and R2 is 0.92. The proposed model reveals significant improvements in the forecast accuracy of the comparison model compared with the CCIR, URSI, NN, and LSTM models. Especially compared with the CCIR and URSI models in the International Reference Ionosphere (IRI), demonstrating superior real-time tracking capability for foF2 and effectively addressing the challenge of poor short-term forecast accuracy observed in the IRI model.

Effect of The Density and Height of F2 layer on Ground-Based Observation of Jupiter's Radio Signal

The density and height of the ionospheric F2 layer affect the observation of Jupiter's radio signals. The study aims to determine an approximate observation threshold from the values of the F2 peak density and the height of the F2 peak. The Florida and Lamy stations in the USA were selected. Utilizing actual observation data of Jupiter's radio signals from the Radio JOVE Data Archive for the years 2014-2015. The Radio Jove Pro software was employed to predict radio emissions from Jupiter. Ionospheric data were sourced from the International Reference Ionosphere (IRI) website. The primary focus of this study is to examine the role of the ionosphere in blocking the radio signals emanating from Jupiter. It was found that 49% and 31% (for the Florida and Lamy stations, respectively) of the predicted radio emission events from Jupiter were not observed. The likelihood of observation is higher after sunset and depends on Jupiter's elevation above the horizon relative to the observer. The F2 peak density during nighttime and throughout the year ranged from approximately 1011 to 1012 m-3 at altitudes of about 260-360 km. 89% and 98% (for the Florida and Lamy stations, respectively) of the observations occurred when the F2 peak density was less than around 6×1011 m-3. In contrast, 80% and 56% (for the Florida and Lamy stations, respectively) of the cases of non-observation occurred when the F2 peak density was greater than approximately 6×1011 m-3. As for The height of the F2 peak (hmF2), 85% and 93% of the observations occurred when the hmF2 was greater than about 300 km for the Florida and Lamy stations, respectively. The probability of observation is significantly influenced by the relationship between the electron density and its corresponding altitude.

Effect of The Density and Height of F2 layer on Ground-Based Observation of Jupiter's Radio Signal

The density and height of the ionospheric F2 layer affect the observation of Jupiter's radio signals. The study aims to determine an approximate observation threshold from the values of the F2 peak density and the height of the F2 peak. The Florida and Lamy stations in the USA were selected. Utilizing actual observation data of Jupiter's radio signals from the Radio JOVE Data Archive for the years 2014-2015. The Radio Jove Pro software was employed to predict radio emissions from Jupiter. Ionospheric data were sourced from the International Reference Ionosphere (IRI) website. The primary focus of this study is to examine the role of the ionosphere in blocking the radio signals emanating from Jupiter. It was found that 49% and 31% (for the Florida and Lamy stations, respectively) of the predicted radio emission events from Jupiter were not observed. The likelihood of observation is higher after sunset and depends on Jupiter's elevation above the horizon relative to the observer. The F2 peak density during nighttime and throughout the year ranged from approximately 1011 to 1012 m-3 at altitudes of about 260-360 km. 89% and 98% (for the Florida and Lamy stations, respectively) of the observations occurred when the F2 peak density was less than around 6×1011 m-3. In contrast, 80% and 56% (for the Florida and Lamy stations, respectively) of the cases of non-observation occurred when the F2 peak density was greater than approximately 6×1011 m-3. As for The height of the F2 peak (hmF2), 85% and 93% of the observations occurred when the hmF2 was greater than about 300 km for the Florida and Lamy stations, respectively. The probability of observation is significantly influenced by the relationship between the electron density and its corresponding altitude.

Calibrating estimates of ionospheric long-term change

Abstract. Long-term reduction (∼20 km) in the height of the ionospheric F2 layer, hmF2, is predicted to result from increased levels of tropospheric greenhouse gases. Sufficiently long sequences of ionospheric data exist in order for us to investigate this long-term change, recorded by a global network of ionosondes. However, direct measurements of ionospheric-layer height with these instruments is not possible. As a result, most estimates of hmF2 rely on empirical formulae based on parameters routinely scaled from ionograms. Estimates of trends in hmF2 using these formulae show no global consensus. We present an analysis in which data from the Japanese ionosonde station at Kokubunji were used to estimate monthly median values of hmF2 using an empirical formula. These were then compared with direct measurements of the F2 layer height determined from incoherent-scatter measurements made at the Shigaraki MU Observatory, Japan. Our results reveal that the formula introduces diurnal, seasonal, and long-term biases in the estimates of hmF2 of ≈±10% (±25 km at an altitude of 250 km). These are of similar magnitude to layer height changes anticipated as a result of climate change. The biases in the formula can be explained by changes in thermospheric composition that simultaneously reduce the peak density of the F2 layer and modulate the underlying F1 layer ionization. The presence of an F1 layer is not accounted for in the empirical formula. We demonstrate that, for Kokobunji, the ratios of F2 / E and F2 / F1 critical frequencies are strongly controlled by changes in geomagnetic activity represented by the am index. Changes in thermospheric composition in response to geomagnetic activity have previously been shown to be highly localized. We conclude that localized changes in thermospheric composition modulate the F2 / E and F2 / F1 peak ratios, leading to differences in hmF2 trends. We further conclude that the influence of thermospheric composition on the underlying ionosphere needs to be accounted for in these empirical formulae if they are to be applied to studies of long-term ionospheric change.

Ionosonde Measurement Comparison during an Interplanetary Coronal Mass Ejection (ICME)- and a Corotating Interaction Region (CIR)-Driven Geomagnetic Storm over Europe

A comparison of three types of ionosonde data from Europe during an interplanetary coronal mass ejection (ICME)- and a corotating interaction region (CIR)-driven geomagnetic storm event is detailed in this study. The selected events are 16–20 March 2015 for the ICME-driven storm and 30 May to 4 June 2013 for the CIR-driven one. Ionospheric data from three European ionosonde stations, namely Pruhonice (PQ), Sopron (SO) and Rome (RO), are investigated. The ionospheric F2-layer responses to these geomagnetic events are analyzed with the ionospheric foF2 and h’F2 parameters, the calculated deltafoF2 and deltahF2 values, the ratio of total electron content (rTEC) and Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics (TIMED) satellite Global Ultraviolet Imager (GUVI) thermospheric [O]/[N2] measurement data. The storm-time and the quiet-day mean values are also compared, and it can be concluded that the quiet-day curves are similar at all the stations while the storm-time ones show the latitudinal dependence during the development of the storm. As a result of the electron density comparison, during the two events, it can be concluded that the sudden storm commencement (SSC) that characterized the ICME induced a traveling atmospheric disturbance (TAD) seen in the European stations in the main phase, while this is not seen in the CIR-driven ionospheric storm, which shows a stronger and more prolonged negative effect in all the stations, probably due to the season and the depleted O/N2 ratio.

Long-Term Trends in the Height of the Ionospheric F2 Layer Peak

Long-Term Trends in the Height of the Ionospheric F2 Layer Peak

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 Perturbations after Stromboli Volcano Eruptions

Based on data from ground-based vertical sounding of the ionosphere, we analyze disturbances in the region of the maximum of the ionospheric F2-layer during the period of a strong eruption of the Stromboli volcano (Italy) in the form of two explosions in July and August 2019, as well as after the resumption of volcanic activity on October 9, 2022. As characteristics of the ionospheric response to these events, we research variations in the critical frequency of the F2-layer at the Giebilmann, Rome, and San Vito stations located near (no further than 450 km) the volcano. The measurement results indicate the influence on the ionosphere of atmospheric acoustic-gravity waves generated by volcanic activity and causing the appearance of long-lived disturbances in the ionosphere.

Variability of ionospheric ionization over Eurasia according to data from a high-latitude ionosonde chain during extreme magnetic storms in 2015

. We have examined longitudinal-temporal variations in ionospheric parameters over Eurasia by analyzing data from a chain of high-latitude ionosondes along a latitude circle ~70° N (geomagnetic latitudes 58°<Glat<65°) in the longitudinal sector 26–171° E during severe magnetic storms of solar cycle 24 in March and June 2015. To analyze the response of ionospheric ionization to geomagnetic disturbances, we have used ionosonde data on hourly average critical frequency foF2 of the ionospheric F2 layer. Strong differences were observed between common peculiarities of temporal variations in foF2 for the analyzed periods of magnetic storms, which are likely associated with the characteristic features of the seasonal and diurnal variations in the background high-latitude ionosphere of the given geographic region. During the main and early recovery phases of magnetic storms there were periods of blackouts of ionosonde radio signals. Differences in the character of the ionospheric response to geomagnetic disturbances have been noted. This is probably due to seasonal features of the probability of occurrence of the ionospheric storm positive or negative phase in different seasons of the year. The trends of increasing ionospheric ionization over the vast region of Eastern, Western Siberia and Europe after the end of the extreme magnetic storm in March 2015, according to measurements from the chain of high-latitude ionosondes, may be associated with the formation of an area of increased [O]/[N₂] ratio over this territory. Such an increase in ionospheric ionization exceeding the background level of foF2 values can be considered as a clear manifestation of the after-effect of magnetic storms.

Изменчивость ионизации ионосферы над Евразией по данным цепи высокоширотных ионозондов во время экстремальных магнитных бурь 2015 г.

. We have examined longitudinal-temporal variations in ionospheric parameters over Eurasia by analyzing data from a chain of high-latitude ionosondes along a latitude circle ~70° N (geomagnetic latitudes 58°<Glat<65°) in the longitudinal sector 26–171° E during severe magnetic storms of solar cycle 24 in March and June 2015. To analyze the response of ionospheric ionization to geomagnetic disturbances, we have used ionosonde data on hourly average critical frequency foF2 of the ionospheric F2 layer. Strong differences were observed between common peculiarities of temporal variations in foF2 for the analyzed periods of magnetic storms, which are likely associated with the characteristic features of the seasonal and diurnal variations in the background high-latitude ionosphere of the given geographic region. During the main and early recovery phases of magnetic storms there were periods of blackouts of ionosonde radio signals. Differences in the character of the ionospheric response to geomagnetic disturbances have been noted. This is probably due to seasonal features of the probability of occurrence of the ionospheric storm positive or negative phase in different seasons of the year. The trends of increasing ionospheric ionization over the vast region of Eastern, Western Siberia and Europe after the end of the extreme magnetic storm in March 2015, according to measurements from the chain of high-latitude ionosondes, may be associated with the formation of an area of increased [O]/[N₂] ratio over this territory. Such an increase in ionospheric ionization exceeding the background level of foF2 values can be considered as a clear manifestation of the after-effect of magnetic storms.

Doppler variations in radar observations of resident space objects: Likely ionospheric Pc1 plasma waves

Radars performing observations of resident space objects (RSO) measure Doppler variations in wave events of several minutes duration, with frequencies in the 0.2–1 Hz range peaking near 0.5–0.7 Hz, consistent with variations in electron density induced by waves in the intervening ionosphere. The two mid-latitude radars used were a Very High Frequency (VHF) radar operating at 55 MHz, and a High Frequency (HF) radar operating at 30 MHz, both in southern Australia.The VHF radar wave observations exibited a peak in wave occurrence in the post-dawn sector (0600–1200 local solar time). The seasonal occurrence of the waves had a strong minimum during winter compared with the other seasons. Comparison between observations in 2018/19 (near solar minimum) and 2021/22 (mid-rise to cycle 25 peak) suggests wave occurrence is anti-correlated with sunspot number and hence with EUV and ionospheric strength. Generally the waves had higher frequencies during night than day, and low sunspot number than mid solar cycle, when there was a weaker ionosphere.Given the oscillation frequency of the wave events, the most likely geophysical phenomena that is consistent with the observations are electro-magnetic ion cyclotron (EMIC) plasma waves in the Pc1 (0.2–5 Hz) frequency range. No other candidate geophysical disturbance appears to fit the wave characteristics. The majority of geomagnetic field-guided transverse Pc1 EMICWs project from the outer magnetosphere down onto the polar ionosphere, where they can convert to compressional fast-mode waves propagating parallel to the Earths surface in the ionospheric F2 layer waveguide, both equatorwards to mid-latitudes and polewards. It is likely the majority of the Doppler oscillations in the Pc1 frequency range observed by the radars at mid-latitudes are these ducted compressional waves. However, sources of transverse EMICWs from the magnetosphere onto the mid-latitude ionosphere do exist, and these may cause some of the observed oscillations. The micro-physics of these compressional waves causing Doppler oscillations in radio observations is not inconsistent with the history of ionospheric Doppler measurements and theory, although the radar trans-ionospheric radio propagation and the observed waves being higher frequency than previous studies is different.If the observed Doppler oscillations are compressional EMICW in the ionospheric waveguide then several of the statistical results can be explained. The anti-correlation of the wave occurrence with sunspot number (and resultant ionospheric strength) can be attributed to lower ionospheric attenuation at the higher latitudes, between where geomagnetically field-guided transverse EMIC waves initially enter the high-latitude ionospheric waveguide from the magnetosphere above, and their observation at mid-latitudes. The observation of higher frequency waves during low sunspot number may also be explained by a source effect in the magnetosphere that preferentially selects the higher frequency field-guided transverse EMIC waves to propagate down to the ionosphere.Comparisons will be shown with results from ground and space based magnetometers of compressional waves in the waveguide, highlighting consistent results and areas where the measurement techniques differ. Theory suggests the radar Doppler measurements are far more sensitive to variations in in-situ ionospheric electron density than magnetic field variations. This agrees with existing literature which highlights the very strong contribution from the compressional component. Theory also suggests that the Doppler sensitivity of a radar to ionospheric electron density variations is frequency dependent, with lower frequencies being more sensitive. This is borne out by the measurements, with the HF radar being more sensitive than the VHF radar.

Temporal and Spatial Variation of The Virtual Height of Ionosperic F2–layer Over Two Equatorial Stations During the Minimum to Ascending Phase of Solar Cycle 25

The research examines ionospheric F2-layer virtual height (h’F2) variations at Ilorin (14.80°N, 17.40°W) in the Africa sector and Boa Vista (2.80°N, 299.30°E) in the America sector, during Solar Cycle 25's minimum and ascending phases. The aim is to investigate the temporal and spatial variations of the virtual height of the F2-layer over two equatorial stations during the minimum to ascending phase of Solar Cycle 25 at two equatorial stations in two different longitudinal sectors. Analyzing data from these stations statistically, the paper investigates diurnal, seasonal, and annual variations in h’F2.Diurnally, the h’F2 demonstrates greater responsiveness during daytime (06:00 – 18:00 LT) compared to nighttime (18:00 – 05:00 LT). Seasonally, peak values occur around noon and post-noon periods, displaying significant disparities during equinoxes and solstices over both stations in the different solar phases. During the minimum phase year (2020), peak heights of h’F2 reached 387 km at Ilorin and 372 km at Boa Vista. In the ascending phase year (2021), these peaks slightly shifted to 389 km at Ilorin and 404 km at Boa Vista. Annually, the highest peak values of h’F2 occur at noon, measuring 376 km at Ilorin and 331 km at Boa Vista during the minimum phase, while during the ascending phase, both stations recorded almost identical values of 305 km at noon. Overall, h’F2 variation exhibited higher magnitude at Ilorin in the African longitudinal sector than at Boa Vista in the American longitudinal sector during the minimum phase of solar cycle 25, with the reverse observed during the ascending phase. This detailed analysis illuminates the complex variations in ionospheric behavior across various time frames and geographic locations, showcasing substantial variability and sensitivity to solar influences in equatorial stations across Africa and America.

Response of the lower and upper ionosphere after the eruption of Shiveluch volcano on april 10, 2023

The disturbances in the lower ionosphere and in the region of the maximum of the ionospheric F2 layer during the Shiveluch volcanic eruption in April 2023 are analyzed based on data from ground-based magnetometers and GPS radio sounding of the ionosphere. The magnetic stations were located at distances of 455 km (Paratunka) and 752 km (Magadan) from the volcano. The variations in the magnetic field and total electron content of the ionosphere were studied as characteristics of the ionospheric response to this event. An analysis of the measurements showed that the impact on the ionosphere is carried out by seismic Rayleigh waves and atmospheric acoustic-gravity waves generated by volcanic explosions. The energy of several explosions was estimated from the amplitude of the ionospheric signal in the total electron content.

Damped Kadomtsev Petviashvilli equation for magnetosonic waves in a dissipative OH plasma in the ionospheric F-Layer

In this paper we study the linear and nonlinear dynamics of magnetosonic waves in a dissipative Oxygen-Hydrogen (OH) plasma. It is shown that such waves can propagate nonlinearly as solitary structures for both super and sub, acoustic and Alfvenic regimes. We use the hyperbolic tangent method to solve the collisional Kadomtsev-Petviashvili (KP) equation and obtain a damped solitary wave solution. Both compressive and rarefactive damped solitary structures are obtained and are significantly affected by the oxygen ion-neutral collision frequency, temperature, propagation angle, and ambient magnetic field present in the F-layer of Earth’s ionosphere.

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.

HF radio channel modeling by a waveguide approach

We present a modified method of HF radio channel modeling based on a waveguide approach. The waveguide approach represents the electromagnetic field of radiation inside the Earth—ionosphere waveguide as an eigenfunction series of a radial boundary problem with impedance conditions on the Earth surface and radiation conditions at infinity. The transfer function of the radio channel is represented as a series of products of angular-operator Green functions, excitation coefficients, and coefficients for receiving individual normal modes. We have obtained a solution of the boundary value problem of determining the eigenfunctions and eigenvalues of the radial operator. The solution can be applied to the frequency range below the ionospheric F-layer critical frequency. We examine algorithms for calculating distance-frequency, frequency-angular, and amplitude characteristics of signals by analyzing and numerically summarizing the series in terms of strongly damped normal modes.

Examining the effects of a pre-noon annular Solar Eclipse on equatorial electrodynamics: Evidence for a subsequent post-noon enhancement in plasma density

On 26 December 2019, an annular solar eclipse occurred in the southern part of the Indian subcontinent, which falls within the Equatorial ElectroJet (EEJ) region. This presented an opportunity to study the effects of a high-obscuration annular solar eclipse (93.3%) and of the special tides that accompany an eclipse. Eclipses are known to affect the electrodynamics of the equatorial region and the distribution of plasma in the low-latitude ionosphere. On December 26, 2019, different phenomena were indeed seen over different time scales. Around the time of the eclipse, there was a depletion in the total electron content (TEC) of the ionosphere, as inferred from GNSS receiver systems placed along the eclipse path in and around the EEJ region. Magnetometer measurements indicated a weakening of the EEJ current in this area not just when the eclipse took place but for the rest of the day as well. Observations from a digital-ionosonde located in Trivandrum (8.52°N, 76.94°E; 0.33°N dip-latitude) revealed that the ionospheric F-layer moved downwards just after obscurity maximum. Shortly after the F region was observed to move back upward, a one-hour long strong blanketing sporadic E-layer was triggered even though there was only a weakening of the EEJ but no reversal in the associated magnetic perturbations. Simulations from our quasi-two dimensional model clearly show that though there was no Counter Electrojet, there was indeed a weakening of the zonal field on 26 December 2019 during the eclipse and the post-eclipse period. The overall weakening trend lasted until late afternoon. Other notable features were uncovered on a time scale of several hours after the passage of the eclipse. While the day-long weakening of the EEJ is consistent with special tides related to the lunar trajectory, we also observed unusually large amplitude undulations in both vertical-TEC and F2-region peak plasma density over a five-hour time scale, starting around 2:00 PM LT. These undulations were consistent with the zonal electric field variations reconstructed from the magnetometer data.

Моделирование КВ-радиоканала на основе волноводного подхода

We present a modified method of HF radio channel modeling based on a waveguide approach. The waveguide approach represents the electromagnetic field of radiation inside the Earth—ionosphere waveguide as an eigenfunction series of a radial boundary problem with impedance conditions on the Earth surface and radiation conditions at infinity. The transfer function of the radio channel is represented as a series of products of angular-operator Green functions, excitation coefficients, and coefficients for receiving individual normal modes. We have obtained a solution of the boundary value problem of determining the eigenfunctions and eigenvalues of the radial operator. The solution can be applied to the frequency range below the ionospheric F-layer critical frequency. We examine algorithms for calculating distance-frequency, frequency-angular, and amplitude characteristics of signals by analyzing and numerically summarizing the series in terms of strongly damped normal modes.

CLIMF2: A climatological model of the ionospheric F2 layer. Part 1: Model methodology

The ionospheric F2 layer is of key importance to systems dependent on the propagation of radio waves through the ionosphere, including over-the-horizon (OTH) radar, high frequency (HF) communications, global navigation satellite systems (GNSS), and low-frequency radio astronomy. The currently accepted F2 layer model, the International Reference Ionosphere (IRI), does not provide the variance in the parameters used to describe the layer and furthermore, was developed from a limited dataset. The newly developed model, CLIMF2, can be used in conjunction with IRI to overcome these limitations, and thereby improve applications such as the climatological modelling of OTH radar performance. CLIMF2 is an empirical climatological model of the F2 layer parameters derived from a global network of vertical incidence sounder (VIS) observations, consisting of 267 sites with data from the 1950s to 2021. CLIMF2 has the added functionality of providing the variance in the foF2 and hmF2 parameters.