Propagation conditions of 10 MHz signals along the paths between Rostov and Moscow

To determine the conditions for the propagation of HF signals through the ionosphere along various paths, there are several possibilities: (1) ionograms of vertical sounding, (2) ionograms of oblique sounding between transmission and receiver points, (3) receiving signals from transmitters of exact time at fixed frequencies (here ~10 MHz), (4) using ionospheric models. This paper presents the results of a comprehensive study that implements all these possibilities. They refer to the propagation of HF signals on reciprocal paths between Rostov and Moscow during the period of the lowest solar activity of cycle 24 (April-May 2020). It is shown that the maximum usable frequency (MUF) of propagation through the F2 layer of the ionosphere in the overwhelming majority of cases did not exceed 10 MHz both in the experiment and according to model calculations. The signals were propagated through the Es layer. If earlier it was shown that such a joint experiment allows revealing the presence of traveling ionospheric disturbances, the results of this work emphasize the role of the Es layer.

Adjusting CCIR Maps to Improve Local Behaviour of Ionospheric Models

The objective of this article is to present a concept for single-frequency Global Navigation Satellite System (GNSS) positioning local ionospheric mitigation over a certain area. This concept is based on input parameters driving the NeQuick-G algorithm (the ionospheric single-frequency GNSS correction algorithm adopted by Galileo GNSS system), estimated on a local as opposed to a global scale, from ionospheric characteristics measured by a digital ionosonde and a collocated dual-frequency Total Electron Content (TEC) monitor. This approach facilitates the local adjustment of Committee Consultative for Ionospheric Radiowave propagation (CCIR) files and the Az ionization level, which control the ionospheric electron density profile in NeQuick-G, therefore enabling better estimation of positioning errors under quiet geomagnetic conditions. This novel concept for local ionospheric positioning error mitigation may be adopted at any location where ionospheric characteristics foF2 and M(3000)F2 can be measured, as a means to enhance the accuracy of single-frequency positioning applications based on the NeQuick-G algorithm.

Radon prediction using metrological parameters, and its significance in Seismo-Ionospheric coupling

In order to derive boundary conditions, atmospheric and seismo-ionospheric models are coupled with generic assumptions. These boundary conditions are used to simulate possible interaction between earth’s atmospheric, geological processes and the Ionosphere. Rn is one of the major contributors to surface ionization, which is also believed to contribute to the geophysical and geochemical processes causing disturbance in the Ionosphere. Its relationship with metrological parameters in a given region gives an insight on the natural processes in the underground, as well as the relationship with atmospheric processes. It can enable models to establish realistic results rather than ideal theoretical consequences. Rn can be influenced by a number of physical variables, and therefore, this influence is sometimes very complicated to study, because of the Forcing researchers to make ideal assumptions. The relationship between Rn and some geological variables are studied, namely; soil temperature at 5 cm, 10 cm, 20 cm, and 50 cm, atmospheric pressure, and atmospheric temperature. A hybrid model is established based on the artificial neural network (ANN), which is referred to as multiANN model. This model is a combination of multi-regression and ANN models. Itenables Rn prediction to metrological parameters. To test the robustness of our model 50% training periods is employed with 50% testing periods. The model is able to forecast the remaining 50% effectively. With the aid of the Monte-Carlo method, it is possible to predict multiple future Rn variations with high precision. The regions with low performance of the multiANN are identified for possibly relationship to seismic events. The model could be a good candidate for predicting of Rn concentration from metrological parameters, especially in establishing the lower boundary conditions in seismo-ionospheric coupling models.

Comparative analysis of global ionospheric models used in GNSS data processing based on selected stations

<p>Among the many error sources affecting GNSS <em>(Global Navigation Satellite System)</em> positioning accuracy, the ionosphere is the cause of those of the greatest value. The ionized gas layer, where also free electrons are present, extends from the upper atmosphere to 1,000 km above the Earth's surface (conventionally). As the GNSS satellite orbits altitude is more than 20,000 km, the wave transmitted from the satellite to the receiver on the Earth’s ground passes through this layer, but not unscathed. The ionosphere is a dispersive medium for the electromagnetic waves in the microwave band, including UHF <em>(Ultra High Frequency)</em> waves transmitted by GNSS satellites. As a result, the group velocity of the wave decreases, while its phase velocity – increases.</p><p>Ionospheric delay compensation methods include among others multi-frequency measurements;  however, when considering measurements on one frequency, the usage of ionospheric models is an option. The key element is the number of free electrons, its inclusion in the course of calculations is possible thanks to the TEC <em>(Total Electron Content)</em> maps. Taking into account the variability of the coefficient in the daily and annual course, as well as depending on the activity of the Sun and its 11-year cycle, it is important to use the current value for a given place and time.</p><p>For the European Galileo satellite system a dedicated ionospheric model NeQuick-G was developed. As a simple modification of the formula allows it to be applied to other satellite systems, it can be considered in a broader context, regardless of the system and receiver location. In our study the TEC maps published by IGS are used as the comparative data. As a reference, the station located in Warsaw, Poland, is adopted.</p><p>The subject of this research is the reliability and validity of the model in equatorial region. The analysis is performed for the stations belonging to the IGS <em>(International GNSS Service)</em> network, located in the discussed area. For each hour of the day, independently for each month of 2019, statistic parameters are determined for both models as well as for the difference between them. The results are analysed taking into account the local time of individual stations. The decisive element is the comparison of the station position time series during disturbed and quiet ionospheric conditions (selected based on the K-index), using each of the models (single-frequency observations). The station coordinates are determined from GPS <em>(Global Positioning System)</em> data using the PPP <em>(Precise Point Positioning)</em> method; the position determined for the iono-free combination (dual-frequency observations) is used as a reference.</p><p>The ionospheric delay is directly proportional to the value of the TEC parameter. The difference between the models, exceeding on average even 20 TECU <em>(Total Electron Content Unit)</em> during some periods, translates into a station coordinate differences. The presented analysis may indicate the need for local improvement of global ionospheric models in the discussed region, which will consequently affect the GNSS positioning quality.</p>

Observation and modelling of whistlers in the ELF as observed by Swarm satellites during regular ASM burst sessions

<p>The magnetic component of electromagnetic signals in the Extremely Low Frequencies (ELF) has been rarely observed from space. The Swarm satellites have the capability of observing part of this spectral band during burst sessions of the Absolute Scalar Magnetometer (ASM), when the sampling frequency of the instrument is raised to 250 Hz. Burst sessions of one week duration have been acquired regularly since 2019. Swarm satellites drift slowly in local time, therefore it has been possible to progressively acquire burst data to cover all hours at all latitudes. This is a unique opportunity at Low Earth Orbits (LEO) in recent years.</p><p>This study focuses on whistlers excited by lightning strikes generated by strong storm systems in the troposphere. The ELF component of the lightning signal propagates in the neutral atmosphere at very long distances. We used data from the ground stations of the World ELF Radiolocation Array (WERA) in order to estimate lightning locations and intensity for remarkable events. Part of the lightning signal penetrates into the ionosphere, where the ionospheric plasma produces its dispersion, depending on the spatial distribution of the plasma and the direction of the magnetic field.</p><p>We selected events to simulate their propagation through the ionosphere, using ionosonde data, IRI Real-Time Assimilative Mapping (IRTAM) and International Reference Ionosphere (IRI) model as backgrounds, along with the latest version of the International Geomagnetic Reference Field (IGRF). This technique allows to use these signals to sound the ionosphere and validate ionospheric models.</p><p>A database of whistler occurrences and parameters has been constructed and a new Swarm L2 product has been defined to make this data accessible to the scientific community.</p>

An innovative methodology for locating ionosphere layer height: case study on 2011 Tohoku-Oki earthquake and tsunami

<p>One of the main issues in GNSS ionosphere seismology is to localize the exact height of the single thin layer (H<sub>ion</sub>) with which the ionosphere is approximated. H<sub>ion</sub> is generally assumed to be the altitude of the maximum ionospheric ionization (hmF2), i.e., in the ionospheric F-layer. In this sense, H<sub>ion</sub> is often  be presumed from physical principles or ionospheric models. The determination of  H<sub>ion </sub>is, therefore, fundamental since it affects the coordinates of the ionospheric pierce point (IPP) and subsequentely of the sub-ionospheric pierce point (SIP).</p><p>In this work, we present a new developed methodology to determine the exact localization of H<sub>ion.</sub> We tested this approach on the TIDs (Travelling ionospheric disturbances) connected with the 2011 Tohoku-Oki earthquake and tsunami [1]. In detail, we computed the slant Total Electron Content (sTEC) variations at different H<sub>ion </sub>(in the range from 100 to 600 km) with the VARION (Variometric Approach for Real-Time Ionosphere Observation) algorithm [2,3], then we interpolated the different pattern in sTEC values related to different waves detected in the ionosphere (AGW<sub>epi</sub>, IGW<sub>tsuna</sub> and AW<sub>Rayleigh</sub>) finding the mean velocity value of these waves. Subsequentely, the minimized difference between the estimated propagation velocity and the values from physical models fix us the correct H<sub>ion.</sub></p><p>Our results show a H<sub>ion </sub>of 370 km, while ionopshere model IRI 2006 located the maximum of ionospheric ionization at an height of 270 km. This difference is important to understand how a different H<sub>ion</sub> can impact on the location of the sTEC perturbation, affecting the shape and the extent of the source from TEC observations.</p><p> </p><p> </p><p> </p><p> </p><p><strong>References</strong></p><p>[1] https://earthquake.usgs.gov/earthquakes/eventpage/official20110311054624120_30/executive</p><p>[2] Giorgio Savastano, Attila Komjathy, Olga Verkhoglyadova, Augusto Mazzoni, Mattia Crespi, Yong Wei, and Anthony J Mannucci, “Real-time detection of tsunami ionospheric disturbances with a stand-alone gnss receiver: A preliminary feasibility demonstration, ”Scientific reports, vol. 7, pp. 46607, 2017.</p><p>[3] Giorgio Savastano, Attila Komjathy, Esayas Shume, Panagiotis Vergados, Michela Ravanelli, Olga Verkhoglyadova, Xing Meng, and Mattia Crespi, “Advantages of geostationary satellites for ionospheric anomaly studies: Ionospheric plasma depletion following a rocket launch,”Remote Sensing, vol. 11, no. 14, pp. 1734, 2019</p>