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

2021 ◽  
Author(s):  
Pierdavide Coïsson ◽  
Vladimir Truhlik ◽  
Janusz Mlynarczyk ◽  
Gauthier Hulot ◽  
Laura Brocco ◽  
...  
Keyword(s):  
Spectral Band ◽  
Neutral Atmosphere ◽  
Iri Model ◽  
Low Frequencies ◽  
Lightning Strikes ◽  
Ionospheric Models ◽  
Swarm Satellites ◽  
Burst Data ◽  
Low Earth Orbits ◽  
Electromagnetic Signals

<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>

Reconstructing the propagation of Whistlers observed in ELF during ASM burst sessions from the lightning strikes to their detection and validation of IRI model

2020 ◽  
Author(s):  
Pierdavide Coïsson ◽  
Vladimir Truhlik ◽  
Janusz Mlynarczyk ◽  
Gauthier Hulot ◽  
Rémi Madelon ◽  
...  
Keyword(s):  
Spectral Band ◽  
Lightning Discharge ◽  
Geomagnetic Latitude ◽  
Propagation Path ◽  
Topside Ionosphere ◽  
Iri Model ◽  
Experimental Conditions ◽  
Lightning Strikes ◽  
Swarm Satellites ◽  
The World

<p>New sessions of burst-mode acquisition of the Absolute Scalar Magnetometers (ASM) onboard Swarm satellites have been conducted during 2019 , with the aim of acquiring events covering various geophysical conditions, in terms of geomagnetic latitude, spacecraft Local Time and season, to better understand the conditions under which the ELF component of whistlers is excited and can be detected at satellite altitude and to provide an additional ionospheric monitoring.</p><p>Among all candidate events detected using an automatic algorithm specifically designed for that purpose, a selection of remarkable whistler events have been further studied. Firstly, from the estimation of the whistler dispersions, the origin times of the lightning discharge have been estimated and validated with ground data from the World ELF Radiolocation Array (WERA), providing the locations of the lightning strikes and their intensity in the ELF spectral band. These locations have also been validated using data from the World Wide Lightning Location Network (WWLLN) providing measurements.</p><p>Subsequently, to reconstruct the propagation path inside the ionosphere of the ELF component of the whistler, a dedicated ray-tracing algorithm has been designed. It uses a background ionosphere model of electron and ions based on the International Reference Ionosphere. For the purposes of producing a ionospheric representation as close as possible to the experimental conditions, the update of the main ionospheric parameters based on worldwide ionosonde data IRTAM has been applied, validating it by using ionosonde data available in the vicinity of specific whistler events. The in-situ electron density measurements of the Electric Field Instrument (EFI) of Swarm satellite have also been used to constrain the model in the topside ionosphere.</p><p>We present the recent results obtained during some of these burst sessions, and discuss the possibility offered by this new dataset to validate global ionospheric models and provide a new avenue in ionospheric research, that could be also pursued by the NanoMagSat mission.</p>

scholarly journals Polar F-layer model-observation comparisons: a neutral wind surprise

2005 ◽  
Vol 23 (1) ◽  
pp. 191-199 ◽  
Author(s):  
J. J. Sojka ◽  
M. David ◽  
R. W. Schunk ◽  
A. P. van Eyken
Keyword(s):  
Input Parameter ◽  
Auroral Oval ◽  
Neutral Wind ◽  
Neutral Atmosphere ◽  
State University ◽  
Utah State University ◽  
Daily Weather ◽  
Magnetospheric Convection ◽  
Ionospheric Models ◽  
Model Input Parameter

Abstract. The existence of a month-long continuous database of incoherent scatter radar observations of the ionosphere from the EISCAT Savlbard Radar (ESR) at Longyearbyen, Norway, provides an unprecedented opportunity for model/data comparisons. Physics-based ionospheric models, such as the Utah State University Time Dependent Ionospheric Model (TDIM), are usually only compared with observations over restricted one or two day events or against climatological averages. In this study, using the ESR observations, the daily weather, day-to-day variability, and month-long climatology can be simultaneously addressed to identify modeling shortcomings and successes. Since for this study the TDIM is driven by climatological representations of the magnetospheric convection, auroral oval, neutral atmosphere, and neutral winds, whose inputs are solar and geomagnetic indices, it is not surprising that the daily weather cannot be reproduced. What is unexpected is that the horizontal neutral wind has come to the forefront as a decisive model input parameter in matching the diurnal morphology of density structuring seen in the observations.

scholarly journals Mesoscale Convective Systems as a source of electromagnetic signals registered by ground-based system and DEMETER satellite

2020 ◽  
Author(s):  
Karol Martynski ◽  
Jan Blecki ◽  
Roman Wronowski ◽  
Andrzej Kulak ◽  
Janusz Mlynarczyk ◽  
...  
Keyword(s):  
Mesoscale Convective Systems ◽  
Atmospheric Conditions ◽  
The West ◽  
Low Frequencies ◽  
Air Masses ◽  
Convective Systems ◽  
Demeter Satellite ◽  
Mesoscale Convective ◽  
Electromagnetic Signals ◽  
Maritime Air

Abstract. Mesoscale Convective Systems (MCS) are especially visible in the summertime, when there is an advection of warm maritime air from the West. Advection of air masses is enriched by water vapour, which source can be found over the Mediterranean Sea. In propitious atmospheric conditions, thus significant convection, atmospheric instability or strong vertical thermal gradient, lead to the development of strong thunderstorm systems. In this paper we discuss one case of MCS, which generated a significant amount of +CG, -CG and IC discharges. We have focused on the ELF (Extremely Low Frequencies,

Seasonal, Kp and IMF dependence of hemispheric asymmetry in ionospheric horizontal and field-aligned currents 

2021 ◽  
Author(s):  
Abiyot Workayehu ◽  
Heikki Vanhamäki ◽  
Anita Aikio ◽  
Simon Shepherd
Keyword(s):  
Hemispheric Asymmetry ◽  
Current System ◽  
Statistical Investigation ◽  
Magnetic Data ◽  
Hemispheric Differences ◽  
Iri Model ◽  
Swarm Satellites ◽  
The Difference ◽  
The Moment

<p>We present statistical investigation of the seasonal, geomagnetic activity and interplanetary magnetic field (IMF) dependence of  hemispheric asymmetry in the auroral currents. Magnetic data from the Swarm satellites has been analyzed by applying the spherical elementary current system (SECS) method. Bootstrap resampling has been used to remove the difference in the number of samples as well as activity and IMF conditions between the local seasons and the hemispheres. In general, the currents are larger in the Northern Hemisphere (NH) than in the Southern Hemisphere (SH). Asymmetry is larger during low (Kp<2) than high Kp (Kp≥2) and during local winter and local autumn than local summer and local spring. Averaging over all Kp and IMF conditions, we find larger currents flowing in the NH than in the SH with the NH/SH ratio for FACs: 17­±5%, 14±5%,7±4% and 2±4% in winter, autumn spring and summer, respectively.  When making the statistical analysis for different IMF directions, we find that the orientation of IMF By has strong influence on the hemispheric asymmetry in the auroral currents, but this influence depends on local season. When IMF By is positive in NH (negative in SH), on average FACs as well as ionospheric horizontal currents are stronger in NH than inSH in most local seasons under both signs of IMF Bz. Conversely, when IMF By is negative in NH (positive in SH), the hemispheric differences of auroral currents during most local seasons are small except in local winter. Overall, comparing the hemispheres for opposite signs of IMF By, we find larger hemispheric asymmetry when IMF By is positive in  NH (negative <sup> </sup>in SH) than vice versa.</p><p>The factors causing the observed hemispheric asymmetries in the auroral currents are not understood at the moment. Background conductances from the IRI model and cross polar cap potential values from SuperDARN dynamic modelsuggest that solar induced ionospheric conductances and convection electric field cannot explain all the observed features of the hemispheric asymmetry in auroral currents. The role of conductance enhancements due to auroral particle precipitation and possible asymmetries in the energy  flux of precipitating particles need to be investigated in future studies.</p>

scholarly journals Strong influence of solar X-ray flares on low-frequency electromagnetic signals in middle latitudes

2019 ◽  
Author(s):  
Alexandr Rozhnoi ◽  
Mariya Solovieva ◽  
Viktor Fedun ◽  
Peter Gallagher ◽  
Joseph McCauley ◽  
...  
Keyword(s):  
Solar Flares ◽  
Low Frequency ◽  
Signal Frequency ◽  
Frequency Range ◽  
Effective Height ◽  
X Ray ◽  
Middle Latitudes ◽  
Burst Data ◽  
Path Lengths ◽  
Electromagnetic Signals

Abstract. In this paper we analysed Sudden Phase Anomalies (SPAs) of VLF/LF signals recorded at Graz (Austria), Birr (Ireland) and Moscow (Russia) stations during two strong solar flares in September 2017. The first X-class 9.3 flare occurred on 6 September at 12:02 UT and the second X-class 8.2 flare was observed on 10 September 2017 at 16:06 UT. Data from seven transmitters in a frequency range between 20–45 kHz are used for the analysis. The SPAs were observed in all middle-latitudes paths (differently orientated) with path lengths from 350 km to 7000 km. Solar X-ray burst data were taken from GOES satellite observations in the wavelength band of 0.05–0.4 nm. If was found that (i) the amplitude of SPAs in different paths varies from 10 to 282 degrees, and (ii) the correlation between the amplitudes of SPAs, the lengths of paths and the signal frequency is weak. The change in effective height of reflection due to lowering of the reflecting layer during the flares was found to be about 12 km for the first event and about 9 km for the second event. Spectral analysis of the X-ray and LF data, filtered in the range between 5 s and 16 min, showed that the LF signal spectra are very similar to X-ray spectra. Maxima of both X-ray and LF spectra are in 2–16 min interval.

scholarly journals Advanced Machine Learning Optimized by The Genetic Algorithm in Ionospheric Models Using Long-Term Multi-Instrument Observations

2020 ◽  
Vol 12 (5) ◽  
pp. 866 ◽  
Author(s):  
Wang Li ◽  
Dongsheng Zhao ◽  
Changyong He ◽  
Andong Hu ◽  
Kefei Zhang
Keyword(s):  
Genetic Algorithm ◽  
Reference Value ◽  
Weddell Sea ◽  
Single Frequency ◽  
Radio Communication ◽  
Iri Model ◽  
Frequency Model ◽  
Ionospheric Models ◽  
Mean Square Errors

The ionospheric delay is of paramount importance to radio communication, satellite navigation and positioning. It is necessary to predict high-accuracy ionospheric peak parameters for single frequency receivers. In this study, the state-of-the-art artificial neural network (ANN) technique optimized by the genetic algorithm is used to develop global ionospheric models for predicting foF2 and hmF2. The models are based on long-term multiple measurements including ionospheric peak frequency model (GIPFM) and global ionospheric peak height model (GIPHM). Predictions of the GIPFM and GIPHM are compared with the International Reference Ionosphere (IRI) model in 2009 and 2013 respectively. This comparison shows that the root-mean-square errors (RMSEs) of GIPFM are 0.82 MHz and 0.71 MHz in 2013 and 2009, respectively. This result is about 20%–35% lower than that of IRI. Additionally, the corresponding hmF2 median errors of GIPHM are 20% to 30% smaller than that of IRI. Furthermore, the ANN models present a good capability to capture the global or regional ionospheric spatial-temporal characteristics, e.g., the equatorial ionization anomaly and Weddell Sea anomaly. The study shows that the ANN-based model has a better agreement to reference value than the IRI model, not only along the Greenwich meridian, but also on a global scale. The approach proposed in this study has the potential to be a new three-dimensional electron density model combined with the inclusion of the upcoming Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC-2) data.

scholarly journals On the Electron Temperature in the Topside Ionosphere as Seen by Swarm Satellites, Incoherent Scatter Radars, and the International Reference Ionosphere Model

2021 ◽  
Vol 13 (20) ◽  
pp. 4077
Author(s):  
Alessio Pignalberi ◽  
Fabio Giannattasio ◽  
Vladimir Truhlik ◽  
Igino Coco ◽  
Michael Pezzopane ◽  
...  
Keyword(s):  
Electron Temperature ◽  
Time Window ◽  
European Space Agency ◽  
International Reference Ionosphere ◽  
Topside Ionosphere ◽  
Iri Model ◽  
International Reference ◽  
Incoherent Scatter ◽  
Swarm Satellites ◽  
Incoherent Scatter Radars

The global statistical median behavior of the electron temperature (Te) in the topside ionosphere was investigated through in-situ data collected by Langmuir Probes on-board the European Space Agency Swarm satellites constellation from the beginning of 2014 to the end of 2020. This is the first time that such an analysis, based on such a large time window, has been carried out globally, encompassing more than half a solar cycle, from the activity peak of 2014 to the minimum of 2020. The results show that Swarm data can help in understanding the main features of Te in the topside ionosphere in a way never achieved before. Te data measured by Swarm satellites were also compared to data modeled by the empirical climatological International Reference Ionosphere (IRI) model and data measured by Jicamarca (12.0°S, 76.8°W), Arecibo (18.2°N, 66.4°W), and Millstone Hill (42.6°N, 71.5°W) Incoherent Scatter Radars (ISRs). Moreover, the correction of Swarm Te data recently proposed by Lomidze was applied and evaluated. These analyses were performed for two main reasons: (1) to understand how the IRI model deviates from the measurements; and (2) to test the reliability of the Swarm dataset as a new possible dataset to be included in the underlying empirical dataset layer of the IRI model. The results show that the application of the Lomidze correction improved the agreement with ISR data above all at mid latitudes and during daytime, and it was effective in reducing the mismatch between Swarm and IRI Te values. This suggests that future developments of the IRI Te model should include the Swarm dataset with the Lomidze correction. However, the existence of a quasi-linear relation between measured and modeled Te values was well verified only below about 2200 K, while for higher values it was completely lost. This is an important result that IRI Te model developers should properly consider when using the Swarm dataset.

scholarly journals Strong influence of solar X-ray flares on low-frequency electromagnetic signals in middle latitudes

2019 ◽  
Vol 37 (5) ◽  
pp. 843-850
Author(s):  
Alexander Rozhnoi ◽  
Maria Solovieva ◽  
Viktor Fedun ◽  
Peter Gallagher ◽  
Joseph McCauley ◽  
...  
Keyword(s):  
Solar Flares ◽  
Low Frequency ◽  
Middle Latitude ◽  
Signal Frequency ◽  
Effective Height ◽  
X Ray ◽  
Middle Latitudes ◽  
Burst Data ◽  
Path Lengths ◽  
Electromagnetic Signals

Abstract. In this paper we analysed sudden phase anomalies (SPAs) of VLF–LF signals recorded at Graz (Austria), Birr (Ireland) and Moscow (Russia) stations during two strong solar flares in September 2017. The first X-class 9.3 flare occurred on 6 September at 12:02 UT, and the second X-class 8.2 flare was observed on 10 September 2017 at 16:06 UT. Data from seven transmitters in a frequency range between 20 and 45 kHz are used for the analysis. The SPAs were observed in all middle-latitude paths (differently orientated) with path lengths from 350 to 7000 km. Solar X-ray burst data were taken from GOES satellite observations in the wavelength band of 0.05–0.4 nm. It was found that (i) the amplitude of SPAs in different paths varies from 10 to 282∘, and (ii) the correlation between the amplitudes of SPAs, the lengths of paths and the signal frequency is weak. The change in effective height of reflection due to lowering of the reflecting layer during the flares was found to be about 12 km for the first event and about 9 km for the second event. Spectral analysis of the X-ray and LF data, filtered in the range between 5 s and 16 min, showed that the LF signal spectra are very similar to X-ray spectra. Maxima of both X-ray and LF spectra are in 2–16 min interval.

The S-SH Confusion Test and the Effects of Frequency Lowering

2019 ◽  
Vol 62 (5) ◽  
pp. 1486-1505
Author(s):  
Joshua M. Alexander
Keyword(s):  
Cognitive Processing ◽  
Hearing Aids ◽  
Response Times ◽  
Nonlinear Frequency ◽  
Low Frequencies ◽  
Frequency Compression ◽  
Negative Side ◽  
Minimal Word ◽  
Low Pass ◽  
Negative Side Effects

PurposeFrequency lowering in hearing aids can cause listeners to perceive [s] as [ʃ]. The S-SH Confusion Test, which consists of 66 minimal word pairs spoken by 6 female talkers, was designed to help clinicians and researchers document these negative side effects. This study's purpose was to use this new test to evaluate the hypothesis that these confusions will increase to the extent that low frequencies are altered.MethodTwenty-one listeners with normal hearing were each tested on 7 conditions. Three were control conditions that were low-pass filtered at 3.3, 5.0, and 9.1 kHz. Four conditions were processed with nonlinear frequency compression (NFC): 2 had a 3.3-kHz maximum audible output frequency (MAOF), with a start frequency (SF) of 1.6 or 2.2 kHz; 2 had a 5.0-kHz MAOF, with an SF of 1.6 or 4.0 kHz. Listeners' responses were analyzed using concepts from signal detection theory. Response times were also collected as a measure of cognitive processing.ResultsOverall, [s] for [ʃ] confusions were minimal. As predicted, [ʃ] for [s] confusions increased for NFC conditions with a lower versus higher MAOF and with a lower versus higher SF. Response times for trials with correct [s] responses were shortest for the 9.1-kHz control and increased for the 5.0- and 3.3-kHz controls. NFC response times were also significantly longer as MAOF and SF decreased. The NFC condition with the highest MAOF and SF had statistically shorter response times than its control condition, indicating that, under some circumstances, NFC may ease cognitive processing.ConclusionsLarge differences in the S-SH Confusion Test across frequency-lowering conditions show that it can be used to document a major negative side effect associated with frequency lowering. Smaller but significant differences in response times for correct [s] trials indicate that NFC can help or hinder cognitive processing, depending on its settings.

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